Composition for positive electrode of nonaqueous electrolyte secondary battery, positive electrode, and nonaqueous electrolyte secondary battery

Abstract

To provide a composition for a positive electrode of a nonaqueous electrolyte secondary battery capable of enhancing dispersibility of solid particles to a dispersion medium and forming a positive electrode active material layer excellent in oxidation resistance, and to provide a positive electrode and a secondary battery.SOLUTION: The composition for a positive electrode contains a polymer X containing a constituent (a) and a dispersion medium, the constituent (a) is represented by any one of the following (i) to (iii), the HSP distances from the dispersion medium are 4. 0MPa1 / 2 or less, and the HOMO energy levels are - 6. 4eV or less. R11 and R21 represent hydrogen atoms or alkyl groups, and * represents a bonding site.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composition for a positive electrode of a non-aqueous electrolyte secondary battery, a positive electrode, and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, typified by lithium-ion secondary batteries, have high energy density and excellent storage performance, low-temperature operation, etc., and are widely used in portable electronic devices such as mobile phones and laptop computers. Furthermore, larger batteries are being used in transportation equipment such as automobiles, and their use as storage devices for nighttime electricity and electricity generated by natural energy sources is also progressing.

[0003] The electrodes (positive and negative electrodes) of non-aqueous electrolyte secondary batteries generally have an electrode active material layer (positive electrode active material layer or negative electrode active material layer), which contains electrode active material particles capable of absorbing or releasing lithium ions during charge and discharge. The electrode active material layer is usually formed by forming a film using a slurry (composition) containing the constituent components of the electrode active material layer (electrode active material, conductive additive, etc.). With regard to improving the performance of non-aqueous electrolyte secondary batteries, studies have been conducted focusing on the positive electrode active material layer.

[0004] For example, Patent Document 1 discloses a carbon nanotube dispersant composition containing a copolymer including an alkyl(meth)acrylate or alkylacrylamide-based structural unit A and a (meth)acrylate-based structural component B having an alkyleneoxy chain, and a solvent. Patent Document 1 also describes that by mixing this carbon nanotube dispersant composition with carbon nanotubes, which are a conductive material, and subjecting the mixture to a dispersion treatment, it is possible to prepare a conductive material dispersion liquid in which carbon nanotubes are well dispersible, and that by using a positive electrode paste obtained by mixing this conductive material dispersion liquid with a positive electrode active material, a low-resistance positive electrode composite layer can be obtained.

[0005] In addition, Patent Document 2 states: Contains a polymer (A) and a liquid medium (B), When the total amount of repeating units contained in the polymer (A) is taken as 100 mass %, the polymer (A) 50 to 99 mass% of repeating units (a1) derived from a conjugated diene compound; 1 to 19% by mass of repeating units (a2) derived from an α,β-unsaturated nitrile compound; Contains A binder composition for an electricity storage device, wherein the polymer (A) has a weight average molecular weight (Mw) of 100,000 to 2,000,000. Patent Document 2 discloses that a binder composition containing the polymer (A) and N-methyl-2-pyrrolidone (NMP) was prepared in the examples. Patent Document 2 also describes that when this binder composition is mixed with a positive electrode active material to obtain a slurry, and this slurry is applied and dried to form a positive electrode active material layer, coating defects can be suppressed, this positive electrode active material layer has excellent adhesion to the current collector, and the resulting secondary battery is less likely to increase in resistance and has improved cycle characteristics. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 208800 [Patent Document 2] International Publication No. 2024 / 009866 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, the positive electrode active material layer is prepared by dispersing solid particles (e.g., a positive electrode active material, a conductive additive, etc.) in a dispersion medium to prepare a slurry (positive electrode slurry), followed by film formation. In this process, it is necessary to control the properties of the positive electrode slurry from various angles to improve production efficiency, the resulting battery performance, and other factors. For example, to improve the handleability of the positive electrode slurry and form a uniform and precise positive electrode active material layer, the positive electrode slurry is required to exhibit an appropriately low viscosity (excellent dispersibility). The dispersibility of solid particles can be improved by incorporating a polymer (polymer dispersant) such as that described in Patent Document 1 into the positive electrode slurry. To improve dispersibility, it is particularly important to improve the dispersibility of the conductive additive, which has a smaller particle size, a larger specific surface area, and is prone to aggregation. The technology described in Patent Document 1 also aims to improve the dispersibility of carbon nanotubes, which function as a conductive additive in the positive electrode active material layer. However, as the inventors of the present invention furthered their research, they found that the positive electrode active material layer containing the polymer dispersant described in Patent Document 1 does not have sufficient oxidation resistance when incorporated into a battery and operated, and as a result, the discharge capacity of the resulting secondary battery is likely to decrease during large current charging and discharging.

[0008] An object of the present invention is to provide a positive electrode composition for a nonaqueous electrolyte secondary battery, which, when used to prepare a positive electrode slurry containing solid particles such as a conductive additive, can effectively improve the dispersibility of the solid particles in a dispersion medium and enable the formation of a positive electrode active material layer with excellent oxidation resistance when used in the preparation of a positive electrode slurry containing solid particles such as a conductive additive. Another object of the present invention is to provide a positive electrode formed using this positive electrode composition, and a nonaqueous electrolyte secondary battery incorporating this positive electrode. [Means for solving the problem]

[0009] The above-mentioned problems of the present invention have been solved by the following means. [1] A positive electrode composition containing polymer X and a dispersion medium, The polymer X comprises at least component (a), The component (a) is represented by any one of the following (i) to (iii), and the HSP distance from the dispersion medium is 4.0 MPa. 1 / 2 Hereinafter, a composition for a positive electrode of a nonaqueous electrolyte secondary battery, having a HOMO energy level of −6.4 eV or less. [ka] In the above formula, R 11 and R 21 represents a hydrogen atom or an alkyl group. R 12 , R 22 , and R 3 indicates a substituent. * indicates a binding site for incorporation into the polymer. [2] R in the above component (a) 12 , R 22 , and R 3 represents a substituent having a chemical formula weight of 40 to 400. [3] R in the above component (a) 12 , R 22 , and R 3 represents a substituent having 2 to 10 carbon atoms. [4] R in the above component (a) 12 and R 22 The positive electrode composition according to any one of [1] to [3], wherein includes a ring structure. [5] The positive electrode composition according to any one of [1] to [4], wherein the content of the component (a) in the polymer X is 20% by mass or more. [6] The positive electrode composition according to any one of [1] to [5], wherein the polymer X contains a component (b) different from the component (a), and the component (b) has a hydrocarbon group having 2 to 50 carbon atoms. [7] The positive electrode composition according to any one of [1] to [6], wherein the polymer X has a weight average molecular weight of 1,000 to 30,000. [8] The positive electrode composition according to any one of [1] to [7], which contains a conductive additive. [9] The positive electrode composition according to any one of [1] to [8], which contains a positive electrode active material.

[10] A positive electrode for a non-aqueous electrolyte secondary battery formed using the positive electrode composition according to any one of [1] to [9].

[12]

[10] A non-aqueous electrolyte secondary battery having the positive electrode for a non-aqueous electrolyte secondary battery according to

[10] as a positive electrode.

[0010] In the description of the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present invention, "nonaqueous electrolyte" refers to an electrolyte that is substantially free of water. That is, the "nonaqueous electrolyte" may contain a small amount of water as long as the effect of the present invention is not impaired. In the present invention, the "nonaqueous electrolyte" has a water concentration of 200 ppm (by mass) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. Note that it is practically difficult to make a nonaqueous electrolyte completely anhydrous, and it usually contains 1 ppm or more of water. In the present invention, the term "non-aqueous solvent" also refers to a solvent that is substantially free of water. That is, the "non-aqueous solvent" may contain a small amount of water as long as the effect of the present invention is not impaired. In the present invention, the "non-aqueous solvent" has a water concentration of 200 ppm (by mass) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. Note that it is practically difficult to make a non-aqueous solvent completely anhydrous, and it usually contains 1 ppm or more of water. [Effects of the Invention]

[0011] The positive electrode composition of the present invention for a non-aqueous electrolyte secondary battery can form a positive electrode active material layer with high production efficiency and can also improve the oxidation resistance of the resulting positive electrode active material layer in the battery. The positive electrode of the present invention can be incorporated into a non-aqueous electrolyte secondary battery to improve its oxidation resistance. The non-aqueous electrolyte secondary battery of the present invention has excellent oxidation resistance. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a longitudinal cross-sectional view showing a schematic basic layer structure of an embodiment of a secondary battery according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Although preferred embodiments of the present invention will be described, the present invention is not limited to these embodiments except as defined in the present invention.

[0014] [Positive electrode composition] The positive electrode composition of the non-aqueous electrolyte secondary battery of the present invention (hereinafter also referred to as "positive electrode composition of the present invention") contains a polymer X and a dispersion medium. This polymer X contains at least a component (a), and this component (a) is represented by any one of the following (i) to (iii). Furthermore, this component (a) has an HSP distance from the dispersion medium of 4.0 MPa. 1 / 2 and the HOMO energy level is −6.4 eV or less.

[0015] [ka]

[0016] In the above formula, R 11 and R 21 represents a hydrogen atom or an alkyl group. R 12 , R 22 , and R 3 indicates a substituent. * indicates a binding site for incorporation into the polymer.

[0017] The positive electrode composition of the present invention can be suitably used as a material for forming a positive electrode active material layer that constitutes a nonaqueous electrolyte secondary battery. The positive electrode composition of the present invention can contain a conductive additive in addition to the polymer X and the dispersion medium. It may also contain a positive electrode active material. Regarding the positive electrode composition of the present invention, a composition containing polymer X and a dispersion medium but not containing any positive electrode active material or conductive additive is referred to as a first embodiment. A composition containing polymer X, a dispersion medium, and a positive electrode active material but not containing any conductive additive is referred to as a second embodiment. A composition containing polymer X, a dispersion medium, and a conductive additive but not containing any positive electrode active material is referred to as a third embodiment. A composition containing polymer X, a dispersion medium, a positive electrode active material, and a conductive additive is referred to as a fourth embodiment.

