Flame retardants for lithium batteries

Abstract

The present invention provides a non-aqueous electrolyte solution for a lithium battery, comprising one or more brominated flame retardants. The non-aqueous electrolyte solution comprises a) a liquid electrolyte medium; b) a lithium-containing salt; and c) at least one brominated flame retardant. The brominated flame retardant is present in the electrolyte solution in a flame-retarding amount.

Description

Technical Field

[0001] The present invention relates to a flame retardant for lithium batteries. Background Art

[0002] One factor that impacts the safety of lithium-ion batteries is their use of flammable solvents in lithium-containing electrolyte solutions. Including flame retardants in electrolyte solutions is one way to mitigate the flammability of these solutions. For a flame retardant to be a suitable component of an electrolyte solution, it needs to be soluble in the electrolyte, electrochemically stable within the battery's operating range, and have minimal negative impact on battery performance. Negative impacts on battery performance can include reduced conductivity and / or chemical instability of the active materials.

[0003] What is needed are flame retardants that can effectively inhibit the flammability of lithium-ion batteries at a reasonable cost and with minimal impact on the electrochemical performance of lithium-ion batteries. Summary of the Invention

[0004] The present invention provides non-aqueous electrolyte solutions for lithium batteries containing at least one brominated flame retardant. In the presence of one or more brominated flame retardants, flames in these non-aqueous electrolyte solutions are extinguished, at least under laboratory conditions.

[0005] One embodiment of the present invention is a non-aqueous electrolyte solution for a lithium battery, the solution comprising i) a liquid electrolyte medium; ii) a lithium-containing salt; and iii) a flame retardant amount of A) tribromoethylene or tribromoneopentyl alcohol, or B) a flame retardant mixture of a) 1,2-dibromoethane and tribromoethylene in a weight ratio of about 0.75:1 to about 3:1 or b) tribromoethylene and 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphinine in a weight ratio of 0.75:1 to about 2.25:1.

[0006] When the material present in a flame retardant amount is A) tribromoethylene or tribromoneopentyl alcohol, optionally present is iv) at least one electrochemical additive selected from the group consisting of: a) an unsaturated cyclic carbonate having three to about six carbon atoms, b) a fluorine-containing saturated cyclic carbonate having three to about five carbon atoms and one to about four fluorine atoms, c) tris(trihydrocarbylsilyl) phosphites having three to about nine carbon atoms, d) trihydrocarbyl phosphates having three to about twelve carbon atoms, e) a cyclic sultone having three to about eight carbon atoms, f) a saturated cyclic hydrocarbyl sulfite having a 5- or 6-membered ring and containing two to about six carbon atoms, g) a saturated cyclic hydrocarbyl sulfate having a 5- or 6-membered ring and containing two to about six carbon atoms, h) a cyclic dioxadithiopolyoxide compound having a 6-, 7-, or 8-membered ring and containing two to about six carbon atoms, i) another lithium-containing salt, and j) a mixture of any two or more of the foregoing.

[0007] These and other embodiments and features of the present invention will be further apparent from the ensuing description and appended claims. DETAILED DESCRIPTION

[0008] Throughout this document, the phrase "electrolyte solution" is used interchangeably with the phrase "non-aqueous electrolyte solution."

[0009] The liquid electrolyte medium contains one or more solvents, which typically form the liquid electrolyte medium for the lithium electrolyte solution used in lithium batteries. The solvent is polar aprotic, stable to electrochemical cycling, and preferably has a low viscosity. These solvents typically include non-cyclic carbonates, cyclic carbonates, ethers, sulfur-containing compounds, and esters of boric acid.

[0010] Solvents that may form the liquid electrolyte medium in the practice of the present invention include ethylene carbonate (1,3-dioxolane-2-one), dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dioxolane, dimethoxyethane (glyme), tetrahydrofuran, methanesulfonyl chloride, 1,3,2-dioxathiolane 2-oxide (ethylene sulfite), 1,3-propylene glycol borate, and mixtures of any two or more of the foregoing.

[0011] Preferred solvents include ethylene carbonate, ethyl methyl carbonate, and mixtures thereof. More preferably, the mixture of ethylene carbonate and ethyl methyl carbonate, particularly ethylene carbonate: the volume ratio of ethyl methyl carbonate is approximately 20:80 to approximately 40:60, more preferably the mixture of ethylene carbonate and ethyl methyl carbonate of approximately 25:75 to approximately 35:65.

[0012] Suitable lithium-containing salts in the practice of the present invention include lithium chloride, lithium bromide, lithium iodide, lithium perchlorate, lithium nitrate, lithium thiocyanate, lithium aluminate, lithium tetrachloroaluminate, lithium tetrafluoroaluminate, lithium tetraphenylborate, lithium tetrafluoroborate, lithium bis(oxalato)borate (LiBOB), lithium bis(fluoro)(oxalato)borate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium titanium oxide, lithium manganese oxide, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium alkyl carbonates in which the alkyl group has from 1 to 6 carbon atoms, lithium methanesulfonate, lithium trifluoromethylsulfonate, lithium pentafluoroethylsulfonate, lithium pentafluorophenylsulfonate, lithium fluorosulfonate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium (ethylsulfonyl)(trifluoromethylsulfonyl)imide, and mixtures of any two or more of the foregoing. Preferred lithium-containing salts include lithium hexafluorophosphate and lithium bis(oxalato)borate.

[0013] Typical concentrations of the lithium-containing salt in the electrolyte solution range from about 0.1 M to about 2.5 M, preferably from about 0.5 M to about 2 M, more preferably from about 0.75 M to about 1.75 M, and even more preferably from about 0.95 M to about 1.5 M. When more than one lithium-containing salt forms the lithium-containing electrolyte, the concentration refers to the total concentration of all lithium-containing salts present in the electrolyte solution.

[0014] The electrolyte solution may contain other salts in addition to the lithium salt, unless one or more of such other salts substantially degrades the performance of the battery for the desired application or the flame retardancy of the electrolyte solution. Suitable electrolytes other than lithium salts include other alkali metal salts, such as sodium salts, potassium salts, rubidium salts, and cesium salts, and alkaline earth metal salts, such as magnesium salts, calcium salts, strontium salts, and barium salts. In some aspects, the salt in the non-aqueous electrolyte solution is only one or more lithium salts.

