Slurry for forming electrode for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for manufacturing non-aqueous electrolyte secondary battery

Abstract

Provided are: a method for manufacturing a slurry for forming an electrode, the slurry containing an electrode active material, an electrically conductive assistant, and an electrolyte solution, wherein the electrolyte solution contains an electrolyte and a non-aqueous solvent, the non-aqueous solvent contains an ester compound expressed by the following formula (I), and the amount of the ester compound contained in the non-aqueous solvent is 5–80 mass%; a non-aqueous electrolyte secondary battery; and a method for manufacturing the non-aqueous electrolyte secondary battery.　R 1 and R2 denote hydrocarbon groups, and the carbon number of the above ester compound satisfies the following formula (2).　Formula (2): 4≤(carbon number of R1)+(carbon number of R2)≤8

Description

Slurry for forming electrodes of non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery, and method for manufacturing non-aqueous electrolyte secondary battery

[0001] The present invention relates to a slurry for forming an electrode of a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery, and a method for manufacturing a nonaqueous electrolyte secondary battery.

[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] Technologies for increasing the capacity of non-aqueous electrolyte secondary batteries have been studied. For example, Patent Document 1 describes an electrochemical cell including: a positive electrode made of a non-binding material containing a first active material and an electrolyte solution in a first non-aqueous liquid electrolyte; a negative electrode made of a non-binding material containing a second active material and an electrolyte solution in a second non-aqueous liquid electrolyte; and an ion-permeable membrane disposed between the positive electrode and the negative electrode, wherein the positive electrode and the negative electrode each have a thickness of about 200 μm to about 3000 μm. According to the technology described in Patent Document 1, the electrode active material layers (positive electrode active material layer and negative electrode active material layer) are in a slurry state and in a non-binding state, as in the positive electrode and negative electrode, so that the electrode active material layers can be made thick while maintaining their flexibility, and no binder is required to bind the solid particles. This significantly increases the overall charge capacity and energy density while maintaining the flexibility of the battery. A nonaqueous electrolyte secondary battery in which an electrode active material layer is formed in the form of a slurry containing an electrolyte, as described in Patent Document 1, may be referred to as a quasi-solid secondary battery in the following description.

[0004] The following technologies have been disclosed focusing on the electrolyte solution of nonaqueous electrolyte secondary batteries. For example, Patent Document 2 discloses an electrolyte solution for use in quasi-solid-state secondary batteries and other types of nonaqueous electrolyte secondary batteries, which contains a lithium source electrolyte containing lithium hexafluorophosphate, a carbonate-based solvent containing γ-butyrolactone and ethylene carbonate, and an additive containing at least one of maleic anhydride and lithium bis(oxalato)borate, wherein the γ-butyrolactone content is greater than the ethylene carbonate content. The technology in Patent Document 2 is said to reduce fluctuations in the electrolyte solution components due to solvent volatilization during the battery manufacturing process, thereby reducing variations in battery characteristics due to the influence of environmental temperature. Furthermore, although this is an electrolyte solution for use in batteries other than quasi-solid secondary batteries, Patent Document 3, for example, proposes a battery electrolyte solution that contains ethylene carbonate, propylene carbonate, and an acetate ester, and that contains one of dimethoxyethane, dimethyl carbonate, and diethyl carbonate, and that has an acetate ester content of 50% by volume or less, and that has a lithium salt appropriately dissolved in the non-aqueous solvent. According to Patent Document 3, this electrolyte solution can maintain high conductivity even at low temperatures, and secondary batteries using this electrolyte solution are said to be able to maintain high charge / discharge capacities even at low temperatures.

[0005] JP 2017-147222 A International Publication No. 2023 / 106214 JP 8-195221 A

[0006] In recent years, as the applications of non-aqueous electrolyte secondary batteries have expanded, there has been a demand for higher energy density (higher capacity) non-aqueous electrolyte secondary batteries. For example, non-aqueous electrolyte secondary batteries are used as power sources for electric vehicles (EVs) and drones. Increasing the capacity of non-aqueous electrolyte secondary batteries is important for improving the driving range of EVs and the flight time of drones. To increase the capacity (higher energy density) of quasi-solid secondary batteries, attempts have been made to increase the content of electrode active material that stores ions in the slurry-like electrode active material layer. However, even if high capacity is achieved, it has become clear that repeated charge and discharge can lead to poor cycle characteristics. Furthermore, Patent Document 2 states that the use of γ-butyrolactone can suppress fluctuations in electrolyte components during battery manufacturing due to volatilization. However, the inventors' investigations have revealed that γ-butyrolactone is prone to decomposition during charge and discharge of quasi-solid secondary batteries, resulting in poor cycle characteristics.

[0007] An object of the present invention is to provide an electrode-forming slurry for a nonaqueous electrolyte secondary battery, which can be used as an electrode active material layer of a secondary battery to obtain a nonaqueous electrolyte secondary battery that exhibits excellent cycle characteristics. Another object of the present invention is to provide a nonaqueous electrolyte secondary battery using this electrode-forming slurry as an electrode active material layer of the secondary battery, and a method for producing the same.

