ANODES, CATHODES, AND SEPARATORS FOR BATTERIES AND METHODS TO MAKE AND USE SAME
Anodes, cathodes, and separators for batteries (electrochemical energy storage devices). The anodes are Li metal anodes having lithiated carbon films (Li-MWCNT) (as dendrite suppressors and protective coatings for the Li metal anodes). The cathodes are sulfurized carbon cathodes. The separators are GNR-coated (or modified) separators. The invention includes each of these separately (as well as in combination both with each other and with other anodes, cathodes, and separators) and the methods of making each of these separately (and in combination). The invention further includes a battery that uses at least one of (a) the anode having a lithiated carbon film, (b) the sulfurized carbon cathode, and (c) the GNR-modified separator in the anode/cathode/separator arrangement. For instance, a full battery can include the sulfurized carbon cathode in combination with the Li-MWCNT anode or a full battery can include the sulfurized carbon cathode in combination with other anodes (such as a GCNT-Li anode).
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This application claims priority to U.S. Patent Appl. 62/381,782, entitled “Sulfurized Carbon As Stable High Capacity Cathodes In High Concentrated Electrolytes,” filed Aug. 31, 2016, and U.S. Patent Appl. 62/460,985, entitled “Anode, Cathodes, and Separators For Batteries And Methods To Make And Use Same,” filed Feb. 20, 2017, which patent application are commonly owned by the owner of the present invention. This patent application is hereby incorporated by reference in its entirety for all purposes.
GOVERNMENT INTERESTThis invention was made with government support under Grant No. FA9550-14-1-0111 and FA9550-12-1-0035, awarded by the U.S. Department of Defense, Air Force Office of Scientific Research. The United States government has certain rights in the invention.
FIELD OF INVENTIONAnodes, cathodes, and separators for batteries (electrochemical energy storage devices), and more particularly (a) Li metal anodes having lithiated carbon films (as dendrite suppressors and protective coatings for the Li metal anodes), (b) sulfurized carbon cathodes, (c) graphene nanoribbon (GNR) coated (or modified) separators. This includes the methods of making each of these anodes, cathodes, and separators, and the methods of using each of these alone or in combination with one another, such as in batteries.
BACKGROUND OF INVENTIONLithium-ion batteries are today's energy storage device technology of choice for electronic devices and electric vehicles. Since its commercialization in 1991, the lithium-ion battery (LIB) enabled wireless electronic devices, revolutionizing global communications. Almost three decades later, the LIB is expected to facilitate the integration of renewable energy into the electrical grid, as well as to allow affordable electric transportation. [Goodenough 2013; Noorden 2014; Dunn 2011; J. Zhang 2017]. However, these applications demand energy storage capabilities that the LIBs will be unable to meet, even if the theoretical energy density is reached. Therefore, new battery chemistries with higher energy densities have attracted the attention of the scientific community. There are new efforts to develop new battery chemistries with higher energy densities, such as lithium-air (Li—O2) and lithium-sulfur (Li—S), while also resolving the current limitations with pure lithium, commonly called lithium metal anodes. Li-air (Li—O2) and Li-sulfur (Li—S) systems have shown great promise as the energy densities are almost one order of magnitude higher than that of the LIB. [Noorden 2014; Bruce 2011; Girishkumar 2010; Manthiram 2015; Armand 2008].
In Li-air and Li-sulfur batteries, the positive electrode or cathode is coupled with Li as the negative electrode or anode. [Bruce 2011] Li metal (as opposed to lithium ion=Li+) possess one of the highest theoretical specific capacities (3,860 mAh g−1) and the lowest electrochemical potential (−3.040 V vs. standard hydrogen electrode) of all possible anode materials [Xu 2014]; far surpassing presently used graphite anodes in LIBs. While Li metal was extensively investigated as an anode material in the late 1980s, safety issues associated with its use and the short life of the battery hampered its commercialization. Li metal was eventually replaced by graphite and lithium ions. [Goodenough 2013; Xu 2014; Whittingham 2012]. The growing demand for energy storage has revived the attempts to overcome the safety and lifetime issues of Li metal anodes.
A main challenge of Li metal anode is its tendency to form whisker and needle-like structures, often called “dendrites,” during the charging process. These dendrites can either isolate Li, shortening the life of the battery, or penetrate through the separator, forming an internal short circuit. The formation of dendrites is related to the reactivity between Li and the electrolyte; the low electrochemical potential of Li makes possible the instantaneous reduction of the electrolyte on its surface, creating a passivation layer or solid electrolyte interface (SEI). This SEI layer is typically inhomogeneous and can easily break as a result of the volume change during the charge-discharge cycle, which promotes the growth of dendrites through the fractures, as well as the production of dead Li (electrically isolated Li). [Xu 2014; Cohen 2000; Lin I 2017].
Thus, in spite of these advantages, the practical application of using Li metal in commercial batteries has been hindered by the safety concerns associated with the Li dendrite growth upon repeated charge/discharge cycling. In contact with the electrolyte, Li forms an inhomogeneous solid electrolyte interphase, which provides nucleation sites for dendrite formation at any current density, in addition to the parasitic reactions that occur. These issues give rise to a low coulombic efficiency, a gap formation between the anode and the interface layer, the depletion of the electrolyte and short circuits that can generate fires and explosions.
The different approaches that have been tried to suppress the formation of Li can be divided into three different categories. The first category is based in the modification of the electrolyte composition to improve the ion transportation and consequently the properties of the SEI. [Qian 2015; Besenhard 1993; Ding 12013; Osaka 1997; Li 2015; Jin 2015; Ding II 2013]. The second involves the development of solid electrolytes that acts as barriers to stop dendrite propagation without compromising the ion transportation. [Bates 1993; Zhou 2016; Wang 2017]. The third category focuses on protecting the interface Li-electrolyte by forming a protective layer that will control the Li deposition. [Zheng 2014; Lee 2015; Kim 2015; Kozen 2015; Li 2016]. To ensure a homogenous deposition of Li, this protective layer needs to be mechanically strong, chemically stable, and able to control the flow of Li ions. Different carbon materials, metal oxides and polymers have been used and proven to form a stable protective layer that prevent the Li dendrite formation. Nevertheless, in most cases, current collectors and complex fabrication methods are required, and, in most cases, still result in the formation of a gap between the anode and the protective layer giving rise to dendrite formation.
Another interesting strategy is the use of three dimensional (3D) porous frameworks as host structures for Li metal. In this approach, Li metal is electrodeposited in a 3D structure, where it is accommodated and distributed in the empty volume of the porous framework, which reduces local current density and minimizes Li dendrite formation. [Zhang 2016; Yang 2015; Y. Zhang I 2017; Lin 2016; Liu 2016; Lin II 2017; Y. Zhang II 2017; Tour PCT '052 Application]. The use of scaffolds or 3D frameworks implies that the gravimetric or volumetric capacity of the Li metal anode is reduced by including the mass or volume of the framework component. An ideal framework structure for Li dendrite suppression would involve a high surface area, low density material with a homogeneously conductive surface for Li deposition that would maximize the gravimetric capacity of the Li metal anode. In addition, a non-tortuous path for Li plating/stripping is desired for reversible operation and high rate applications.
Furthermore, improved high capacity cathodes are desired, such as to achieve batteries with improved energy density and lower cost effectiveness. The development of high capacity cathodes for lithium ion batteries (LIBs) is desired to achieve batteries with improved energy density. Commercially available cathodes such as lithiated metal oxides (e.g., LiCoO2, LiMnO2, LiFePO4, and the like) present lower gravimetric capacity. However, such cathodes display high voltage operation (>3 V vs. Li/Li+) during charge/discharge processes, thereby leading to batteries with comparatively high energy density compared to other battery technologies.
