WO2013149073A1

WO2013149073A1 - Electrolyte additive with improved cycle life

Info

Publication number: WO2013149073A1
Application number: PCT/US2013/034463
Authority: WO
Inventors: Jeong Ju CHO
Original assignee: A123 Systems, LLC
Priority date: 2012-03-28
Filing date: 2013-03-28
Publication date: 2013-10-03

Abstract

A lithium ion battery with excellent cycle life and characteristics was obtained including an alkali transition metal oxoanion material as a cathode material and an electrolyte containing a sulfur trioxide amine complex additive. The electrolyte additive delays thermal decomposition of the electrolyte and is particularly suited to non-aqueous electrolytes. Additionally, the additive provides an improvement in battery capacity retention and decreased cell impedance after storage. Materials for the cathode are selected alkali transition metal oxoanion materials, including composite oxide materials of lithium and transition metal such as lithium metal phosphates, chosen for their high lithium-insertion potential, high theoretical capacity, low cost, ease of synthesis, and stability when used with common organic electrolyte systems.

Description

ELECTROLYTE ADDITIVE WITH IMPROVED CYCLE LIFE

INCORPORATION BY REFERENCE

[0001] All patents, patent applications and publications cited herein are hereby incorporated by reference in their entirety in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described herein.

FIELD OF THE INVENTION

The field of the invention is batteries, and especially battery electrolytes.

BACKGROUND

[0002] Battery power is considered one of the more convenient and better performing choices as a power supply in many applications, including portable-power, transportation, grid and backup applications. Advantages to utilizing battery power include portability, isolation from power lines and from earth ground, minimization of heat management, and

uninterruptibility in light of momentary AC power interruptions.

[0003] Batteries find application in back-up power, electric and hybrid vehicles, and consumer electronics. As batteries gain wide-spread acceptance in the market, reliability becomes increasingly important. Specifically, a batteries ability to charge and discharge repeatedly and reliably is critical in most applications.

[0004] Batteries comprise two major components: (1) electrodes, specifically an anode and a cathode, and (2) an electrolyte. The electrode is a phase through which charge is carried by electronic movement. Electrodes can be metals or semiconductors, and they can be solid or liquid. The electrolyte is generally defined as a phase through which charge is carried by the movement of ions. Electrolytes may be any phase on the continuum of liquid to solid, including gels, pastes, fused salts, or ionically conducting solids, such as, sodium. P-alumina, which has mobile sodium ions. (Bard, Allen J. and Larry R. Faulkner, Electrochemical Methods: Fundamentals and Applications, John Wiley & Sons (New York), 1980).

[0005] The electrolyte is generally the most unstable component of a battery or cell, particularly because it can be compromised or decomposed much faster than the electrodes. When the electrolyte is subject to decomposition, its ability to cycle from charge to discharge becomes compromised. In an attempt to improve cycle life of batteries a variety of electrolyte additives have been proposed. However, the proposed additives either cause an increased impedance of the electrolyte or are detrimental to cell capacity. SUMMARY OF THE INVENTION

[0006] A lithium ion battery with excellent cycle life and characteristics was obtained including an alkali transition metal oxoanion material as a cathode material and an electrolyte containing a sulfur trioxide amine complex additive. The electrolyte additive delays thermal decomposition of the electrolyte and is particularly suited to non-aqueous electrolytes.

Additionally, the additive provides an improvement in battery capacity retention and decreased cell impedance after storage. Materials for the cathode are selected alkali transition metal oxoanion materials, including composite oxide materials of lithium and transition metal such as lithium metal phosphates, chosen for their high lithium-insertion potential, high theoretical capacity, low cost, ease of synthesis, and stability when used with common organic electrolyte systems.

[0007] In one aspect, a battery includes an anode, a cathode, and an electrolyte comprising a lithium salt and a sulfur trioxide amine complex that suppresses electrolyte decomposition, wherein, the cathode includes an alkali transition metal oxoanion electroactive material.

[0008] In one or more embodiments, the alkali transition metal oxoanion material is selected from the group consisting of: (i) a composition Ax(M'l-aM"a)y(XD4)z,

Ax(M'l-aM"a)y(DXD4)z, or Ax(M'l-aM"a)y(X2D7)z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" is any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.00014, X2D7, or DXD4 group; (ii)a composition (Al-aM"a)xM'y(XD4)z, (Al-aM"a)xM'y(DXD4)z, or (Al-aM"a)xM'y(X2D7)z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.00014, X2D7 or DXD4 group. In some of these embodiments, the compound has a conductivity at 27° C of at least about 10-8 S/c; and (iii) a composition (Ab-aM"a)xM'y(XD4)z, (Ab-aM"a)xM'y(DXD4)z, or

(Ab-aM"a)xM'y(X2D7)z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.0001<A<0.1, z x, that such values have and than greater are zero y, (b-a)x plus the quantity ax times the formal valence or valences of M" plus y times the formal valence or valences of M is equal to z times the formal valence of the XD4, X2D7 or DXD4 group.

