JP5727985B2 - Battery electrode and battery using the same - Google Patents

Description

  The present invention relates to a battery electrode and a battery using the same.

  A battery such as a lithium ion secondary battery is used as a power source for a mobile phone, a personal computer, a power source for an automobile, and the like. In addition, for batteries used in such applications, research aimed at improving various characteristics such as ensuring safety, improving cycle characteristics and increasing output has been repeated.

  For example, in Patent Document 1, as a technique for preventing a battery from thermal runaway due to a reaction between a positive / negative active material and an organic electrolyte solution in a battery due to an increase in battery temperature due to overcharging of a nonaqueous electrolyte secondary battery. A technique is disclosed in which a reaction inhibitor made of a redox agent or a radical scavenger is contained in the outermost periphery of the positive electrode or electrode body of a battery. Moreover, in patent document 2, in the manufacturing process by the rise in electrolyte solution viscosity which is a problem at the time of improving the high output characteristic and cycling characteristic of a battery by using high concentration electrolyte solution, or the liquid permeability fall to an electrode plate. In order to suppress problems and variations in quality, a technique in which a part of a lithium salt added to an electrolytic solution is supported on a positive electrode in advance is disclosed.

JP 2003-282063 A JP 2011-192561 A

  As described above, various studies have been made on improving battery characteristics. However, as the battery application spreads, the battery is required to further improve the characteristics that have been required so far, such as extending the life and stabilizing the cycle characteristics.

  The present invention has been made paying attention to the circumstances as described above, and its purpose is to prevent battery characteristics such as discharge capacity from being deteriorated over time and to improve the cycle characteristics of the battery electrode, and It is to provide a used battery.

The battery electrode of the present invention that can achieve the above object has a gist in that it contains an imide-based alkali metal salt represented by the following general formula (1).
MN (R ¹ SO ₂ ) (R ² SO ₂ ) (1)
(Wherein, M represents an alkali metal ion, R ^1, R ² independently represents a fluorine atom, an alkyl group or a fluoroalkyl group having 1 to 6 carbon atoms having 1 to 6 carbon atoms, R ^1, R ^At least one of ² is a fluorine atom.)

  The imide-based alkali metal salt (1) is eluted from the electrode into the nonaqueous electrolytic solution when the battery is driven, and reacts with the positive electrode and / or the negative electrode to form a film on the electrode surface. As a result, it is considered that elution of the electrode active material and decomposition of the solvent, the supporting salt (electrolyte) and the like are suppressed, and a stable capacity maintaining action (cycle characteristics) is exhibited.

  In the present invention, the electrode is preferably used as a positive electrode of a battery.

  The battery including the electrode containing the imide-based alkali metal salt represented by the general formula (1) is also included in the present invention. The electrode is preferably a positive electrode. The battery of the present invention is preferably a lithium ion secondary battery.

  According to the present invention, since the battery electrode contains the imide-based alkali metal salt represented by the general formula (1), it is difficult to cause deterioration of characteristics over time, and a battery capable of stable driving is provided. I can expect.

FIG. 1 is a graph showing the results of a cycle test (relationship between the number of cycles and discharge capacity) in Examples.

The battery electrode of the present invention is characterized in that it contains an imide-based alkali metal salt represented by the following general formula (1).
MN (R ¹ SO ₂ ) (R ² SO ₂ ) (1)
(Wherein, M represents an alkali metal ion, R ^1, R ² independently represents a fluorine atom, an alkyl group or a fluoroalkyl group having 1 to 6 carbon atoms having 1 to 6 carbon atoms, R ^1, R ^At least one of ² is a fluorine atom.)

  When the battery electrode contains an imide-based alkali metal salt represented by the general formula (1) (hereinafter sometimes referred to as an imide-based alkali metal salt (1)), The present inventors completed the present invention by finding that the discharge capacity is increased, the discharge capacity does not easily decrease with time, and the cycle characteristics are excellent.

  When the battery electrode contains an imide-based alkali metal salt (1), there is no clear reason why the effect of improving the characteristics described above is obtained, but the present inventors consider as follows. .