[0008] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that when a specific amount of a specific carboxylic acid ester compound is used as an electrolyte solution contained in an electrode-forming slurry for forming an electrode active material layer of a quasi-solid secondary battery, the cycle characteristics of a secondary battery having this electrode-forming slurry as an electrode active material layer can be improved. Based on this finding, the present inventors have conducted further research and have now completed the present invention.

[0009] The above-described problems of the present invention have been solved by the following means: <1> A slurry for forming an electrode of a non-aqueous electrolyte secondary battery, which contains an electrode active material, a conductive additive, and an electrolyte solution, wherein the electrolyte solution contains an electrolyte and a non-aqueous solvent, the non-aqueous solvent contains an ester compound represented by the following formula (I), and the content of the ester compound in the non-aqueous solvent is 5 to 80 mass %: R １ and R ２ represents a hydrocarbon group, and the number of carbon atoms in the ester compound satisfies the following formula (2): 4≦(R １ (number of carbon atoms in R ２ <2> The electrode-forming slurry according to <1>, wherein the number of carbon atoms in the ester compound satisfies the following formula (3): 5≦(R １ (number of carbon atoms in R ２ (number of carbon atoms)≦6...Equation (3) <3> The electrode-forming slurry according to <1> or <2>, wherein the non-aqueous solvent contains a carbonate compound. <4> The electrode-forming slurry according to any one of <1> to <3>, wherein the non-aqueous solvent contains a cyclic ester compound. <5> The electrode-forming slurry according to any one of <1> to <4>, wherein the electrolyte contains a lithium salt, and the content of the lithium salt in the electrolytic solution is 0.9 to 1.5 M. <6> The electrode-forming slurry according to any one of <1> to <5>, wherein the viscosity of the electrolytic solution is 2.8 to 7.5 mPa s. <7> A non-aqueous electrolyte secondary battery having a positive electrode, a separator, and a negative electrode in this order, wherein the electrode-forming slurry according to any one of <1> to <6> is used as a positive electrode active material layer constituting the positive electrode and / or a negative electrode active material layer constituting the negative electrode. <8> A method for producing a non-aqueous electrolyte secondary battery, comprising applying the electrode-forming slurry according to any one of <1> to <6> onto an electrode current collector to form a slurry-like electrode active material layer.

[0010] In the description of the present invention, a numerical range expressed using "to" means a range including the numerical values ​​written before and after "to" as the lower and upper limits. In the present invention, "nonaqueous electrolyte" means an electrolyte that does not substantially contain water. In other words, the "nonaqueous electrolyte" may contain a small amount of water within a range that does not impair the effects of the present invention. 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, "nonaqueous solvent" also means a solvent that does not substantially contain water. In other words, the "nonaqueous solvent" may contain a small amount of water within a range that does not impair the effects of the present invention. In the present invention, the "nonaqueous solvent" has a water concentration of 200 ppm (by mass) or less, preferably 100 ppm or less, and more preferably 20 ppm or less. In reality, it is difficult to make a non-aqueous solvent completely free of water, and it usually contains 1 ppm or more of water.

[0011] The electrode-forming slurry for a nonaqueous electrolyte secondary battery of the present invention can be used to form an electrode active material layer, thereby further improving the cycle characteristics of the resulting nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery of the present invention has excellent cycle characteristics. According to the method for producing a nonaqueous electrolyte secondary battery of the present invention, a nonaqueous electrolyte secondary battery with excellent cycle characteristics can be obtained.

[0012] FIG. 1 is a longitudinal sectional view showing a schematic diagram of a basic layer structure of an embodiment of a secondary battery according to the present 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] [Slurry for forming an electrode] The slurry for forming an electrode of the present invention (also referred to as "slurry of the present invention") is a slurry containing an electrode active material, a conductive additive, and an electrolyte, and is suitable as an electrode active material layer for a non-aqueous electrolyte secondary battery. The electrode active material may be a positive electrode active material or a negative electrode active material. When the slurry of the present invention contains a positive electrode active material, the slurry of the present invention can be used as a slurry for forming a positive electrode active material layer. When the slurry of the present invention contains a negative electrode active material, the slurry of the present invention can be used as a slurry for forming a negative electrode active material layer.