[0015] Suitable alkali metal salts that may be present in the electrolyte solution include sodium salts such as sodium chloride, sodium bromide, sodium iodide, sodium perchlorate, sodium nitrate, sodium thiocyanate, sodium aluminate, sodium tetrachloroaluminate, sodium tetrafluoroaluminate, sodium tetraphenylborate, sodium tetrafluoroborate and sodium hexafluorophosphate; and potassium salts such as potassium chloride, potassium bromide, potassium iodide, potassium perchlorate, potassium nitrate, potassium thiocyanate, potassium aluminate, potassium tetrachloroaluminate, potassium tetrafluoroaluminate, potassium tetraphenylborate, potassium tetrafluoroborate and potassium hexafluorophosphate.

[0016] Suitable alkaline earth metal salts that may be present in the electrolyte solution include magnesium salts such as magnesium chloride, magnesium bromide, magnesium iodide, magnesium perchlorate, magnesium nitrate, magnesium thiocyanate, magnesium aluminate, magnesium tetrachloroaluminate, magnesium tetrafluoroaluminate, magnesium tetraphenylborate, magnesium tetrafluoroborate, and magnesium hexafluorophosphate; and calcium salts such as calcium chloride, calcium bromide, calcium iodide, calcium perchlorate, calcium nitrate, calcium thiocyanate, calcium aluminate, calcium tetrachloroaluminate, calcium tetrafluoroaluminate, calcium tetraphenylborate, calcium tetrafluoroborate, and calcium hexafluorophosphate.

[0017] In the practice of the present invention, the flame retardant is miscible with the liquid medium of the non-aqueous electrolyte solution, where "miscible" means that the flame retardant does not form a phase separate from the electrolyte solution. More specifically, if after shaking in a mechanical shaker for 24 hours, the flame retardant forms a single phase in a mixture of 30% by weight ethylene carbonate and 70% by weight ethyl methyl carbonate containing 1.2M lithium hexafluorophosphate, and does not form a separate phase after shaking is stopped, and the flame retardant does not precipitate from the non-aqueous electrolyte solution or form a suspension or slurry in the non-aqueous electrolyte solution, then the flame retardant is miscible. It is recommended and preferred that the brominated flame retardant does not precipitate or form a suspension or slurry with any other component of the non-aqueous electrolyte solution.

[0018] In the practice of the present invention, a mixture of two or more brominated flame retardants can be used. In the mixture of brominated flame retardants, one component is 1,2-dibromoethane and the other component is tribromoethylene. In the mixture, the weight ratio of 1,2-dibromoethane to tribromoethylene is in the range of about 0.75:1 to about 3:1, more preferably about 1:1 to about 3:1, and even more preferably about 1:1 to about 2.5:1.

[0019] In a mixture of two or more brominated flame retardants, the flame retardant amount is about 6 wt% or more of the flame retardant molecules relative to the total weight of the non-aqueous electrolyte solution, wherein this amount refers to the total amount of the brominated flame retardant in the non-aqueous electrolyte solution, particularly when the weight ratio of 1,2-dibromoethane to tribromoethylene is in the range of about 0.75:1 to about 1.25:1. In other embodiments, the flame retardant amount is about 20 wt% or more of the flame retardant molecules relative to the total weight of the non-aqueous electrolyte solution, wherein this amount refers to the total amount of the brominated flame retardant in the non-aqueous electrolyte solution, particularly when the weight ratio of 1,2-dibromoethane to tribromoethylene is in the range of about 2:1 to about 2.5:1.

[0020] If desired, the electrolyte solution may include one or more non-brominated flame retardants. These other flame retardants are typically fluorinated cyclotriphosphaphene derivatives, such as 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphaphene and 2-ethoxy-2,4,4,6,6-pentafluoro-triazatriphosphaphene. A preferred non-brominated flame retardant is 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphaphene.

[0021] In mixtures containing non-brominated flame retardants, the brominated flame retardant is tribromoethylene and the non-brominated flame retardant is 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphaphene. In these mixtures containing non-brominated flame retardants, the weight ratio of tribromoethylene to 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphaphene is from about 0.75:1 to about 2.25:1, preferably from about 0.75:1 to about 2:1, and more preferably from about 0.9:1 to about 1.5:1.

[0022] When a non-brominated flame retardant is used, the flame retardant amount is about 4 wt% or more of the flame retardant molecules relative to the total weight of the non-aqueous electrolyte solution, wherein the amount refers to the total amount of the brominated flame retardant and the non-brominated flame retardant in the non-aqueous electrolyte solution. In a preferred embodiment, the flame retardant amount is about 4 wt% or more of the flame retardant molecules relative to the total weight of the non-aqueous electrolyte solution, particularly when the weight ratio of tribromoethylene to 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5triazatriphosphazene is in the range of about 0.75:1 to about 1.25:1 or in the range of about 1.5:1 to about 2:1.

[0023] In some embodiments of the present invention, at least one electrochemical additive is included in the non-aqueous electrolyte solution along with tribromoethylene or tribromoneopentyl alcohol.

[0024] In the practice of the present invention, the flame retardant amount in the non-aqueous electrolyte solution means that there is enough flame retardant to make the solution pass the modified horizontal UL-94 test described below. Preferred flame retardants can also pass the thermal abuse test described below. The flame retardant amount is different for different flame retardants and their combinations. For tribromoethylene, the flame retardant amount is typically more than about 4 weight % flame retardant molecules, preferably about 6 weight % or more flame retardant molecules, more preferably about 8 weight % or more flame retardant molecules. More preferably, the flame retardant amount of tribromoethylene is from about 8 weight % to about 10 weight % flame retardant molecules. In some embodiments, the flame retardant amount of tribromoethylene is preferably about 10 weight % or more flame retardant molecules, and in other embodiments, preferably about 15 weight % or more flame retardant molecules, all relative to the total weight of the non-aqueous electrolyte solution. For tribromoneopentyl alcohol, the flame retardant amount is more than about 10 weight % flame retardant molecules, preferably more than about 15 weight % flame retardant molecules, relative to the total weight of the non-aqueous electrolyte solution.

[0025] When the flame retardant is tribromoethylene, the flame retardant amount in terms of bromine content in the non-aqueous electrolyte solution (which passes the modified level UL-94 test described below) is generally about 5% by weight or more of bromine (atoms) relative to the total weight of the non-aqueous electrolyte solution. When the flame retardant is tribromoneopentyl alcohol, the flame retardant amount in terms of bromine content is generally about 8% by weight or more of bromine (atoms) relative to the total weight of the non-aqueous electrolyte solution.

[0026] In some embodiments, the flame retardant amount of tribromoethylene is about 5.4 wt% or more of bromine (atoms) relative to the total weight of the non-aqueous electrolyte solution. Preferably, for tribromoethylene, the flame retardant amount in terms of bromine content is about 7 wt% or more, preferably about 9 wt% or more of bromine (atoms) relative to the total weight of the non-aqueous electrolyte solution.