  The imide-based alkali metal salt (1) dissolves into the non-aqueous electrolyte from the electrode when the battery is driven, and reacts with the positive electrode and / or the negative electrode to form a film on the electrode surface. The coating has an electrolytic solution decomposition inhibiting effect, and thereby, a stable capacity maintaining action (cycle characteristics) is exhibited without impairing the performance of the electrolytic solution. In addition, the formation of the film suppresses the elution of electrode components such as the electrode active material. As a result, the increase in the internal resistance of the battery can be suppressed, and the discharge voltage can be maintained at a high value. It is thought that the characteristics are improved. Further, the imide-based alkali metal salt (1) is contained in the electrode and is gradually released from the electrode. Therefore, the coating film is continuously formed on the electrode surface by the imide-based alkali metal salt (1) eluted from the electrode, and it is considered that the above effect can be continuously obtained without decreasing over time. It is done.

  First, the imide alkali metal salt (1) contained in the battery electrode of the present invention will be described.

1. Imide Alkali Metal Salt The imide alkali metal salt according to the present invention is a compound represented by the above general formula (1). In general formula (1), M represents an alkali metal ion. Among the alkali metal ions, lithium ions, sodium ions, and potassium ions are preferable, and lithium ions are more preferable.

In the general formula ^{(1), R 1, R} 2 independently represents a fluorine atom, an alkyl group or a fluoroalkyl group having 1 to 6 carbon atoms having 1 to 6 carbon atoms. Note that at least one of R ¹ and R ² is a fluorine atom. Since at least one of R ¹ and R ² is a fluorine atom, the molecular weight is reduced, so that an increase in the viscosity of the electrode material composition is suppressed and an electrode can be produced with good workability. Moreover, even if the imide-based alkali metal salt (1) is dissolved from the electrode, the viscosity of the non-aqueous electrolyte is hardly increased, and the influence on the conductivity of the non-aqueous electrolyte can be reduced.

  The alkyl group and the fluoroalkyl group may be either linear or branched, may have these structures, and may have a substituent. The number of fluorine atoms that the fluoroalkyl group has is not particularly limited as long as a part or all of the hydrogen atoms of the corresponding alkyl group are substituted with fluorine atoms.

  Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a heptyl group, a hexyl group, and a cyclohexyl group. On the other hand, as the fluoroalkyl group, for example, fluoromethyl group, difluoromethyl group, trifluoromethyl group, fluoroethyl group, difluoroethyl group, trifluoroethyl group, pentafluoroethyl group, fluoropropyl group, fluorobutyl group, fluoro A pentyl group, a fluorohexyl group, etc. are mentioned.

  Specific examples of the imide-based alkali metal salt (1) include lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide, lithium ( Lithium salts such as fluorosulfonyl) (ethylsulfonyl) imide, potassium salts such as potassium bis (fluorosulfonyl) imide, potassium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, sodium bis (fluorosulfonyl) imide, sodium (fluorosulfonyl) ) (Trifluoromethylsulfonyl) imide and the like. Of these, lithium bis (fluorosulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, and lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide are preferable, and lithium bis (fluorosulfonyl) imide is more preferable. . Two or more imide-based alkali metal salts (1) may be mixed and used within a range not affecting the battery performance.

2. Battery Electrode The battery electrode of the present invention contains an imide-based alkali metal salt represented by the general formula (1). When the electrode contains an imide-based alkali metal salt (1), the concentration of the imide-based alkali metal salt (1) in the vicinity of the electrode can be easily improved, and a coating can be rapidly formed on the electrode surface, which is preferable. In addition, since the imide-based alkali metal salt (1) is gradually released from the electrode, the discharge capacity and cycle characteristics are more unlikely to deteriorate over time. The electrode containing the imide-based alkali metal salt (1) is preferably a positive electrode.

  The electrode of the present invention preferably contains 0.01 part by mass to 10 parts by mass of the imide-based alkali metal salt (1) with respect to 100 parts by mass of the positive electrode mixture composed of an active material, a conductive additive, and a binder. More preferably, it is 0.05 mass part-5 mass parts, More preferably, it is 0.1 mass part-3 mass parts. If the content of the imide-based alkali metal salt (1) is too small, it may be difficult to obtain an effect of inhibiting electrode corrosion or solvent decomposition. On the other hand, even if it is used in a large amount, an effect proportional to the amount used can be obtained. In addition, the ratio of the imide-based alkali metal salt (1) in the electrode constituent material is increased, which may make it difficult to manufacture the electrode.

