Positive electrode active material coating material and secondary battery provided with same

Abstract

This positive electrode active material coating material is characterized by containing, as a constituent material (A), a compound composed of F and at least one or more elements selected from an alkali metal, an alkaline earth metal, and Al, and containing, as a constituent material (B), one or more compounds represented by chemical formula (1) and / or chemical formula (2). Also provided are a positive electrode coated with the coating material, and a secondary battery provided with the positive electrode. The positive electrode active material coating material according to the present embodiment can be suitably used for a secondary battery.

Description

Positive electrode active material coating material and secondary battery including same

[0001] The present invention relates to a coating material for a positive electrode active material and a secondary battery including the same.

[0002] Lithium-ion secondary batteries using nonaqueous electrolytes have become widely used as power sources for portable information terminals such as laptops, digital cameras, mobile phones, smartphones, and tablets. In recent years, lithium-ion secondary batteries have been installed in electric vehicles (xEVs) as key devices toward achieving carbon neutrality. Furthermore, their applications have expanded to include household power sources and stationary storage batteries for power storage systems such as mega-solar power generation, leading to the development of nonaqueous electrolyte lithium-ion secondary batteries with higher energy density.

[0003] In non-aqueous electrolyte lithium-ion secondary batteries, the elution of transition metals from the positive electrode active material at the interface between the positive electrode active material and the electrolyte, or the degradation of the electrolyte during charging, can lead to degradation of battery performance, such as a decrease in discharge capacity and an increase in internal resistance. To increase the energy density of batteries, approaches such as increasing the charging potential and adopting positive electrode materials with even slightly higher operating potentials have been attempted, but at the same time, the challenge of how to suppress the degradation of battery performance has also been faced.

[0004] Conventionally, attempts have been made to prevent the elution of transition metals and the deterioration of the electrolyte during charging by adding additives to a non-aqueous electrolyte to form a stable film called an SEI (Solid Electrolyte Interphase) that has lithium ion conductivity but no electronic conductivity. Patent Document 1 discloses a technique for suppressing the elution of metal elements in the positive electrode by adding lithium sulfonate containing an alkylamine in its molecular skeleton to form an SEI on the positive electrode surface. Patent Document 2 discloses a technique for suppressing the decomposition of the electrolyte by incorporating a large amount of a highly thermally stable polyanionic compound into the surface of the positive electrode composite layer. However, even with these techniques, there are limitations to their applicability to batteries with higher operating potentials.

[0005] The technology of Patent Document 1 for forming an SEI on a positive electrode by adding an additive to a non-aqueous electrolyte is in demand for further improvement in the performance of non-aqueous electrolyte-based lithium ion batteries. However, the effectiveness of the technology is not primarily achieved by the additive in the electrolyte, and there are many issues to be investigated regarding performance stabilization, such as tuning of the chemical conversion conditions in the battery production process, in terms of how to form a stable SEI.

[0006] For example, to form an SEI using a nonaqueous electrolyte, the nonaqueous electrolyte undergoes a decomposition reaction during the first charge. This generates gas components such as hydrogen, carbon dioxide, and methane as by-products. These gas components may inhibit lithium ion conduction at the electrode-electrolyte interface and increase internal resistance, so a gas component removal process is required after the first charge.

[0007] Furthermore, when the non-aqueous electrolyte solution decomposes, the composition of the electrolyte and solvent contained in the non-aqueous electrolyte solution may change, and the ionic conductivity may decrease due to changes in the lithium ion concentration or the viscosity of the non-aqueous electrolyte solution, resulting in a decrease in discharge capacity and an increase in internal resistance.

[0008] Meanwhile, in recent years, solid-state batteries have been attracting attention from the viewpoints of improving safety, increasing power output, and increasing energy density. In solid-state batteries, the construction of a good interface between the positive electrode active material or negative electrode active material and the solid electrolyte layer is a challenge. In lithium-ion secondary batteries using a nonaqueous electrolyte, a good interface can be constructed between the positive electrode active material layer and the negative electrode active material layer and the electrolyte. On the other hand, in the case of solid-state lithium-ion secondary batteries, since they are entirely composed of solids, point contact is likely to occur between the positive electrode active material or negative electrode active material and the solid electrolyte, and voids are likely to form, raising concerns about a decrease in performance due to insufficient contact interfaces.

[0009] Therefore, in solid-state lithium-ion secondary batteries, forming a good solid-solid interface by coating at least a portion of the positive electrode active material with a coating material has been studied, and Patent Document 1 discloses a solid-state battery using a positive electrode material in which at least a portion of the surface of a positive electrode active material containing nickel, cobalt, and manganese is coated with lithium niobate. Patent Document 3 also discloses that using lithium niobate as a coating material for coating the positive electrode in a solid-state lithium-ion battery improves discharge capacity and suppresses an increase in internal resistance.

[0010] Although a good contact interface can be obtained by using such a coating material, in solid-state lithium-ion secondary batteries, as in the case of non-aqueous electrolyte lithium-ion secondary batteries, reactions other than electrode reactions can occur between the electrode active material and the solid electrolyte at the interface between the electrode active material and the solid electrolyte when a potential is applied during charging. The influence of these reaction products increases the interfacial resistance even if a good contact interface is formed. In fact, lithium niobate does not have sufficient oxidation resistance, so it cannot be said that the improvement in terms of discharge capacity and internal resistance is sufficient, and it cannot be said that sufficient performance is ensured when considering use in fields requiring high performance, such as automotive applications.

[0011] Thus, in solid-state lithium-ion secondary batteries, it is important to maintain low interfacial resistance, and it can be said that it is necessary to coat the positive electrode active material with an appropriate material so as not to increase the interfacial resistance. Providing an appropriate coating material for the positive electrode active material is expected to lead to an improvement in interfacial resistance in solid-state lithium-ion secondary batteries, as well as to suppress deterioration of the electrolyte in non-aqueous electrolyte lithium-ion secondary batteries, thereby contributing to improved battery performance.

[0012] JP 2023-137680 A JP 2023-010319 A International Publication No. 2019 / 146216 A

[0013] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a coating material for a positive electrode active material that improves the discharge capacity of a secondary battery and suppresses an increase in internal resistance.

[0014] The present invention relates to the following items [1] to [4]: ​​[1] A coating material for a positive electrode active material for coating a positive electrode active material, the coating material comprising, as a constituent material (A), a compound composed of at least one element selected from the group consisting of alkali metals, alkaline earth metals, and Al, and F, and comprising, as a constituent material (B), one or more compounds represented by chemical formula (1) and / or chemical formula (2). (However, the above M ｎ＋ represents an alkali metal ion or an alkaline earth metal ion, and n represents a valence. １ ~X ４ represents a halogen atom, a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms, or a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms and at least one of a halogen atom and an unsaturated bond, or X １ ~X ４ two groups are bonded to each other, -OOC-COO-, -OOCO-, -OOC-Y １ -COO-, -OOC-Y ２ -O- or -O-Y ３ A ring structure of —O— is formed. １、 Y ２ , and Y ３ represents a hydrocarbon group having a linear or cyclic structure and having 1 to 10 carbon atoms, or a hydrocarbon group having at least one of a halogen atom, an unsaturated bond, or a hetero atom. １ ~X ４ At least one of them is a fluorine atom. (However, the above M ｎ＋ represents an alkali metal ion or an alkaline earth metal ion, and n represents a valence. ５ ~X １０ represents a halogen atom, a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms, or a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms and at least one of a halogen atom and an unsaturated bond, or X ５ ~X １０At least two groups among —OOC-COO—, —OOCO—, and —OOC-Y １ -COO-, -OOC-Y ２ -O- or -O-Y ３ A ring structure of —O— is formed. １、 Y ２ , and Y ３ are each independently a hydrocarbon group having a linear or cyclic structure and having 1 to 10 carbon atoms, or a hydrocarbon group having at least one of a halogen atom, an unsaturated bond, or a hetero atom. ５ ~X １０ At least one of the atoms is a fluorine atom. [2] A positive electrode using a positive electrode active material coated with the positive electrode active material coating material according to [1], wherein the positive electrode active material contains a transition metal oxide. [3] A positive electrode using a positive electrode active material coated with the positive electrode active material coating material according to [1], wherein the positive electrode active material contains a binary transition metal oxide or a ternary transition metal oxide. [4] A secondary battery comprising the positive electrode, an electrolyte, and a negative electrode according to any one of [2] to [3].