Newer cathodes such as those based on elemental sulfur can lead to much higher energy density because the specific capacity to store Li ions is much higher (1675 mAh g−1) compared to lithiated metal oxide cathodes (<200 mAh g−1), even though sulfur's voltage operation is lower (˜2.1 V vs. Li/Li+).
Sulfur cathodes are also especially attractive considering their cost, low toxicity and abundance when compared to metal oxide cathodes. However, the challenge posed by sulfur cathodes is to control and suppress the “shuttle” effect, by which lithiated species of sulfur, namely lithium polysulfides (i.e., linear chains of sulfur bonded to lithium ion at their ends, LixSy with x=2, y=4-8), can be dissolved into the battery electrolyte.
Moreover, the dissolution of Li polysulfides to the electrolyte has two main deleterious effects: one is that it depletes sulfur content from the cathode and the second is that there is an accumulative reaction of Li polysulfides over the surface of the Li metal anode. These two factors lead to a fast capacity drop in Li—S batteries with a concomitant increased resistance to lithiate/delithiate the cathode.
The approaches to mitigate the Li polysulfide dissolution have been focused on four main strategies: (1) chemical/physical blocking barriers to slow/stop diffusion of Li polysulfides, (2) coated sulfur particles to suppress Li polysulfide dissolution, (3) solid electrolytes, and (4) sulfurized carbon species. Among these options, the sulfurized carbon species involves the chemical covalent bonding between sulfur and a carbon species, in which elemental sulfur is no longer present.
A separator is generally a porous membrane that functions to keep an anode and a cathode apart electrically while still allowing the transport of ionic charge carriers between them. Improved or modified separators are also desired to improve the cycling stability and decrease the self-discharge effect in batteries. The surface modification of the separator prevents the diffusion of undesirable materials between an anode and a cathode of a battery.
SUMMARY OF INVENTIONThe present invention includes new anodes and new processes for modifying the Li metal surface enabling its safe use in lithium metal batteries. The modification includes coating the Li metal surface with a multi-walled carbon nanotubes (MWCNTs) (or graphene nanoribbons, single walled nanotubes, or ultrathin carbon films) free-standing thin film (“Li-MWCNT” and, alternatively “MWCNT-Li” and “rLi”) and an electrolyte. (“rLi”, i.e., “red lithium,” is indicative of the MWCNT acquiring a dark red color as a result of the lithiation (doping) process). The thin film is typically 20 to 80 microns in thickness, but it could be thinner or thicker as desired. This thin film coating becomes a lithiated carbon nanotube layer on top of the Li surface driven by the surface reaction between the Li metal and the MWCNT film. The entire MWCNT thin film then becomes doped by the Li metal. Then the Li-doped MWCNT becomes the surface which ejects Li ions toward the cathode upon discharging. This Li-doped MWCNT layer protects the underlying Li metal from parasitic reactions, preventing the formation of dendrites on the surface of Li to practical current densities of 1 and 2 mA cm−2 and high areal capacities, such as 2 and 4 mAh cm−2, considering one side of the electrode. The ranges could be much broader; these numbers are merely illustrative. The lithiated MWCNT layer that is in direct contact with the lithium metal also eliminates the creation of potential gaps or inhomogeneities between the solid electrolyte interphase layer and the Li metal anode because the MWCNT layer is electrostatically drawn to the lithium metal by the doping process, further reducing the possibility of dendrite formation and loss of coulombic efficiency.
Thus, among other things, the Li-MWCNT protects lithium from the electrolyte and lithium polysulfides in Li—S batteries. The Li-MWCNT can also be utilized in lithium-air (LiO2) batteries to protect the lithium from the dissolved oxygen.
In some embodiment, the present invention encompasses full batteries and new processes by combining the anodes with sulfurized carbon as stable high capacity cathodes. In some embodiments, the present invention includes a full battery (FB) that combines the GCNT-Li anode with a sulfurized carbon (SC) cathode with high sulfur content (up to 60 wt %). This affords a stable device with an operation voltage of 2.15 V, high energy density (752 Wh kg−1 total electrodes, total electrodes=GCNT-Li+SC+binder), high areal capacity (2 mAh cm−2), and good cyclability (80% retention at >500 cycles), and the system is free of Li polysulfides and dendrites that would cause severe capacity fade. In some embodiments, the full batteries of the present disclosure also include high concentration electrolytes. In some embodiments, the cathodes of the present disclosure also include additional additives, such as graphene nanoribbons (GNRs) (SC/GNR).
The present invention further includes new separators and new processes for making separators having a thin coating of graphene nanoribbons (GNRs). This thin coating could also be made of MWCNTs, single-walled carbon nanotubes (SWCNTs) or graphene that is not in a ribbon shape, graphene oxide, or other form of carbon that can form a barrier to prevent sulfur species from migrating through the membrane. Here, a ribbon is defined as having a length to width aspect ratio of at least 3:1.
The present invention further includes batteries that include one or more of the anodes, cathodes, and separators described above and methods of using same.
In general, in one embodiment, the invention features a lithium metal anode that includes a lithium metal coated with a lithiated carbon material.
In general, in another embodiment, the invention features a cathode that includes a sulfurized carbon cathode.
In general, in another embodiment, the invention features a GNR-modified separator that includes a polymer material coated with a layer of GNRs. The GNR-modified separator is operable for use as a separator in a battery.
In general, in another embodiment, the invention features a battery that includes an anode, a cathode, and a separator positioned between the anode and the cathode. The battery comprises a component selected from the group consisting of: (a) a lithium metal anode that includes a lithium metal coated with a lithiated carbon material; (b) a cathode that includes a sulfurized carbon cathode; (c) a GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery; and (d) combinations thereof.
Implementations of the invention can include one or more of the following features:
The battery can include the lithium metal anode that includes the lithium metal coated with the lithiated carbon material.
The battery can include (a) the lithium metal anode that includes the lithium metal coated with the lithiated carbon material and (b) the cathode that includes the sulfurized carbon cathode.
The battery can include (a) the lithium metal anode that includes the lithium metal coated with the lithiated carbon material, (b) the cathode that includes the sulfurized carbon cathode, and (c) the GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery.
The battery can include the cathode that includes the sulfurized carbon cathode.
The battery can include (a) the cathode that includes the sulfurized carbon cathode, and (b) the GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery.
The battery can include the GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery.
In general, in another embodiment, the invention features a method that includes making a lithium metal anode. The method includes selecting a lithium metal having a surface. The method further includes coating the surface of the lithium metal with a carbon material and an electrolyte. The method further includes performing a reaction involving the lithium metal, carbon material, and the electrolyte) to form a lithiated layer on top of the lithium metal.
In general, in another embodiment, the invention features a method that includes making a sulfurized carbon cathode.
In general, in another embodiment, the invention features a method that includes selecting a polymer material operable for use as a separator in a battery, and modifying the polymer material by adding a layer of GNRs to form a GNR-modified separator.
In general, in another embodiment, the invention features a method of forming a battery that includes the steps of combining an anode, a cathode, and a separator positioned between the anode and cathode. The method further includes the step selected from the group consisting of: (a) making the lithium metal anode as set forth above, (b) making the sulfurized carbon cathode as set forth above; (c) making the GNR-modified separator as set forth above; and (d) combinations thereof.
Implementations of the invention can include one or more of the following features:
In the method of forming the battery, the anode can be made by making the lithium metal anode as set forth above.
In the method of forming the battery, (a) the anode can be made by making the lithium metal anode as set forth above and (b) the cathode can be made by making the sulfurized carbon cathode as set forth above.
In the method of forming the battery, (a) the anode can be made by making the lithium metal anode as set forth above, (b) the cathode can be made by making the sulfurized carbon cathode as set forth above, and (c) the GNR-modified separator can be made as set forth above.
In the method of forming the battery, the cathode can be made by making the sulfurized carbon cathode as set forth above.