[0027] In other embodiments, the flame retardant amount of tribromoneopentyl alcohol is about 9 wt% or more of bromine (atoms) relative to the total weight of the non-aqueous electrolyte solution; preferably about 10 wt% or more, more preferably about 12 wt% or more of bromine (atoms) relative to the total weight of the non-aqueous electrolyte solution.

[0028] In the practice of the present invention, the electrochemical additive is soluble in or miscible with the liquid medium of the non-aqueous electrolyte solution. The electrochemical additive in liquid form is miscible with the liquid medium of the non-aqueous electrolyte solution, wherein "miscible" means that the electrochemical additive does not form a phase separate from the electrolyte solution. More specifically, if after shaking for 24 hours in a mechanical shaker, the electrochemical additive forms a single phase in a mixture of 30 weight percent ethylene carbonate and 70 weight percent ethyl methyl carbonate containing 1.2 M lithium hexafluorophosphate, and does not form a separate phase after shaking is stopped, and the electrochemical additive does not precipitate from the non-aqueous electrolyte solution or form a suspension or slurry in the non-aqueous electrolyte solution, then the electrochemical additive is miscible.

[0029] The term "soluble" as used generally for electrochemical additives in solid form means that once dissolved, the electrochemical additive does not precipitate from the non-aqueous electrolyte solution or form a suspension or slurry in the non-aqueous electrolyte solution. More specifically, if the electrochemical additive is dissolved in a mixture of 30 wt% ethylene carbonate and 70 wt% ethyl methyl carbonate containing 1.2 M lithium hexafluorophosphate after shaking in a mechanical shaker for 24 hours, then after shaking is stopped, if no precipitate, suspension or slurry is formed, then the electrochemical additive is soluble. It is recommended and preferred that the electrochemical additive does not cause any other components of the non-aqueous electrolyte solution to precipitate or form a suspension or slurry.

[0030] Brominated flame retardants, electrochemical additives, and mixtures thereof are generally stable to electrochemical cycling and preferably have low viscosity and / or do not significantly increase the viscosity of the non-aqueous electrolyte solution.

[0031] In various embodiments, the electrochemical additive is selected from a) an unsaturated cyclic carbonate containing three to about four carbon atoms, b) a fluorine-containing saturated cyclic carbonate containing three to about four carbon atoms and one to about two fluorine atoms, c) a tris(trialkylsilyl) phosphite containing three to about six carbon atoms, d) a trialkyl phosphate containing three to about nine carbon atoms, e) a cyclic sultone containing three to about four carbon atoms, f) a saturated cyclic alkyl sulfite having a five-membered ring and containing two to about four carbon atoms, g) a saturated cyclic alkyl sulfate having a five-membered ring and containing two to about four carbon atoms, h) a cyclic dioxadithiopolyoxide compound having a six- or seven-membered ring and containing two to about four carbon atoms, i) another lithium-containing salt, and j) a mixture of any two or more of the foregoing.

[0032] In other embodiments, the electrochemical additive is selected from a) unsaturated cyclic carbonate in an amount of about 0.5 wt % to about 12 wt % relative to the total weight of the non-aqueous electrolyte solution; b) fluorine-containing saturated cyclic carbonate in an amount of about 0.5 wt % to about 15 wt % relative to the total weight of the non-aqueous electrolyte solution; c) tris(trialkylsilyl) phosphite in an amount of about 0.1 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; d) trialkyl phosphate in an amount of about 0.5 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; e) cyclic sultone in an amount of about 0.1 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; f) a saturated cyclic alkyl sulfite in an amount of about 0.5 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; g) a saturated cyclic alkyl sulfate in an amount of about 0.25 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; h) a cyclic dioxadithiopolyoxide compound in an amount of about 0.5 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; i) another lithium-containing salt in an amount of about 0.5 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution; and j) a mixture of any two or more of the foregoing.

[0033] In some embodiments, the electrochemical additive is an unsaturated cyclic carbonate containing three to about six carbon atoms, preferably three to about four carbon atoms. Suitable unsaturated cyclic carbonates include vinylene carbonate (1,3-dioxole-2-one), 4-methyl-1,3-dioxole-2-one and 4,5-dimethyl-1,3-dioxole-2-one; vinylene carbonate is a preferred unsaturated cyclic carbonate. The amount of the unsaturated cyclic carbonate is preferably about 0.5 wt % to about 12 wt % relative to the total weight of the non-aqueous electrolyte solution, more preferably about 0.5 wt % to about 3 wt % or about 8 wt % to about 11 wt %.

[0034] When the electrochemical additive is a fluorine-containing saturated cyclic carbonate containing three to about five carbon atoms, preferably three to about four carbon atoms and one to about four fluorine atoms, preferably one to about two fluorine atoms, suitable fluorine-containing saturated cyclic carbonate includes 4-fluoro-ethylene carbonate and 4,5-difluoro-ethylene carbonate. Preferably, the fluorine-containing saturated cyclic carbonate is 4-fluoro-ethylene carbonate. The amount of the fluorine-containing saturated cyclic carbonate is preferably about 0.5 weight % to about 15 weight %, more preferably about 5 weight % to about 12 weight % relative to the gross weight of the non-aqueous electrolyte solution.

[0035] The tris(trihydrocarbylsilyl) phosphite electrochemical additive contains three to about nine carbon atoms, preferably about three to about six carbon atoms; the trihydrocarbylsilyl groups can be the same or different. Suitable tris(trihydrocarbylsilyl) phosphites include tris(trimethylsilyl) phosphite, bis(trimethylsilyl) (triethylsilyl) phosphite, tris(triethylsilyl) phosphite, bis(trimethylsilyl) (triethylsilyl) phosphite, bis(trimethylsilyl) (tri-n-propylsilyl) phosphite, and tris(tri-n-propylsilyl) phosphite; tris(trimethylsilyl) phosphite is the preferred tris(trihydrocarbylsilyl) phosphite. The amount of tris(trihydrocarbylsilyl) phosphite is preferably about 0.1 wt % to about 5 wt %, more preferably about 0.15 wt % to about 4 wt %, and even more preferably about 0.2 wt % to about 3 wt % relative to the total weight of the non-aqueous electrolyte solution.

