STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC Not applicable.
BACKGROUND Technical Field The present disclosure relates to rechargeable battery systems, and more specifically to the chemistry of such systems, including operative, electrolyte additives and electrodes, for improving the properties of the rechargeable lithium-ion-battery systems.
Background Rechargeable batteries are an integral component of energy-storage systems for electric vehicles and for grid storage (for example, for backup power during a power outage, as part of a microgrid, etc.). Depending on the application, the energy-storage systems require different properties. Tradeoffs in the chemistry of a battery system may need to be made to create a suitable system for a particular application. For example, in automobile applications—particularly those in an electric vehicle—the ability to charge and discharge quickly is an important property of the system. An electric vehicle owner may need to quickly accelerate in traffic, which requires the ability to quickly discharge the system. Further, fast charging and discharging places demands on the system, so the components of the system may also need to be chosen to provide sufficient lifetime under such operation conditions.
Electrolyte additives have been shown to be operative and increase the lifetime and performance of Li-ion-based batteries. For example, in J. C. Burns et al., Journal of the Electrochemical Society, 160, A1451 (2013), five proprietary, undisclosed electrolyte additives were shown to increase cycle life compared to an electrolyte system with no or only one additive. Other studies have focused on performance gains from electrolyte systems containing three or four additives as described in US20170025706. However, researchers typically do not understand the interaction between different additives that allow them to work together synergistically with the electrolyte and specific positive and negative electrodes. Thus, the identity of certain systems is often based on trial and error and cannot be predicted beforehand.
Prior studies have not identified two-additive electrolyte systems that can be combined into a lithium-ion battery system to yield a robust system with sufficient properties for grid or automobile applications. As discussed in US20170025706, two-additive systems studied (for example, 2% VC+1% allyl methanesulfonate and 2% PES+1% TTSPi) typically performed worse than the three- and four-additive electrolyte systems. (See, e.g., US20170025706 at Tables 1 and 2.) US20170025706 discloses that a third compound, often tris(-trimethly-silyl)-phosphate (TTSP) or tris(-trimethyl-silyl)-phosphite (TTSPi), was necessary in concentrations of between 0.25-3 wt % to produce a robust lithium-ion-battery system. (See, e.g., US20170025706 at ¶72.) However, because additives can be expensive and difficult to include within Li-ion batteries on a manufacture scale, more simple, yet effective battery systems are needed, including those with fewer additives.
SUMMARY This disclosure covers novel battery systems with fewer operative, electrolyte additives that may be used in different energy storage applications, for example, in vehicle and grid-storage. More specifically, this disclosure includes two-additive electrolyte systems that enhance performance and lifetime of Li-ion batteries, while reducing costs from other systems that rely on more additives. This disclosure also discloses effective positive electrodes and negative electrodes that work with the disclosed two-additive electrolyte systems to provide further systematic enhancements.
Two-operative, additive electrolyte systems disclosed include 1) vinylene carbonate (VC) combined with 1,3,2-dioxathiolane-2,2-dioxide (DTD, also known as ethylene sulfate) or another sulfur-containing additive (such as methylene methane disulfonate, trimethylene sulfate, 3-hydroxypropanesulfonic acid γ-sultone, glycol sulfite, or another sulfur-containing additive), 2) fluoro ethylene carbonate (FEC) combined with DTD or another sulfur-containing additive, and 3) prop-1-ene-1,3-sultone (PES) combined with DTD or another sulfur-containing additive. Further, because VC and FEC provide similar improvements (and are believed to function similarly), a mixture of VC and FEC may be considered as only a single operative electrolyte. That is, another disclosed two-operative, additive electrolyte system includes a mixture of VC and FEC combined with DTD or another sulfur-containing additive. When used as part of a greater battery system (which includes the electrolyte, electrolyte solvent, positive electrode, and negative electrode), these two-operative, additive electrolyte systems produce desirable properties for energy storage applications, including in vehicle and grid applications.
More specifically, lithium nickel manganese cobalt oxide (NMC) positive electrodes, a graphite negative electrodes, a lithium salt dissolved in an organic or non-aqueous solvent, which may include methyl acetate (MA), and two additives to form a battery system with desirable properties for different applications. The electrolyte solvent may be the following solvents alone or in combination: ethylene carbonate (EC), ethyl methyl carbonate (EMC), methyl acetate, propylene carbonate, dimethyl carbonate, diethyl carbonate, another carbonate solvent (cyclic or acyclic), another organic solvent, and/or another non-aqueous solvent. Solvents are present in concentrations greater than the additives, typically greater than 6% by weight. The solvent may be combined with the disclosed two-additive pairs (such as VC with DTD, FEC with DTD, a mixture of VC and FEC with DTD, or another combination) to form a battery system with desirable properties for different applications. The positive electrode may be coated with a material such as aluminum oxide (Al2O3), titanium dioxide (Ti02), or another coating. Further, as a cost savings, the negative electrode may be formed from natural graphite, however depending on the pricing structure, in certain instances artificial graphite is cheaper than natural graphite.
The disclosure herein is supported by experimental data that shows the symbiotic nature of the two-additive electrolyte systems and selected electrodes. Exemplary battery systems include two additives (for example, FEC, VC, or PES and DTD or another sulfur-based additive), a graphite negative electrode (either naturally occurring graphite or an artificial, synthetic graphite), an NMC positive electrode, a lithium electrolyte (formed from, for example, a lithium salt such as lithium hexafluorophosphate with chemical composition LiPF6), and an organic or non-aqueous solvent.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a vehicle containing a battery storage system.
FIG. 2 is a schematic diagram of an exemplary battery storage system.
FIG. 3 is a schematic diagram of a lithium-ion, battery-cell system.
FIGS. 4A-J illustrate typical experimental data collected during ultra-high-precision-charging experiments of battery systems with different electrolyte compositions.
FIG. 4A illustrates time normalized coulombic inefficiency per hour (CIE/h) versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD.
FIG. 4B illustrates coulombic efficiency (CE) versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD.
FIG. 4C illustrates the capacity of the charge endpoint plotted versus cycle number for number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD.
FIG. 4D illustrates the discharge capacity verses cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD.
FIG. 4E illustrates the change in open circuit voltage versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD.
FIG. 4F illustrates time normalized coulombic inefficiency per hour (CIE/h) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD.
FIG. 4G illustrates coulombic efficiency (CE) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD.
FIG. 4H illustrates the capacity of the charge endpoint plotted versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD.
FIG. 4I illustrates the discharge capacity verses cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD.
FIG. 4J illustrates the difference between the average charge voltage and the average charge voltage (Delta V) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD.
FIGS. 5A-C illustrates the average of the last three cycles of data shown in FIG. 4, and shows lower coulombic inefficiency per hour and lower fractional slippage per hour for the combinations of FEC+DTD and VC+DTD compared to any single additive of FEC, VC, or DTD.
FIG. 5A illustrates the average coulombic inefficiency per hour for the last three cycles of data generated during the experiments shown in FIG. 4.
FIG. 5B illustrates the average fractional slippage for the last three cycles of data generated during the experiments shown in FIG. 4.
FIG. 5C illustrates the average fractional fade for the last three cycles of data generated during the experiments shown in FIG. 4.
FIGS. 6A-F illustrate typical experimental data studying long term cycling at 40° C., C/3 CCCV showing the advantage of including DTD as an additive to an electrolyte system containing VC or FEC.
FIG. 6A illustrates capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V.
FIG. 6B illustrates normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V.
FIG. 6C illustrates voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V.
FIG. 6D illustrates capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V.
FIG. 6E illustrates normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V.
FIG. 6F illustrates voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V.
FIGS. 7A-F illustrate typical experimental data studying long term cycling at 20° C., C/3 CCCV showing the advantage of including DTD as an additive to an electrolyte system containing VC or FEC.
FIG. 7A illustrates capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V.
FIG. 7B illustrates normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V.
FIG. 7C illustrates voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V.
FIG. 7D illustrates capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V.
FIG. 7E illustrates normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V.
FIG. 7F illustrates voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V.
FIGS. 8A-I illustrate typical experiential data collected during cycling experiments for electrolyte compositions according to certain embodiments of the present disclosure.