[0015] In the slurry of the present invention, the electrolytic solution contains an electrolyte and a non-aqueous solvent, and the non-aqueous solvent contains 5 to 80 mass % of the ester compound represented by formula (I). R １ and R ２ represents a hydrocarbon group, and the number of carbon atoms in the ester compound satisfies the following formula (2): 4≦(R １ (number of carbon atoms in R ２ (number of carbon atoms)≦8... Formula (2) R １ and R ２ It is more preferable that the number of carbon atoms in R satisfies the following formula (3): 5≦(R １ (number of carbon atoms in R ２ (number of carbon atoms)≦6... Formula (3) R １ and R ２ The hydrocarbon group that R can take may be a chain (acyclic) hydrocarbon group or a cyclic hydrocarbon group, with a chain hydrocarbon group being preferred. This chain hydrocarbon group may be linear or branched. The hydrocarbon group may be a saturated hydrocarbon group or an unsaturated hydrocarbon group. １ The number of carbon atoms in the hydrocarbon group that R can take is not particularly limited as long as it satisfies the above formula (2), and preferably has 1 to 7 carbon atoms, more preferably has 1 to 5 carbon atoms, even more preferably has 1 to 3 carbon atoms, still more preferably has 1 or 2 carbon atoms, and even more preferably has 1 carbon atom. １ is preferably propyl (n-propyl or isopropyl), ethyl, or methyl, and more preferably methyl. ２The number of carbon atoms in the hydrocarbon group that R can take is not particularly limited as long as it satisfies the above formula (2), and preferably has 1 to 7 carbon atoms, more preferably has 2 to 7 carbon atoms, even more preferably has 3 to 6 carbon atoms, even more preferably has 4 or 5 carbon atoms, and even more preferably has 4 carbon atoms. ２ is preferably n-heptyl, n-pentyl, n-butyl or n-propyl, more preferably n-butyl.

[0016] Specific examples of the ester compound represented by formula (I) include n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, sec-butyl acetate, n-pentyl acetate, n-hexyl acetate, n-heptyl acetate, ethyl propionate, n-propyl propionate, n-butyl propionate, n-pentyl propionate, n-hexyl propionate, methyl butyrate, methyl isobutyrate, ethyl butyrate, n-propyl butyrate, n-butyl butyrate, n-pentyl butyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0017] The content of the ester compound represented by formula (I) in the non-aqueous solvent is 5 to 80% by mass, preferably 10 to 70% by mass, more preferably 20 to 60% by mass, even more preferably 30 to 60% by mass, and even more preferably 40 to 60% by mass. The content of the ester compound represented by formula (I) in the non-aqueous solvent can be 50 to 80% by mass, 50 to 70% by mass, or even 50 to 60% by mass. The content of the ester compound represented by formula (I) can be more than 50% by volume, and can be 55% by volume or more, in the non-aqueous solvent (100% by volume).

[0018] The slurry of the present invention contains the ester compound represented by formula (I) in the above-mentioned specific amount as a non-aqueous solvent, and thus can effectively improve cycle characteristics when incorporated as an electrode active material layer in a non-aqueous electrolyte secondary battery (quasi-solid secondary battery).

[0019] The slurry of the present invention will now be described in more detail.

[0020] <Electrolyte> (Non-aqueous Solvent) The non-aqueous solvent contains, in addition to the ester compound represented by formula (I), a non-aqueous solvent X other than the ester compound represented by formula (I). This non-aqueous solvent X is not particularly limited, and non-aqueous solvents typically used in electrode-forming slurries can be used. As the non-aqueous solvent X, aprotic organic solvents other than the ester compound represented by formula (I) are preferred, and aprotic organic solvents having 2 to 10 carbon atoms are more preferred. Examples of such non-aqueous solvents include linear or cyclic carbonate compounds, linear or cyclic ether compounds, cyclic ester compounds, nitrile compounds, amide compounds, oxazolidinone compounds, nitro compounds, linear or cyclic sulfone or sulfoxide compounds, and phosphate ester compounds. Among these, linear or cyclic carbonate compounds, cyclic ester compounds, linear or cyclic ether compounds, etc. are preferred, and linear or cyclic carbonate compounds and / or cyclic ester compounds are more preferred.

[0021] The carbonate compound may be linear or cyclic. The carbonate compound may be a non-fluorinated carbonate compound or a fluorinated carbonate compound. Examples of the carbonate compound include cyclic carbonate compounds such as ethylene carbonate (EC), fluorinated ethylene carbonate, vinylene carbonate, propylene carbonate (PC), and butylene carbonate. Examples of linear carbonate compounds include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate (EMC), and methyl propyl carbonate. In the present invention, a carbonate compound selected from ethylene carbonate, propylene carbonate, and ethyl methyl carbonate is more preferred.

[0022] Examples of the cyclic ester compound include lactone compounds (γ-butyrolactone (GBL), γ-valerolactone, etc.).

[0023] The ether compound may be linear or cyclic, and examples of the ether compound include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and 1,2-dimethoxyethane.

[0024] In addition to the above, specific examples of the non-aqueous solvent X include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidone (NMP), N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphate.

[0025] In the present invention, the non-aqueous solvent X is preferably a non-aqueous solvent selected from a carbonate compound, a cyclic ester compound, and an ether compound, more preferably a carbonate compound, a combination of a carbonate compound and a cyclic ester compound, or a combination of a cyclic ester compound and an ether compound, and even more preferably a combination of a carbonate compound and a cyclic ester compound. When a cyclic carbonate compound is used as the non-aqueous solvent X, a chain carbonate compound may be used in combination, or a chain carbonate compound may not be used in combination. Furthermore, when a chain carbonate compound is used as the non-aqueous solvent X, a cyclic carbonate compound may be used in combination, or a cyclic carbonate compound may not be used in combination.

