JP7566754B2 - Localized ultra-concentrated electrolytes for silicon anodes - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of U.S. Patent Application No. 16/247,143, filed January 14, 2019, which is incorporated by reference in its entirety.

ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT This invention was made with Government support under Contract No. DE-AC05-76RL01830 awarded by the U.S. Department of Energy. The Government has certain rights in this invention.

FIELD The present invention relates to a localized ultra-high concentration electrolyte for stable repeated use of a system including a silicon-based or carbon/silicon composite-based anode, the localized ultra-high concentration electrolyte comprising an active salt, a solvent in which the active salt is soluble, and a diluent in which the active salt is insoluble or poorly soluble.

SUMMARY A localized very-high concentration electrolyte (LSE), also referred to as a localized high concentration electrolyte (LHCE), for use in lithium-ion batteries having silicon-based or carbon/silicon composite-based anodes is disclosed. A system including such an LSE is also disclosed.

Some embodiments of the disclosed system include an anode comprising silicon, and an electrolyte comprising (a) an active salt comprising lithium cations, (b) a non-aqueous solvent comprising (i) a carbonate other than fluoroethylene carbonate (FEC), (ii) a flame retardant compound, or (iii) both (i) and (ii), where the active salt is soluble in the non-aqueous solvent, and (c) a diluent comprising a fluoroalkyl ether, a fluorinated orthoformate ester, or a combination thereof, where the active salt has a solubility in the diluent that is at least 10 times lower than the solubility of the active salt in the non-aqueous solvent. In some embodiments, the electrolyte further comprises 0.1-30 wt % FEC. The system may further comprise a cathode.

In any of the above embodiments, the active salt may include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(oxalato)borate (LiBOB), LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiClO ₄ , lithium difluorooxalatoborate (LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO ₃ , LiNO ₂ , Li ₂ SO ₄ , or any combination thereof. In some embodiments, the active salt has a molar concentration in the electrolyte in the range of 0.5 to 6 M.

In some embodiments, the non-aqueous solvent comprises a carbonate ester other than FEC. In certain embodiments, the carbonate ester is a mixture of ethylene carbonate (EC) and ethyl carbonate (EMC). In some embodiments, the non-aqueous solvent comprises a flame retardant compound comprising an organic phosphate ester, an organic phosphite ester, an organic phosphonate ester, an organic phosphoramide, a phosphazene, or any combination thereof. In certain embodiments, the flame retardant compound comprises triethyl phosphate, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl)phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl)methylphosphonate; hexamethylphosphoramide; hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof.

In any of the above embodiments, the diluent is bis(2,2,2-trifluoroethyl)ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB, ethoxynonafluorobutane (EOFB), tris(2,2,2-trifluoroethyl)orthoformate (TFEO), tris(hexafluoroisopropyl)orthoformate (THFiPO ... Bis(2,2-difluoroethyl) orthoformate (TDFEO), bis(2,2,2-trifluoroethyl)methyl orthoformate (BTFEMO), tris(2,2,3,3,3-pentafluoropropyl) orthoformate (TPFPO), tris(2,2,3,3-tetrafluoropropyl) orthoformate (TTPO), 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE), or any combination thereof. In some embodiments, the diluent comprises BTFE, TTE, TFEO, or any combination thereof.

In some embodiments, the electrolyte comprises 1-3M LiFSI, EC-EMC or TEPa in a ratio of 4:6 to 2:8 by weight, 0-30 wt% FEC (e.g., 0 wt% FEC, 5-30 wt% FEC, or 5-10 wt% FEC), and a diluent, where the diluent comprises BTFE, TTE, TFEO, or any combination thereof. In one embodiment, the electrolyte comprises EC-EMC and the molar ratio of EC-EMC to diluent is within the range of 1-4, such as within the range of 1-3. In another embodiment, the electrolyte comprises TEPa and the molar ratio of TEPa to diluent is within the range of 1-4, such as within the range of 2-4.

In any of the above embodiments, the anode may include a graphite/silicon composite. In some embodiments, the anode further includes a lithium polyacrylate binder, a polyimide binder, or a carboxymethyl cellulose binder. In certain embodiments, the silicon is carbon-coated nanosilicon.

In some embodiments, the anode comprises a graphite/silicon composite with a polyimide binder, the silicon is carbon-coated nanosilicon, the electrolyte comprises 1-3 M LiFSI, TEPa, 0-30 wt % FEC, and a diluent, where the diluent is BTFE, TTE, TFEO, or any combination thereof, and the molar ratio of TEPa to diluent is within the range of 1-4, such as within the range of 2-4. In certain embodiments, the anode is prelithiated, the system further comprises a cathode, and the system has a capacity retention of 80% or greater after 100 cycles.

In some embodiments, the anode comprises a graphite/silicon composite with a lithium polyacrylate binder, and the electrolyte comprises 1-3 M LiFSI, EC-EMC (3:7, by weight), 0-30 wt % FEC, and a diluent, where the diluent is BTFE, TTE, TFEO, or any combination thereof, and the molar ratio of EC-EMC to diluent is within the range of 1-4, such as within the range of 1-3. In certain embodiments, the system further comprises a cathode and has a capacity retention of 70% or greater after 100 cycles.

The above objects, features and advantages of the present invention, as well as other objects, features and advantages, will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic illustration of a super-concentrated electrolyte (SE) that includes a lithium salt and a solvent.

FIG. 2 is a schematic illustration of an exemplary localized super-concentrated electrolyte (LSE) that includes a lithium salt, a solvent in which the lithium salt is soluble, and a diluent, i.e., a component in which the lithium salt is insoluble or poorly soluble compared to the solvent.

FIG. 3 is a schematic illustration of an exemplary "bridging" solvent molecule between a solvent molecule and a diluent molecule.

FIG. 4 is a schematic diagram of an exemplary battery.

FIG. 5 shows the cycling performance of the coin cell over 100 cycles by using a silicon/graphite (Si/Gr) anode with LiPAA binder, an NMC532 cathode, and a baseline electrolyte containing 1.2 M _LiPF6 in EC/EMC (3:7, weight ratio) with 10 wt% FEC.

FIG. 6 shows the cycling performance of coin cells over 100 cycles using a Si/Gr anode with LiPAA binder, an NMC532 cathode, and various electrolytes including the baseline electrolyte of FIG. 5, the ultra-high concentration electrolyte, and several LSEs as disclosed herein.

FIG. 7 is a graph of voltage versus specific capacity for the 1st, 2nd, and 4th cycles of a coin cell using a Si/Gr anode with LiPAA binder, an NMC532 cathode, and an LSE (E-313) with 1.2 M LiFSI in TEPa-3BTFE.

FIG. 8 shows the cycling performance of the coin cell of FIG. 7 over 100 cycles.

FIG. 9 is a graph of specific capacity versus voltage for the first, second, and third cycles of a coin cell using a Si/Gr anode with a polyimide binder, an NMC532 cathode, and a baseline electrolyte.

FIG. 10 shows the cycling performance of the coin cells over 100 cycles by using the baseline electrolyte, NMC532 cathode, and various anodes, namely, Si/Gr anode with LiPAA binder, Si/Gr anode with PI binder, and carbon-coated Si/Gr anode with PI binder.

FIG. 11 shows the cycling performance of coin cells over 100 cycles using an NMC cathode, a carbon-coated Si/Gr anode with PI binder, and baseline electrolytes, LSE (E-103) containing 2.5 M LiFSI in EC-EMC (3:7, wt. ratio)-1.5BTFE (molar ratio vs. EC-EMC) + 5 wt. % FEC, and LSE (E-313) containing 1.2 M LiFSI in TEPa-3BTFE (molar ratio vs. TEPa).

FIG. 12 is a graph of voltage versus specific capacity for the first and fourth cycles of coin cells with an NMC cathode, an LSE (E-313) with 1.2 M LiFSI in TEPa-3BTFE (molar ratio relative to TEPa), and a carbon-coated Si/Gr anode with PI binder with and without prelithiation.

FIG. 13 shows the cycling performance of coin cells over 100 cycles using an NMC cathode and a carbon-coated Si/Gr anode with PI binder with prelithiation, a carbon-coated Si/Gr anode with PI binder without prelithiation, and an LSE with 1.2 M LiFSI in TEPa-3BTFE (molar ratio vs. TEPa) or 1.2 M LiFSI in TEPa-3BTFE (molar ratio vs. TEPa) + 1.2 wt % FEC.

FIG. 14 shows the cycling performance of coin cells over 80 cycles by using an NMC cathode and a Si/Gr anode with LiPAA binder or a carbon-coated Si/Gr anode with PI binder and an exemplary LSE as disclosed herein.

FIG. 15 shows the cycling performance of Si/Gr∥NMC532 in LSEs containing 1.8 M LiFSI in EC-EMC (3:7, wt. ratio) + 5 wt. % FEC, and BTFE, TTE, or TFEO (molar ratio is 2 relative to EC/EMC).

Figure 16 shows the cyclic voltammetry curves of 1.8 M LiFSI (E-104) in EC-EMC (3:7, weight ratio)-2BTFE (molar ratio to EC/EMC) + 5 wt% FEC. The scan rate was 0.1 mV/s.

FIG. 17 shows the cycling performance of Li∥NMC532 in LSE E-104 or baseline electrolyte at different upper voltage plateaus.

FIG. 18 is a graph showing the cycling performance of a Li||Si/Gr battery using two non-flammable electrolytes, LiFSI-1.33TEPa-4BTFE and LiFSI-1.2TEPa-0.13FEC-4BTFE, and three control electrolytes, ₁ M LiPF in EC-EMC (3:7, wt.) + 2 wt.% FEC, ₁ M LiPF in EC-EMC (3:7, wt.) + ₅ wt.% FEC, and 1 M LiPF in EC-EMC (3:7, wt.) + 10 wt.% FEC.

FIG. 19 is a graph showing the cycling performance of a Si/Gr∥NMC333 battery using two non-flammable electrolytes, namely LiFSI-1.33TEPa-4BTFE and LiFSI-1.2TEPa-0.13FEC-4BTFE.

FIG. 20 is a graph showing the cycling performance of a Si/Gr∥NMC333 battery using a non-flammable electrolyte, i.e., LiFSI-1.2TEPa-0.13FEC-4BTFE, and a control electrolyte, i.e., 1 M _LiPF6 in EC-EMC (3:7, wt. ratio) + 10 wt. % FEC.

FIG. 21 is a graph showing areal capacity, specific capacity and coulombic efficiency over 140 cycles of a Si/Gr∥NMC333 battery using LiFSI-1.2TEPa-0.13FEC-4BTFE.

FIG. 22 is a graph showing the specific capacity and coulombic efficiency over 100 cycles of a high areal capacity Si/Gr∥NMC333 battery using LiFSI-1.2TEPa-0.13FEC-4BTFE.

FIG. 23 is a graph showing the specific capacity and coulombic efficiency over 600 cycles at 25° C. of Si/Gr∥NMC333 batteries using LiFSI-1.33TEPa-4BTFE and LiFSI-1.2TEPa-0.13FEC-4BTFE.

FIG. 24 is a graph showing the specific capacity and coulombic efficiency of the battery of FIG. 23 at 45° C.

DETAILED DESCRIPTION The present disclosure relates to various embodiments of localized ultra-high concentration electrolytes (LSEs) for use in various systems, such as lithium ion battery systems. Systems including the LSEs are also disclosed. Some embodiments of the disclosed LSEs are stable in electrochemical cells having silicon-based, carbon/silicon-based, carbon-based (e.g., graphite-based and/or hard carbon-based), tin-based or antimony-based anodes and various cathode materials. The LSEs include an active salt, a solvent in which the active salt is soluble, and a diluent in which the active salt is insoluble or poorly soluble.

