JP5402216B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

 The present invention relates to a nonaqueous electrolyte battery having an improved nonaqueous electrolyte.

In recent years, non-aqueous electrolyte batteries using various non-aqueous electrolytes capable of obtaining a high energy density have attracted attention as power supplies for electronic devices, power storage power supplies, electric vehicle power supplies, etc., which are becoming higher performance and smaller. .

Currently, commercially available lithium ion batteries use lithium cobalt oxide (LiCoO ₂ ) for the positive electrode, use a carbon material that absorbs and releases lithium ions for the negative electrode, and use non-aqueous electrolytes such as ethylene carbonate and diethyl carbonate. A non-aqueous electrolyte in which a lithium salt is dissolved in a liquid organic solvent at room temperature is used.

On the other hand, there is a lithium ion battery using a room temperature molten salt as a non-aqueous electrolyte. For example, Patent Document 1 uses a room temperature molten salt composed of a cyclic quaternary ammonium organic cation having an aromatic ring typified by an imidazolium cation and a non-aqueous electrolyte containing a lithium salt, and lithium titanium as a negative electrode. There has been proposed a battery using a negative electrode active material such as an oxide, whose operating potential is nobler than 1 V with respect to the potential of metallic lithium. According to this technique, since the electrolyte is flame retardant, a battery suitable for an application requiring particularly high safety can be obtained.

Patent Documents 2 to 4 describe batteries using a carbon material for the negative electrode of a battery using the same room temperature molten salt. However, when a room temperature molten salt composed of a cyclic quaternary ammonium organic cation having an aromatic ring typified by an imidazolium cation is used as the nonaqueous electrolyte, the nonaqueous electrolyte is 1 V (vs Li / Li). ⁺ ) It is easy to be decomposed at a potential of less than or equal to, and when the negative electrode is operated at 1 V (vs. Li ^/ Li ⁺ ) or less, the battery performance is extremely poor. For this reason, as described in Patent Document 1, it is necessary to use a negative electrode active material that has an operating potential nobler than 1 V with respect to the potential of metallic lithium, such as lithium titanium oxide. Therefore, if a negative electrode active material that operates at a potential of 1 V (vs. Li ^/ Li ⁺ ) or less, such as a carbon material, is used for the negative electrode, a battery with good performance cannot be obtained, and a battery with high energy density is obtained. There was a problem that it was not possible.

JP 2001-319688 A JP-A-10-92467 JP-A-11-86905 JP-A-11-260400

Study Group of Molten Salt / Thermal Technology “Basics of Molten Salt / Thermal Technology”, Agne Technology Center, 1993, 313p (ISBN 4-900041-24-6)

The present invention has been made in view of the above problems, and provides a non-aqueous electrolyte battery having a high energy density while ensuring high safety obtained by using a room temperature molten salt as a non-aqueous electrolyte. This is one purpose.

The inventors of the present invention have intensively studied to solve the above problems, and surprisingly, when the type of anion contained in the nonaqueous electrolyte is specified, it is surprisingly surprising that the negative electrode could not be used conventionally. It was found that the decomposition of the non-aqueous electrolyte containing the room temperature molten salt can be greatly suppressed even when operated at a low potential, and the present invention has been achieved. That is, the configuration of the present invention is as follows. However, the action mechanism includes estimation, and the success or failure of the action mechanism does not limit the present invention.

The present invention uses a nonaqueous electrolyte containing a cyclic quaternary ammonium organic cation having a five-membered or six-membered aromatic ring, a lithium cation, and an anion, and includes a positive electrode and a negative electrode. In the water electrolyte battery, the negative electrode operates at a potential of 1.0 V (vs. Li / Li ⁺ ) or less in the battery, and the non-aqueous electrolyte is N (C _n F _{2n + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) ⁻ (where n is an integer of 1 to 4 and m is an integer of 1 to 4) and an inorganic anion It is a non-aqueous electrolyte secondary battery.

The cyclic quaternary ammonium organic cation includes an imidazolium cation having a structure of (Chemical Formula 1), a pyrrolium cation having a structure of (Chemical Formula 2), a pyrazolium cation having a structure of (Chemical Formula 3), and (Chemical Formula) Ru can be one or more selected from the group consisting of pyridinium cation having a structure of 4).

(However, R1 and R3 are alkyl groups having 1 to 6 carbon atoms, and R2, R4, and R5 are either hydrogen atoms or alkyl groups having 1 to 6 carbon atoms.)

(However, R1 and R2 are alkyl groups having 1 to 6 carbon atoms, and R3 to R6 are either hydrogen atoms or alkyl groups having 1 to 6 carbon atoms.)