FIG. 8A illustrates peak capacity versus cycle number for electrolyte systems including 2% FEC, 1% FEC+1% DTD, 2% FEC+1% DTD, 1% FEC+1% MMDS, and 2% FEC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIG. 8B illustrates normalized capacity versus cycle number for electrolyte systems including 2% FEC, 1% FEC+1% DTD, 2% FEC+1% DTD, 1% FEC+1% MMDS, and 2% FEC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIG. 8C illustrates voltage hysteresis (difference between the average charge voltage and the average charge voltage) for electrolyte systems including 2% FEC, 1% FEC+1% DTD, 2% FEC+1% DTD, 1% FEC+1% MMDS, and 2% FEC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIG. 8D illustrates peak capacity versus cycle number for electrolyte systems including 2% VC, 1% VC+1% DTD, 2% VC+1% DTD, 1% VC+1% MMDS, and 2% VC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIG. 8E illustrates normalized capacity versus cycle number for electrolyte systems including 2% VC, 1% VC+1% DTD, 2% VC+1% DTD, 1% VC+1% MMDS, and 2% VC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIG. 8F illustrates voltage hysteresis (difference between the average charge voltage and the average charge voltage) for electrolyte systems including 2% FEC, 1% VC+1% DTD, 2% VC+1% DTD, 1% VC+1% MMDS, and 2% VC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate by weight.
FIG. 8G illustrates peak capacity versus cycle number for electrolyte systems including 2% PES, 1% PES+1% DTD, 2% PES+1% DTD, 1% PES+1% MMDS, and 2% PES+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIG. 8H illustrates normalized capacity versus cycle number for electrolyte systems including 2% PES, 1% PES+1% DTD, 2% PES+1% DTD, 1% PES+1% MMDS, and 2% PES+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIG. 8I illustrates voltage hysteresis (difference between the average charge voltage and the average charge voltage) for electrolyte systems including 2% FEC, 1% PES+1% DTD, 2% PES+1% DTD, 1% PES+1% MMDS, and 2% PES+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate.
FIGS. 9A-9I illustrate typical experimental data collected during some of the ultra-high-precision-charging experiments that show that methyl acetate can be added to electrolyte systems containing VC or FEC with DTD to increase electrolyte conductivity and lower viscosity without sacrificing much lifetime. Increasing conductivity and decreasing viscosity is important for certain applications requiring a faster rate of charge.
FIG. 9A illustrates typical experimental data showing coulombic efficiency (CE) versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIG. 9B illustrates typical experimental data showing the capacity of the charge endpoint plotted versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIG. 9C illustrates typical experimental data showing the discharge capacity versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIG. 9D illustrates typical experimental data showing the difference between the average charge voltage and the average charge voltage (Delta V) in open circuit voltage versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIG. 9F illustrates typical experimental data of coulombic efficiency (CE) versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIG. 9G illustrates typical experimental data of the capacity of the charge endpoint plotted versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIG. 9H illustrates typical experimental data of the discharge capacity versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIG. 9I illustrates typical experimental data of the difference between the average charge voltage and the average charge voltage (Delta V) versus cycle number for electrolyte systems according to certain embodiments of the present disclosure.
FIGS. 10A-C are plots that summarize experimental data and illustrate that as the MA content increases, the electrolyte additives VC and FEC, both alone and in the presence of DTD, still offer acceptable performance.
FIG. 10A is a plot that summarizes experimental data of time normalized CIE as a function of MA content.
FIG. 10B is a plot that summarizes experimental data of time normalized fractional fade as a function of MA content.
FIG. 10C is a plot that summarizes experimental data of time normalized fractional charge endpoint capacity slippage as a function of MA content.
FIG. 11 is a plot that summarizes experimental data of parasitic heat flow and difference between the parasitic heat flow and that of the cell containing 2% FEC+0% MA as a function of the voltage for different electrolyte compositions that contain FEC in the voltage range of 4.0 V to 4.2 V.
FIG. 12A-B are plots that summarizes experimental data of parasitic heat flow and difference between the parasitic heat flow and that of the cell containing 2% FEC+0% MA as a function of the voltage for different electrolyte compositions that contain FEC in the voltage range of 4.0 V to 4.3 V. FIG. 12A shows results for the first cycle to 4.3 V. FIG. 12B shows results for the second cycle.
FIG. 13A-B are plots that summarizes experimental data of parasitic heat flow and difference between the parasitic heat flow and that of the cell containing 2% FEC+0% MA as a function of the voltage for different electrolyte compositions that contain FEC in the voltage range of 4.0 V to 4.4 V. FIG. 13A shows results for the first cycle to 4.4 V. FIG. 13B shows results for the second cycle.
FIG. 14 is a plot that summarizes experimental parasitic heat flow data, including the data shown in FIGS. 11-13.
FIGS. 15A-F are plots of experimental data taken at 20° C. of capacity, normalized capacity, and voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain FEC.
FIG. 15A is a plot of experimental data taken at 20° C. of capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.2 V.
FIG. 15B is a plot of experimental data taken at 20° C. of normalized capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.2 V.
FIG. 15C is a plot of experimental data taken at 20° C. of voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain FEC with cycling up to 4.2 V.
FIG. 15D is a plot of experimental data taken at 20° C. of capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIG. 15E is a plot of experimental data taken at 20° C. of normalized capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIG. 15F is a plot of experimental data taken at 20° C. of voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIGS. 16A-F are plots of experimental data taken at 40° C. of capacity, normalized capacity, and voltage hysteresis for electrolyte systems that contain FEC.
FIG. 16A is a plot of experimental data taken at 40° C. of capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.2 V.
FIG. 16B is a plot of experimental data taken at 40° C. of normalized capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.2 V.
FIG. 16C is a plot of experimental data taken at 40° C. of voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain FEC with cycling up to 4.2 V.
FIG. 16D is a plot of experimental data taken at 40° C. of capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIG. 16E is a plot of experimental data taken at 40° C. of normalized capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIG. 16F is a plot of experimental data taken at 40° C. of voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIGS. 17A-F are plots of experimental data of capacity, normalized capacity, and voltage hysteresis for electrolyte systems that contain FEC, VC, and/or DTD.
FIG. 17A is a plot of experimental data of capacity versus cycle number for electrolyte systems that contain FEC and/or DTD with cycling up to 4.3 V.
FIG. 17B is a plot of experimental data of normalized capacity versus cycle number for electrolyte systems that contain FEC and/or DTD with cycling up to 4.3 V.
FIG. 17C is a plot of experimental data of voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain FEC and/or DTD with cycling up to 4.3 V.
FIG. 17D is a plot of experimental data of capacity versus cycle number for electrolyte systems that contain VC and/or DTD with cycling up to 4.3 V.
FIG. 17E is a plot of experimental data of normalized capacity versus cycle number for electrolyte systems that contain VC and/or DTD with cycling up to 4.3 V.
FIG. 17F is a plot of experimental data of voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain VC and/or DTD with cycling up to 4.3 V.
FIG. 18A is a plot of experimental data of capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIG. 18B is a plot of experimental data of normalized capacity versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIG. 19 is a plot of experimental data of voltage hysteresis (difference between the average charge voltage and the average charge voltage) versus cycle number for electrolyte systems that contain FEC with cycling up to 4.3 V.
FIG. 20 is a plot that summarizes experimental data of the volume of formation gas generated during cell formation for different electrolyte systems.
FIG. 21 is a plot that summarizes experimental data of charge transfer impedance for different electrolyte systems.
FIG. 22 is a plot summarizing experimental data measuring the low rate capacity loss for different electrolyte systems after cells were charged at three different charge rates at 20° C. for 30 cycles.
FIG. 23 is a plot summarizing experimental data summarizing the peak capacity as a function of cycle number for different electrolyte systems used in cells being charged at different charge rates at 20° C.
FIG. 24 is a plot summarizing experimental data summarizing the peak capacity as a function of cycle number for different electrolyte systems used in cells being charged at different charge rates at 20° C.
FIG. 25 is a plot that summarizes experimental data of the volume of formation gas for different additives in varying concentrations of MA solvent.