In the method of forming the battery, (a) the cathode can be made by making the sulfurized carbon cathode as set forth above and (b) the GNR-modified separator can be made as set forth above.
In the method of forming the battery, the GNR-modified separator can be made as set forth above.
In general, in another embodiment, the invention features a method of forming a battery that includes the steps of combining an anode, a cathode, and a separator positioned between the anode and the cathode. The battery comprises a component selected from the group consisting of: (a) a lithium metal anode that includes a lithium metal coated with a lithiated carbon material; (b) a cathode that includes a sulfurized carbon cathode; (c) a GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery; and (d) combinations thereof.
Implementations of the invention can include one or more of the following features:
The method of forming the battery can include the lithium metal anode that includes the lithium metal coated with the lithiated carbon material.
The method of forming the battery can include (a) the lithium metal anode that includes the lithium metal coated with the lithiated carbon material and (b) the cathode that includes the sulfurized carbon cathode.
The method of forming the battery can include (a) the lithium metal anode that includes the lithium metal coated with the lithiated carbon material, (b) the cathode that includes the sulfurized carbon cathode, and (c) the GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery.
The method of forming the battery can include the cathode that includes the sulfurized carbon cathode.
The method of forming the battery can include (a) the cathode that includes the sulfurized carbon cathode, and (b) the GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery.
The method of forming the battery can include the GNR-modified separator that includes a polymer material coated with a layer of GNRs in which the GNR-modified separator is operable for use as a separator in a battery.
Implementations of the invention can include one or more of the following features:
The lithium metal can be in the form of a lithium foil.
The carbon material can include multi-walled carbon nanotubes.
The multi-walled carbon nanotubes can be in the form of a bucky paper.
The carbon material can include graphene nanoribbons.
The nanoribbons can be in the form of a filtered nanoribbon paper.
The carbon material can be selected from a group consisting of multi-walled carbon nanotubes, single-walled carbon nanotubes, few-walled carbon nanotubes, graphene nanoribbons, graphene oxide, graphene oxide nanoribbons, graphoil, graphene nanoplatelets, graphite, activated carbon, thermally treated asphalt, amorphous carbon, carbon black, and mixtures thereof.
The carbon materials can further be treated with a polymer to make the carbon materials more flexible without cracking.
The polymer can include polydimethylsiloxane.
The polymer can be selected from a group consisting of polydimethylsiloxane, polyurethane, thermoplastic polyurethane, polybutadiene, poly(styrene butadiene), poly(styrene butadiene styrene), polyacrylonitrile, polyaniline, poly fluorinated systems, poly(methyl methacrylate), poly(ethylene glycol), poly(ethylene oxide), polyacrylates, vinyl polymers, chain growth polymers, step growth polymers, condensation polymers, and mixtures thereof.
The electrolyte can be selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), dimethoxyethane (DME), and 1,3-dioxolane (DOL), and mixtures thereof.
The electrolyte can include a mixture of the 1 mol L−1 lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a ratio of 1:1 of the dimethoxyethane (DME) and the 1,3-dioxolane (DOL).
The electrolyte can be an ionic liquid or a mixture of the ionic liquid with an organic solvent.
The electrolyte can be formed from a salt in a solvent. The salt can be selected from the group consisting of lithium hexafluorophosphate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium tetrafluoroborate, and combinations thereof. The solvent can be selected from the group consisting of ethlylene carbonate, propylene carbonate, butylene carbonate, vinyl ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethylene carbonate, tetraethylene glycol dimethyl ether, and combinations thereof.
The electrolyte can be placed on or between the carbon material and the lithium metal in the initial phases of the method.
The electrolyte can be in a high concentration.
The electrolyte can be between 0.5 and 10 mol/L of lithium bis(fluorosulfonyl)imide (LIFSI) in dimethoxyethane (DME).
The electrolyte can be between 2 and 8 mol/L of the lithium bis(fluorosulfonyl)imide (LIFSI) in the dimethoxyethane (DME).
The electrolyte can be between 3 and 5 mol/L of the lithium bis(fluorosulfonyl)imide (LIFSI) in the dimethoxyethane (DME).
The electrolyte can be 4 mol/L of the lithium bis(fluorosulfonyl)imide (LIFSI) in the dimethoxyethane (DME).
An electrolyte can be added to the battery in combination with the anode.
The electrolyte can be between 0.5 and 10 mol/L of lithium bis(fluorosulfonyl)imide (LIFSI) in dimethoxyethane (DME).
The lithium metal can dope the carbon material.
The carbon material can become red or silver in color.
The carbon material can be operable to suppress lithium dendrite formation of the lithium metal anode.
The doped carbon material can become the source of lithium ions injected across into the electrolyte and then into a cathode.
The lithium metal can be a metallic Li foil. The doped carbon material can act as a buffer between an SEI layer and the metallic Li foil.
The buffer can eliminate any gap formation between the SEI layer and the metallic Li foil.
The lithium metal, the carbon material, and the electrolyte can be part of a battery.
The lithium metal, the carbon material, and the electrolyte can be part of a battery anode.
The battery can include a sulfur cathode.
The sulfurized carbon cathode can include sulfur, carbon, and thermally treated polyacrylonitrile.
The sulfurized carbon cathode can include sulfur in an amount between about 47% and about 60 wt%.
The amount of the sulfur in the sulfurized carbon cathode can be between about 47% and about 57 wt %.
The amount of the sulfur in the sulfurized carbon cathode can be between about 55% and about 60 wt %.
The cathode can lack elemental sulfur.
The cathode can include a carbon additive that is a conductive filler.
The carbon additive can be selected from the group consisting of carbon black, graphene, carbon nanotubes, graphene nanoribbons, and combinations thereof.
The method of making the sulfurized carbon cathode can include heat treating elemental sulfur with a carbon source.
The carbon source can include PAN.
The step of heat treating can occur in the presence of an additive.
The additive can be selected from a group consisting of carbon black, graphene, carbon nanotubes, graphene nanoribbons, and combinations thereof.
The step of heat treating can occur at a temperature of at least about 100° C.
The step of heat treating can occur at a temperature of at least about 450° C.
The step of heat treating can occur for at least about 3 hours.
The method of making the sulfurized carbon cathode can include forming a powder that includes elemental sulfur, a carbon source, and an additive. The method of making the sulfurized carbon cathode can include heat treating the powder at a temperature of at least about 450° C. for at least three hours.
The carbon source can include PAN. The additive can include graphene nanoribbons.
The sulfurized carbon cathode can be part of a seamless hybrid of nanotubes grown from a graphene layer.
The polymer materials can include at least one of polypropylene (PP) and polyethylene (PE).
In general, in another embodiment, the invention features a method to form an anode that includes selecting a lithium metal having a surface. The method further includes coating the surface of the lithium metal with a carbon material and an electrolyte. The method further includes forming a lithiated carbon material by lithiating the carbon material with lithium from the lithium metal.
Implementations of the invention can include one or more of the following features:
The method can further include continuing the step of lithiating the carbon material until there is no remaining lithium in the lithium metal. The lithiated carbon material can be the anode.
In general, in another embodiment, the invention features a lithium metal anode. The lithium metal is coated with a thin film material and an electrolyte.
The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
It is also to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.
The present invention is directed to anodes, cathodes, and separators for improved batteries (electrochemical energy storage devices), and more particularly (a) Li metal anodes having lithiated carbon films (as dendrite suppressors and protective coatings for the Li metal anodes), (b) sulfurized carbon cathodes, (c) GNR-coated separators. This includes the methods of making each and the methods of using each of these alone or in combination with one another, such as in batteries.
As used herein, a “lithiated carbon film” is a carbon film to which lithium is bound to, or doped with, the carbon material in the carbon film. Furthermore, the lithium could be in the 0 or +1 oxidation state, being lithium metal or lithium ion when bound to the carbon material.