(However, R1 and R2 are alkyl groups having 1 to 6 carbon atoms, and R3 to R5 are either hydrogen atoms or alkyl groups having 1 to 6 carbon atoms.)

(However, R1 is an alkyl group having 1 to 6 carbon atoms, and R2 to R6 are either a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)

That is, according to the present invention, in a non-aqueous electrolyte battery using a cyclic quaternary ammonium organic cation having an aromatic ring as an electrolyte , N (C _n F _{2n + 1} S O ₂ ) (C _{m ^{F 2m + 1 SO 2) -}} ( where, n is 1 to 4 integer, m is 1 or 4 by containing the electrolyte integer) follows, the negative electrode potential 1V in a conventional battery (V.S.Li / Li ⁺ ) or less, it is possible to remarkably suppress the remarkable electrolyte decomposition.

Although the cause of this is not necessarily clear, in the process of initial charging performed after the battery is assembled, the nitrogen-containing organic anion forms a good protective film on the negative electrode surface, and this protective film has the aromatic ring. It is presumed that the decomposition of the cyclic quaternary ammonium organic cation is suppressed.

That is, in a general lithium ion battery, a film formed by decomposing an organic solvent mainly constituting an electrolyte on a negative electrode surface having a base potential of 1 V (vs Li ^/ Li ⁺ ) or less is a negative electrode. It is thought that the further decomposition of the electrolyte is suppressed. On the other hand, when a normal temperature molten salt composed of a cyclic quaternary ammonium organic cation having an aromatic ring is used as the electrolyte, the cyclic quaternary ammonium organic cation having an aromatic ring is similarly a negative electrode surface having a base potential In this case, the protective coating does not form a coating that can sufficiently suppress further decomposition of the cyclic quaternary ammonium organic cation having an aromatic ring, so that the initial charging can be performed. Therefore, it is considered that the decomposition of the electrolyte containing the room temperature molten salt proceeds. However, according to the present invention, when the non-aqueous electrolyte contains a nitrogen-containing organic anion, a good protective film is formed, thereby suppressing the decomposition of the cyclic quaternary ammonium organic cation having an aromatic ring. Therefore, the negative electrode is 1 V v. s. It is considered that good performance could be exhibited even when operated at Li / Li ⁺ or lower.

The electrolyte of the battery of the present invention may further contain an organic solvent used for a general lithium ion battery. At this time, it is preferable to select and use an organic solvent having a dielectric constant of 35 or more because the effects of the present invention can be exhibited more effectively.

Examples of the organic solvent having a dielectric constant of 35 or more include propylene carbonate, ethylene carbonate, γ-butyrolactone, γ-valerolactone, tetramethylene sulfone, dimethyl sulfoxide, and the like, but are not limited thereto. Especially, it is preferable from the point of the said effect to use ethylene carbonate as an organic solvent with the said dielectric constant of 35 or more.

Although this mechanism of action is not necessarily clear, an organic solvent having a dielectric constant of 35 or more typified by ethylene carbonate is formed on the surface of the negative electrode during the initial charge due to the presence of nitrogen-containing organic anions in the electrolyte. It is presumed that the protective film becomes better and the decomposition of the cyclic quaternary ammonium organic cation having an aromatic ring is more effectively suppressed.

According to the present invention, the negative electrode can be operated with high performance in a potential region of 0 to 1.0 V while using a room temperature molten salt composed of a cyclic quaternary ammonium cation having an aromatic ring as a non-aqueous electrolyte. Therefore, it is possible to provide a nonaqueous electrolyte battery having a high energy density while ensuring high safety obtained by using a room temperature molten salt as a nonaqueous electrolyte.

It is sectional drawing of the nonaqueous electrolyte battery of this invention.

The present invention is described in detail below, but the present invention is not limited to these descriptions.

First, the room temperature molten salt used in the nonaqueous electrolyte battery of the present invention will be described in detail.

In the present specification, the room temperature molten salt refers to a salt that is at least partially liquid at room temperature. The normal temperature is a temperature range in which the battery is assumed to normally operate. The upper limit is about 100 ° C., in some cases about 60 ° C., and the lower limit is about −50 ° C., and in some cases about −20 ° C. On the other hand, an inorganic molten salt such as Li ₂ CO ₃ —Na ₂ CO ₃ —K ₂ CO ₃ used for various electrodepositions as described in Non-Patent Document 1 has a melting point of 300 ° C. or higher. However, it is not a liquid in the temperature range in which the battery is normally assumed to operate, and is not included in the room temperature molten salt in the present invention.