FIG. 26 is a plot that summarizes experimental data of charge transfer impedance for different additives in electrolytes containing varying concentrations of MA solvent.
FIG. 27 is a plot that summarizes experimental data of low rate capacity loss for different electrolyte compositions and after charging at 1, 1.5, and 2 C for 30 cycles at 20° C.
FIG. 28 is a blowup of certain experimental data shown in FIG. 27.
FIG. 29 summarizes experimental data of delta V (difference between the average charge voltage and the average charge voltage) as a function of cycle number for electrolyte systems containing FEC.
FIG. 30 summarizes experimental data of peak capacity as a function of cycle number for electrolyte systems containing FEC.
FIG. 31 summarizes experimental data of energy hysteresis as a function of cycle number for electrolyte systems containing FEC.
FIG. 32 summarizes experimental data of delta V (difference between the average charge voltage and the average charge voltage) as a function of cycle number for electrolyte systems containing VC.
FIG. 33 summarizes experimental data of peak capacity as a function of cycle number for electrolyte systems containing VC.
FIG. 34 summarizes experimental data of energy hysteresis as a function of cycle number for electrolyte systems containing VC.
DETAILED DESCRIPTION OF THE DISCLOSURE FIG. 1 illustrates the basic components of a battery powered electric vehicle (electric vehicle) 100. The electric vehicle 100 includes at least one drive motor (traction motor) 102A and/or 102B, at least one gear box 104A and/or 104B coupled to a corresponding drive motor 102A and/or 102B, battery cells 106 and electronics 108. Generally, the battery cells 106 provide electricity to power electronics of the electric vehicle 100 and to propel the electric vehicle 100 using the drive motor 102A and/or 102B. The electric vehicle 100 includes a large number of other components that are not described herein but known to one or ordinary skill. While the construct of the electric vehicle 100 of FIG. 1 is shown to have four wheels, differing electric vehicles may have fewer or more than four wheels. Further, differing types of electric vehicles 100 may incorporate the inventive concepts described herein, including motor cycles, aircraft, trucks, boats, train engines, among other types of vehicles. Certain parts created using embodiments of the present disclosure may be used in vehicle 100.
FIG. 2 illustrates a schematic view of an exemplary energy storage system 200 showing various components. The energy storage system 200 typically includes a modular housing with at least a base 202 and four side walls 204 (only two shown in the figure). The module housing is generally electrically isolated from the housed battery cells 206. This may occur through physical separation, through an electrically insulating layer, through the choice of an insulating material as the module housing, any combination thereof, or another through another method. The base 202 may be an electrically insulating layer on top of a metal sheet or a nonconductive/electrically insulating material, such as polypropylene, polyurethane, polyvinyl chlorine, another plastic, a nonconductive composite, or an insulated carbon fiber. Side walls 204 may also contain an insulating layer or be formed out of a nonconductive or electrically insulating material, such as polypropylene, polyurethane, polyvinyl chlorine, another plastic, a nonconductive composite, or an insulated carbon fiber. One or more interconnect layers 230 may be positioned above the battery cells 206, with a top plate 210 positioned over the interconnect layer 230. The top plate 210 may either be a single plate or be formed from multiple plates.
Individual battery cells 106 and 206 often are lithium-ion battery cells, with an electrolyte containing lithium ions and positive and negative electrodes. FIG. 3 illustrates a schematic of a lithium ion cell 300. Lithium ions 350 are dispersed throughout electrolyte 320, within container 360. Container 360 may be part of a battery cell. The lithium ions 350 migrate between positive electrode 330 and negative electrode 340. Separator 370 separates the negative electrode and positive electrode. Circuitry 310 connects the negative electrode and positive electrode.
New studies by the inventors have identified novel electrolyte and battery systems for use in grid and electric vehicle applications. These systems are based on two-additive electrolyte systems combined with solvents and electrodes, including 1) vinylene carbonate (VC) combined with 1,3,2-Dioxathiolane-2,2-dioxide (DTD, also known as ethylene sulfate) or another sulfur-containing additive, 2) fluoro ethylene carbonate (FEC) combined with DTD or another sulfur-containing additive, and 3) prop-1-ene-1,3-sultone (PES) combined with DTD or another sulfur-containing additive. These two-additive electrolyte systems are paired with a positive electrode made from lithium nickel manganese cobalt oxide with the composition LNixMnyCozO2 (abbreviated NMC generally or NMCxyz where the x, y, and z are the molar ratios of nickel, manganese and cobalt respectively, and x+y+z=1). In certain embodiments, the positive electrode is formed from NMC111, NMC532, NMC811, or NMC622. In certain embodiments, NMC532 positive electrodes formed from single-crystal, micrometer-side particles, which resulted in an electrode with micrometer-size areas of continuous crystal lattice (or grains), have been shown to be particularly robust, in part because the materials and processing conditions result in larger grain sizes than using conventional materials and processing conditions.
Typical processing conditions lead to NMC electrodes with nanometer-sized particles packed into larger micrometer-sized agglomerates, creating grain boundaries on the nanometer scale. Grain boundaries are defects that tend to reduce desirable properties (for example, electrical properties), so it is typically desirable to reduce the number of grains and increase the grain size. Processing can create larger domains, on the micrometer size scale, thereby reducing the number of grain boundaries in the NMC electrodes, increasing electrical properties. The increase in properties is results in more robust battery systems. In certain embodiments, other NMC electrodes may be processed to create larger domain sizes (on the micrometer-size scale or larger), for example, NMC111, NMC811, NMC622, or another NMC compound to create more robust systems.
The positive electrode may be coated with a material such as aluminum oxide (Al2O3), titanium dioxide (TiO2), or another coating. Coating the positive electrode is advantageous because it can help reduce interfacial phenomena at the positive electrode, such as parasitic reactions, thermal abuse, or another phenomenon, that can deteriorate the system. The negative electrode may be made from natural graphite, artificial graphite, or another material.
The electrolyte may be a lithium salt dissolved (such as LiPF6) in a combination of organic or non-aqueous solvents, including ethylene carbonate, ethyl methyl carbonate, methyl acetate, propylene carbonate, dimethyl carbonate, diethyl carbonate, another carbonate solvent (cyclic or acyclic), another organic solvent, and/or another non-aqueous solvent. Solvents are present in concentrations greater than the additives, typically greater than 6% by weight. While the experimental data was generated using an electrolyte solvent that included EC and EMC (with or without MA), these solvents are merely exemplary of other carbonate solvents in particular and to other non-aqueous solvents. EC and EMC solvents were used in the experiments to control the systems tested in order to understand the effects of the additives, electrodes, and addition of MA as a solvent. Electrolyte systems may therefore may use other carbonate solvents and/or other non-carbonate solvents, including propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, another carbonate solvent (cyclic or acyclic), another organic solvent, and/or another non-aqueous solvent. Solvents are present in concentrations greater than the additives, typically greater than 6% by weight.
In the two-additive mixture FEC and DTD, the concentration of FEC is preferentially between 0.5 to 6% by weight and the concentration of the DTD is preferentially between 0.25 to 5% by weight. In the two-additive mixture VC and DTD, the concentration of VC is preferentially between 0.5 to 6% by weight and the concentration of the DTD is preferentially between 0.25 to 5% by weight.
Certain of these new battery systems may be used in energy-storage applications and also automobile application (including energy storage within an electric vehicle) in which charge and discharge speeds, and lifetime when charging and discharging quickly are important. Specifically, MA may be used as an electrolyte solvent to provide longer lifetime when charging and discharging at higher current rates.
Pre-Experimental Setup Although the battery systems themselves may be packaged differently according to the present disclosure, the experimental setup typically used machine made “pouch cells” to systematically evaluate the battery systems using a common setup, including the two-additive electrolyte systems and the specific materials for use the positive and negative electrodes. All percentages mentioned within this disclosure are weight percentages unless otherwise specified. A person of skill in the art will appreciate that the type of additive to be used and the concentration to be employed will depend on the characteristics which are most desirably improved and the other components and design used in the lithium ion batteries to be made and will be apartment from this disclosure.
Pouch Cells The pouch cells used in the experimental setup contain 1 M LiPF6 in the solvent to which additives were added. Depending on the concentration of methyl acetate (0, 20, or 40%), the electrolyte consisted of 1 M LiPF6 in (1) 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate, (2) 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; or (3) 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate. To this electrolyte, the additive components were added at specified weight percentages.