As noted above, the batteries shown in
The present invention demonstrates that lithiated MWCNT, as an example, can act as a layer that effectively protects the Li surface against parasitic reactions and suppresses the formation of Li dendrites on the surface of the Li foil. The lithiation of the MWCNT film is achieved by contacting the Li surface and the MWCNT film with the use of electrolyte (4 mol L−1 of lithium bis(fluorosulfonyl)imide (LIFSI) in dimethoxyethane), as an example. The lithiation reaction is spontaneous (complete in less than 30 minutes) and the MWCNT acquire a red color as a result of the lithiation (doping) process. It is believed that the lithiated carbon layer can act as an ion/electron transport medium, mediating the Li plating and stripping processes, thus suppressing the dendrite and rendering the Li a modified surface that is more chemically resistant against parasitic reactions with the liquid electrolyte. The dendrite suppression ability was observed by Li plating/stripping experiments between two Li foils in a 2032 coin cell configuration.
The stripping/plating process was investigated using the common electrolyte for sulfur cathodes: 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a ratio of 1:1 of dimethoxyethane (DME) and 1,3-dioxolane (DOL). Moreover, to investigate protection against parasitic reactions, the same electrolyte with the addition of S in the form of lithium polysulfides (Li2S6) was used. The control experiments consisted of a bare Li foil under the same conditions. The additive lithium nitrate (LiNO3) used to protect Li was not used in the electrolyte.
Although lithium polysulfides have been found to improve the stability of Li by forming a strong SEI layer, the bare Li anode still exhibited fluctuations in the voltage profile and a larger overpotential, indicating the enhanced chemical resistance of the Li-MWCNT. The cycling stability at different current densities was investigated, Li-MWCNT exhibited lower overpotential and less fluctuations than the bare Li (
For certain anodes of the present invention, the MWCNT film preparation was performed as follows: Pristine MWCNT (diameter=70-80 nm; M-grade; NanoTech Labs, Inc.) were dispersed in N-methyl-2-pyrrolidone (Sigma-Aldrich) using tip sonication. Alternatively, a dispersion of MWCNT can be achieved in a water and 2-propanol mixture (4:1 volume proportion ratio, respectively). The homogeneous dispersion was vacuum-filtrated through a porous aluminum membrane to produce a homogenous film (1.5 mg/cm2) which is often referred to as a bucky paper. To obtain the free-standing film, the aluminum was dissolved in a 1 N sodium hydroxide solution.
For certain anodes of the present invention, the Li coating was carried out in an argon-filled glove box; 25 μL of 4 M LiFSI (Oakwoods Products, Inc.) in DME (Sigma-Aldrich) were placed on a Li foil (thickness=0.45 mm, MTI Corporation), following by the MWCNT film. The Li foil surface was cleaned before the reaction by scraping the surface to remove an oxide layer. Another 25 μL portion of 4 M LiFSI was added, followed by a second Li foil with the same thickness as the first Li foil. After 30 min, the upper Li foil was removed, resulting in a Li foil covered by a lithiated MWCNT film. See
For the battery assembly regarding certain embodiments of the present invention, to study the Li stripping/plating, symmetric cells were prepared by assembling the Li-MWCNT electrodes into 2032-type coin cells. The electrolytes employed were either 1 M LiTFSI (Sigma-Aldrich) in a 1:1 ratio of DME and DOL (Sigma-Aldrich) or 4 M LiFSI in DME. The separator used was Celgard K2045. For the controls, symmetric cells using freshly scraped Li foils were assembled. A constant current was applied to the electrodes, and the potential and coulombic efficiencies were recorded over time.
For these embodiments, it was found that the MWCNT film was preferably well-attached to the Li surface. Furthermore, the MWCNT films after lithiation could become brittle. Also, though not required, the lithiation process of MWCNT was facilitated by high concentrated electrolyte.
In further anodes of the present invention, different carbon nanomaterials can be used (single walled CNTs, graphene oxide, graphene nanoribbons, high porosity ultra-thin graphite films, porous ultra-thin conductive films). For these alternative carbon materials, the graphene nanoribbons appeared to provide best performance for these selected, and they also appear to be as good as using the MWCNTs.
Furthermore, in further embodiments of the present invention, a thin and porous polymer coating with the MWCNTs, such as polydimethylsiloxane (PDMS), can be coated onto MWCNT films to render them more flexible and foldable (which would generally be desirable for large batteries, scrolled electrodes, and for flexible batteries).
The present invention will enable the safe use of pure Li metal anodes in advanced battery technologies required for the next generation of high energy density batteries, such as metallic rechargeable, sulfur and oxygen batteries. By solving the lithium dendrite formation with a simple fabrication process, the fabrication of batteries that can safely provide more energy storage will be possible. Furthermore, the fabrication process is simple and allows scalable production. This protective (buffer) layer can be also used to protect other type of metal electrodes, such as sodium or potassium or magnesium or sulfur or selenium.
Moreover, the lithiated carbon film is not only a protection layer, it also assists mediating the lithiation (plating and stripping reaction).
In other embodiments of the present invention, a MWCNT mat can be positioned on the anode without lithium. Either electrochemically or by evaporation a Li layer can be applied atop the MWCNT layer, which can diffuse to the underside of the MWCNT layer. In some embodiments, the diffusion through the MWCNT layer can be facilitated by an initial or subsequent treatment with electrolyte.
In addition to the simple fabrication process, the present invention also has advantages over the prior art that include: Li dendrite suppression using mediated lithiation; mediation of Li deposition by the MWCNTs during the charge/discharge cycle; and creating an ion/electron conductive/protective layer that evenly distributes the Li metal deposition.
It should further be noted that, in extreme discharge, all of the lithium metal might end up in the lithiated carbon material, such that there is no remaining lithium metal (such as the lithium foil) under the lithium carbon material. Such lithiated carbon material (without any underlying lithium metal) can be utilized as an anode in the present invention.
Sulfurized Carbon CathodesFurther embodiments of the present invention utilize sulfurized carbon cathodes. The cathodes can further include high concentrations of electrolytes. The cathodes can also further include additional additives, such as graphene nanoribbons (GNRs) (SC/GNR).
The cathodes can have a sulfur content of more than about 50 wt % (e.g., between about 47 and about 56 wt % of S in mass related to the mass of the electrode excluding the mass contribution of the current collector). The sulfur content in the cathodes can lack any elemental sulfur. The sulfur content in the cathodes can contain minimal amounts of elemental sulfur.
The cathodes can be associated with electrolyte concentrations of more than about 1 mol L−1 (e.g., about 4 mol L−1). The cathodes can be associated with various types of electrolytes. The electrolytes can include commercial electrolytes, such as lithium hexafluorphosphate in ethylene carbonate:diethyl carbonate (LiPF6 in EC:DEC), lithium bis(fluorosulfonyl)imide in dimethoxyethane, and combinations thereof.
The cathodes can include various types of carbons additives as conductive fillers. For instance, in some embodiments, the additives can be carbon black, graphene, carbon nanotubes, graphene nanoribbons, among others.
The cathodes can be fabricated by various methods. For instance, in some embodiments, the cathodes of the present disclosure can be fabricated by heat treating elemental sulfur with a carbon source (e.g., PAN). In some embodiments, the heat treatment can also occur in the presence of additives, such as GNRs. In some embodiments, the heat treatment can occur at temperatures of more than about 100° C. (e.g., about 450° C. and higher). In more specific embodiments, the cathodes can be fabricated by slowly heat treating elemental sulfur, PAN and GNRs (such as at 450° C.) in a sealed container and an inert atmosphere. The final material can have about 55 wt % to about 60 wt % of S in mass. In some embodiments, the final material can be further heat treated with additional amount of elemental sulfur.