[0009] In one or more embodiments, the alkali transition metal oxoanion includes lithium metal phosphate.

[0010] In one or more embodiments, the sulfur trioxide amine complex is selected from the group comprising: sulfur trioxide trimethylamine complex; sulfur trioxide pyridine complex; sulfur trioxide triethylamine complex; sulfur trioxide Ν,Ν-dimethylfromide complex, or mixtures thereof.

[0011] In one or more embodiments, the sulfur trioxide amine complex comprises a sulfur trioxide pyridine complex.

[0012] In one or more embodiments, the electrolyte contains from 0.01%(wt) to 3%(wt) of said sulfur trioxide amine complex.

[0013] In one or more embodiments, the electrolyte contains from 0.1% (wt) to l%(wt) of said sulfur trioxide amine complex.

[0014] In one or more embodiments, the molar concentration of the lithium salt is between 0.5 amd 2.0 mol/l.

[0015] In one or more embodiments, the lithium salt is selected from the group consisting of LiC104, LiPF6, LiBF4, LiCF3 S03, LiN (CF3 S02)2, LiN (CF3 CF2 S02)2, LiN (CF3 S02) (C4 F9 S02) and LiC (CF3 S02)3.

[0016] In one or more embodiments, the electrolyte further includes aprotic solvents.

[0017] In one or more embodiments, the solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, γ-butyrolactone, γ -valerolactone, methyl acetate, methyl propionate, tetrahydrofuran, 2-methyl tetrahydrofuran, tetrahydropyran, dimethoxy ethane,

dimethoxymethane, ethylene methyl phosphate, ethyl ethylene phosphate, trimethyl phosphate, triethyl phosphate, halides thereof, vinyl ethylene carbonate and

fluoroethylenecarbonate, poly(ethylene glycol), diacrylate, and combinations thereof.

[0018] In one or more embodiments, the solvent includes a mixture of ethylene carbonate, propylene carbonate, ethylmethyl carbonate, and diethyl carbonate.

[0019] In one or more embodiments, the anode comprises graphite.

[0020] In another aspect, a battery includes an anode, a cathode, and an electrolyte comprising a lithium salt, a sulfur trioxide amine complex that suppresses electrolyte decomposition, and a nitrile compound, wherein, the cathode includes a alkali transition metal oxoanion electroactive material selected from the group consisting of: (i) a composition Ax(M^*l-aM"a)y(XD4)z, Ax(M^*l-aM"a)y(DXD4)z, or Ax(M^*l-aM"a)y(X2D7)z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" is any of a Group IIA, A, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, and a halogen, 0.00014, X2D7, or DXD4 group; (ii) a composition

(Al-aM"a)xM^*y(XD4)z, (Al-aM"a)xM^*y(DXD4)z, or (Al-aM"a)xM^*y(X2D7)z, wherein A is at least one of an alkali metal or hydrogen, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any of a Group IIA, A, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.00014, X2D7 or DXD4 group. In some of these embodiments, the compound has a conductivity at 27° C of at least about 10-8 S/c; and (iii) a composition (Ab-aM"a)xM^*y(XD4)z, (Ab-aM"a)xM^*y(DXD4)z, or (Ab-aM"a)xM^*y(X2D7)z, wherein A is at least one of an alkali metal or hydrogen, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any of a Group IIA, A, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.0001<A<0.1, z x, that such values have and than greater are zero y, (b-a)x plus the quantity ax times the formal valence or valences of M" plus y times the formal valence or valences of M is equal to z times the formal valence of the XD4, X2D7 or DXD4 group.

[0021] In one or more embodiments, the sulfur trioxide amine complex is selected from the group comprising: sulfur trioxide trimethylamine complex; sulfur trioxide pyridine complex; sulfur trioxide triethylamine complex; sulfur trioxide Ν,Ν-dimethylfromide complex, or mixtures thereof, and the nitrile compound is selected from succinonitrile, cyanobenzene, or mixtures thereof.

[0022] In one or more embodiments, the sulfur trioxide amine complex is a sulfur trioxide pyridine complex.

[0023] In one or more embodiments, the electrolyte contains from 0.01%(wt) to 3%(wt) of said sulfur trioxide amine complex.

[0024] In one or more embodiments, the electrolyte contains from 0.1%(wt) to l%(wt) of said sulfur trioxide amine complex.

[0025] In one or more embodiments, the electrolyte contains from 0.01%(wt) to 3%(wt) of said nitrile compound.

[0026] In one or more embodiments, the electrolyte contains from l%(wt) to 2%(wt) of said nitrile compound. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention is described with reference to the following figures, which are presented for the purpose of illustration only and are not intended to be limiting. In the Drawings:

[0028] Figure 1 shows a photograph of two electrolyte samples after 2 months of storage at 55°C, according to one or more embodiments.