[0036] In some embodiments, the electrochemical additive is a trialkyl phosphate containing three to about twelve carbon atoms, preferably three to about nine carbon atoms. The hydrocarbon groups can be saturated or unsaturated, and the hydrocarbon groups in the trialkyl phosphate can be the same or different. Suitable trialkyl phosphates include trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate, tri-n-propyl phosphate, triallyl phosphate, and triethylene phosphate; triallyl phosphate is a preferred trialkyl phosphate. The amount of the trialkyl phosphate is typically from about 0.5% to about 5% by weight, preferably from about 1% to about 5% by weight, and more preferably from about 2% to about 4% by weight, relative to the total weight of the non-aqueous electrolyte solution.

[0037] When the electrochemical additive is a cyclic sultone containing three to about eight carbon atoms, preferably three to about four carbon atoms, suitable cyclic sultones include 1,3-propane sultone, 1,3-propylene sultone, 1,3-butane sultone (5-methyl-1,2-oxathiolane 2,2-dioxide), 2,4-butane sultone (3-methyl-1,2-oxathiolane 2,2-dioxide), 1,4-butane sultone (1,2-oxathiolane 2,2-dioxide), 2-hydroxy-α-toluenesulfonic acid sultone (3H-1,2-benzooxathiolane 2,2-dioxide) and 1,8-naphthalene sultone; preferred cyclic sultones include 1,3-propane sultone and 1,3-propylene sultone. The amount of the cyclic sultone is preferably about 0.25 wt % to about 5 wt %, more preferably about 0.5 wt % to about 4 wt %, relative to the total weight of the non-aqueous electrolyte solution.

[0038] The saturated cyclic alkyl sulfite electrochemical additive contains two to about six carbon atoms, preferably two to about four carbon atoms, and has a 5-membered or 6-membered ring, preferably a 5-membered ring. One or more substituents may be present on the ring, such as methyl or ethyl, preferably one or more methyl groups, and more preferably no substituents are present on the ring. Suitable saturated cyclic alkyl sulfites include 1,3,2-dioxathiolane 2-oxide (1,2-ethylene sulfite), 1,2-propylene glycol sulfite (1,2-propylene sulfite), 4,5-dimethyl-1,3,2-dioxathiolane 2-oxide, 1,3,2-dioxathiolane 2-oxide, 4-methyl-1,3-dioxathiolane 2-oxide (1,3-butylene sulfite); preferred cyclic alkyl sulfites include 1,3,2-dioxathiolane 2-oxide. The amount of the cyclic alkyl sulfite is preferably about 0.5 wt % to about 5 wt %, more preferably about 1 wt % to about 4 wt %, relative to the total weight of the non-aqueous electrolyte solution.

[0039] In some embodiments, the electrochemical additive is a saturated cyclic sulfuric acid alkyl ester containing two to about six carbon atoms, preferably two to about four carbon atoms, and having a 5-membered or 6-membered ring, preferably a 5-membered ring. One or more substituents may be present on the ring, such as methyl or ethyl, preferably one or more methyl groups, more preferably no substituents are present on the ring. Suitable saturated cyclic sulfuric acid alkyl esters include 1,3,2-dioxathiolane 2,2-dioxide (1,2-ethylene sulfate), 1,3,2-dioxathiolane 2,2-dioxide (1,3-propylene sulfate), 4-methyl-1,3,2-dioxathiolane 2,2-dioxide (1,3-butylene sulfate) and 5,5-dimethyl-1,3,2-dioxathiolane 2,2-dioxide. The amount of the saturated cyclic sulfuric acid alkyl ester is preferably from about 0.25 wt % to about 5 wt %, more preferably from about 1 wt % to about 4 wt % relative to the total weight of the non-aqueous electrolyte solution.

[0040] When the electrochemical additive is a cyclic dioxadithiopolyoxide compound, the cyclic dioxadithiopolyoxide compound contains two to about six carbon atoms, preferably two to about four carbon atoms, and has a 6-membered, 7-membered, or 8-membered ring. Preferably, the cyclic dioxadithiopolyoxide compound contains two to about four carbon atoms and has a 6-membered or 7-membered ring. One or more substituents, such as methyl or ethyl groups, may be present on the ring, preferably one or more methyl groups, and more preferably no substituents are present on the ring. Suitable cyclic dioxadithiopolyoxide compounds include 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide, 1,5,2,4-dioxadithiepane 2,2,4,4-tetraoxide (cyclodisone), 3-methyl-1,5,2,4-dioxadithiepane 2,2,4,4-tetraoxide, and 1,5,2,4-dioxadithiooctane 2,2,4,4-tetraoxide; 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide is preferred. The amount of the cyclic dioxadithiopolyoxide compound is preferably about 0.5 wt % to about 5 wt %, more preferably about 1 wt % to about 4 wt %, relative to the total weight of the non-aqueous electrolyte solution.

[0041] The phrases "another lithium-containing salt" and "other lithium-containing salts" indicate that at least two lithium salts are used to prepare the electrolyte solution. When the electrochemical additive is another lithium-containing salt, its amount is preferably from about 0.5% to about 5% by weight relative to the total weight of the non-aqueous electrolyte solution. Suitable lithium-containing salts include all of the lithium-containing salts listed above; lithium bis(oxalato)borate is preferred.

[0042] Mixtures of any two or more of the aforementioned electrochemical additives may be used, including different electrochemical additives of the same type and / or different types of electrochemical additives. When a mixture of electrochemical additives is used, the combined amount of the electrochemical additives is from about 0.25 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution. Mixtures of unsaturated cyclic carbonates and saturated cyclic hydrocarbyl sulfites or mixtures of cyclic sultones, tris(trihydrocarbylsilyl) phosphites, and cyclic dioxadithiopolyoxide compounds are preferred.

[0043] Preferred types of electrochemical additives include saturated cyclic alkyl sulfates, cyclic sultones, tris(trihydrocarbylsilyl) phosphites, and another lithium-containing salt, particularly when used without other electrochemical additives. More preferably, the amount of saturated cyclic alkyl sulfate is from about 1 wt% to about 4 wt%, the amount of cyclic sultone is from about 0.5 wt% to about 4 wt%, the amount of tris(trihydrocarbylsilyl) phosphite is from about 0.2 wt% to about 3 wt%, and the amount of another lithium-containing salt is from about 1 wt% to about 4 wt%, each relative to the total weight of the non-aqueous electrolyte solution.