I. Definitions and Abbreviations The following explanations of terms and abbreviations are provided to better explain the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. As used herein, "comprising" means "including" and the singular forms "a" or "an" or "the" include plural references unless the context clearly indicates otherwise. The term "or" refers to only one element of the specified alternative elements or a combination of two or more elements, unless the context clearly indicates otherwise.

Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, suitable methods and materials are described below. These materials, methods, and examples are illustrative only and are not intended to be limiting. Other features of the present disclosure will be apparent from the following detailed description and claims.

Unless otherwise indicated, all numbers expressing amounts of ingredients, molecular weights, molarity, voltages, volumes, and volumes, etc., when used in the specification or claims should be understood as being modified by the term "about". Thus, unless otherwise indicated, implicitly or explicitly, or appropriately understood by one of ordinary skill in the art from the context to have a clearer configuration, the numerical parameters indicated are approximations that may depend on the desired properties sought under standard test conditions/methods and/or the detection limits under such standard test conditions/methods as known to those of ordinary skill in the art. When directly and explicitly distinguishing the embodiments from the prior art discussed, the numbers of the embodiments are not approximations unless the word "about" is stated.

Although various alternatives exist for the various components, parameters, operating conditions, etc., set forth herein, that does not mean that the alternatives are necessarily equivalent and/or will function equally satisfactorily, nor is it meant that the alternatives are listed in any order of preference, unless otherwise expressly stated.

Definitions of various common terms in chemistry may be found in Richard J. Lewis, Sr. (ed.), Hawley's Condensed Chemical Dictionary (published by John Wiley & Sons, Inc., 2016) (ISBN 978-1-118-13515-0).
In order to facilitate review of the various embodiments of the disclosure, the following explanations of specific terms are provided:

Active Salt: As used herein, the term "active salt" refers to a salt that constitutes at least 5% of the redox active material that participates in redox reactions during repeated use of the battery after the initial charge.
AN: acetonitrile

Anode: The electrode through which charge flows in a polar electrical device. From an electrochemical perspective, negatively charged anions migrate toward the anode and/or positively charged cations leave the anode to balance the electrons leaving through the external circuit. In a discharging battery or galvanic cell, the anode is the negative terminal through which electrons flow out. If the anode is composed of a metal, the electrons it passes to the external circuit are accompanied by metal cations that leave the electrode and migrate into the electrolyte. When the battery is recharged, the anode becomes the positive terminal through which electrons flow and where metal cations are reduced.

Associated: As used herein, the term "associated" means coordinated to or solvated by. For example, a cation that is associated with a solvent molecule is coordinated to or solvated by the solvent molecule. Solvation is the attraction of the solvent molecule to the solute molecule or ion. Association can be due to electronic interactions between the cation and the solvent molecule (e.g., ion-dipole interactions and/or van der Waals forces). Coordination indicates that one or more coordinate bonds are formed between the cation and the electron lone pair of a solvent atom. Coordination bonds can also occur between a cation and an anion of the solute.

Bridged Solvent: A solvent having amphiphilic molecules that have a polar end or portion and a non-polar end or portion.
BTFE: bis(2,2,2-trifluoroethyl) ether

Capacity: The capacity of a battery is the amount of charge that the battery can deliver. Capacity is typically expressed in units of mAh or Ah and indicates the maximum constant current that the battery can deliver over a period of one hour. For example, a battery with a capacity of 100 mAh can deliver a current of 100 mA for one hour, or a current of 5 mA for 20 hours. Areal capacity or specific areal capacity is the capacity per unit area of electrode (or active material) surface, typically expressed in units of mAh cm ^-2 .

Carbon black: A finely divided form of carbon, typically produced by the incomplete combustion of vaporized heavy petroleum fractions. Carbon black can also be produced from methane or natural gas by cracking or combustion.

Carbon/silicon composite: As used herein, the term carbon/silicon composite refers to a material that contains both carbon (e.g., graphite and/or hard carbon) and silicon. Composites are made from two or more constituent materials that, when combined, result in a material with characteristics that differ from those of the individual components. Carbon/silicon composites can be prepared, for example, by pyrolysis of pitch in which graphite and silicon powders are embedded (see, for example, Wen et al., Electrochem Comm 2003, 5(2):165-168).

Cathode: The electrode from which charge flows out of a polar electrical device. From an electrochemical point of view, positively charged cations always move toward the cathode and/or negatively charged anions move away from the cathode to balance electrons arriving from the external circuit. In a discharging battery or galvanic cell, the cathode is the positive terminal with respect to the direction of the current flow. This outward charge is carried internally by positive ions moving from the electrolyte to the cathode at a higher potential where they can be reduced. When the battery is recharged, the cathode becomes the negative terminal from which electrons flow out and metal atoms (or cations) are oxidized.

Cell: As used herein, cell refers to an electrochemical device used to produce a voltage or current from a chemical reaction, or vice versa, where a chemical reaction is induced by an electric current. Examples include voltaic cells, electrolytic cells, and fuel cells, among others. A battery contains one or more cells. The terms "cell" and "battery" are used interchangeably when referring to a battery that contains only one cell.

Coin cell: A small, typically circular battery. Coin cells are characterized by their diameter and thickness.

Conversion Compound: A compound containing one or more cations that are replaced by another metal when the battery is discharged. For example, when iron(II) selenide (FeSe) is used as the cathode material, Fe is replaced by Na when a Na battery is discharged.
2Na ⁺ +2e ^- +FeSe ←→ Na ₂ Se + Fe

Coulombic Efficiency (CE): The efficiency with which charge is transferred in a system that facilitates an electrochemical reaction. CE may be defined as the amount of charge leaving a battery during a discharge cycle divided by the amount of charge entering the battery during a charge cycle. The CE of a Li||Cu or Na||Cu battery may be defined as the amount of charge leaving the battery during a stripping process divided by the amount of charge entering the battery during a plating process.
DEC: Diethyl carbonate DMC: Dimethyl carbonate DME: 1,2-dimethoxyethane DMSO: Dimethyl sulfoxide DOL: 1,3-dioxolane

Donor Number: A quantitative measure of Lewis basicity, such as the ability of a solvent to solvate a cation. The donor number is defined as the negative enthalpy value for the formation of a 1:1 adduct between a Lewis base and _SbCl5 in dilute solution in 1,2-dichloroethane, where the donor number is 0. Donor numbers are typically reported in units of kcal/mol. For example, acetonitrile has a donor number of 14.1 kcal/mol. As another example, dimethylsulfoxide has a donor number of 29.8 kcal/mol.
EC: Ethylene carbonate

Electrolyte: A substance containing free ions that behaves as an electrically conductive medium. Electrolytes generally contain ions in solution, although molten and solid electrolytes are also known.
EMC: Ethyl methyl carbonate EMS: Ethyl methyl sulfone EOFB: Ethoxynonafluorobutane EVS: Ethyl vinyl sulfone FEC: Fluoroethylene carbonate FCE: Initial coulombic efficiency

Flame retardant: As used herein, the term "flame retardant" refers to an agent that, when incorporated in a sufficient amount into an electrolyte, renders the electrolyte non-flammable or flame retardant as defined herein.

Flammable: The term "flammable" refers to a material that will ignite easily and burn rapidly. As used herein, the term "nonflammable" means that the electrolyte will not ignite or burn during operation of an electrochemical device that contains the electrolyte. As used herein, the terms "flammable" and "low flammability" are interchangeable and mean that a portion of the electrolyte may ignite under some conditions, but the resulting ignition will not propagate through the electrolyte. Flammability can be estimated by determining the self-extinguishing time (SET) of the electrolyte. SET is determined by a modified Underwriters Laboratories test standard 94HB. The electrolyte is immobilized in an inert spherical wick (such as a spherical wick with a diameter of about 0.3 to 0.5 cm) that is capable of absorbing 0.05 to 0.10 g of electrolyte. The wick is then ignited and the time for the flame to extinguish is recorded. Time is normalized to sample weight. If the electrolyte does not ignite, the SET is 0 and the electrolyte is non-flammable. Electrolytes with a SET below 6 s/g (e.g., the flame goes out within about 0.5 seconds) are also considered to be non-flammable. If the SET is above 20 s/g, the electrolyte is considered to be flammable. If the SET is between 6-20 s/g, the electrolyte is considered to be flame-retardant or have low flammability.

（式中、Ｒ、Ｒ’およびＲ”の少なくとも１つがフルオロアルキルであり、それ以外の２つの置換基が独立して、フルオロアルキルまたはアルキルである）。アルキル鎖は直鎖または分枝状であり得る。Ｒ、Ｒ’およびＲ”は互いに同じであり得、または互いに異なり得る。Ｒ、Ｒ’およびＲ”の１つまたは複数がペルフルオロ化され得る。 Fluorinated orthoformates: Fluorinated compounds having the general formula:

where at least one of R, R' and R" is fluoroalkyl and the other two substituents are independently fluoroalkyl or alkyl. The alkyl chain can be linear or branched. R, R' and R" can be the same as or different from each other. One or more of R, R' and R" can be perfluorinated.

Fluoroalkyl: An alkyl group in which at least one H atom is replaced by an F atom. A perfluoroalkyl group is an alkyl group in which all H atoms are replaced by F atoms.

Fluoroalkyl ethers (hydrofluoroethers, HFEs): As used herein, the terms fluoroalkyl ethers and HFEs refer to fluorinated ethers having the general formula R-O-R', where one of R and R' is a fluoroalkyl and the other of R and R' is a fluoroalkyl or an alkyl. The alkyl chain can be linear or branched. The ethers can be perfluorinated, in which case each of R and R' is a perfluoroalkyl. R and R' can be the same as each other or different from each other.

Hard carbon: A carbon material that is not easily graphitized. At high temperatures (e.g., above 1500°C), hard carbon remains substantially amorphous, whereas "soft" carbon will undergo crystallization and become graphitic.

Immiscible: This term describes two substances of the same physical state that cannot be homogeneously mixed or blended. Oil and water are a common example of two immiscible liquids.

Intercalation: A term indicating that a substance (e.g., ion or molecule) enters the microstructure of another substance. For example, lithium ions can enter or intercalate into graphite ( _C6 ) to form lithiated graphite ( _LiC6 ).
LiFSI: Lithium bis(fluorosulfonyl)imide LiTFSI: Lithium bis(trifluoromethylsulfonyl)imide LiBOB: Lithium bis(oxalato)borate LiDFOB: Lithium difluorooxalatoborate LiPAA: Lithium polyacrylate LSE: Localized ultra-high concentration electrolyte MEC: Methylene ethylene carbonate
MOFB: Methoxynonafluorobutane OTE: 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether PC: Propylene carbonate

Phosphate ester: As used herein, phosphate ester refers to an organophosphate ester having the general formula P(=O)(OR) ₃ , where each R is independently alkyl (e.g., _C1 - _C10 alkyl) or aryl. Each alkyl or aryl group can be substituted or unsubstituted.

Phosphite: As used herein, phosphite refers to an organophosphite having the general formula P(OR) ₃ or HP(O)(OR) ₂ , where each R is independently alkyl (e.g., _C1 - _C10 alkyl) or aryl. Each alkyl or aryl group can be substituted or unsubstituted.

Phosphonate ester: A compound having the general formula P(═O)(OR) ₂ (R′), where each R and R′ is independently alkyl (e.g., C ₁ -C ₁₀ alkyl) or aryl. Each alkyl or aryl group can be substituted or unsubstituted.

Phosphoramide: A compound having the general formula P(=O)( _NR2 ) ₃ , where each R is independently hydrogen, alkyl (e.g., _C1 - _C10 alkyl), or alkoxy (e.g., _C1 - _C10 alkoxy). At least one R is not hydrogen. Each alkyl or aryl group can be substituted or unsubstituted.