Since the non-aqueous electrolyte battery according to the present invention uses a room temperature molten salt, it is liquid at room temperature, has almost no volatility, and has the properties of a room temperature molten salt such as flame retardancy or nonflammability. since the one having, overcharge, that Do and excellent safety in safety and a high-temperature environment during Abuyusu such as overdischarge or short.

Examples of the imidazolium cation represented by (Chemical Formula 1) include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-butyl-3-methylimidazole as dialkylimidazolium ions. Examples of trialkylimidazolium ions include 1,2,3-trimethylimidazolium ions, 1,2-dimethyl-3-ethylimidazolium ions, 1,2-dimethyl-3-propylimidazolium ions, Examples include 1-butyl-2,3-dimethylimidazolium ion, but are not limited thereto.

Examples of the pyrrolium cation represented by (Chemical Formula 2) include 1,1-dimethylpyrrolium ion, 1-ethyl-1-methylpyrrolium ion, 1-methyl-1-propylpyrrolium ion, and 1-butyl-1-methyl. Although pyrrolium ion etc. are mentioned, it is not limited to these.

Examples of the pyrazolium cation represented by (Chemical Formula 3) include 1,2-dimethylpyrazolium ion, 1-ethyl-2-methylpyrazolium ion, 1-propyl-2-methylpyrazolium ion, and 1-butyl. Examples include, but are not limited to, -2-methylpyrazolium ion.

As the pyridinium cation represented by (Chemical Formula 4), N-methylpyridinium ion, N-ethylpyridinium ion, N-propylpyridinium ion, N-butylpyridinium ion 1-ethyl-2-methylpyridinium ion, 1-butyl-4 -Methylpyridinium ion, 1-butyl-2,4-dimethylpyridinium ion, and the like are exemplified, but not limited thereto.

The electrolyte of the battery of the present invention must contain at least one nitrogen-containing organic anion. In the present invention, the nitrogen-containing organic anion emission _{is, N (C n F 2n +} 1 SO 2) (C m F 2m + 1 SO 2) -, ( where, n is 1 to 4 integer, m is 1 to 4 integer) to. Examples of such nitrogen-containing organic anions include N (CF ₃ SO ₂ ) ₂ ⁻ , N (C ₂ F ₅ SO ₂ ) ₂ ⁻ , and N (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ^−. Such anions are easily available and preferred.

The electrolyte of the present battery must have an inorganic anion other than at least one or more nitrogen-containing organic anion coexist. Of these, the presence of inorganic anions such as BF ₄ ⁻ and PF ₆ ⁻ is preferable because corrosion of the current collector (particularly aluminum) can be prevented. In particular, the corrosion prevention effect is particularly prominent when the nitrogen-containing organic anion contains N (CF ₃ SO ₂ ) ₂ ^— .

In the electrolyte of the battery of the present invention, anions other than the nitrogen-containing organic anions and inorganic anions described above may coexist. For example, C (CF ₃ SO ₂ ) ₃ ⁻ , C (C ₂ F ₅ SO ₂ ) ₃ ^{— and the} like may be used.

By configuring the electrolyte of the battery of the present invention as described above, an active material that operates at a potential of 1.0 V (vs. Li / Li ⁺ ) or less in the battery while using a room temperature molten salt in the battery. Even if is used, good battery performance is exhibited. In other words, in the battery of the present invention, it is extremely preferable to design the battery so that the potential of the negative electrode changes in the range of 0 V to 1.0 V when the battery is charged and discharged. Thereby, while using room temperature molten salt, a high terminal voltage can be taken out and the battery which can be used stably can be provided.

The “active material that operates at a potential of 1.0 V (vs. Li / Li ⁺ ) or less in the battery” that can be used for the negative electrode of the battery of the present invention is not particularly limited. According to the present invention, since the negative electrode active material can be satisfactorily operated at a potential of 1 V (vs. Li / Li ⁺ ) or less, the negative electrode active material used for the negative electrode of the battery of the present invention is discharged from the active material. It is preferable to select one having a flat portion of the curve at 1 V (vs. Li / Li ⁺ ) or less. That is, an active material in which the main part of the potential at which the negative electrode transitions during an effective discharge process of the battery is 1 V (vs. Li / Li ⁺ ) or less is preferable. Specifically, the amount of lithium ions that the negative electrode active material can release in the entire potential region is Q1, and the amount of lithium ions that the negative electrode active material can release in the potential region of 1 V (vs Li / Li ⁺ ). Is preferably a negative electrode active material having a Q2 / Q1 value of at least 0.2, preferably 0.5 or more, and more preferably 0.8 or more.