For example, a sulfurized carbon cathode can be prepared as follows: A powder can be prepared by grinding elemental sulfur, PAN (Sigma-Aldrich, 150000 molecular weight) and GNRs in the mass proportion of 55:11:1 for 10 minutes. The powder is then submitted to heat treatment in a sealed tube at 450° C. First, the powder is loaded into an alumina boat. The alumina boat is inserted in the tube and the tube is evacuated to remove air. Next, the tube is filled with argon until it reaches room pressure. At this point, the tube is sealed. The heating from room temperature (25° C.) to 450° C. proceeded at a rate of 5° C. min−1. The heat treatment at 450° C. proceeded for 3-15 h and then the mixture was allowed to cool to room temperature.
If, for example, this sulfurized carbon cathode is to be included in a battery assembly, this can be further performed as follows: Electrodes can be prepared by 80 wt % of SC/GNR, 10wt % carbon black (Black Pearl 2000) and 10 wt % PVDF (polyvinylidene fluoride) as binder, prepared as slurry. The slurry is coated over steel foil and dried under vacuum at 60° C. for 12 hours. Half-cells are assembled inside a glove box (oxygen and water level<2 ppm) as coin cells (2032) with Celgard K2045 as separator and Li foil as counter and reference electrode (two electrode configuration). The electrolyte can be 1 mol L−1 LiPF6 in EC:DEC or 4 mol L−1 LiFS1 in DME. The charge-discharge can be tested at 0.1 C (it was considered only the mass of sulfur to calculate the current density) with the voltage limits of 1 to 3 V (vs. Li/Li+).
The cathodes can have various advantageous properties. For instance, in some embodiments, the cathodes display very stable behavior during continuous charge/discharge cycles (i.e., minimal capacity loss over cycles) and compatibility in different electrolytes, in which a better performance (i.e., high capacity and stability) is observed in high concentration electrolytes. In more specific embodiments, the cathodes of the present disclosure are able to deliver a capacity of 704 mAh g−1 using common commercial electrolytes (e.g., 1 mol L−1 LiPF6 in EC:DEC (lithium hexafluorphosphate in ethylene carbonate:diethyl carbonate)) and 1050 mAh g−1 using high concentration electrolytes (e.g., 4 mol L−1 lithium bis(fluorosulfonyl)imide in dimethoxyethane).
Furthermore, the carbon in the sulfurized carbon cathode can be part of a seamless hybrid of nanotubes grown from a graphene layer disclosed and taught in U.S. Pat. No. 9,455,094, issued Sep. 27, 2016, to Tour et al. (“the '094 Tour Patent”). See also Appendix A, at p. 7 (discussing several commonly-owned patent applications, including U.S. Patent Appl. Serial No. 2014/0313636, which issued as the '094 Tour Patent).
The produced GNR-containing cathodes (SC/GNRs) can act as efficient cathodes without the problems associated with typical elemental sulfur cathodes. The sulfur species in this cathode embodiment corresponds to 55% to 60% of the mass of the material, according to thermogravimetric (TG) curves (
According to the literature, the sulfur in sulfurized carbon species are believed to be composed mainly by small sulfur chains (S2—S3) chemically bonded to the sp2 carbon lattice produced by the decomposition of the PAN, therefore suppressing the Li polysulfide dissolution. The TG curves (curves 1201-1203) in
The heat treating time of S, PAN and GNR was varied from 3 to 15 hours. The heating time does not significantly affect the amount of S in the SC/GNR according to
However, the capacity of half-cell batteries using SC/GNR cathodes produced with 3, 6 and 15 hour heat treatment time (SC/GNR-3 h, SC/GNR-6 h and SC/GNR-15 h) presented very different electrochemical behavior, as observed in
The tests were conducted in 4 mol L−1 LiFSI (lithium bis(fluorosulfonyl)imide in DME (dimethoxyethane)) as electrolyte. The capacity of the sample SC/GNR-15 h is lower (˜600 mAh g−1) than the samples SC/GNR-3 h/6 h (˜1000 mAh g−1). The cycling stability and coulombic efficiency (CE) of these tests are presented in the graphs of
The samples SC/GNR-6 h and SC/GNR-15 h present stable behavior during continuous cycling compared to the sample SC/GNR-3 h. See
Using the sample SC/GNR-6 h, the compatibility of the cathode was tested in common commercial electrolytes composed by 1 mol L−1 LiPF6 (lithium hexafluorphosphate) in EC:DEC (ethylene carbonate:diethylcarbonate) and the performance was compared with the high concentration electrolyte (4 mol L−1 LiFSI in DME). See
Curve 1601 is the discharge curve during the first cycle. Curves 1602 reflect subsequent discharge curves (going from ˜3 volts to 1 volt with a specific capacity of ˜800 mAh g−1. Curves 1603 reflect subsequent charge curves (going from ˜1 volt to 3 volts with a specific capacity of again around ˜800 mAh g−1. The same cathode and anode in this battery could also operate under other concentrations (0.5 M to 10 M), Li salts, and other electrolyte compositions.
Sulfurized carbon cathodes have various utilities. For example, anodes and cathodes with high capacity and optimal rate performance are desired to compose batteries that have much higher energy density compared to the current technology. In some embodiments, the compatibility and optimal performance of sulfurized carbon cathodes with high concentration electrolytes make them compatible with high capacity and advanced anodes, such as Li metal anodes, allowing the possibility to replace both anodes.
Moreover, the methods of making the sulfurized carbon cathodes are facile, thereby allowing scalable production of the cathode. In some embodiments, the resulting material also has a high proportion of S (about 55 wt % to about 60 wt %) and N (12 wt %), which could be of interest in other catalytic applications.
Sulfurized carbon cathodes solve issues related to cathodes by using a formulation combination of sulfur covalently bound to carbon in the presence of high electrolyte concentration.
The sulfurized carbon cathodes complement the many developments in anodes, providing the other requisite half of the battery configuration. The sulfurized carbon cathodes demonstrate that covalent sulfur carbon species can afford a stable high capacity cathode if the electrolyte used is at much higher concentrations than typically disclosed by others in the literature.
In some embodiments, the use of such high concentrations of electrolytes along with sulfur-based cathodes produce enhanced effects.
In some embodiments, the sulfurized carbon cathodes can be used in conjunction with Applicants' monolithic seamless graphene-carbon nanotube hybrid electrodes (GCNTs) to afford optimal properties for GCNTs in cathodes as GCNT benefitted anodes as formerly disclosed. [See e.g., Tour '052 Application and Tour '636 Application]. In some embodiments, the sulfurized carbon cathodes can also be used in conjunction with ultrahigh surface area carbons (e.g., uGil-900 made from asphalt and KOH activation) to afford optimal properties for asphalt-derived cathodes just as asphalt-derived carbons benefitted anodes as formerly disclosed. [See, e.g., Tour PCT '950 Application].
In some embodiments, the high concentration electrolyte for the sulfurized carbon cathodes resembles the electrolyte concentration and type that has been shown to work well for Li-GCNT anodes [e.g., Tour PCT '052 Application] and Li-asphalt derived anodes [e.g., Tour PCT '950 Application]. As such, in some embodiments, the sulfurized carbon cathodes complement the afore-mentioned systems, which are now permitted as both cathodes and anodes to work in unison, as required.
In some embodiments where GCNT electrodes are utilized, the sulfurized carbon cathodes could be fabricated by the methods of the present disclosure through the use of sulfur, PAN, and GCNT (with or without GNRs). In some embodiments where asphalt-derived electrodes are utilized, then the sulfurized carbon cathodes could be fabricated by using sulfur, PAN, and uGil-900 high surface area carbon from KOH activation of asphalt (with or without the GNRs).