[0018] The positive electrode composition of the first embodiment is usually a polymer solution in which polymer X is dissolved in a dispersion medium, and can be used to enhance the dispersibility of solid particles when mixed with solid particles such as a conductive additive and a positive electrode active material to prepare a slurry. That is, the positive electrode composition of the first embodiment can be used to prepare the positive electrode composition of the second, third, or fourth embodiment. The positive electrode composition of the second embodiment is a composition in which a positive electrode active material is dispersed in a polymer solution. The positive electrode composition of the second embodiment may be further mixed with a conductive additive (i.e., a positive electrode composition of the fourth embodiment) and used to form a positive electrode active material layer. The positive electrode composition of the third embodiment is a composition in which a conductive additive is dispersed in a polymer solution, and can be used to form a positive electrode active material layer by further mixing the positive electrode composition of the third embodiment with a positive electrode active material (i.e., preparing a positive electrode composition of the fourth embodiment). The positive electrode composition of the fourth embodiment is a composition in which a positive electrode active material and a conductive additive are dispersed in a polymer solution, and can be used to form a positive electrode active material layer as is or after dilution, concentration, etc.

[0019] In the above-described first to fourth preferred aspects of the present invention, the positive electrode composition of the present invention can be used to prepare a positive electrode slurry for a general nonaqueous electrolyte secondary battery (a nonaqueous electrolyte secondary battery that is not a quasi-solid secondary battery), and can also be used as the positive electrode slurry itself for a general nonaqueous electrolyte secondary battery. The positive electrode composition of the present invention may further contain an electrolyte, and this form of the positive electrode composition can be used to prepare a positive electrode slurry for a quasi-solid secondary battery, or can be used as the positive electrode slurry itself for a quasi-solid secondary battery. The positive electrode slurry for a quasi-solid secondary battery differs from a positive electrode composition for a general non-aqueous electrolyte in that it contains an electrolyte (i.e., it contains an electrolyte solution in which an electrolyte is added to a dispersion medium). Quasi-solid secondary batteries themselves are known, and reference can be made to, for example, JP 2017-147222 A and WO 2023 / 106214 A.

[0020] The polymer X contained in the positive electrode composition of the present invention is considered to function primarily as a dispersant for solid particles (such as a positive electrode active material and a conductive additive) in a dispersion medium in the positive electrode composition. In particular, the conductive additive can be dispersed efficiently. Typically, a conductive additive has poor dispersibility due to its large specific surface area and small particle size relative to the positive electrode active material. The positive electrode composition of the present invention has an HSP distance between the component (a) of the polymer X and the dispersion medium of 4.0 MPa. 1 / 2 Within this range, the compatibility between the polymer X and the dispersion medium is controlled. As a result, the solid particles can be efficiently dispersed in the dispersion medium. Furthermore, in the positive electrode composition of the present invention, the polymer X contains a component (a) whose HOMO energy level is −6.4 eV or less, so that the polymer X is less susceptible to oxidation. As a result, by forming a positive electrode active material layer using the positive electrode composition of the present invention, the oxidation resistance of the positive electrode during battery operation can be improved.

[0021] Each component constituting the positive electrode composition of the present invention will be described in more detail.

[0022] <Polymer X> In the positive electrode composition of the present invention, the polymer X is usually dissolved in a dispersion medium. The positive electrode composition of the present invention contains at least one or more constituents (a). The constituent (a) contained in the polymer X mainly functions to enhance compatibility with the dispersion medium. It is also preferable that the constituent (a) has the ability to adsorb to solid particles. The specific chemical structure of the constituent (a) will be described later. When the polymer X contains two or more constituents (a), each of them satisfies the above-mentioned conditions for the HSP distance with the dispersion medium and the HOMO energy level. In the present invention, polymer X may be either a homopolymer or a copolymer, preferably a copolymer, as long as it contains component (a). When it is a copolymer, the polymerization form may be either random or block. Polymer X is a so-called chain polymerization polymer in which component (a) is incorporated into the main chain of the polymer via * in structures (i) to (iii). The positive electrode composition of the present invention may contain, in addition to polymer X, a polymer other than polymer X.

[0023] - Component (a) - The HSP distance between the component (a) of polymer X and the dispersion medium is 4.0 MPa. 1 / 2 less than 3.0 MPa 1 / 2 Preferably less than 2.5MPa 1 / 2 Less than 2.0MPa is more preferable. 1 / 2 More preferably, 1.5 MPa or less 1 / 2 More preferably, 1.0 MPa or less 1 / 2 More preferably, 0.5 MPa or less 1 / 2 The lower limit is not particularly limited, and is more preferably 0.1 MPa or less. 1 / 2 Therefore, the HSP distance is 0.1 to 4.0 MPa. 1 / 2 is preferably 0.1 to 3.0 MPa 1 / 2 More preferably, 0.1 to 2.5 MPa 1 / 2 is more preferably 0.1 to 2.0 MPa 1 / 2 is more preferably 0.1 to 1.5 MPa 1 / 2 is more preferably 0.1 to 1.0 MPa 1 / 2 is more preferably 0.1 to 0.5 MPa1 / 2 is more preferable. Here, the HSP distance will be explained.

[0024] -- HSP distance -- HSP stands for Hansen solubility parameter and is composed of three components: dispersion term (δD), polarization term (δP), and hydrogen bonding term (δH). The shorter the HSP distance between two substances, the higher the compatibility of the two substances. In the present invention, the HSPs of the constituent component (a) of polymer X and the dispersion medium are calculated using the HSPiP software (Pirika.com, version 5). More specifically, the Smiles formulas for the structure of the constituent component (a) and the structure of the dispersion medium are input into the software to calculate the respective HSPs. Note that when calculating the HSP of the constituent component (a), the structure of the monomer from which the constituent component (a) is derived is used as the structure of the constituent component (a). The HSP distance between component (a) and the dispersion medium is δD of component (a) = δD a , δP to δP a , δH to δH a and δD of the dispersion medium is δD d , δP to δP d , δH to δH d and calculate it using the following formula: HSP distance={4.0*(δD a -δD d ) 2 +(δP a -δP d ) 2 +(δH a -δH d ) 2} 0.5 When the dispersion medium is a mixed solvent, the three components of HSP (δD, δP, δH) of each solvent constituting the mixed solvent are calculated, and each of the three components calculated for each solvent is multiplied by the mass ratio of each solvent in the mixed solvent. The obtained values ​​for each of the three components are summed to obtain the values ​​of the three components of HSP of the mixed solvent. For example, if the dispersion medium is solvent S1 80% by mass and solvent S 2 In the case of a mixed solvent with 20 mass %, the δD of this dispersion medium is 1 δD × 0.8 + solvent S 2 It is calculated as δD x 0.2. The same applies to δP and δH.

[0025] The HSP of component (a) of polymer X is 4.0 MPa relative to the HSP of the dispersion medium. 1 / 2 There are no particular limitations as long as the following is shown. The HSP of component (a) of polymer X is δD is 16.5 to 20.0 MPa 1 / 2 and δP is 9.0 to 12.0 MPa 1 / 2 and δH is 5.0 to 8.0 MPa 1 / 2 It is preferable that: From the viewpoint of improving dispersibility and oxidation resistance, δD is 17.0 to 19.5 MPa 1 / 2 and δP is 9.7 to 10.5 MPa 1 / 2 and δH is 6.0 to 7.8 MPa 1 / 2 Preferably, δD is 17.0 to 18.5 MPa 1 / 2 and δP is 9.7 to 10.0 MPa 1 / 2 and δH is 7.0 to 7.6 MPa 1 / 2 It is more preferable that:

[0026] The HOMO energy level of the component (a) of the polymer X is -6.4 eV or less, preferably -6.5 eV or less, and more preferably -6.6 eV or less. There is no particular lower limit to the HOMO energy level of the component (a) of the polymer X, and -9.0 eV is practical. The HOMO energy level of the component (a) of the polymer X is preferably -9.0 eV to -6.4 eV, more preferably -8.5 to -6.4 eV, even more preferably -7.5 to -6.5 eV, and even more preferably -7.0 to -6.6 eV. The HOMO energy level of the component (a) of the polymer X is calculated using the quantum chemistry calculation program Gaussian 16 (manufactured by Gaussian Inc.) with the calculation method: B3LYP / 6-31G(d). When calculating the HOMO energy level of the component (a) of the polymer X, the structure of the monomer from which the component (a) is derived is used as the structure of the component (a).

[0027] The structure of the component (a) is represented by any one of the following (i) to (iii).

[0028] [ka]

[0029] In the above (i) to (iii), R 11 and R 21 represents a hydrogen atom or an alkyl group. 11 and R 21 The alkyl group that can be taken as R is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, further preferably methyl or ethyl, and even more preferably methyl. 11 and R 21 When R is an alkyl group, a heteroatom (e.g., an oxygen atom, a sulfur atom, or a nitrogen atom) may be incorporated in the carbon chain of the alkyl group. 11 and R 21 When R is an alkyl group, the hydrogen atoms of the alkyl group may be further substituted with halogen atoms. 11 and R 21 is preferably a hydrogen atom, methyl or methoxymethyl, more preferably a hydrogen atom.

