HIGH ENERGY MATERIALS FOR A BATTERY AND METHODS FOR MAKING AND USE
A method of forming an electrode active material by reacting a metal fluoride and a reactant. The method includes a coating step and a comparatively low temperature annealing step. Also included is the electrode formed following the method.
This application is a continuation-in-part of International Application No. PCT/US2014/028506, having an international filing date of Mar. 14, 2014 entitled “High Energy Materials For A Battery And Methods For Making And Use,” which claims priority to U.S. Provisional Application No. 61/786,602 filed Mar. 15, 2013 entitled “High Energy Materials For A Battery And Methods For Making And Use.” This application claims priority to and the benefit of each of these applications, and each application is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION
The present invention is in the field of battery technology, and more particularly in the area of materials for making high-energy electrodes for batteries, including metal-fluoride materials.
One type of battery consists of a negative electrode made primarily from lithium and a positive electrode made primarily from a compound containing a metal and fluorine. During discharge, lithium ions and electrons are generated from oxidation of the negative electrode while fluoride ions are produced from reduction of the positive electrode. The generated fluoride ions react with lithium ions near the positive electrode to produce a compound containing lithium and fluorine, which may deposit at the positive electrode surface.
Metal fluoride based batteries are an attractive energy storage technology because of their extremely high theoretical energy densities. For example, certain metal fluoride active materials can have theoretical energy densities greater than about 1600 Wh/kg or greater than about 7500 Wh/L. Further, metal fluorides have a relatively low raw material cost, for example less than about $10/kg. However, a number of technical challenges currently limit their widespread use and realization of their performance potential.
One challenge for certain metal fluoride materials is comparatively poor rate performance. Many metal fluoride active materials have electrochemical potentials greater than about 2.5 V because of their relatively large bandgap produced by the highly ionic bonding between the metal and fluorine, and in particular between a transition metal and fluorine. Unfortunately, one of the drawbacks to wide bandgap materials is the intrinsically low electronic conductivity that results from the wide bandgap. As a result of this low conductivity, discharge rates of less than 0.1 C are required in order to obtain full theoretical capacity. More typically, discharge rates of 0.05 C to 0.02 C are reported in the literature. Such low discharge rates limit the widespread use of metal fluoride active materials.
Another challenge for certain metal fluoride active materials is a significant hysteresis observed between the charge and discharge voltages during cycling. This hysteresis is typically on the order of about 1.0V to about 1.5V. While the origin of this hysteresis is uncertain, current evidence suggests that kinetic limitations imposed by low conductivity play an important role. Further, asymmetry in the reaction paths upon charge and discharge may also play a role. Since the electrochemical potential for many of the metal fluorides is on the order of 3.0V, this hysteresis of about 1.0V to about 1.5V limits the overall energy efficiency to approximately 50%.
Limited cycle life is another challenge for certain metal fluoride active materials. Although rechargeability has been demonstrated for many metal fluoride active materials, their cycle life is typically limited to tens of cycles and is also subject to rapid capacity fade. Two mechanisms are currently believed to limit the cycle life for the metal fluoride active materials: agglomeration of metallic nanoparticles and mechanical stress due to volume expansion. It is believed that metal fluoride active materials can cycle by virtue of the formation during lithiation of a continuous metallic network within a matrix of insulating LiF. As the number of cycles increases, the metal particles tend to accumulate together into larger, discrete particles. The larger agglomerated particles in turn create islands that are electrically disconnected from one another, thus reducing the capacity and ability to cycle the metal fluoride active materials. The second limitation to extended cycle life is the mechanical stress imparted to the binder materials by the metal fluoride particles as a result of the volume expansion that occurs during the conversion reaction. Over time, the binder is pulverized, compromising the integrity of the cathode. Notably, for the metal fluoride CuF2, no demonstrations of rechargeability have been reported.