[0029] Figures 2A-2C show plots of the retained and recovered capacities of batteries after 1 month storage at 55°C, with and without a sulfur trioxide pyridine additive, according to one or more embodiments.

[0030] Figures 3A-3C show plots of the DC resistance of batteries before and after 1 month storage at 55°C, with and without a sulfur trioxide pyridine additive, according to one or more embodiments.

[0031] Figure 4 shows a plot of capacity versus cycle number for batteries with an without the sulfur trioxide additive, according to one or more embodiments. The cycles were performed at 1C/-1C rates at 35°C.

DETAILED DESCRIPTION

[0032] An electrochemical lithium ion battery with excellent cycle life and characteristics was obtained with alkali transition metal oxoanion as a cathode material and an electrolyte containing a sulfur trioxide amine complex additive. The cell includes cathodes of selected transition metal polyanion compounds, which are the materials of choice for applications requiring their high lithium-insertion potential, high capacity, low cost, ease of synthesis, and stability when used with common organic electrolyte systems. The electrolyte is chosen to be stable within the electrochemical cell comprising such cathode materials. The sulfur trioxide amine complex electrolyte additive delays thermal decomposition of the electrolyte and is particularly suited to non-aqueous electrolytes. The additive also contributes to an

improvement in battery capacity retention and decreased cell impedance after storage.

[0033] Sulfur trioxide is a chemical compound with the formula S0₃. In some

embodiments, a sulfur trioxide amine complex is selected from the group comprising: sulfur trioxide trimethylamine complex; sulfur trioxide pyridine complex; sulfur trioxide

triethylamine complex; sulfur trioxide Ν,Ν-dimethylfromide complex, or mixtures thereof.

[0034] The sulfur trioxide amine complex compounds according to one or more embodiment are defined as follows: Sulfur trioxide trimethylamine complex:

[0035] Synonym: NSC 9838, Trimethylamine sulfur trioxide complex

[0036] CAS Number: 3162-58-1

[0037] Linear Formula: (CH₃)₃N · S0₃

[0038] Molecular Weight: 139.17 (

13

[0039] Beilstein Registry Number: 3681759 ^

[0040] EC Number: 221-614-7 H3C" T '3

[0041] MDL number: MFCD00012421

[0042] PubChem Substance ID : 24848242

Sulfur trioxide Pyridine complex

[0043] Synonym: NSC 75831 , Pyridine sulfur trioxide complex

[0044] CAS Number: 26412-87-3

[0045] Empirical Formula (Hill Notation): C₅H₅N0₃S

[0046] Molecular Weight: 159.16

[0047] Beilstein Registry Number: 3704116

[0048] EC Number: 247-683-3

[0049] MDL number: MFCD00012437

[0050] PubChem Substance ID: 24899756

Sulfur trioxide triethylamine complex

[0051] Synonym: NSC 68185, NSC 8168, Triethylamine sulfur trioxide complex

[0052] CAS Number: 761-01-3

[0053] Linear Formula: (CH₃CH₂)₃N · S0₃

[0054] Molecular Weight: 181.25

[0055] Beilstein Registry Number: 3993165 ^" CH 3

[0056] MDL number: MFCD00043315

[0057] PubChem Substance ID: 24899639

Sulfur trioxide NJSf-Dimethylfromide complex

[0058] Synonym: DMF-sulfur trioxide complex

[0059] CAS Number: 29584-42-7

[0060] Linear Formula: HCON(CH₃)₂ · S0₃ O

[0061] Molecular Weight: 153.16 H3C V

N ! ^'

C H3 [0062] EC Number: 249-701 -5

[0063] MDL number: MFCD00043411

[0064] PubChem Substance ID : 24863252

[0065] The practice of the present invention can employ, unless otherwise indicated, conventional techniques of battery fabrication, battery chemistry, and electrolyte chemistry. All patents, patent applications, publications and other types of references cited herein, whether supra or infra, are hereby incorporated by reference in their entirety. Despite the incorporation of references, the present text does not necessarily adopt the definitions and usages set forth in the references. Therefore, to clarify the definitions and usages of specific terms that are not defined elsewhere herein, we set forth the following.

[0066] The singular forms "a", "an" and "the" are used herein to include the plural unless the content clearly dictates otherwise. Thus, for example, reference to "an electrolyte additive" includes mixtures of such additives; reference to "the anode material" includes more than one such material, and the like.

[0067] As used herein the term "electrode" is used herein to mean a phase through which charge is carried by electronic movement. Electrodes can be metals or semiconductors, and they can be solid or liquid. Also as used herein, the term "electrolyte" is generally defined as a phase through which charge is carried by the movement of ions. Electrolytes may be any phase on the continuum of liquid to solid, including gels, pastes, fused salts, or ionically conducting solids, such as sodium P-alumina, which has mobile sodium ions.