[0030] R 12 , R 22 , and R 3 indicates a substituent. R 12 , R 22 , and R 3The substituents which can be adopted as the substituents preferably have a chemical formula weight of 40 to 400, more preferably 40 to 250, even more preferably 50 to 200, and even more preferably 70 to 150. R 12 , R 22 , and R 3 The substituents which can be adopted as the substituent are preferably those having 2 to 10 carbon atoms, more preferably those having 3 to 10 carbon atoms, and even more preferably those having 4 to 8 carbon atoms. R 12 , R 22 , and R 3 The substituent may contain a heteroatom, such as an oxygen atom, a nitrogen atom, or a sulfur atom, with an oxygen atom being preferred. R 12 , R 22 , and R 3 The substituent that can be taken as may be an alkyl group, preferably an alkyl group having 2 to 6 carbon atoms. A heteroatom may be incorporated into the carbon chain of this alkyl group, and in this case, it is preferable that an oxygen atom and / or a nitrogen atom is incorporated. More specifically, the alkyl group may have a structure in which at least one of -O-, -COO-, -OCO-, -CO-, and -NH- is incorporated into the carbon chain. R 12 , R 22 , and R 3 can be a substituent containing a ring structure. The ring structure may be an aliphatic ring or an aromatic ring, with an aliphatic ring being preferred. The aliphatic ring may be an aliphatic hydrocarbon ring or an aliphatic heterocycle (a non-aromatic ring containing carbon atoms and atoms other than carbon atoms as ring constituent atoms). The aliphatic heterocycle preferably contains an oxygen atom and / or a nitrogen atom as ring constituent atoms. The aliphatic heterocycle is preferably an oxacycloalkane ring, a lactone ring, or a lactam ring. When the aliphatic ring is a monocyclic ring, it is preferably a 4- to 10-membered ring, more preferably a 5- to 7-membered ring. The aliphatic ring may be a fused ring, and in the case of a fused ring, it is preferably a fused ring structure in which two to four of the above monocyclic aliphatic rings are fused together. The substituent containing the ring structure may have a ring structure, and may be a ring group obtained by removing one hydrogen atom from the ring structure, or may be a group having a structure in which the ring structure is bonded to a linking group. Examples of the linking group include an aliphatic hydrocarbon group, and this aliphatic hydrocarbon group may have at least one of an oxygen atom and a nitrogen atom. More specifically, the linking group is preferably an alkylene group, -O-, -COO-, -OCO-, -CO-, -NH-, or a divalent linking group formed by combining these.

[0031] R 12 and R 22 is preferably a substituent containing a lactone ring structure or an aliphatic hydrocarbon ring structure. 12 and R 22 may contain both a lactone ring structure and an aliphatic hydrocarbon ring structure. The lactone ring structure is preferably a 4- to 7-membered lactone ring structure, more preferably a 5- or 6-membered lactone ring structure, and even more preferably a 5-membered lactone ring structure. When referring to a Z-membered ring (where Z represents a number), Z refers to the number of ring-constituting atoms that directly constitute the ring. Therefore, the oxygen atom of the carbonyl group in the lactone ring structure (oxygen atom bonded to a ring-constituting carbon atom) is not a ring-constituting atom. The lactone ring structure may be a structure in which another ring structure is fused to the 4- to 7-membered lactone ring structure in the form of a bicyclo structure or a spiro structure. The lactone ring structure is preferably not a fused ring structure. The lactone ring structure may have a substituent, for example, an alkyl group having 1 to 4 carbon atoms. R 12 and R 22 Examples of the lactone ring structure that may be included include a γ-butyrolactone ring (five-membered ring), a mevalonolactone ring (six-membered ring), and a 5,3-bicyclo[2.2.1]heptanecarbolactone ring (a structure in which a bicyclo[2.2.1]heptane ring is fused to a five-membered lactone ring).

[0032] The aliphatic hydrocarbon ring structure may be a cycloalkane structure or a cycloalkene structure, with a cycloalkane structure being preferred. The aliphatic hydrocarbon ring structure may be a monocyclic structure or a fused ring structure in which monocyclic aliphatic hydrocarbon rings are fused together. For example, it may be a cyclocyclic, dicyclocyclic, or tricyclocyclic structure. The aliphatic hydrocarbon ring structure is preferably a monocyclic structure. The aliphatic hydrocarbon ring structure preferably has 4 to 20 carbon atoms, more preferably 4 to 15 carbon atoms, and even more preferably 5 to 10 carbon atoms. The aliphatic hydrocarbon ring structure may have a substituent. Examples of the substituent that the aliphatic hydrocarbon ring structure may have include an alkyl group having 1 to 4 carbon atoms. It is preferable that the aliphatic hydrocarbon ring structure does not have a substituent. R 12 and R 22 Examples of the aliphatic hydrocarbon ring structure that may be contained include cyclopentane, cycloheptane, and adamantane.

[0033] R 12 is preferably a substituent having a lactone ring structure from the viewpoint of improving dispersibility and oxidation resistance. R 22 From the viewpoint of improving dispersibility and oxidation resistance, is preferably an alkyl group, a substituent having a lactone ring structure, or a substituent having an aliphatic hydrocarbon ring structure. R 3 is more preferably an alkyl group from the viewpoint of improving dispersibility and oxidation resistance.

[0034] The structure of the component (a) is preferably (i) or (ii), and more preferably (ii).

[0035] For the structures represented by the formulas (i) to (iii) above, specific preferred examples of the monomers that lead to each structure are shown below, taking the case where the dispersion medium is NMP as an example, but the present invention is not limited to these specific examples. When the dispersion medium is other than NMP, it may not be preferable from the viewpoint of the HSP distance with this dispersion medium.

[0036] Monomers leading to the constituents represented by (i)

[0037] [ka]

[0038] Monomers leading to the constituents represented by (ii)

[0039] [ka]

[0040] Monomers leading to the constituents represented by (iii)

[0041] [ka]

[0042] When polymer X is a copolymer, from the viewpoint of improving dispersibility and oxidation resistance, polymer X preferably contains 20% by mass or more of component (a), more preferably 30% by mass or more, and even more preferably 40% by mass or more of component (a). There is no particular upper limit, and it can be 80% by mass. Therefore, the content of component (a) in polymer X is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass.

[0043] - Component (b) - In addition to the component (a), the polymer X may also contain a component (b) different from the component (a). The component (b) preferably contains a hydrocarbon group having 2 to 50 carbon atoms. Here, the component (b) is a component that does not satisfy the requirements of the component (a) in terms of either or both of the HSP distance from the dispersion medium and the HOMO energy level. Therefore, when a component (b) does not satisfy either or both of the HSP distance from the dispersion medium and the HOMO energy level and contains a hydrocarbon group having 2 to 50 carbon atoms, it is considered to be the component (b) even if it has a chemical structure represented by any of the above (i) to (iii). The hydrocarbon group having 2 to 50 carbon atoms contained in component (b) is thought to function mainly as an adsorptive group for solid particles.

[0044] The hydrocarbon group having 2 to 50 carbon atoms that can be contained in component (b) preferably has 4 to 50 carbon atoms, more preferably 4 to 40 carbon atoms, even more preferably 10 to 40 carbon atoms, still more preferably 15 to 35 carbon atoms, and even more preferably 15 to 30 carbon atoms. The hydrocarbon group having 2 to 50 carbon atoms that can be contained in component (b) may be linear, branched, or cyclic. It may also be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The hydrocarbon group having 2 to 50 carbon atoms that can be contained in component (b) may be unsubstituted or substituted. The aliphatic hydrocarbon group having 2 to 50 carbon atoms may have a heteroatom incorporated in the carbon chain, and in this case, it is preferable that an oxygen atom and / or a nitrogen atom be incorporated. More specifically, the aliphatic hydrocarbon group may have a structure in which at least one of -O-, -COO-, -OCO-, -CO-, and -NH- is incorporated in the carbon chain. The aromatic hydrocarbon group that can be contained in component (b) may be a single ring or a fused ring. The aromatic hydrocarbon group that can be contained in component (b) preferably has 6 to 20 carbon atoms, more preferably 6 to 12 carbon atoms. The aromatic hydrocarbon group that can be contained in component (b) is preferably a phenyl group or a naphthyl group, more preferably a phenyl group. Component (b) may contain both an aromatic hydrocarbon group and an aliphatic hydrocarbon group having 2 to 50 carbon atoms. For example, an aliphatic hydrocarbon group having 2 to 50 carbon atoms may have an aromatic hydrocarbon group as a substituent, or an aromatic hydrocarbon group may have an aliphatic hydrocarbon group having 2 to 50 carbon atoms as a substituent. When an aliphatic hydrocarbon group has an aromatic hydrocarbon group as a substituent, the aliphatic hydrocarbon group preferably has 2 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 2 to 5 carbon atoms. The hydrocarbon group that can be contained in component (b) is preferably an alkyl group having 4 to 50 carbon atoms, an aromatic hydrocarbon group, or a group in which an alkyl group having 2 to 5 carbon atoms has an aromatic hydrocarbon group as a substituent, more preferably a phenyl group, an alkyl group having 10 to 40 carbon atoms, or a group in which an alkyl group having 2 to 5 carbon atoms has an aromatic hydrocarbon group as a substituent, and even more preferably an alkyl group having 15 to 30 carbon atoms or a benzyl group.

[0045] The constituent (b) is not particularly limited as long as it has the above-mentioned hydrocarbon group having 2 to 50 carbon atoms. The constituent (b) is preferably a constituent derived from a compound in which the above-mentioned hydrocarbon group is introduced into a (meth)acrylic acid ester compound, a (meth)acrylamide component, or a maleimide component. More specifically, the ... 12 , R 22 , and R 3 The groups corresponding to R 13 , R 23 , R 33 In the structure, R 13 , R 23 and R 33 However, the component (b) may have the above hydrocarbon group having 2 to 50 carbon atoms. The component (b) may also be a component derived from a compound in which a vinyl group and the above hydrocarbon group are bonded together.

[0046] The HSP distance between component (b) and the dispersion medium is 4.0 MPa. 1 / 2 Exceeds 4.5MPa 1 / 2 More than 5.5MPa is preferable. 1 / 2More preferably, 6.2 MPa or more 1 / 2 The upper limit of the HSP distance between the component (b) and the dispersion medium is 15.0 MPa. 1 / 2 Therefore, the HSP distance between component (b) and the dispersion medium is 4.5 to 15.0 MPa. 1 / 2 is preferably 5.5 to 15.0 MPa 1 / 2 More preferably, 6.2 to 15.0 MPa 1 / 2 is more preferable. The HSP of component (b) can be calculated in the same manner as the HSP of component (a).