Examples of the negative electrode active material that can be used in the battery of the present invention include lithium metal, lithium alloy (lithium such as lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloy). In addition to (metal-containing alloys), alloys capable of occluding and releasing lithium, carbon materials (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

Among these, it is preferable to use a carbon material. This is due to the following reason. In the carbon material, the potential at the time of battery assembly greatly exceeds 1.0 V (vs Li / Li ⁺ ), and the potential at which decomposition of the cyclic quaternary ammonium organic cation having an aromatic ring starts (about 1.1 V). More noble, the negative electrode potential gradually changes in a base direction in the first charging process performed after the assembly of the battery, and the protective coating is formed in this process. Therefore, the physical properties of the protective coating can be arbitrarily designed by devising the initial charge conditions (initial charge rate, initial charge current waveform, initial charge process (intermittent charge, etc.), initial charge temperature, etc.). Therefore, it is very preferable.

For the same reason, a negative electrode active material mainly composed of silicon is also preferable in that the physical properties of the protective coating can be arbitrarily designed.

On the other hand, when metallic lithium or a lithium alloy is used, the apparent initial efficiency value is observed to be high, but the coating as described above is rapidly formed in the process of initial charging, so that the quaternary ring having an aromatic ring is formed. It is difficult to be a protective film that can effectively suppress decomposition of ammonium organic cation. Furthermore, since the construction / disintegration of the coating is repeated each time the charge / discharge cycle is repeated, the charge / discharge cycle performance tends to be inferior.

As the carbon material, for example, graphite such as artificial graphite and natural graphite is preferable. In particular, graphite in which the surface of the negative electrode active material particles is modified with amorphous carbon or the like is desirable because it generates less gas during charging.

Below, the analysis result by X-ray diffraction etc. of the graphite which can be used suitably is shown;
Lattice spacing (d002) 0.333 to 0.350 nm
a-axis direction crystallite size La 20 nm or more c-axis direction crystallite size Lc 20 nm or more True density 2.00 to 2.25 g / cm 3

It is also possible to modify graphite by adding a metal oxide such as tin oxide or silicon oxide, phosphorus, boron, amorphous carbon or the like. In particular, by modifying the surface of graphite by the above-described method, it is possible to suppress the decomposition of the electrolyte and improve the battery characteristics, which is desirable. In addition to graphite, lithium metal-containing alloys such as lithium metal, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys can be used in combination. Graphite in which lithium is inserted by chemical reduction can also be used as the negative electrode active material.

The positive electrode is not particularly limited. For example, an electrode composed of a lithium-containing transition metal oxide is preferably used. Further, lithium-containing transition metal oxides, lithium-containing phosphates, lithium-containing sulfates and the like may be used alone or in combination. Examples of the lithium-containing transition metal oxide include Li—Co based composite oxide, Li—Mn based composite oxide, and Li—Ni based composite oxide. Here, a part of the transition metals (Co, Mn, Ni) is one or more metals selected from Group I to Group VIII metals (for example, Li, Ca, Cr, Ni, Fe, Co, Mn). Those substituted with an element are preferred) can also be suitably used. Examples of the Li—Mn composite oxide include those having a spinel crystal structure and those having an α-NaFeO 2 crystal structure, both of which are preferably used. These lithium-containing transition metal oxides can be appropriately selected according to the battery design, or can be used in combination.

In addition, other positive electrode active materials may be used by mixing with the lithium-containing compound. Examples of other positive electrode active materials include group I metal compounds such as CuO, Cu ₂ O, Ag ₂ O, CuS, and CuSO ₄ , TiS _{2, SiO 2,} IV group metal compound of SnO, _{etc., V 2 O 5, V 6} O 12, VO x, Nb 2 O 5, Bi 2 O, V metal compounds such as _Sb 2 _{O 3, CrO 3, cr 2 O 3, MoO 3,} MoS 2, WO 3, SeO VI metal compounds such as _2, VII metal compounds such as _{MnO 2, Mn 2 O 3,} Fe 2 O 3, FeO, Fe 3 O 4, Ni _{2 O 3, NiO 2, CoO} 2, represented by CoO VIII group metal compound such as such as, for example, lithium - cobalt composite oxide and lithium - manganese-based composite oxide such as metal compounds, further, disulfide Polypyrrole, polyaniline, polyparaphenylene, polyacetylene, although conductive polymer compounds such as polyacene-based material include, but are not limited thereto.