[0068] As used herein the terms "anode material" and "anode" are used interchangeably, except where the context clearly indicates otherwise. Similarly, the terms the terms "cathode material" and "cathode" are used interchangeably. These definitions are intended to eliminate confusion over the exact point at which the respective electrode material(s) is/are incorporated into, and thus becomes an electrode.

[0069] The battery according to one or more embodiments includes electrodes (cathode and anode), a separator, and an electrolyte.

Electrodes

[0070] Materials for the cathode are alkali transition metal oxoanions, including selected composite oxide materials of lithium and transition metal such as lithium metal phosphates or combinations of lithium metal phosphates and lithium oxides.

[0071] The cathode (i.e. positive electrode) material used in the nonaqueous electrolytic solution cell of the present invention properly be selected from those capable of occluding and liberating lithium, which are exemplified as alkali transition metal oxoanions such as composite oxide materials of lithium and transition metal such as lithium metal phosphates or combinations of lithium metal phosphates and lithium oxides. Oxoanion are anion moieties that include one or more elements, one of which is oxygen, such as phosphates, sulfates, silicates and the like. Oxoanions may include moieties such as X₂O₇ and OXO₄, where X may be at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten. A preferred oxoanion is phosphate.

[0072] A cathode material comprises a composition A_x(M'i__aM"_a)_y(XD4)_z,

A_x(M'i__aM"_a)_y(DXD₄)_z, or A_x(M'i__aM"_a)_y(X₂D₇)_z, wherein A is at least one of an alkali metal or hydrogen, M' is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" is any of a Group IIA, IIIA, IV A, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen, carbon, or a halogen, 0.00014, X₂D₇, or DXD₄ group. In some of these embodiments, the compound has a conductivity at 27° C. of at least about 10^"8 S/cm. In some of these embodiments, the compound has a specific surface area of at least 15 m²/g. In some of these embodiments, the compound crystallizes in an ordered or partially disordered structure of the olivine (A_xMX0₄), NASICON (A^MM^iXO^), VOP0₄, LiFe(P₂0₇) or Fe₄(P₂0₇)₃ structure-types, and has a molar concentration of the metals (M'+M") relative to the concentration of the elements X that exceeds the ideal stoichiometric ratio y/z of the prototype compounds by at least 0.0001.

[0073] The cathode compound can also comprise a composition (Ai__aM"_a)_xM '_y(XD₄)_z, (Ai__aM"_a)_xM _y(DXD₄)_z, or (Ai__aM"_a)_xM '_y(X₂D₇)_z, wherein A is at least one of an alkali metal or hydrogen, M' is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen, carbon, or a halogen, 0.00014, X₂D₇, or DXD₄ group. In some of these embodiments, the compound has a conductivity at 27° C. of at least about 10^"8 S/cm. In some of these embodiments, the compound has a specific surface area of at least 15 m²/g. In some of these embodiments, the compound crystallizes in an ordered or partially disordered structure of the olivine (A_xMX0₄), NASICON (A_x,(M',M")₂(X0₄)₃), VOP0₄, LiFe(P₂0₇) or Fe₄P₂0₇)₃ structure-types, and has a molar concentration of the metals (M'+M") relative to the concentration of the elements X that exceeds the ideal stoichiometric ratio y/z of the prototype compounds by at least 0.0001. [0074] Still further, the cathode compound comprise a composition (Ab__aM"_a)_xM '_y(XD₄)_z, (A_b-_aM "_a)xM _y(DXD₄)_z, or (A_b__aM "_a)_xM '_y(X₂D₇)_z, wherein A is at least one of an alkali metal or hydrogen, M' is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M" any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is at least one of oxygen, nitrogen, carbon, or a halogen, 0.0001<A<0.1, z x, that such values have and than greater are zero y, (b-a)_x plus the quantity ax times the formal valence or valences of M " plus y times the formal valence or valences of M' is equal to z times the formal valence of the XD₄, X₂D₇ or DXD₄ group. In some of these embodiments, the compound has a conductivity at 27° C. of at least about 10^~8 S/cm. In some of these embodiments, the compound has a specific surface area of at least 15 m²/g. In some of these embodiments, the compound crystallizes in an ordered or partially disordered structure of the olivine (A_xMX0₄), NASICON

(A_x(M',M")₂(X0₄)₃), VOP0₄, LiFe(P₂0₇) or Fe₄(P₂0₇)₃ structure-types, and has a molar concentration of the metals (M '+M ") relative to the concentration of the elements X that exceeds the ideal stoichiometric ratio y/z of the prototype compounds by at least 0.0001.

