CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Nos. 63/476,768, filed December 22, 2022, and 63/368,629, filed July 15, 2022, each of which is incorporated herein in its entirety for all purposes.

BACKGROUND OF THE INVENTION

[0002] Over the past decades, lithium-ion batteries (Li-ion batteries) have developed as the dominant high-energy chemistry due to their uniquely high energy density while maintaining high power and cyclability at acceptable prices. The energy density of current commercial Li- ion battery chemistries is however approaching the technology’s theoretical limit, whereas demand for higher energy density batteries at lower unit cost is increasing with the rapid trend towards electrification of the transport and energy industries. There is indeed a need for batteries with improved capacity, long cycle life and high stability. Replacing graphite anodes in Li-ion with lithium metal anodes provides an opportunity to significantly increase the energy density of lithium batteries. However, after repetitive charge-discharge cycles, lithium metal batteries suffer from irreversible capacity loss driven by electrolyte depletion and loss of lithium inventory due to parasitic reactivity between the highly reactive lithium metal anode and the electrolyte components. This process contributes to local non-uniformities in the lithium anode surface, propagating further uneven plating and stripping and resulting in physically isolated “dead” lithium. Further, uneven lithium plating increases the risk of dendrite formation, which can cause thermal runaway resulting in catastrophic cell failure, posing a significant hurdle to the commercialization of lithium metal batteries. Mitigation of dendrite formation in lithium metal batteries is critical to enabling their safe, stable use in commercial applications.

[0003] Battery separators are a critical component of Li-ion batteries since they isolate the electrodes, providing ion transport through large pores filled with electrolyte and insulating electronic conductivity that would otherwise induce a short circuit. Whereas separators are not involved directly in cell reactions, their physical properties play an important role in determining the performance of the battery including energy density, power density, and safety. Importantly, separators’ mechanical integrity throughout the entire lifetime of the battery cell is critical for prevention of internal short circuit.

[0004] Several porous membrane separator materials and composites are currently utilized in Li-ion batteries, such as separators made of made of polyolefin, for example polyethylene (PE), polypropylene (PP) and polypropylene-polyethylene-polypropylene (PP/PE/PP), as well as ceramic-coated separators, which include PP, PE or multilayer porous substrates with at least one surface coated with a ceramic composite layer. As described in US 6,432,583 (Celgard Inc.), the ceramic composite layer is intended to block dendrite growth and to prevent electronic shorting. Although ceramic coated separators have been successfully utilized in Li-ion batteries to improve mechanical properties, their utility is limited in lithium metal batteries due to parasitic reactions induced at the anode by the binding materials which host the ceramic coatings and with some of the ceramic materials themselves.

[0005] WO 2018/106957 (Sepion Technologies, Inc et al.) describes the application of porous polymers (10-40% porosity, 0.5-2.0 nm pores) as templates that deliver solution- processed precursors of solid-state plus halide containing salts as a conformal coating between the Li-metal surface and the separator surface, in order to increase separator wettability and to increase Li-ion concentration and mobility at the separator-anode interface. The document also describes electrochemical cells including separators comprising several layers: a first polymer layer, comprising a planar species and a linker. The separator may also comprise a porous support made of PP or PE, laminated to the first polymer layer. The separator may also comprise a second membrane layer laminated to the porous support, such second layer comprising a ceramic material.

[0006] The use of Polymers of Intrinsic Microporosity (PIMs) as a selective battery membrane has been investigated. PIMs are composed of fused rings providing rigidity and sites of contortion, which may be provided by spiro-centers, by bent or bridged ring moieties, or by similar structural components which serve as a barrier preventing conformational relaxation of polymer chains. PIMs have been described and studied since 2006, as they create continuous networks of interconnected voids used as gas separation membranes, hydrogen storage materials, adsorbents and heterogeneous catalysts. The intrinsic microporosity of PIMs is defined as a continuous network of interconnected intermolecular voids, which form as a direct consequence of the shape and rigidity of the component macromolecules. Notably, the article of Li et al. (Nano Lett. 2015, 15, 5724-5729) describes the use of PIMs as a membrane platform for achieving high-flux, ion-selective transport in nonaqueous electrolytes.

[0007] As lithium metal is highly reactive, a solid-electrolyte-interphase (SEI) forms at the interface of the electrode and the adjacent electrolyte-filled separator. The composition and morphology of the SEI impacts the performance of the electrochemical cell. On one hand, the consumption of part of the lithium inventory inherent to the in situ SEI formation process reduces the coulombic efficiency of the electrochemical cell. On the other hand, optimal SEI limits the further decomposition of electrolyte components and improves lithium-ion transport at the electrode-separator interface, improving the cycling performance and service life of the batteries.