[0047] The HSP of component (b) of polymer X is δD is 15.0 to 20.0 MPa 1 / 2 and δP is 1.5 to 7.0 MPa 1 / 2 and δH is 2.0 to 8.0 MPa 1 / 2 From the viewpoint of improving dispersibility and oxidation resistance, δD is 15.5 to 18.5 MPa 1 / 2 and δP is 1.5 to 5.0 MPa 1 / 2 and δH is 2.0 to 6.0 MPa 1 / 2 It is preferable that: δD is 16.0 to 18.0 MPa 1 / 2 and δP is 1.5 to 4.0 MPa 1 / 2 and δH is 2.5 to 5.5 MPa 1 / 2 It is preferable that:

[0048] When polymer X is a copolymer, from the viewpoint of improving dispersibility and oxidation resistance, polymer X preferably contains 20% by mass or more of component (b), more preferably 30% by mass or more, and even more preferably 40% by mass or more. The upper limit is not particularly limited and can be, for example, 80% by mass. Therefore, the content of component (b) in polymer X is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass.

[0049] Preferred specific examples of the monomer from which component (b) is derived are shown below.

[0050] Monomers that lead to component (b)

[0051] [ka]

[0052] - Other components - The polymer X may contain components other than the above-mentioned component (a) and component (b) (“other components”), as long as the effects of the present invention are not impaired. When polymer X contains other constituent components, the content of the other constituent components is preferably 20% by mass or less, more preferably 15% by mass or less, and more preferably 10% by mass or less.

[0053] The weight average molecular weight (Mw) of the polymer X is not particularly limited, and is preferably 1,000 to 80,000, more preferably 1,000 to 50,000, even more preferably 1,000 to 30,000, still more preferably 2,000 to 20,000, still more preferably 2,000 to 15,000, still more preferably 2,000 to 12,000, still more preferably 3,000 to 10,000, still more preferably 3,000 to 8,000, and still more preferably 3,000 to 7,000.

[0054] -- Measurement of weight average molecular weight -- In the present invention, the Mw of polymer X is measured by gel permeation chromatography (GPC). Mw is calculated as polyethylene oxide. In principle, Mw is measured by the following method. However, depending on the type of polymer, an appropriate eluent (carrier) may be selected and used. Measuring instrument: HLC-8320GPC (product name, manufactured by Tosoh Corporation) Column: TOSOH TSKgel guard column SuperHZ-L, Super HZM-H, Super HZ4000, Super HZ2000 (product names, manufactured by Tosoh Corporation) Carrier: Tetrahydrofuran solution Measurement temperature: 40℃ Carrier flow rate: 0.35 ml / min Sample concentration: 0.2% by mass Detector: RI (refractive index) detector

[0055] Polymer X can be synthesized by selecting raw materials using known methods. For example, a monomer from which component (a), a monomer from which component (b), and monomers from which other components are derived can be dissolved in a dispersion medium together with a polymerization initiator, and the resulting solution can be added dropwise to a heated dispersion medium to cause polymerization. In this way, a polymer X solution (a first embodiment of the positive electrode composition of the present invention) in which polymer X is dissolved in the dispersion medium can be obtained. The polymer X solution can be used as is to prepare the second to fourth embodiments of the positive electrode composition of the present invention.

[0056] In the first embodiment (polymer solution) of the positive electrode composition of the present invention, the content of polymer X is not particularly limited, and is preferably 1 to 70 mass % of the composition (total of polymer X and dispersion medium), more preferably 3 to 50 mass %, and even more preferably 5 to 40 mass %. In the second embodiment of the positive electrode composition of the present invention, the content of polymer X is not particularly limited, and is preferably 0.001 to 10 mass %, more preferably 0.005 to 5 mass %, and even more preferably 0.01 to 1 mass %, of the composition (total of polymer X, dispersion medium, and positive electrode active material). In the third embodiment of the positive electrode composition (conductive additive slurry) of the present invention, the content of polymer X is not particularly limited, and is preferably 0.01 to 69 mass %, more preferably 0.1 to 57 mass %, and even more preferably 0.5 to 45 mass %, of the composition (total of polymer X, dispersion medium, and conductive additive). In the fourth embodiment of the positive electrode composition (positive electrode slurry) of the present invention, the content of polymer X is not particularly limited, and is preferably 0.001 to 10 mass %, more preferably 0.005 to 5 mass %, and even more preferably 0.01 to 1 mass %, of the composition (total of polymer X, dispersion medium, positive electrode active material, and conductive additive).

[0057] In the second embodiment of the positive electrode composition of the present invention, the content of polymer X in the total of polymer X and the positive electrode active material is preferably 0.01 to 10.00 mass%, more preferably 0.05 to 5.00 mass%, and even more preferably 0.10 to 1.00 mass%. In the third embodiment of the positive electrode composition (conductive additive slurry) of the present invention, the content of polymer X in the total of polymer X and the conductive additive is preferably 0.1 to 90 mass%, more preferably 1 to 80 mass%, and even more preferably 5 to 70 mass%. In the fourth embodiment of the positive electrode composition (positive electrode slurry) of the present invention, the content of polymer X in the total of polymer X, the positive electrode active material, and the conductive additive is preferably 0.01 to 10 mass%, more preferably 0.05 to 5 mass%, and even more preferably 0.10 to 1 mass%.

[0058] <Dispersion medium> The positive electrode composition of the present invention contains a dispersion medium, which functions as a solvent or dispersion medium for the polymer or solid particles in the positive electrode composition. The HSP of the dispersion medium is related to the HSP of component (a) at an HSP distance of 4.0 MPa. 1 / 2 There are no particular limitations as long as the following is shown. The HSP of the dispersion medium preferably has ΔD of 16.50 to 20.0, ΔP of 8.0 to 11.0, and ΔH of 4.0 to 9.0. From the viewpoint of improving dispersibility and oxidation resistance, it is preferable that ΔD is 17.0 to 18.5, ΔP is 9.0 to 11.0, and ΔH is 6.0 to 8.0.

[0059] The dispersion medium has an HSP distance of 4.0 MPa in relation to the HSP of component (a). 1 / 2 The solvent may be any of the following, for example, water or an organic solvent (preferably a non-aqueous solvent). The organic solvent is preferably an aprotic organic solvent, and more preferably an aprotic organic solvent having 2 to 10 carbon atoms. Such organic solvents are preferably non-aqueous solvents containing a heteroatom (such as an oxygen atom, a nitrogen atom, a sulfur atom, or a phosphorus atom), and examples thereof include linear or cyclic carbonate compounds, lactone compounds, linear or cyclic ether compounds, ester compounds, nitrile compounds, amide compounds, oxazolidinone compounds, nitro compounds, linear or cyclic sulfone or sulfoxide compounds, phosphate ester compounds, and cyclic ketone compounds. Among these, compounds having an ether bond, a carbonyl bond, an ester bond or a carbonate bond, and cyclic ketone compounds are preferred. These compounds may have a substituent. The organic solvent is preferably an alkylpyrrolidone compound, more preferably an N-alkylpyrrolidone compound.

[0060] Specific preferred examples of the organic solvent include ethylene carbonate, fluorinated ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, methyl acetate, and ethyl acetate. Examples of suitable solvents include methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidone (NMP), N-ethylpyrrolidone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide or dimethyl sulfoxide phosphate, cyclohexanone, etc. These may be used alone or in combination of two or more. However, the organic solvents used in the present invention are not limited to these. In the present invention, the dispersion medium is preferably N-methylpyrrolidone (NMP), N-ethylpyrrolidone or cyclohexanone, and more preferably NMP.

[0061] In the first embodiment (polymer solution) of the positive electrode composition of the present invention, the content of the dispersion medium is not particularly limited, and is preferably 30 to 99 mass %, more preferably 50 to 97 mass %, and even more preferably 60 to 95 mass % of the composition (total of polymer X and dispersion medium). In the second embodiment of the positive electrode composition of the present invention, the content of the dispersion medium is not particularly limited, and is preferably 5 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 29 mass % in the composition. In the third embodiment of the positive electrode composition of the present invention (conductive assistant slurry), the content of the dispersion medium is not particularly limited, and is preferably 30 to 95 mass %, more preferably 40 to 90 mass %, and even more preferably 50 to 80 mass % in the composition. In the fourth embodiment of the positive electrode composition (positive electrode slurry) of the present invention, the content of the dispersion medium is not particularly limited, and is preferably 5 to 50 mass %, more preferably 10 to 40 mass %, and even more preferably 15 to 30 mass % in the composition.

[0062] <Cathode active material> The positive electrode composition of the present invention can contain a positive electrode active material. The positive electrode active material is preferably one that can reversibly insert and release lithium ions. There are no particular limitations on the material, and examples include transition metal oxides, organic substances, sulfur, and other substances that can be combined with Li, as well as sulfur-metal composites. Among these, it is preferable to use a lithium-containing transition metal oxide as the positive electrode active material, and the transition metal element M a A lithium-containing transition metal oxide containing Co or Ni is more preferred. In addition, the lithium-containing transition metal oxide may further contain the element M. b (Elements of Group 1 (Ia) of the periodic table other than lithium, elements of Group 2 (IIa), Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc.) may be mixed. The amount of the mixed element is determined by the following formula: a The amount of Li / M is preferably 0 to 30 mol% relative to the amount of Li (100 mol%). a More preferably, the compounds are synthesized by mixing them so that the molar ratio is 0.3 to 2.2. Specific examples of lithium-containing transition metal oxides include (MA) lithium-containing transition metal oxides having a layered rock salt structure, (MB) lithium-containing transition metal oxides having a spinel structure, (MC) lithium-containing transition metal phosphate compounds, (MD) lithium-containing transition metal halide phosphate compounds, and (ME) lithium-containing transition metal silicate compounds.