[0044] In other embodiments, the electrochemical additive is selected from vinylene carbonate, 4-fluoro-ethylene carbonate, tris(trimethylsilyl) phosphite, triallyl phosphate, 1-propane-1,3-sultone, 1-propylene-1,3-sultone, 1,3,2-dioxathiolane 2-oxide, 1,3,2-dioxathiolane 2,2-dioxide, 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide, lithium bis(oxalato)borate, lithium hexafluorophosphate, and mixtures of any two or more of these. The electrochemical additive is preferably vinylene carbonate, 1,3,2-dioxathiolane 2,2-dioxide, 1-propane-1,3-sultone, 1-propylene-1,3-sultone, tris(trimethylsilyl) phosphite, or lithium bis(oxalato)borate, more preferably 1,3,2-dioxathiolane 2,2-dioxide, 1-propylene-1,3-sultone, or lithium bis(oxalato)borate. More preferred electrochemical additives are 1,3,2-dioxathiolane 2,2-dioxide and lithium bis(oxalato)borate. Their amounts and preferred materials are as described above.

[0045] Mixtures of any two or more of the foregoing electrochemical additives may be used. When a mixture of electrochemical additives is used, the combined amount of the electrochemical additives is from about 0.25 wt % to about 5 wt % relative to the total weight of the non-aqueous electrolyte solution.

[0046] Additional ingredients commonly included in electrolyte solutions for lithium batteries may also be present in the electrolyte solution of the present invention. Such additional ingredients include succinonitrile and silazane compounds, such as hexamethyldisilazane. Typically, the amount of the optional ingredients ranges from about 1% to about 5% by weight, preferably from about 2% to about 4% by weight, relative to the total weight of the non-aqueous electrolyte solution.

[0047] Another embodiment of the present invention provides a process for preparing a non-aqueous electrolyte solution for a lithium battery. The process comprises combining components comprising: i) a liquid electrolyte medium; ii) a lithium-containing salt; iii) tribromoethylene or tribromoneopentyl alcohol; and optionally iv) at least one electrochemical additive as described above. The tribromoethylene or tribromoneopentyl alcohol is present in the electrolyte solution in a flame retardant amount. The ingredients may be combined in any order, but preferably all of the components are added to the liquid electrolyte medium. It is also preferred to add the optional ingredients to the liquid electrolyte medium. The characteristics and preferences of the liquid electrolyte medium, the lithium-containing salt, the flame retardant, the one or more electrochemical additives, and the amounts of each component are as described above.

[0048] In some preferred embodiments of the present invention in which electrochemical additives are used, the electrochemical additive is selected from vinylene carbonate, 4-fluoro-ethylene carbonate, tris(trimethylsilyl) phosphite, triallyl phosphate, 1-propane-1,3-sultone, 1-propylene-1,3-sultone, 1,3,2-dioxathiolane 2-oxide, 1,3,2-dioxathiolane 2,2-dioxide, 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide, lithium bis(oxalato)borate, lithium hexafluorophosphate, and mixtures of any two or more of these.

[0049] Another embodiment of the present invention provides a process for preparing a non-aqueous electrolyte solution for a lithium battery. The process comprises combining components comprising: i) a liquid electrolyte medium; ii) a lithium-containing salt; and iii) a flame-retardant amount of a flame retardant mixture of a) 1,2-dibromoethane and tribromoethylene in a weight ratio of about 0.75:1 to about 3:1, or b) tribromoethylene and 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphinine in a weight ratio of 0.75:1 to about 2.25:1. The characteristics and preferences of the liquid electrolyte medium, lithium-containing salt, and flame retardant, as well as the amounts of each component, are as described above.

[0050] The non-aqueous electrolyte solution of the present invention containing one or more brominated flame retardants is generally used in a non-aqueous lithium battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. A non-aqueous lithium battery can be obtained by injecting the non-aqueous electrolyte solution between the negative electrode and the positive electrode, optionally with a separator therebetween.

[0051] The following examples are given for illustrative purposes and are not intended to limit the scope of the present invention.

[0052] In Examples 1-4, a modified horizontal UL-94 test was performed. This modified horizontal UL-94 test is very similar to the known published horizontal UL-94 test. In this regard, see, for example, Otsuki, M. et al., "Flame-Retardant Additives for Lithium-Ion Batteries." Lithium-Ion Batteries, ed. M. Yoshio et al., New York, Springer, 2009, 275-289. The modified UL-94 test is as follows:

[0053] Cut the wicks from the round fiberglass wicks and smooth the cut edges. Then remove dust and particles from the wick surface. Dry the wicks at 120°C for 20 hours before testing. The wick length is 5 ± 0.1 inches (12.7 ± 0.25 cm).

[0054] Each sample to be tested was prepared in a 4 oz (120 mL) glass jar in a dry box by combining the desired amount of flame retardant and electrochemical additive (if present) with the desired amount of common electrolyte solution, for example, 8 wt% brominated flame retardant, 2 wt% electrochemical additive, and 90 wt% common electrolyte solution to form an electrolyte solution containing one or more flame retardants. Prior to combining with the flame retardant, the common electrolyte solution contained 1.2 M LiPF6 in ethylene carbonate / ethyl methyl carbonate (3:7 weight ratio) in a 4 oz (120 mL) glass jar. Each wick was soaked in the electrolyte solution for 30 minutes.

[0055] Each sample was removed from the electrolyte solution and held over the electrolyte solution until dripping stopped, then placed in a 4 ounce (120 mL) glass jar; the lid was closed to prevent evaporation of the electrolyte solution.

[0056] Light the burner and adjust it to produce a blue flame 20 ± 1 mm high.

[0057] The sample was removed from its 4 ounce (120 mL) glass jar and placed in a horizontal position on a metal support fixture with one end of the wick secured.

[0058] If the exhaust fan is running, turn it off for testing.

[0059] The flame is angled at 45 ± 2 degrees to the horizontal wick. One way to achieve this when the burner has a burner tube is to tilt the central axis of the burner tube towards the end of the sample at an angle of 45 ± 2 degrees to the horizontal.

[0060] Apply the flame to the free end of the specimen for 30 ± 1 seconds without changing its position; remove the burner after 30 ± 1 seconds or as soon as the burning front on the specimen reaches the 1 inch (2.54 cm) mark.

[0061] If the specimen continues to burn after the test flame is removed, record the time (in seconds) for the flame to extinguish or for the burning front (flame) to travel from the 1 inch (2.54 cm) mark to the 4 inch (10.16 cm) mark.

[0062] If the flame goes out when the burner is removed, the sample is considered "non-flammable." If the flame goes out before reaching the 1-inch (2.54 cm) mark, the sample is considered "flame retardant." If the flame goes out before reaching the 4-inch (10.16 cm) mark, the sample is considered "self-extinguishing."

[0063] Each modified level UL-94 test result reported below is the average of three runs.