[0008] Artificial SEI layers have been investigated in order to limit lithium inventory and electrolyte component depletion processes at the surface of anode materials. One of the approaches is based on the use of a layer of PIMs which is coated on porous supports. Notably, WO 2020/037246 Al (The Regents of the University of California) describes microporous ladder polymer according to the formula -[A-AB-B]- containing amine- functionalized monomer segments, amidoxime functionalized monomer segments, or a combination thereof, such microporous polymers being used in the separator which may comprise one or more support material such as glass fibers. Thin films of microporous polymers on porous supports, such as a polyolefin battery separator (e.g., Celgard) are described in the examples. The article of Chengyin Fu et al. (Nature Materials, April 2020) describes a lithium electrode laminated with a TBAF@PIM-1 coated polyolefin separator, i.e., a separator coated with microporous polymer host (e.g., PIM-1) in combination with tetrabutylammonium fluoride (TBAF), with the separator (Celgard 2325). The coated separator was then assembled in either Li-Li or Li-NMC-622 cells along with a carbonate electrolyte containing an ionizable lithium salt (e.g., LiPF6). The composites are described to act as dendrite-suppressing sohd-ion conductors (SICs) in lithium metal batteries. What is needed are new battery separators. Surprisingly, the present invention meets this and other needs. BRIEF SUMMARY OF THE INVENTION

[0009] In one embodiment, the present invention provides a separator comprising a porous support having a first surface and a second opposing surface; and a polymer layer comprising poly (aery lonitrile-co-methyl acrylate) coated on the first surface of the porous support.

[0010] In another embodiment, the present invention provides an electrochemical cell comprising: an anode; a cathode; a separator of the present invention; and an electrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 shows the discharge capacity vs cycle life plot of lithium metal battery cells built with and without P(AN-co-MA) Coating 2E on the separator, wherein the electrolyte is El. Curves represent the mean discharge capacity of a set of lithium metal battery cells (n = 4), with error bars representing one standard deviation above and below this average. Cells were cycled from 3.0 V to 4.3 V using current densities of 0.76 mA/cm ² charge and 3.8 mA/cm ² discharge.

[0012] FIG. 2 shows confocal microscope image of P(AN-co-MA) coated separator showing conformal surface coating of separator.

[0013] FIG. 3A and FIG. 3B show a separator of the present invention.

[0014] FIG. 4A and FIG. 4B show an electrochemical cell of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

I. DEFINITIONS

[0015] The abbreviations used herein have their conventional meaning within the chemical and biological arts.

[0016] Where substituent groups are specified by their conventional chemical formulae, written from left to right, they equally encompass the chemically identical substituents that would result from writing the structure from right to left, e.g., -CH2O- is equivalent to - OCH2-.

[0017] “Carbonate” refers to a compound of the formula R'OC(O)OR”, where R’ and R” can be the same or different, or combined to form a cyclic structure. R’ and R” can be alkyl, haloalkyl, or combined to form an alkylene that is optionally substituted with halogen. Representative carbonates include, but are not limited to, dimethyl carbonate and fluoroethylene carbonate.

[0018] “Electrochemical device” or “electrochemical cell” refers to a device wherein an electric current is produced by a chemical reaction, wherein electrons are transferred directly between molecules and/or atoms in oxidation-reduction reactions.

[0019] “Electrode” refers to an electrically conductive material in a circuit that is in contact with a nonmetallic part of the circuit, such as the electrolyte. The electrode can be a positive electrode or cathode. The electrode can be a negative electrode or anode.

[0020] “Electrolyte” refers to a solution of the electrochemical cell that includes ions, such as metal ions and protons as well as anions, that provides ionic communication between the positive and negative electrodes. Representative electrolytes include carbonate electrolytes.

[0021] “Electrolyte Solvent” refers to the molecules solvating ions in the liquid electrolyte, such as small organic carbonates or ethereal molecules, that enable diffusion of ions in the electrolyte. The Electrolyte Solvent may also be an ionic liquid or a gas at standard temperature and pressure.

[0022] “Lithium salt” refers to an inorganic salt having a lithium ion, Li ⁺ , and an anionic counterion.

[0023] “Conformal polymer layer” refers to a layer of the separator that is permeable to a first species of the electrolyte while substantially impermeable to liquid electrolyte, and that is substantially free of pinholes. The membrane layer can be of any suitable material that can provide the selective permeability, such as composites of microporous polymers and inorganic materials. “Substantially impermeable” refers to less than 10% of the electrolyte solvent passing through the membrane layer, or less than 1%, or less than 0.1%, or less than 0.01%, or less than 0.001% of the liquid electrolyte passing through the membrane layer.

[0024] “Molecular weight” refers to the molecular weight of the polymer as determined by Size Exclusion Chromatograph (SEC), laser-light scattering, MALDI-TOF, or other methods. The molecular weight can be measured by the weight average or the number average.

“Number average molecular weight” (MN) refers to the mole fraction of molecules in the polymer sample, i.e., the total weight of polymer divided by the total number of molecules, or the arithmetic mean. “Weight average molecular weight” (Mw) refers to the weight fraction of molecules in the polymer sample, emphasizing the weight of the individual molecules such that the Mw is greater than the MN. The ratio of the MW/MN, the poly dispersity index, represents the distribution of molecular weights in the polymer.

[0025] “Polymer coat weight” refers to the density of the polymer layer deposited on the separator. The polymer coat weight can be measured in a variety of different ways and units, including grams per meter squared (g/m ² ).

[0026] “Oxide” refers to a chemical compound having an oxygen, such as metal oxides or molecular oxides.

[0027] “Pore size” or “pore diameter” refers to the average diameter of interstitial space not occupied by the pore forming material. This may include, but is not limited to, the space remaining between polymer chains due to inefficient packing, the space remaining between organic linkers and metal ions in a metal-organic framework, the space between layers and within the holes of stacked 2D material, and the space left in an amorphous or semicrystalline carbon due to unaligned covalent bonding. The pore size may also change once wetted with electrolyte or it may stay the same.