For CuF2, an additional challenge prevents rechargeability. The potential required to recharge a CuF2 electrode is 3.55V. However, in typical electrolytes for lithium ion batteries, Cu metal oxidizes to Cu2+ at approximately 3.4 V vs. Li/Li+. The oxidized copper can migrate to the anode, where it is irreversibly reduced back to Cu metal. As a result, Cu dissolution competes with the recharge of Cu+2LiF to CuF2, preventing cycling of the cell. The Cu metal accumulating on the anode surface can increase the impedance and/or destroy the solid-electrolyte interphase (SEI) on the anode.
The following papers and patents are among the published literature on metal fluorides that employ mixed conductors that are not electrochemically active within the voltage window of the metal fluoride: Badway, F. et al., Chem. Mater., 2007, 19, 4129; Badway, F. et al., J. Electrochem. Soc., 2007, 150, A1318; “Bismuth fluoride based nanocomposites as electrode materials” U.S. Pat. No. 7,947,392; “Metal Fluoride And Phosphate Nanocomposites As Electrode Materials” US 2008/0199772; “Copper fluoride based nanocomposites as electrode materials” US 2006/0019163; and “Bismuth oxyfluoride based nanocomposites as electrode materials” U.S. Pat. No. 8,039,149.
Certain embodiments of the present invention can be used to form electrochemical cells having metal fluoride active material that exhibit improved rate performance, improved energy efficiency, and improved cycle life when compared to prior batteries. Thus, these and other challenges can be addressed by embodiments of the present invention described below.BRIEF SUMMARY OF THE INVENTION
Certain embodiments of the invention include a method of making a composition for use in forming a cathode for a battery. The method includes coating a metal fluoride material with a coating precursor material including a metal or a metal complex and annealing coated metal fluoride material, wherein at least a portion of the metal fluoride material and at least a portion of the coating undergo a phase change. The metal fluoride material is preferably CuF2. The metal can be, for example, Ni, Ba, or Ta. The metal complex can be, for example a metal oxide, such as A12O3, SiO2, Ta2O5, TiO2; a metal nitride, such as AlN, TaN; a metal silicate, such as ZrSiO4; or other materials that are volatile enough to be evaporated and re-condensed onto a substrate. The annealing temperature is less than 450 degrees C, less than 400 degrees C, less than 325 degrees C, or less than 200 degrees C. Preferably, the annealing temperature is about 325 degrees C. The temperature is chosen such that it is sufficiently high for the metal complex to react with the metal fluoride, but not high enough to decompose the metal fluoride. Without such heat treatment and the resulting reaction, the material is not rechargeable, as is demonstrated by experiments described herein.
Certain embodiments of the invention include a composition formed by the methods disclosed herein. The composition is characterized by having reversible capacity. The composition can include particles with a grain size greater than 100 nm, 110 nm, 120 nm, or 130 nm. The composition can include a particle having a first phase and a coating on the particle having a second phase. Preferably, the first phase includes the metal fluoride and the second phase includes the metal oxide. The coating can be covalently bonded to the particle.
Certain embodiments of the invention include batteries having electrodes formed from the compositions disclosed herein, the method of making such batteries, and the method of use of such batteries.
The following definitions apply to some of the aspects described with respect to some embodiments of the invention. These definitions may likewise be expanded upon herein. Each term is further explained and exemplified throughout the description, figures, and examples. Any interpretation of the terms in this description should take into account the full description, figures, and examples presented herein.
The singular terms “a,” “an,” and “the” include the plural unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise.
The terms “substantially” and “substantial” refer to a considerable degree or extent. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation, such as accounting for typical tolerance levels or variability of the embodiments described herein.
The term “about” refers to the range of values approximately near the given value in order to account for typical tolerance levels, measurement precision, or other variability of the embodiments described herein.
The terms “conductive,” “conductor,” “conductivity,” and the like refer to the intrinsic ability of a material to facilitate electron or ion transport and the process of doing the same. The terms include materials whose ability to conduct electricity may be less than typically suitable for conventional electronics applications but still greater than an electrically-insulating material.
The term “active material” and the like refers to the material in an electrode, particularly in a cathode, that donates, liberates, or otherwise supplies the conductive species during an electrochemical reaction in an electrochemical cell.