Phosphazene: A compound in which a phosphorus atom is covalently linked by a double bond to a nitrogen atom or nitrogen-containing group and by single bonds to three other atoms or groups.
PI: Polyimide

Separator: A battery separator is a porous sheet or film placed between the anode and cathode. The separator prevents physical contact between the anode and cathode while facilitating ion transport.

Soluble: Capable of being molecularly or ionically dispersed in a solvent to form a homogeneous solution. As used herein, the term "soluble" means that the active salt has a solubility in a given solvent of at least 1 mol/L (M, molar concentration) or at least 1 mol/kg (m, molar concentration).

Solution: A homogeneous mixture of two or more substances. A solute (minor component) is dissolved in a solvent (major component). Multiple solutes and/or multiple solvents can be present in a solution.

Ultra-concentrated: As used herein, the term "ultra-concentrated electrolyte" refers to an electrolyte having a salt concentration of at least 3M.
TDFEO: Tris(2,2-difluoroethyl) orthoformate
TEPa: triethyl phosphate TFEO: tris(2,2,2-trifluoroethyl) orthoformate
TFTFE: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether THFiPO: tris(hexafluoroisopropyl) orthoformate
TMPa: trimethyl phosphate TMTS: tetramethylene sulfone or tetramethylene sulfolane TPFPO: tris(2,2,3,3,3-pentafluoropropyl) orthoformate
TTE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether TTPO: tris(2,2,3,3-tetrafluoropropyl) orthoformate
VC: vinylene carbonate VEC: 4-vinyl-1,3-dioxolan-2-one

II. Localized Ultra-High Concentration Electrolytes Ultra-high concentration electrolytes include a solvent and a salt with a salt concentration of at least 3M. Some ultra-high concentration electrolytes have a salt concentration of at least 4M or at least 5M. In certain cases, the salt molar concentration can be up to 20m or more (e.g., aqueous LiTFSI). Figure 1 is a schematic illustration of a conventional ultra-high concentration electrolyte including a solvent and a lithium salt. Desirably, all or most of the solvent molecules are associated with the lithium cations in the ultra-high concentration electrolyte. The reduced presence of free non-associated solvent molecules can result in increasing the coulombic efficiency (CE) of lithium metal anodes and/or the reversible insertion of Li ions into carbon (e.g., graphite and/or hard carbon)-based and/or silicon-based anodes, facilitating the formation of a stabilized solid electrolyte interface (SEI) layer, and/or increasing the cycling stability of batteries including the electrolyte. However, ultra-high concentration electrolytes have drawbacks, such as high material costs, high viscosity, and/or poor wetting of battery separators and/or electrodes, etc. Dilution with additional solvent can address one or more of these drawbacks, but dilution results in free solvent molecules that often reduce the CE, prevent the formation of a stable SEI layer, and/or reduce the cycling stability of the battery.

FIG. 2 is a schematic illustration of an exemplary "localized superconcentrated electrolyte" (LSE). The LSE includes a lithium salt, a solvent in which the lithium salt is soluble, and a diluent in which the lithium salt is insoluble or poorly soluble. As shown in FIG. 2, the lithium ions remain associated with the solvent molecules after the addition of the diluent. Anions also reside in close proximity to or associate with the lithium ions. Thus, localized regions of solvent-cation-anion aggregates are formed. In contrast, the lithium ions and anions are not associated with the diluent molecules, and therefore they remain free in solution. Evidence of this electrolyte structure, with regions of localized high salt/solvent concentration and regions of free diluent molecules, is shown by Raman spectroscopy (e.g., as shown in U.S. Patent Application Publication No. 2018/0251681 A1, which is incorporated herein by reference), NMR characterization, and molecular dynamics (MD) simulations. Thus, although the overall solution is less concentrated than the solution in FIG. 1, there are localized regions of high concentration where the lithium cations are associated with the solvent molecules. Dilute electrolytes have few or no free solvent molecules, thereby providing the benefits of ultra-concentrated electrolytes without the associated disadvantages.

Conventional electrolytes and conventional ultra-high concentration electrolytes often provide only limited cycle life in battery systems with silicon-containing anodes. Some LSEs also provide poor results with silicon-containing anodes. In some cases, the compatibility of the electrolyte with the silicon-containing anode depends, at least in part, on the composition of the binder present in the anode. However, certain embodiments of the disclosed LSEs can solve some or all of the problems discussed above. In addition to being compatible with silicon-containing anodes, including carbon/silicon composite-based anodes, some embodiments of the disclosed LSEs are also compatible with carbon-based, tin-based and/or antimony-based anodes.

Various embodiments of the disclosed LSE include an active salt, a solvent A, where the active salt is soluble in solvent A, and a diluent, where the active salt is insoluble or sparingly soluble in the diluent. As used herein, "sparingly soluble" means that the active salt has a solubility in the diluent that is at least one-tenth of the solubility of the active salt in solvent A.

The solubility of the active salt in solvent A (in the absence of diluent) may be greater than 3M, such as at least 4M or at least 5M. In some embodiments, the solubility and/or concentration of the active salt in solvent A is in the range of 3M to 10M, such as in the range of 3M to 8M, 4M to 8M, or 5M to 8M. In certain embodiments, such as when solvent A includes water, the concentration may be expressed in terms of molar concentration, and the concentration of the active salt in solvent A (in the absence of diluent) may be in the range of 3m to 25m, such as in the range of 5m to 21m, or 10m to 21m. In contrast, the molar or moral concentration of the active salt in the electrolyte as a whole (salt, solvent A and diluent) can be at least 20% less than the molar or moral concentration of the active salt in solvent A, for example, at least 30% less, at least 40% less, at least 50% less, at least 60% less, or even at least 70% less than the molar or moral concentration of the active salt in solvent A. For example, the molar or moral concentration of the active salt in the electrolyte can be 20-80% less, 20-70% less, 30-70% less, or 30-50% less than the molar or moral concentration of the active salt in solvent A. In some embodiments, the molar concentration of the active salt in the electrolyte is in the range of 0.5M to 6M, 0.5M to 3M, 0.5M to 2M, 0.75M to 2M, or 0.75M to 1.5M.

The active salt is a salt or combination of salts that participates in the charging and discharging process of a battery containing an electrolyte. The active salt includes a cation that can form a redox pair with different oxidation and reduction states, such as ionic species with different oxidation states, or a metal cation and its corresponding neutral metal atom. In some embodiments, the active salt is an alkali metal salt, an alkaline earth metal salt, or any combination thereof. The active salt can be a lithium salt or a mixture of lithium salts. Exemplary salts include, but are not limited to, lithium bis(fluorosulfonyl)imide (LiFSI ₎ , lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), _LiPF6 , _LiAsF6 , LiBF4, LiN( _SO2CF3 ) _{2 ,} LiN( _SO2F ) ₂ , LiCF3SO3, LiClO4, lithium _{difluorooxalatoborate} ( _LiDFOB ), LiI _, LiBr, _LiCl , LiOH, _LiNO3 , _Li2SO4 , and combinations thereof. In some embodiments, the salt is LiFSI, LiTFSI, or a combination thereof. In certain instances, the salt is LiFSI.

The solvent associates with (e.g., solvates or coordinates with) the cations of the active salt or active salt mixture. When prepared as a super-concentrated electrolyte containing the active salt and a solvent, a solvent-cation-anion aggregate results. Some embodiments of the disclosed super-concentrated electrolytes are stable with anodes (e.g., carbon- and/or silicon-, tin-, or antimony-based anodes), cathodes (cathodes containing ionic intercalation and conversion compounds), and/or current collectors (e.g., Cu, Al) that may be unstable when lower concentration electrolytes are used and/or when other solvents are used.

Suitable solvents for use as solvent A include, but are not limited to, certain carbonate ester solvents, ether solvents, phosphorus-containing solvents, and mixtures thereof. In some embodiments, solvent A comprises, or consists essentially of, a carbonate ester solvent, a flame retardant compound, or a combination thereof. The term "consists essentially of" means that the solvent does not contain other solvents, such as ethers and water, in any appreciable amount (e.g., greater than 1 wt %). Suitable carbonate ester solvents include, but are not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoroethylene carbonate (TFEC), 4-vinyl-1,3-dioxolan-2-one (VEC), 4-methylene-1,3-dioxolan-2-one, 4-methylene ethylene carbonate (MEC), methyl 2,2,2-trifluoroethyl carbonate (MFEC), 4,5-dimethylene-1,3-dioxolan-2-one, and combinations thereof.

Suitable flame retardant compounds include, but are not limited to, phosphorus-containing compounds. The amount of flame retardant in solvent A is sufficient to maintain low flammability or non-flammability of the electrolyte. In some embodiments, the flame retardant compound includes one or more organic phosphorus compounds (e.g., organic phosphates, phosphites, phosphonates, phosphoramides), phosphazenes, or any combination thereof. Organic phosphates, phosphites, phosphonates, phosphoramides include substituted and unsubstituted aliphatic and aryl phosphates, phosphites, phosphonates, and phosphoramides. Phosphazenes can be organic or inorganic. Exemplary flame retardant compounds include, for example, TMPa, TEPa, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate, trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl)phosphite, dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl)methylphosphonate, hexamethylphosphoramide, hexamethoxyphosphazene (cyclo-tris(dimethoxyphosphonitrile), hexamethoxycyclotriphosphazene), hexafluorophosphazene (hexafluorocyclophosphazene), and combinations thereof. In some embodiments, the low flammable or non-flammable LSE comprises at least 5 wt % or at least 10 wt % of a flame retardant compound. In certain embodiments, the low flammability or non-flammability LSE comprises 5-75 wt% flame retardant compound, such as 5-60 wt%, 5-50 wt%, 5-40 wt% or 5-30 wt%, 10-60 wt%, 10-50 wt%, 10-40 wt%, or 10-30 wt% flame retardant compound.

In some embodiments, solvent A includes a carbonate other than FEC, a flame retardant compound, or a combination thereof. In certain embodiments, the carbonate other than FEC, the flame retardant compound, or a combination thereof constitutes at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, or at least 90 wt% of solvent A. In some embodiments, solvent A is EC, EMC, TEPa, or a combination thereof. In one embodiment, solvent A includes, consists essentially of, or consists of EC and EMC, where EC and EMC are present in a weight ratio of 2:8 to 4:6. In some instances, solvent A includes, consists essentially of, or consists of EC-EMC in a ratio of 3:7 by weight. In one independent embodiment, solvent A includes, consists essentially of, or consists of TEPa.

In any of the above embodiments, solvent A may further comprise FEC. In some embodiments, the electrolyte further comprises greater than 0 to 30 wt% FEC, e.g., greater than 0 to 20 wt%, greater than 0 to 10 wt%, 0.1 to 30 wt% FEC, 0.5 to 30 wt% FEC, 2 to 30 wt% FEC, 5 to 30 wt% FEC, 2 to 10 wt% FEC, or 5 to 10 wt% FEC. In another embodiment, the electrolyte comprises greater than 0 to 10 mol% FEC, e.g., 0.2 to 10 mol% FEC. In one embodiment, solvent A comprises, consists essentially of, or consists of EC, EMC, and FEC, where EC and EMC are present in a weight ratio of 2:8 to 4:6. In some instances, solvent A comprises, consists essentially of, or consists of EC-EMC and FEC in a ratio of 3:7 by weight. In one independent embodiment, solvent A comprises, consists essentially of, or consists of TEPa and FEC.

The concentration of the active salt may be selected to minimize the number of free solvent A molecules in the electrolyte. The molar ratio of active salt to solvent A may not be 1:1 because more than one molecule of solvent A may be associated with each cation of the active salt and/or more than one cation of the active salt may be associated with each molecule of solvent A. In some embodiments, the molar ratio of active salt to solvent A (moles salt/moles solvent A) is in the range of 0.33 to 1.5, such as 0.5 to 1.5, 0.67 to 1.5, 0.8 to 1.2, or 0.9 to 1.1.