The pouch cells used a positive electrode made of NMC532 with micrometer-sized grains (sometimes referred to as single-crystal NMC532), and a negative electrode made of artificial graphite, unless otherwise specified. To test certain battery systems, other positive, including standard NMC532 (with smaller grains than the NMC with micrometer-sized grains) and NMC622, and negative electrodes (including natural graphite) were used.
Before electrolyte filling, the pouch cells were cut open below the heat seal and dried at 100° C. under vacuum for 12 h to remove any residual water. Then the cells were transferred immediately to an argon-filled glove box for filling and vacuum sealing and then were filled with electrolyte. After filling, cells were vacuum-sealed.
After sealing, the pouch cells were placed in a temperature box at 40.0+/−0.1° C. and held at 1.5 V for 24 hours to allow for the completion of wetting. Then, pouch cells were subjected to the formation process. Unless specified otherwise, the formation process consisted of charging the pouch cells at 11 mA (C/20) to 4.2 V and discharging to 3.8 V. C/x indicates the that the time to charge or discharge the cell at the current selected is x hours when the cell has its initial capacity. For example, C/20 indicates that a charge or discharge would take 20 hours. After formation, cells were transferred and moved into the glove box, cut open to release any generated gas and then vacuum sealed again and the appropriate experiments were performed.
Ultrahigh Precision Cycling and Storage Experiments To study the effectiveness of the battery systems of the present disclosure, including the operative electrolyte additives and electrodes, ultrahigh precision cycling (UHPC) was performed. The standard UHPC procedure consisted of cycling cells between 2.8 and 4.3 V at 40° C. using a current corresponding to C/20 for 15 cycles to produce the data. UPHC is employed to measure the coulombic efficiency, charge endpoint capacity slippage and other parameters to an accuracy of 30 ppm, in the case of the coulombic efficiency. Details of the UHPC procedure are described in in T. M. Bond, J. C. Burns, D. A. Stevens, H. M. Dahn, and J. R. Dahn, Journal of the Electrochemical Society, 160, A521 (2013), which is incorporated herein in its entirety.
Metrics measured and/or determined from the UHPC measurements of particular interest include the following: coulombic efficiency, normalized coulombic inefficiency, normalized charge endpoint capacity slippage, normalized discharge capacity (or fade rate), and delta V. Coulombic efficiency is the discharge capacity (Qd) divided by charge capacity (Qc) of the previous cycle. It tracks the parasitic reactions happening at the in the Li-ion cell and includes contributions from both the positive and negative electrodes. A higher CE value indicates less electrolyte degradation in the cell. Coulombic inefficiency per hour (CIE/h) is a normalized (per hour) coulombic inefficiency where the coulombic inefficiency is defined as 1-CE. It is calculated by taking 1-CE and dividing by the time of the cycle for which the CE was measured. Charge endpoint capacity motion (or slippage) tracks the parasitic reactions occurring at the positive electrode as well as the positive material mass loss, if any. Less motion is better and relates to less electrolyte oxidation. Normalized discharge capacity, or fade rate, is another important metric, with a lower fade rate desirable and normally indicative of a battery system with a longer lifetime. Delta V is calculated as the difference between the average charge voltage and average discharge voltage. Delta V change relates closely to polarization growth with lower Delta V change as cycling occurs is preferable. UHPC measurements are particularly appropriate for comparing electrolyte compositions because it allows for the tracking of metrics with a higher accuracy and precision and allows for the evaluation of various degradation mechanisms in a relatively rapid fashion.
Two-Electrolyte Systems With FEC Or VC As Additive: In certain embodiments, two-additive electrolyte systems, the concentration of each additive about 0.25-6%, form part of the battery system. The battery systems may also include positive electrodes made from NMC111, NMC532, NMC811, NMC622, or another NMC composition (NMCxyz). In certain embodiments, positive electrodes made from NMC532 with micrometer-scale grains have been shown to be particularly robust, in part because processing conditions created larger the grain sizes than typically processing conditions create.
Typical processing conditions lead to NMC electrodes with nanometer-sized particles packed into larger micrometer-sized agglomerates, creating grain boundaries on the nanometer scale. Grain boundaries are defects that tend to reduce desirable properties (for example, electrical properties), so it is typically desirable to reduce the number of grains and increase the grain size. Current processing can create larger domains, on the micrometer size scale, thereby reducing the number of grain boundaries in the NMC electrodes, increasing electrical properties. The increase in properties is results in more robust battery systems. In certain embodiments, other NMC electrodes may be processed to create larger domain sizes (on the micrometer-size scale or larger), for example, NMC111, NMC811, NMC622, or another NMC compound to create more robust systems.
The positive electrode may be coated with a material such as aluminum oxide (Al2O3), titanium dioxide (TiO2), or another coating. FIGS. 4A-J illustrate typical experimental data of two-additive systems of the present disclosure collected during UHPC experiments comparing single-additive electrolyte systems with the novel two-additive electrolyte systems (VC+DTD and FEC+DTD) in a base electrolyte system containing 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate, using a positive electrode consisting of single-crystal NMC532 and a negative electrode consisting of artificial graphite. FIGS. 4A-J illustrate benefits of two-additive systems of the present disclosure, specifically adding DTD to an electrolyte system containing VC or FEC.
FIG. 4A illustrates time normalized coulombic inefficiency per hour (CIE/h) versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD. FIG. 4B illustrates coulombic efficiency (CE) versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD. FIG. 4C illustrates the capacity of the charge endpoint plotted versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD. FIG. 4D illustrates the discharge capacity versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD. FIG. 4E illustrates the difference between average charge voltage and average discharge voltage versus cycle number for electrolyte systems including 1% DTD, 2% VC, and 2% VC+1% DTD. FIG. 4F illustrates time normalized coulombic inefficiency per hour (CIE/h) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD. FIG. 4G illustrates coulombic efficiency (CE) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD. FIG. 4H illustrates the capacity of the charge endpoint plotted versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD. FIG. 4I illustrates the discharge capacity verses cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD. FIG. 4J illustrates the difference between average charge voltage and average discharge voltage versus cycle number for electrolyte systems including 1% DTD, 2% FEC, and 2% FEC+1% DTD.
FIGS. 4A-J show the benefits of electrolytes with two additives—specifically VC+DTD and FEC+DTD. The experimental data shows that adding DTD to an electrolyte system containing VC or FEC in a base electrolyte system containing 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate by weight increases the performance of electrolyte systems that contain only VC or FEC as additives. Specifically, FIGS. 4A-J illustrate that two-additive systems containing (VC+DTD and FEC+DTD) have a higher CE (lower electrolyte degradation in the cell) and lower charge endpoint motion (lower electrolyte degradation at the positive electrode) compared to systems without the additives, or with only one additive. Further, FIGS. 4A-J also show a desirable lower fade rate (Qd). Thus, an electrolyte system with two additives (VC+DTD and/or FEC+DTD) performs better (in terms of CIE/h, CE, charge end point slippage) than an electrolyte system that only contains a single additive of DTD, VC, or FEC.
FIG. 5 summarizes the last three cycles of data generated during the experiments shown in FIGS. 4A-J. FIG. 5A shows a summary of the last three cycles of the time normalized coulombic inefficiency per hour (CIE/h) for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD. FIG. 5B shows a summary of the last three cycles of the fractional slippage per hour for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD. FIG. 5C shows a summary of the last three cycles of the fractional fade per hour for 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD.
FIGS. 5A-C show that electrolyte systems that contain VC+DTD and FEC+DTD exhibit lower time normalize coulombic inefficiency (CIE/h), and lower fractional slippage per hour (meaning that these electrolyte systems have longer lifetimes) compared to systems that only contained one additional additive-2% FEC, 2% VC, or 1% DTD. FIGS. 5A and 5B show that 1% DTD without another additive shows the highest CIE/h and fractional slippage. However, when DTD is combined with VC or FEC, the two additives form a previously unexpected, synergistic effect causing the CIE/h and fractional slippage to be less in the two-additive electrolyte system compared to either single additive. FIG. 5C shows that the presence of 1% DTD decreases the fractional fade per hour, either as a single additive or as part of a two-additive electrolyte system with VC or FEC. This indicates that DTD is an important additive for increasing lifetime of the battery systems of the current invention. In addition to DTD, other sulfur-containing compounds can function in a similar manner and increase battery lifetime.