[0026] The content of non-aqueous solvent X in the non-aqueous solvent is 20 to 95% by mass, preferably 30 to 90% by mass, more preferably 40 to 80% by mass, even more preferably 40 to 70% by mass, and even more preferably 40 to 60% by mass. Therefore, when the non-aqueous solvent contains a carbonate compound, a cyclic ester compound, or an ether compound alone as non-aqueous solvent X, the content of non-aqueous solvent X is the content of the carbonate compound, the cyclic ester compound, or the ether compound. When non-aqueous solvent X is a plurality of compounds, for example, when non-aqueous solvent X is two types of compounds, a carbonate compound and an ether compound, the content of non-aqueous solvent X is the sum of the content of the carbonate compound and the content of the ether compound. When non-aqueous solvent X is a combination of a carbonate compound and a cyclic ester compound, the content of the carbonate compound in non-aqueous solvent X is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, even more preferably 30 to 70% by mass, even more preferably 40 to 70% by mass, and even more preferably 50 to 70% by mass. The content of the cyclic ester compound is preferably low relative to the content of the carbonate compound. When non-aqueous solvent X is a combination of a cyclic ester compound and an ether compound, the content of the cyclic ester compound in non-aqueous solvent X is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, even more preferably 30 to 70% by mass, even more preferably 30 to 60% by mass, and even more preferably 40 to 50% by mass. The content of the cyclic ester compound is preferably low relative to the content of the ether compound.

[0027] (Electrolyte) As the electrolyte, an electrolyte solution used for an electrolyte solution of a quasi-solid secondary battery can be used. Metal salts are preferred, and examples thereof include lithium salts, potassium salts, sodium salts, calcium salts, and magnesium salts. As the lithium salt, lithium salts that are commonly used for the electrolyte of a lithium ion secondary battery are preferred, and examples thereof include the following lithium salts:

[0028] (L-1) Inorganic lithium salt: LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF ６ Inorganic fluoride salts such as LiClO４ , LiBrO ４ , LiIO ４ perhalogenates such as LiAlCl ４ Inorganic chloride salts, etc.

[0029] (L-2) Fluorine-containing organic lithium salt: LiCF ３ SO ３ perfluoroalkanesulfonates such as LiN(CF ３ SO ２ ) ２ , LiN(CF ３ CF ２ SO ２ ) ２ , LiN(FSO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ perfluoroalkanesulfonylimide salts such as LiC(CF ３ SO ２ ) ３ perfluoroalkanesulfonylmethide salts such as Li[PF ５ (CF ２ CF ２ CF ３ ) )], Li[PF ４ (CF ２ CF ２ CF ３ ) ２ ], Li[PF ３ (CF ２ CF ２ CF ３ ) ３ ], Li[PF ５ (CF ２ CF ２ CF ２ CF ３ ) )], Li[PF ４ (CF ２ CF ２ CF ２ CF ３ ) ２ ], Li[PF ３ (CF ２ CF ２ CF ２ CF ３ ) ３perfluoroalkyl fluorophosphates such as

[0030] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0031] Among these, LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF ６ , LiClO ４ , Li(R ｆ１ SO ３ ), LiN(R ｆ１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) is preferred, and LiPF ６ , LiBF ４ , LiN(R ｆ１ SO ２ ) ２ , LiN(FSO ２ ) ２ , or LiN(R ｆ１ SO ２ ) (R ｆ２ SO ２ ) is more preferred, and LiPF ６ , or LiN(FSO ２ ) ２ is more preferred, and LiPF ６ is particularly preferred. ｆ１ and R ｆ２ Each of the groups represents a perfluoroalkyl group, and the number of carbon atoms is preferably 1 to 6. The lithium salts used in the electrolytic solution of the present invention may be used alone or in any combination of two or more.

[0032] The concentration of the lithium salt in the electrolyte solution is usually 10.0 to 50.0% by mass, preferably 15.0 to 30.0% by mass. The molar concentration of the lithium salt in the electrolyte solution is preferably 0.5 to 1.5 M, more preferably 0.9 to 1.5 M. When multiple types of lithium salts are used, the concentration of the lithium salt refers to the total amount thereof.

[0033] (Viscosity of Electrolyte) In the slurry of the present invention, the viscosity of the electrolyte is preferably 2.8 to 7.5 mPa s, more preferably 3.0 to 7.0 mPa s, even more preferably 3.2 to 6.0 mPa s, still more preferably 3.2 to 5.0 mPa s, and still more preferably 3.3 to 4.5 mPa s. The viscosity of the electrolyte can be measured by the method described in the examples.

[0034] <Electrode Active Material> When the slurry of the present invention is used to form a positive electrode active material layer, it contains a positive electrode active material as the electrode active material, and when the slurry is used to form a negative electrode active material layer, it contains a negative electrode active material as the electrode active material.