[0063] (MA) Specific examples of lithium-containing transition metal oxides with a layered rock salt structure include LiCoO2 (lithium cobalt oxide [LCO]), LiNi2O2 (lithium nickel oxide), and LiNi 0.85 Co 0.10 Al 0.05 O2 (nickel cobalt lithium aluminate [NCA]), LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (lithium nickel manganese cobalt oxide [NMC]) and LiNi 0.5 Mn 0.5 O2 (lithium manganese nickel oxide). (MB) Specific examples of lithium-containing transition metal oxides having a spinel structure include LiMn2O4 (LMO), LiCoMnO4, Li2FeMn3O8, Li2CuMn3O8, Li2CrMn3O8, and Li2NiMn3O8. (MC) Examples of lithium-containing transition metal phosphate compounds include olivine-type iron phosphates such as LiFePO4 and Li3Fe2(PO4)3, iron pyrophosphates such as LiFeP2O7, cobalt phosphates such as LiCoPO4, and monoclinic Nasicon-type vanadium phosphates such as Li3V2(PO4)3 (lithium vanadium phosphate). (MD) Examples of lithium-containing transition metal halide phosphate compounds include iron fluorophosphates such as Li2FePO4F, manganese fluorophosphates such as Li2MnPO4F, and cobalt fluorophosphates such as Li2CoPO4F. (ME) Examples of lithium-containing transition metal silicate compounds include Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4. In the present invention, the positive electrode active material is preferably a lithium-containing transition metal oxide having an (MA) layered rock salt structure, and more preferably LiCoO2. In the present invention, since the polymer X has high oxidation resistance, it is suitable for use in a positive electrode active material having a high redox potential. From this viewpoint, the positive electrode active material is preferably LiCoO2 and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2 and the like are preferred.

[0064] The shape of the positive electrode active material is not particularly limited, but a particulate shape is preferred. The average particle size (average particle size in terms of spheres) of the positive electrode active material is not particularly limited and can be, for example, 0.1 to 50 μm, preferably 0.2 to 30 μm, more preferably 0.5 to 20 μm, and even more preferably 0.8 to 10 μm. The positive electrode active material can be made to have a predetermined particle size by using a conventional grinder or classifier. The positive electrode active material obtained by the firing method may be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

[0065] When a commercially available positive electrode active material is used, the average particle size of the positive electrode active material is the value listed in the manufacturer's catalog. When information on the average particle size from the manufacturer is unavailable or when a synthesized positive electrode active material is used, the positive electrode active material is dispersed in water and measured using a laser diffraction / scattering particle size distribution analyzer (e.g., HORIBA Particle LA-960V2) to obtain the particle size value (volume-based median diameter D50 in water). This also applies to the average particle size of solid particles other than the positive electrode active material.

[0066] The chemical formula of the compound obtained by the above calcination method can be measured by inductively coupled plasma (ICP) emission spectroscopy, or simply calculated from the difference in mass of the powder before and after calcination.

[0067] The surface of the positive electrode active material may be coated with an oxide such as another metal oxide, a carbon-based material, etc. These surface coating layers can function as an interface resistance stabilizing layer. Examples of surface coating materials include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds, such as Li4Ti5O 12, Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li2B4O7, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, SiO2, TiO2, ZrO2, Al2O3, BO3, and Li3AlF6. Carbon-based materials such as C, SiC, and SiOC (carbon-doped silicon oxide) can also be used as surface coating materials.

[0068] The positive electrode active material is preferably surface-coated with a carbonaceous material in order to increase the electronic conductivity to a desired level. In this case, the positive electrode active material is preferably surface-coated with carbon (C). The carbon surface coating can be formed by baking the positive electrode active material in the presence of an additive (organic substance) that serves as a carbon source. Examples of the additive that can be used include styrene-maleic anhydride copolymer, polystyrene, and polycarbonate.

[0069] The surface of the positive electrode active material may be treated with sulfur or phosphorus. Furthermore, the particle surfaces of the positive electrode active material may be subjected to a surface treatment with actinic rays or an active gas (plasma, etc.) before or after the above surface coating.

[0070] The positive electrode active materials may be used alone or in combination of two or more.

[0071] In the second embodiment of the positive electrode composition of the present invention, the content of the positive electrode active material in the composition is preferably 30 to 90 mass %, more preferably 50 to 85 mass %, and even more preferably 70 to 80 mass %. In the fourth embodiment of the positive electrode composition (positive electrode slurry) of the present invention, the content of the positive electrode active material is preferably as high as possible within a range that allows achieving the desired low viscosity. For example, the content of the positive electrode active material in the composition can be 49 to 90 mass %, more preferably 59 to 88 mass %, and even more preferably 65 to 83 mass %.

[0072] In the second embodiment of the positive electrode composition of the present invention, the content of the positive electrode active material in the total of the polymer X and the positive electrode active material is preferably 90.00 to 99.99 mass%, more preferably 95.00 to 99.95 mass%, and even more preferably 99.0 to 99.90 mass%. In the fourth embodiment of the positive electrode composition (positive electrode slurry) of the present invention, the content of the positive electrode active material in the total of the polymer X, the positive electrode active material, and the conductive additive is preferably 30.0 to 99.8 mass%, more preferably 50.0 to 99.0 mass%, and even more preferably 70.0 to 97.0 mass%.

[0073] <Conductive additive> The positive electrode composition of the present invention may contain a conductive assistant. The conductive additive may be any of those known as general conductive additives. For example, the conductive additive may be an electron conductive material such as graphites (e.g., natural graphite, artificial graphite), carbon blacks (e.g., acetylene black, ketjen black, furnace black), amorphous carbon (e.g., needle coke), carbon fibers (e.g., vapor-grown carbon fiber, carbon nanotube), carbonaceous materials (e.g., graphene, fullerene), metal powders (e.g., copper, nickel), metal fibers, or conductive polymers (e.g., polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene derivatives). In the present invention, the conductive additive is preferably a carbonaceous material, more preferably carbon black, and more preferably acetylene black. The positive electrode composition of the present invention has improved dispersibility of solid particles. From this viewpoint, carbon fibers such as carbon nanotubes, which usually have low dispersibility, can be preferably used. When a positive electrode active material and a conductive additive are used in combination, the conductive additive is one that does not insert or release Li when the battery is charged or discharged and does not function as an active material. Therefore, among the conductive additives, one that can function as an active material in the active material layer when the battery is charged or discharged is classified as an active material rather than a conductive additive. Whether or not a conductive additive functions as an active material when the battery is charged or discharged is not uniquely determined, but is determined by the combination with the active material.

[0074] The conductive additive may be used alone or in combination of two or more.

[0075] The shape of the conductive additive is not particularly limited, but is preferably in the form of particles. The median diameter (D50) of the conductive additive is not particularly limited and is, for example, preferably 0.01 to 50 μm, more preferably 0.1 to 10 μm, and even more preferably 0.2 to 2.0 μm.

[0076] In the third embodiment of the positive electrode composition of the present invention, the content of the conductive additive in the composition is preferably 1 to 40 mass %, more preferably 3 to 30 mass %, and even more preferably 5 to 20 mass %. In the fourth embodiment of the positive electrode composition (positive electrode slurry) of the present invention, the content of the conductive additive in the composition is preferably 0.1 to 20 mass %, more preferably 0.5 to 10 mass %, and even more preferably 1 to 5 mass %.

[0077] In the third embodiment of the positive electrode composition (conductive additive slurry) of the present invention, the content (mass %) of the conductive additive in the total of the polymer X and the conductive additive is preferably 10 to 99.9 mass %, more preferably 20 to 99 mass %, and even more preferably 30 to 95 mass %. In the fourth embodiment of the positive electrode composition (positive electrode slurry) of the present invention, the content (mass %) of the conductive additive in the total of the polymer X, the positive electrode active material, and the conductive additive is preferably 0.1 to 20 mass %, more preferably 0.5 to 15 mass %, even more preferably 1 to 10 mass %, and particularly preferably 2 to 5 mass %.

[0078] <Electrolytes> When the positive electrode composition of the present invention is a positive electrode slurry for a quasi-solid secondary battery, it contains an electrolyte. As the electrolyte, any electrolyte that can be used as an electrolytic solution for a quasi-solid secondary battery can be used appropriately. The electrolyte is preferably a metal salt, such as lithium salt, potassium salt, sodium salt, calcium salt, or magnesium salt. As the lithium salt, lithium salts that are commonly used in electrolytes for lithium ion secondary batteries are preferred, and examples thereof include the following lithium salts.

[0079] (L-1) Inorganic lithium salts: inorganic fluoride salts such as LiPF6, LiBF4, LiAsF6, and LiSbF6; perhalogenates such as LiClO4, LiBrO4, and LiIO4; inorganic chloride salts such as LiAlCl4;

[0080] (L-2) Fluorine-containing organic lithium salts: perfluoroalkanesulfonates such as LiCF3SO3, perfluoroalkanesulfonylimide salts such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(FSO2)2, LiN(CF3SO2)(C4F9SO2), perfluoroalkanesulfonylmethide salts such as LiC(CF3SO2)3, perfluoroalkyl fluorophosphates such as Li[PF5(CF2CF2CF3)], Li[PF4(CF2CF2CF3)2], Li[PF3(CF2CF2CF3)3], Li[PF5(CF2CF2CF2CF3)], Li[PF4(CF2CF2CF2CF3)2], Li[PF3(CF2CF2CF2CF3)3], etc.

[0081] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0082] Among these, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, Li(R f1 SO3), LiN(R f1 SO2)2, LiN(FSO2)2, or LiN(R f1 SO2)(R f2 SO2) are preferred, LiPF6, LiBF4, LiN(R f1 SO2)2, LiN(FSO2)2, or LiN(R f1 SO2)(R f2 SO2) is more preferred, and LiPF6 is particularly preferred. f1 and R f2 represents a perfluoroalkyl group, preferably having 1 to 6 carbon atoms.