Moreover, in the oxide fired body according to the battery of the present invention, a part of the transition metal may be substituted with the different element M. For example, the chemical composition formula _{Li a Mn b Ni c Co d} M e O 2 ( where, 0 <a <1.3,0 <d + e <1, e <0.1, b + c + d + e = 1) and represented those There may be. Here, M is one or more elements of Group 1 to 16 excluding Mn, Ni, Co, Li and O, and elements that can be exchanged for Mn, Ni, and Co are preferable. Examples of such elements include Be, B, V, C, Si, P, Sc, Cu, Zn, Ga, Ge, As, Se, Sr, Mo, Pd, Ag, Cd, In, Sn, and Sb. Te, Ba, Ta, W, Pb, Bi, Co, Fe, Cr, Ni, Ti, Zr, Nb, Y, Al, Na, K, Mg, Ca, Cs, La, Ce, Nd, Sm, Eu , Tb and the like, but are not limited thereto. These may be used alone or in combination of two or more. Among these, it is more preferable to use any of Al, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, In, Sn, and Yb.

The lithium salt content in the non-aqueous electrolyte used in the battery of the present invention is preferably in the range of 0.1 to 3 mol / l. When the content of the lithium salt is less than 0.1 mol / l, the electrolyte resistance is too large, and the charge / discharge efficiency of the battery decreases. On the contrary, if the content of the lithium salt exceeds 3 mol / l, the melting point of the non-aqueous electrolyte rises and it becomes difficult to maintain a liquid state at room temperature. Furthermore, since the reduction potential of the nonaqueous electrolyte shifts to the base, the potential stability on the reduction side can be improved, and the mobility of lithium ions at low temperatures can be expected due to the disappearance of the melting point. The lithium salt content in the water electrolyte is desirably in the range of 0.5 to 2 mol / l.

The non-aqueous electrolyte in the present invention may be used by solidifying the non-aqueous electrolyte into a gel by combining a polymer other than a lithium salt and a room temperature molten salt. Here, examples of the polymer include, for example, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, various acrylic monomers, methacrylic monomers, acrylamide monomers, allyl monomers, and styrene monomers. Examples include, but are not limited to, polymers. These may be used alone or in combination of two or more.

The non-aqueous electrolyte in the present invention may be used by adding an organic solvent that is liquid at room temperature in addition to a lithium salt and a room temperature molten salt. Here, as said organic solvent, the organic solvent generally used for the electrolyte solution for nonaqueous electrolyte batteries can be used. For example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, .gamma.-butyrolactone, propylene Oh lactone, valerolactone, tetrahydrofuran, dimethoxyethane, diethoxyethane, although such methoxyethoxy ethane, limited to Is not to be done. However, since these organic solvents are flammable as described above, if the addition amount is too large, the non-aqueous electrolyte may be flammable and sufficient safety may not be obtained, which is not preferable. Moreover, the phosphate ester which is a flame-retardant solvent generally added to the electrolyte solution for nonaqueous electrolyte batteries can also be used. For example, trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl phosphate, methyl, phosphate, tripropyl, tributyl phosphate, although etc.-phosphate tri (trifluoroethyl) can be mentioned, it is limited to It is not a thing. These may be used alone or in combination of two or more.

The method and means for producing the nonaqueous electrolyte battery in the present invention are not particularly limited. For example, a power generation element composed of a positive electrode, a negative electrode, and a separator is placed in a battery package made of an exterior material. Then, a method may be used in which a nonaqueous electrolyte is injected into the battery package and finally sealed, and the positive electrode, the negative electrode, and the separator are connected to the positive electrode as in, for example, a coin-type battery. Each of the battery packages having a storage unit, a negative electrode storage unit, and a separator storage unit is stored independently, and then a nonaqueous electrolyte is injected into the battery package made of an exterior material, and finally sealed. You may use the method obtained by doing.

The positive electrode and the negative electrode are preferably produced using a conductive agent and a binder as constituent components in addition to the active material as a main constituent component.

The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one kind or a mixture thereof. .

Among these, as the conductive agent, acetylene black is desirable from the viewpoints of conductivity and coating properties. The addition amount of the conductive agent is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

As the binder, usually, thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, and the like These polymers having rubber elasticity, polysaccharides such as carboxymethylcellulose, and the like can be used as one or a mixture of two or more. When a binder having a functional group that reacts with lithium, such as a polysaccharide, is used in a lithium battery, it is desirable to deactivate the functional group by, for example, methylation. The addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

A positive electrode and a negative electrode active material, a conductive agent, and a binder are added to an organic solvent such as toluene or water, kneaded, formed into an electrode shape, and dried, whereby the positive electrode and the negative electrode can each be suitably produced.