[0015] The present invention provides a coating material for a positive electrode active material that improves the discharge capacity of a secondary battery and suppresses an increase in internal resistance.

[0016] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery evaluation cell, and FIG. 2 is a cross-sectional view of a solid-state battery evaluation cell.

[0017] As a result of intensive research conducted by the present inventors to solve the above problems, they have newly discovered that the problems can be solved by using specific constituent materials (A) and (B) as a coating material for a positive electrode active material. Although the mechanism behind this is unclear, it is thought that preventing the deterioration of the positive electrode due to the elution of transition metals can improve discharge capacity and suppress an increase in internal resistance.

[0018] (Positive Electrode Active Material Coating Material) First, the positive electrode active material coating material according to the present embodiment will be described below. The positive electrode active material coating material according to the present embodiment is characterized in that it contains, as a constituent material (A), a compound composed of at least one element selected from the group consisting of alkali metals, alkaline earth metals, and Al, and F, and also contains, as a constituent material (B), one or more compounds represented by chemical formula (1) and / or chemical formula (2). (However, the above M ｎ＋ represents an alkali metal ion or an alkaline earth metal ion, and n represents a valence. １ ~X ４ represents a halogen atom, a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms, or a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms and at least one of a halogen atom and an unsaturated bond, or X １ ~X ４ two groups are bonded to each other, -OOC-COO-, -OOCO-, -OOC-Y １ -COO-, -OOC-Y ２ -O- or -O-Y ３ A ring structure of —O— is formed. １、 Y ２ , and Y ３ represents a hydrocarbon group having a linear or cyclic structure and having 1 to 10 carbon atoms, or a hydrocarbon group having at least one of a halogen atom, an unsaturated bond, or a hetero atom. １ ~X ４ At least one of them is a fluorine atom. (However, the above M ｎ＋ represents an alkali metal ion or an alkaline earth metal ion, and n represents a valence. ５ ~X １０ represents a halogen atom, a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms, or a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms and at least one of a halogen atom and an unsaturated bond, or X ５ ~X １０At least two groups among —OOC-COO—, —OOCO—, and —OOC-Y １ -COO-, -OOC-Y ２ -O- or -O-Y ３ A ring structure of —O— is formed. １、 Y ２ , and Y ３ are each independently a hydrocarbon group having a linear or cyclic structure and having 1 to 10 carbon atoms, or a hydrocarbon group having at least one of a halogen atom, an unsaturated bond, or a hetero atom. ５ ~X １０ At least one of them is a fluorine atom.

[0019] Examples of the alkali metal element in the constituent material (A) include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs), and preferably one or more of Li, K, and Na, and more preferably Li.

[0020] Examples of alkaline earth elements in the constituent material (A) include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0021] Examples of the constituent material (A) include LiF, NaF, KF, RbF, CsF, and AlF ３ , Li ３ AlF ６ , Na ３ AlF ６ , K. ３ AlF ６ , Rb ３ AlF ６ , Cs ３ AlF ６ , Na ５ Al ３ F ４ , MgF ２ , CaF ２ , BaF ２ and it is preferable to include at least one compound of these, and LiF, AlF ３ and Li ３ AlF ６It is more preferable that the composition contains at least one of the compounds listed above. These compounds may be used alone or in combination.

[0022] In the chemical formulas (1) and (2), M ｎ＋ represents an alkali metal ion or an alkaline earth metal ion, and n represents the valence thereof.

[0023] In the chemical formulas (1) and (2), the alkali metal ion is not particularly limited and examples thereof include lithium ion, sodium ion, potassium ion, rubidium ion, cesium ion, etc., and lithium ion is preferred. These ions may be used alone or in combination of two or more.

[0024] In the chemical formulas (1) and (2), the alkaline earth metal ion is not particularly limited and examples thereof include beryllium ion, magnesium ion, calcium ion, strontium ion, barium ion, radium ion, etc. These ions may be used alone or in combination of two or more.

[0025] In the chemical formulas (1) and (2), M ｎ＋ Among those listed as examples, lithium ions are preferred from the viewpoint of battery characteristics, and lithium ions and sodium ions are preferred from the viewpoint of availability and ease of synthesis.

[0026] In the chemical formulas (1) and (2), examples of the halogen atom include F, Cl, Br, I, and At.

[0027] In the chemical formulas (1) and (2), the hydrocarbon group having 1 to 10 carbon atoms or the hydrocarbon group having 1 to 10 carbon atoms and at least one of a halogen atom and an unsaturated bond is not particularly limited, and examples thereof include linear and branched chain alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, and decyl group; cyclic alkyl groups such as cyclopentyl group and cyclohexyl group; 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group; 1, chain-type halogen-containing alkyl groups such as a 2-diiodoethyl group, a 1,2-dibromoethyl group, a 1,2-dichloroethyl group, a 1,2-difluoroethyl group, a 2,2-diiodoethyl group, a 2,2-dibromoethyl group, a 2,2-dichloroethyl group, a 2,2-difluoroethyl group, a 2,2,2-tribromoethyl group, a 2,2,2-trichloroethyl group, a 2,2,2-trifluoroethyl group, and a hexafluoro-2-propyl group; cyclic halogen-containing alkyl groups such as a 2-iodocyclohexyl group, a 2-bromocyclohexyl group, a 2-chlorocyclohexyl group, and a 2-fluorocyclohexyl group; alkyl groups, chain alkenyl groups such as 2-propenyl, isopropenyl, 2-butenyl, and 3-butenyl groups, cyclic alkenyl groups such as 2-cyclopentenyl, 2-cyclohexenyl, and 3-cyclohexenyl groups, chain alkynyl groups such as 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-pentynyl, 2-pentynyl, 3-pentynyl, and 4-pentynyl groups, phenyl groups such as phenyl, 3-methoxyphenyl, 4-methoxyphenyl, 3,5-dimethoxyphenyl, and 4-phenoxyphenyl groups, 2- Examples thereof include halogen-containing phenyl groups such as iodophenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group, 3-fluorophenyl group, 4-iodophenyl group, 4-bromophenyl group, 4-chlorophenyl group, 4-fluorophenyl group, 3,5-diiodophenyl group, 3,5-dibromophenyl group, 3,5-dichlorophenyl group, and 3,5-difluorophenyl group; and naphthyl groups such as 1-naphthyl group, 2-naphthyl group, and 3-amino-2-naphthyl group.

[0028] In the chemical formulas (1) and (2), the alkoxy group having 1 to 10 carbon atoms, or the alkoxy group having 1 to 10 carbon atoms and at least one of a halogen atom and an unsaturated bond, is not particularly limited, and examples thereof include chain alkoxy groups such as a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group, and a hexoxy group; cyclic alkoxy groups such as a cyclopentoxy group and a cyclohexoxy group; 2-iodoethoxy group, a 2-bromoethoxy group, a 2-chloroethoxy group, a 2-fluoroethoxy group, a 1,2-diiodoethoxy group, a 1,2-dibutyl alkoxy group, a 2-iodoethoxy group, a 2-bromoethoxy group, a 2-chloroethoxy group, a 2-fluoroethoxy group, a 1,2-diiodoethoxy group, a 2-dibutyl alkoxy group, a 2-iodoethoxy group, a 2-bromoethoxy group, a 2-chloroethoxy group, a 2-fluoroethoxy group, a 1,2-dibutyl alkoxy group, a 2- ...dibutyl alkoxy group, a 2-iodoethoxy group, a 2-dibutyl alkoxy group, a 2-iodoethoxy group, a 2-dibutyl alkoxy group, a 2-iodoethoxy group, a 2-dibutyl alkoxy group, a 2-iodoethoxy group, a 2-dibutyl alkoxy group, a 2-iodoeth Chain halogen-containing alkoxy groups such as bromoethoxy group, 1,2-dichloroethoxy group, 1,2-difluoroethoxy group, 2,2-diiodoethoxy group, 2,2-dibromoethoxy group, 2,2-dichloroethoxy group, 2,2-difluoroethoxy group, 2,2,2-tribromoethoxy group, 2,2,2-trichloroethoxy group, 2,2,2-trifluoroethoxy group, and 1,1,1,3,3,3-hexafluoro-2-propoxy group; 2-iodocyclohexoxy group, 2-bromocyclohexoxy group, 2-chlorocyclohexoxy group, and 2-fluorocyclohexoxy group; cyclic halogen-containing alkoxy groups such as 2-propenoxy, isopropenoxy, 2-butenoxy, and 3-butenoxy groups; chain alkenylalkoxy groups such as 2-cyclopentenoxy, 2-cyclohexenoxy, and 3-cyclohexenoxy groups; chain alkynylalkoxy groups such as 2-propynoxy, 1-butynoxy, 2-butynoxy, 3-butynoxy, 1-pentynoxy, 2-pentynoxy, 3-pentynoxy, and 4-pentynoxy groups; phenoxy, 3-methylphenoxy, 4-methylphenoxy, and 3-methylphenoxy groups; phenoxy groups such as a 2-iodophenoxy group, a 2-bromophenoxy group, a 2-chlorophenoxy group, a 2-fluorophenoxy group, a 3-iodophenoxy group, a 3-bromophenoxy group, a 3-chlorophenoxy group, a 3-fluorophenoxy group, a 4-iodophenoxy group, a 4-bromophenoxy group, a 4-chlorophenoxy group, a 4-fluorophenoxy group, a 3,5-diiodophenoxy group, a 3,5-dibrophenoxy group, a 3,5-dichlorophenoxy group, and a 3,5-difluorophenoxy group.