[0064] Example 1

[0065] Several non-aqueous electrolyte solutions containing tribromoethylene or tribromoneopentyl alcohol, prepared as described above, were subjected to the modified UL-94 test described above. The results are summarized in Table 1 below; as noted above, the reported numbers are the average of three runs.

[0066] Table 1

[0067]

[0068]

[0069] Example 2

[0070] Several non-aqueous electrolyte solutions containing a mixture of brominated flame retardants prepared as described above were subjected to the modified UL-94 test described above. The results are summarized in Table 2 below; as noted above, the reported numbers are the average of three runs.

[0071] Table 2

[0072]

[0073] *Compare runs.

[0074] Example 3

[0075] Several non-aqueous electrolyte solutions containing the flame retardant mixtures prepared as described above were subjected to the modified UL-94 test described above. The results are summarized in Table 3 below; as noted above, the reported numbers are the average of three runs.

[0076] Table 3

[0077]

[0078]

[0079] 1 Compare runs.

[0080] 2 O is 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5triazatriphosphabenzene (Nippon Chemical Co.).

[0081] Example 4

[0082] Several non-aqueous electrolyte solutions containing brominated flame retardants were also tested in coin-type cells. Coin-type cells were assembled using the non-aqueous electrolyte solutions containing the desired amount of flame retardant. The coin-type cells were then subjected to the following electrochemical cycling: CCCV charging at C / 5 to 4.2 V (with a current cutoff of C / 50 during the CV portion) and CC discharge at C / 5 to 3.0 V.

[0083] One sample was a non-aqueous electrolyte solution without a flame retardant and contained 1.2 M LiPF6 in ethylene carbonate / ethyl methyl carbonate (3:7 weight ratio). The remaining samples contained the desired amount of flame retardant in the electrolyte solution; some solutions contained additives in addition to the flame retardant. The results are summarized in Table 4 below; the error range for the coulombic efficiency is from about ±0.5% to about ±1.0%. The results reported in Table 4 are averages of multiple unit cells; "multiple unit cells" generally means two or three unit cells.

[0084] Table 4

[0085]

[0086] * Compare runs.

[0087] Example 5

[0088] Additional flammability testing of non-aqueous electrolyte solutions was conducted at Sandia National Laboratories. In these thermal abuse tests, a closer estimate was made of the conditions under which the electrolyte would need to exhibit non-flammable properties under abuse conditions, particularly for cells that combine venting with an ignition source. The tests were conducted as follows: an 18650-sized battery cell was filled with approximately 5 mL of non-aqueous electrolyte solution, the cell was crimped with a typical cell tab assembly, and the electrolyte-containing cell was heated at a fixed rate of 5°C / minute using a spark wire ignition source at a fixed position approximately 2 inches above the cell tab. At approximately 200°C, the cell began to vent, the hot electrolyte solution became aerosolized, and was exposed to the spark wire ignition source. Each sample was monitored for ignition; failure to ignite was considered a pass, while samples that ignited were considered a fail.

[0089] One sample was a non-aqueous electrolyte solution without a flame retardant and contained 1.2 M LiPF6 in ethylene carbonate / ethyl methyl carbonate (weight ratio 3:7). The remaining samples contained the required amount of flame retardant in the electrolyte solution. The results are summarized in Table 5 below.

[0090] Table 5

[0091]

[0092] 1 Compare runs.

[0093] 2 2-Phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphabenzene ( O, Nippon Chemical Co.).

[0094] Additional embodiments include, but are not limited to:

[0095] A. A non-aqueous electrolyte solution for a lithium battery, the solution comprising

[0096] a) liquid electrolyte medium;

[0097] b) lithium-containing salts; and

[0098] c) a flame retardant amount of a brominated flame retardant, wherein the brominated flame retardant is selected from the group consisting of tribromoethylene and tribromoneopentyl alcohol.

[0099] B. The solution as described in A, wherein the flame retardant amount is greater than 4 weight percent relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0100] C. A solution as described in A, wherein the flame retardant amount is greater than 6 wt % relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0101] D. A solution as described in A, wherein the flame retardant amount is greater than 8 weight percent relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0102] E. The solution of claim 1, wherein the flame retardant amount is from about 8 wt% to about 10 wt% relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0103] F. A solution as described in A, wherein the flame retardant amount is greater than 10 wt % relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0104] G. A solution as described in A, wherein the flame retardant amount is more than 10 wt % relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoneopentyl alcohol.

[0105] H. A solution as described in A, wherein the flame retardant amount is more than 15 wt % relative to the total weight of the solution.

[0106] I. A solution as described in any of AH, wherein the liquid electrolyte medium is ethylene carbonate, ethyl methyl carbonate or a mixture thereof, and / or wherein the lithium-containing salt is lithium hexafluorophosphate or lithium bis(oxalato)borate.

[0107] J. A non-aqueous lithium battery comprising a positive electrode, a negative electrode and the non-aqueous electrolyte solution described in any one of AI.

[0108] K. A process for preparing a non-aqueous electrolyte solution for a lithium battery, the process comprising combining components comprising:

[0109] a) liquid electrolyte medium;

[0110] b) lithium-containing salts; and

[0111] c) a flame retardant amount of a brominated flame retardant, wherein the brominated flame retardant is selected from the group consisting of tribromoethylene and tribromoneopentyl alcohol.

[0112] L. A process as described in K, wherein the flame retardant amount is greater than 4 wt % relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0113] M. A process as described in K, wherein the flame retardant amount is greater than 6 wt % relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0114] N. A process as described in K, wherein the flame retardant amount is greater than 8 weight percent relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0115] O. A process as described in K, wherein the flame retardant amount is from about 8 wt% to about 10 wt% relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoethylene.

[0116] P. A process as described in K, wherein the flame retardant amount is greater than 10 wt % relative to the total weight of the solution, and wherein the brominated flame retardant is tribromoneopentyl alcohol.

[0117] Q. A process as described in K, wherein the liquid electrolyte medium is ethylene carbonate, ethyl methyl carbonate, or a mixture thereof, and / or wherein the lithium-containing salt is lithium hexafluorophosphate or lithium bis(oxalato)borate.

[0118] R. A process as described in any of KQ, wherein the liquid electrolyte medium is ethylene carbonate, ethyl methyl carbonate or a mixture thereof, and / or wherein the lithium-containing salt is lithium hexafluorophosphate or lithium bis(oxalato)borate.