The positive electrode is preferably in close contact with the positive electrode current collector, and the negative electrode is preferably in close contact with the negative electrode current collector. For example, the positive electrode current collector may be aluminum, titanium, stainless steel, nickel. In addition to baked carbon, conductive polymer, conductive glass, etc., the surface of aluminum, copper, etc. treated with carbon, nickel, titanium, silver, etc. for the purpose of improving adhesion, conductivity and oxidation resistance Can be used. In addition to copper, nickel, iron, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., the negative electrode current collector is adhesive, conductive, and oxidation resistant. For the purpose of improving the property, a material obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver or the like can be used. The surface of these materials can be oxidized.

Regarding the shape of the current collector, a film shape, a sheet shape, a net shape, a punched or expanded material, a lath body, a porous body, a foamed body, a formed body of fiber groups, and the like are used in addition to the foil shape. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

Among these current collectors, an aluminum foil excellent in oxidation resistance is used as a positive electrode current collector, and as a negative electrode current collector, it is stable in a reduction field, has excellent conductivity, and is inexpensive. It is preferable to use a copper foil, a nickel foil, an iron foil, and an alloy foil containing a part thereof. Further, the foil is preferably a foil having a rough surface surface roughness of 0.2 μmRa or more, whereby the adhesion between the positive electrode and the negative electrode and the current collector is excellent. Therefore, it is preferable to use an electrolytic foil because it has such a rough surface. In particular, an electrolytic foil that has been subjected to a cracking treatment is most preferable.

(Nonaqueous electrolyte 1)
1 mol of LiN (CF ₃ SO ₂ ) ₂ is dissolved in 1 liter of room temperature molten salt (EMITFSI) composed of 1-ethyl-3-methylimidazolium cation (EMI ⁺ ) and N (CF ₃ SO ₂ ) ₂ ⁻ anion. By doing so, the nonaqueous electrolyte 1 was obtained.

(Nonaqueous electrolyte 2)
1 mol of LiN (C ₂ F ₅ SO ₂ ) is added to 1 liter of a room temperature molten salt (EMIBETI) composed of 1-ethyl-3-methylimidazolium cation (EMI +) and N (C ₂ F ₅ SO ₂ ) ₂ ⁻ anion. ) ₂ was dissolved to obtain a nonaqueous electrolyte 2.

(Nonaqueous electrolyte 3)
1-ethyl-3-methylimidazolium cation (EMI +) and _{N (CF 3 SO 2) (} C 4 F 9 SO 2) - the ionic liquid 1 liter made of anionic, 1 mole of LiN _(CF 3 SO ₂ ) (C ₄ F ₉ SO ₂ ) was dissolved to obtain a nonaqueous electrolyte 3.

(Nonaqueous electrolyte 4)
1-ethyl-1-Mechirupiro Liu Mukachion and _{N (CF 3 SO 2) 2} - in ambient temperature molten salt 1 liter made of anion, by dissolving 1 mole of _{LiN (CF 3 SO 2) 2} , a non-aqueous electrolyte 4 Got.

(Nonaqueous electrolyte 5)
Ethyl 1 - 2 - Mechirupirazo Li Umukachion and _{N (CF 3 SO 2) 2} - in ambient temperature molten salt 1 liter made of anion, by dissolving 1 mole of _{LiN (CF 3 SO 2) 2} , a non-aqueous electrolyte 5 Got.

(Nonaqueous electrolyte 6)
N- butyl pyridinium cation (BPy ⁺⁾ and _{N (CF 3 SO 2) 2} - in ambient temperature molten salt (BPyTFSI) 1 liter made of anion, by dissolving 1 mole of _{LiN (CF 3 SO 2) 2} , non A water electrolyte 5 was obtained.

(Nonaqueous electrolyte 7)
1-ethyl-3-methylimidazolium cation (EMI ⁺⁾ and _{N (CF 3 SO 2) 2} - in ambient temperature molten salt (EMITFSI) 1 liter made of anion, by dissolving 1 mole of LiBF _4, non-aqueous An electrolyte 7 was obtained.

(Nonaqueous electrolyte 8)
1 mol of LiN (CF ₃ SO ₂ ) ₂ is dissolved in 1 liter of room temperature molten salt (EMITFSI) composed of 1-ethyl-3-methylimidazolium cation (EMI ⁺ ) and N (CF ₃ SO ₂ ) ₂ ⁻ anion. A non-aqueous electrolyte 8 was obtained by mixing 10 wt% diethyl carbonate (dielectric constant 2.82 at 20 ° C.).