The diluent is a component in which the active salt is insoluble or has poor solubility, i.e., a solubility that is at least 10 times lower than the solubility of the active salt in solvent A. For example, if the salt has a solubility of 5 M in solvent A, the diluent is selected so that the salt has a solubility of less than 0.5 M in the diluent. In some embodiments, the active salt has a solubility in solvent A that is at least 10 times lower, at least 15 times lower, at least 20 times lower, at least 25 times lower, at least 30 times lower, at least 40 times lower, or at least 50 times lower than the solubility of the active salt in the diluent. The diluent is selected to be stable with respect to the anode, cathode, and current collector at low active salt concentrations (e.g., 3 M or lower) or even without the active salt. In some embodiments, the diluent is selected to have a low dielectric constant (e.g., a relative dielectric constant of 7 or lower) and/or a low donor number (e.g., a donor number of 10 or lower). Advantageously, the diluent does not interact with the active salt, so it does not disrupt the solvation structure of the solvent A-cation-anion aggregate and is considered inert. In other words, there is no significant coordination or association between the diluent molecules and the active salt cations. The active salt cations remain associated with the solvent A molecules. Thus, even though the electrolyte is diluted, there are few or no free solvent A molecules in the electrolyte.

In some embodiments, the diluent comprises an aprotic organic solvent. In certain embodiments, the diluent is a fluorinated solvent with a wide electrochemical stability window (e.g., greater than 4.5 V), such as hydrofluoroethers (HFEs) (also referred to as fluoroalkyl ethers) or fluorinated orthoformates. HFEs advantageously have low dielectric constants, low donor numbers, reduction stability with respect to the metals (e.g., lithium, sodium, and/or magnesium) of the active salt, and/or high stability against oxidation due to the electron-withdrawing fluorine atoms. Exemplary fluorinated solvents include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl)ether (BTFE), 1,1,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB), triorthoformate, tris(2,2,2-trifluoroethyl) orthoformate (TFEO), tris(hexafluoroisopropyl) orthoformate (THFiPO), tris(2,2-difluoroethyl) orthoformate (TDFEO), bis(2,2,2-trifluoroethyl)methyl orthoformate (BTFEMO), tris(2,2,3,3,3-pentafluoropropyl) orthoformate (TPFPO), tris(2,2,3,3-tetrafluoropropyl) orthoformate (TTPO), and combinations thereof.

The diluent may be flammable or non-flammable. In some embodiments, the safety of practical rechargeable batteries is significantly improved by selecting a non-flammable fluoroalkyl ether or fluorinated orthoformate ester. For example, MOFB and EOFB are non-flammable linear fluoroalkyl ethers. Some embodiments of fluorinated orthoformates have higher boiling points, higher flash points and lower vapor pressures than other fluoroalkyl ethers. For example, bis(2,2,2-trifluoroethyl)ether (BTFE) has a boiling point of 62-63°C and a flash point of 1°C, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) has a boiling point of 92°C and a flash point of 27.5°C. These properties may limit their application at high temperatures and may also pose some safety concerns associated with thermal issues. In contrast, the higher boiling point, higher flash point and lower vapor pressure of the fluorinated orthoformates reduces diluent evaporation, making the electrolyte composition easier to manage. In addition, such higher boiling points may provide the electrolyte with increased stability when the battery is operating at high temperatures, for example, up to 55°C. For example, TFEO has a boiling point of 144-146°C and a flash point of 60°C. The disclosed embodiments of the fluorinated orthoformates also have low melting points and a wide electrochemical stability window. In certain embodiments, flammable diluents may be used when solvent A includes a flame retardant compound in an amount sufficient to render the electrolyte flame retardant or non-flammable. In other embodiments, flammable diluents may be used when the expected operating conditions of the system are relatively non-hazardous (e.g., relatively low operating temperatures).

In some embodiments of the disclosed LSE, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% of the molecules of solvent A are associated (e.g., solvated or coordinated) with the cations of the active salt. In certain embodiments, less than 10% of the diluent molecules are associated with the cations of the active salt, such as less than 5%, less than 4%, less than 3%, or less than 2% of the diluent molecules. The degree of association can be quantified by any suitable means, such as by calculating the peak intensity ratio of the solvent molecules associated with the cations to the free solvent in a Raman spectrum or by using an NMR spectrum.

The relative amounts of solvent A and diluent are selected to reduce material costs for the electrolyte, to reduce the viscosity of the electrolyte, to maintain the stability of the electrolyte against oxidation at a high voltage cathode, to improve the ionic conductivity of the electrolyte, to improve the wettability of the electrolyte, to facilitate the formation of a stable solid electrolyte interface (SEI) layer, or any combination thereof. In one embodiment, the molar ratio of solvent A to diluent in the electrolyte (moles solvent A/moles diluent) is in the range of 0.2 to 5, such as in the range of 0.2 to 4, 0.2 to 3, or 0.2 to 2. In an independent embodiment, the volume ratio of solvent A to diluent in the electrolyte (L solvent/L diluent) is in the range of 0.2 to 5, such as in the range of 0.25 to 4, or 0.33 to 3. In another independent embodiment, the mass ratio of solvent A to diluent in the electrolyte (g solvent/g diluent) is in the range of 0.2 to 5, such as in the range of 0.25 to 4, or 0.33 to 3.

Advantageously, certain embodiments of the disclosed LSE allow significant dilution of the active salt without sacrificing electrolyte performance. Due to interactions between the cations of the active salt and the molecules of solvent A, the behavior of the electrolyte corresponds more closely to the concentration of the active salt in solvent A. However, because of the presence of the diluent, the active salt may have a molar concentration in the electrolyte that is at least 20% less than the molar concentration of the active salt in solvent A. In certain embodiments, the molar concentration of the active salt in the electrolyte is at least 25% less, at least 30% less, at least 40% less, at least 50% less, at least 60% less, at least 70% less, or even at least 80% less than the molar concentration of the active salt in solvent A. The inclusion of a diluent reduces electrolyte costs (less salt is used) and reduces the viscosity of the electrolyte, while preserving the unique functionality and benefits of high concentration electrolytes.

In some embodiments, the formation of cation-anion-solvent aggregates also lowers the lowest unoccupied molecular orbital (LUMO) energy of the anion of the active salt (e.g., FSI- ^, etc.), so that the cation-anion-solvent aggregates can form a stable SEI. For example, when the LUMO of the conduction band is located on a solvent molecule (e.g., DMC, etc.), the solvent molecule is first reductively decomposed at the anode, resulting in an SEI layer that is rich in organic or polymeric components and is less mechanically stable, thus causing rapid capacity degradation upon repeated use. In contrast, when the lowest energy level of the conduction band of the anion of the active salt (e.g., FSI- ^, etc.) in certain embodiments of the disclosed LSE is lower than the lowest energy level of the conduction band of the solvent (e.g., DMC, etc.), the anion of the active salt will be decomposed instead of the solvent molecules, which indicates the formation of a stable SEI rich in inorganic components (e.g., LiF, _Li2CO3 , _{Li2O ,} etc.) that is mechanically robust and can protect the anode from degradation during subsequent cycling processes.

In some embodiments, the diluent is miscible with solvent A. In other embodiments, the diluent is immiscible with solvent A, for example when solvent A comprises water and the diluent is a fluorinated organic solvent as disclosed herein. When solvent A and the diluent are immiscible, the electrolyte may not be effectively diluted by the diluent.

Thus, in some embodiments, when the diluent is immiscible with solvent A, the electrolyte further comprises a bridging solvent. The bridging solvent has a different chemical composition than either solvent A or the diluent. The bridging solvent is selected to be miscible with both solvent A and the diluent, thereby enhancing the actual miscibility of solvent A with the diluent. In some embodiments, the molecules of the bridging solvent are amphiphilic, containing both polar and non-polar ends or portions, such that the molecules of the bridging solvent will associate with both the molecules of solvent A and the molecules of the diluent, as shown in FIG. 3, thereby improving the miscibility between solvent A and the diluent. Exemplary bridging solvents include, but are not limited to, acetonitrile, dimethyl carbonate, diethyl carbonate, propylene carbonate, dimethyl sulfoxide, 1,3-dioxolane, 1,2-dimethoxyethane, diglyme (bis(2-methoxyethyl) ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), and combinations thereof.

In some embodiments, the electrolyte consists essentially of or consists of the active salt, the non-aqueous solvent, and the diluent. In certain embodiments, the electrolyte consists essentially of or consists of the active salt, the non-aqueous solvent, 0-30 wt % FEC, and the diluent. In some instances, the electrolyte consists essentially of or consists of the active salt, the non-aqueous solvent, 2-30 wt % FEC, and the diluent. By "consisting essentially of," it is meant that the electrolyte does not include other components that have a substantial effect on the properties of the electrolyte alone or in a system that includes the electrolyte. For example, the electrolyte does not contain any electrochemically active components other than the active salt (i.e., components (elements, ions or compounds) capable of forming redox pairs having different oxidation and reduction states, e.g., ionic species having different oxidation states, or a metal cation and its corresponding neutral metal atom) in a quantity sufficient to affect the performance of the electrolyte, or does not contain any additional solvents other than the carbonate ester or the flame retardant compound, or does not contain any diluent in which the active salt is soluble, or does not contain any other additives in significant amounts (e.g., greater than 1 wt %). Exemplary electrolytes include LiFSI/EC-EMC-BTFE, LiFSI/EC-EMC-FEC-BTFE, LiFSI/TEPa-BTFE, LiFSI/TEPa-FEC-BTFE, LiFSI/EC-EMC-TTE, LiFSI/EC-EMC-FEC-TTE, LiFSI/TEPa-TTE, LiFSI/TEPa-FEC-TTE, Li FSI/EC-EMC-TFEO, LiFSI/EC-EMC-FEC-TFEO, LiFSI/TEPa-TFEO, LiFSI/TEPa-FEC-TFEO, LiFSI/TEPa-EC-BTFE, LiFSI/TEPa-EC-TTE, LiFSI/TEPa -EC-TFEO, LiFSI/TEPa-EC-FEC-BTFE, LiFSI/TE Pa-EC-FEC-TTE, LiFSI/TEPa-EC-FEC-TFEO, LiFSI/TEPa-EC-VC-BTFE, LiFSI/TEPa-EC-VC-TTE, LiFSI/TEPa-EC-VC-TFEO, LiFSI/TEPa-EC-LiDFO B-BTFE, LiFSI/TEPa-EC-LiDFOB-TTE, LiFSI/T These include, but are not limited to, EPa-EC-LiDFOB-TFEO, LiFSI/TEPa-VC-DMC-BTFE, LiFSI/TEPa-VC-DMC-TTE, LiFSI/DMC-TTE, LiFSI/DMC-FCE-TTE, LiFSI/DMC-VC-FEC-TTE, and LiFSI/TEPa-VC-DMC-TFEO.

In certain embodiments, the electrolyte comprises, consists essentially of, or consists of LiFSI, EC-EMC or TEPa, 0-30 wt % FEC, and a diluent, where the diluent is BTFE, TTE, OTE, TFEO, or a combination thereof. The active salt may have a molar concentration in the electrolyte in the range of 0.5M to 3M. In one embodiment, the electrolyte comprises, consists essentially of, or consists of 1-3 M LiFSI, EC-EMC in a ratio of 4:6 to 2:8 by weight, 0-30 wt % FEC (e.g., 0 wt % FEC, 0.5-30 wt % FEC, 2-30 wt % FEC, 2-10 wt % FEC, or 5-10 wt % FEC, etc.), and a diluent, where the molar ratio of EC-EMC (moles EC+moles EMC) to diluent is in the range of 1-4, such as in the range of 1-3. In another embodiment, the electrolyte comprises, consists essentially of, or consists of 1-3M LiFSI, TEPa, 0-30 wt% FEC (e.g., 0 wt% FEC, 0.5-30 wt% FEC, or 5-10 wt% FEC, etc.), and a diluent, where the diluent is BTFE, TTE, OTE, TFEO, or any combination thereof, and the molar ratio of TEPa to diluent is in the range of 1-4, such as in the range of 2-4. In some instances, the diluent is BTFE.