[0075] Preferred cathode compounds are described in US Patent No. 7338734 and US Published application no. 2009/0123813, both incorporated herein by reference. The preferred blended cathode materials are described in USSN 61/524532, filed 8/17/11, and USSN 61/511,280, filed 7/25/11, also incorporated herein by reference.

[0076] In some embodiments, the cathode material is preferably a lithiated metal phosphate. In one or more embodiments the lithiated metal phosphate is lithiated iron phosphate.

[0077] The cathode material may also be affixed to a support using a suitable binder. Known supports for this purpose are aluminum, aluminum alloys, titanium, stainless steel, and the like. Acetylene black may also be included in the cathode.

[0078] For lithium ion batteries, the anode is preferably fabricated using a material capable of intercalating lithium. Various metal phosphates, metal oxides and chalcogenides satisfy this requirement, including especially iron phosphate, tin oxide, molybdenum oxide, tungsten oxide, and titanium disulfide.

[0079] Any suitable form of carbon may alternatively be used for the anode, include coke, synthetic or natural graphite, mesophase microbeads, a soft or hard disordered carbon, and the like.

[0080] Combinations of anode materials are also contemplated. It is particularly contemplated, however, that the anode material comprises at least 15%, 25%, 50%>, 75%> or 90% of a compound selected from the group comprising at least one metal oxide, at least one chalcogenide, and at least one form of carbon, and at least of silicone or Si/C composites

[0081] In preferred embodiments the electrodes are formed by mixing a polymeric binder with the cathode and anode materials in an appropriate liquid medium such as an organic solvent. This forms a paste or slurry, which is then coated onto a current collector grid, foil or mesh. The resulting intermediates are then pressed into a sheet form, dried and cut to appropriate dimensions.

[0082] Types of the binder used for the fabrication of the electrode is not particularly limited as far as it is stable to the solvent and electrolytic solution used in the fabrication of the electrode. Examples of the binder include resinous polymers such as polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, and cellulose; rubbery polymers such as styrene-butadiene rubber, isoprene rubber, butadiene rubber, and ethylene -propylene rubber; thermoplastic elastomeric polymers such as

styrene-butadiene-styrene block copolymer and its hydrogenated product,

styrene-ethylene-butadiene-styrene block copolymer and its hydrogenated product, and styrene-isoprene-styrene block copolymer and its hydrogenated product; flexible resinous polymers such as syndiotactic 1 ,2-polybutadiene, ethylene-vinyl acetate copolymer, and propylene-a-olefm (having 2 to 12 carbon atoms) copolymer; and fluorocarbon polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and polytetrafluoroethylene-ethylene copolymer.

Separator

[0083] Separator materials in battery cells are, in some instances, formed from bodies of porous polymer materials. In other instances, separator materials are formed from bodies of fibrous or particulate material, and such materials can include glass fibers, mineral fibers such as asbestos, ceramics, synthetic polymeric fibers as well as natural polymeric fibers such as cellulose.

Electrolyte Composition

[0084] An electrolyte may occur in any form, including liquid, semi-solid, or even solid. Of course, the electrolyte must cooperate with the active electrode material(s) to provide chemical reactions that store and release electrical energy, and many such chemistries are already known. [0085] Non-aqueous electrolyte solvents are preferred in certain embodiments, and may include cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; cyclic esters such as γ-butyrolactone and γ -valerolactone; chain esters such as methyl acetate and methyl propionate; cyclic ethers such as tetrahydrofuran, 2-methyl tetrahydrofuran and tetrahydropyran; chain ethers such as dimethoxyethane and

dimethoxymethane; cyclic phosphoric acid esters such as ethylene methyl phosphate and ethyl ethylene phosphate; chain phosphoric acid esters such as trimethyl phosphate and triethyl phosphate; halides thereof; sulfur-containing organic solvents, Vinyl ethylene carbonate (VEC) and Fluoroethylenecarbonate (FEC), Poly(ethylene glycol) diacrylate. The organic solvent may be used singly, or two or more of such solvents may be used in combination.

[0086] Examples of the solute used for the nonaqueous electrolytic solution are inorganic lithium salts such as LiC10₄, LiPF₆, LiBF₄ ; and fluorine-containing organic lithium salts such as LiCF₃ S0₃, LiN (CF₃ S0₂₎₂, LiN (CF₃ CF₂ S0₂₎₂, LiN (CF₃ S0₂₎ (C₄ F₉ S0₂₎ and LiC (CF₃ S0₂₎₃. These solutes may be used singly or in combination of two or more. Molar concentration of the lithium salt as a solute in the electrolytic solution is preferably within a range from 0.5 to 2.0 mol/1. In a preferred embodiment, LiPF6 is used.

[0087] A general electrolyte may be stable or unstable on the electrode, e.g. the anode. Many known electrolytes having desirable characteristics such as low volatility, high flash point, low freezing point, or high dielectric constant, for example, are unstable on the electrodes and will ultimately affect the formation of the solid electrolyte interface (SEI).