[0028] “Porous support” refers to any suitable material that is capable of supporting the membrane layer of the present invention, and is permeable to the electrolyte.

[0029] “Separator” refers to an electrically insulating membrane between the positive and negative electrodes to prevent electrical shorts, i.e., provides electronic isolation. The separator also allows the ions to move between the positive and negative electrodes. The separator can include any suitable polymeric or inorganic material that is electrically insulating. The separator can include several layers including one or more membrane layers, and a porous support material for the membrane layers.

[0030] “Surface area” refers to the surface area of a porous material as measured by a variety of methods, such as nitrogen adsorption BET.

[0031] “Metal” refers to elements of the periodic table that are metallic and that can be neutral, or negatively or positively charged as a result of having more or fewer electrons in the valence shell than is present for the neutral metallic element. Metals useful in the present invention include the alkali metals, alkali earth metals, transition metals and post-transition metals. Alkali metals include Li, Na, K, Rb and Cs. Alkaline earth metals include Be, Mg, Ca, Sr and Ba. Transition metals include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg and Ac. Post-transition metals include Al, Ga, In, Tl, Ge, Sn, Pb, Sb, Bi, and Po. Rare earth metals include Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. One of skill in the art will appreciate that the metals described above can each adopt several different oxidation states, all of which are useful in the present invention. In some instances, the most stable oxidation state is formed, but other oxidation states are useful in the present invention.

[0032] “Laminated” refers to the deposition of one layer on another, such as the microporous polymer layer or first polymer layer onto the porous support.

[0033] ‘ ‘Mol%” refers to the mole percentage of a component based on the total number of moles in the composition.

[0034] “Wt%” or “weight %” refers to the weight percentage of a component based on the total weight of the composition.

[0035] “Gurley” refers to a unit of measure of porosity of a layer determined by measuring the air permeability of the layer. The Gurley value refers to the number of seconds required for 100 cubic centimeters (1 deciliter) of air to pass through 1.0 square inch of a given material at a pressure differential of 4.88 inches of water (0. 176 psi) according to ISO 5636- 5:2003.

II. COATED SEPARATOR

[0036] In some embodiments, the present invention provides a separator comprising a porous support having a first surface and a second opposing surface; and a polymer layer comprising poly(acrylonitrile-co-methyl acrylate) coated on the first surface of the porous support.

[0037] FIG. 3 A shows coated separator 100, having porous support 110 having a first surface 111 and a second opposing surface 112, and a polymer layer 120. FIG. 3B shows separator 150, having porous support 110 having a first surface 111 and a second opposing surface 112, a polymer layer 120, and a polymer layer 130.

Porous support

[0038] In some embodiments, the pore size of the porous support is between about 0.01 micrometers and 5 micrometers, more specifically between about 0.02 micrometers and 1.5 micrometers, or even more specifically between about 0.03 micrometers and 1 micrometers. The porosity of porous support may be between about 20% and 85%, or more specifically, between about 30% and 60%. One having ordinary skills in the art would understand that pore sizes may be affected by the composition of electrolyte that is provided in the pores of separator. For example, some components of separator (e.g., porous support or first polymer layer) may swell when come in contact with some materials of electrolyte causing the pore size to change. Unless specifically noted, the pore size and other like parameter refer to components of separator before they come in contact with electrolyte.

[0039] Larger pore sizes allow using porous support that is much thicker than first polymer layer without significantly undermining the overall permeability of separator to first species. In some embodiments, the thickness of porous support is between about 5 micrometers and 500 micrometers, or in specific embodiment between about 5 micrometers and 50 micrometers, or more specifically between about 10 micrometers and 30 micrometers. In the same or other embodiments, the thickness of porous support may be between about 1 to 50 times greater than the thickness of first polymer layer or, more specifically, between about 5 and 25 times greater.

[0040] Some examples of suitable materials for porous support include, but are not limited, fluoro-polymeric fibers of poly(ethylene-co-tetrafluoroethylene (PETFE) and poly(ethylenechloro-co-trifluoroethylene) (e.g., a fabric woven from these used either by itself or laminated with a fluoropolymeric microporous film), poly vinylidene difluoride, polytetrafluoroethylene (PTFE), polystyrenes, polyarylether sulfones, polyvinyl chlorides, polypropylene, polyethylene (including LDPE, LLDPE, HDPE, and ultrahigh molecular weight polyethylene), polyamides, polyimides, polyacrylics, polyacetals, polycarbonates, polyesters, polyetherimides, polyimides, polyketones, polyphenylene ethers, polyphenylene sulfides, polymethylpentene, polysulfones non-woven glass, glass fiber materials, ceramics, metal oxides, composites of organic and inorganic species, and a polypropylene membrane. Porous support may also be supplied with an additional coating of a second suitable material including, but not limited to, PTFV, PVDF, and PETFE. These examples of porous support may or may not be commercially available under the designation CELGARD from Celanese Plastic Company, Inc. in Charlotte, N.C., USA, as well as Asahi Kasei Chemical Industry Co. in Toky o, Japan, Tonen Corporation, in Tokyo, Japan, Ube Industries in Tokyo, Japan, Nitto Denko K K in Osaka, Japan. Nippon Kodoshi Corporation, in Kochi, Japan, Entek in Lebanon, Oregon, USA, SK Innovation in Jongro-Gu, Korea, Sumitomo Corporation, in Tokyo, Japan, Toray Industries in Tokyo, Japan, Dupont USA, in Wilmington, DE, USA, W- Scope in Japan, and Parker Hannifin Filtration Group, in Carson, CA, USA.