[0119] Components referred to by chemical name or chemical formula anywhere in the specification or its claims (whether in the singular or in the plural) are identified as existing before contact with another substance referred to by chemical name or chemical type (e.g., another component, solvent, etc.). It is not important what kind of chemical changes, conversions, and / or reactions (if any) occur in the resulting mixture or solution, because such changes, conversions, and / or reactions are the natural result of bringing the specified components together under the conditions required by the present disclosure. Therefore, the components are identified as the ingredients to be combined together that are relevant to performing the required operation or forming the required combination. In addition, even if the attached claims may mention substances, components, and / or ingredients in the present tense ("comprising," "is," etc.), what is mentioned is the substance, component, or ingredient that existed before the first contact, blending, or mixing with one or more other substances, components, and / or ingredients according to the present disclosure. Therefore, if the contact, blending, or mixing operation is performed according to the present disclosure and the ordinary skills of a chemist, the fact that the substance, component, or ingredient may have lost its original properties through chemical reaction or conversion during this process is of no practical significance.

[0120] The present invention may comprise, consist of, or consist essentially of the materials and / or procedures enumerated herein.

[0121] As used herein, the term "about," which modifies the amount of an ingredient in a composition of the present invention or used in a method of the present invention, refers to variations in the numerical amount that may occur, for example, due to typical measurement and liquid handling procedures used to prepare actual concentrates or use solutions; due to accidental errors in such procedures; due to differences in the manufacture, source, or purity of the ingredients used to prepare the composition or perform the method; and so forth. The term "about" also encompasses amounts that vary due to differences in the equilibrium conditions of the composition resulting from a particular initial mixture. Whether or not modified by the term "about," the claims encompass amounts equivalent to the recited amounts.

[0122] Except where otherwise expressly indicated, the article "a" or "an" as used herein is not intended and should not be interpreted as limiting the specification or claims to the single element to which the article refers. Rather, the article "a" or "an" as used herein is intended to encompass one or more such elements, unless the context clearly indicates otherwise.

[0123] The present invention is susceptible to considerable variation in its practice. Therefore, the foregoing description is not intended and should not be construed as limiting the invention to the particular exemplifications set forth hereinabove.

Claims

1. A non-aqueous electrolyte solution for a lithium battery, the solution comprising i) liquid electrolyte medium; ii) a lithium-containing salt; and iii) a flame retardant amount of A) tribromoethylene or tribromoneopentyl alcohol, wherein the flame retardant amount is greater than 15 wt% relative to the total weight of the solution; or B) a) 1,2-dibromoethane and tribromoethylene in a weight ratio of 0.75:1 to 3:1, wherein the flame retardant amount is 20 wt% or more relative to the total weight of the solution or b) a flame retardant mixture of tribromoethylene and 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphazene in a weight ratio of 0.75:1 to 2.25:1, wherein the flame retardant amount is 4 wt% or more relative to the total weight of the solution.

2. The solution of claim 1 , further comprising 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphazene, wherein the flame retardant is tribromoethylene, wherein the weight ratio of tribromoethylene to 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphazene is 0.75:1 to 2:1, and the flame retardant amount is 4 wt% or more of the flame retardant molecules relative to the total weight of the non-aqueous electrolyte solution.

3. A solution as claimed in claim 1 or 2, wherein the liquid electrolyte medium is ethylene carbonate, ethyl methyl carbonate or a mixture thereof, and / or wherein the lithium-containing salt is lithium hexafluorophosphate or lithium bis(oxalato)borate.

4. The solution as claimed in claim 1, wherein iii) is tribromoethylene or tribromoneopentyl alcohol, and wherein the solution further comprises iv) at least one electrochemical additive selected from the group consisting of: a) unsaturated cyclic carbonates containing three to six carbon atoms, b) a fluorine-containing saturated cyclic carbonate containing three to five carbon atoms and one to four fluorine atoms, c) tris(trihydrocarbylsilyl) phosphites containing three to nine carbon atoms, d) trihydrocarbyl phosphates containing three to twelve carbon atoms, e) cyclic sultones containing three to eight carbon atoms, f) a saturated cyclic hydrocarbyl sulfite having a 5-membered or 6-membered ring and containing two to six carbon atoms, g) a saturated cyclic alkyl sulfate having a 5-membered or 6-membered ring and containing two to six carbon atoms, h) cyclic dioxadithiopolyoxide compounds having a 6-, 7- or 8-membered ring and containing two to six carbon atoms, i) another lithium-containing salt, and j) mixtures of any two or more of the foregoing.

5. The solution of claim 4, wherein the electrochemical additive is selected from: a) unsaturated cyclic carbonates containing three to four carbon atoms, b) a fluorine-containing saturated cyclic carbonate containing three to four carbon atoms and one to two fluorine atoms, c) tris(trihydrocarbylsilyl) phosphites containing three to six carbon atoms, d) trihydrocarbyl phosphates containing three to nine carbon atoms, e) cyclic sultones containing three to four carbon atoms, f) a saturated cyclic hydrocarbon sulfite having a 5-membered ring and containing two to four carbon atoms, g) a saturated cyclic alkyl sulfate having a 5-membered ring and containing two to four carbon atoms, h) cyclic dioxadithiopolyoxide compounds having a 6-membered or 7-membered ring and containing two to four carbon atoms, i) another lithium-containing salt, and j) mixtures of any two or more of the foregoing.

6. The solution of claim 4, wherein the electrochemical additive is selected from: a) an unsaturated cyclic carbonate in an amount of 0.5 wt % to 12 wt % relative to the total weight of the non-aqueous electrolyte solution, b) a fluorine-containing saturated cyclic carbonate in an amount of 0.5 to 15 wt % relative to the total weight of the non-aqueous electrolyte solution, c) tris(trihydrocarbylsilyl) phosphite in an amount of 0.1 wt % to 5 wt % relative to the total weight of the non-aqueous electrolyte solution, d) trialkyl phosphate in an amount of 0.5 wt % to 5 wt % relative to the total weight of the non-aqueous electrolyte solution, e) a cyclic sultone in an amount of 0.25 wt % to 5 wt % relative to the total weight of the non-aqueous electrolyte solution, f) a saturated cyclic alkyl sulfite in an amount of 0.5 to 5 wt % relative to the total weight of the non-aqueous electrolyte solution, g) a saturated cyclic alkyl sulfate in an amount of 0.25 wt % to 5 wt % relative to the total weight of the non-aqueous electrolyte solution, h) a cyclic dioxadithiopolyoxide compound in an amount of 0.5 wt % to 5 wt % relative to the total weight of the non-aqueous electrolyte solution, i) another lithium-containing salt in an amount of 0.5 wt % to 5 wt % relative to the total weight of the non-aqueous electrolyte solution, and j) mixtures of any two or more of the foregoing.