  The method for supporting (holding) the imide-based alkali metal salt (1) on the electrode is not particularly limited. For example, when the imide-based alkali metal salt (1) is used as a part of the electrode constituent material and the electrode is manufactured by a conventionally known manufacturing method, an electrode carrying the imide-based alkali metal salt (1) can be obtained. Specifically, the imide-based alkali metal salt (1) is mixed with an electrode material such as an electrode active material, a conductive additive, and a binder described later to prepare an electrode material composition, and this is applied to a current collector. A sheet obtained by kneading, molding and drying an electrode material composition containing an imide-based alkali metal salt (1), bonding the sheet to a current collector via a conductive adhesive, pressing and drying. Method: Method of applying or spraying a solution containing an imide-based alkali metal salt (1) to a sheet-like electrode obtained by applying an electrode material composition to a current collector and drying it; The added liquid or slurry electrode material composition (including the imide-based alkali metal salt (1)) is applied or cast onto the positive electrode current collector to form a desired shape, and then the liquid lubricant is removed. And then a method of stretching in a uniaxial or multiaxial direction. Since the imide-based alkali metal salt (1) includes a hygroscopic material, the electrode is preferably produced in an atmosphere having a dew point of −20 ° C. or lower.

3. Battery The battery of the present invention is not particularly limited as long as it uses an electrode containing an imide-based alkali metal salt represented by the general formula (1), but as a specific battery, For example, a lithium ion secondary battery, a lithium ion polymer secondary battery, a lithium primary battery, a multivalent cation secondary battery, and the like can be given. Further, the configuration of these batteries is not particularly limited, and in the present invention, conventionally known battery configurations such as an electrolytic solution, an electrode, and a separator can be adopted. In addition, it is preferable to manufacture any battery in an atmosphere with a dew point of −20 ° C. or lower. This is because the imide-based alkali metal salt (1) includes those having hygroscopicity.

  An electrolyte solution having a configuration common to the batteries will be described.

3-1. Electrolytic Solution The electrolytic solution used for the battery usually includes an electrolyte and a medium. First, the electrolyte will be described.

3-1-1. Electrolyte In the present invention, a conventionally known electrolyte can be used. As the electrolyte, those having a large dissociation constant in the electrolytic solution and having an anion that is difficult to solvate with a non-aqueous solvent described later are preferable. Specific examples of the electrolyte include alkali metal salts and alkaline earth metal salts of trifluoromethanesulfonic acid such as LiCF ₃ SO ₃ , NaCF ₃ SO ₃ , KCF ₃ SO ₃ ; LiC (CF ₃ SO ₂ ) ₃ , LiN ( Perfluoroalkanesulfonic acid imide such as CF ₃ CF ₂ SO ₂ ) ₂ , LiN (FSO ₂ ) ₂ or alkali metal salt or alkaline earth metal salt of fluorosulfonyl imide; hexafluoro such as LiPF ₆ , NaPF ₆ , KPF ₆ Alkali metal salts and alkaline earth metal salts of phosphoric acid; alkali metal salts and alkaline earth metal salts of perchloric acid such as LiClO ₄ and NaClO ₄ ; tetrafluoroborate salts such as LiBF ₄ and NaBF ₄ ; lithium tetracyanoborate; Lithium tricyanomethoxyborate, sodium tricyanomethoxyborate, magnesium bis Anomethoxyborate), lithium tricyanoisopropoxyborate, lithium tricyanobutoxyborate, lithium tricyanophenoxyborate, lithium tricyano (pentafluorophenoxy) borate, lithium tricyano (trimethylsiloxy) borate, lithium tricyano (hexafluoroiso) propoxy) borate, lithium tricyanomethylphosphine thio borate, lithium dicyano-dimethoxy borate, lithium cyano trimethoxy borate, lithium dicyano-dimethoxy-borate, alkali metal salts of cyanoborohydride acids such as lithium cyano trimethoxy _{borate; LiAsF 6, LiI, LiSbF 6} , LiAlO 4 _{, LiAlCl 4, LiCl, NaI,} NaAsF 6, alkali metal salts of KI and the like; perchlorate tetraethylammonium en Quaternary ammonium salts of perchloric acid bromide, _{etc.; (C 2 H 5) 4} NBF 4, (C 2 H 5) 3 (CH 3) quaternary ammonium salts of tetrafluoroborate of ₄ such NBF; tetraethylammonium Tetracyanoborate, 1-ethyl-3-methylimidazolium tetracyanoborate, triethylmethylammonium tetracyanoborate, tetraethylammonium tetracyanoborate, tetraethylammonium tricyanomethoxyborate, triethylmethylammonium tricyanomethoxyborate, triethylmethylammonium tricyano Isopropoxyborate, triethylmethylammonium tricyanobutoxyborate, triethylmethylammonium tricyanophenoxyborate, triethylmethylammonium tricyano (Pentafluorophenoxy) borate, triethylmethylammonium tricyano (trimethylsiloxy) borate, triethylmethylammonium tricyanomethylthioborate, triethylmethylammonium tricyano (hexafluoroisopropoxy) borate, 1-ethyl-3-methylimidazolium tricyano Cyanoborates, triethylammonium tricyanomethoxyborate, tributylammonium tricyanomethoxyborate, ammonium salts of cyanoboric acid such as triethylmethylammonium dicyanodimethoxyborate, triethylmethylammonium cyanotrimethoxyborate; (C ₂ H ₅ ) ₄ NPF ₆ Quaternary ammonium salts; quaternary ammonium salts such as (CH ₃ ) ₄ P · BF ₄ and (C ₂ H ₅ ) ₄ P · BF ₄ Um salt; and the like. These electrolytes may be used individually by 1 type, and may be used in combination of 2 or more type.

