Positive electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and conductive agent dispersion liquid

Abstract

A positive electrode for a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises a current collector and a mixture layer disposed on a surface of the current collector. The mixture layer contains an active material, a binder, and a conductive agent. The conductive agent is added as a conductive agent dispersion liquid when the mixture layer is fabricated. The conductive agent dispersion liquid contains the conductive agent, a dispersant, and a solvent. The Rsp measured by pulsed NMR is 4 or greater and the viscosity at 60 rpm in a 25°C environment is 200 mPa·s to 2000 mPa·s.

Description

Positive electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and conductive agent dispersion.

[0001] This disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a conductive agent dispersion, and more particularly to a high-quality positive electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and a conductive agent dispersion.

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been widely used in various applications such as automotive and energy storage, and much research has been conducted on non-aqueous electrolyte secondary batteries. Patent Document 1 discloses that a positive electrode active material having an affinity value of 5,000 to 20,000 for N-methyl-2-pyrrolidinone as determined by pulsed NMR can solve the problem of the carbonaceous coating formed on the surface of the positive electrode active material peeling off due to pulverization, which reduces the rate characteristics.

[0003] Japanese Patent Publication No. 2016-72135

[0004] Incidentally, electrodes are a major component in non-aqueous electrolyte secondary batteries, and the stable production of high-quality electrodes is important for the production of non-aqueous electrolyte secondary batteries. The inventors of this invention have conducted extensive research and have found that high-quality positive electrodes can be stably produced by using a conductive agent dispersion liquid in which the Rsp measured by pulsed NMR is 4 or higher and the viscosity at 60 rpm in a 25°C environment is 200 mPa·s to 2000 mPa·s.

[0005] The purpose of this disclosure is to provide high-quality electrodes in a stable manner.

[0006] A positive electrode for a non-aqueous electrolyte secondary battery, according to one aspect of the present disclosure, comprises a current collector and a composite layer disposed on the surface of the current collector, wherein the composite layer contains an active material, a binder and a conductive agent, the conductive agent being added as a conductive agent dispersion when the composite layer is prepared, the conductive agent dispersion containing a conductive agent, a dispersant and a solvent, and having an Rsp of 4 or higher as measured by pulsed NMR, and a viscosity of 200 mPa·s to 2000 mPa·s at 60 rpm in a 25°C environment.

[0007] One embodiment of the non-aqueous electrolyte secondary battery described herein is characterized by comprising the above-mentioned positive electrode for the non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

[0008] A conductive agent dispersion, one embodiment of the present disclosure, comprises a conductive agent, a dispersant, and a solvent, characterized in that its Rsp, as measured by pulsed NMR, is 4 or higher, and its viscosity at 60 rpm in a 25°C environment is 200 mPa·s to 2000 mPa·s.

[0009] The positive electrode for non-aqueous electrolyte secondary batteries relating to this disclosure is of high quality and can be produced stably.

[0010] This is a longitudinal cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. This is a cross-sectional view of a positive electrode for a non-aqueous electrolyte secondary battery, which is an example of an embodiment.

[0011] Electrodes for non-aqueous electrolyte secondary batteries such as lithium-ion batteries are generally manufactured by a wet process in which an electrode mixture slurry containing an active material, binder, conductive agent, etc., is applied to the surface of a current collector, which is a metal foil, and the coating is dried and rolled. Electrodes are a major component in non-aqueous electrolyte secondary batteries, and the stable production of high-quality electrodes is important for the production of non-aqueous electrolyte secondary batteries. The inventors have conducted extensive research and have found that high-quality positive electrodes can be stably manufactured by using a conductive agent dispersion liquid in which the Rsp measured by pulsed NMR is 4 or higher and the viscosity at 60 rpm in a 25°C environment is 200 mPa·s to 2000 mPa·s. It should be noted that the technology described in Patent Document 1, as described above, uses pulsed NMR to identify the properties of the positive electrode active material, and while it shares the use of pulsed NMR with the invention discovered by the inventors, it is significantly different.

[0012] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail. In the following, a cylindrical battery in which a wound electrode body is housed in a cylindrical outer casing will be given as an example, but the electrode body is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are stacked alternately one by one with separators in between. Furthermore, the outer casing is not limited to a cylindrical shape and may be, for example, rectangular, coin-shaped, etc., or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0013] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10, which is an example of an embodiment. As shown in Figure 1, the secondary battery 10 comprises a wound electrode body 14, an electrolyte, and an outer casing 16 that houses the electrode body 14 and the electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening of the outer casing 16 is closed by a sealing body 17. In the following, for convenience of explanation, the side of the battery with the sealing body 17 will be referred to as the top, and the bottom side of the outer casing 16 as the bottom.