[0088] In some embodiments, the sulfur trioxide amine complex is present in the electrolyte solution in an amount effective to retard electrolyte degradation and provide improved cycle life of the battery Preferably, the electrolyte contains from 0.01%(wt) to 3%(wt) of the sulfur trioxide trimethylamine complex. Most preferably, the electrolyte contains from 0.1%(wt) to l%(wt) of the sulfur trioxide trimethylamine complex. .

[0089] In some embodiments, the additive promotes the formation of SEI that is highly conductive to lithium ions, thus leading to an improvement in battery capacity retention and decreased cell impedance after storage. In a preferred embodiment, the formed SEI allows for high Li⁺ ion conductivity while isolating electronic transport. In some embodiments, the additive suppresses the reduction and decomposition of the electrolyte solvent at the electrode (e.g., anode), reducing gas formation. The electrolyte is chosen to be stable within the electrochemical cell comprising cathodes of selected transition metal polyanion compounds. [0090] Methods for fabricating the nonaqueous electrolytic solution cell using such nonaqueous electrolytic solution, negative electrode (anode), positive electrode (cathode), outer container and separator, is of no specific limitation, and can properly be selected from those being generally employed. The nonaqueous electrolytic solution cell of the present invention may include, if necessary, a gasket, a sealing plate and a cell case besides such nonaqueous electrolytic solution, negative electrode, positive electrode, outer can or pouch material and separator.

[0091] The present invention will be explained in more detail with reference to the following examples. Materials, amounts of uses, ratios, operations and so forth described hereinafter can be properly be altered without departing from the spirit of the present invention. The scope of the present invention, therefore, is not limited to specific examples described below. The invention is applicable to any form of battery, e.g. prismatic, button-cell, can, etc.

Example 1

[0092] Two electrolyte solutions were fabricated, one with and one without a sulfur trioxide pyridine complex additive.

[0093] The composition with the additive consisted of:

[0094] 1.15M LiPFg in EC/PC/EMC/DEC = 30:5:55: 10 v/v% + 0.5wt% sulfur trioxide pyridine complex.

[0095] The composition without the additive consisted of:

[0096] 1.15M LiPF6 in EC/PC/EMC/DEC = 30:5:55: 10 v/v%

[0097] As used above: "EC" denotes ethylene carbonate; "PC" denotes propylene carbonate; "EMC" denotes ethylmethyl carbonate; and "DEC" denotes diethyl carbonate.

[0098] Figure 1 shows a photograph of two electrolyte samples after 2 month storage at 55C . The sample on the left 110, labeled "Electrolyte + Additive" is an electrolyte containing the sulfur trioxide pyridine complex. The sample on the right 120, is the composition without the additive. The photograph shows a smaller color change (e.g., darkening) of electrolyte with the additive 110 as compared to that without the additive 120. The color change is due to the thermal decomposition of electrolyte. The reduced color change indicates that the sulfur trioxide amine complex additive improves the thermal stability of electrolyte, leading to better result for calendar life.

Example 2

[0099] A battery was fabricated using a graphitic anode, a LiFeP0₄-containing cathode and the electrolytes of three different compositions: [0100] 1.15M LiPF6 in EC/PC/EMC/DEC = 30:5:55:10 v/v% + PS 2wt%

[0101] 1.15M LiPF6 in EC/PC/EMC/DEC = 30:5:55: 10 v/v% + Siloxane material

[0102] 1.15M LiPFg in EC/PC/EMC/DEC = 30:5:55: 10 v/v% + 0.5wt% sulfur trioxide

[0103] As used above, "PS" denoted propane sultone. Propane sultone is a known anti-gassing agent in electrolytes. It is known to deleteriously increase cell impedance. The siloxane material includes, for example aminopropyl triethoxysilane. Siloxane is another conventional additive used to trap HF from electrolyte solution. Siloxane is not effective in promoting cell life and or preventing electrolyte decomposition, as shown below.

[0104] Figures 2A-C show boxplots of retained and recovered capacity for batteries fabricated with the three electrolyte compositions above. Figure 2A show the % retained capacity after 1 month storage at 55°C. Retained capacity is measured as a first discharge of the cell after storage. Retained capacity is lower than initial capacity and includes some reversible and some irreversible capacity loss. Figure 2B show the % recovered capacity after 1 month storage at 55°C, recovered at a low discharge rate. Recovered capacity is measured after an initial discharge of the cell is used to measure retained capacity. Recovered capacity is typically higher than retained capacity as some reversible loss capacity has been recovered upon cycling. Figure 2C show the % recovered capacity after 1 month storage at 55°C, recovered at a high discharge rate of 6.5C. The plots show a clear advantage of the sulfur trioxide additive over the other electrolyte compositions in terms of retained and recovered charge capacities. This difference is most noticeable at high discharge rates, especially in comparison to the electrolyte composition with the siloxane additive.