(Nonaqueous electrolyte 9)
1 mol of LiN (CF ₃ SO ₂ ) ₂ is dissolved in 1 liter of room temperature molten salt (EMITFSI) composed of 1-ethyl-3-methylimidazolium cation (EMI ⁺ ) and N (CF ₃ SO ₂ ) ₂ ⁻ anion. The nonaqueous electrolyte 9 was obtained by mixing 10% by weight of ethylene carbonate (dielectric constant at 40 ° C. of 89.6).

(Nonaqueous electrolyte 10)
1 mol of LiN (CF ₃ SO ₂ ) ₂ is dissolved in 1 liter of room temperature molten salt (EMITFSI) composed of 1-ethyl-3-methylimidazolium cation (EMI ⁺ ) and N (CF ₃ SO ₂ ) ₂ ⁻ anion. By mixing 10% by weight of ethylene carbonate (dielectric constant at 40 ° C.) and 10% by weight of γ-butyrolactone (dielectric constant 39.1) with the non-aqueous electrolyte. 10 was obtained.

(Nonaqueous electrolyte 11)
1-ethyl-3-methylimidazolium cation (EMI ⁺⁾ and BF ₄ ^- to the room temperature molten salt (EMIBF ₄₎ 1 liter made of anion, by dissolving 1 mole of LiBF _4, to obtain a non-aqueous electrolyte 11 .

A cross-sectional view of the nonaqueous electrolyte battery according to this example is shown in FIG. The nonaqueous electrolyte battery according to this example is composed of a pole group 4 including a positive electrode 1, a negative electrode 2, and a separator 3, a nonaqueous electrolyte, and a metal resin composite film 5. The positive electrode 1 is formed by applying a positive electrode mixture 11 on a positive electrode current collector 12. The negative electrode 2 is formed by applying a negative electrode mixture 21 on a negative electrode current collector 22. The nonaqueous electrolyte is impregnated in the pole group 4. The metal resin composite film 5 covers the pole group 4 and is sealed on all four sides by heat welding.

Next, a method for producing a nonaqueous electrolyte battery according to this example will be described.

An oxide fired body having a layered α-NaFeO ₂ type crystal structure and having a composition represented by LiMn _0.167 Ni _0.167 Co _0.667 O ₂ was used as the positive electrode active material.

The positive electrode active material is mixed with acetylene black as a conductive agent, further mixed with an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as a binder, and this mixture is used as a positive electrode current collector 12 made of aluminum foil. After being coated on one side, the film was dried and pressed so that the thickness of the positive electrode mixture 11 was 0.1 mm. The positive electrode 1 was obtained by the above process.

The graphite as the negative electrode active material is mixed with an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as the binder, and this mixture is applied to one side of the negative electrode current collector 22 made of copper foil and then dried. The negative electrode mixture 21 was pressed so that the thickness was 0.1 mm. The negative electrode 2 was obtained by the above process. Note that the graphite, which is the negative electrode active material used here, has Q1 as the amount of lithium ions that the negative electrode active material can release in the entire potential region, and the negative electrode active material is 1 V (vs Li / Li ⁺ ). The value of Q2 / Q1 is substantially 0.8 or more when the amount of lithium ions that can be released in the potential region is Q2.

Separator 3 was obtained as follows. First, an ethanol solution in which 3% by weight of a bifunctional acrylate monomer having a structure represented by (Chemical Formula 5) is dissolved is prepared, and a polyethylene microporous membrane (average pore size 0.1 μm, porosity 50%) as a porous substrate is prepared. And coated with a thickness of 23 μm, weight of 12.52 g / m ² , air permeability of 89 seconds / 100 ml), the monomer is crosslinked by electron beam irradiation to form an organic polymer layer, and dried at a temperature of 60 ° C. for 5 minutes. It was. The separator 3 was obtained by the above process. The obtained separator 3 has a thickness of 24 μm, a weight of 13.04 g / m ² , and an air permeability of 103 seconds / 100 ml. The weight of the organic polymer layer is about 4% by weight with respect to the weight of the porous material. The thickness of the crosslinked layer was about 1 μm, and the pores of the porous base material were maintained as they were.

The pole group 4 was configured by facing the positive electrode mixture 11 and the negative electrode mixture 21, placing the separator 3 therebetween, and laminating the positive electrode 1, the separator 3, and the negative electrode 2 in this order. Accordingly, the capacity balance between the positive electrode and the negative electrode is designed so that the negative electrode potential becomes 0.05 V when the battery is charged to 4.2 V.