Among the electrolytes, alkali metal salts and / or alkaline earth metal salts are preferable. Further, from the viewpoint of solubility in a non-aqueous solvent and ion conductivity, LiPF ₆ , LiBF ₄ , LiAsF ₆ , alkali metal salts or alkaline earth metal salts of perfluoroalkanesulfonic acid imide, chain quaternary quaternary Ammonium salts are preferred, and chain quaternary ammonium salts are preferred from the viewpoint of reduction resistance. As the alkali metal salt, a lithium salt, a sodium salt, and a potassium salt are preferable, and as the alkaline earth metal salt, a calcium salt and a magnesium salt are preferable. More preferred is a lithium salt.

  The electrolyte concentration is preferably used in the electrolytic solution according to the present invention so as to be 0.1 mol / L or more and a saturation concentration or less. More preferably, it is 0.2 mol / L to 1.5 mol / L, still more preferably 0.8 mol / L to 1.4 mol / L, and still more preferably 0.9 mol / L to 1.3 mol / L. is there. If the electrolytic mass is too small, it may be difficult to obtain a desired conductivity. On the other hand, if the electrolytic mass is too large, ion migration may be hindered.

3-1-2. Medium The medium is not particularly limited as long as it can dissolve the electrolyte, and any conventionally known medium used for batteries, such as a non-aqueous solvent, a polymer, and a polymer gel, can be used.

  As the non-aqueous solvent, a solvent having a large dielectric constant, high electrolyte solubility, a boiling point of 60 ° C. or higher, and a wide electrochemical stability range is preferable. More preferably, it is an organic solvent (non-aqueous solvent) having a low water content. Examples of such organic solvents include ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, Ethers such as tetraethylene glycol dimethyl ether, 1,4-dioxane, 1,3-dioxolane; dimethyl carbonate, ethyl methyl carbonate (methyl ethyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, methyl phenyl carbonate, etc. Chain carbonates of ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), 2,3-dimethylethylene carbonate, butyrate Cyclic carbonates such as vinylene carbonate, 2-vinylethylene carbonate; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, ethyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate; Aromatic carboxylic acid esters such as methyl benzoate and ethyl benzoate; Lactones such as γ-butyrolactone, γ-valerolactone and δ-valerolactone; Trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, phosphoric acid Phosphate esters such as triethyl; Nitriles such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, isobutylnitrile; N-methylformamide, N -Ethylho Amides such as muamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-vinylpyrrolidone; dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4 -Sulfur compounds such as dimethylsulfolane: alcohols such as ethylene glycol, propylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether; sulfoxides such as dimethyl sulfoxide, methyl ethyl sulfoxide, diethyl sulfoxide; benzonitrile, tolunitrile, etc. Aromatic nitriles; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone, 3 -Methyl-2-oxazolidinone and the like can be mentioned.