[0041] In some embodiments, the separator of the present invention is the separator wherein the porous support comprises polyethylene, polypropylene, polytetrafluoroethylene) (PTFE), poly(vinyl chloride) (PVC), poly(vinylidene difluoride) (PVDF), cellulose, a ceramic, or combinations thereof. In some embodiments, the separator of the present invention is the separator wherein the porous support comprises polyethylene.

[0042] The porous support may have a thickness of between about 3 micrometers and 200 micrometers, or between about 5 micrometers and 100 micrometers, or between about 10 micrometers and 50 micrometers, or between about 9 micrometers and 25 micrometers, or between about 10 micrometers and 20 micrometers, or more specifically between about 15 micrometers and 30 micrometers. The porous support can have a thickness of about 5 micrometers, or about 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or about 20 micrometers.

Polymer Laver

[0043] Selective blocking characteristics of one or more polymer layers used in a separator come from the composition or specific pore architectures of these layers. For purposes of this disclosure, the term “blocking” is referred to as sieving, selecting, or excluding. In some embodiments, the pore architectures of polymer layer manifest as networks of interconnected pores with small pore sizes, narrow pore-size distribution, high surface area, and high porosity as further described below. In some embodiments, the pore architectures of polymer layer manifest as an array of channels with small pore sizes, narrow pore-size distribution, high surface area, and high porosity as further described below. In addition to these blocking properties, the polymer layer possesses various other properties making them suitable for electrochemical cell applications, such as chemical and electrochemical stability, wettability, thickness, thermal stability, and the like.

[0044] The blocking mechanism is based on chemical exclusion (non-wettable) or a sizeexclusion effect transpired at a nanometer to sub-nanometer scale where tortuous, ionically percolating, pathways are established in polymer layers. For example, a polymer layer may allow Li-ions (or other like species described below) to pass while blocking larger electrolyte solvent or the like. The membrane may be formed from a ladder polymer with angular spiro centers and absence of rotatable bonds in the polymer backbone or bonds in the backbone with restricted bond rotation. These characteristics provide inefficient solid-state packing with porosity of between about 10% and 40% or, more specifically, between about 20% and 30% of the bulk powder. The pores may then be filled with an inorganic component leaving a non-porous or partially porous polymer layer.

[0045] The separator includes a polymer layer containing poly(acrylonitrile-co-methyl acrylate). The poly(acrylonitrile-co-methyl acrylate) polymer can have any suitable ratio of the acrylonitrile to methyl acry late. For example, the ratio of the acrylonitrile to methyl acrylate can be from 99: 1 to 50:50 (mokmol), or from 99:1 to 55:45, or from 99: 1 to 60:40, or from 99:1 to 65:35, or from 99: 1 to 70:30, or from 99: 1 to 75:25, or from 99: 1 to 80:20, or from 99: 1 to 85: 15, or from 99: 1 to 90: 10, or from 99: 1 to 95:5 (mokmol). Alternatively, the poly (aery lonitrile-co-methyl acrylate) polymer can have at least 50 wt% acrylonitrile, or at least 55, 60, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, or at least 95 wt% acrylonitrle.

[0046] In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a ratio of acrylonitrile to methyl acrylate is 99: 1 to 50:50 (mokmol). In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly (aery lonitrile-co-methyl acrylate) having a ratio of acrylonitrile to methyl acrylate is 99: 1 to 70:30 (mol:mol). In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a ratio of acrylonitrile to methyl acrylate is 99: 1 to 80:20 (mol: mol). In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly (aery lonitrile-co-methyl acrylate) having at least 75 wt% acrylonitrile. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having at least 85 wt% acrylonitrile. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitnle-co-methyl acrylate) having at least 90 wt% acrylonitrile. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having about 94 wt% acrylonitrile. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having 94 wt% acrylonitrile. [0047] The polymer layer of the present invention can include a conformal polymer layer of the separator characterized by being substantially free of pinholes. The hole-free nature of the conformal polymer layer can be measured by a variety of methods. For example, the air permeability as a function of time of the conformal polymer layer can be measured using suitable devices. Suitable units of measuring the air permeability include, but are not limited to, the Gurley value. The Gurley value refers to the number of seconds required for 100 cubic centimeters of air to pass through 1.0 square inch of a given material at a pressure differential of 0. 176 psi. The Gurley value is standardized under ASTM D737-18 and ISO 9237-1995.

[0048] The polymer layer of the present invention can have a suitable Gurley value of, for example, at least 100 seconds, or at least 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, or at least 10000 seconds, as measured according to ASTM D737-18 or ISO 9237-1995. In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a Gurley value of at least 500 seconds. In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a Gurley value of at least 1000 seconds. In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a Gurley value of at least 5000 seconds. In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a Gurley value of at least 10,000 seconds.

[0049] The polymer layer can have any suitable thickness. For example, the thickness of the polymer layer can be between about 0.1 micrometers and 5 micrometers, or between about 0.2 micrometers and 3 micrometers, or between about 0.3 micrometers and 2 micrometers, or between about 0.4 micrometers and 1.5 micrometers, or between about 0.4 micrometers and 1.4 micrometers, or more specifically between about 0.5 micrometers and 1.2 micrometers. The porous support can have a thickness of about 0.8 micrometers, or about 0.9, 1, or about 1.1 micrometers.