III. Systems Various embodiments of the disclosed LSEs are useful in various systems, such as batteries (e.g., rechargeable batteries). In some embodiments, the disclosed LSEs are useful in lithium ion batteries. In some embodiments, a system includes an LSE as disclosed herein and an anode. The system may further include a cathode, a separator, an anode current collector, a cathode current collector, or any combination thereof. In certain embodiments, the anode includes silicon.

In some embodiments, a rechargeable battery includes an LSE as disclosed herein, a cathode, an anode, and optionally a separator. FIG. 4 is a schematic diagram of one exemplary embodiment of a rechargeable battery 100 including a cathode 120, a separator 130 infused with an electrolyte (i.e., the LSE), and an anode 140. In some embodiments, the battery 100 also includes a cathode current collector 110 and/or an anode current collector 150.

The current collector can be a metal or another conductive material, such as, but not limited to, nickel (Ni), copper (Cu), aluminum (Al), iron (Fe), stainless steel, or a conductive carbon material. The current collector can be a foil, foam, or polymer substrate coated with a conductive material. Advantageously, the current collector is stable (i.e., does not corrode or react) when in contact with the anode or cathode and electrolyte at the operating voltage range of the battery. If the anode or cathode, respectively, is freestanding, e.g., when the anode is a metal or a freestanding film containing an intercalation or conversion compound, and/or when the cathode is a freestanding film, the anode and cathode current collectors can be omitted. By "freestanding," it is meant that the film itself has sufficient structural integrity that the film can be placed in the battery without a supporting material.

In some embodiments, including some embodiments of rechargeable lithium ion batteries, the anode is a silicon-based, carbon-based (e.g., graphite-based and/or hard carbon-based), carbon-silicon-based (e.g., carbon/silicon composite), tin-based, or antimony-based anode. By "carbon-based anode" is meant that a majority of the total anode mass is activated carbon material, such as at least 70 wt%, at least 80 wt%, or at least 90 wt%, of the activated carbon material, such as graphite, hard carbon, or mixtures thereof. By "silicon-based anode" is meant that the anode contains a certain minimum amount of silicon, such as at least 30 wt%, at least 50 wt%, at least 60 wt%, or at least 70 wt%, of silicon. By "carbon/silicon-based anode" it is meant that the majority of the total anode mass is activated carbon and silicon, e.g., at least 70 wt%, at least 80 wt%, or at least 90 wt%, etc., a combination of activated carbon and silicon. By "tin-based anode" or "antimony-based anode" it is meant that the majority of the total anode mass is tin or antimony, e.g., at least 70 wt%, at least 80 wt%, or at least 90 wt%, etc., tin or antimony, respectively. In some embodiments, the anode is a graphite-based and/or silicon-based anode, or a tin-based anode. In certain embodiments, the anode comprises silicon, e.g., a silicon-based anode or a carbon/silicon-based (e.g., silicon-graphite composite) anode, etc. In some instances, the silicon is nanosilicon and/or carbon-coated. For example, the silicon can be carbon-coated nanosilicon, where the silicon is carbon-coated by chemical vapor deposition (CVD) or other techniques. In one embodiment, the silicon is a C/Si composite containing 10 wt% CVD carbon.

The anode may further include one or more binders and/or conductive additives. Suitable binders include, but are not limited to, polyacrylates (e.g., lithium polyacrylate, LiPAA), polyimides (PI), polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, ethylene oxide polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, epoxy resins, nylon, and carboxymethyl cellulose. Suitable conductive additives include, but are not limited to, carbon black, acetylene black, ketjen black, carbon fibers (e.g., vapor-grown carbon fibers), metal powders or fibers (e.g., Cu, Ni, Al), and conductive polymers (e.g., polyphenylene derivatives). In some embodiments, the anode is prelithiated to at least 5% of capacity, at least 10% of capacity, at least 20% of capacity, at least 50% of capacity, or up to 100% capacity. Prelithiation is particularly useful when a cathode is used that does not have any lithium source.

In some embodiments, the anode is a silicon/graphite composite anode comprising 70-75 wt% graphite, 10-20 wt% silicon, 0-5 wt% conductive carbon black, and 8-12 wt% binder. The silicon can be carbon-coated nanosilicon, such as a C/Si composite with 5-15 wt% CVD carbon. In certain embodiments, the binder comprises LiPAA or PI. In one example, the anode comprises 70-75 wt% graphite, 12-18 wt% silicon, 0-5 wt% conductive carbon black, and 8-12 wt% LiPAA. In another example, the anode contains 70-75 wt% graphite, 12-18 wt% carbon-coated nanosilicon (20 wt% carbon), >0-5 wt% conductive carbon black, and 5-15 wt% PI.

Exemplary cathodes for lithium ion batteries include Li-rich Li1 _{+ wNixMnyCozO2 (} x+y _{+ z} + _w =1, 0≦w≦0.25), LiNixMnyCozO2 ( _NMC , x+y+ _{z =} 1), LiCoO2, LiNi0.8Co0.15Al0.05O2 ₍ NCA ₎ , LiNi0.5Mn1.5O4 spinel, _LiMn2O4 ( _LMO ), _LiFePO4 (LFP ₎ , _{Li4- xMxTi5O12 ( M} = _Mg , _Al , _Ba , Sr, or Ta; 0≦x≦1), _MnO2 , _{V2O4 ,} and _the like. ₅ , V ₆ O ₁₃ , LiV ₃ O ₈ , LiM ^C1 _x M ^C2 _1-x PO ₄ (M ^C1 or M ^C2 = Fe, Mn, Ni, Co, Cr or Ti; 0≦x≦1), Li ₃ V _2-x M ¹ _x (PO ₄ ) ₃ (M ¹ = Cr, Co, Fe, Mg, Y, Ti, Nb or Ce; 0≦x≦1), LiVPO ₄ F, LiM ^C1 _x M ^C2 _1-x O ₂ ((M ^C1 and M ^C2 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1), LiM ^C1 _x M ^C2 _y M ^C3 _1-x-y O ₂ ((M ^C1 , M ^C2 and M ^C3 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1; 0≦y≦1, 0≦x+y≦1), LiMn _2-y X _y O ₄ (X=Cr, Al or Fe, 0≦y≦1), LiNi _0.5-y X _y Mn _1.5 O ₄ (X=Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0≦y<0.5), xLi ₂ MnO _3. (1-x)LiM ^C1 _y M ^C2 _z M ^C3 _1-y-z O ₂ (M ^C1 , M ^C2 and M ^C3 is independently Mn, Ni, Co, Cr, Fe, or mixtures thereof; x=0.3-0.5; y≦0.5; z≦0.5), Li ₂ M ² SiO ₄ (M ² =Mn, Fe or Co), Li ₂ M ² SO ₄ (M ² =Mn, Fe or Co), LiM ² SO ₄ F (M ² =Fe, Mn or Co), Li _2-x (Fe _1-y Mn _y )P ₂ O ₇ (0≦x≦1; 0≦y≦1), Cr ₃ O ₈ , Cr ₂ O ₅ , a carbon/sulfur composite, or an air electrode (e.g., a carbon-based electrode containing graphitic carbon and optionally a metal catalyst, such as Ir, Ru, Pt, Ag, or Ag/Pd). In separate embodiments, the cathode can be a lithium conversion compound, such as _Li2O2 , _Li2S , or LiF. In some instances _, the cathode is an NMC cathode.

The separator can be fiberglass, a porous polymeric film with or without a ceramic coating (e.g., a polyethylene- or polypropylene-based material), or a composite (e.g., a porous film of inorganic particles and a binder). One exemplary polymeric separator is Celgard® K1640 polyethylene (PE) membrane. Another exemplary polymeric separator is Celgard® 2500 polypropylene membrane. Another exemplary polymeric separator is Celgard® 3501 surfactant-coated polypropylene membrane. The separator can be infused with an electrolyte as disclosed herein.

In some embodiments, the battery includes a carbon-based, silicon-based, carbon-silicon-based, tin-based, or antimony-based anode, a cathode suitable for a lithium-ion battery, a separator, and an LSE including (a) an active salt including lithium cations, (b) a non-aqueous solvent including (i) a carbonate other than fluoroethylene carbonate (FEC), (ii) a flame retardant compound, or (iii) both (i) and (ii), where the active salt is soluble in the non-aqueous solvent, and (c) a diluent including a fluoroalkyl ether, a fluorinated orthoformate ester, or a combination thereof, where the active salt has a solubility in the diluent that is at least 10 times lower than the solubility of the active salt in the non-aqueous solvent. The electrolyte may further include up to 30 wt % FEC, for example, 5-30 wt % FEC or 5-10 wt % FEC. In certain embodiments, the anode includes silicon, i.e., the anode is a silicon-based or carbon/silicon composite-based anode. In some embodiments, the cathode comprises LiNi _x Mn _y Co _z O ₂ (NMC), LiNi _0.85 Co _0.15 Al _0.05 O ₂ (NCA), or LiCoO ₂ (LCO). In certain embodiments, the cathode comprises LiNi _x Mn _y Co _z O ₂ (NMC). In some instances, the electrolyte comprises, consists essentially of, or consists of LiFSI, EC-EMC or TEPa, 0-30 wt % FEC (e.g., 0 wt % FEC, 5-30 wt % FEC, 5-10 wt % FEC), and a diluent, where the diluent consists of BTFE, TTE, OTE, TFEO, or a combination thereof. In some instances, the diluent comprises BFTE, TTE, TFEO, or a combination thereof. In one embodiment, when the anode is a carbon-silicon composite with LiPAA as a binder, the electrolyte comprises EC-EMC. In another embodiment, when the anode is a carbon-silicon composite with PI as a binder, the electrolyte comprises TEPa.

Advantageously, some embodiments of the disclosed lithium ion batteries including the LSE are capable of operating at high voltages, e.g., at or above 4.2 V, e.g., at voltages of 4.3 V or greater. In certain embodiments, the battery is capable of operating at voltages up to 4.5 V.

In some embodiments, a lithium ion battery including a LSE as disclosed herein has performance that is equivalent to or better than a comparable lithium battery including the same anode and cathode with a conventional or ultra-high concentration electrolyte. For example, a lithium ion battery with a disclosed LSE may have a specific capacity, coulombic efficiency, and/or capacity retention that is equivalent to or greater than a comparable battery with a conventional or ultra-high concentration electrolyte. A lithium ion battery with a disclosed LSE may also exhibit cycling stability, as indicated by a percent capacity retention that is equivalent to a comparable lithium ion battery including the same anode and cathode with a conventional or ultra-high concentration electrolyte, or cycling stability that is better than the cycling stability of such a comparable lithium ion battery. For example, a lithium ion battery including a silicon/graphite composite anode and a disclosed LSE may have a capacity retention of at least 70%, at least 75%, at least 80%, at least 85%, or even at least 90% at 100 cycles. The lithium ion battery may have a first coulombic efficiency of at least 50%, at least 60%, at least 70%, or at least 75%. In some instances, the first coulombic efficiency is improved by using a prelithiated anode as disclosed herein.

IV. Representative Embodiments Certain representative embodiments are illustrated in the following numbered paragraphs.

1. A system comprising an electrolyte and an anode, the electrolyte comprising (a) an active salt comprising lithium cations, (b) a non-aqueous solvent comprising (i) a carbonate other than fluoroethylene carbonate (FEC), (ii) a flame retardant compound, or (iii) both (i) and (ii), where the active salt is soluble in the non-aqueous solvent, and (c) a diluent comprising a fluoroalkyl ether, a fluorinated orthoformate ester, or a combination thereof, where the active salt has a solubility in the diluent that is at least 1/10 of the solubility of the active salt in the non-aqueous solvent, and the anode comprises silicon.