[0029] In addition, in the chemical formulas (1) and (2), Y １ , Y ２ , and Y ３are each independently a group having a linear or cyclic structure and is a hydrocarbon group having 1 to 10 carbon atoms or a hydrocarbon group having at least one of a halogen atom, an unsaturated bond, or a heteroatom. These include, for example, linear alkylene groups such as methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, and nonylene, iodomethylene, diiodomethylene, bromomethylene, dibromomethylene, fluoromethylene, difluoromethylene, iodoethylene, 1,1-diiodoethylene, 1,2-diiodoethylene, triiodoethylene, tetraiodoethylene, and chloroethylene. halogen-containing linear alkylene groups such as 1,1-dichloroethylene group, 1,2-dichloroethylene group, trichloroethylene group, tetrachloroethylene group, fluoroethylene group, 1,1-difluoroethylene group, 1,2-difluoroethylene group, trifluoroethylene group, and tetrafluoroethylene group; cyclic hydrocarbon groups such as cyclohexylene group, phenylene group, benzylene group, naphthylene group, anthracylene group, naphthasylene group, and pentasylene group; linear alkylenedioxy groups such as an oxy group, an ethylenedioxy group, a propylenedioxy group, a butylenedioxy group, a pentylenedioxy group, a hexylenedioxy group, a heptylenedioxy group, an octylenedioxy group, or a nonylenedioxy group; cyclic alkylenedioxy groups such as a cyclohexylenedioxy group; an iodomethylenedioxy group, a diiodomethylenedioxy group, a bromomethylenedioxy group, a dibromomethylenedioxy group, a fluoromethylenedioxy group, a difluoromethylenedioxy group, an iodoethylenedioxy group, a 1,1-diiodoethylenedioxy group, a 1,2-diiodoethylenedioxy group, a triiodoethylenedioxy group, a tetraiodoethylenedioxy group, a chloroethylenedioxy group, a 1,1-dichloroethylenedioxy group, a 1,2-dichloroethylenedioxy group, a trichloroethylenedioxy group, a tetrachloroethylenedioxy group, a fluoroethylenedioxy group, a 1,1-difluoroethylenedioxy group, a 1,Examples include halogen-containing linear alkylenedioxy groups such as 2-difluoroethylenedioxy group, trifluoroethylenedioxy group, and tetrafluoroethylenedioxy group, arylenedioxy groups such as phenylenedioxy group, benzylenedioxy group, naphthylenedioxy group, anthracylenedioxy group, naphthacylenedioxy group, and pentacylenedioxy group, and groups in which part or all of these groups have been replaced with halogen atoms or the like.

[0030] The constituent material (B) represented by the chemical formula (1) preferably contains at least lithium difluorooxalatoborate, sodium difluorooxalatoborate, or potassium difluorooxalatoborate, which may be used alone or in combination.

[0031] The constituent material (B) represented by the chemical formula (2) preferably contains at least lithium difluorobisoxalatophosphate, sodium difluorobisoxalatophosphate, potassium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, sodium tetrafluorooxalatophosphate, or potassium tetrafluorooxalatophosphate, which may be used alone or in combination.

[0032] The content of the constituent material A in the positive electrode active material coating material is preferably 30 mol % to 99 mol %, more preferably 40 mol % to 95 mol %, and even more preferably 70 mol % to 90 mol %, from the viewpoints of improving the discharge capacity and suppressing an increase in internal resistance.

[0033] The content of constituent material B in the positive electrode active material coating material is preferably 1 mol % to 70 mol %, more preferably 5 mol % to 60 mol %, and even more preferably 10 mol % to 30 mol %, from the viewpoints of improving the discharge capacity and suppressing an increase in internal resistance.

[0034] The positive electrode active material coating material according to this embodiment may contain, in addition to the constituent materials A and B, any of titanic acids, zirconic acids, hafnic acids, niobic acids, tantalic acids, aluminic acids, and the like.

[0035] The positive electrode active material coating material according to this embodiment can be used as a solid electrolyte in addition to coating the positive electrode active material.

[0036] (Coating on Positive Electrode Active Material) In this specification, coating on a positive electrode active material means that the coating material for a positive electrode active material of the present invention is present on the surface of the positive electrode active material.

[0037] In this embodiment, examples of the coating method on the positive electrode active material include a tumbling fluidization method using a tumbling fluidization granulation coating device, a method using a spray dryer, a mechanochemical milling method, a method of evaporating the solvent from a slurry obtained by mixing the positive electrode active material with a solution in which a precursor of the coating material has been dissolved, followed by sintering, a method of evaporating the solvent from a slurry obtained by mixing the positive electrode active material with a solution of the coating material, a CVD (Chemical Vapor Deposition) method, a PVD (Physical Vapor Deposition) method, a method using a pulverizer, and a manual method using a mortar and pestle, but the coating method on the positive electrode active material is not limited to these.

[0038] The coating amount of the positive electrode active material coating material in this embodiment may be, for example, 0.01 to 100 parts by mass, 0.1 to 50 parts by mass, or 1 to 20 parts by mass per 100 parts by mass of the positive electrode active material.

[0039] By using a positive electrode using a positive electrode active material coated with the positive electrode active material coating material of this embodiment, in a non-aqueous electrolyte lithium ion battery, a protective film similar to an SEI can be formed directly on the surface of the positive electrode active material in advance, without using conventional SEI formation techniques that involve the electrochemical reaction of additives added to a non-aqueous electrolyte during the battery fabrication process. This eliminates the problems associated with forming an SEI through electrochemical reactions and contributes to performance stabilization. Furthermore, it is believed that the use of the positive electrode active material coating material of the present invention can effectively prevent transition metal elution and electrolyte degradation during charging reactions, thereby improving discharge capacity and suppressing increases in internal resistance.

[0040] In all-solid-state batteries, similar to non-aqueous electrolyte lithium-ion secondary batteries, when a potential is applied during charging, reactions other than electrode reactions can occur between the electrode active material and the solid electrolyte. The influence of these reaction products increases interfacial resistance even if a good contact interface is formed. In fact, lithium niobate, which has been used as a coating material for a positive electrode active material, lacks sufficient oxidation resistance, and therefore has not been sufficiently improved in terms of discharge capacity and internal resistance. It is believed that the use of the coating material for a positive electrode active material of the present invention can more effectively prevent the elution of transition metals and the degradation of the solid electrolyte during charging reactions, thereby improving discharge capacity and suppressing an increase in internal resistance.

[0041] (Secondary Battery) Next, the secondary battery of the present invention will be described below using a nonaqueous electrolyte lithium ion secondary battery and an all-solid-state lithium ion secondary battery as examples. Fig. 1 is a cross-sectional schematic diagram showing a nonaqueous electrolyte lithium ion secondary battery provided with the positive electrode active material coating material, and Fig. 2 is a cross-sectional schematic diagram showing an outline of an all-solid-state lithium ion secondary battery provided with the positive electrode active material coating material.