[0014] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all rectangular elongated bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape in the longitudinal direction. The separator 13 separates the positive electrode 11 and the negative electrode 12 from each other. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in both the longitudinal and transverse directions than the positive electrode 11. The two separators 13 are formed to be at least slightly larger in dimensions than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the transverse direction of the positive electrode 11 and the negative electrode 12 is the axial direction. In other words, the end faces in the short direction of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode body 14.

[0015] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends outside the insulating plate 19 towards the bottom of the outer casing 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the bottom inner surface of the outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0016] A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery. The outer casing 16 has a grooved portion 22 formed on its side surface, which protrudes inward to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0017] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side, and functions as a safety valve. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0018] The following describes in detail the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte that constitute the secondary battery 10, with particular emphasis on the positive electrode 11.

[0019] [Positive Electrode] The positive electrode 11 includes, for example, a positive electrode current collector 30 and a positive electrode mixture layer 32 formed on the surface of the positive electrode current collector 30. Preferably, the positive electrode mixture layer 32 is formed on both sides of the positive electrode current collector 30. The positive electrode current collector 30 can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 30 μm or less.

[0020] The thickness of the positive electrode mixture layer 32 is, for example, 10 μm to 200 μm on one side of the positive electrode current collector 30. The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, conductive agent, etc., to the surface of the positive electrode current collector 30, drying the coating film, and then rolling it to form the positive electrode mixture layer 32 on both sides of the positive electrode current collector 30.

[0021] The positive electrode active material is the main component of the positive electrode mixture layer. Here, the main component refers to the component with the highest mass ratio among the constituent components of the positive electrode mixture layer. The positive electrode mixture layer preferably contains 80% by mass or more of the positive electrode active material, and more preferably 90% by mass or more of the positive electrode active material, relative to the total mass of the positive electrode mixture layer.

[0022] As the positive electrode active material contained in the positive electrode mixture layer 32, for example, a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, and Mn is used. Examples of metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. Examples of suitable composite oxides include a lithium transition metal composite oxide containing Ni, Co, and Mn, and a lithium transition metal composite oxide containing Ni, Co, and Al. The lithium transition metal composite oxide may be used alone or in combination of multiple types.

[0023] Lithium transition metal composite oxides, for example, have a layered rock salt structure. Examples of layered rock salt structures include those belonging to space group R-3m and those belonging to space group C2 / m. Among these, the layered rock salt structure belonging to space group R-3m is preferred from the viewpoint of high capacity and crystal structure stability.

[0024] Examples of binders included in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These may be used individually or in combination of two or more. The binder content in the positive electrode mixture layer 32 is, for example, 0.1% by mass or more and 10% by mass or less, relative to the total mass of the positive electrode mixture layer 32.

[0025] Examples of conductive agents included in the positive electrode mixture layer 32 include acetylene black (AB), carbon black (CB) such as Ketjenblack, carbon nanotubes (CNT), graphene, and carbon-based particles such as graphite. These may be used individually or in combination of two or more types. From the viewpoint of improving dispersibility, the conductive agent is preferably acetylene black. In its powder state before being added to the conductive agent dispersion, the conductive agent exists as secondary aggregates, and the particle size of these secondary aggregates is, for example, 1 μm to 1000 μm. As will be described later, the conductive agent exists in a dispersed state in the conductive agent dispersion, and the particle size of the conductive agent in the conductive agent dispersion is, for example, 0.1 μm to 6 μm in the volume-based particle size distribution by laser diffraction. When preparing the mixture layer, adding the conductive agent as a conductive agent dispersion makes it possible to reduce the particle size of the conductive agent in the positive electrode mixture layer 32 compared to adding the conductive agent in powder form. The content of the conductive agent in the positive electrode mixture layer 32 is, for example, 0.1% by mass or more and 10% by mass or less, relative to the total mass of the positive electrode mixture layer 32.

[0026] The conductive agent is added as a conductive agent dispersion containing a conductive agent, a dispersant, and a solvent. Examples of the dispersant contained in the conductive agent dispersion include cellulose derivatives. One of these may be used alone, or two or more thereof may be used in combination. The dispersant may be methyl cellulose. The content of the dispersant in the conductive agent dispersion is, for example, 0.1 mass% or more and 3 mass% or less, and may be 0.5 mass% or more and 1.5 mass% or less. Examples of the solvent contained in the conductive agent dispersion for electrode slurries include N-methyl-2-pyrrolidone (NMP). The solvent is the main component of the conductive agent dispersion for electrode slurries.