2. The system described in paragraph 1, wherein the electrolyte further contains 0.1 to 30 wt % FEC.

3. The system described in item 1, wherein the electrolyte further contains 2 to 30 wt % FEC.

4. The system described in any one of items 1 to 3, wherein the active salt has a molar concentration in the electrolyte within a range of 0.5 M to 6 M.

5. The system of any one of clauses 1 to 4, wherein the active salt comprises lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(oxalato)borate (LiBOB), LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiClO ₄ , lithium difluorooxalatoborate (LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO ₃ , LiNO ₂ , Li ₂ SO ₄ , or any combination thereof.

6. The system according to any one of claims 1 to 5, wherein the non-aqueous solvent comprises a flame retardant compound comprising an organic phosphate ester, an organic phosphite ester, an organic phosphonate ester, an organic phosphoramide, a phosphazene, or any combination thereof.

7. The system of claim 6, wherein the flame retardant compound comprises triethyl phosphate, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl)phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl)methylphosphonate; hexamethylphosphoramide; hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof.

8. The system according to any one of claims 1 to 7, wherein the non-aqueous solvent comprises ethylene carbonate (EC) and ethyl carbonate (EMC), or EC and diethyl carbonate (DEC), or EC and dimethyl carbonate (DMC), or a combination of EC with EMC, DEC, DMC, and propylene carbonate (PC).

9. The diluent is bis(2,2,2-trifluoroethyl)ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE), methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB), tris(2,2 ,2-trifluoroethyl) (TFEO), tris(hexafluoroisopropyl) orthoformate (THFiPO), tris(2,2-difluoroethyl) orthoformate (TDFEO), bis(2,2,2-trifluoroethyl)methyl orthoformate (BTFEMO), tris(2,2,3,3,3-pentafluoropropyl) orthoformate (TPFPO), tris(2,2,3,3-tetrafluoropropyl) orthoformate (TTPO), or any combination thereof. The system according to any one of claims 1 to 8.

10. The system according to any one of claims 1 to 9, wherein the diluent comprises BTFE, TTE, OTE, TFEO, or any combination thereof.

11. The system according to any one of claims 1 to 9, wherein the diluent comprises BTFE, TTE, TFEO, or any combination thereof.

12. The system of claim 10 or 11, wherein the electrolyte comprises 1-3M LiFSI, EC-EMC in a ratio of 4:6-2:8 by weight, 0-30 wt% FEC, and the diluent, wherein the molar ratio of EC-EMC to the diluent is in the range of 1-4.

13. The system of claim 10 or 11, wherein the electrolyte comprises 1-3M LiFSI, EC-EMC in a ratio of 4:6-2:8 by weight, 0-30 wt% FEC, and the diluent, wherein the molar ratio of EC-EMC to the diluent is in the range of 1-3.

14. The system of claim 10 or 11, wherein the electrolyte comprises 1-3 M LiFSI, triethyl phosphate (TEPa) and 0-30 wt % FEC, and the diluent, wherein the molar ratio of TEPa to the diluent is in the range of 1-4.

15. The system of claim 10 or 11, wherein the electrolyte comprises 1-3 M LiFSI, triethyl phosphate (TEPa) and 0-30 wt % FEC, and the diluent, wherein the molar ratio of TEPa to the diluent is in the range of 2-4.

16. The system described in any one of claims 1 to 15, wherein the anode comprises a graphite/silicon composite.

17. The system described in paragraph 16, wherein the anode further comprises a lithium polyacrylate binder or a polyimide binder.

18. The system described in paragraph 16, wherein the silicon is carbon-coated nanosilicon.

19. The system described in claim 18, wherein the binder comprises a polyimide.

20. The system of claim 19, wherein the electrolyte comprises 1-3 M LiFSI, triethyl phosphate (TEPa) and 0-30 wt % FEC, and the diluent, where the diluent is BTFE, TTE, OTE, TFEO, or any combination thereof, and the molar ratio of TEPa to the diluent is in the range of 2-4.

21. The system of claim 19, wherein the electrolyte comprises 1-3 M LiFSI, triethyl phosphate (TEPa) and 0-30 wt % FEC, and the diluent, where the diluent is BTFE, TTE, TFEO, or any combination thereof, and the molar ratio of TEPa to the diluent is in the range of 2-4.

22. The system of claim 19, further comprising a cathode, the anode being prelithiated, and the system having a capacity retention of 80% or more after 100 cycles.

23. The system of claim 17, wherein the binder comprises lithium polyacrylate, the electrolyte comprises 1-3M LiFSI, EC-EMC in a ratio of 3:7 by weight and 0-30 wt % FEC, and the diluent, wherein the diluent is BTFE, TTE, OTE, TFEO, or any combination thereof, and the molar ratio of EC-EMC to the diluent is in the range of 1-3.

24. The system of claim 17, wherein the binder comprises lithium polyacrylate, the electrolyte comprises 1-3M LiFSI, EC-EMC in a ratio of 3:7 by weight, and 0-30 wt % FEC, and the diluent, wherein the diluent is BTFE, TTE, TFEO, or any combination thereof, and the molar ratio of EC-EMC to the diluent is in the range of 1-3.

25. The system according to claim 23 or 24, further comprising a cathode and having a capacity retention rate of 70% or more after 100 cycles.

26. The cathode may further comprise a cathode selected _{from the} group consisting of Li1 _{+ wNixMnyCozO2} (x+ _y +z+ _w =1, 0≦w≦0.25), LiNixMnyCozO2 ₍ x+y+z _{= 1} ), LiNi0.8Co0.15Al0.05O2, _LiCoO2 , LiNi0.5Mn1.5O4 _spinel , _{LiMn2O4 , LiFePO4} , Li4 _{- xMxTi5O12 (} M=Mg, _Al , _Ba , Sr or Ta _{; 0} ≦ _{x ≦ 1} ) _{, MnO2} , _{V2O5 , V6O13} , _LiV3 O ₈ , LiM ^C1 _x M ^C2 _1-x PO ₄ (M ^C1 or M ^C2 = Fe, Mn, Ni, Co, Cr or Ti; 0≦x≦1), Li ₃ V _2-x M ¹ _x (PO ₄ ) ₃ (M ¹ = Cr, Co, Fe, Mg, Y, Ti, Nb or Ce; 0≦x≦1), LiVPO ₄ F, LiM ^C1 _x M ^C2 _1-x O ₂ ((M ^C1 and M ^C2 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1), LiM ^C1 _x M ^C2 _y M ^C3 _1-x-y O ₂ ((M ^C1 , M ^C2 and M ^C3 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1; 0≦y≦1, 0≦x+y≦1), LiMn _2-y X _y O ₄ (X=Cr, Al or Fe, 0≦y≦1), LiNi _0.5-y X _y Mn _1.5 O ₄ (X=Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0≦y<0.5), xLi ₂ MnO _3. (1-x)LiM ^C1 _y M ^C2 _z M ^C3 _1-y-z O ₂ (M ^C1 , M ^C2 and M 26. The system of any one of paragraphs 1 to 25, wherein ^C3 is independently Mn, Ni, Co, Cr, Fe, or a mixture thereof; x=0.3-0.5; y≦0.5; z≦0.5), Li ₂ M ² SiO ₄ (M ² =Mn, Fe or Co), Li ₂ M ² SO ₄ (M ² =Mn, Fe or Co), LiM ² SO ₄ F (M ² =Fe, Mn or Co), Li _2-x (Fe _1-y Mn _y )P ₂ O ₇ (0≦x≦1; 0≦y≦1), Cr ₃ O ₈ , Cr ₂ O ₅ , a carbon/sulfur composite, or an air electrode.

V. Examples Example 1
Si/Gr||NMC532 Cells Using LSE with BTFE Diluent Coin cells were prepared with a 15 mm diameter silicon/ _graphite anode, a 14 mm diameter NMC532 (Li( _{Ni0.5Mn0.3Co0.2} ) _O2 ) cathode, and 45 μL of electrolyte. The coin cell had an n/p ratio of approximately 1.2, where n _/ p is the areal-capacity ratio of the negative electrode to the positive electrode. The anode composition was 73 wt% MagE3 graphite (Hitachi Chemical Co. America, Ltd., San Jose, CA), 15 wt% silicon (Paracrete Energy, Chelsea, MI), 2 wt% Timcal C45 carbon (Imerys Graphite & Carbon USA Inc., Westlake, OH), and 10 wt% LiPAA( _H2O ), titrated with LiOH. The electrode area was 1.77 ^cm2 , the coating thickness was 27 μm, and the total coating loading was 3.00 mg/ ^cm2 . The cathode composition was 90 wt% NMC532 (Toda America, Battle Creek, MI), 5 wt% Timcal C45 carbon, and 5 wt% Solef® 5130 PVDF (Solvay, Brussels, Belgium); electrode area was 1.54 ^cm2 , coating thickness was 42 μm, and total coating loading was 11.40 mg/ ^cm2 . The cathode and anode were provided by the CAMP facility at Argonne National Laboratory. The full cell capacity was 2 mAh.

Battery grade LiPF ₆ , EC, EMC and FEC were purchased from BASF Corporation and used as received. Battery grade LiFSI was obtained from Nippon Shokubai Co., Ltd. Bis(2,2,2-trifluoroethyl)ether (BTFE, 99+%) was purchased from SynQuest Laboratories. The baseline electrolyte was 1.2 M LiPF ₆ in EC/EMC (3:7, by weight) with 10 wt % FEC. The cell performance over 100 cycles is shown in FIG. 5. The initial coulombic efficiency (FCE) was 60-65%, the specific capacity retention at 50 cycles was 71.2%, and the specific capacity retention at 100 cycles was 53.4%.

Further electrolytes were prepared and evaluated over the operating voltage range of 3-4.1 V. Cyclic voltammetry indicates that the electrolytes are stable up to 5 V. The results are summarized in Table 1 and shown in FIG. 6. The results demonstrate that the LSE containing LiFSI, carbonate-based solvent, diluent, and FEC is compatible with the Si/Gr anode containing LiPAA binder. E-104 gave the best results with an FCE of 75%, a specific capacity of 117.6 mAh/g at 4 cycles, and a specific capacity retention of 71% at 100 cycles.

A non-flammable electrolyte containing 1.2 M LiFSI in TEPa-3BTFE was prepared and evaluated in coin cells. The results are shown in Table 2 and Figures 7-8. The TEPA-based LSE was incompatible with the anode as evidenced by an initial coulombic energy of only 37.87% and zero capacity retention after 80 cycles.

The anode was modified to replace the LiPAA binder with a polyimide binder and to include nanosilicon coated with carbon by chemical vapor deposition (CVD). The anode composition was: 73 wt% Hitachi MagE3 graphite, 15 wt% Paraclete Energy C/Si (10% CVD carbon in C/Si composite, 2 wt% Timcal C45 carbon, and 10 wt% polyimide (PI); the coating thickness was 26 μm and the total coating loading was 3 mg/ ^cm2 .

Coin cells were prepared using the modified anode, the cathode of Example 1, and the baseline electrolyte (1.2 M LiPF ₆ /EC/EMC (3:7, by weight) + 10 wt% FEC - "Gen2 + 10% FEC"). Figure 9 is a graph of voltage vs. areal capacity for the first, second, and third cycles.

The effect of binder and carbon coated nanosilicon was evaluated in coin cells with baseline electrolyte using (i) the anode of Example 1 (baseline anode), (ii) an anode with uncoated silicon and PI binder, and (iii) an anode with carbon coated nanosilicon and PI binder. The results are shown in Table 3 and FIG. 10.