[0042] (Cell Structure of Nonaqueous Electrolyte Secondary Battery) As shown in FIG. 1 , the nonaqueous electrolyte lithium ion secondary battery according to this embodiment has a structure in which a stack of a positive electrode 1, a separator 3, a negative electrode 2, and a spacer 7 is housed in an internal space formed by a positive electrode can 4 and a negative electrode can 5, in this order from the positive electrode can 4 side. A spring 8 is interposed between the negative electrode can 5 and the spacer 7, thereby appropriately pressing and fixing the positive electrode 1 and the negative electrode 2. A nonaqueous electrolyte is impregnated between the positive electrode 1, the separator 3, and the negative electrode 2. The positive electrode can 4 and the negative electrode can 5 are sandwiched with a gasket 6 interposed between them to join them and seal the stack.

[0043] The positive electrode active material in the positive electrode active material layer of the positive electrode 1 is not particularly limited, and examples thereof include a transition metal compound having a structure in which lithium ions can diffuse, or an oxide of the transition metal compound and lithium. More specifically, the positive electrode active material is, for example, LiCoO ２ LiNiO ２ LiMnO２ ; LiMn ２ O ４ ; Li ２ MnO ３ and LiMeO ２ (Me = Mn, Co, Ni) solid solution; LiFePO ４ ; LiMn ｘ Fe ｙ P.O. ４ (0.5≦x≦0.75, 0.25≦y≦0.5, x+y=1); LiCoPO ４ LiMnPO ４ ; LiNiPO ４ ; Li ２ CoP ２ O ７ ; Li ２ FePO ４ F; binary transition metal oxide; ternary transition metal oxide; LiFeF ３ TiO ２ , V ２ O ５ , and MoO ３ oxides such as TiS ２ , and sulfides such as FeS. Furthermore, examples of the positive electrode active material include conductive polymers such as polyacetylene, polyparaphenylene, polyaniline, and polypyrrole; activated carbon; radical-generating polymers; and carbon materials. Among the positive electrode active materials listed above, binary transition metal oxides and ternary transition metal oxides are preferred in this embodiment.

[0044] The binary transition metal oxide is not particularly limited, and examples thereof include LiNi ｘ１ Co ｙ１ O ｚ１ (0<x1<2, 0<y1<2, 2≦z1≦4, 1≦x1+y1≦2), LiNi ｘ２ Mn ｙ２ O ｚ２ (0<x2<2, 0<y2<2, 2≦z2≦4, 1≦x2+y2≦2), LiCo ｘ３ Mn ｙ３ O ｚ３(0<x3<2, 0<y3<2, 2≦z3≦4, 1≦x3+y3≦2), etc. These binary transition metal oxides may have some of their oxygen atoms replaced with other non-metal atoms such as phosphorus atoms, boron atoms, or fluorine atoms.

[0045] The LiNi ｘ１ Co ｙ１ O ｚ１ , and LiNi ｘ２ Mn ｙ２ O ｚ２ In the binary transition metal oxide comprising the above formula, x1 and x2 represent the composition ratio of nickel in the binary transition metal oxide. x1 and x2 are each greater than 0 and less than 2, preferably greater than 0.1 and less than 1.9, and more preferably greater than 0.5 and less than 1.5. x1 and x2 can be controlled by adjusting the amount of nickel supplied during the production of the positive electrode active material. y1 represents the composition ratio of cobalt in the binary transition metal oxide. y1 is greater than 0 and less than 2, preferably greater than 0.1 and less than 1.9, and more preferably greater than 0.5 and less than 1.5. y1 can be controlled by adjusting the amount of cobalt supplied during the production of the positive electrode active material. y2 represents the composition ratio of manganese in the binary transition metal oxide. y2 is greater than 0 and less than 2, preferably greater than 0.1 and less than 1.9, and more preferably greater than 0.5 and less than 1.5. y2 can be controlled by adjusting the amount of manganese supplied when producing the positive electrode active material. ｘ２ Mn ｙ２ O ｚ２ As a binary transition metal oxide consisting of LiNi, from the viewpoint of availability and battery characteristics, ０．５ Mn １．５ O ４ is preferred.

[0046] The LiCo ｘ３ Mn ｙ３ O ｚ３In the binary transition metal oxide comprising the above, x3 represents the composition ratio of cobalt in the binary transition metal oxide. x3 is greater than 0 and less than 2, preferably 0.1 or more and 1.9 or less, and more preferably 0.5 or more and 1.5 or less. x3 can be controlled by adjusting the amount of cobalt supplied when producing the positive electrode active material. y3 represents the composition ratio of manganese in the binary transition metal oxide. y3 is greater than 0 and less than 2, preferably 0.1 or more and 1.9 or less, and more preferably 0.5 or more and 1.5 or less. y3 can be controlled by adjusting the amount of manganese supplied when producing the positive electrode active material.

[0047] The ternary transition metal oxides include LiNi ｘ４ Co ｙ４ Mn ｚ４ O ２ (0<x4<1, 0<y4<1, 0<z4<1, x4+y4+z4=1), and LiNi ｘ５ Co ｙ５ Al ｚ５ O ２ (0<x5<1, 0<y5<1, 0<z5<1, x5+y5+z5=1). These ternary transition metal oxides may have some of the oxygen atoms substituted with other non-metal atoms such as phosphorus atoms, boron atoms, or fluorine atoms.

[0048] The LiNi ｘ４ Co ｙ４ Mn ｚ４ O ２In the ternary transition metal oxide comprising the above, x4 represents the composition ratio of nickel in the ternary transition metal oxide. x4 is greater than 0 and less than 1, preferably 0.6 or greater but less than 1, and more preferably 0.6 or greater but less than 0.9. x4 can be controlled by adjusting the amount of nickel supplied during the production of the positive electrode active material. y4 represents the composition ratio of cobalt in the ternary transition metal oxide. y4 is greater than 0 and less than 1, preferably 0.05 or greater but less than 0.2, and more preferably 0.05 or greater but less than 0.1. y4 can be controlled by adjusting the amount of cobalt supplied during the production of the positive electrode active material. z4 represents the composition ratio of manganese in the ternary transition metal oxide. z4 is greater than 0 and less than 1, preferably 0.05 or greater but less than 0.2, and more preferably 0.05 or greater but less than 0.1. z4 can be controlled by adjusting the amount of manganese supplied during the production of the positive electrode active material.

[0049] The LiNi ｘ５ Co ｙ５ Al ｚ５ O ２In the ternary transition metal oxide comprising the above, x5 represents the composition ratio of nickel in the ternary transition metal oxide. x5 is greater than 0 and less than 1, preferably 0.6 or greater but less than 1, and more preferably 0.6 or greater but less than 0.9. x5 can be controlled by adjusting the amount of nickel supplied during the production of the positive electrode active material. y5 represents the composition ratio of cobalt in the ternary transition metal oxide. y5 is greater than 0 and less than 1, preferably 0.05 or greater but less than 0.2, and more preferably 0.05 or greater but less than 0.1. y5 can be controlled by adjusting the amount of cobalt supplied during the production of the positive electrode active material. z5 represents the composition ratio of aluminum in the ternary transition metal oxide. z5 is greater than 0 and less than 1, preferably 0.05 or greater but less than 0.2, and more preferably 0.05 or greater but less than 0.1. z5 can be controlled by adjusting the amount of aluminum supplied during the production of the positive electrode active material.

[0050] Among the positive electrode active materials exemplified above, LiCoO ２ LiNiO ２ ; Li ２ MnO ３ and LiMeO ２ (Me = Mn, Co, Ni) solid solution; LiNi ｘ４ Co ｙ４ Mn ｚ４ O ２ (0<x4<1, 0<y4<1, 0<z4<1, x4+y4+z4=1), or LiNi ｘ５ Co ｙ５ Al ｚ５ O ２ (0<x5<1, 0<y5<1, 0<z5<1, x5+y5+z5=1) is preferred, and LiNi is more preferred. ｘ４ Co ｙ４ Mn ｚ４ O ２ (0.6≦x4<1, 0<y4<0.4, 0<z4<0.4, x4+y4+z4=1, 0<y4+z4≦0.4), or LiNi ｘ５ Co ｙ５Al ｚ５ O ２ A ternary transition metal oxide consisting of (0.6≦x5<1, 0<y5<0.4, 0<z5<0.4, x5+y5+z5=1, 0<y5+z5≦0.4) is used.