In some embodiments, the inclusion of a small proportion of elemental S to the SC/GNR can increase the total capacity of the sulfurized carbon cathodes. In some embodiments, additives other than GNRs can be utilized. In some embodiments, the additives can include, without limitation, carbon nanotubes, graphene, carbon black, and combinations thereof. In some embodiments, mixtures of Se and S can be included during the preparation of sulfurized carbon. In some embodiments, use of GCNT with PAN and S can be efficacious with or without GNR additives. In some embodiments, ultrahigh surface area carbons such as uGil900 can be used in conjunction with PAN and S with or without GNRs. In some embodiments, the content of sulfur is about 55 wt % to about 60 wt %, making the overall content of S in the sulfurized carbon cathodes about 45 wt % to about 50 wt % (including the binder and carbon additives), which reduces the overall capacity of the cathode. In some embodiments, the voltage of discharge (˜2 V) is less flat than an elemental sulfur cathode, even though it is much more stable.
GNR-Modified SeparatorsA separator is utilized to keep the cathode and anode electrically insulated from one another, but allows the transport of electrolyte and ions within. Standard separators are made from materials such as polypropylene (PP) and polyethylene (PE).
The present invention can utilize a separator with a coating on one or both sides, which coating further selectively allows or blocks materials from moving from one side to the other (i.e., moving from the anode side to the cathode side or vice versa). As shown in
The GNR-coated separator was fabricated as follows: Pristine GNR (AZ Electronic Materials) were dispersed in N-methyl-2-pyrrolidone (NMP) via 10 min of tip sonication. Then, the dispersion was vacuum-filtered through a Celgard separator and dried at 60° C. under vacuum for 12 h. This fabrication method makes possible large scale applications and can produce GNR-coated separators with different thicknesses by only changing the concentration of GNR in the dispersion.
Such a GNR-coated separator decreases the diffusion of unwanted materials from traversing from one side to the other side of the battery (such as lithium polysulfides from a sulfur-based cathode traversing through the separator to the anode). In addition, the electrical conductivity of GNR provides new electron pathways that reactivate the intercepted material, thus improving the capacity retention. This means that, because the GNRs are conductive, they can transfer electrons to the trapped species (lithium polysulfides and lithium sulfide). Had these intercepted materials not been reactivated, a severe agglomeration of Li2S after cycling would have been observed and the capacity retention would instead have been similar to the cell without a coated separator.
By reducing the diffusion of such unwanted materials (such as sulfur or lithiated polysulfides) this better enables the use of such materials in the cathodes and anodes (such as sulfur based cathodes).
BatteriesBatteries can be utilized that utilize one or more of the improved anodes, cathodes, and separators and their modifications described herein. In some embodiments, the battery includes an anode having a lithiated carbon film, a sulfurized carbon cathode, and a GNR-modified separator. In other embodiments, the battery has just two of the three being complemented by other standard/commercial component when needed (i.e., an anode having a lithiated carbon film and a sulfurized carbon cathode; an anode having a lithiated carbon film and a GNR-modified separator; or a sulfurized carbon cathode and a GNR-modified separator. In still other embodiments, the battery has only one of the three (an anode having a lithiated carbon film, a sulfurized carbon cathode, and a GNR-modified separator).
FB with GCNT-Li Anode and Sulfurized Carbon CathodeA full battery (FB) was assembled by combining a GCNT-Li anode [Zhu 2012; Lin 2015] with a sulfurized carbon cathode.
For the graphene-carbon nanotube preparation, the preparation of GCNT was similar to the previously reported methods. [Zhu 2012; Lin 2015]. First, Bernal-stacked multilayer graphene was grown on copper foil (25 μm) using the CVD method as reported elsewhere. [Sun 2012]. The catalysts for CNT growth are deposited by e-beam evaporation over the graphene/Cu foil in the order graphene/Fe (1 nm)/Al2O3 (3 nm). The CNT growth was conducted under reduced pressure using a water-assisted CVD method at 750° C. First, the catalyst is activated by using atomic hydrogen (H•) generated in situ by H2 decomposition on the surface of a hot filament (0.25 mm W wire, 10 A, 30 W) for 30 s, under 25 Torr (210 sccm H2, 2 sccm C2H2 and water vapor generated by bubbling 200 sccm of H2 through ultrapure water). After the activation of the catalyst for 30 s, the pressure is reduced to 8.3 Torr and the growth is carried out for 15 min.
For the electrochemical plating/stripping of Li into/from GCNT, the electrochemical reaction was performed in 2032 coin-type cells using GCNT substrates and Li foil as both counter and reference electrodes. The GCNT substrates are circular with total area of ˜2 cm2. The electrolyte used was 4 M lithium bis(fluorosulfonyl)imide (LiFSI) (Oakwood Inc.) in 1,2-dimethoxyethane (DME). The LiFSI salt is vacuum-dried (<20 Torr) at 100° C. for 24 h, and DME was distilled over Na strips. The GCNT substrate was prelithiated by putting one drop of electrolyte on the surface of GCNT, pressing a Li coin gently against the GCNT and leaving it with the Li coin on top for 3 h. Adding excessive amounts of the electrolyte solution during the pretreatment was found to yield ineffective prelithiation due to poor contact between the GCNT and the Li. After the prelithiation, the GCNT was assembled in a coin cell using the same Li chip used in the prelithiation.
For the sulfurized carbon cathode preparation, the sulfurized carbon cathode was prepared by the decomposition of polyacrylonitrile (PAN) (Sigma-Aldrich, Mw 150 k) in the presence of excess elemental sulfur. PAN, S, and graphene nanoribbons (GNRs) (EMD-Merck) in the mass ratio of 55:11:1 were ground together using a mortar and pestle. (The GNRs improved the conductivity of the final material). The resulting powder is heated from room temperature to 450° C. at a rate of 5° C. min−1 in an argon atmosphere (1 atm). After 6 h, the sulfurized carbon powder was removed and used without purification. The sulfurized carbon powder had approximately 60 wt % S. The sulfurized carbon cathodes were prepared by mixing the SC powder with carbon black (Black Pearls 2000, Cabot Corp.) and polyvinylidene fluoride (PVDF, Sigma-Aldrich) in a mass proportion of 8:1:1, resulting in a total S content in the electrode of 48 wt %. Typical mass loading was 4-5 mg in 1 cm2 electrodes.
For the full battery assembly, the FB was assembled by combining the GCNT-Li and sulfurized carbon cathode using a 4 M LiFSI/DME electrolyte and Celgard K2045 as separator. The electrodes were ˜1 cm2. The areal capacity of the GCNT-Li was set to match the 30% irreversible capacity loss of the first cycle of the sulfurized carbon cathode.
By this assembly, a FB can be obtained that matching the dendrite-free GCNT-Li anode with a sulfurized carbon cathode with S content of ˜60 wt %. The S content in the cathode was reduced to 48 wt % with the addition of binder and carbon additives. Cathodes based on sulfurized carbon have advantages over elemental sulfur (S8) cathodes, such as high compatibility with different electrolytes and absence of Li polysulfide diffusion [Wei 2015]; the latter generally leads to capacity fading over cycling in elemental sulfur cathodes. [Yang 2013].
A pouch FB 2305 based on GCNT-Li/SC is shown in
As shown in
At the lowest power density, the energy density of the GCNT-Li/SC full-cell is 1423 Wh kg−1active material (752 Wh kg−1total electrodes), where active materials=Li+S only and total electrodes=GCNT-Li+sulfurized carbon+carbon additives+binder. This is 3× higher energy density than that seen in Li—S full-cells with respect to the mass of active materials (Li—S). [Jin 2016]. Moreover, the data appear attractive when compared to commercial LIB performances with 310 Wh kg−1active materials (220 Wh kg−1total electrodes) [Zhang 2006], where active materials=graphite+LiCoO2; total electrodes=graphite+LiCoO2+carbon additives+binder.
However, a definitive comparison with a commercial cell is difficult at this stage because commercial cells are dual-sided and stacked, designed to minimize the contribution of current collectors and packaging materials.