[0027] The content of the conductive agent in the conductive agent dispersion is, for example, 10 mass% or more and 20 mass% or less, and may be 10 mass% or more and 15 mass% or less.

[0028] The conductive agent dispersion has an Rsp measured by pulsed NMR of 4 or more, and a viscosity of 200 mPa·s to 2000 mPa·s at 60 rpm in an environment of 25°C. A high-quality electrode can be obtained by using such a conductive agent dispersion.

[0029] Rsp can be measured, for example, using a MagnoMeter XRS VT manufactured by Magritek. Pulsed NMR is also called Low-field NMR (low-field nuclear magnetic resonance method), and measures the relaxation time of irradiated radio waves. Rsp can be calculated from the average relaxation time Tav and the relaxation time Tb of the solvent in a bulk state. Rsp = (Tb / Tav)-1

[0030] Rsp indicates the affinity of the conductive agent for the solvent; the larger Rsp is, the greater the wettability of the conductive agent to the solvent is. The upper limit of Rsp is not particularly limited, and is, for example, 8. When Rsp exceeds 8, the conductive path in the positive electrode mixture layer may be broken, increasing the resistance of the positive electrode.

[0031] The viscosity of the conductive agent dispersion is measured with a Brookfield viscometer. As the Brookfield viscometer, for example, TV-150B manufactured by Toki Sangyo Co., Ltd. can be used.

[0032] The conductive agent dispersion for electrode slurry is produced through, for example, a mixing step of mixing a conductive agent, a dispersant and a solvent to prepare a mixed liquid, and a dispersing step of dispersing the conductive agent in the mixed liquid.

[0033] In the mixing step, for example, an in-line mixer or the like is used to prepare the mixed liquid while allowing the dispersant to adsorb onto the conductive agent. Adsorption of the dispersant onto the conductive agent can suppress re-agglomeration of the conductive agent. As the in-line mixer, for example, magic LAB manufactured by IKA can be used.

[0034] In the dispersing step, for example, a high-pressure homogenizer or the like is used to loosen and disperse the conductive agent contained in the mixed liquid, thereby improving the dispersion state of the conductive agent. As the high-pressure homogenizer, for example, Econizer Lab 02 manufactured by Sanmaru Kikai Kogyo Co., Ltd. can be used. In the treatment using a high-pressure homogenizer, the dispersion state of the conductive agent can be changed by adjusting the treatment pressure, treatment time and the like. For example, increasing the treatment pressure or prolonging the treatment time increases Rsp and decreases the viscosity. Furthermore, increasing the content of the conductive agent or the dispersant in the conductive agent dispersion decreases Rsp and increases the viscosity. Rsp and the viscosity can be adjusted to appropriate ranges by adjusting the content of each component in the conductive agent dispersion and the treatment conditions in the dispersing step.

[0035] [Negative Electrode] The negative electrode 12 may, for example, have a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector, or a metallic Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode current collector, and lithium metal may be deposited on the surface of the negative electrode current collector by charging. When the negative electrode 12 has a negative electrode mixture layer, it is preferable that the negative electrode mixture layer is formed on both sides of the negative electrode current collector. For the negative electrode current collector, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on the surface layer, can be used. The thickness of the negative electrode current collector is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode current collector. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc., to the surface of a negative electrode current collector, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode current collector.

[0036] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly intercept and release lithium ions, and generally carbon materials such as graphite are used. The graphite may be any of the following: natural graphite such as flake graphite, lump graphite, or clay graphite; lump artificial graphite; or artificial graphite such as graphitized mesophase carbon microbeads. In addition, metals that alloy with Li such as Si and Sn, metal compounds containing Si and Sn, or lithium titanium composite oxides may be used as the negative electrode active material. Furthermore, materials with a carbon coating may also be used. For example, SiO ｘ Si-containing compounds represented by (0.5 ≤ x ≤ 1.6), or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine Si particles are dispersed in a lithium silicate phase represented by (0 < y < 2) may be used in combination with graphite.

[0037] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0038] [Separator] The separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. In addition, a heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13.

[0039] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphoric acid compounds. The filler layer can be formed by coating the surface of the positive electrode 11, the negative electrode 12, or the separator 13 with a slurry containing the filler.