[0051] The positive electrode 1 can be obtained by pressure molding the positive electrode active material listed above together with a known conductive additive and binder, or by mixing the positive electrode active material together with a known conductive additive and binder in an organic solvent such as pyrrolidone to form a paste, applying the paste to a current collector such as aluminum foil, and then drying the paste.

[0052] The material for the negative electrode active material layer in the negative electrode 2 is not particularly limited as long as it is a material capable of absorbing and releasing lithium, and examples thereof include metal composite oxides, lithium metal, lithium alloys, silicon, silicon-based alloys, silicon-based materials, SiC, SiOC, tin-based alloys, metal oxides, and carbon materials.

[0053] The metal composite oxide is not particularly limited, and examples thereof include Li ４ Ti ５ O １２ , LiFe ２ O ３ , LiWO ２ , Sn ｘ Me １ １－ｘ Me ２ ｙ O ｚ (Me １ = Mn, Fe, Pb, Ge, Me ２ =Al, B, P, Si, elements of groups 1 to 3 of the periodic table, halogens, where 0<x≦1, 1≦y≦3, 1≦z≦8), etc.

[0054] The metal oxide is not particularly limited, and examples thereof include SnO, SnO ２ , SiO ｘ (0<x≦2), PbO, PbO ２ , Pb ２ O ３ , Pb ３ O ４ , Sb ２ O ３ , Sb ２ O ４ , Sb２ O ５ , GeO, GeO ２ , Bi ２ O ３ , Bi ２ O ４ , Bi ２ O ５ etc.

[0055] The carbon material is not particularly limited, and examples thereof include natural graphite, artificial graphite, boronized graphite, fluorinated graphite, mesocarbon microbeads, pitch-based graphitized carbon fibers, carbon nanotubes, hard carbon, and fullerene.

[0056] The electrode material in foil or powder form can be used for the negative electrode 2. In the case of powder form, it can be obtained by pressure molding together with a known conductive additive and binder, or by mixing together with a known conductive additive and binder in an organic solvent such as pyrrolidone to form a paste, which is then applied to a current collector such as copper foil and then dried.

[0057] The electrode material in foil or powder form can be used for the negative electrode 2. In the case of powder form, it can be obtained by pressure molding together with a known conductive additive and binder, or by mixing together with a known conductive additive and binder in an organic solvent such as pyrrolidone to form a paste, which is then applied to a current collector such as copper foil and then dried.

[0058] <Electrolyte in Nonaqueous Electrolyte Secondary Battery> The electrolyte according to this embodiment will be described below.

[0059] The electrolytic solution is composed of an organic solvent and an electrolyte, and may also contain one or more additives.

[0060] <Electrolyte> As the electrolyte, a conventionally known electrolyte used in various secondary batteries can be used. From the viewpoint of solubility in a non-aqueous solvent and the characteristics of the secondary battery, the electrolyte preferably has an alkali metal ion as a cation. Examples of alkali metal ions include lithium ions, sodium ions, and potassium ions. For example, when the secondary battery is a lithium ion secondary battery, a lithium salt can be used as the electrolyte.

[0061] The electrolyte preferably has a fluorine-containing anion. The fluorine-containing anion is not particularly limited, and examples thereof include BF ４ － , P.F. ６ － , B.F. ３ CF ３ － , B.F. ３ C ２ F ５ － , C.F. ３ SO ３ － , C ２ F ５ SO ３ － , C ３ F ７ SO ３ － , C ４ F ９ SO ３ － , N(SO ２ F) ２ － , N(CF ３ SO ２ ) ２ － , N(C ２ F ５ SO ２ ) ２ － , N(CF ３ SO ２ ) (CF ３ CO) － , N(CF ３ SO ２ ) (C ２ F ５ SO ２ ) － , and C(CF ３ SO ２ ) ３ － These electrolytes having fluorine-containing anions can be used alone or in combination of two or more. Among the fluorine-containing anions, BF is particularly preferred from the viewpoint of safety and stability of the non-aqueous electrolyte, as well as improvement of electrical conductivity and cycle characteristics. ４ － , P.F.６ － and N(CF ３ SO ２ ) ２ － is preferred, and BF ４ － and PF ６ － is particularly preferred.

[0062] The concentration of the electrolyte relative to the organic solvent is not particularly limited, and is usually 0.1 to 2 M, preferably 0.15 to 1.8 M, more preferably 0.2 to 1.5 M, and particularly preferably 0.3 to 1.2 M. By setting the concentration to 0.1 M or more, it is possible to prevent the electrical conductivity of the non-aqueous electrolyte from becoming insufficient. On the other hand, by setting the concentration to 2 M or less, it is possible to suppress a decrease in electrical conductivity due to an increase in the viscosity of the non-aqueous electrolyte, and to prevent a decrease in secondary battery performance.

[0063] <Organic Solvent> The organic solvent (nonaqueous solvent) used in the nonaqueous electrolyte solution is not particularly limited, and examples thereof include cyclic carbonate esters, chain carbonate esters, phosphate esters, cyclic ethers, chain ethers, lactone compounds, chain esters, nitrile compounds, amide compounds, sulfone compounds, etc. Among these organic solvents, carbonate esters are preferred because they are commonly used as organic solvents for secondary batteries.

[0064] The cyclic carbonate is not particularly limited, and examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate partially substituted with fluorine, trans-difluoroethylene carbonate, and cis-difluoroethylene carbonate.

[0065] The chain carbonate ester is not particularly limited, and examples thereof include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoromethyl methyl carbonate partially substituted with fluorine, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, bis(fluoromethyl)carbonate, bis(difluoro)methyl carbonate, bis(trifluoromethyl)carbonate, 2-fluoroethyl methyl carbonate, ethyl fluoromethyl carbonate, 2,2-difluoroethyl methyl carbonate, 2-fluoroethyl fluoromethyl carbonate, ethyl difluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, and 2,2-difluoroethyl fluoromethyl carbonate. Examples of difluoromethyl carbonate, 2-fluoroethyl difluoromethyl carbonate, ethyl trifluoromethyl carbonate, and diethyl carbonate include ethyl (2-fluoroethyl) carbonate, ethyl (2,2-difluoroethyl) carbonate, bis (2-fluoroethyl) carbonate, ethyl (2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl-2'-fluoroethyl carbonate, bis (2,2-difluoroethyl) carbonate, 2,2,2-trifluoroethyl-2'-fluoroethyl carbonate, 2,2,2-trifluoroethyl-2',2'-difluoroethyl carbonate, and bis (2,2,2-trifluoroethyl) carbonate.

[0066] The carbonate ester partially substituted with fluorine functions not only as an organic solvent but also as the additive described above. When used as both a solvent and an additive, the content is not specifically limited, and the solvent can be used in the mixing ratio as a solvent, and the additive can be used in the content described as an additive.

[0067] The phosphate ester is not particularly limited, and examples thereof include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, trifluoroethyl dimethyl phosphate partially substituted with fluorine, bis(trifluoroethyl)methyl phosphate, and tris(trifluoroethyl)phosphate.

[0068] The cyclic ether is not particularly limited, and examples thereof include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane.

[0069] The chain ether is not particularly limited, and examples thereof include dimethoxyethane, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0070] The lactone compound is not particularly limited, and examples thereof include γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

[0071] The chain ester is not particularly limited, and examples thereof include methyl propionate, methyl acetate, ethyl acetate, methyl formate, methyl difluoroacetate partially substituted with fluorine, and ethyl trifluoroacetate.

[0072] The nitrile compound is not particularly limited, and examples thereof include acetonitrile, adiponitrile, and valeronitrile.

[0073] The amide compound is not particularly limited, and examples thereof include dimethylformamide.

[0074] The sulfone compound is not particularly limited, and examples thereof include sulfolane, sulfolene, and 3-methylsulfolane.

[0075] These organic solvents may be used singly or in combination of two or more.

[0076] <Additives> Examples of additives include cyclic carbonates having an unsaturated bond, cyclic carbonates having a halogen atom, cyclic sulfonates, cyclic sulfates, cyclic sulfites, phosphates, sulfonylimide salts, and sulfonates.