  Among these, chain carbonic acid esters, cyclic carbonic acid esters, aliphatic carboxylic acid esters, lactones, ethers are preferable, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone and the like are more preferable. The said non-aqueous solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  Polymers used as the medium include polyether polymers such as polyethylene oxide (PEO) and polypropylene oxide, which are homopolymers or copolymers of epoxy compounds (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.) Methacrylic polymers such as methyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), fluoropolymers such as polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof Is mentioned. In addition, a polymer gel obtained by mixing these polymers with another organic solvent can also be used as the medium according to the present invention. Examples of the other organic solvent include the non-aqueous solvents described above.

  When the polymer gel is used as a medium, a solution in which an electrolyte is dissolved in the above-described non-aqueous solvent is dropped onto a polymer formed by a conventionally known method, and the electrolyte and the non-aqueous solvent are impregnated and supported; A method in which a polymer and an electrolyte are melted and mixed at a temperature equal to or higher than the melting point of the polymer, and then formed into a film and impregnated with a non-aqueous solvent (the gel electrolyte); an electrolyte in which an electrolyte is dissolved in an organic solvent in advance A method in which a polymer is mixed and then formed into a film by a casting method or a coating method, and an organic solvent is volatilized; a method in which a polymer and an electrolyte are melted at a temperature equal to or higher than the melting point of the polymer, mixed and molded (an intrinsic polymer) Electrolyte); and the like.

3-1-3. Additive The electrolyte solution according to the present invention may contain an additive for the purpose of improving various characteristics of the battery.

  As additives, cyclic carbonates having unsaturated bonds such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (MVC), ethyl vinylene carbonate (EVC); fluoroethylene carbonate, trifluoropropylene carbonate, Carbonate compounds such as phenylethylene carbonate and erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetra Carboxylic anhydrides such as carboxylic dianhydride and phenyl succinic anhydride; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methane sulfone Sulfur-containing compounds such as methyl, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3- Nitrogen-containing compounds such as dimethyl-2-imidazolidinone and N-methylsuccinimide; phosphates such as monofluorophosphate and difluorophosphate; saturated hydrocarbon compounds such as heptane, octane and cycloheptane; biphenyl and alkyl Biphenyl, terphenyl, partially hydrogenated terphenyl, unsaturated hydrocarbon compounds such as cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, and the like.

  The additive is preferably used in the range of 0.1% by mass to 10% by mass in the electrolytic solution of the present invention (more preferably 0.2% by mass to 8% by mass, and still more preferably 0.3%. Mass% to 5 mass%). When the amount of the additive used is too small, it may be difficult to obtain an effect derived from the additive. On the other hand, even if a large amount of the additive is used, it is difficult to obtain an effect commensurate with the added amount. There is a possibility that the viscosity of the resin increases and the conductivity decreases.

  In the battery of the present invention, the positive electrode potential at the time of full charge is not particularly limited, but is preferably 4.0 V or more, more preferably 4.1 V or more on the basis of lithium. In addition, although the positive electrode potential at the time of a full charge is so preferable that it is high, it is preferable that it is 5.5V or less from a viewpoint of safety | security. More preferably, it is 5.0 V or less.

  The rated charging voltage of the battery of the present invention is not particularly limited, but is preferably 2.5 V or more, more preferably 3.0 V or more, still more preferably 3.5 V or more, and even more preferably 4. 1V or more. In addition, although an energy density can be raised, so that a rated charge voltage is high, when too high, it may be difficult to ensure safety. Therefore, it is preferable that the rated charging voltage is 5.5 V or less. More preferably, it is 5.0 V or less.