[0105] Figures 3A-C show boxplots of DC resistance for batteries fabricated with the three electrolyte compositions above. Figure 3 A shows the resistance of each cell before storage, Figure 3B shows the resistance of each cell after storage for 1 month at 55°C, and Figure 3C shows the % change in resistance before and after storage for the three batteries. Remarkably, only the battery with the sulfur trioxide additive showed a decrease in cell impedance after storage.

[0106] Figure 4 shows a plot of capacity versus cycle number for batteries with an without the sulfur trioxide additive. The cycles were performed at 1C/-1C rates at 35°C. The electrolyte compositions consisted of (1) a control composition that included no additives, (2) a composition that included a siloxane additive, (3) a composition that included a sulfur trioxide pyridine additive, and (4) a composition that included γ-butyrolactone (GBL). It is clear that discharge capacity is not deleteriously affected by the presence of the additive. Typical cells can be cycled at least 500 times, preferably more than 1000 times and most preferably more than 2000 times.

[0107] Thus, the additive improves electrolyte stability at elevated temperatures and helps prevent decomposition in the presence of water and HF. The combined effects of the sulfur trioxide pyridine complex result in improvement of electrolyte calendar life and cycle life.

Mechanism

[0108] Water contaminants are known to produce LiF in electrolyte using LiPF₆ salt. Water reacts with the PF₅ present in solution to produce fluoride ions (Reaction 1) or HF. These fluoride ions react with the Li⁺ ions present in solution, leading to the precipitation of LiF. Precipitated LiF highly impedes lithium ion transport through SEI layer on the electrode surface (e.g., anode). Additionally, HF can readily decompose to form hydrogen gas, which can lead to unwater swelling of the battery cell.

[0109] H₂0 + PF₅ -> F₃PO + 1/2H₂ + 2F^" (LiF precipitation with Li⁺) (1)

[0110] Without being bound by theory, it is believed that the sulfur trioxide pyridine complex acts as a salt-stabilizer and water-getter. The SO₃ group in the sulfur trioxide pyridine complex is a dehydrated form of sulfuric acid, H₂SO₄. Thus, SO₃ readily produces H₂SO₄ in the presence of water impurities in electrolyte. In this way, the sulfur trioxide functions as a water-getter, suppressing formation of HF. The resulting H₂SO₄ leads to precipitation of L1₂SO₄ instead of LiF, which is more ionically conductive than LiF. (Reaction 2). L1₂SO₄ precipitates as part of the SEI, hindering electronic transport and promoting ionic transport.

[0111] H2SO4 -> 1/2H₂ + S0₄ ^2" (L12SO4 precipitation with Li⁺) (2)

[0112] The pyridine group of the additive acts as a salt stabilizer. It forms quaternary amonium salt with HF, preventing it from decomposing in the electrolyte. The pyridine group also stabilizes PF₅ as Lewis base, further suppressing the decomposition of the LiPF₆ salt in electrolyte (Reaction 1).

[0113] An excess of H₂SO₄ formation to the sulfur trioxide additive may lead to corrosion metallic component, especially a Cu foil, which is a common anode current collector. In one or more embodiment, the corrosion reaction is suppressed by adding nitrile compounds such as succinonitrile or phenylnitirle into the electrolyte solution.

[0114] It will be appreciated that while a particular sequence of steps or combination of materials has been shown and described for purposes of explanation, the sequence or combination may be varied in certain respects, or the steps may be combined, while still obtaining the desired configuration. Additionally, modifications to the disclosed embodiment and the invention asclaimed are possible and within the scope of this disclosed invention.

Claims

CLAIMS What is claimed is:

1. A battery comprising: an anode, a cathode, and an electrolyte comprising a lithium salt and a sulfur trioxide amine complex that suppresses electrolyte decomposition, wherein, the cathode comprises a alkali transition metal oxoanion electroactive material.

2. The battery of clam 1 , wherein the alkali transition metal oxoanion material is selected from the group consisting of:

• a composition A_X(M JA "_a)_y(XD4)_z, A_X(M JA "_a)_y(DXD₄)_z, or

A_x(M'i__aM"_a)_y(X₂D7)_z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M " is any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.00014, X₂D₇, or DXD₄ group;

• a composition (Ai__aM "_a)_xM '_y(XD₄)_z, (Ai__aM "_a)_xM '_y(DXD₄)_z, or

(Ai__aM "_a)_xM _y(X₂D₇)_z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M " any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.00014, X₂D₇ or DXD₄ group. In some of these embodiments, the compound has a conductivity at 27° C of at least about 10^"8 S/c; and

• a composition (A_b__aM "_a)_xM '_y(XD₄)_z, (A_b__aM "_a)_xM '_y(DXD₄)_z, or

(A_b__aM "_a)_xM _y(X₂D₇)_z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M " any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.0001 <A<0.1 , z x, that such values have and than greater are zero y , (b-a)_x plus the quantity ax times the formal valence or valences of M " plus y times the formal valence or valences of M is equal to z times the formal valence of the XD₄, X₂D₇ or DXD₄ group.