[0083] The positive electrode composition may contain one electrolyte alone or two or more electrolytes in any combination.

[0084] When the positive electrode composition of the present invention is a positive electrode composition for a quasi-solid secondary battery, the electrolyte concentration of the positive electrode composition is not particularly limited as long as it functions as a non-aqueous electrolyte. For example, it can be 10.0 to 50.0 mass %, preferably 15.0 to 30.0 mass %. The molar concentration is preferably 0.5 to 1.5 M.

[0085] <Other ingredients> In addition to the above-described components, the positive electrode composition of the present invention may optionally contain a binder, an ionic liquid, a thickener, an antifoaming agent, a leveling agent, a dehydrating agent, an antioxidant, etc. These may be those typically used in non-aqueous electrolyte secondary batteries. The binder is preferably polyvinylene difluoride (PVDF). The content of the binder in the positive electrode composition of the present invention is preferably 0.10 to 3.00 mass%, more preferably 0.20 to 2.00 mass%, still more preferably 0.20 to 1.00 mass%, and particularly preferably 0.25 to 0.40 mass%, based on the solid content of the positive electrode composition in the fourth embodiment (positive electrode slurry) of the positive electrode composition of the present invention. When a binder is added to the positive electrode compositions of the first to third embodiments of the present invention, it can be added so that the content falls within the above range when the fourth positive electrode composition is prepared.

[0086] <Method for preparing positive electrode composition> The positive electrode composition of the present invention can be prepared as a mixture, preferably as a solution or slurry, by mixing the components constituting this composition in a mixer of various types.

[0087] <Positive electrode (positive electrode sheet) for non-aqueous electrolyte secondary batteries> The positive electrode (positive electrode sheet) for a non-aqueous electrolyte secondary battery of the present invention is a positive electrode formed using the positive electrode composition of the fourth embodiment. More specifically, it is a positive electrode including a positive electrode active material layer formed using the positive electrode composition of the fourth embodiment. The positive electrode of the present invention is an electrode suitable as a positive electrode for a non-aqueous electrolyte secondary battery. In the present invention, the simple term "positive electrode" encompasses both an embodiment in which it is incorporated as a constituent member of a nonaqueous electrolyte secondary battery (a state in which it is incorporated into a secondary battery) and an embodiment in which it is a positive electrode material before being incorporated into a nonaqueous electrolyte secondary battery. In other words, the structure (area, thickness, etc.) of the positive electrode may be any structure that can be used as a positive electrode or a structure that can be processed into a structure that can be used as a positive electrode. The positive electrode of the present invention can have the same configuration as the positive electrode of a general non-aqueous electrolyte secondary battery, except that it has a positive electrode active material layer formed using the positive electrode composition of the fourth embodiment. The positive electrode of the present invention may have a positive electrode active material layer formed using the positive electrode composition of the fourth embodiment, and may be in a form in which the positive electrode active material layer and a positive electrode current collector are laminated. More specifically, the positive electrode active material layer may be laminated on both sides of the positive electrode current collector, or the positive electrode active material layer may be laminated on one side of the positive electrode current collector. The positive electrode is usually a sheet configured by laminating the positive electrode active material layer on the positive electrode current collector.

[0088] The positive electrode of the present invention can be obtained by forming a positive electrode active material layer using the positive electrode composition of the fourth embodiment. For example, the positive electrode of the present invention can be produced by forming a film using the positive electrode composition of the present invention. More specifically, the positive electrode can be prepared by forming the positive electrode active material layer on a substrate such as the above-mentioned positive electrode current collector. When the positive electrode composition of the present invention is a positive electrode composition for a general secondary battery, the positive electrode current collector is used as a substrate, and the positive electrode composition of the present invention is applied thereon (optionally via another layer) to form a coating film, which is then dried to obtain a positive electrode having a positive electrode active material layer (coated and dried layer) on the substrate. The coating film may be subjected to a press treatment as necessary. When the positive electrode composition of the present invention is a positive electrode composition for a quasi-solid secondary battery, the positive electrode active material layer can be formed by forming a coating film on the substrate. The method for applying the positive electrode composition of the present invention to a substrate is not particularly limited, and a conventional method can be used. The positive electrode active material layer obtained as described above may or may not contain a dispersion medium.

[0089] [Nonaqueous electrolyte secondary battery] The nonaqueous electrolyte secondary battery of the present invention (hereinafter also referred to as "secondary battery of the present invention") has the positive electrode of the present invention as its positive electrode. The secondary battery of the present invention can have the same configuration as a conventional nonaqueous electrolyte secondary battery, except that it has the positive electrode of the present invention as its positive electrode. That is, the secondary battery of the present invention can be obtained by incorporating the positive electrode of the present invention as the positive electrode of a conventional non-aqueous electrolyte secondary battery.

[0090] The structure of a typical non-aqueous electrolyte secondary battery will be described below. FIG. 1 is a cross-sectional view showing a schematic representation of the laminated structure of a typical nonaqueous electrolyte secondary battery 10, including the operating parts when the battery is in operation. The nonaqueous electrolyte secondary battery 10 has a laminated structure, viewed from the negative electrode side, having a negative electrode current collector 1, a negative electrode active material layer 2, a separator 3, a positive electrode active material layer 4, and a positive electrode current collector 5, in this order. The negative electrode active material layer 2, the positive electrode active material layer 4, and the space between them are filled with a nonaqueous electrolyte (not shown), and are separated by the separator 3. The separator 3 has pores, and during normal battery use, it functions as a separator between the positive and negative electrodes, allowing the electrolyte and ions to pass through these pores, insulating the positive and negative electrodes. With this structure, for example, in the case of a lithium-ion secondary battery, electrons (e - ) is supplied, and at the same time, lithium ions (Li + ) moves and accumulates in the negative electrode. On the other hand, during discharge, the lithium ions (Li + ) is returned to the positive electrode side through the electrolyte, and electrons are supplied to the operating part 6. In the example shown, a light bulb is used as the operating part 6, and it is lit by the discharge. The secondary battery of the present invention has the positive electrode of the present invention in place of the positive electrode active material layer 4 and the positive electrode current collector 5 of the above-mentioned general non-aqueous electrolyte secondary battery.

[0091] Next, the basic structure characteristic of quasi-solid secondary batteries will be described. In quasi-solid secondary batteries, the electrode active material layer is an electrode slurry layer formed by dispersing an electrode active material in a non-aqueous electrolyte. Therefore, the structure of a quasi-solid secondary battery differs from that of a general non-aqueous electrolyte secondary battery in that the electrode active material layer is a slurry (suspension, dispersion) formed by dispersing an electrode active material in a non-aqueous electrolyte. That is, in a typical nonaqueous electrolyte secondary battery, a coating solution is prepared by dispersing an electrode active material in a medium that does not contain an electrolyte, and the coating solution is applied to a current collector to form a coating film, which is then dried to form a thin-film electrode active material layer. A binder is usually blended into the coating solution, forming a hard electrode active material layer in which the electrode active material particles are firmly bound together. Since the nonaqueous electrolyte is present on the electrode active material layer thus formed (between the negative electrode active material layer and the positive electrode active material layer), the electrode active material layer is in the form of a hard solid particle layer overall, and is not a slurry layer, even if there are portions in the electrode active material layer through which the nonaqueous electrolyte can penetrate. In contrast, in a quasi-solid secondary battery, the electrode active material layer is an electrode slurry layer formed by dispersing solid particles containing an electrode active material and a conductive additive in a non-aqueous electrolyte solution obtained by dissolving a lithium salt (electrolyte) in a non-aqueous solvent. For this electrode slurry layer to function as an electrode active material layer, strong binding between the electrode active material particles is not required, and therefore the electrode slurry layer usually does not contain a binder. Except for the fact that the electrode active material layer is an electrode slurry layer and that the electrode slurry layer is in contact with a separator, the basic layer configuration of a quasi-solid secondary battery is the same as the layer configuration shown in FIG. 1.

[0092] When the secondary battery of the present invention is a general non-aqueous electrolyte secondary battery, the positive electrode active material layer is a layer obtained by applying the positive electrode composition of the second or fourth aspect of the present invention and drying it as necessary. When the secondary battery of the present invention is a quasi-solid secondary battery, the positive electrode active material layer is a layer formed from the positive electrode composition for a quasi-solid secondary battery of the present invention.

[0093] The secondary battery of the present invention is provided with the positive electrode of the present invention as the positive electrode of the secondary battery, and other components such as the negative electrode active material layer, the negative electrode current collector, the electrolyte (aqueous electrolyte, non-aqueous electrolyte), and the separator are not particularly limited. These materials and components can be appropriately applied to those used in ordinary secondary batteries. In addition, for the method of manufacturing the secondary battery of the present invention, ordinary methods can be appropriately adopted, except that the positive electrode of the present invention is used as the positive electrode. For components and manufacturing methods commonly used in these secondary batteries, for example, JP 2016-201308 A, JP 2005-108835 A, JP 2012-185938 A, and WO 2020 / 067106 A can be appropriately referenced.

[0094] The secondary battery of the present invention can be installed in electronic devices such as notebook computers, pen-input PCs, mobile PCs, electronic book players, mobile phones, cordless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, headphone stereos, video camcorders, LCD televisions, handheld vacuum cleaners, portable CD players, mini-discs, electric shavers, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, and memory cards. It can also be installed in consumer devices such as automobiles, electric vehicles, motors, lighting fixtures, toys, game devices, road conditioners, clocks, flash devices, cameras, and medical devices (pacemakers, hearing aids, shoulder massagers, etc.). It can also be used for various military and space applications. It can also be combined with solar cells.