Methyl Acetate As Electrolyte Solvent: In certain embodiments, methyl acetate is used as a solvent (in concentrations of up to 60%) to improve battery-system lifetime when higher charging and discharging rates are expected as well as other properties. This is particularly important for vehicle and other applications. FIGS. 9A-I illustrate typical data collected during some of the ultra-high-precision-charging experiments that show that methyl acetate can be added to electrolyte systems containing VC or FEC with DTD to increase electrolyte conductivity and lower viscosity without sacrificing much lifetime. Increasing conductivity and decreasing viscosity is important for certain applications requiring a faster rate of charge.
FIG. 9A illustrates coulombic efficiency (CE) versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIG. 9B illustrates the capacity of the charge endpoint plotted versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIG. 9C illustrates the discharge capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIG. 9D illustrates the difference between average charge voltage and average discharge voltage versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIG. 9F illustrates coulombic efficiency (CE) versus cycle number for electrolyte systems including 2% VC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIG. 9G illustrates the capacity of the charge endpoint plotted versus cycle number for electrolyte systems including 2% VC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIG. 9H illustrates the discharge capacity versus cycle number for electrolyte systems including 2% VC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIG. 9I illustrates the difference between average charge voltage and average discharge voltage versus cycle number for electrolyte systems including 2% VC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% VC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% VC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% VC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate.
FIGS. 9A-I show that in systems that include both VC and FEC, the addition of MA as an electrolyte solvent does not significantly sacrifice the overall performance of the battery system and as the long-term-cycling and plating experiments to be described later will show, it increases lifetime under higher charging rates. In particular, the performance of the two-additive electrolyte systems of the present disclosure are not sacrificed with the addition of MA as a solvent. FIGS. 10A-C show the average of three last cycles of data generated during the experiments shown in FIGS. 9A-I. FIGS. 10A-C confirm that the addition of MA as an electrolyte solvent does not significantly sacrifice the overall performance of the battery systems of the present disclosure that include two-additive electrolyte systems.
Long Term Cycling Lifetime of a battery system is an important property of a battery system. Charging and discharging rates can affect lifetime. Long term cycling experiments help determine how resilient battery systems are over time under anticipated operation conditions. It is important to select battery systems that have sufficient lifetimes for the desired application.
Embodiments of the present disclosure exhibit desirable long term cycling for different applications, including grid and vehicle storage. Specifically, two-additive electrolyte systems of VC+DTD and FEC+DTD in which MA, in concentrations of up to 60%, is used as a solvent are particularly relevant for automobile applications (especially energy storage within an electric vehicle) in which charging and discharging rates are typically higher than for grid-storage applications.
In the long-term-cycling experiments, single-crystal NMC532 was typically used as the positive electrode (unless otherwise specified) and artificial graphite was used as the negative electrode (unless otherwise specified). Before the long term cycling experiments, pouch cells were subjected to the formation process. The cells were first charged at 11 mA (C/20) to 4.2 V and discharged to 3.8 V. Cells were transferred and moved into the glove box, cut open to release gas generated and then vacuum sealed again. After formation, cells were cycled on a Neware charging systems. Cells were housed in a temperature controlled box at 40° C.+/−0.2° C. or 20° C.+/−0.2° C. The cells were cycled between 3.0 V and the top of charge (4.2 V or 4.3 V) with a current of C/3 (half cycle of 3 h) and a constant voltage step at the top of charge until the current dropped below C/20. Every 50 cycles, cells underwent one full cycle at C/20.
Two-Electrolyte Systems With FEC Or VC As Additive: In certain embodiments, two-additive electrolyte systems, the concentration of each additive about 0.25-6%, form part of the battery system. FIGS. 6A-F illustrate typical experimental data studying long term cycling at 40° C., and a C/3 constant charge, constant voltage (CCCV) charging rate. FIGS. 6A-F illustrate the advantage of two-additive electrolyte systems of the present disclosure, specifically, electrolytes that include DTD with VC or FEC. FIG. 6A shows experimental data of capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V. FIG. 6B shows experimental data of normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V. FIG. 6C shows experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V. FIG. 6D shows experimental data of capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V. FIG. 6E shows experimental data of normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V. FIG. 6F shows experimental data of voltage hysteresis versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.2 V. The experimental data shows that the two-additive electrolyte systems (DTD+FEC and DTD+VC) experience less capacity loss when cycling to 4.2 or 4.3 V and also lower polarization growth compared to the single additive electrolyte systems of VC or FEC.
FIGS. 7A-F illustrate typical experimental data studying long term cycling at 20° C., C/3 CCCV charging rate. Similar to FIGS. 6A-F, FIGS. 7A-F illustrate the advantage of including DTD as an additive to an electrolyte system containing VC or FEC. FIGS. 7A-F confirm that the advantages seen at 40° C. are still present at lower temperatures, 20° C. in this case. FIG. 7A shows experimental data of capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V. FIG. 7B shows experimental data of normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V. FIG. 7C shows experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V. FIG. 7D shows experimental data of capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V. FIG. 7E shows experimental data of normalized capacity versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0 V and 4.3 V. FIG. 7F shows experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 1% DTD, 2% FEC, 2% FEC+1% DTD, 2% VC, and 2% VC+1% DTD, cycling between 3.0V and 4.3V. FIGS. 7A-F confirm the advantages of including DTD in the electrolyte with VC or FEC, especially when cycling occurs up to 4.3 V.
FIGS. 6A-F illustrate the benefits of two-additive electrolyte systems consisting of DTD+VC or DTD+FEC. FIGS. 6A-F show that the inclusion of DTD with VC or FEC as part of a two-additive electrolyte system and cycling at 40° C., leads to less capacity loss at 4.2 and 4.3 V and lowers polarization growth. Similarly, FIGS. 7A-F shows the benefits of DTD when long-term cycling at 20° C. FIGS. 7A-F show that the inclusion of DTD with VC or FEC as part of a two-additive electrolyte system and cycling at 20° C., leads to less capacity loss at 4.2 V (slightly) and 4.3 V (more significantly) and lowers polarization growth. Thus, at either 20° C. or 40° C., two-additive systems including DTD with VC or FEC improves the battery system by reducing the capacity loss and lowering the polarization growth.
In certain embodiments, the positive electrode is formed from NMC111, NMC532, NMC822, NMC622, and/or NMCxyz. In particular, positive electrodes made from single-crystal NMC532 have been shown to be particularly robust, in part because the grain size of NMC532 is larger than the grain size of other standard NMC materials that are more polycrystalline, having smaller grain sizes. FIGS. 8A-I shows typical experiential data collected during cycling experiments for electrolyte compositions according to certain embodiments of the present disclosure that include a positive electrode formed from single-crystal NMC532. FIG. 8A shows experimental data of peak capacity versus cycle number for electrolyte systems including 2% FEC, 1% FEC+1% DTD, 2% FEC+1% DTD, 1% FEC+1% MMDS, and 2% FEC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIG. 8B shows experimental data of normalized capacity versus cycle number for electrolyte systems including 2% FEC, 1% FEC+1% DTD, 2% FEC+1% DTD, 1% FEC+1% MMDS, and 2% FEC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIG. 8C shows experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 2% FEC, 1% FEC+1% DTD, 2% FEC+1% DTD, 1% FEC+1% MMDS, and 2% FEC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIG. 8D shows experimental data of peak capacity versus cycle number for electrolyte systems including 2% VC, 1% VC+1% DTD, 2% VC+1% DTD, 1% VC+1% MMDS, and 2% VC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIG. 8E shows experimental data of normalized capacity versus cycle number for electrolyte systems including 2% VC, 1% VC+1% DTD, 2% VC+1% DTD, 1% VC+1% MMDS, and 2% VC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIG. 8F shows experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 2% FEC, 1% VC+1% DTD, 2% VC+1% DTD, 1% VC+1% MMDS, and 2% VC+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate by weight. FIG. 8G shows experimental data of peak capacity versus cycle number for electrolyte systems including 2% PES, 1% PES+1% DTD, 2% PES+1% DTD, 1% PES+1% MMDS, and 2% PES+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIG. 8H shows experimental data of normalized capacity versus cycle number for electrolyte systems including 2% PES, 1% PES+1% DTD, 2% PES+1% DTD, 1% PES+1% MMDS, and 2% PES+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIG. 8I shows experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) for electrolyte systems including 2% FEC, 1% PES+1% DTD, 2% PES+1% DTD, 1% PES+1% MMDS, and 2% PES+1% MMDS, cycling between 3.0 V and 4.3 V at 40° C. in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. FIGS. 8A-I illustrate that NMC532 performs well with two-additive electrolyte systems of 1% DTD with 1% VC, 2% VC, 1% FEC, or 2 FEC. DTD performed better as an additive with VC or FEC than did MMDS.