[0050] The polymer layer of the separator of the present invention can be substantially insoluble in one or more ty pes of electrolytes. In some embodiments, the separator of the present invention is the separator wherein the polymer layer is substantially insoluble in carbonate electrolytes. Representative carbonate electrolytes are described within. For example, the polymer layer can be more than 50% insoluble in the carbonate electrolyte, or more than 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, or more than 99% insoluble in the carbonate electrolyte. The solubility of the polymer layer in the carbonate electrolyte can be characterized by less than 10% by weight of the polymer layer dissolving in the carbonate electrolyte, or less than 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or less than 0. 1% by weight of the polymer layer dissolving in the carbonate electrolyte. In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a solubility of less than 1% in carbonate electrolytes. In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a solubility of less than 0.5% in carbonate electrolytes. In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a solubility' of less than 0.1% in carbonate electrolytes. In some embodiments, the separator of the present invention is the separator wherein the polymer layer is insoluble in carbonate electrolytes.

[0051] The polymer layer includes a poly(acrylonitrile-co-methyl acrylate) polymer of any suitable molecular weight. For example, the poly(acrylonitrile-co-methyl acrylate) polymer of the polymer layer can have a number average molecular weight (M _n ) of greater than 1 kg/mol and less than 1,000 kg/mol, or at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, or greater than 250 kg/mol, as measured using a Malvern OMNISEC SEC equipped with a refractive index, light scattering, and intrinsic viscosity triple detector and a using DMF + 0.2% LiBr mobile phase. The number average molecular weight (Mn) of the polymer layer can be measured by a variety of methods. In some embodiments, the number average molecular weight (M _n ) of the polymer layer can be determined using a Malvern OMNISEC SEC equipped with a refractive index, light scattering, and intrinsic viscosity triple detector and a using DMF + 0.2% LiBr mobile phase.

[0052] In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises a polymer having a number average molecular weight (M _n ) of greater than 10 kg/mol. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of greater than 100 kg/mol. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of greater than 150 kg/mol. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of greater than 175 kg/mol. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of greater than 190 kg/mol. In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile- co-methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol.

[0053] In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (M _n ) of greater than 10 kg/mol, and wherein the ratio of acrylonitrile to methyl acrylate is 99: 1 to 50:50 (mol:mol). In some embodiments, the separator of the present invention is the separator wherein the polymer layer consists of poly (aery lomtrile-co-methyl acrylate) having a number average molecular weight (M _n ) of greater than 10 kg/mol, and wherein the ratio of acrylonitrile to methyl acrylate is 99: 1 to 50:50 (mol:mol).

[0054] In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of greater than 100 kg/mol, and wherein the ratio of acrylonitrile to methyl acrylate is 99: 1 to 70:30 (mol:mol). In some embodiments, the separator of the present invention is the separator wherein the polymer layer consists of poly (aery lonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of greater than 100 kg/mol, and wherein the ratio of acrylonitrile to methyl acrylate is 99: 1 to 70:30 (mol:mol).

[0055] In some embodiments, the separator of the present invention is the separator wherein the polymer layer comprises poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, and wherein the ratio of acrylonitrile to methyl acrylate is 99: 1 to 80:20 (mol: mol). In some embodiments, the separator of the present invention is the separator wherein the polymer layer consists of poly(acrylonitrile-co- methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, and wherein the ratio of acrylonitrile to methyl acrylate is 99: 1 to 80:20 (mol:mol).

[0056] In some embodiments, the separator of the present invention is the separator wherein the polymer layer consists essentially of poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, and having at least 90 wt% acrylonitrile. In some embodiments, the separator of the present invention is the separator wherein the polymer layer consists of poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, and having at least 90 wt% acrylonitrile. In some embodiments, the separator of the present invention is the separator wherein the polymer layer consists essentially of poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, and having about 94 wt% acrylonitrile. In some embodiments, the separator of the present invention is the separator wherein the polymer layer consists of poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, and having about 94 wt% acrylonitrile.

[0057] In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a coat weight of from 0. 1 to 2 g/m ² . In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a coat weight of from 0.2 to 1.9 g/m ² , from 0.3 to 1.8 g/m ² , from 0.5 to 1.7 g/m ² or from 0.6 to 1.6 g/m ² . In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a coat weight of from 0.6 to 1.6 g/m ² . In some embodiments, the separator of the present invention is the separator wherein the polymer layer has a coat weight of from 0.8 and 1.2 g/m ² .

[0058] In some embodiments, the separator of the present invention is the separator wherein the porous support comprises polyethylene; and the polymer layer consists essentially of poly(acrylonitrile-co-methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, wherein the ratio of acrylonitrile to methyl acrylate is 99:1 to 80:20 (mol:mol), wherein the polymer layer has a Gurley value of at least 10,000 seconds, and wherein the polymer layer is coated on the first surface of the porous support. In some embodiments, the separator of the present invention is the separator wherein the porous support comprises polyethylene; and the polymer layer consists of poly(acrylomtnle-co- methyl acrylate) having a number average molecular weight (Mn) of about 194 kg/mol, wherein the ratio of acrylonitrile to methyl acrylate is 99: 1 to 80:20 (mol:mol), wherein the polymer layer has a Gurley value of at least 10,000 seconds, and wherein the polymer layer is coated on the first surface of the porous support.