4). Lithium Ion Secondary Battery Among the above exemplified batteries, the lithium ion secondary battery will be described in more detail. The lithium ion secondary battery has a positive electrode, a negative electrode, and an electrolytic solution. More specifically, a separator is provided between the positive electrode and the negative electrode, and the electrolytic solution is the separator. In an impregnated state, it is housed in an outer case together with a positive electrode, a negative electrode, and the like.

  The lithium ion secondary battery of the present invention has the electrode of the present invention containing an imide-based alkali metal salt (1). The electrode containing the imide-based alkali metal salt (1) is preferably a positive electrode.

  The shape of the lithium ion secondary battery according to the present invention is not particularly limited, and any conventionally known shape can be used as the shape of the lithium ion secondary battery, such as a cylindrical shape, a square shape, a laminate shape, a coin shape, and a large size. Can do. Further, when used as a high voltage power source (several tens of volts to several hundreds of volts) for mounting on an electric vehicle, a hybrid electric vehicle, etc., a battery module configured by connecting individual batteries in series can be used. .

4-1. Positive electrode The positive electrode is formed by supporting a positive electrode active material composition containing a positive electrode active material, a conductive additive, a binder, a dispersion solvent and the like on a positive electrode current collector, and is usually formed into a sheet shape. .

  As a method for producing the positive electrode, for example, a method in which the positive electrode active material composition is applied to the positive electrode current collector by the doctor blade method or the like and dried after being immersed; the positive electrode active material composition is kneaded and dried. A method in which the obtained sheet is bonded to the positive electrode current collector via a conductive adhesive, pressed, and dried; a positive electrode active material composition to which a liquid lubricant is added is applied or cast on the positive electrode current collector; Examples include a method in which after forming into a desired shape, the liquid lubricant is removed, and then the film is stretched in a uniaxial or multiaxial direction. In order to support the imide-based alkali metal salt (1) on the positive electrode, the imide-based alkali metal salt (1) may be used as a material constituting the positive electrode active material composition. Alternatively, a solution containing the imide-based alkali metal salt (1) may be applied or sprayed on the positive electrode obtained by the above method, and dried to support the imide-based alkali metal salt (1) on the positive electrode. The positive electrode is preferably produced in an atmosphere having a dew point of −20 ° C. or lower.

4-1-1. Positive electrode current collector The material of the positive electrode current collector is not particularly limited, and for example, conductive metals such as aluminum, aluminum alloy, SUS (stainless steel), and titanium can be used. Among these, aluminum is preferable because it is easy to process into a thin film and is inexpensive.

4-1-2. Positive Electrode Active Material As the positive electrode active material, any known positive electrode active material used in lithium secondary batteries may be used as long as it can occlude and release lithium ions.

Specifically, lithium cobalt acid, lithium nickel acid, lithium manganese acid, LiNi was replaced with some Ni with LiMn ₂ O ₄ system _{0.5 Mn 1.5 O 4, LiNi 1} -xy Co x Mn y O 2 or LiNi _{1- xy Co x Al y O 2 (} 0 <x <1,0 <y <1,0 <x + y <1) a transition metal oxide such as ternary oxide represented _{by, LiAPO 4 (a = Fe,} Mn , Ni, Co) and other olivine-structured compounds, solid solution materials incorporating a plurality of transition metals (electrochemically inactive layered Li ₂ MnO _3, and electrochemically active layered LiM ″ O A solid solution with [M ″ = transition metal such as Co, Ni, etc.] can be exemplified as the positive electrode active material. These positive electrode active materials may be used individually by 1 type, or may be used in combination of multiple.

4-1-3. Conductive aid Examples of the conductive aid include acetylene black, carbon black, graphite, metal powder material, single-walled carbon nanotube, multi-walled carbon nanotube, and vapor grown carbon fiber.

4-1-4. Binders As binders, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide resins such as polyamideimide; polyethylene, polypropylene and the like Polyolefin resin; poly (meth) acrylic resin; polyacrylic acid; cellulose resin such as carboxymethylcellulose; These binders may be used alone or in combination of two or more. Further, these binders may be in a state dissolved in a solvent at the time of use, or may be in a state dispersed in a solvent.

  The blending amounts of the conductive auxiliary agent and the binder can be appropriately adjusted in consideration of the intended use of the battery (emphasis on output, importance on energy, etc.), ion conductivity, and the like.