Methyl Acetate As Electrolyte Solvent: In certain embodiments, methyl acetate is used as an electrolyte solvent, in concentrations up to 60% (by weight) and generally in combination with ethylene carbonate and/or ethyl methyl carbonate. FIGS. 15A-F and 16A-F shows the results of experiments run at 20° C. and 40° C., respectively. Cells with DTD performed better than cells without DTD in cells containing MA as a solvent.
FIG. 15A is a plot of experimental data taken at 20° C. of capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.2 V.
FIG. 15B is a plot of experimental data taken at 20° C. of normalized capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.2 V.
FIG. 15C is a plot of experimental data taken at 20° C. of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.2 V.
FIG. 15D is a plot of experimental data taken at 20° C. of capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.3 V.
FIG. 15E is a plot of experimental data taken at 20° C. of normalized capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.3 V.
FIG. 15F is a plot of experimental data taken at 20° C. of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.3 V.
FIGS. 15A-F illustrates the importance of DTD in systems containing FEC and systems that use MA as a solvent at 20° C. Cells with DTD performed better than cells without DTD, especially in the cells that contained MA. In particular, 2% FEC+1% DTD with 20% MA solvent shows very stable capacity retention at 4.3 V.
FIGS. 16A-F shows the results of experiments run at 40° C. Cells with DTD performed better than cells without DTD in cells containing MA. FIG. 16A is a plot of experimental data taken at 40° C. of capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.2 V.
FIG. 16B is a plot of experimental data taken at 40° C. of normalized capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.2 V.
FIG. 16C is a plot of experimental data taken at 40° C. of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.2 V.
FIG. 16D is a plot of experimental data taken at 40° C. of capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.3 V.
FIG. 16E is a plot of experimental data taken at 40° C. of normalized capacity versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.3 V.
FIG. 16F is a plot of experimental data taken at 40° C. of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems including 2% FEC in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 1% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; 2% FEC in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate; and 2% FEC+1% DTD in a base electrolyte of 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate with cycling up to 4.3 V.
FIGS. 16A-F illustrates the importance of DTD in systems containing FEC and systems that use MA as a solvent at 40° C. Generally, cells with DTD performed better than cells without DTD, especially in the cells that contained MA. In the two-additive electrolyte system with 2% FEC+1% DTD with 20% MA solvent, the impact of the DTD is a bit muted compared to the same-two additive electrolyte system, but without MA as a solvent. Further, the addition of up to 40% MA at 4.3 V reduces the cycle life. That is, DTD and MA can have a symbiotic increase of the performance of the two-additive electrolyte system, but this increase is muted when operating on cycles up to 4.3 V. Thus, in certain embodiments of this present disclosure, the electrolyte system only operates up to 4.2 V. In other embodiments of the present disclosure, the electrolyte system operates up to 4.3 V, but with a MA concentration of less than 40%.
NMC622 As Positive Electrode: In certain embodiments, the battery systems have a positive electrode made from NMC622. In certain embodiments, the positive electrode is coated with a material such as aluminum oxide (Al2O3), titanium dioxide (TiO2), or another coating. FIGS. 17A-F shows experimental data for long term cycling of one- and two-additive electrolyte systems with a coated NMC622 as the positive electrode at 40° C., C/3 CCCV. The dashed lines are extrapolated from the experimental data.
More specifically, FIG. 17A is a plot of experimental data of capacity versus cycle number for electrolyte systems that contain FEC and/or DTD with cycling up to 4.3 V. FIG. 17B is a plot of experimental data of normalized capacity versus cycle number for electrolyte systems that contain FEC and/or DTD with cycling up to 4.3 V. FIG. 17C is a plot of experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems that contain FEC and/or DTD with cycling up to 4.3 V. FIG. 17D is a plot of experimental data of capacity versus cycle number for electrolyte systems that contain VC and/or DTD with cycling up to 4.3 V. FIG. 17E is a plot of experimental data of normalized capacity versus cycle number for electrolyte systems that contain VC and/or DTD with cycling up to 4.3 V. FIG. 17F is a plot of experimental data of voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number for electrolyte systems that contain VC and/or DTD with cycling up to 4.3 V.
FIGS. 17A-F illustrate that even when a different positive electrode is chosen, the experimental data shows that an electrolyte system with two additives—VC+DTD and FEC+DTD—performs superior to any single additive of VC, FEC, or DTD.
Natural Graphite As Negative Electrode: In certain embodiments, the battery systems have negative electrode made from natural graphite. FIGS. 18A-B and 19 show data from additional long-term cycling experiments carried out using single-crystal NMC532 as the positive electrode and natural graphite as the negative electrode at 40° C., C/3 CCCV. FIG. 18A shows capacity plotted versus cycle number. FIG. 18B shows normalized capacity plotted versus cycle number. FIG. 19 shows voltage hysteresis (difference between average charge voltage and average discharge voltage) versus cycle number. FIGS. 18A-B and 19 illustrate that the two-electrolyte additive system, including DTD+FEC improves performance over an electrolyte system that only includes FEC as an additive, but comparisons to FIGS. 6-F in which an artificial-graphite negative electrode was used, suggests that the performance of this specific artificial-graphite negative electrode outperforms this specific natural-graphite negative electrode in the two-additive electrolyte systems of the present disclosure.
In certain embodiments, the battery system has a natural graphite negative electrode. Using natural graphite as the negative electrode is important as a cost savings measure over artificial graphite, which is typically more expensive. Thus, when cost is the primary driver and some performance tradeoffs may be made, natural graphite may be a good choice.
Microcalorimetry Measurements Microcalorimetry measures heat flow to the cell during operation. The heat flow to the cell is a combination of three different effects: (1) ohmic heating, (2) entropy changes due to Li intercalating in the electrodes, and (3) parasitic reactions (electrolyte, including additive, degradation at either electrode). Because the test cells contain the same physical design, different only in the electrolyte, the difference in heat flow is primarily due to the differences in parasitic heat flow. Nevertheless, the parasitic heat flow can be extracted from the total heat flow using the procedures developed by Downie et al. (Journal of the Electrochemical Society, 161, A1782-A1787 (2014)) and by Glazier et al. (Journal of the Electrochemical Society, 164 (4) A567-A573 (2017)). Both of these references are incorporated herein in their entirety. Cells that have lower parasitic heat flow during cycling have better lifetimes. The voltage dependence of the parasitic reaction rate may be observed by plotting the measured parasitic heat flow as a function of cell voltage.
Microcalorimetry Measurement Procedure: Two cells of each electrolyte were connected to a Maccor charger and inserted into a TAMIII Microcalorimeter (TA Instruments, stability+/−0.0001° C., accuracy+/−1 μW, precision+/−1 nW) at 40.0° C. The baseline drift over the course of the experiments did not exceed+/−0.5 μW. All specifications and information regarding microcalorimetry calibration, cell connections, and operation procedures can be found in previous literature. (For example, Downie et al, ECS Electrochemical Letters 2, A106-A109 (2013).) Cells were cycled four times at a C/20 rate between 3.0 V and 4.2 V to ensure well-formed, stable SEIs and were then charged between 4.0 V and different upper cut off limits at 1 mA to investigate the performance and the parasitic heat flow in different voltage ranges. Each pair of cells yielded near identical performance, so only one set of heat flow data is presented for each electrolyte.