III. ELECTROLYTE

[0059] The present invention also includes an electrolyte for use with the coated separator. [0060] The electrolyte can include a variety of components, such as a carbonate electrolyte. In some embodiments, the electrolyte is a carbonate electrolyte. The carbonate electrolytes can include a variety of carbonates such as, but not limited to, fluorinated carbonates. In some embodiments, the electrolyte is a carbonate electrolyte comprising a fluorinated carbonates. For example, the carbonate electrolyte may comprise from 20 % to 65 % (mol/mol) of a fluorinated carbonate, based on the total number of moles in the electrolyte, or from 25% to 60% (mol/mol), from 30% to 50%, from 32% to 48% (mol/mol), or from 35% to 45%.

[0061] The carbonate electrolyte can include additional components, such as one or more lithium salts. In some embodiments, the electrolyte is a carbonate electrolyte comprising a fluorinated carbonate and a lithium salt. An exemplary electrolyte of the present invention includes a liquid electrolyte solvent which is a fluorinated carbonate solvent and a lithium salt. Another exemplary electrolyte of the present invention includes a liquid electrolyte solvent which is a fluorinated carbonate solvent and a lithium salt which is a fluorinated lithium salt.

[0062] In some embodiments, the electrolyte is a carbonate electrolyte comprising a fluorinated carbonate, an alkyl carbonate and a lithium salt. An exemplary electrolyte of the present invention includes two liquid electrolyte solvents which are an alky l carbonate solvent and a fluorinated carbonate solvent, and a lithium salt.

[0063] In some embodiments, the electrolyte is a carbonate electrolyte comprising a fluorinated carbonate, an alkyl carbonate and two distinct lithium salts. An exemplary electrolyte of the present invention includes two liquid electrolyte solvents which are an alkyd carbonate solvent and a fluorinated carbonate solvent, and two distinct lithium salts.

[0064] The present invention also includes an electrolyte having an alkyl carbonate, a fluorinated carbonate, a diisocyanate, and a lithium salt. In some embodiments, the present invention provides an electrolyte comprising an alkyl carbonate, a fluorinated carbonate, a diisocyanate, and a first lithium salt. In some embodiments, the electrolyte comprises a second lithium salt different from the first lithium salt.

[0065] Representative alkyl carbonates of the electrolyte include, but are not limited to, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, n-propyl propionate, vinylene carbonate, ethylene carbonate, fluoroethylene carbonate, or propy lene carbonate. In some embodiments, the alkyl carbonate is dimethyl carbonate. [0066] Representative fluorinated carbonates of the electrolyte include, but are not limited to, fluoroethylene carbonate, CH3OC(O)OCH ₂ CF3, CH3OC(O)OCH ₂ CF ₂ CHF ₂ , CH3OC(O)OCH ₂ CF ₂ CHF ₂ , CF3CH ₂ OC(O)OCH ₂ CF3, CH3OC(O)OCH2CF ₂ CF ₂ CF3, CH3CH2OC(O)OCH ₂ CF ₂ CF3, CH ₃ CH ₂ OC(O)OCH2CF2CHF2, or CH ₃ OC(O)OCH ₂ CF ₂ CF ₂ CF3.

[0067] Representative diisocyanates of the electrolyte include, but are not limited to, tolylene-2,4-diisocyanate, or tolylene-2,6-diisocyanate.

[0068] The lithium salt of the electrolyte compositions of the present invention can be any suitable lithium salt. For example, suitable lithium salts include, but are not limited to, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium 4,5-dicyano-2- (trifluoromethyl)imidazolium, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium nitrate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or combinations thereof. In some embodiments, the lithium salt can be lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium nitrate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or combinations thereof.

[0069] In some embodiments, the electrolyte composition is the electrolyte composition wherein the first lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSi), lithium hexafluorophosphate, or combinations thereof. In some embodiments, the electrolyte composition is the electrolyte composition wherein the first lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSi).

[0070] The first lithium salt can be present in the electrolyte composition in any suitable amount. For example, the first lithium salt can be present in the electrolyte composition in an amount of from 0.1 to 20 mol%, from 0.1 to 20 mol%, from 1 to 20 mol%, from 5 to 20 mol%, from 5 to 15 mol%, from 8 to 12 mol%, or from 9 to 11 mol%, based on the total number of moles in the electrolyte. Representative amounts of the first lithium salt in the electrolyte compositions of the present invention include, but are not limited to, about 5 mol%, or about 6, 7, 8, 9, 10, 11, 12, 13, 14, or about 15 mol%.

[0071] The electrolyte composition of the present invention can include one or more lithium salts. For example, the electrolyte composition can include 1, 2, 3, 4, or more different lithium salts as defined above. In some embodiments, the electrolyte composition is the electrolyte composition comprising a single lithium salt. In some embodiments, the electrolyte composition is the electrolyte composition comprising two different lithium salts. In some embodiments, the electrolyte composition is the electrolyte composition comprising three different lithium salts.

[0072] The electrolyte compositions of the present invention can also include a second lithium salt that is different from the first lithium salt. In some embodiments, the electrolyte composition is the electrolyte composition including a second lithium salt that is different from the first lithium salt.