[0035] (Positive Electrode Active Material) The positive electrode active material is preferably one that can reversibly insert and release lithium ions. The material is not particularly limited as long as it has the above-mentioned properties, and may be a transition metal oxide, an organic substance, an element that can be composited with Li, such as sulfur, or a composite of sulfur and a metal. Among them, it is preferable to use a transition metal oxide as the positive electrode active material, and a transition metal element M ａ A transition metal oxide containing one or more elements selected from Co, Ni, Fe, Mn, Cu, and V is more preferred. 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 may be determined by the following formula: ａThe amount of the transition metal oxide is preferably 0 to 30 mol % relative to the amount (100 mol %) of the metal. More preferably, the transition metal oxide is synthesized by mixing so that the Li / Ma molar ratio is 0.3 to 2.2. Specific examples of the transition metal oxide include (MA) transition metal oxides having a layered rock salt structure, (MB) 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.

[0036] (MA) Specific examples of transition metal oxides having a layered rock salt structure include LiCoO ２ (Lithium cobalt oxide [LCO]), LiNi ２ O ２ (lithium nickel oxide), LiNi ０．８５ Co ０．１０ Al ０．０５ O ２ (nickel cobalt lithium aluminum oxide [NCA]), LiNi １／３ Co １／３ Mn １／３ O ２ (Lithium nickel manganese cobalt oxide [NMC]) and LiNi ０．５ Mn ０．５ O ２ (Lithium manganese nickel oxide). (MB) Specific examples of transition metal oxides having a spinel structure include LiMn ２ O ４ (LMO), LiCoMnO ４ , Li ２ FeMn ３ O ８ , Li ２ CuMn ３ O ８ , Li ２ CrMn ３ O ８ and Li ２ NiMn ３ O ８ Examples of the (MC) lithium-containing transition metal phosphate compound include LiFePO ４ and Li ３ Fe ２ (P.O. ４ ) ３Olivine-type iron phosphate salts such as LiFeP ２ O ７ Iron pyrophosphates such as LiCoPO ４ Cobalt phosphates such as Li ３ V ２ (P.O. ４ ) ３ (MD) Examples of lithium-containing transition metal halide phosphate compounds include, for example, Li ２ FePO ４ Fluorophosphate iron salts such as F, Li ２ MnPO ４ Fluorophosphate manganese salts such as F and Li ２ CoPO ４ Examples of the (ME) lithium-containing transition metal silicate compound include cobalt fluoride phosphates such as Li ２ FeSiO ４ , Li ２ MnSiO ４ and Li ２ CoSiO ４ In the present invention, the positive electrode active material is preferably a lithium-containing transition metal phosphate compound (MC), such as LiFePO ４ is more preferred.

[0037] The shape of the positive electrode active material is not particularly limited, but particulate form is preferred. The average particle size (average particle size in equivalent spheres) of the positive electrode active material is not particularly limited. For example, it can be 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. A conventional grinder or classifier can be used to adjust the positive electrode active material to a predetermined particle size. The positive electrode active material obtained by the calcination method may be used after washing with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.

[0038] 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 the manufacturer's average particle size information is unavailable or when a synthesized positive electrode active material is used, the positive electrode active material is dispersed in water and the average particle size (volume-based median diameter D50 in water) obtained by measurement using a laser diffraction / scattering particle size distribution measurement device (e.g., HORIBA Particle LA-960V2) is used. This also applies to the average particle size of solid particles other than the positive electrode active material.

[0039] 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.

[0040] The surface of the positive electrode active material may be coated with an oxide such as another metal oxide, a carbon-based material, etc. As the surface coating material, a surface coating material that can be used to coat the surface of a negative electrode active material, which will be described later, can be used.

[0041] 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 treated with actinic rays or an active gas (plasma, etc.) before or after the surface coating.

[0042] The positive electrode active material may be used alone or in combination of two or more. When forming a positive electrode active material layer, the positive electrode active material layer has a unit area (cm ２ The mass (mg) (basis weight) of the positive electrode active material per unit area is not particularly limited and can be determined appropriately depending on the designed battery capacity.

[0043] When the slurry of the present invention contains a positive electrode active material (in the case of a positive electrode-forming slurry), the content of the positive electrode active material in the slurry solids (positive electrode active material and conductive additive) is preferably 95.00 to 99.95 mass%, more preferably 96.00 to 99.90 mass%, and even more preferably 97.00 to 99.80 mass%, although it depends on the content of the conductive additive.

[0044] When the slurry of the present invention contains a positive electrode active material (in the case of a positive electrode-forming slurry), the content of the positive electrode active material in the slurry is preferably as high as possible within a range that allows the desired low viscosity to be achieved. For example, the content of the positive electrode active material in the slurry can be 60 to 90 mass%, more preferably 65 to 85 mass%, even more preferably 65 to 80 mass%, and even more preferably 65 to 75 mass%.

[0045] (Negative electrode active material) The negative electrode active material is preferably one that can reversibly absorb and release lithium ions. The material is not particularly limited as long as it has the above-mentioned properties, and examples thereof include carbonaceous materials, silicon-based materials, metal oxides, metal composite oxides, lithium alone, lithium alloys, and negative electrode active materials that can form alloys with lithium. Among these, carbonaceous materials or silicon-based materials are preferably used from the viewpoint of reliability.