[0095] The present invention will be described in more detail below with reference to examples, but the present invention should not be construed as being limited thereto. [Example]

[0096] [HSP calculation method] The HSP of each component and each dispersion medium was calculated using the HSPiP software from pirika.com, as described above. The HSP was calculated by inputting the Smiles formula for the structure of each component (a), component (b), and dispersion medium shown in Table 1 into the software.

[0097] [HOMO energy level calculation method] The HOMO energy level of each component was calculated using the quantum chemistry calculation program Gaussian 16 (Gaussian Inc.) with the calculation method: B3LYP / 6-31G(d) as described above. The structure of each component (a) was determined using the structure of the monomer from which component (a) is derived, as shown in Table 1.

[0098] [Method for synthesizing polymer X and method for preparing polymer X solution (first embodiment of the positive electrode composition of the present invention)] (Polymer used in Example 1) To a 100 mL measuring cylinder were added 15 g of N-ethylmaleimide (NEM) (manufactured by Tokyo Chemical Industry Co., Ltd.) as a monomer that leads to component (a), 15 g of ethyl acrylate (EA) (manufactured by Tokyo Chemical Industry Co., Ltd.) as a monomer that leads to component (b), 35 g of N-methylpyrrolidone (NMP) (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) as a dispersion medium, and 0.1 g of polymerization initiator V-601 (trade name, manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.), to prepare monomer solution a. 35 g of N-methylpyrrolidone was added to a 300 mL three-neck flask and stirred at 80°C under a nitrogen atmosphere, to which the above-mentioned monomer solution a was added dropwise over 2 hours. After the dropwise addition was completed, the temperature was raised to 90°C and stirring was continued for 2 hours to obtain polymer solution S1 containing a polymer containing N-ethylmaleimide as component (a) and ethyl acrylate as component (b), and NMP as a dispersion medium. The weight-average molecular weight (Mw) of the obtained polymer was 6000. The solids concentration of polymer solution S1 was 30 mass%.

[0099] (Polymer used in Example 2) The polymer used in Example 2 and its polymer solution S2 were obtained in the same manner as in the synthesis of the polymer used in Example 1, except that the type of monomer from which component (a) was derived was i-propylacrylamide (IPAM).

[0100] (Polymer used in Example 3) The polymer used in Example 3 and its polymer solution S3 were obtained in the same manner as in the synthesis of the polymer used in Example 1, except that the type of monomer from which component (a) was derived was N-cyclopentylacrylamide (CyPAM).

[0101] (Polymer used in Example 4) The polymer used in Example 4 and its polymer solution S4 were obtained in the same manner as in the synthesis of the polymer used in Example 1, except that the type of monomer from which component (a) was derived was γ-butyrolactone acrylate (GBLA).

[0102] (Polymer used in Example 5) The polymer used in Example 5 and its polymer solution S5 were obtained in the same manner as in the synthesis of the polymer used in Example 1, except that in the synthesis method of the polymer used in Example 1, the type of monomer from which component (a) was derived was N-cyclopentylacrylamide, and the type of monomer from which component (b) was derived was benzyl acrylate (BZA).

[0103] (Polymer used in Example 6) The polymer used in Example 6 and its polymer solution S6 were obtained in the same manner as in the synthesis of the polymer used in Example 5, except that in the synthesis method of the polymer used in Example 5, the monomer from which component (b) was derived was stearyl acrylate (SA).

[0104] (Polymer used in Example 7) The polymer used in Example 7 and its polymer solution S7 were obtained in the same manner as in the synthesis of the polymer used in Example 6, except that in the synthesis method for the polymer used in Example 6, the amount of the monomer leading to component (a) was 7.5 g and the amount of the monomer leading to component (b) was 22.5 g.

[0105] (Polymer used in Example 8) The polymer used in Example 8 and its polymer solution S8 were obtained in the same manner as in the synthesis of the polymer used in Example 6, except that in the synthesis method of the polymer used in Example 6, the amount of the monomer leading to component (a) was 22.5 g and the amount of the monomer leading to component (b) was 7.5 g.

[0106] (Polymer used in Example 9) The polymer used in Example 9 and its polymer solution S9 were obtained in the same manner as in the synthesis of the polymer used in Example 6, except that in the synthesis method of the polymer used in Example 6, the amount of monomer leading to component (a) was 30 g and no monomer leading to component (b) was used.

[0107] (Polymer used in Example 10) The polymer used in Example 10 and its polymer solution S10 were obtained in the same manner as in Example 6, except that the Mw was adjusted to 30,000 in the synthesis method for the polymer used in Example 6.

[0108] (Polymer used in Example 11) The polymer used in Example 11 and its polymer solution S11 were obtained in the same manner as in Example 6, except that the Mw was adjusted to 80,000.

[0109] (Polymer used in Example 12) The polymer used in Example 11 and its polymer solution S12 were obtained in the same manner as in the synthesis of the polymer used in Example 6, except that the Mw was set to 6,400 and cyclohexanone was used as the dispersion medium.

[0110] (Polymer used in Comparative Example 1) The polymer used in Comparative Example 1 and its polymer solution cS1 were obtained in the same manner as in Example 1, except that in the synthesis method for the polymer used in Example 1, the type of monomer from which component (a) was derived was methoxyethyl acrylate (MEA).

[0111] (Polymer used in Comparative Example 2) The polymer used in Comparative Example 2 and its polymer solution cS2 were obtained in the same manner as in Example 1, except that in the synthesis method for the polymer used in Example 1, the type of monomer from which component (a) was derived was vinylpyrrolidone (VP).

[0112] (Polymer used in Comparative Example 3) The polymer used in Comparative Example 3 and its polymer solution cS3 were obtained in the same manner as in the synthesis of the polymer used in Example 1, except that the type of monomer from which component (a) was derived was acroylmorpholine (ACM).

[0113] (Polymer used in Comparative Example 4) The polymer used in Comparative Example 4 and its polymer solution cS4 were obtained in the same manner as in Example 5, except that the dispersion medium was changed to N,N-dimethylformamide (DMF).

[0114] [Preparation of Conductive Aid Slurry (Third Form of Positive Electrode Composition of the Present Invention)] (Conductive assistant slurry CAS1 of Example 1) Conductive additive slurry CAS1 was prepared using acetylene black (AB) (Denka Black Powder, manufactured by Denka Co., Ltd.) as the conductive additive, a polyvinylidene fluoride NMP solution (12 mass% NMP solution of #1100, manufactured by Kureha Corporation) as the binder, and NMP as the dispersion medium. Furthermore, polymer solution S1 was used. The mass ratio of conductive additive, binder, and polymer X in conductive additive slurry CAS1 was 50:50:2.5 (solid content equivalent). The amount of NMP was adjusted to a solid content of 14 mass%. The conductive additive slurry CAS1 was degassed and stirred using a planetary centrifugal mixer (Awatori Rentaro) (stirring: 2000 rpm × 4 min, degassing: 2200 rpm × 1 min). In this way, conductive additive slurry CAS1 containing a polymer composed of N-ethylmaleimide and ethyl acrylate as constituent components and NMP was obtained.

[0115] (Conductive assistant slurries CAS2 to CAS11 of Examples 2 to 11) Conductive assistant slurries CAS2 to CAS11 of Examples 2 to 11 were obtained in the same manner as in the preparation of the conductive assistant slurry CAS1 of Example 1, except that the polymer solutions shown in Table 1 were used instead of the conductive assistant slurry CAS1 of Example 1.

[0116] (Conductive assistant slurry CAS12 of Example 12) A conductive additive slurry CAS12 of Example 12 was obtained in the same manner as in the preparation of the conductive additive slurry CAS1 of Example 1, except that in the preparation of the conductive additive slurry CAS1 of Example 1, cyclohexanone was used instead of NMP as the dispersion medium, powdered polyvinylidene fluoride (manufactured by Kureha Corporation, #1100 (product name)) was added instead of the polyvinylidene fluoride NMP solution, and polymer liquid S12 was used as the polymer liquid.

[0117] (Conductive assistant slurries cCAS1 to cCAS3 of Comparative Examples 1 to 3) Conductive assistant slurries cCAS1 to cCAS3 of Comparative Examples 1 to 3 were obtained in the same manner as in the preparation of the conductive assistant slurry CAS1 of Example 1, except that the polymer solutions shown in Table 1 were used instead of the conductive assistant slurry CAS1 of Example 1.

[0118] (Conductive assistant slurry cCAS4 of Comparative Example 4) A conductive additive slurry cCAS4 of Comparative Example 4 was obtained in the same manner as in the preparation of the conductive additive slurry CAS1 of Example 1, except that in the preparation of the conductive additive slurry CAS1 of Example 1, DMF was used instead of NMP as the dispersion medium, powdered polyvinylidene fluoride (manufactured by Kureha Corporation, #1100 (product name)) was added instead of the polyvinylidene fluoride NMP solution, and polymer liquid cS4 was used as the polymer liquid.