[0073] In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt comprises lithium 4,5-dicyano-2- (trifluoromethyl)imidazolium, lithium difluoro(oxalato)borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium nitrate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or combinations thereof. In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt comprises lithium 4,5-dicyano-2- (trifluoromethyl)imidazolium, lithium difluoro(oxalato)borate (LiDFOB), or combinations thereof. In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt comprises lithium 4,5-dicyano-2- (trifluoromethyl)imidazolium. In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt comprises lithium difluoro(oxalato)borate (LiDFOB). In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt comprises lithium nitrate.

[0074] The second lithium salt can be present in the electrolyte composition in any suitable amount. For example, the second lithium salt can be present in the electrolyte composition in an amount of from 0.1 to 10 mol%, from 0.1 to 5 mol%, from 0.5 to 5 mol%, from 0.5 to 4 mol%, from 0.5 to 3.5 mol%, from 1 to 3 mol%, from 1.0 to 2.5 mol%, or from 1.5 to 2.5 mol%, based on the total number of moles in the electrolyte. Representative amounts of the second lithium salt in the electrolyte compositions of the present invention include, but are not limited to, about 1.5 mol%, or about l.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or about 2.5 mol%. [0075] In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt is present in the electrolyte composition in an amount of from 0. 1 to 5 mol%. In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt is present in the electrolyte composition in an amount of from 0.5 to 3.5 mol%. In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt is present in the electrolyte composition in an amount of 1 to 3 mol%. In some embodiments, the electrolyte composition is the electrolyte composition wherein the second lithium salt is present in the electrolyte composition in an amount of from 1.5 to 2.5 mol%.

[0076] An exemplary electrolyte of the present invention includes two distinct lithium salts, in particular two distinct fluorinated lithium salts. For example, the electrolyte may comprise lithium bis(fluorosulfonyl)imi de (LiFSi) and lithium difluoro(oxalato)borate (LiDFOB).

[0077] In some embodiments, the present invention provides an electrolyte comprising, based on the total number of moles in the electrolyte: dimethyl carbonate in an amount of from 25% to 75% (mol/mol); fluoroethylene carbonate in an amount of from 20% to 65% (mol/mol); tolylene-2,6-diisocyanate in an amount of from 0.1% to 10% (mol/mol); lithium bis(fluorosulfonyl)imide (LiFSi)in an amount of from 1% to 20% (mol/mol); and lithium difluoro(oxalato)borate (LiDFOB) in an amount of from 0.1% to 10% (mol/mol).

[0078] In some embodiments, the present invention provides an electrolyte comprising, based on the total number of moles in the electrolyte: dimethyl carbonate in an amount of from 30% to 70% (mol/mol), or from 40% to 60%; fluoroethylene carbonate in an amount of from 25% to 60% (mol/mol), or from 30% to 50%; tolylene-2,6-diisocyanate in an amount of from 0.5% to 5% (mol/mol), or from 0.7% to 3%; lithium bis(fhiorosulfonyl)imide (LiFSi) in an amount of from 5% to 15% (mol/mol), or from 7% to 13%; andlithium difluoro(oxalato)borate (LiDFOB) in an amount of from 0.5% to 5% (mol/mol), or from 0.7% to 2%.

[0079] In some embodiments, the present invention provides an electrolyte comprising, based on the total number of moles in the electrolyte: dimethyl carbonate in an amount of about 48% (mol/mol); fluoroethylene carbonate in an amount of about 39% (mol/mol); tolylene-2,6-diisocyanate in an amount of about 1% (mol/mol); lithium bis(fluorosulfonyl)imide (LiFSi) in an amount of about 10% (mol/mol); and lithium difluoro(oxalato)borate (LiDFOB) in an amount of about 2% (mol/mol).

IV. ELECTROCHEMICAL CELL

[0080] In some embodiments, the electrochemical device is an electrochemical cell. In some embodiments, an electrochemical cell includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0081] In some embodiments, the present invention provides an electrochemical cell comprising: an anode; a cathode; a separator of the present invention; and an electrolyte. FIG. 4A shows the electrochemical cell 200, having anode 210, cathode 220, and the separator 100. The separator 100, having porous support 110 having a first surface 111 and a second opposing surface 112, and a polymer layer 120, is disposed between the anode 210 and the cathode 220. FIG. 4B shows the electrochemical cell 200, having anode 210, cathode 220, and the separator 100. The separator 100, having porous support 110 having a first surface 111 and a second opposing surface 112, a polymer layer 120, a polymer layer 130, is disposed between the anode 210 and the cathode 220. The separator provides electronic isolation between the anode and the cathode. At least a portion of the electrolyte is disposed within the separator.

[0082] In some embodiments, the electrochemical cell is the electrochemical cell wherein the separator is between the anode and the cathode. In some embodiments, the electrochemical cell is the electrochemical cell wherein the separator is oriented such that the first surface of the support material is oriented towards the anode.

[0083] In some embodiments, the electrochemical cell of the present invention is the electrochemical cell wherein the electrolyte is an electrolyte of the present invention.

[0084] In some embodiments, the electrochemical device is a lithium-ion battery with a carbon-based, metallic, or metalloid anode and a metal oxide or conversion cathode.