[0046] The carbonaceous material used as the negative electrode active material is a material essentially composed of carbon. Examples include carbon black such as petroleum pitch, graphite (natural graphite, artificial graphite such as vapor-grown graphite, etc.), and carbonaceous materials obtained by calcining various synthetic resins such as PAN (polyacrylonitrile)-based resins and furfuryl alcohol resins. Further examples include various carbon fibers such as PAN-based carbon fiber, cellulose-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, dehydrated PVA (polyvinyl alcohol)-based carbon fiber, lignin carbon fiber, glassy carbon fiber, and activated carbon fiber, as well as mesophase microspheres, graphite whiskers, and tabular graphite.

[0047] The metal oxides and metal composite oxides used as the negative electrode active material are not particularly limited as long as they are oxides capable of absorbing and releasing lithium. Amorphous oxides are preferred, and chalcogenides, which are reaction products of metal elements and elements of Group 16 of the periodic table, are also preferred. The term "amorphous" as used herein refers to a compound having a broad scattering band with a peak in the 2θ range of 20° to 40° in an X-ray diffraction method using CuKα radiation, and may also have crystalline diffraction lines. Among the compounds consisting of the above amorphous oxides and chalcogenides, amorphous oxides and chalcogenides of metalloid elements are more preferred, and oxides or chalcogenides consisting of one or a combination of two or more of elements from Groups 13 (IIIB) to 15 (VB) of the periodic table, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi, are particularly preferred. Specific examples of preferred amorphous oxides and chalcogenides include, for example, Ga, ２ O ３ , GeO, PbO, PbO ２ , Pb ２ O ３ , Pb ２ O ４ , Pb ３ O ４ , Sb ２ O ３ , Sb ２ O ４ , Sb ２ O ８ Bi ２ O ３ , Sb ２ O ８ Si ２ O ３ , Sb ２ O ５ , Bi ２ O ３ , Bi ２ O ４ , GeS, PbS, PbS ２ , Sb ２ S ３ and Sb ２ S ５ are preferred.

[0048] The metal (composite) oxide and the chalcogenide preferably contain at least one of titanium and lithium as a constituent component from the viewpoint of high current density charge / discharge characteristics. Examples of the lithium-containing metal composite oxide (lithium composite metal oxide) include, for example, composite oxides of lithium oxide and the metal (composite) oxide or the chalcogenide, more specifically, Li ２ SnO ２ Examples include:

[0049] The negative electrode active material preferably contains titanium atoms. More specifically, TiNb ２ O ７ (Niobium titanate oxide [NTO]), Li ４ Ti ５ O １２ Lithium titanate (LTO) is preferred because it has small volume fluctuations during absorption and desorption of lithium ions, has excellent rapid charge and discharge characteristics, suppresses electrode deterioration, and enables an improvement in the life of the lithium ion secondary battery.

[0050] The lithium alloy as the negative electrode active material is not particularly limited as long as it is an alloy that is commonly used as a negative electrode active material for secondary batteries, and an example thereof is a lithium aluminum alloy.

[0051] The negative electrode active material capable of forming an alloy with lithium is not particularly limited as long as it is one commonly used as a negative electrode active material for secondary batteries. Examples of such active materials include negative electrode active materials containing silicon atoms or tin atoms, and metals such as Al and In. A negative electrode active material containing silicon atoms (silicon atom-containing active materials) that enables higher battery capacity is preferred, and silicon atom-containing active materials with a silicon atom content of 40 mol% or more of the total constituent atoms are more preferred. Generally, negative electrodes containing these negative electrode active materials (e.g., Si negative electrodes containing silicon atom-containing active materials, Sn negative electrodes containing tin atom-containing active materials) can absorb more Li ions than carbon negative electrodes (e.g., graphite and acetylene black). That is, the amount of Li ion absorption per unit mass increases. Therefore, the battery capacity (energy density) can be increased. As a result, there is an advantage in that the battery operating time can be extended. Examples of silicon-atom-containing active materials include silicon-based materials such as Si and SiOx (0<x≦1), and alloys containing titanium, vanadium, chromium, manganese, nickel, copper, or lanthanum (e.g., LaSi ２ , VSi ２ ), or structured active materials (e.g., LaSi ２ / Si), and also SnSiO ３ , SnSiS ３ Examples of the active material containing silicon atoms and tin atoms include SiOx itself as a negative electrode active material (semi-metal oxide), and can also be used as an active material (precursor material) that can be alloyed with lithium because it generates Si during battery operation. Examples of the negative electrode active material containing tin atoms include Sn, SnO, and SnO ２ , SnS, SnS ２ and active materials containing silicon atoms and tin atoms. Also, composite oxides with lithium oxide, for example, Li ２ SnO ２ Also included are:

[0052] In the present invention, the negative electrode active material is preferably a carbonaceous material, more preferably artificial graphite.