The term “transition metal” refers to a chemical element in groups 3 through 12 of the periodic table, including scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), and meitnerium (Mt).
The term “halogen” refers to any of the chemical elements in group 17 of the periodic table, including fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
The term “chalcogen” refers to any of chemical elements in group 16 of the periodic table, including oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).
The term “alkali metal” refers to any of the chemical elements in group 1 of the periodic table, including lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
The term “alkaline earth metals” refers to any of the chemical elements in group 2 of the periodic table, including beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
The term “rare earth element” refers to scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
A rate “C” refers to either (depending on context) the discharge current as a fraction or multiple relative to a “1 C” current value under which a battery (in a substantially fully charged state) would substantially fully discharge in one hour, or the charge current as a fraction or multiple relative to a “1 C” current value under which the battery (in a substantially fully discharged state) would substantially fully charge in one hour.
In certain embodiments, a novel active material is prepared for use in a cathode with metal fluoride (MeFx) active materials. In some embodiments, the novel active material, sometimes referred to herein as a hybrid material, is prepared by combining a metal fluoride and a metal complex, followed by heat treatment of the mixture under an inert atmosphere according to the Formula (I)
According to certain embodiments, the heat treatment of the metal fluoride and metal complex causes a reaction to form a new phase according to the formula (II)
where x, y, z, a, b, and c depend on the identity and valence of the Me, Me′, and X. In some instances, 0<a≦1, O<b≦1, 0≦c≦1, and 0≦d≦1. In other embodiments, the heat treatment causes the formation of covalent bonds between the metal fluoride and the metal complex, improving conductivity and passivating the surface.
Suitable metal complexes, which can act as precursors for the reaction described herein, for use in synthesizing the active material include, but are not limited to, MoO3, MoO2, NiO, CuO, VO2, V2O5, TiO2, A12O3, SiO2, LiFePO4, LiMeTPO4 (where MeT is one or more transition metal(s)), metal phosphates, and combinations thereof. According to embodiments of the invention, these oxides can be used in Formula (I).
It is understood that the synthetic route for achieving the active material may vary, and other such synthetic routes are within the scope of the disclosure. The material can be represented by MeaMe′bXcF and in the examples herein is embodied by a Cu3Mo2O9 active material. Other active materials are within the scope of this disclosure, for example, NiCuO2, Ni2CuO3, and Cu3TiO4.
The coating materials disclosed herein provide rechargeability to otherwise non-rechargeable metal fluoride materials. Without being bound by a particular theory or mechanism of action, the rechargeability may be due to the electrochemical properties of the novel hybrid material, the coating of the metal fluoride to prevent copper dissolution, or a more intimate interface between the metal fluoride and the coating material as a result of the heat treatment and reaction. Further, the novel hybrid material may provide a kinetic barrier to the Cu dissolution reaction, or to similar dissolution reactions for other metal fluoride materials to the extent such dissolution reactions occur in the cycling of electrochemical cells.
In the case of oxide-based hybrid materials, intimate mixing of the metal fluoride and the metal complex (or other suitable precursor material) and moderate heat treatment can be used to generate rechargeable electrode materials. Suitable coating precursors include materials that decompose to form metal oxides (and in particular, transition metal oxides) as opposed to using a metal oxide to directly react with the metal fluoride. Examples of such precursors include, but are not limited to, metal acetates, metal acetylacetonates, metal hydroxides, metal ethoxides, and other similar organo-metal complexes. In either event, the final rechargeable material is not necessarily a pure oxide or a purely crystalline material. The reaction of Formula II predicts that there would not be a pure oxide or a purely crystalline material. In some instances, the metal oxide precursor or metal oxide material can form a coating, or at least a partial coating, on the metal fluoride active material. Without being bound by a particular theory or mechanism of action, the reaction of the metal oxide precursor or metal oxide material with the surface of the metal fluoride (and in particular copper fluoride) active material is important for generating a rechargeable electrode active material.EXAMPLES
The following examples describe specific aspects of some embodiments of the invention to illustrate and provide a description for those of ordinary skill in the art. The examples should not be construed as limiting the invention, as the examples merely provide specific methodology useful in understanding and practicing some embodiments of the invention.Example 1 Fabrication of Hybrid and/or Coated Electrodes for Rechargeable Cells
Materials and Synthetic Methods.