3. A battery according to claim 2 where the alkali transition metal oxoanion comprises lithium metal phosphate.

4. A battery according to claim 1 where the sulfur trioxide amine complex is selected from the group comprising: sulfur trioxide trimethylamine complex; sulfur trioxide pyridine complex; sulfur trioxide triethylamine complex; sulfur trioxide N,N-dimethylfromide complex, or mixtures thereof.

5. A battery according to claim 3 where the sulfur trioxide amine complex comprises a sulfur trioxide pyridine complex.

6. A battery according to claim 1 where the electrolyte contains from 0.01%(wt) to 3%(wt) of said sulfur trioxide amine complex.

7. A battery according to claim 6 where the electrolyte contains from 0.1% (wt) to 1 %(wt) of said sulfur trioxide amine complex.

8. A battery according to claim 1 , wherein the molar concentration of the lithium salt is between 0.5 amd 2.0 mol/1.

9. A battery according to claim 1, wherein the lithium salt is selected from the group consisting of LiC10₄, LiPF₆, LiBF₄, LiCF₃ S0₃, LiN (CF₃ S0₂₎₂, LiN (CF₃ CF₂ S0₂₎₂, LiN (CF₃ S0₂₎ (C₄ F₉ S0₂₎ and LiC (CF₃ S0₂)₃.

10. A battery according to claim 1, wherein the electrolyte further comprises aprotic solvents.

11. A battery according to claim 10, wherein the solvent comprises at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, γ-butyrolactone, γ -valerolactone, methyl acetate, methyl propionate, tetrahydrofuran, 2-methyl tetrahydrofuran, tetrahydropyran, dimethoxy ethane,

12. A battery according to claim 10, wherein the solvent comprises a mixture of ethylene carbonate, propylene carbonate, ethylmethyl carbonate, and diethyl carbonate.

13. A battery according to claim 10, wherein the anode comprises graphite.

14. A battery comprising : an anode, a cathode, and an electrolyte comprising a lithium salt, a sulfur trioxide amine complex that suppresses electrolyte decomposition, and a nitrile compound, wherein, the cathode comprises a alkali transition metal oxoanion electroactive material selected from the group consisting of:

• a composition A_X(M 'i__aM "_a)_y(XD4)_z, A_X(M 'i__aM "_a)_y(DXD₄)_z, or

A_x(M 'i__a "_a)_y(X₂D₇)_z, wherein A is at least one of an alkali metal, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M " is any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, and a halogen, 0.00014, X₂D₇, or DXD₄ group;

(Ai__aM"_a)_xM _y(X₂D₇)_z, wherein A is at least one of an alkali metal or hydrogen, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M " any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.00014, X₂D₇ or DXD₄ group. In some of these embodiments, the compound has a conductivity at 27° C of at least about 10^"8 S/c; and

(A_b__aM "_a)_xM _y(X₂D₇)_z, wherein A is at least one of an alkali metal or hydrogen, M is a first-row transition metal, X is at least one of phosphorus, sulfur, arsenic, boron, aluminum, silicon, vanadium, molybdenum and tungsten, M " any of a Group IIA, IIIA, IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB, IVB, VB, and VIB metal, D is oxygen, 0.0001<A<0.1, z x, that such values have and than greater are zero y, (b-a)_x plus the quantity ax times the formal valence or valences of M" plus y times the formal valence or valences of M is equal to z times the formal valence of the XD₄, X₂D₇ or DXD₄ group.

15. A battery according to claim 14 where the sulfur trioxide amine complex is selected from the group comprising: sulfur trioxide trimethylamine complex; sulfur trioxide pyridine complex; sulfur trioxide triethylamine complex; sulfur trioxide N,N-dimethylfromide complex, or mixtures thereof, and where the nitrile compound is selected from succinonitrile, cyanobenzene, or mixtures thereof.

16. A battery according to claim 15 where the sulfur trioxide amine complex is a sulfur trioxide pyridine complex.

17. A battery according to claim 16 where the electrolyte contains from 0.01%(wt) to 3%(wt) of said sulfur trioxide amine complex.

18. A battery according to claim 17 where the electrolyte contains from 0.1%(wt) to l%(wt) of said sulfur trioxide amine complex.

19. A battery according to claim 15 where the electrolyte contains from 0.01%(wt) to 3%(wt) of said nitrile compound.

20. A battery according to claim 19 where the electrolyte contains from l%(wt) to 2%(wt) of said nitrile compound.