V. EXAMPLES

[0085] Anode: Lithium metal, 20 pm or thinner when fully discharged. [0086] Cathode: Lithium nickel manganese cobalt oxide, nickel content 60 mol% or greater metals basis, cobalt 20% or fewer metals basis, for example NMC-622 or NMC-811, with 3.5 mAh/cm ² or greater aerial capacity.

[0087] Separator support: poly(ethylene) or poly(propylene), 9-16 pm, 40-50% porosity.

[0088] P(AN-co-MA): poly(acrylonitrile-co-methyl acrylate) (94 wt% acrylonitrile) from Sigma-Aldrich:

[0089] P(AN-co-MA) having a number average molecular weight (M _n ) of about 194 kg/mol was used.

[0090] Molecular weight information for P(AN-co-MA) was determined using a Malvern OMNISEC SEC equipped with a refractive index, light scattering, and intrinsic viscosity triple detector and a using DMF + 0.2% LiBr mobile phase. A combination of specific refractive index increment and light scattering signal were used to calculate molecular weight, and a viscometer used to calculate intrinsic viscosity.

[0091] Conductivity measurements were performed with Extech Instruments Conductivity meter EC210. Freezing point and flash point of the electrolytes was determined through differential scanning calorimetry (Perkin-Elmer, Diamond DSC) and a small scale closed cup tester (Koehler, Model # KI 6502), respectively. Freezing point of the electrolytes was analyzed from 18°C to -40°C (limit of the equipment) with a temperature rate of 10°C/minute.

Example 1: Preparation of the Electrolyte (El)

[0092] An electrolyte mixture was prepared by mixing the following components (mol %): dimethyl carbonate 48%, fluoroethylene carbonate 39%, tolylene-2,6-diisocyanate 1%, Lithium bis(fluorosulfonyl)imide 10% (LiFSi), Lithium difluoro(oxalato)borate 2% (LiDFOB). The density of El was 1.35, the conductivity at 22 °C was 8 mS/cm, the freezing point was < -30 °C, and the flash point (closed-cup) was 40 °C. Example 2; Preparation of Coated Separator

[0093] The coating solution (also called “ink” herewith) was prepared by stirring the polymer in N,N-dimethylformamide at a specified concentration (wt. %) of P(AN-co-MA) solids for 24 hours, followed by filtration through a 1 -micron pore glass fiber syringe filter. The solids content of the ink is based on the thickness and porosity of the base separator and the desired weight of the coating (Table 1).

Table 1. P(AN-co-MA) coating on separator support

[0094] The following process to apply coating solutions onto separators were used: either Meyer rod, microgravure, or slot die coating methods to apply the polymer solutions via roll- to-roll coating onto the porous support and dried via heating in an air dryer at ambient humidity at temperatures between room temperature and 70 °C.

[0095] A carbonate electrolyte El was used in the present examples.

[0096] The coat weights and Gurley numbers of the layers are then measured to qualify the samples for cell testing. Specification for coat weight - 0.5 to 1.0 g/m ² . Exemplified range 0.6-1.6 g/m ² . Specification for Gurley >10,000.

[0097] Coat weight is determined gravimetrically, in which a 12 cm ² area of coated matenal is weighed, the coating stopped using an appropnate solvent, and the separator weighted again. The coat weight is determined by subtracting these two values and normalizing to the surface area of the test sample.

[0098] Gurley measurement is designed to ensure that the polymer layer(s) coated onto the porous support comprise a conformal layer over the support and is exempt of pinhole defects. Air permeability measurements were made using an oil-sealed high pressure densometer (Gurley Precision Instruments, Model #4150N) following the method described in testing standard TAPPI T-536-88 ("Resistance of paper to passage of air, high pressure Gurley method"). In the present examples, a coated material with a Gurley value greater than 10,000 validates the material as free of pinhole defects and appropriate for testing in cells. All the coated separators described below present a Gurley value greater than 10,000.

Example 3: Lithium metal battery cell configurations

[0099] A lithium metal pouch cell battery was fabricated using a 20 um lithium metal anode on 10 um copper foil current collector as received from Honjo without further treatment. P(AN-co-MA) was applied to 9 um or 16 um commercially available polyethylene battery separator according to process 2E or 2A as denoted in the respective figure, with the P(AN-co-MA) layer interfacing with the lithium metal anode and the uncoated PE side interfacing the cathode. An NMC-811 cathode with aerial capacity of 3.8 mAh/cm ² was applied to the stack. The cell was laminated, filled with 2 grams of electrolyte El per nominal Ah of cathode capacity, sealed, and fixtured to a stack pressure of 100 psi. The cells were cycled at 30 °C.

[0100] The stack-level energy density of these cells at 2, 10, and 100 Ah sizes were modeled assuming a C/3 discharge rate according to USABC (United States Advanced Battery Consortium LLC ) standards and are depicted in Table 2. One of ordinary skill in the art will appreciate that as the battery size increases, the packing efficiency of active:inactive cell materials increases and there is a commensurate improvement in energy density. Energy density is modeled at the cell level; stack level energy densities will be higher than those described in Table 2.

Table 2. Energy density models for high energy density batteries with P(AN-co-MA) coated battery separator with El electrolyte.

[0101] Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, one of skill in the art will appreciate that certain changes and modifications may be practiced within the scope of the appended claims. In addition, each reference provided herein is incorporated by reference in its entirety to the same extent as if each reference was individually incorporated by reference. Where a conflict exists between the instant application and a reference provided herein, the instant application shall dominate.