[0040] [Non-aqueous electrolytes] Non-aqueous electrolytes, for example, have lithium ion conductivity. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0041] A liquid electrolyte (electrolyte solution) includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted solvents include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0042] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0043] Examples of the aforementioned ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and crown ether; and chain ethers such as 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0044] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lithium lower aliphatic carboxylate, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of the phosphate include lithium difluorophosphate (LiPO ２ F ２Examples include lithium difluorobis(oxalato)phosphate (LiDFOBP), lithium tetrafluoro(oxalato)phosphate, etc. Examples of borates include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), etc. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO)). ２ ) ２ ), bistrifluoromethanesulfonate lithium (LiN(CF ３ SO ２ ) ２ ), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), bispentafluoroethanesulfonate lithium (LiN(C) ２ F ５ SO ２ ) ２ ) etc. are used. Of these, LiPF is used from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ It is preferable to use the following. The concentration of the lithium salt may be, for example, 4 moles or less per liter of non-aqueous solvent, or 3 moles or less, preferably 1.8 moles or less, and more preferably 0.8 moles or more and 1.8 moles or less.

[0045] Non-aqueous electrolytes may contain additives. Examples of additives include unsaturated carbonate esters, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0046] Examples of unsaturated cyclic carbonate esters include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. Unsaturated cyclic carbonate esters may be used individually or in combination of two or more. Some hydrogen atoms in the unsaturated cyclic carbonate esters may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, but it is preferable that it be an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0047] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0048] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanate methylcyclohexane (BIMCH). Examples of sultone compounds include propanesultone and propensultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethylborate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethylphosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethylphosphite and tris(trimethylsilyl)phosphite.

[0049] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0050] The present disclosure will be further illustrated below with reference to examples, but the present disclosure is not limited to these examples.

[0051] <Example 1> [Preparation of Conductive Agent Dispersion] Acetylene black manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used as the conductive agent. Methylcellulose 100 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used as the methylcellulose. This acetylene black (AB), methylcellulose (MC), and N-methyl-2-pyrrolidone (NMP) were mixed using an in-line mixer (magic LAB manufactured by IKA Corporation) to prepare a mixed solution (mixing step). At this time, the proportion of AB was set to 12.5% ​​by mass and the proportion of MC was set to 0.85% by mass of the total mass of the mixed solution. Furthermore, the mixed solution was processed using a high-pressure homogenizer (Econizer Lab 02 manufactured by Sanmaru Machinery Industry Co., Ltd.) at a rate of 1000 mL / batch and a processing pressure of 20 MPa for 50 minutes to prepare a conductive agent dispersion for electrode slurry (dispersion step). The Rsp of this dispersion was measured using a pulsed NMR spectrometer (MagnoMeter XRS VT, manufactured by Majelica Corporation) and was found to be 4.35. Furthermore, the viscosity of this dispersion at 60 rpm under 25°C was measured using a B-type viscometer (TVB10M, manufactured by Toki Sangyo Co., Ltd.) and was found to be 226 mPa·s.

[0052] [Preparation of the positive electrode] A lithium transition metal composite oxide of the NCM (Ni-Co-Mn) type was used as the positive electrode active material. This positive electrode active material, a conductive agent dispersion for electrode slurry, and polyvinylidene fluoride (PVDF) were mixed, an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added, and the mixture was kneaded in a planetary mixer to prepare a positive electrode mixture slurry. At this time, the mass ratio of the positive electrode active material, conductive agent, and PVDF was set to 98:1:1. This positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of Al foil, the coating was dried, the coating was rolled using a roller, and cut to a predetermined electrode size to obtain a positive electrode in which positive electrode mixture layers were arranged on both sides of the positive electrode current collector.

[0053] <Example 2> In preparing the conductive agent dispersion for the electrode slurry, the positive electrode was prepared in the same manner as in Example 1, except that the ratio of AB to the total mass of the mixture was 14% by mass and the processing time with a high-pressure homogenizer was 60 minutes.

[0054] <Comparative Example 1> In the preparation of the conductive agent dispersion for electrode slurry, the positive electrode was prepared in the same manner as in Example 1, except that the ratio of AB to the total mass of the mixture was 12.5% ​​by mass and the processing time with a high-pressure homogenizer was 30 minutes.

[0055] <Comparative Example 2> In the preparation of the conductive agent dispersion for electrode slurry, a positive electrode was prepared in the same manner as in Example 1, except that methylcellulose 15 manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used as the methylcellulose, the ratio of AB to the total mass of the mixture was set to 12.5% ​​by mass, and the processing time with a high-pressure homogenizer was set to 60 minutes. The viscosity of methylcellulose 15 is 12 mPa·s to 18 mPa·s, and the viscosity of methylcellulose 100 is 80 mPa·s to 120 mPa·s.