[0077] [Cyclic Carbonate Having Unsaturated Bond] The cyclic carbonate having unsaturated bonds in the additive is not particularly limited in type, and various types can be selected as long as it does not impair the properties of the nonaqueous electrolyte solution and the secondary battery using the same. The number of unsaturated bonds is preferably 1 to 10, more preferably 1 to 5, and particularly preferably 1 to 3. Specific examples of cyclic carbonates having an unsaturated bond include vinylene carbonate, iodovinylene carbonate, bromovinylene carbonate, chlorovinylene carbonate, fluorovinylene carbonate, 1,2-diiodovinylene carbonate, 1,2-dibromovinylene carbonate, 1,2-dichlorovinylene carbonate, 1,2-difluorovinylene carbonate, methylvinylene carbonate, iodomethylvinylene carbonate, bromomethylvinylene carbonate, chloromethylvinylene carbonate, fluoromethylvinylene carbonate, Examples of the cyclic carbonate include dichloromethyl vinylene carbonate, dibromomethyl vinylene carbonate, dichloromethyl vinylene carbonate, difluoromethyl vinylene carbonate, triiodomethyl vinylene carbonate, tribromomethyl vinylene carbonate, trichloromethyl vinylene carbonate, trifluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, vinyl ethylene carbonate, etc. Among the cyclic carbonates having an unsaturated bond, vinylene carbonate is preferred from the viewpoint of availability.

[0078] [Cyclic Carbonate Having a Halogen Atom] The cyclic carbonate having a halogen atom in the additive is not particularly limited in type, and various types can be selected as long as it does not impair the characteristics of the nonaqueous electrolyte solution of this embodiment and the secondary battery using the same. Here, a halogen atom refers to a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. Specific examples of cyclic carbonates having a halogen atom include iodoethylene carbonate, bromoethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, 1,2-diiodoethylene carbonate, 1,2-dibromoethylene carbonate, 1,2-dichloroethylene carbonate, and 1,2-difluoroethylene carbonate. From the viewpoint of availability, chloroethylene carbonate and fluoroethylene carbonate are preferred as the cyclic carbonate having an unsaturated bond.

[0079] [Cyclic Sulfonate Ester] The cyclic sulfonate ester in the additive is not particularly limited in type, and various cyclic sulfonates can be selected as long as they do not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Specific examples of cyclic sulfonates include 1,3-propane sultone, 2,4-butane sultone, 1,4-butane sultone, and ethylene sulfite. From the viewpoint of availability, 1,3-propane sultone and ethylene sulfite are preferred as the cyclic sulfonate ester.

[0080] [Cyclic Sulfate] The cyclic sulfate in the additive is not particularly limited in type, and various types can be selected as long as they do not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Specific examples of cyclic sulfate include ethylene sulfate.

[0081] [Cyclic Sulfite] The cyclic sulfite in the additive is not particularly limited in type, and various types can be selected as long as they do not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Specific examples of cyclic sulfates include ethylene sulfite and 1,3-propylene sulfite.

[0082] [Phosphates] The phosphates in the additives are not particularly limited in type, and various types can be selected as long as they do not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Specific examples of cyclic sulfates include lithium difluorophosphate and lithium monofluorophosphate.

[0083] [Sulfonylimide Salts] The sulfonylimide salts in the additives are not particularly limited in type, and various salts can be selected as long as they do not impair the properties of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Specific examples of sulfonylimide salts include lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0084] [Sulfonates] The sulfonates in the additives are not particularly limited in type, and various types can be selected as long as they do not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Specific examples of sulfonates include lithium fluorosulfonate, lithium methanesulfonate, and lithium trifluoromethanesulfonate.

[0085] The additives may be used singly or in combination of two or more.

[0086] <Solid electrolyte in solid secondary battery> As the solid electrolyte, a conventionally known material used in various energy storage elements can be used. For example, when the energy storage element is a solid-state lithium ion secondary battery, an inorganic solid material containing lithium as a constituent element can be suitably used.

[0087] The electrolyte preferably contains sulfur or oxygen. Specific examples of such electrolytes containing sulfur include Li ９．５４ Si １．７４ P １．４４ S １１．７ Cl ０．３ , Li １０ GeP ２ S １２ (LGPS), Li ６ P.S. ５ Cl, 30Li ２ S・26B ２ S ３ ・44LiI, 50Li ２ S・17P ２ S ５ ・33LiBH ４ , 63Li ２ S・36SiS ２ ・1Li ３ P.O. ４ , 57Li ２ S・38SiS ２ ・5Li ４ SiO ４ , 70Li ２ S・30P ２ S ５ , Li ７ P ３ S １１ , Li ３．２５ P ０．９５ S ４ Specific examples of electrolytes containing oxygen include Li ０．３４ La ０．５１ TiO ２．９４ , Li １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３ , Li ７ La ３ Zr ２ O １２ (LLZ), 50Li ４ SiO ４ ・50Li ３ BO ３ , Li ２．９ P.O. ３．３ N ０．４６ (LiPON), Li ３．６ Si ０．６ P０．４ O ４ , Li １．０７ Al ０．６９ Ti １．４６ (P.O. ４ ) ３ , Li １．５ Al ０．５ Ge １．５ (P.O. ４ ) ３ These can be used alone or in combination of two or more. ６ P.S. ５ Cl is particularly preferred.

[0088] When used in a solid-state secondary battery, the solid electrolyte or the positive electrode active material coating material may contain an electrolytic solution. In this case, unlike conventional nonaqueous electrolyte-based lithium ion secondary batteries, a large amount of nonaqueous electrolyte is not contained, but a small amount of nonaqueous electrolyte is used to compensate for incomplete contact between the active material and the solid electrolyte. Because only a small amount of nonaqueous electrolyte is used, the battery appears similar to a solid-state battery at first glance, and is therefore sometimes called a quasi-solid-state battery.

[0089] The electrolyte solution that may be contained when used in the solid secondary battery is composed of an organic solvent and an electrolyte, and may also contain one or more additives, and the electrolyte solution in the nonaqueous electrolyte secondary battery described above can be used.

[0090] (Cell Configuration of Solid-State Battery) As shown in Figure 2, a cylindrical insulating tube 11 is filled with a solid electrolyte 14, and a cathode composite 13, which is a mixture of a cathode active material using a cathode active material coated with a cathode active material coating material, a solid electrolyte, and a conductive additive in a predetermined ratio, is placed on top of the solid electrolyte 14, resulting in a two-layered compact. Furthermore, below the solid electrolyte 14, an indium foil 15 and a lithium foil 16 are present, and these are pressed onto a stainless steel jig 12 to form a battery. The cylindrical insulating tube 11, sandwiched between the stainless steel jigs 12 on the top and bottom, is housed in a sealed battery evaluation cell (KP-solidCell) manufactured by Hohsen Co., Ltd.

[0091] The shape of the secondary battery of this embodiment is not particularly limited, and examples thereof include a coin-type cell, a cylindrical type, a square type, a laminate type, and the like.

[0092] The all-solid-state lithium ion secondary battery provided with the coating material of the present embodiment is suitable as an on-board power source for, for example, electric vehicles (xEVs) and hybrid electric vehicles, which require high operating voltage and high-temperature storage performance.

[0093] The charging voltage of the lithium secondary battery of this embodiment is, for example, LiCoO ２ and LiNi １／３ Co １／３ Mn １／３ O ２ When using LiMn, the end-of-charge voltage of the positive electrode is preferably set in the range of 4.3 to 5.0 V, more preferably 4.35 to 4.8 V, and particularly preferably 4.4 to 4.7 V, based on lithium metal. １．５ Ni ０．５ O ４ When using a lithium metal battery, the end-of-charge voltage of the positive electrode is preferably set within the range of 4.7 to 6.0 V, more preferably 4.9 to 5.9 V, and particularly preferably 5.0 to 5.8 V, based on the lithium metal. ＋ In the cell configuration of the solid-state battery shown in FIG. 2, an indium foil 15 and a lithium foil 16 are pressed together to form a negative electrode. The potential of the negative electrode made of the indium foil and the lithium foil at this time, that is, Li ＋ / LiIn is +0.6 V based on lithium metal, so if we describe it as the voltage between the positive and negative electrodes in the cell configuration of the solid-state battery in Figure 2, for example, LiCoO ２ and LiNi １／３ Co １／３ Mn １／３ O ２ When using LiMn, the end-of-charge voltage is preferably set in the range of 3.7 to 4.4 V, more preferably 3.75 to 4.2 V, and particularly preferably 3.8 to 4.1 V. １．５ Ni ０．５ O ４When using the above, the inter-electrode voltage between the positive electrode and the negative electrode in the cell configuration of the solid state battery of FIG. 2 is preferably set within the range of 4.1 to 5.4 V, more preferably 4.3 to 5.3 V, and particularly preferably 4.4 to 5.2 V.