[0119] [Dispersion viscosity] The dispersibility of solid particles in the positive electrode composition was confirmed using dispersion viscosity as an indicator. Among the solid particles that can be contained in the positive electrode composition, the conductive additive is usually the least dispersible. For this reason, in this test, only the conductive additive was used as the dispersoid. The dispersion viscosity of each of the conductive additive slurries obtained above was measured. An E-type viscometer was used to measure the viscosity, and the dispersion viscosity was read at a shear rate of 10 / s. The obtained dispersion viscosity was evaluated according to the following evaluation criteria. - Evaluation Criteria - A: Less than 8000cP B: 8000cP or more, less than 10000cP C: 10,000 cP or more, less than 15,000 cP D: 15,000 cP or more, less than 20,000 cP E: 20,000 cP or more, less than 30,000 cP F:30000cP or more

[0120] [Oxidation resistance evaluation] The oxidation resistance of polymer X was confirmed using the oxidation voltage as an index. Each of the above conductive additive slurries was applied to one side of an aluminum foil having a thickness of 20 μm and then thoroughly dried to prepare an aluminum foil having a conductive additive layer (aluminum foil with a conductive additive layer). The coating mass of each conductive additive slurry was 10 mg / cm. 2 It was. Three-electrode cells were assembled using each of the aluminum foils with conductive additive layers as the working electrode and lithium foils as the counter and reference electrodes. Cyclic voltammetry measurements were performed using the resulting three-electrode cells at a sweep voltage of 3 to 5 V and a sweep rate of 1 mV / sec. The electrolyte used was a 1 M solution of LiPF6 in a mixed solvent of EC and DEC in a volume ratio of 3:7. The voltage at which current began to flow (oxidation voltage) was measured. The resulting voltages were evaluated according to the following criteria: the higher the voltage, the better the oxidation resistance. - Evaluation Criteria - A:4.4V or more B: 4.2V or more, less than 4.4V C: 4.0V or more, less than 4.2V D: 3.8V or more, less than 4.0V E: 3.6V or more, less than 3.8V F: Less than 3.6V

[0121] [Preparation of Positive Electrode Slurry (Fourth Form of Positive Electrode Composition of the Present Invention)] (Positive electrode slurry of Example 1) The conductive additive slurry CAS1, NMP, and polyvinylidene fluoride NMP solution (12 mass% NMP solution of #1100 manufactured by Kureha Corporation) were weighed into a 50 ml sample bottle, and LiCoO2 (Cellseed (product name) manufactured by Nippon Chemical Industry Co., Ltd.) was added as a positive electrode active material. The mixture was further stirred for 5 minutes using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro (product name)) to obtain the positive electrode slurry of Example 1. The mass ratio of the positive electrode active material, binder (PVDF), conductive additive, and polymer X was 100:3:3:0.15 (solid content equivalent), and the solid content (mass %) of the positive electrode slurry was 73.8 mass %. The total solid content of the positive electrode slurry is the total mass of the positive electrode active material, binder, conductive additive, and polymer contained in the positive electrode slurry.

[0122] (Positive electrode slurries of Examples 2 to 11) Positive electrode slurries of Examples 2 to 11 were obtained in the same manner as in the preparation of the positive electrode slurry of Example 1, except that the conductive assistant slurries were changed to conductive assistant slurries CAS2 to CAS11.

[0123] (Positive electrode slurry of Example 12) A positive electrode slurry of Example 12 was obtained in the same manner as in the preparation of the positive electrode slurry of Example 1, except that in the preparation of the positive electrode slurry of Example 1, the conductive additive slurry was changed to conductive additive slurry CAS12, cyclohexanone was used instead of NMP, and powdered polyvinylidene fluoride (manufactured by Kureha Corporation, #1100 (trade name)) was added instead of the polyvinylidene fluoride NMP solution.

[0124] (Positive electrode slurries of Comparative Examples 1 to 3) Positive electrode slurries of Comparative Examples 1 to 3 were obtained in the same manner as in the preparation of the positive electrode slurry of Example 1, except that the conductive assistant slurries were changed to conductive assistant slurries cCAS1 to cCAS3.

[0125] (Positive electrode slurry of Comparative Example 4) A positive electrode slurry of Comparative Example 4 was obtained in the same manner as in the preparation of the positive electrode slurry of Example 1, except that in the preparation of the positive electrode slurry of Example 1, the conductive additive slurry was changed to conductive additive slurry cCAS4, DMF was used instead of NMP, and powdered polyvinylidene fluoride (manufactured by Kureha Corporation, #1100 (trade name)) was added instead of the polyvinylidene fluoride NMP solution.

[0126] [Preparation of positive electrode] Each of the positive electrode slurries obtained above was applied to one side of a 20 μm thick aluminum foil (current collector) as a substrate and thoroughly dried to prepare a positive electrode having a positive electrode active material layer on the aluminum foil. The mass of the positive electrode active material layer after drying was 17 mg / cm. 2 It was.

[0127] [Preparation of negative electrode] 94.8 parts by weight of commercially available graphite for negative electrode active materials, 1.7 parts by weight of acetylene black, 2 parts by weight of SBR (styrene-butadiene rubber), and 1.5 parts by weight of CMC (carboxymethyl cellulose) were mixed. Subsequently, distilled water, a solvent, was added to the mixture to prepare a slurry. The slurry was applied to a surface of electrolytic copper foil to a thickness of approximately 100 μm, dried at 120°C, and then roll-pressed to prepare a negative electrode.

[0128] [Evaluation method: Battery evaluation] <Discharge capacity maintenance rate> A 1M solution of LiPF6 as a solute in a non-aqueous organic solvent prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 mass ratio was prepared as electrolyte I. A coin battery was manufactured using the negative electrode, positive electrode, and electrolyte I prepared above, and the battery characteristics were measured as follows. The coin battery was charged at a C rate of 0.2C under the following conditions in an environment of 25°C until the battery voltage reached 4.2V, and then discharged at a C rate of 0.2C until the battery voltage reached 3V, and the discharge capacity (Ah) at 0.2C was determined. (Charging conditions) 0.2C CC (constant current)-CV (constant voltage) charging: Upper limit voltage 4.2V, end current 0.02C (discharge conditions) 0.2C CC (constant current) discharge: End voltage 3V Next, the discharge capacity at 5C was determined in the same manner as in the measurement of the discharge capacity at 0.2C, except that the C rates during charging and discharging were changed to 5C. The discharge capacity retention rate at 5 C was calculated using the discharge capacity at 0.2 C as the reference discharge capacity according to the following formula: The obtained discharge capacity retention rate was applied to the following evaluation criteria to evaluate the battery performance. Discharge capacity retention rate at 5 C (%) = (discharge capacity at 5 C / discharge capacity at 0.2 C) × 100 - Evaluation Criteria - A: 75% or more B: 70% or more, less than 75% C: 65% or more, less than 70% D: 60% or more, less than 65% E: 55% or more, less than 60% F: Less than 55%

[0129] The results obtained are shown in Tables 1 and 2.

[0130] [Table 1]

[0131] (Note to Table 1) The "structure" of component (a) and component (b) describes the monomers that lead to each component. The "composition ratio" indicates the content (% by mass) of the constituent component (a) or (b) in the polymer X.

[0132] [Table 2]

[0133] The HSP distance between the dispersion medium of component (a) contained in polymer X is 4.0 MPa. 1 / 2 In Comparative Example 1, the dispersion viscosity of the conductive additive slurry was as high as 30,000 cP or more, resulting in poor dispersibility. The HSP distance between the component (a) contained in polymer X and the dispersion medium is 4.0 MPa. 1 / 2Although the following conditions were satisfied, Comparative Examples 2 and 3, in which the HOMO energy level of component (a) exceeded −6.4 eV, resulted in poor oxidation resistance, with the oxidation voltage of the positive electrode being less than 3.6 V. Furthermore, the secondary battery having this positive electrode had a poor discharge capacity retention rate of less than 55%. Although the component (a) contained in polymer X satisfies the requirements of the present invention in terms of the HSP distance and HOMO energy level relative to NMP, the component (a) has an HSP distance of 4.0 MPa relative to DMF. 1 / 2 In Comparative Example 4, the dispersion viscosity of the conductive additive slurry was as high as 30,000 cP or more, and the oxidation voltage of the positive electrode was less than 3.6 V. Furthermore, the secondary battery having this positive electrode had a poor discharge capacity retention rate of less than 55%. In contrast, in Examples 1 to 12, in which the HSP distance and HOMO energy level of the component (a) contained in the polymer X relative to the dispersion medium satisfied the requirements of the present invention, the dispersion viscosity of the conductive additive slurry was less than 15,000 cP, the oxidation voltage of the positive electrode was 4.0 V or higher, and the discharge capacity retention rate was 65% or higher. It can be seen that by using the positive electrode composition of the present invention, solid particles can be dispersed efficiently, and when used in a positive electrode, oxidation resistance can be improved. [Explanation of symbols]

[0134] 10 Nonaqueous electrolyte secondary battery 1 Negative electrode current collector 2 Negative electrode active material layer 3 Separator 4 Cathode active material layer 5 Positive electrode current collector 6. Working part (bulb)

Claims

1. A positive electrode composition containing a polymer X and a dispersion medium, The polymer X comprises at least component (a), The component (a) is represented by any one of the following (i) to (iii), and the HSP distance to the dispersion medium is 4.0 MPa. １／２ Hereinafter, a composition for a positive electrode of a nonaqueous electrolyte secondary battery, having a HOMO energy level of −6.4 eV or less. 【Chemistry 1】 In the above formula, R １１ and R ２１ represents a hydrogen atom or an alkyl group. R １２ , R ２２ , and R ３ indicates a substituent. * indicates a binding site for incorporation into the polymer.

2. R in the component (a) １２ , R ２２ , and R ３ The positive electrode composition according to claim 1, wherein represents a substituent having a chemical formula weight of 40 to 400.

3. R in the component (a) １２ , R ２２ , and R ３ The positive electrode composition according to claim 2, wherein represents a substituent having 2 to 10 carbon atoms.

4. R in the component (a) １２ and R ２２ The positive electrode composition according to claim 3 , wherein includes a ring structure.

5. 5. The positive electrode composition according to claim 4, wherein the content of the component (a) in the polymer X is 20% by mass or more.

6. 6. The positive electrode composition according to claim 5, wherein the polymer X comprises a component (b) different from the component (a), and the component (b) has a hydrocarbon group having 2 to 50 carbon atoms.

7. 7. The positive electrode composition according to claim 6, wherein the polymer X has a weight average molecular weight of 1,000 to 30,000.

8. The positive electrode composition according to claim 1 , further comprising a conductive additive.

9. The positive electrode composition according to claim 8 , comprising a positive electrode active material.

10. A positive electrode for a non-aqueous electrolyte secondary battery formed using the positive electrode composition according to claim 9.

11. A non-aqueous electrolyte secondary battery having the positive electrode for a non-aqueous electrolyte secondary battery according to claim 10 as a positive electrode.

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