  In producing the positive electrode, examples of the solvent used in the positive electrode active material composition include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetone, ethanol, ethyl acetate, and water. These solvents may be used in combination. The amount of the solvent used is not particularly limited, and may be appropriately determined according to the production method and the material to be used.

4-2. Negative electrode A negative electrode is a negative electrode active material composition containing a negative electrode active material, a dispersing solvent, a binder and, if necessary, a conductive additive, etc. supported on a negative electrode current collector. Molded.

4-2-1. Negative Electrode Current Collector As a material for the negative electrode current collector, a conductive metal such as copper, iron, nickel, silver, stainless steel (SUS) can be used. From the viewpoint of easy processing into a thin film, copper is preferable.

4-2-2. Negative electrode active material As the negative electrode active material, a conventionally known negative electrode active material used in lithium ion secondary batteries can be used as long as it can occlude and release lithium ions. Specifically, graphite materials such as artificial graphite and natural graphite, mesophase fired bodies made from coal / petroleum pitch, carbon materials such as non-graphitizable carbon, Si, Si alloys, Si-based negative electrode materials such as SiO, Sn An Sn-based negative electrode material such as an alloy, or a lithium alloy such as lithium metal or a lithium-aluminum alloy can be used.

  As a manufacturing method of the negative electrode, a method similar to the manufacturing method of the positive electrode can be employed. In addition, the same conductive auxiliary agent, binder, and material dispersing solvent as used in the positive electrode are used in the production of the negative electrode.

4-3. Separator The separator is disposed so as to separate the positive electrode and the negative electrode. There is no restriction | limiting in particular in a separator, In this invention, all the conventionally well-known separators can be used. Specific examples of the separator include a porous sheet made of a polymer that absorbs and retains a nonaqueous electrolytic solution (for example, a polyolefin microporous separator or a cellulose separator), a nonwoven fabric separator, a porous metal body, and the like. It is done. Among these, a polyolefin-based microporous separator is preferable because it has a property of being chemically stable to an organic solvent.

  Examples of the material for the porous sheet include polyethylene, polypropylene, and a laminate having a three-layer structure of polypropylene / polyethylene / polypropylene.

  Examples of the material of the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc., depending on the mechanical strength required for the non-aqueous electrolyte layer, etc. The above-exemplified materials can be used alone or in combination.

4-4. Battery exterior material A battery element equipped with a positive electrode, a negative electrode, a separator, and the electrolyte solution of the present invention is housed in a battery exterior material to protect the battery element from external impact and environmental degradation when using a lithium ion secondary battery. Is done. In the present invention, the material of the battery exterior material is not particularly limited, and any conventionally known exterior material can be used. In addition, when imide type | system | group alkali metal salt (1) has a hygroscopic property, it is preferable to manufacture a lithium secondary battery in an atmosphere with a dew point of -20 degrees C or less.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Experimental example Battery characteristics evaluation Production of positive electrode sheet LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNMC), acetylene black (AB, conductive auxiliary agent 1, manufactured by Denki Kagaku Kogyo Co., Ltd.), graphite ( Conductive aid 2, particle size D50 = 3.2 μm, specific surface area 245 m ² / g), polyvinylidene fluoride (PVdF, “KF1120”, manufactured by Kureha) in N-methyl-2-pyrrolidone (NMP) solution uniformly And a paste-like positive electrode mixture A having a solid content concentration of 67% (solid content ratio (mass ratio), positive electrode active material (LNMC): AB: graphite: PVdF = 92: 2: 2: 4) Was made.

  Next, lithium bis (fluorosulfonyl) imide (LiFSI, imide-based alkali metal salt) with respect to the positive electrode mixture A in a solid content ratio (mass ratio), LNMC: AB: graphite: PVdF: LiFSI = 91.6: The mixture was kneaded so that the ratio was 2: 2: 4: 0.4 to prepare a paste-like positive electrode mixture B. Table 1 shows the composition (solid content ratio) of the positive electrode mixture A and B.

The obtained paste-like positive electrode mixtures A and B were each coated on an aluminum current collector and dried to prepare a positive electrode sheet (initial charge capacity: 2.3 mAh / cm ² ).