The 1 mA cycling protocol was:
- 1. Charge to 4.2 V, discharge to 4.0 V
- 2. Charge to 4.3 V, discharge to 4.0 V (repeat)
- 3. Charge to 4.4 V, discharge to 4.0 V (repeat)
- 6. Charge to 4.2 V, discharge to 4.0 V
Additional experimental detail is described in the Journal of the Electrochemical Society, 164 (4) A567-A573 (2017), which is incorporated herein by reference in its entirety.
In the experimental data shown in FIGS. 11-14, pouch cells with a positive electrode made from single-crystal NMC532 and an artificial-graphite negative electrode were used. Excluding additives, the electrolyte was either (1) 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate, (2) 1.2M LiPF6 in 24% ethylene carbonate, 56% ethyl methyl carbonate, and 20% methyl acetate; or (3) 1.2M LiPF6 in 18% ethylene carbonate, 42% ethyl methyl carbonate, and 40% methyl acetate, depending on the concentration of methyl acetate (0, 20, or 40%).
FIG. 11 shows experimental data of calorimetry experiments (parasitic heat flow versus voltage) when charging to 4.2 V. FIGS. 12A and B show experimental data of calorimetry experiments (parasitic heat flow versus voltage) when charging to 4.3 V. Since the charging to 4.3 V was repeated, each plot shows the results of the one charging. FIGS. 13A and B show experimental data (parasitic heat flow versus voltage) when charging to 4.4 V. Since the charging to 4.4V was repeated, each plot shows the results of the one charging. The plot of the difference (lower plot in FIGS. 11, 12A, 12B, 13A, and 13B) is calculated by taking the heat flow for each electrolyte mixture and subtracting the heat flow produced by the control (2% FEC). FIG. 14 shows a summary of the experimental data conveyed in FIGS. 11-13. Table 1 summarizes the data displayed in FIG. 14 in tabular form.
TABLE 1
Average Parasitic Heat Flow per Cycle (μW)
(40.° C., 4.0 V to UCV, 1 mA)
Upper
Cut
Off 20 MA + 2
Voltage 2 FEC Error FEC Error 40 MA + 2 FEC Error
4.2 70.4 0.2 82 3 94 2
4.3 60.9 0.1 75 3 93 1
4.3 41.00 0.07 54 2 69.6 0.9
4.4 53.7 0.2 73 3 95 1
4.4 38.3 0.3 54 3 74.5 0.7
4.2 27.1 0.6 36 2 46.3 0.5
20 MA + 2
2 FEC FEC 40 MA + 2 FEC
1 DTD Error 1 DTD Error 1 DTD Error
4.2 63.9 0.2 69.7 0.3 77.3 0.3
4.3 54.7 0.3 64.9 0.7 76.95 0.07
4.3 36.8 0.2 46.5 0.3 58.6 0.1
4.4 48.4 0.5 65.0 0.6 84.7 0.1
4.4 34.6 0.4 49.1 0.6 66.0 0.2
4.2 24.44 0.04 31.4 0.3 39.3 0.7
FIGS. 11-14 and Table 1 show that that adding DTD to FEC leads to lowers parasitic heat flow (lower parasitic reaction rate). FIGS. 11-14 and Table 1 also show that adding MA leads to higher parasitic heat flow (higher parasitic reaction rate), but this increase may be mitigated by DTD, which helps reduce the increased parasitic reaction rate from the addition of the MA.
Plating Experiments Plating experiments test the ability to charge at a fast rate. Fast charging is very important in energy-storage when part of a vehicle, while slower charging rates may be acceptable in grid-storage applications. High rate charging is mainly limited by lithium plating on the negative electrode which leads to safety issues and diminishes cycle and calendar life. Electrolyte systems that allow higher charging rates without plating are thus advantageous. To study plating on the negative electrode, plating experiments were performed. Larger capacity loss indicates greater lithium plating.
Plating experiments were performed to test the charging ability of cells. After EIS measurements, cells were charged and discharged with constant currents (C-rates) of 1 C, 1.5 C, and 2.0 C between 2.8 and 4.1 V using a Maccor charger system at 20.0±0.1° C. Pair cells were tested for every charge rate to ensure reproducibility. In order to determine the active lithium loss during cycling, cells were cycled at C/20 one time before and after the high charge rate segments. The upper cutoff voltage was set to 4.1 V in order to minimize electrolyte oxidation at the positive electrode and to ensure that the cells were far from having a fully loaded negative electrode which would occur at 4.4 V for these cells. All pouch cells were cycled with external clamps to eliminate effects of small amounts of gas that may be produced during cycling. Cells were stopped after about 350 hours cycling or after the capacity loss reached 20%.
Two-Electrolyte Systems With FEC Or VC As Additive: In certain embodiments, two-additive electrolyte systems, the concentration of each additive at about 0.25-6%, form part of the battery system. FIG. 22 shows experimental data of the plating experiments for different battery systems at different current charging rates. FIG. 22 indicates that addition of DTD does not significantly increase the maximum current at which plating occurs. For example, the low rate capacity loss of the electrolyte system consisting of two additives-2% FEC+1% DTD—is decreased compared to the electrolyte system consisting of the single additive 2% FEC at 1 C, 1.5 C, and 2 C. Similarly, FIG. 22 shows that the low rate capacity loss of the electrolyte system consisting of two additives-1% FEC+1% DTD—is decreased compared to the electrolyte system consisting of the single additive 2% FEC at 1 C and 1.5 C. It is also only slightly higher at 2 C.
FIG. 23 shows experimental data from plating tests, in which after every 30 cycles, the charging current was increased. A large capacity loss rate indicates lithium plating. At a charging current of 2 C, every cell began to plate lithium. However, cells with DTD lose less capacity during plating. This indicates that the amount of plating in cells with DTD is less than in cells without. In addition to DTD, other sulfur-containing compounds can function in a similar manner to decrease plating.
FIG. 24 shows the results of experimental data of peak capacity as a function of cycle number for different electrolyte systems. DTD performed better than MMDS in retaining the peak capacity of the two-additive electrolyte system when DTD or MMDS were combined with VC.
Methyl Acetate As Electrolyte Solvent: Methyl acetate, in concentrations of up to 60% by weight, is used as a solvent to reduce plating according to certain embodiments. FIGS. 27-34 illustrate the impact of using MA as a solvent in the presence of different electrolyte systems. FIG. 27 shows the results of plating experiments to determine the impact of MA as a solvent and the presence of DTD as an additive on the cell impedance. The electrolyte systems tested include 2% of an additive (VC, FEC, and PES) in an electrolyte with 0%, 20%, and 40% MA. The remaining electrolyte for 0% MA is 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. The remaining electrolyte for 20% MA is 1.2M LiPF6 in 24% ethylene carbonate and 56% ethyl methyl carbonate. The remaining electrolyte for 40% MA is 1.2M LiPF6 in 18% ethylene carbonate and 42% ethyl methyl carbonate. FIG. 28 is an expanded view of certain data shown in in FIG. 27 that had a small low rate capacity loss.
In FIGS. 27 and 28, a larger capacity loss indicates greater lithium plating. FIGS. 27 and 28 show that the presence of MA decreases the low rate capacity loss, even at charging rates of 2 C. Thus, electrolyte systems containing 20% or 40% of MA are good candidates for use in applications that fast charging, such as energy storage in a vehicle that may be subjected to high charging current rates.
FIGS. 29, 30, and 31 show the results of experimental data of electrolyte systems containing FEC as an additive. Different data sets include DTD and/or MA, as indicated by the legend in the figures. FIGS. 29, 30, and 31 show that the addition of MA to one- and two-additive electrolyte systems with FEC allows for higher charging rates, including charging up to 2 C, without significant plating.
Similarly, FIGS. 32, 33, and 34 show the results of experimental data of electrolyte systems containing VC as an additive. Different data sets include DTD and/or MA, as indicated by the legend in the figures. FIGS. 32, 33, and 34 show that the addition of MA to one- and two-additive electrolyte systems with VC allows for higher charging rates, including charging up to 2 C, without significant plating.