The PI binder resulted in a lower specific capacity than the baseline anode, which can be associated with the irreversible capacity and lower FCE from the PI. The combination of carbon-coated Si and the PI binder had improved cycling stability compared to the PI binder with uncoated Si.

The carbon-coated Si/Gr anode with PI binder was further evaluated in coin cells with the baseline electrolyte and E-103 and E-313 electrolytes. The results are shown in Table 4 and Figure 11. The modified anode showed significantly improved cycling stability in E-313 electrolyte. However, the capacity is still lower due to the irreversible capacity and low FCE that can be attributed to the PI binder.

The effect of anode prelithiation was evaluated in coin cells containing carbon-coated Si/Gr anodes with PI binder, NMC cathodes, and electrolytes E-313 or E-313 + 1.2 wt% FEC. Prelithiation was performed by three formation cycles of the anode in a half-cell configuration. The results are shown in Table 5 and Figures 12 and 13. The results reveal that E-313 provides significant advantages in combination with prelithiated anodes, both in terms of specific capacity at the fourth cycle and capacity retention. The inclusion of FEC resulted in a higher specific capacity at the fourth cycle, but a lower retention. The results confirm that the cell specific capacity can be greater than 90 mAh/g by the prelithiation process, and that the low specific capacity can be attributed to the low FCE of the PI binder.

In Figure 14, the effective LSE electrolyte results are summarized for the Si/Gr anode with LiPAA binder and the prelithiated carbon coated Si/Gr anode with PI binder. The electrolytes are baseline "Gen2,FEC" (1.2 M _LiPF6 /EC/EMC (3:7, by weight) + 10 wt% FEC), E-104 (Table 1), E-313 (Table 5), and E-313 + FEC (Table 5). The results show that the LSE with LiFSI in EC-EMC effectively enhances the capacity and cycling stability for the Si/Gr anode with LiPAA binder. With the LSE with LiFSI in TEPa, the cycling stability is effectively improved for the carbon-coated Si/Gr anode with PI binder; the capacity is higher than that of the cell with the Si/Gr-LiPAA anode with the baseline “Gen2,FEC” electrolyte, but remains lower than that of the cell with the Si/Gr-LiPAA anode and the LSE with LiFSI in EC-EMC.

Example 2
Si/Gr||NMC532 Cells Using LSEs with Different Diluents Different diluents were similarly investigated and compared with LiFSi-EC:EMC-based LSEs (LHCEs). The salt concentrations for these three electrolytes were the same. The results in FIG. 15 and Table 6 show that all three diluents (BTFE, TTE, and TFEO) improved cycling stability and FCE. The TTE-based LHCE revealed higher specific capacity but slightly inferior cycling stability compared to the BTFE-based LHCE. The TFEO-based LHCE showed lower specific capacity compared to both the TTE-based LHCE and the BTFE-based LHCE, which may be due to the difference in viscosity and electrical conductivity of these three electrolytes. Both the TTE-based LHCE and the TFEO-based LHCE showed similar cycling stability (80%) after 80 cycles. Among these three electrolytes, the BTFE-based LHCE showed the best electrochemical behavior in terms of cycling stability and specific capacity.

The voltage range of E-104 LSE was investigated by cyclic voltammetry (CV) measurements as shown in Figure 16. The results show that E-104 is stable up to 5 V. The electrochemical performance of E-104 at different upper voltage limits was also investigated using Li||NMC532 cell configuration as shown in Figure 17. The Li||NMC532 cell revealed stable cycling stability up to 4.5 V with E-104. In contrast, the cell with baseline electrolyte (Gen2, 10 wt% FEC) showed rapid capacity fade when the cell was charged to 4.3 V.

Example 3
Si/Gr||NMC333 Cell with LSE The non-flammable electrolyte was evaluated with a silicon (Si)-based anode. A Si/graphite (Si/Gr) composite with a theoretical capacity of 1000 mAh/g was obtained from BTR New Energy Materials Inc. (China). The Si/Gr electrode was composed of 80 wt% BTR-1000 as the active material, 10 wt% Super-P® carbon as the conductive agent, and 10 wt% polyimide (PI) as the binder. Electrode disks with a diameter of 1.27 cm and an average mass coating weight of 2.15 mg cm ⁻² were punched out, dried, and stored in a glove box filled with purified argon. Battery grade LiPF ₆ , EC, EMC and FEC were purchased from BASF Corporation and used as received. Battery grade LiFSI was obtained from Nippon Shokubai Co., Ltd. Bis(2,2,2-trifluoroethyl)ether (BTFE, 99+%) was purchased from SynQuest Laboratories. TEPa was purchased from Sigma-Aldrich. Two BTFE diluted non-flammable electrolytes were prepared: NFE-1 contained LiFSI, TEPa and BTFE in a molar ratio of 0.75:1:3, and NFE-2 contained LiFSI-1.2TEPa-0.13FEC-4BTFE (molar ratio; amount of FEC is 1.2 wt %). The molarity of LiFSI in NFE-2 was 1.2 M. Three control electrolytes, namely 1.15 M LiPF 6 in EC-EMC (3:7, weight ratio) containing different amounts of FEC (2 wt %, ₅ wt % and 10 wt %), named as E-Control 1, E-Control 2 and E-Control 3, respectively, were prepared and evaluated for comparison, as summarized in Table 7.

Figure 18 shows the cycling performance of Li||Si/Gr half-cells with BTFE-diluted electrolyte (NFE-1, squares; NFE-2, circles) and three control electrolytes. The Si/Gr electrode in NFE-1 electrolyte gave an initial reversible capacity of 770 mAh/g with a capacity retention of 66.2% after 300 cycles, while the Si/Gr electrode with FEC-containing non-flammable electrolyte (NFE-2) had an initial reversible capacity of 762 mAh/g with a capacity retention of 73% after 300 cycles. For the conventional electrolyte (E-control-3) with a similar FEC content as NFE-2, the capacity dropped rapidly after 40 cycles. When the amount of FEC was increased to 5 and 10 wt%, the cycling performance was extended to 60 and 140 cycles, respectively.

Full cells using Si/Gr anodes and NMC333 commercial cathode material were also investigated. When charged at 0.5 mA cm ⁻² and discharged at 0.75 mA cm ⁻² in the operating voltage range of 2.8-4.2 V, the specific capacity of the NMC333 cathode was about 150 mAhg ⁻¹ and the areal capacity was about 1.5 mAh cm ⁻² . The anode part was precycled against Li metal in half cells to mitigate the challenges arising from SEI formation and reassembled into full cells. The capacity ratio of the cathode and anode was matched at 1:1.1 to obtain good full cell performance. The slightly higher Si content is advantageous to prevent the anode from being over-lithiated during the charging of the full cell. Figure 19 shows the cycling performance of Si/Gr||NMC333 full cells with two BTFE diluted electrolytes. The full cell with NFE-2 showed better cycling performance, with 86% capacity retention after 300 cycles (versus 81% for NFE-1 electrolyte).

A second batch of Si/Gr||NMC333 cells using NFE-2 and E-control-3 was prepared. The first discharge capacity based on the NMC cathode was 147.9 mAh ^g-1 , and the initial coulombic efficiency was 89%, very close to the value obtained in the Li||NMC333 half-cell (Figs. 20-21). The areal capacity was around 1.5 mAh/ ^cm2 (Fig. 21), and all cells were still working after 140 cycles. In the case of the full cell based on E-control-3, the cells showed comparable specific capacity, but the specific capacity started to decrease rapidly after 90 cycles. In addition, the cycle coulombic efficiency of the half-cell based on NFE-2 was higher than that of the cell based on E-control-3.

Batteries with higher areal capacities of Si/Gr (3.2 mAh/cm ² ) and NMC333 (2.8 mAh/cm ² ) were prepared and evaluated using NFE-2 and E-control 3. After extreme cycling at 0.15 mA cm ² , the reversible areal capacity reached 3.1 mA cm ² ( FIG. 22 ). At a high ratio of 0.75 mA cm ² for charging and 0.3 mA cm ² for discharging from the 4th to the 100th cycles, the capacity retention for NFE-2 reached up to 95.0% after 100 cycles.

Figure 23 reveals the long-term cycling stability at 25 °C of Si/Gr||NMC333 cells with NFE-1, NFE-2 and E-Control-3 electrolytes. Cells in all three electrolytes showed similar reversible capacities of 150 mAh g ^-1 (based on the cathode) for the first three formation cycles at a current density of 0.15 mA cm ^-2 . When the current density was increased to 0.3 mA cm ^-2 for charging and 0.75 mA cm ^-2 for discharging in the subsequent 600 cycles, the cycling stability changed in the order NFE-2 > NFE-1 > E-Control-3. Reversible capacities of 126.5 and 112.5 mAh g ^-1 were obtained with NFE-2 and NFE-1, respectively, at a 5C rate. When the long-term cycling stability of the complete cells was carefully analyzed, E-Control 3 resulted in fast capacity fade, with a capacity retention of 50.3% after 500 cycles. For NFE-1, the capacity retention was 65.7% over 500 cycles. In contrast, the cell with NFE-2 showed excellent long-term cycling performance, with a capacity retention of 89.8% after 600 cycles. The CE was close to 100%.

Moreover, the full battery with NFE-2 also showed better cycling stability at a high temperature of 45°C (Figure 24). The average CE of the full battery with NFE-2 at 45°C was 99.6%, which was only slightly lower than the average CE (about 100%) of the full battery cycled at 25°C, which could be attributed to the formation of a thicker by-product film resulting from the electrolyte decomposing more at the electrode/electrolyte interface at high temperature. The by-products accompanied by the formation of both thicker SEI and CEI led to an increase in the impedance and capacity loss of the battery. However, NFE-2 still allowed the capacity retention to be 90.2% over 200 cycles when the battery was cycled at 45°C.