All reactions were prepared in a high purity argon filled glove box (M-Braun, O2 and humidity contents<0.1 ppm). Unless otherwise specified, materials were obtained from commercial sources (e.g., Sigma-Aldrich, Advanced Research Chemicals Inc., Alfa Aesar, Strem) without further purification.
Preparation of CuF2 Hybrid.
Milling vessels were loaded with CuF2 at from about 85 wt % to about 95 wt % and reactant (metal oxide or metal oxide precursor) at from about 5 wt % to about 15 wt %, and the vessels were sealed. The mixture was milled. After milling, samples were annealed at from about 200 degrees C to about 575 degrees C for 1 to 12 hours under flowing N2. Specific hybrid-forming reactants were processed as described below.
Preparation of CuF2/Cu3Mo2O9.
Milling vessels were loaded with CuF2 (85 wt %) and MoO3 (15 wt %), sealed, and then milled. After milling, samples were annealed at 450 degrees C for 6 hours under flowing N2.
Preparation of CuF2/NiO.
Milling vessels were loaded with CuF2 (85 wt %) and NiO (15 wt %), sealed, and then milled. After milling, samples were annealed at 325 degrees C for 6 hours under flowing N2.
Preparation of CuF2Nickel(II) acetylacetonate.
A fine dispersion of CuF2 was prepared by milling in the presence of THF (40-120 mg CuF2/mL THF). The dispersed sample was then added to a solution of Ni(AcAc)2 in THF such that Nickel(II) acetylacetonate accounted for 15 wt % of the solids in the solution. The solution was then agitated by either shaking, sonication, or low energy milling for from about 1 to about 12 hours. The solution was then dried at room temperature under vacuum and the resulting solid was annealed at 450 degrees C for 6 hours under dry air.
Preparation of Vapor Deposited Coatings
The coating material (nickel metal) was vaporized and then physically condensed onto the substrate at 20 weight percent. X-ray diffraction measurements were performed on the coated material to confirm the bulk CuF2 was not altered. The coated material was then annealed similarly to materials prepared by other methods.
Preparation of Atomic Layer Deposited Coatings
CuF2 was coated with TiO2 by atomic layer deposition methods. The expected coating thickness was about 8.5 nm based on ellipsometry measurements on a silicon witness sample, which represented a nominal 3 weight percent coating on the CuF2. The coated material was then annealed similarly to materials prepared by other methods.
Cathodes were prepared using a formulation composition of 80:15:5 (active material:binder:conductive additive) according to the following formulation method: 133 mg PVDF (Sigma Aldrich) and about 44 mg Super P Li (Timcal) was dissolved in 10 mL NMP (Sigma Aldrich) overnight. 70 mg of coated composite powder was added to 1 mL of this solution and stirred overnight. Films were cast by dropping about 70 μL of slurry onto stainless steel current collectors and drying at 150 degrees C for about 1 hour. Dried films were allowed to cool, and were then pressed at 1 ton/cm2. Electrodes were further dried at 150 degrees C under vacuum for 12 hours before being brought into a glove box for battery assembly.Example 2 Electrochemical Characterization of Electrochemical Cells Containing Rechargeable Electrodes
All batteries were assembled in a high purity argon filled glove box (M-Braun, O2 and humidity contents<0.1 ppm), unless otherwise specified. Cells were made using lithium as an anode, Celgard 2400 separator, and 90 μL of 1M LiPF6 in 1:2 EC:EMC electrolyte. Electrodes and cells were electrochemically characterized at 30 degrees C with a constant current C/50 charge and discharge rate between 4.0 V and 2.0 V. A 3 hour constant voltage step was used at the end of each charge. In some instances, cathodes were lithiated pressing lithium foil to the electrode in the presence of electrolyte (1M LiPF6 in 1:2 EC:EMC) for about 15 minutes. The electrode was then rinsed with EMC and built into cells as described above, except graphite was used as the anode rather than lithium.