Gas Volume Measurements The formation process is performed prior to cells being used in their intended application, such as grid storage or energy storage in an automobile, such as an electric vehicle. During formation, cells are subject to a precisely controlled charge and discharge cycle, which is intended to activate the electrodes and electrolyte for use in their intended application. During formation, gas is generated. If sufficient amounts of gas are generated (depending on the specific tolerances allowed by the cell and cell packaging), the gas may need to be released after the formation process and prior to application use. This typically requires the additional steps of breaking of a seal followed by a resealing. While these steps are common for many battery systems, it is desirable to remove them if possibly by choosing a system that produces less gas.
Gas volume experiments proceeded as follows: Ex-situ (static) gas measurements were used to measure gas evolution during formation and during cycling. The measurements were made using Archimedes' principle with cells suspended from a balance while submerged in liquid. The changes in the weight of the cell suspended in fluid, before and after testing are directly related to the volume changes by the change in the buoyant force. The change in mass of a cell, Δm, suspended in a fluid of density, ρ, is related to the change in cell volume, Δv, by Δv=Δm/ρ.
Two-Electrolyte Systems With FEC Or VC As Additive: In certain embodiments, two-additive electrolyte systems, the concentration of each additive about 0.25-6%, form part of the battery system. FIG. 20 shows the results of gas-generation experiments, in which the amount of gas generated was measured according to the procedure described above. FIG. 20 shows that systems without DTD typically performed better, for example a system containing only 2% FEC as an additive, performs better than 1% FEC+1% DTD and 2% FEC+1% DTD. That is, DTD leads to higher gas volume production during formation, if DTD is to be used as an additive because of its desirable properties when combined with other additives, for example VC and FEC, then the system must include a mechanism to safely deal with the gas produced by the DTD, such as gas release after formation as discussed above. FIG. 20 shows that two-additive electrolyte systems that include MMDS and PES or FEC do not produce much (if any) additional gas than when 2% PES or FEC is the only additive.
Methyl Acetate As Electrolyte Solvent: Methyl acetate, in concentrations of up to 60% by weight, is used as a solvent to reduce plating according to certain embodiments. FIG. 25 shows the results of gas-generation experiments to determine the impact of MA as a solvent and presence of DTD as an additive on the formation gas generated. The electrolyte systems tested include 2% of an additive (VC, FEC, and PES) in an electrolyte with 0%, 20%, and 40% MA. The remaining electrolyte for 0% MA is 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. The remaining electrolyte for 20% MA is 1.2M LiPF6 in 24% ethylene carbonate and 56% ethyl methyl carbonate. The remaining electrolyte for 40% MA is 1.2M LiPF6 in 18% ethylene carbonate and 42% ethyl methyl carbonate.
FIG. 25 shows that in two-additive electrolyte systems that contain VC or FEC with DTD, the increase of the amount of gas with the addition of MA varies less as the amount of MA increases. That is, the marginal amount of gas generated is less when DTD is part of the two-additive electrolyte system compared to a one-additive electrolyte system that has only VC or FEC.
Cell Impedance The two-additive electrolyte systems and novel battery systems disclosed herein have low cell impedance. Minimizing cell impedance is desirable since cell impedance decrease the energy efficiency of a cell. Conversely, low impedance leads to a higher charging rate and higher energy efficiency.
Cell impedance was measured using electrochemical impedance spectroscopy (EIS). The pouch cells used a single-crystal NMC532 positive electrode and an artificial negative electrode unless stated otherwise, with the EIS measurements performed after formation. Cells were charged or discharged to 3.80 V before they were moved to a 10.0+/−0.1° C. temperature box. AC impedance spectra were collected with ten points per decade from 100 kHz to 10 mHz with a signal amplitude of 10 mV at 10.0+/−0.1° C. From the measured AC impedance, the charge transfer resistance (Rct) was calculated and plotted.
Two-Electrolyte Systems With FEC Or VC As Additive: In certain embodiments, two-additive electrolyte systems, the concentration of each additive about 0.25-6%, form part of the battery system. FIG. 21 shows experimental data of cell charge transfer impedance experiments for two-additive electrolyte systems consisting of 1% DTD with 1% or 2% of PES, FEC, or VC. FIG. 21 shows that these two-additive electrolyte systems of 1% DTD with 1% or 2% of PES, FEC, or VC do not significantly increase the cell charge transfer impendence. In particular, systems of 1% DTD with 1% VC, 1% DTD with 2% VC, 1% DTD with 1% FEC, and 1% DTD with 2% FEC exhibit cell impedance values similar to the cell charge transfer impendence observed for the single-additive systems with DTD excluded. Therefore, these novel two-additive electrolyte systems do not sacrifice significant charge transfer impedance performance by including DTD.
Methyl Acetate As Electrolyte Solvent: Methyl acetate, in concentrations of up to 60% by weight, is used as a solvent to reduce plating according to certain embodiments. FIG. 26 shows the results of cell-charge transfer impedance experiments on electrolyte systems consisting of one- and two-additive systems with MA as one of the solvents. The additive-electrolyte systems tested included 2% of additives VC, FEC, and PES without and without 1% DTD to show impact of the DTD and MA to the electrolyte system in an electrolyte solvent with 0%, 20%, and 40% MA. The electrolyte for 0% MA is 1.2M LiPF6 in 30% ethylene carbonate and 70% ethyl methyl carbonate. The remaining electrolyte for 20% MA is 1.2M LiPF6 in 24% ethylene carbonate and 56% ethyl methyl carbonate. The remaining electrolyte for 40% MA is 1.2M LiPF6 in 18% ethylene carbonate and 42% ethyl methyl carbonate. FIG. 26 shows that DTD produces only slight increases in charge transfer impedance. Further, in two-additive electrolyte systems that contain VC or FEC with DTD, the addition of MA decreases cell charge transfer impedance. At 40% MA solvent, the VC+DTD and FEC+DTD systems showed reduced charge transfer impedance from the corresponding systems without DTD and no MA as a solvent. In the PES+DTD two-additive electrolyte system, MA also reduced the charge transfer impedance of the system.
The foregoing disclosure is not intended to limit the present disclosure to the precise forms or particular fields of use disclosed. As such, it is contemplated that various alternative embodiments and/or modifications to the present disclosure, whether explicitly described or implied herein, are possible in light of the disclosure. Having thus described embodiments of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made in form and detail without departing from the scope of the present disclosure. Thus, the present disclosure is limited only by the claims. Reference to additives in the specification are generally to operative additives unless otherwise noted in the specification.
In the foregoing specification, the disclosure has been described with reference to specific embodiments. However, as one skilled in the art will appreciate, various embodiments disclosed herein can be modified or otherwise implemented in various other ways without departing from the spirit and scope of the disclosure. Accordingly, this description is to be considered as illustrative and is for the purpose of teaching those skilled in the art the manner of making and using various embodiments of the disclosed battery system. It is to be understood that the forms of disclosure herein shown and described are to be taken as representative embodiments. Equivalent elements, or materials may be substituted for those representatively illustrated and described herein. Moreover, certain features of the disclosure may be utilized independently of the use of other features, all as would be apparent to one skilled in the art after having the benefit of this description of the disclosure. Expressions such as “including”, “comprising”, “incorporating”, “consisting of”, “have”, “is” used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. Reference to “about” or “approximately” is to be construed to mean plus or minus 10%. Similarly, reference to any percentage of an additive is construed to mean plus or minus 10%.
Further, various embodiments disclosed herein are to be taken in the illustrative and explanatory sense, and should in no way be construed as limiting of the present disclosure. All joinder references (e.g., attached, affixed, coupled, connected, and the like) are only used to aid the reader's understanding of the present disclosure, and may not create limitations, particularly as to the position, orientation, or use of the systems and/or methods disclosed herein. Therefore, joinder references, if any, are to be construed broadly. Moreover, such joinder references do not necessarily infer that two elements are directly connected to each other.
Additionally, all numerical terms, such as, but not limited to, “first”, “second”, “third”, “primary”, “secondary”, “main” or any other ordinary and/or numerical terms, should also be taken only as identifiers, to assist the reader's understanding of the various elements, embodiments, variations and/or modifications of the present disclosure, and may not create any limitations, particularly as to the order, or preference, of any element, embodiment, variation and/or modification relative to, or over, another element, embodiment, variation and/or modification.
It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application.