[0053] The shape of the negative electrode active material is not particularly limited, but particulate form is preferred. The average particle size (average particle size in spherical equivalent) of the negative electrode active material is preferably 0.1 to 60 μm, for example, preferably 0.5 to 50 μm, more preferably 1.0 to 40 μm, and even more preferably 5.0 to 30 μm. To achieve the desired particle size, a conventional grinder or classifier is used. For example, a mortar, ball mill, sand mill, vibration ball mill, satellite ball mill, planetary ball mill, swirling airflow jet mill, or sieve is preferably used. Wet grinding in the presence of water or an organic solvent such as methanol can also be performed during grinding. Classification is preferred to achieve the desired particle size. The classification method is not particularly limited, and a sieve, air classifier, or the like can be used as desired. Classification can be performed using either a dry or wet method.

[0054] The negative electrode active material may be used alone or in combination of two or more. When forming a negative electrode active material layer, the negative electrode active material layer has a unit area (cm ２ The mass (mg) (basis weight) of the negative electrode active material per unit area is not particularly limited and can be determined appropriately depending on the designed battery capacity.

[0055] When the slurry of the present invention contains a negative electrode active material (in the case of a negative electrode-forming slurry), the content of the negative electrode active material in the slurry solids (negative electrode active material and conductive additive) is preferably 95.00 to 99.95 mass%, more preferably 96.00 to 99.90 mass%, and even more preferably 97.00 to 99.80 mass%, although it depends on the content of the conductive additive.

[0056] When the slurry of the present invention contains a negative electrode active material (in the case of a negative electrode-forming slurry), the content of the negative electrode active material in the slurry is preferably as high as possible within a range that allows the desired low viscosity to be achieved. For example, the content of the negative electrode active material in the slurry can be 50 to 80 mass%, more preferably 52 to 75 mass%, even more preferably 52 to 70 mass%, and even more preferably 55 to 65 mass%.

[0057] <Conductive Aid> The conductive aid is not particularly limited, and any known conductive aid can be used. For example, the conductive aid 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 fibers or carbon nanotubes), carbonaceous materials (e.g., graphene or 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 aid is preferably a carbonaceous material, and acetylene black and ketjen black are more preferred. When an electrode active material and a conductive aid are used in combination, the conductive aid is one of the above conductive aids that does not undergo Li insertion and release during charging and discharging of the battery and does not function as an active material. Therefore, among the conductive additives, those that can function as an active material in the active material layer when the battery is charged and discharged are classified as active materials rather than as conductive additives. Whether or not a conductive additive functions as an active material when the battery is charged and discharged is not uniquely determined, but is determined by the combination with the active material.

[0058] The conductive additive may be used alone or in combination of two or more.

[0059] The shape of the conductive additive is not particularly limited, but a particulate shape is preferred. The average particle size (average particle size in equivalent sphere form) of the conductive additive is also not particularly limited. For example, it is preferably 0.01 to 50 μm, more preferably 0.1 to 10 μm, and even more preferably 0.2 to 2.0 μm.

[0060] Whether the slurry of the present invention is a slurry for forming a positive electrode or a slurry for forming a negative electrode, the content of the conductive assistant in the solid content of the slurry of the present invention is preferably 0.05 to 5.00 mass%, more preferably 0.10 to 4.00 mass%, and even more preferably 0.20 to 3.00 mass%.

[0061] Whether the slurry of the present invention is a slurry for forming a positive electrode or a slurry for forming a negative electrode, the content of the conductive auxiliary agent in the slurry of the present invention can be, for example, 0.1 to 10 mass%, preferably 0.1 to 7 mass%, more preferably 0.2 to 5 mass%, even more preferably 0.4 to 3 mass%, and still more preferably 0.6 to 2 mass%.

[0062] <Other Components> The slurry of the present invention may optionally contain 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.

[0063] [Non-aqueous electrolyte secondary battery] The non-aqueous electrolyte secondary battery of the present invention (hereinafter also referred to as "secondary battery of the present invention") has a positive electrode, a separator, and a negative electrode, in this order, and uses the slurry of the present invention as the positive electrode active material layer constituting the positive electrode and / or the negative electrode active material layer constituting the negative electrode. That is, it is a so-called quasi-solid secondary battery in which at least one of the positive electrode active material layer and the negative electrode active material layer is composed of the slurry of the present invention. The secondary battery of the present invention usually has a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector, in this order, and at least one of the positive electrode active material layer and the negative electrode active material layer is composed of the slurry of the present invention. In the non-aqueous electrolyte secondary battery of the present invention, it is preferable that both the positive electrode active material layer and the negative electrode active material layer are composed of the slurry of the present invention.

[0064] Prior to describing the secondary battery of the present invention, the structure of a general nonaqueous electrolyte secondary battery will be described. FIG. 1 is a cross-sectional view showing a schematic representation of the laminated structure of a general nonaqueous electrolyte secondary battery 10, including the working electrode when the battery is operated. The nonaqueous electrolyte secondary battery 10 has a laminated structure (hereinafter also referred to as an electrode laminate) including, as viewed from the negative electrode side, 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 and the positive electrode active material layer 4 are filled with a nonaqueous electrolyte (not shown) and separated by the separator 3. The separator 3 has pores, and during normal battery use, functions as a separator between the positive and negative electrodes, insulating them by allowing the electrolyte and ions to pass through the pores. 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 illustrated example, a light bulb is used as the operating part 6, and it is lit by discharge.