In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it must be recognized that the illustrated embodiments are merely preferred illustrations of the invention and should not be construed as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.
In one embodiment, for example, the following items are provided:
(Item 1)
A system comprising an electrolyte and an anode,
The electrolyte is
an active salt containing a lithium cation;
(i) a carbonate ester other than fluoroethylene carbonate (FEC); (ii) a flame retardant compound; or (iii) a non-aqueous solvent comprising both (i) and (ii), wherein the active salt is soluble in the non-aqueous solvent; and
a diluent comprising a fluoroalkyl ether, a fluorinated orthoformate ester, or a combination thereof, wherein the active salt has a solubility in the diluent that is at least 10 times lower than the solubility of the active salt in the non-aqueous solvent;
Including,
The system wherein the anode comprises silicon.
(Item 2)
2. The system of claim 1, wherein the electrolyte further comprises 0.1 to 30 wt % FEC.
(Item 3)
2. The system of claim 1, wherein the active salt has a molar concentration in the electrolyte in the range of 0.5 M to 6 M.
(Item 4)
2. The system of claim 1, wherein the active salt comprises lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(oxalato)borate (LiBOB), LiPF6 _{, LiAsF6} , LiBF4 _, LiCF3SO3 _, LiClO4 _, lithium difluorooxalatoborate (LiDFOB ) , LiI, LiBr _, LiCl, LiSCN, LiNO3 _{, LiNO2} , _Li2SO4 , _or any combination thereof.
(Item 5)
2. The system of claim 1, wherein the non-aqueous solvent comprises a flame retardant compound comprising an organophosphate, an organophosphite, an organophosphonate, an organophosphoramide, a phosphazene, or any combination thereof.
(Item 6)
6. The system of claim 5, wherein the flame retardant compound comprises triethyl phosphate, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl)phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl)methylphosphonate; hexamethylphosphoramide; hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof.
(Item 7)
2. The system of claim 1, wherein the non-aqueous solvent comprises ethylene carbonate (EC) and ethyl carbonate (EMC), or EC and diethyl carbonate (DEC), or EC and dimethyl carbonate (DMC), or a combination of EC, EMC, DEC, DMC, and propylene carbonate (PC).
(Item 8)
The diluent is selected from the group consisting of bis(2,2,2-trifluoroethyl)ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE), methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB), tris orthoformate, 2. The system of claim 1, comprising tris(2,2,2-trifluoroethyl)methyl orthoformate (TFEO), tris(hexafluoroisopropyl)orthoformate (THFiPO), tris(2,2-difluoroethyl)orthoformate (TDFEO), bis(2,2,2-trifluoroethyl)methyl orthoformate (BTFEMO), tris(2,2,3,3,3-pentafluoropropyl)orthoformate (TPFPO), tris(2,2,3,3-tetrafluoropropyl)orthoformate (TTPO), or any combination thereof.
(Item 9)
2. The system of claim 1, wherein the diluent comprises BTFE, TTE, OTE, TFEO, or any combination thereof.
(Item 10)
The electrolyte is
1-3M LiFSI;
EC-EMC in a weight ratio of 4:6 to 2:8 and 0 to 30 wt % FEC;
and said diluent, wherein the molar ratio of EC-EMC to said diluent is in the range of 1 to 4.
(Item 11)
The electrolyte is
1-3M LiFSI;
Triethyl phosphate (TEPa) and 0-30 wt % FEC;
and said diluent, wherein the molar ratio of TEPa to said diluent is in the range of 1 to 4.
(Item 12)
2. The system of claim 1, wherein the anode comprises a graphite/silicon composite.
(Item 13)
14. The system of claim 13, wherein the anode further comprises a lithium polyacrylate binder or a polyimide binder.
(Item 14)
14. The system of claim 13, wherein the silicon is carbon coated nanosilicon.
(Item 15)
15. The system of claim 14, wherein the binder comprises a polyimide.
(Item 16)
The electrolyte is
1-3M LiFSI;
Triethyl phosphate (TEPa) and 0-30 wt % FEC;
and a diluent, wherein the diluent is BTFE, TTE, OTE, TFEO, or any combination thereof, and the molar ratio of TEPa to the diluent is in the range of 2 to 4.
(Item 17)
16. The system of claim 15, further comprising a cathode, wherein the anode is prelithiated and the system has a capacity retention of 80% or greater after 100 cycles.
(Item 18)
The binder comprises lithium polyacrylate and the electrolyte comprises
1-3M LiFSI;
EC-EMC and 0-30 wt % FEC in a weight ratio of 3:7;
and a diluent, wherein the diluent is BTFE, TTE, OTE, TFEO, or any combination thereof, and the molar ratio of EC-EMC to the diluent is in the range of 1 to 3.
(Item 19)
20. The system of claim 18, further comprising a cathode, wherein the system has a capacity retention of 70% or greater after 100 cycles.
(Item 20)
_The cathode may further comprise a cathode selected from the group consisting of Li1 ₊ wNixMnyCozO2 _{( x} + _{y +} z + _w =1 , 0≦w≦0.25), LiNixMnyCozO2 (x+y + z _{= 1} ) _, LiNi0.8Co0.15Al0.05O2 _, LiCoO2 , LiNi0.5Mn1.5O4 spinel _{, LiMn2O4} , _{LiFePO4 ,} Li4 - _xMxTi5O12 ( M = _Mg , Al _{, Ba} , Sr or Ta ; _{0 ≦ x ≦ 1 ) , MnO2 ,} V2O5 , V6O13 _{, LiV3} O ₈ , LiM ^C1 _x M ^C2 _1-x PO ₄ (M ^C1 or M ^C2 = Fe, Mn, Ni, Co, Cr or Ti; 0≦x≦1), Li ₃ V _2-x M ¹ _x (PO ₄ ) ₃ (M ¹ = Cr, Co, Fe, Mg, Y, Ti, Nb or Ce; 0≦x≦1), LiVPO ₄ F, LiM ^C1 _x M ^C2 _1-x O ₂ ((M ^C1 and M ^C2 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1), LiM ^C1 _x M ^C2 _y M ^C3 _1-x-y O ₂ ((M ^C1 , M ^C2 and M ^C3 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1; 0≦y≦1, 0≦x+y≦1), LiMn _2-y X _y O ₄ (X=Cr, Al or Fe, 0≦y≦1), LiNi _0.5-y X _y Mn _1.5 O ₄ (X=Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0≦y<0.5), xLi ₂ MnO _3. (1-x)LiM ^C1 _y M ^C2 _z M ^C3 _1-y-z O ₂ (M ^C1 , M ^C2 and M 2. The system of claim 1, wherein ^C3 is independently Mn, Ni, Co, Cr, Fe, or a mixture thereof; x=0.3-0.5; y≦0.5; z≦0.5), Li ₂ M ² SiO ₄ (M ² =Mn, Fe, or Co), Li ₂ M ² SO ₄ (M ² =Mn, Fe, or Co), LiM ² SO ₄ F (M ² =Fe, Mn, or Co), Li _2-x (Fe _1-y Mn _y )P ₂ O ₇ (0≦x≦1; 0≦y≦1), Cr ₃ O ₈ , Cr ₂ O ₅ , a carbon/sulfur composite, or an air electrode.

Claims (18)

1. A lithium ion battery system comprising an electrolyte and an anode,
The electrolyte is
an active salt comprising a lithium cation , wherein the active salt comprises lithium bis(fluorosulfonyl)imide (LiFSI);
(i) a carbonate ester other than fluoroethylene carbonate (FEC); (ii) a flame retardant compound; or (iii) a non-aqueous solvent comprising both (i) and (ii), wherein the active salt is soluble in the non-aqueous solvent;
0-30 wt % FEC; and a diluent comprising a fluoroalkyl ether, a fluorinated orthoformate ester, or a combination thereof, wherein the active salt has a solubility in the diluent that is at least 10 times lower than the solubility of the active salt in the non-aqueous solvent.
It essentially consists of
the anode comprises a carbon /silicon composite and a binder, the binder comprising polyacrylate, polyimide, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, ethylene oxide polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, epoxy resin, nylon, or carboxymethyl cellulose;
the carbonate ester comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), or any combination thereof;
Wherein, when the binder contains polyacrylate, the electrolyte does not contain triethyl phosphate (TEPa);
Lithium-ion battery system. The lithium-ion battery system of claim 1, wherein the electrolyte further contains 0.1 to 30 wt % FEC. The lithium ion battery system of claim 1, wherein the active salt has a molar concentration in the electrolyte within the range of 0.5M to 6M. The lithium ion battery system of claim 1, wherein the non-aqueous solvent comprises a flame retardant compound comprising an organophosphate, an organophosphite, an organophosphonate, an organophosphoramide, a phosphazene, or any combination thereof. 5. The lithium ion battery system of claim 4, wherein the flame retardant compounds include triethyl phosphate, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris (2,2,2-trifluoroethyl)phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl)methylphosphonate; hexamethylphosphoramide; hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof. The lithium ion battery system of claim 1, wherein the non-aqueous solvent comprises EC and EMC, or EC and DEC, or EC and DMC, or a combination of EC and EMC, DEC, DMC, and PC. The diluent is bis(2,2,2-trifluoroethyl)ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE), 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE), methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB), tris(2,2,2- The lithium ion battery system of claim 1, comprising tris(2,2-difluoroethyl) orthoformate (TFEO), tris(hexafluoroisopropyl) orthoformate (THFiPO), tris(2,2-difluoroethyl) orthoformate (TDFEO), bis(2,2,2-trifluoroethyl)methyl orthoformate (BTFEMO), tris(2,2,3,3,3-pentafluoropropyl) orthoformate (TPFPO), tris(2,2,3,3-tetrafluoropropyl) orthoformate (TTPO), or any combination thereof. The lithium ion battery system of claim 1, wherein the diluent comprises BTFE, TTE, OTE, TFEO, or any combination thereof. The electrolyte is
1-3M LiFSI;
EC-EMC in a weight ratio of 4:6 to 2:8 and 0 to 30 wt % FEC;
and said diluent, wherein a molar ratio of EC-EMC to said diluent is in the range of 1-4 . The electrolyte is
1-3M LiFSI;
Triethyl phosphate (TEPa) and 0-30 wt % FEC;
and said diluent, wherein a molar ratio of TEPa to said diluent is in the range of 1-4 . 10. The lithium ion battery system of claim 1, wherein the anode comprises 70-75 wt % graphite, 10-20 wt % silicon as the carbon/silicon composite , 0-5 wt % conductive carbon black, and 8-12 wt % binder. The lithium ion battery system of claim 1, wherein the anode further comprises a lithium polyacrylate binder or a polyimide binder. The lithium ion battery system of claim 1, wherein the silicon is carbon-coated nanosilicon. The lithium ion battery system of claim 13 , wherein the binder comprises a polyimide. The electrolyte is
1-3M LiFSI;
Triethyl phosphate (TEPa) and 0-30 wt % FEC;
and a diluent, wherein the diluent is BTFE, TTE, OTE, TFEO, or any combination thereof, and the molar ratio of TEPa to the diluent is in the range of 2 to 4 . The binder comprises lithium polyacrylate and the electrolyte comprises
1-3M LiFSI;
EC-EMC and 0-30 wt % FEC in a weight ratio of 3:7;
and a diluent, wherein the diluent is BTFE, TTE, OTE, TFEO, or any combination thereof, and the molar ratio of EC-EMC to the diluent is in the range of 1 to 3 . The cathode may further comprise a cathode selected _{from the} group consisting of Li1 _{+ wNixMnyCozO2} (x+ _y +z+ _w =1, 0≦w≦0.25), LiNixMnyCozO2 ₍ x+y+z _{= 1} ), LiNi0.8Co0.15Al0.05O2, _LiCoO2 , LiNi0.5Mn1.5O4 _spinel , _{LiMn2O4 , LiFePO4} , Li4 _{- xMxTi5O12 (} M=Mg, _Al , _Ba , Sr or Ta _{; 0} ≦ _{x ≦ 1} ) _{, MnO2} , _{V2O5 , V6O13} , _LiV3 O ₈ , LiM ^C1 _x M ^C2 _1-x PO ₄ (M ^C1 or M ^C2 = Fe, Mn, Ni, Co, Cr or Ti; 0≦x≦1), Li ₃ V _2-x M ¹ _x (PO ₄ ) ₃ (M ¹ = Cr, Co, Fe, Mg, Y, Ti, Nb or Ce; 0≦x≦1), LiVPO ₄ F, LiM ^C1 _x M ^C2 _1-x O ₂ ((M ^C1 and M ^C2 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1), LiM ^C1 _x M ^C2 _y M ^C3 _1-x-y O ₂ ((M ^C1 , M ^C2 and M ^C3 are independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; 0≦x≦1; 0≦y≦1, 0≦x+y≦1), LiMn _2-y X _y O ₄ (X=Cr, Al or Fe, 0≦y≦1), LiNi _0.5-y X _y Mn _1.5 O ₄ (X=Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0≦y<0.5), xLi ₂ MnO _3. (1-x)LiM ^C1 _y M ^C2 _z M ^C3 _1-y-z O ₂ (M ^C1 , M ^C2 and M 2. The lithium ^ion battery system of claim 1, comprising: ^C3 independently is Mn, Ni, ^Co , Cr, Fe, or a mixture thereof; x=0.3-0.5; y≦0.5; z≦0.5), _Li2M2SiO4 ( _M2 =Mn, Fe or Co), ^{Li2M2SO4 (M2=Mn, Fe or Co), LiM2SO4F (M2 = Fe ,} _Mn or Co), Li2 _-x ( _{Fe1 -yMny ) P2O7 (} 0≦ _x ≦1; 0≦y _≦ 1), _Cr3O8 , _Cr2O5 , _a carbon/sulfur composite, or an air electrode. The lithium ion battery system of claim 1, wherein the anode is prelithiated to at least 5% of its capacity.