Next, the electrode group was brought into a reduced pressure state, and then immersed in a non-aqueous electrolyte in a reduced pressure state, whereby the positive electrode mixture 11, the negative electrode mixture 21, and the separator were impregnated with the non-aqueous electrolyte.

( Reference batteries 1 to 6, present invention battery 7 and reference batteries 8 to 10)
Using the nonaqueous electrolytes 1 to 10 described above as the nonaqueous electrolyte, nonaqueous electrolyte batteries were produced according to the above method. These are designated as reference batteries 1 to 6, inventive battery 7 and reference batteries 8 to 10, respectively.

(Comparative battery 1)
Using the nonaqueous electrolyte 11 described above as the nonaqueous electrolyte, a nonaqueous electrolyte battery was produced according to the method described above. This is referred to as the ratio較電pond 1.

(Initial charge / discharge efficiency test)
Using the reference batteries 1 to 6, the inventive battery 7, the reference batteries 8 to 10 and the comparative battery 1 assembled as described above, an initial charge / discharge efficiency test was performed. The initial charging was constant current and constant voltage charging, the current was 0.1 ItmA, the voltage was 4.2 V, and the charging time was 15 hours. At this time, the initial charge electricity quantity was measured with a coulomb meter. The initial discharge was a constant current discharge, the current was 0.1 ItmA, the final voltage was 2.7 V, and the initial discharge electricity was measured. The percentage of the ratio of the initial discharge electricity amount to the initial charge electricity amount was determined and was defined as “initial charge / discharge efficiency (%)”. The results are shown in Table 1.

As is clear from the results shown in Table 1, the comparative battery 1 that does not contain a nitrogen-containing organic anion in the nonaqueous electrolyte has extremely low initial charge / discharge efficiency. This is because the negative electrode potential was operated in a potential region of 1 V (vs Li / Li ⁺ ) or less while using a room temperature molten salt composed of a cyclic quaternary ammonium organic cation having an aromatic ring. This is probably because the cyclic quaternary ammonium organic cation having an aromatic ring was significantly decomposed on the negative electrode. On the other hand, in the reference batteries 1 to 6, the present invention battery 7 and the reference batteries 8 to 10 containing the nitrogen-containing organic anion in the nonaqueous electrolyte, it was confirmed that the initial charge / discharge efficiency was remarkably improved. It was done. Among these, it can be seen that the reference batteries 9 and 10 in which the nonaqueous electrolyte further contains an organic solvent having a dielectric constant of 35 or more have improved initial charge / discharge efficiency. In REFERENCE battery 8, the non-aqueous electrolyte, despite further comprises an organic solvent, the value of the initial charge-discharge efficiency, a marked improvement compared to the reference cell 1-6 free of organic solvent It cannot be said that it is seen. This is presumably because the organic solvent has a low dielectric constant, so that the effect of assisting the protective film formation effect by the nitrogen-containing organic anion is not necessarily large.

DESCRIPTION OF SYMBOLS 1 Positive electrode 11 Positive electrode mixture 12 Positive electrode collector 2 Negative electrode 21 Negative electrode mixture 22 Negative electrode collector 3 Separator 4 Electrode group 5 Metal resin composite film

Claims (2)

In a nonaqueous electrolyte battery comprising a positive electrode and a negative electrode, wherein a nonaqueous electrolyte containing a cyclic quaternary ammonium organic cation having a five-membered ring or a six-membered aromatic ring, a lithium cation, and an anion is used. The negative electrode operates at a potential of 1.0 V (vs Li / Li ⁺ ) or less in the battery, and the non-aqueous electrolyte is N (C _n F _{2n + 1} SO) which is a nitrogen-containing organic anion. ₂ ) (C _m F _{2m + 1} SO ₂ ) ⁻ (where n is an integer of 1 or more and 4 or less, m is an integer of 1 or more and 4 or less) and an inorganic anion. Secondary battery (wherein the cyclic quaternary ammonium organic cation is represented by the chemical formula 11)

(Wherein R1 and R3 are each an alkyl group having 1 to 8 carbon atoms, and R2, R4 and R5 are hydrogen or an alkyl group having 1 to 3 carbon atoms)
In are those shown, and, the nitrogen-containing organic anion _{(C 2 F 5 SO 2)} 2 N - excluding those that are. ). The nonaqueous electrolyte secondary battery according to claim 1, wherein the nitrogen-containing organic anion is (CF ₃ SO ₂ ) ₂ N ^— .