For many of the rechargeable matrices described herein (and in particular for matrices including Mo, Ni, or Ti), the reactions described herein yield a new material at least at the surface of the particles of the metal fluoride active material. The novel material present at least at the surface of the particles of the metal fluoride active material is believed to provide many of the benefits disclosed herein.
Table 1 presents the results of further electrochemical characterization of certain embodiments disclosed herein. Table 1 shows that many metal oxide and metal oxide precursor starting materials can be used in the reactions described herein to yield rechargeable metal fluoride electrode materials. The materials in Table 1 include metal oxides, metal phosphates, metal fluorides, and precursors expected to decompose to oxides. In particular, nickel oxide showed excellent performance.
The solution, vapor, and atomic layer deposition methods can provide comparatively more uniform coatings on metal fluoride particles than the coatings obtained by milling methods. A comparatively thinner, more uniform coatings can provide the benefits of the coating material, such as more complete protection of the metal fluoride particle, with less precursor material. To the extent that excess precursor material is less active (and therefore less desirable) than the active material, thin, conformal coatings can provide an advantage in terms of weight-normalized reversible capacity.
Notably, the non-milling coating methods shown in
While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the invention.
1. A method of making an electrode, comprising:
- coating particles, wherein each particle includes a metal fluoride material, with a coating precursor material, wherein the coating precursor material includes a transition metal;
- annealing the particles such that at least a portion of the metal fluoride material and at least a portion of the transition metal react to undergo a phase change; and
- forming the coated particles into an electrode.
2. The method of claim 1, wherein the electrode forming step comprises preparing a formulation composition of coated particles, binder, and conductive additive.
3. The method of claim 1, wherein the metal fluoride material comprises copper fluoride.
4. The method of claim 1, wherein the coating step comprising milling the particles with the coating precursor material.
5. The method of claim 4, wherein the coating precursor material comprises a organo-metal complex.
6. The method of claim 4, wherein the coating precursor material comprises a metal oxide.
7. The method of claim 4, wherein the coating precursor material comprises elemental metal.
8. The method of claim 4, wherein the coating precursor material comprises NiO.
9. The method of claim 4, wherein the coating precursor material comprises TiO2.
10. The method of claim 4, wherein the coating precursor material is Ni.
11. The method of claim 4, wherein the coating precursor material comprises nickel(II) acetylacetonate.
12. The method of claim 4, wherein the coating precursor material comprises nickel acetate.
13. The method of claim 1, wherein the coating step comprises a solution coating process.
14. The method of claim 13, wherein the coating precursor material comprises an organo-metal complex.
15. The method of claim 13, wherein the coating precursor material comprises nickel(II) acetylacetonate.
16. The method of claim 1, wherein the coating step comprises a physical vapor deposition process.
17. The method of claim 16, wherein the coating precursor material comprises a metal oxide.
18. The method of claim 16, wherein the coating precursor material comprises a metal nitride.
19. The method of claim 16, wherein the coating precursor material comprises a metal silicate.
20. The method of claim 16, wherein the coating precursor material is Ni or Ti.
21. The method of claim 1, wherein the coating step comprises an atomic layer deposition process.
22. The method of claim 21, wherein the coating precursor material is Ni.
23. The method of claim 21, wherein the coating precursor material comprises a metal oxide.
24. The method of claim 21, wherein the coating precursor material comprises a metal nitride.
25. The method of claim 1, wherein the annealing step is conducted at a temperature less than or equal to 450 degrees C.
26. The method of claim 1, wherein the annealing step is conducted at a temperature less than or equal to 325 degrees C.
27. An electrode formed by the method of claim 1.
28. The electrode of claim 27 wherein the electrode is characterized by having reversible capacity.
29. The electrode of claim 27 comprising particles having a first phase and a coating on the particle having a second phase.
30. The electrode of claim 29 wherein the coating is covalently bonded to the particle
International Classification: H01M 4/04 (20060101); C23C 14/06 (20060101); C23C 14/08 (20060101);