In a non-optimized device, a volumetric energy density of 234 Wh/Ltotal electrodes was achieved. There is no dendritic or mossy Li in the full-cell electrodes after 500 cycles. These results represent a significant achievement for a Li polysulfide- and dendrite-free battery.
The present invention thus achieves superior energy density due to the near theoretical Li storage capacity and serves as the basis for the demonstrated sulfurized carbonλGCNT-Li full-cell in a high concentration electrolyte to produce a safe, stable, and high-performance battery.
FB with Li-MWCNT Anode and Sulfurized Carbon CathodeA full battery (FB) was assembled by combining a Li-MWCNT anode with a sulfurized carbon cathode.
For the MWCNT film preparation, free standing carbon nanotubes films were prepared by dispersing MWCNTs (NTL, C-grade, 70-80 nm diameter) in N-methylpyrrolidone (NMP). The MWCNTs were used as received without further purification. MWCNTs (68 mg) were dispersed in NMP (250 mL) using tip sonication; the as prepared dispersion was vacuum filtered through a porous Al membrane (9 cm dia). The MWCNTs were trapped on the surface forming a MWCNT film. This resulting film was rinsed with methanol and dried overnight at 70° C. The Al film was later dissolved using an aqueous etching solution of HF (2.5 v/v%) and HCl (2.5 v/v%) at room temperature. After the Al was completely dissolved, the MWCNT film was removed from the solution, rinsed with water and ethanol, and dried overnight at 70° C. The porous Al membrane was previously prepared by etching commercial Al foil (60 μm thickness, Fisher Scientific Inc.) in the aqueous etching solution mentioned above for approximately 10 min.
For the lithiated-MWCNT preparation, Li metal foils from MTI Corporation (1.6 cm diameter chips, 230 μm thickness) were used or they were extracted from an Ultimate Lithium AA battery-Duracell Inc. (25×3.5 cm, 130 μm thick). The Li foils were cleaned before their use by scraping the surface until a shiny metallic surface appeared. The lithiated MWCNT film (Li-MWCNT) was produced by placing the MWCNT film between two Li foils wetted by 50 μL of 4 M lithium bis(fluorosulfonyl)imide (LiFSI) in dimethoxyethane (DME). The lithiation process took approximately 10 min and it could be visualized by the reddish color acquired by the CNT film.
For the sulfurized carbon preparation, The sulfurized carbon powder was prepared by grinding polyacrylonitrile (PAN) (Sigma-Aldrich, Mw 150 k), elemental sulfur (S8) and graphene nanoribbons (GNRs, EMD-Merck) in a mass ratio of 55:11:1 (S:PAN:GNR, respectively). The mixture was heated at 450° C. for 6 h under argon atmosphere (1 atm), at a heating rate of 5° C. min−2. After the heat treatment, the resulting sulfurized carbon powder was used without further purification. A content of ˜60 wt % S was measured in the sulfurized carbon powder by thermogravimetric analysis (TGA). The cathode slurry was prepared by mixing the SC, carbon black (Black Pearls 2000, Cabot Corp.) and polyvinylidene fluoride (PVDF, Sigma Aldrich) in a mass ratio of 8:1:1 in NMP. The slurry was used to coat stainless steel foils (30 μm thick, 40 mg cm−2) or carbon-coated Al foils (10 μm, 5.5 mg cm−2, MTI Corp.). The typical mass loading of sulfurized carbon cathodes was 3-5 mg per cm−2, with a final S content of 47 wt % to 57 wt %.
For
For
As discussed above,
While embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described and the examples provided herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Accordingly, other embodiments are within the scope of the following claims. The scope of protection is not limited by the description set out above.
The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated herein by reference in their entirety, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.
Concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of approximately 1 to approximately 4.5 should be interpreted to include not only the explicitly recited limits of 1 to approximately 4.5, but also to include individual numerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges reciting only one numerical value, such as “less than approximately 4.5,” which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.
Following long-standing patent law convention, the terms “a” and “an” mean “one or more” when used in this application, including the claims.
Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.
As used herein, the term “about,” when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.
As used herein, the term “and/or” when used in the context of a listing of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and/or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C, and D.
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Claims
1. A lithium metal anode comprising a lithium metal coated with a lithiated carbon material.
2. A cathode comprising a sulfurized carbon cathode.
3. A GNR-modified separator comprising a polymer material coated with a layer of GNRs, wherein the GNR-modified separator is operable for use as a separator in a battery.
4. A battery comprising an anode, a cathode, and a separator positioned between the anode and the cathode, wherein the battery comprises a component selected from the group consisting of:
- (a) anodes comprising the lithium metal anode of claim 1;
- (b) anodes comprising the sulfurized carbon cathode of claim 2;
- (c) separators comprising the GNR-modified separator of claim 3; and
- (d) combinations thereof.
5. The battery of claim 4, wherein the anode comprises the lithium metal anode of claim 1.
6. The battery of claim 5, wherein the cathode comprises the sulfurized carbon cathode of claim 2.
7. The battery of claim 6, wherein the separator comprises the GNR-modified separator of claim 3.
8. The battery of claim 4, wherein the cathode comprises the sulfurized carbon cathode of claim 2.
9. The battery of claim 8, wherein the separator comprises the GNR-modified separator of claim 3.
10. The battery of claim 4, wherein the separator comprises the GNR-modified separator of claim 3.
11. A method comprising making a lithium metal anode, wherein the method includes the steps of:
- (a) selecting a lithium metal having a surface;
- (b) coating the surface of the lithium metal with a carbon material and an electrolyte,
- (c) performing a reaction involving the lithium metal, the carbon material, and the electrolyte to form a lithiated layer on the surface of the lithium metal.
12. A method comprising making a sulfurized carbon cathode.
13. A method comprising selecting a polymer material operable for use as a separator in a battery, and modifying the polymer material by adding a layer of GNRs to form a GNR-modified separator.
14. A method of forming a battery comprising the steps of combining an anode, a cathode, and a separator positioned between the anode and cathode, wherein the method comprises the step selected from the group consisting of:
- (a) making the lithium metal anode of claim 11;
- (b) making the sulfurized carbon cathode of claim 12;
- (c) making the GNR-modified separator of claim 13; and
- (d) combinations thereof.
15. The method of claim 14, wherein the method comprises making the lithium metal anode of claim 11.
16. The method of claim 15, wherein the method comprises making the sulfurized carbon cathode of claim 12.
17. The method of claim 16, wherein the method comprises making the GNR-modified separator of claim 13.
18. The method of claim 14, wherein the method comprises making the sulfurized carbon cathode of claim 12.
19. The method of claim 18, wherein the method comprises making the GNR-modified separator of claim 13.
20. The method of claim 14, wherein the method comprises making the GNR-modified separator of claim 13.
21. A method of forming a battery comprising the steps of combining an anode, a cathode, and a separator positioned between the anode and cathode, wherein the battery comprises a component selected from the group consisting of:
- (a) anodes comprising the lithium metal anode of claim 1;
- (b) anodes comprising the sulfurized carbon cathode of claim 2;
- (c) separators comprising the GNR-modified separator of claim 3; and
- (d) combinations thereof.
22. The method of claim 21, wherein the anode comprises the lithium metal anode of claim 1.
23. The method of claim 22, wherein the cathode comprises the sulfurized carbon cathode of claim 2.
24. The method of claim 23, wherein the separator comprises the GNR-modified separator of claim 3.
25. The method of claim 21, wherein the cathode comprises the sulfurized carbon cathode of claim 2.
26. The method of claim 25, wherein the separator comprises the GNR-modified separator of claim 3.
27. The method of claim 25, wherein the sulfurized carbon cathode comprises a seamless hybrid of nanotubes grown from a graphene layer.
28. The method of claim 21, wherein the separator comprises the GNR-modified separator of claim 3.
29. The lithium metal anode of claim 1 or the method of claim 11, wherein the lithium metal is in the form of a lithium foil.