[0056] [Evaluation of Quality Stability] Positive electrodes were prepared as described in the Examples and Comparative Examples, such that the thickness of the positive electrode mixture layer on one side of the positive electrode current collector was 200 μm. In this process, positive electrodes were prepared until the volume of the positive electrode mixture slurry from 5 L was reduced to 1 L. The mass W1 of the first positive electrode prepared and the mass W2 of the last positive electrode prepared were measured, and W1 / W2 was calculated. A W1 / W2 ratio closer to 100% indicates more stable positive electrode preparation. For "quality stability," a W1 / W2 ratio of 95% to 105% was evaluated as "○," and any other ratio was evaluated as "×."

[0057] [Evaluation of electrode quality] Among the positive electrodes prepared as described above, some showed string-like irregularities on the surface of the positive electrode mixture layer, near the end of the positive electrode mixture slurry application. Products with such defects were marked with "×", and all others were marked with "○".

[0058] Table 1 shows the evaluation results for quality stability and electrode quality of the positive electrodes in the examples and comparative examples.

[0059]

[0060] The positive electrode in the example exhibited good quality stability and electrode quality. On the other hand, the positive electrode in the comparative example exhibited poor quality stability or electrode quality. Therefore, it can be seen that a high-quality electrode can be stably obtained by forming the positive electrode mixture layer using a conductive agent dispersion with an Rsp of 4 or higher and a viscosity at 60 rpm in a 25°C environment.

[0061] This disclosure is further illustrated by the following embodiments. Configuration 1: A positive electrode for a non-aqueous electrolyte secondary battery having a current collector and a composite layer disposed on the surface of the current collector, wherein the composite layer comprises an active material, a binder and a conductive agent, the conductive agent is added as a conductive agent dispersion when the composite layer is prepared, the conductive agent dispersion comprises the conductive agent, a dispersant and a solvent, and has an Rsp of 4 or more as measured by pulsed NMR and a viscosity of 200 mPa·s to 2000 mPa·s at 60 rpm in a 25°C environment. Configuration 2: The positive electrode for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein the content of the conductive agent in the conductive agent dispersion is 10% by mass or more and 20% by mass or less. Configuration 3: The positive electrode for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the conductive agent is acetylene black. Configuration 4: A non-aqueous electrolyte secondary battery comprising a positive electrode for a non-aqueous electrolyte secondary battery described in any one of Configurations 1 to 3, a negative electrode, and a non-aqueous electrolyte. Configuration 5: A conductive agent dispersion comprising a conductive agent, a dispersant, and a solvent, wherein the Rsp measured by pulsed NMR is 4 or higher, and the viscosity at 60 rpm in a 25°C environment is 200 mPa·s to 2000 mPa·s. Configuration 6: The conductive agent dispersion according to Configuration 5, wherein the content of the conductive agent is 10% by mass or more and 20% by mass or less. Configuration 7: The conductive agent dispersion according to Configuration 5 or 6, wherein the conductive agent is acetylene black.

[0062] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 32 Positive electrode mixture layer

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery, comprising a current collector and a composite layer disposed on the surface of the current collector, wherein the composite layer comprises an active material, a binder, and a conductive agent, the conductive agent is added as a conductive agent dispersion when the composite layer is prepared, and the conductive agent dispersion comprises the conductive agent, a dispersant, and a solvent, wherein the Rsp measured by pulsed NMR is 4 or higher, and the viscosity at 60 rpm in a 25°C environment is 200 mPa·s to 2000 mPa·s.

2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the conductive agent in the conductive agent dispersion is 10% by mass or more and 20% by mass or less.

3. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive agent is acetylene black.

4. A non-aqueous electrolyte secondary battery comprising a positive electrode for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 3, a negative electrode, and a non-aqueous electrolyte.

5. A conductive agent dispersion comprising a conductive agent, a dispersant, and a solvent, wherein the Rsp measured by pulsed NMR is 4 or higher, and the viscosity at 60 rpm in a 25°C environment is 200 mPa·s to 2000 mPa·s.

6. The conductive agent dispersion according to claim 5, wherein the content of the conductive agent is 10% by mass or more and 20% by mass or less.

7. The conductive agent dispersion according to claim 5, wherein the conductive agent is acetylene black.

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