[0094] The solid-state lithium-ion secondary battery according to this embodiment can exhibit excellent discharge characteristics and internal resistance characteristics, and the coating material according to this embodiment can be suitably used for, for example, all-solid-state lithium-ion secondary batteries. However, the solid-state lithium-ion secondary battery shown in FIG. 2 is an exemplary embodiment of the secondary battery of the present invention, and the secondary battery of the present invention is not limited thereto.

[0095] Preferred manufacturing examples and working examples of the present invention are described in detail below. However, the described manufacturing examples, materials, compounding amounts, etc., do not limit the scope of the present invention unless otherwise specified.

[0096] Example 1 Synthesis of a coating material for a positive electrode active material Li was used as a raw material powder in an argon atmosphere having a dew point of −80° C. or less. ３ AlF ６ (manufactured by Stella Chemifa Corporation), and lithium difluorooxalatoborate (manufactured by Sigma-Aldrich, LiFOB) ３ AlF ６ The mixture was prepared so that the molar ratio of LiF:LiFOB was 4.0:1.0. The mixture was placed in a 45 mL zirconia pot (manufactured by Fritsch) containing seven zirconia balls (manufactured by Nikkato Corporation) with a diameter of 10 mm and 3 g of a zirconia ball (manufactured by Fritsch) and milled at 600 rpm for 7.5 hours using a planetary ball mill (manufactured by Fritsch, P-7S). In this way, a powder of the coating material according to Example 1 was obtained.

[0097] <Implementation of Positive Electrode Coating> Lithium cobalt oxide (LCO, manufactured by Nippon Chemical Industry Co., Ltd.) with an average particle size of 10 μm was used as the positive electrode active material for the positive electrode active material layer. This LCO and coating material were weighed out to a mass ratio of 60:3 (=LCO:coating material), and placed in a PTFE container together with zirconia balls with a diameter of 10 mm. The mixture was mixed in a mini mill (P-23, manufactured by Fritsch) at 15 Hz for 7 minutes to prepare a positive electrode material.

[0098] <Preparation of Positive Electrode Composite> Positive electrode material and solid electrolyte (Sigma-Aldrich, Li ６ P.S. ５ Cl) and a conductive additive (AB, manufactured by Denka Co., Ltd.) were weighed out to a mass ratio of 63:39:1 (=positive electrode material:solid electrolyte:AB), and the mixture was placed in a PTFE container together with zirconia balls having a diameter of 10 mm. The mixture was mixed in a mini mill (P-23, manufactured by Fritsch) at 15 Hz for 1 minute to obtain a positive electrode composite.

[0099] <Preparation of All-Solid-State Battery> In an argon atmosphere having a dew point of -80°C or less, 80 mg of solid electrolyte was introduced into a cylindrical polycarbonate insulating tube with an inner diameter of 10 mm, and electronically conductive stainless steel members were inserted from above and below. A solid electrolyte layer was prepared by pre-molding at 1 MPa. 10.3 mg of the cathode composite prepared above was stacked on top of this solid electrolyte layer and again press-molded at 28 MPa for 10 minutes. The lower member was then removed, and a lithium foil (manufactured by Honjo Metals Co., Ltd.) pre-cut to φ = 7 mm was crimped onto it, and an indium foil (manufactured by Nilaco Corporation) pre-cut to φ = 8 mm was crimped onto it so that the lithium foil was covered. The lower member was attached to an insulating tube and placed in a sealed battery evaluation cell (manufactured by Hosen Co., Ltd., KP-SolidCell), and the evaluation cell was assembled by restraining it at 5 N m for 5 minutes. This evaluation cell was designed to be continuously pressed with a predetermined restraining force in the stacking direction.

[0100] <Cycle test> Each cell was charged in a thermostatic chamber at 25°C with a charging current of 0.066 mA / cm ２ The battery was charged to a final voltage of 3.9 V at a discharge current of 0.066 mA / cm ２The battery was discharged to a final voltage of 2.0 V at 1000 kJ / s. Here, the voltage indicated does not refer to the lithium metal standard explained in paragraph 0094, but to the voltage between the negative electrode and the positive electrode. Unless otherwise specified, the voltage indicated in the following examples and comparative examples is the voltage between the negative electrode and the positive electrode. Two cycles of charge and discharge were performed under these conditions. Subsequently, a charge current of 0.33 mA / cm was applied. ２ The battery was charged to a final voltage of 3.9 V at a discharge current of 0.33 mA / cm ２ The battery was discharged at a discharge current of 0.66 mA / cm until the final voltage was 2.0 V. Three charge-discharge cycles were performed under these conditions. ２ The battery was charged to a final voltage of 3.9 V and discharged at a current of 0.66 mA / cm ２ The battery was discharged to a cut-off voltage of 2.0 V. Five charge / discharge cycles were performed under these conditions. The discharge capacity at the first cycle for each example and comparative example is shown as a ratio, with Comparative Example 1 in Table 1, Comparative Example 4 in Table 2, and Comparative Example 7 in Table 3 set to 100.

[0101] <Measurement of Internal Resistance> After the 10 cycle tests described above, the evaluation cell was connected to a potentiostat (Biologic, VSP-300S) equipped with a frequency response analyzer while pressure was still applied. The upper part of the evaluation cell was connected to the working electrode and a potential measurement terminal. The lower part of the evaluation cell was connected to the counter electrode and a reference electrode. The impedance of the all-solid-state batteries in each example and comparative example was measured at 25°C by electrochemical impedance measurement. The measurement data at this time are shown as a ratio, with Comparative Example 1 in Table 1, Comparative Example 4 in Table 2, and Comparative Example 7 in Table 3 each set to 100.

[0102] (Example 2) In Example 2, the positive electrode active material coating material was ３ AlF ６ The molar ratio of LiFOB to LiFOB was 5.0:1.0.

[0103] (Example 3) In Example 3, Li was added to the positive electrode active material coating material. ３ AlF ６ The molar ratio of LiFOB to LiFOB was 1.0:1.0.

[0104] Comparative Example 1 Comparative Example 1 does not use the positive electrode active material coating material.

[0105] Comparative Example 2 Comparative Example 2 uses only lithium niobate as the coating material for the positive electrode active material.

[0106] Comparative Example 3 Comparative Example 3 is a comparative example in which Li was used as the positive electrode active material coating material. ３ AlF ６ Only the above was used.

[0107] Example 4 In Example 4, LiMn was used as the positive electrode active material. １．５ Ni ０．５ O ４ As the positive electrode active material coating material, Li ３ AlF ６ The molar ratio of LiF:LiFOB was 4.0:1.0. The cycle test was performed by charging up to a cut-off voltage of 4.9 V and discharging up to a cut-off voltage of 2.0 V.

[0108] Comparative Example 4 Comparative Example 4 uses LiMn as the positive electrode active material. １．５ Ni ０．５ O ４ The cycle test was carried out by charging up to a cut-off voltage of 4.9 V and discharging up to a cut-off voltage of 2.0 V.

[0109] Comparative Example 5 Comparative Example 5 uses LiMn as the positive electrode active material. １．５ Ni ０．５ O ４ The positive electrode active material was coated with only lithium niobate. The cycle test was carried out by charging up to a cut-off voltage of 4.9 V and discharging up to a cut-off voltage of 2.0 V.

[0110] Comparative Example 6 Comparative Example 6 uses LiMn as the positive electrode active material. １．５ Ni ０．５ O ４ As the positive electrode active material coating material, Li ３ AlF ６ The cycle test was carried out by charging up to a cut-off voltage of 4.9 V and discharging up to a cut-off voltage of 2.0 V.

[0111] (Example 5) In Example 5, LiNi was used as the positive electrode active material. １／３ Co １／３ Mn １／３ O ２ As the positive electrode active material coating material, Li ３ AlF ６ The molar ratio of LiFOB to LiFOB was 4.0:1.0.