2. Preparation of non-aqueous electrolyte Lithium hexafluorophosphate (LiPF ₆ , manufactured by Kishida Chemical Co., Ltd., LBG grade) as an electrolyte was mixed with a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC: EMC = 3: 7 (volume ratio), all were dissolved in Kishida Chemical Co., Ltd., LBG grade) to prepare a 1.0 mol / L non-aqueous electrolyte.

3. Production of coin-type lithium battery Positive electrode sheet obtained by producing the positive electrode, a commercially available negative electrode sheet (negative electrode current collector: copper foil, negative electrode active material: graphite, discharge capacity: 2.4 mAh / cm ² ), and polyethylene Each made separator was punched into a circular shape (positive electrode φ12 mm, negative electrode φ14 mm). CR2032 coin-type battery parts purchased from Hosen Co., Ltd. (positive electrode case (made of aluminum clad SUS304L), negative electrode cap (made of SUS316L), spacer (1 mm thickness, made of SUS316L), wave washer (made of SUS316L), gasket (made of polypropylene) )) To produce a coin-type lithium battery. Specifically, a negative electrode cap equipped with a gasket, a wave washer, a spacer, a negative electrode sheet (installed so that the copper foil side of the negative electrode faces the spacer), and a separator are stacked in this order, and then 70 μL of the nonaqueous electrolyte solution is added. The separator was impregnated. Next, a positive electrode sheet was placed so that the surface coated with the positive electrode mixture was opposite to the negative electrode active material layer side, a positive electrode case was stacked on the sheet, and caulking was performed to produce a coin-type lithium battery.

4). Cycle characteristic test About the obtained coin type lithium battery, using a charge / discharge test apparatus (manufactured by Instrument Center Co., Ltd.), a charge / discharge rate of 1.0 C (constant current mode), a condition of 2.75 V to 4.2 V In each charge / discharge, a cycle test was conducted with a charge / discharge pause time of 10 minutes. The results are shown in FIG.

  As shown in FIG. 1, the coin-type lithium battery of the present invention produced using a positive electrode sheet manufactured from a positive electrode mixture B containing LiFSI as an imide-based alkali metal salt (1) has an imide-based alkali metal salt (1 Compared with the example using the positive electrode sheet manufactured from the positive electrode mixture A not containing), the initial capacity is high, and in addition, the capacity deterioration with the lapse of time is suppressed, and the improved cycle characteristics are obtained. .

Claims (6)

Look containing imide-based alkali metal salt represented by the following general formula (1), the positive electrode for a lithium ion secondary battery, wherein the rated charging voltage is for a lithium ion secondary battery is 3.5V or more.
MN (R ¹ SO ₂ ) (R ² SO ₂ ) (1)
(Wherein, M represents an alkali metal ion, R ^1, R ² independently represents a fluorine atom, an alkyl group or a fluoroalkyl group having 1 to 6 carbon atoms having 1 to 6 carbon atoms, R ^1, R (At least one of ² is a fluorine atom.) 2. The positive electrode for a lithium ion secondary battery according to claim 1, comprising 10 parts by mass or less of the imide-based alkali metal salt with respect to 100 parts by mass of a positive electrode mixture comprising an active material, a conductive additive, and a binder. The positive electrode for a lithium ion secondary battery according to claim 1 or 2, wherein M in the general formula (1) is a lithium ion. R in the general formula (1) ¹ And R ² Is a fluorine atom, The positive electrode for lithium ion secondary batteries in any one of Claims 1-3. A lithium ion secondary battery comprising: a positive electrode containing an imide-based alkali metal salt represented by the following general formula (1); and a negative electrode having at least one selected from a graphite material and a carbon material as a negative electrode active material .
MN (R ¹ SO ₂ ) (R ² SO ₂ ) (1)
(Wherein, M represents an alkali metal ion, R ^1, R ² independently represents a fluorine atom, an alkyl group or a fluoroalkyl group having 1 to 6 carbon atoms having 1 to 6 carbon atoms, R ^1, R (At least one of ² is a fluorine atom.) The lithium ion secondary battery according to claim 5, wherein the rated charging voltage is 3.5 V or more.