7. The solution of any one of claims 4 to 6, wherein the electrochemical additive is a saturated cyclic hydrocarbyl sulfate, a cyclic sultone, tris(trihydrocarbylsilyl) phosphite, or another lithium-containing salt.

8. The solution of claim 4 , wherein the electrochemical additive is a saturated cyclic alkyl sulfate in an amount of 1 to 4 weight percent, a cyclic sultone in an amount of 0.5 to 4 weight percent, tris(trialkylsilyl) phosphite in an amount of 0.2 to 3 weight percent, or another lithium-containing salt in an amount of 1 to 4 weight percent, each relative to the total weight of the non-aqueous electrolyte solution.

9. The solution of claim 4 or 8, wherein the electrochemical additive is vinylene carbonate, 1,3,2-dioxathiolane 2,2-dioxide, 1,3-propylene sultone, 1,3-propane sultone, tris(trimethylsilyl) phosphite or lithium bis(oxalato)borate.

10. The solution of claim 8, wherein each electrochemical additive is used without other electrochemical additives.

11. The solution of any one of claims 4 to 6, wherein the electrochemical additive is selected from the group consisting of vinylene carbonate, 4-fluoro-ethylene carbonate, tris(trimethylsilyl) phosphite, triallyl phosphate, 1-propane-1,3-sultone, 1-propylene-1,3-sultone, 1,3,2-dioxathiolane 2-oxide, 1,3,2-dioxathiolane 2,2-dioxide, 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide, lithium bis(oxalato)borate, and mixtures of any two or more of these.

12. The solution of claim 11, wherein the electrochemical additive is selected from: vinylene carbonate in an amount of 0.5 wt % to 3 wt % relative to the total weight of the non-aqueous electrolyte solution; vinylene carbonate in an amount of 8 wt % to 11 wt % relative to the total weight of the non-aqueous electrolyte solution; 4-Fluoro-ethylene carbonate in an amount of 0.5 wt % to 15 wt % relative to the total weight of the non-aqueous electrolyte solution; tris(trimethylsilyl) phosphite in an amount of 0.2 wt % to 3 wt % relative to the total weight of the non-aqueous electrolyte solution; triallyl phosphate in an amount of 1 wt % to 5 wt % relative to the total weight of the non-aqueous electrolyte solution; 1,3-propane sultone or 1,3-propylene sultone in an amount of 0.5 wt % to 4 wt % relative to the total weight of the non-aqueous electrolyte solution; 1,3,2-dioxathiolane 2-oxide in an amount of 1 wt % to 4 wt % relative to the total weight of the non-aqueous electrolyte solution; 1,3,2-dioxathiolane 2,2-dioxide in an amount of 1 wt % to 4 wt % relative to the total weight of the non-aqueous electrolyte solution; 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide in an amount of 1 wt % to 4 wt % relative to the total weight of the non-aqueous electrolyte solution; lithium bis(oxalato)borate in an amount of 1 wt % to 4 wt % relative to the total weight of the non-aqueous electrolyte solution; and mixtures of any two or more of these.

13. The solution of claim 11, wherein the electrochemical additive is selected from the group consisting of vinylene carbonate, 1-propane-1,3-sultone, 1-propylene-1,3-sultone, 1,3,2-dioxathiolane 2,2-dioxide, tris(trimethylsilyl) phosphite, and lithium bis(oxalato)borate.

14. The solution of claim 11 , wherein the electrochemical additive is selected from 1-propane-1,3-sultone in an amount of 0.5 wt % to 4 wt %, 1-propylene-1,3-sultone in an amount of 0.5 wt % to 4 wt %, 1,3,2-dioxathiolane 2,2-dioxide in an amount of 1 wt % to 4 wt %, and lithium bis(oxalato)borate in an amount of 1 wt % to 4 wt %, each relative to the total weight of the non-aqueous electrolyte solution.

15. A solution as claimed in claim 13 or 14, wherein each electrochemical additive is used without any other electrochemical additive. 16 . A non-aqueous lithium battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte solution according to claim 1 .

17. A process for preparing a non-aqueous electrolyte solution for a lithium battery, the process comprising combining components comprising: i) liquid electrolyte medium; ii) a lithium-containing salt; and iii) a flame retardant amount of A) tribromoethylene or tribromoneopentyl alcohol, wherein the flame retardant amount is greater than 15 wt% relative to the total weight of the solution; or B) a) 1,2-dibromoethane and tribromoethylene in a weight ratio of 0.75:1 to 3:1, wherein the flame retardant amount is 20 wt% or more relative to the total weight of the solution or b) a flame retardant mixture of tribromoethylene and 2-phenoxy-2,4,4,6,6-pentafluoro-1,3,5,2λ5,4λ5,6λ5 triazatriphosphazene in a weight ratio of 0.75:1 to 2.25:1, wherein the flame retardant amount is 4 wt% or more relative to the total weight of the solution.

18. The process of claim 17, wherein iii) is tribromoethylene or tribromoneopentyl alcohol, and the component further comprises iv) at least one electrochemical additive selected from the group consisting of: a) unsaturated cyclic carbonates containing three to six carbon atoms, b) a fluorine-containing saturated cyclic carbonate containing three to five carbon atoms and one to four fluorine atoms, c) tris(trihydrocarbylsilyl) phosphites containing three to nine carbon atoms, d) trihydrocarbyl phosphates containing three to twelve carbon atoms, e) cyclic sultones containing three to eight carbon atoms, f) a saturated cyclic hydrocarbyl sulfite having a 5-membered or 6-membered ring and containing two to six carbon atoms, g) a saturated cyclic alkyl sulfate having a 5-membered or 6-membered ring and containing two to six carbon atoms, h) cyclic dioxadithiopolyoxide compounds having a 6-, 7- or 8-membered ring and containing two to six carbon atoms, i) another lithium-containing salt, and j) mixtures of any two or more of the foregoing.

19. A process as claimed in claim 18, wherein the electrochemical additive is selected from the group consisting of vinylene carbonate, 4-fluoro-ethylene carbonate, tris(trimethylsilyl) phosphite, triallyl phosphate, 1-propane-1,3-sultone, 1-propylene-1,3-sultone, 1,3,2-dioxathiolane 2-oxide, 1,3,2-dioxathiolane 2,2-dioxide, 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide, lithium bis(oxalato)borate and mixtures of any two or more of these.

20. A process as claimed in claim 17 or 18, wherein the liquid electrolyte medium is ethylene carbonate, ethyl methyl carbonate or a mixture thereof, and / or wherein the lithium-containing salt is lithium hexafluorophosphate or lithium bis(oxalato)borate.

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