[0112] Comparative Example 7 Comparative Example 7 uses LiNi as the positive electrode active material. １／３ Co １／３ Mn １／３ O ２ and does not use the positive electrode active material coating material.

[0113] Comparative Example 8 Comparative Example 8 uses LiNi as the positive electrode active material. １／３ Co １／３ Mn １／３ O ２ and only lithium niobate was used as the coating material for the positive electrode active material.

[0114] Comparative Example 9 Comparative Example 9 uses LiNi as the positive electrode active material. １／３ Co １／３ Mn １／３ O ２ As the positive electrode active material coating material, Li ３ AlF ６ Only the above was used.

[0115] Example 6: In an argon atmosphere having a dew point of −80° C. or less, Li ３ AlF ６ (manufactured by Stella Chemifa Co., Ltd.), and lithium difluorobisoxalatophosphate (manufactured by Tokyo Chemical Industry Co., Ltd., LiDFBOP). ３ AlF ６The mixture was prepared so that the molar ratio of LiDFBOP was 4.0:1.0. The mixture was placed in a 45 mL zirconia pot (manufactured by Fritsch) containing seven zirconia balls (manufactured by Nikkato Corporation) with a diameter of 10 mm and 3 g of zirconia balls (manufactured by Fritsch), and milled for 7.5 hours at 600 rpm using a planetary ball mill (manufactured by Fritsch, P-7S). In this way, powder of the coating material according to Example 6 was obtained. In Example 6, LCO was used as the positive electrode active material, and Li was added to the positive electrode active material coating material. ３ AlF ６ The molar ratio of LiDFBOP to LiDFBOP was 4.0:1.0.

[0116] Example 7 In Example 7, LCO was used as the positive electrode active material, and Li was used as the coating material for the positive electrode active material. ３ AlF ６ The molar ratio of LiDFBOP to LiDFBOP was 5.0:1.0.

[0117] Example 8 In Example 8, LCO was used as the positive electrode active material, and Li was used as the coating material for the positive electrode active material. ３ AlF ６ The molar ratio of LiDFBOP to LiDFBOP was 1.0:1.0.

[0118] Example 9 In Example 9, LiMn was used as the positive electrode active material. １．５ Ni ０．５ O ４ As the positive electrode active material coating material, Li ３ AlF ６ The molar ratio of LiDFBOP to LiDFBOP was 4.0:1.0. The cycle test was performed by charging to a cut-off voltage of 4.9 V and discharging to a cut-off voltage of 2.0 V.

[0119] (Example 10) In Example 10, LiNi was used as the positive electrode active material. １／３ Co １／３ Mn １／３ O ２ As the positive electrode active material coating material, Li ３ AlF ６ The molar ratio of LiDFBOP to LiDFBOP was 4.0:1.0.

[0120]

[0121]

[0122]

[0123] As shown in Tables 1 to 3, each example exhibited excellent discharge capacity and suppressed increases in internal resistance. Furthermore, comparisons of Examples 1 to 3 with 6 to 8, Examples 4 and 9, and Examples 5 and 10 reveal that the embodiment using chemical formula (1) as constituent material (B) and the embodiment using chemical formula (2) exhibited comparable results. While the above examples illustrate the application of the present invention to a solid-state lithium-ion secondary battery using an inorganic solid electrolyte as the electrolyte, the present invention is not limited to these. For example, a material having lithium ion conductivity, such as a polymer solid electrolyte composed of an electrolyte and a polymer compound that dissolves the electrolyte, can be used. Examples of polymers that can be used include ether-based polymers such as polyethylene oxide, poly(methacrylate) esters, and acrylates, either alone or copolymerized or mixed in a molecule.

[0124] The positive electrode active material coating material according to this embodiment can be suitably used in secondary batteries.

[0125] REFERENCE SIGNS LIST 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode can 5 Negative electrode can 6 Gasket 7 Spacer 8 Spring 11 Cylindrical insulating tube 12 Stainless steel jig 13 Positive electrode mixture 14 Solid electrolyte 15 Indium foil 16 Lithium foil

Claims

1. A coating material for a positive electrode active material for coating a positive electrode active material, the coating material for a positive electrode active material comprising, as a constituent material (A), a compound composed of at least one element selected from the group consisting of an alkali metal, an alkaline earth metal, and Al, and F, and comprising, as a constituent material (B), one or more of the compounds represented by chemical formula (1) and / or chemical formula (2). (However, the above M ｎ＋ is an alkali metal ion or an alkaline earth metal ion, and n represents a valence. １ ~X ４ represents a halogen atom, a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms, or a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms and having at least one halogen atom or unsaturated bond, or X １ ~X ４ two of the groups are bonded to each other, -OOC-COO-, -OOCO-, -OOC-Y １ -COO-, -OOC-Y ２ -O- or -O-Y ３ In this case, the Y １、 Y ２ , and Y ３ represents a hydrocarbon group having a linear or cyclic structure and having 1 to 10 carbon atoms, or a hydrocarbon group having at least one of a halogen atom, an unsaturated bond, or a hetero atom. １ ~X ４ At least one of them is a fluorine atom. (However, the above M ｎ＋ is an alkali metal ion or an alkaline earth metal ion, and n represents a valence. ５ ~X １０ represents a halogen atom, a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms, or a hydrocarbon group or alkoxy group having 1 to 10 carbon atoms and having at least one halogen atom or unsaturated bond, or X ５ ~X １０ At least two of the groups -OOC-COO-, -OOCO-, and -OOC-Y １ -COO-, -OOC-Y ２ -O- or -O-Y ３ In this case, the Y １、 Y ２ , and Y ３ Each of X independently has a linear or cyclic structure and represents a hydrocarbon group having 1 to 10 carbon atoms or a hydrocarbon group having at least one of a halogen atom, an unsaturated bond, or a hetero atom. ５ ~X １０ At least one of them is a fluorine atom.

2. The coating material for a positive electrode active material according to claim 1, wherein the alkali metal of the constituent material (A) is at least one of Li, K and Na.

3. The coating material for a positive electrode active material according to claim 1, wherein the alkali metal of the constituent material (A) is Li.

4. The constituent material (A) is LiF, AlF ３ and Li ３ AlF ６ The positive electrode active material coating material according to claim 1 , comprising at least one compound selected from the group consisting of:

5. The coating material for a positive electrode active material according to claim 1, wherein the alkali metal ion of the constituent material (B) is a lithium ion.

6. The positive electrode active material coating material according to claim 1, characterized in that the compound represented by chemical formula (1) includes one or more compounds selected from the group consisting of lithium difluorooxalatoborate, sodium difluorooxalatoborate, and potassium difluorooxalatoborate.

7. The positive electrode active material coating material according to claim 1, characterized in that the compound represented by the chemical formula (2) contains one or more compounds selected from the group consisting of lithium difluorobisoxalatophosphate, sodium difluorobisoxalatophosphate, potassium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, sodium tetrafluorooxalatophosphate, and potassium tetrafluorooxalatophosphate.

8. A coating material for a positive electrode active material, wherein the content of the constituent material (B) in the coating material for a positive electrode active material is 1 mol % to 70 mol %.

9. A positive electrode using a positive electrode active material coated with the positive electrode active material coating material according to claim 1, wherein the positive electrode active material contains a transition metal oxide.

10. Transition metal oxide is LiCoO ２ The positive electrode of claim 9 , comprising:

11. A positive electrode using a positive electrode active material coated with the positive electrode active material coating material according to claim 1, wherein the positive electrode active material contains a binary transition metal oxide or a ternary transition metal oxide.

12. The binary transition metal oxide is LiNi ｘ２ Mn ｙ２ O ｚ２ 12. The positive electrode of claim 11 comprising: (0<x2<2, 0<y2<2, 2≦z2≦4, 1≦x2+y2≦2).

13. The ternary transition metal oxide is LiNi ｘ４ Co ｙ４ Mn ｚ４ O ２ 12. The positive electrode of claim 11 comprising: (0<x4<1, 0<y4<1, 0<z4<1, x4+y4+z4=1).

14. A secondary battery comprising the positive electrode according to any one of claims 9 to 13, an electrolyte, and a negative electrode.

15. The secondary battery according to claim 14, which is a solid-state lithium ion battery or a non-aqueous electrolyte lithium ion battery.

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