30. The method of claim 11, wherein the carbon material comprises multi-walled carbon nanotubes.
31. The method of claim 30, wherein the multi-walled carbon nanotubes are in the form of a bucky paper.
32. The method of claim 11, wherein the carbon material comprises graphene nanoribbons.
33. The method of claim 32, wherein the nanoribbons are in the form of a filtered nanoribbon paper.
34. The method of claim 11, wherein the carbon material is selected from a group consisting of multi-walled carbon nanotubes, single-walled carbon nanotubes, few-walled carbon nanotubes, graphene nanoribbons, graphene oxide, graphene oxide nanoribbons, graphoil, graphene nanoplatelets, graphite, activated carbon, thermally treated asphalt, amorphous carbon, carbon black, and mixtures thereof.
35. The method of claim 34, wherein the carbon materials are further treated with a polymer to make the carbon materials more flexible without cracking.
36. The method of claim 35, wherein the polymer comprises polydimethylsiloxane.
37. The method of claim 35, wherein the polymer is selected from a group consisting of polydimethylsiloxane, polyurethane, thermoplastic polyurethane, polybutadiene, poly(styrene butadiene), poly(styrene butadiene styrene), polyacrylonitrile, polyaniline, poly fluorinated systems, poly(methyl methacrylate), poly(ethylene glycol), poly(ethylene oxide), polyacrylates, vinyl polymers, chain growth polymers, step growth polymers, condensation polymers, and mixtures thereof.
38. The method of claim 11, wherein the electrolyte is selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), dimethoxyethane (DME), and 1,3-dioxolane (DOL), and mixtures thereof.
39. The method of claim 38, wherein the electrolyte comprises a mixture of the 1 mol L−1 lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a ratio of 1:1 of the dimethoxyethane (DME) and the 1,3-dioxolane (DOL).
40. The method of claim 11, wherein the electrolyte is an ionic liquid or a mixture of the ionic liquid with an organic solvent.
41. The method of claim 11, wherein the electrolyte is formed from a salt in a solvent, wherein
- (a) the salt is selected from the group consisting of lithium hexafluorophosphate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium tetrafluoroborate, and combinations thereof, and
- (b) the solvent is selected from the group consisting of ethlylene carbonate, propylene carbonate, butylene carbonate, vinyl ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethylene carbonate, tetraethylene glycol dimethyl ether, and combinations thereof.
42. The method of claim 11, wherein the electrolyte is placed on or between the carbon material and the lithium metal in the initial phases of the method.
43. The method of claim 41, wherein the electrolyte is in a high concentration.
44. The method of claim 11, wherein the electrolyte is between 0.5 and 10 mol/L of lithium bis(fluorosulfonyl)imide (LIFSI) in dimethoxyethane (DME).
45. The method of claim 44, wherein the electrolyte is between 2 and 8 mol/L of the lithium bis(fluorosulfonyl)imide (LIFSI) in the dimethoxyethane (DME).
46. The method of claim 44, wherein the electrolyte is between 3 and 5 mol/L of the lithium bis(fluorosulfonyl)imide (LIFSI) in the dimethoxyethane (DME).
47. The method of claim 44, wherein the electrolyte is 4 mol/L of the lithium bis(fluorosulfonyl)imide (LIFSI) in the dimethoxyethane (DME).
48. The method of claim 22, wherein an electrolyte is added to the battery in combination with the anode.
49. The method of claim 48, wherein the electrolyte is between 0.5 and 10 mol/L of lithium bis(fluorosulfonyl)imide (LIFSI) in dimethoxyethane (DME).
50. The method of claim 11, wherein the lithium metal dopes the carbon material.
51. The method of claim 11, wherein the carbon material becomes red or silver in color.
52. The method of claim 11, wherein the carbon material is operable to suppress lithium dendrite formation of the lithium metal anode.
53. The method of claim 50, wherein the doped carbon material becomes the source of lithium ions injected across into the electrolyte and then into a cathode.
54. The method of claim 50, wherein
- (a) the lithium metal is a metallic Li foil, and
- (b) the doped carbon material acts as a buffer between an SEI layer and the metallic Li foil.
55. The method of claim 54, wherein the buffer eliminates any gap formation between the SEI layer and the metallic Li foil.
56. The method claim 11, wherein the lithium metal, the carbon material, and the electrolyte are part of a battery.
57. The method of claim 11, wherein the lithium metal, the carbon material, and the electrolyte are part of a battery anode.
58. The method of claim 57, where the battery comprises a sulfur cathode.
59. The method of claim 11, wherein the reaction involving the lithium metal, the carbon material, and the electrolyte to form the lithiated layer on the surface of the lithium metal comprises a solid state reaction.
60. The method of claim 12, wherein the sulfurized carbon cathode comprises sulfur, carbon, and thermally treated polyacrylonitrile.
61. The cathode of claim 2 or the method of claim 12, wherein the sulfurized carbon cathode comprises sulfur in an amount between about 47% and about 60 wt %.
62. The cathode of claim 61 or the method of claim 61, wherein the amount of the sulfur in the sulfurized carbon cathode is between about 47% and about 57 wt %.
63. The cathode of claim 61 or the method of claim 61, wherein the amount of the sulfur in the sulfurized carbon cathode is between about 55% and about 60 wt %.
64. The cathode of claim 2 or the method of claim 12, wherein the cathode lacks elemental sulfur.
65. The cathode of claim 2 or the method of claim 12, wherein the cathode comprises a carbon additive that is a conductive filler.
66. The cathode of claim 65 or the method of claim 65, wherein the carbon additive is selected from the group consisting of carbon black, graphene, carbon nanotubes, graphene nanoribbons, and combinations thereof.
67. The method of claim 12, wherein the method of making the sulfurized carbon cathode comprises heat treating elemental sulfur with a carbon source.
68. The method of claim 67, wherein the carbon source comprises PAN.
69. The method of claim 67, wherein the step of heat treating occurs in the presence of an additive.
70. The method of claim 69, wherein the additive is selected from a group consisting of carbon black, graphene, carbon nanotubes, graphene nanoribbons, and combinations thereof.
71. The method of claim 67, wherein the step of heat treating occurs at a temperature of at least about 100° C.
72. The method of claim 71, wherein the step of heat treating occurs at a temperature of at least about 450° C.
73. The method of claim 67, wherein the step of heat treating occurs for at least about 3 hours.
74. The method of claim 12, wherein the method of making the sulfurized carbon cathode comprises:
- (a) forming a powder comprising elemental sulfur, a carbon source, and an additive;
- (b) heat treating the powder at a temperature of at least about 450° C. for at least three hours.
75. The method of claim 74, wherein
- (a) the carbon source comprises PAN; and
- (b) the additive comprises graphene nanoribbons.
76. The method of claim 12, wherein the sulfurized carbon cathode is part of a seamless hybrid of nanotubes grown from a graphene layer.
77. The method of claim 13, wherein the polymer materials comprise at least one of polypropylene (PP) and polyethylene (PE).
78. A method to form an anode comprising:
- (a) selecting a lithium metal having a surface;
- (b) coating the surface of the lithium metal with a carbon material and an electrolyte; and
- (c) forming a lithiated carbon material by lithiating the carbon material with lithium from the lithium metal.
79. The method of claim 78, wherein the method further comprises continuing the step of lithiating the carbon material until there is no remaining lithium in the lithium metal, wherein the lithiated carbon material is the anode.
80. A lithium metal anode, wherein the lithium metal is coated with a thin film material and an electrolyte.
Type: Application
Filed: Mar 8, 2023
Publication Date: Aug 10, 2023
Applicant: WILLIAM MARSH RICE UNIVERSITY (Houston, TX)
Inventors: James M. Tour (Houston, TX), Rodrigo Villegas Salvatierra (Houston, TX), Gladys Anahi Lopez Silva (Houston, TX)
Application Number: 18/118,834