[0065] Next, the basic structure characteristic of quasi-solid secondary batteries will be described. As described above, 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 typical non-aqueous electrolyte secondary battery in that the electrode active material layer is a slurry (suspension, dispersion) formed by dispersion in a non-aqueous electrolyte. That is, in a typical non-aqueous electrolyte secondary battery, a coating liquid is prepared by dispersing an electrode active material in a medium that does not contain an electrolyte, and this coating liquid is applied to a current collector to form a coating film. This coating film is then dried to form a thin-film electrode active material layer. This coating liquid usually contains a binder, which forms a hard electrode active material layer in which the electrode active material particles are firmly bound together. Since the non-aqueous electrolyte solution is present on the electrode active material layer thus formed (between the negative electrode active material layer and the positive electrode active material layer), even if there are portions of the electrode active material layer through which the non-aqueous electrolyte solution can penetrate, the electrode active material layer is in the form of a hard solid particle layer as a whole, and is not a slurry layer. 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.

[0066] In the secondary battery of the present invention, the positive electrode active material layer and / or the negative electrode active material layer is a layer formed using the slurry of the present invention. In the secondary battery of the present invention, it is preferable that both the positive electrode active material layer and the negative electrode active material layer are formed using the slurry of the present invention. When either the positive electrode active material layer or the negative electrode active material layer is formed using an electrode-forming slurry other than the slurry of the present invention, a normal electrode active material layer can be used as the electrode active material layer.

[0067] In the secondary battery of the present invention, the materials and components such as the positive electrode active material, positive electrode current collector, negative electrode active material, negative electrode current collector, and separator are not particularly limited, except that the slurry of the present invention is used to form the positive electrode active material layer and / or the negative electrode active material layer. These materials and components can be appropriately applied from those used in ordinary secondary batteries. For components and manufacturing methods typically used in these secondary batteries, reference can be made to, for example, JP 2016-201308 A, JP 2005-108835 A, JP 2012-185938 A, WO 2018 / 135395, and the like.

[0068] In the secondary battery of the present invention, the thickness of the electrode active material layer (slurry layer) is not particularly limited and can be, for example, 5 to 500 μm, preferably 20 to 400 μm, more preferably 60 to 400 μm, and even more preferably 80 to 350 μm.

[0069] [Method for Manufacturing a Non-Aqueous Electrolyte Secondary Battery] The method for manufacturing a non-aqueous electrolyte secondary battery of the present invention includes applying the slurry of the present invention to an electrode current collector to form a slurry-like electrode active material layer. This electrode active material layer may be either a positive electrode active material layer or a negative electrode active material layer. Preferably, both the positive electrode active material layer and the negative electrode active material layer are formed by applying the slurry of the present invention. When the electrode active material layer is a positive electrode active material layer, the electrode current collector is a positive electrode current collector. When the electrode active material layer is a negative electrode active material layer, the electrode current collector is a negative electrode current collector. The method for applying the slurry is not particularly limited. For example, it can be applied using a roll coater, drop coating, applying the slurry evenly on the current collector and then pressing (roll press or flat press), or applying the slurry within a frame of a specified thickness and spreading it. Regarding the method for manufacturing a non-aqueous electrolyte secondary battery of the present invention, any conventional method can be used as appropriate, except that the electrode active material layer is formed using a specific slurry layer. For example, Japanese Patent Application Laid-Open No. 2016-201308, Japanese Patent Application Laid-Open No. 2005-108835, Japanese Patent Application Laid-Open No. 2012-185938, Japanese Patent Application Laid-Open No. 2017-147222, etc. can be referenced as appropriate.

[0070] The nonaqueous electrolyte secondary battery of the present invention can be installed in electronic devices such as notebook computers, pen-input personal computers, mobile personal computers, 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 electronic 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.

[0071] 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.

[0072] [Preparation of electrode-forming slurry]

[0073] <Preparation of electrode active material> LFP (LiFePO ４ 10 parts by mass of powder raw material (Gelon, particle size 2.5 μm) was mixed with 90 parts by mass of water, and 0.1 parts by mass of styrene-maleic anhydride copolymer was added as an additive. The mixture was stirred and mixed for 3 hours. The mixture was then baked at 700°C for 10 hours in a nitrogen atmosphere. In this way, a positive electrode active material LFP1 with a surface coated with a carbon-based material was obtained. The electronic conductivity of the positive electrode active material was 1.4 mS / cm.

[0074] <Preparation of Electrolyte Solution> Each electrolyte solution was prepared by mixing the ester compound of formula (I), carbonate compound, cyclic ester compound, and other compounds shown in Table 1 as a non-aqueous solvent in a weight ratio shown in Table 1, and dissolving the electrolyte shown in Table 1 in the mixture to give a salt concentration shown in Table 1. ６ or LiN (FSO ２ ) ２ (also referred to as "LiFSI") was used.

[0075] <Measurement of Electrolyte Viscosity> The viscosity of each obtained electrolyte solution was measured as follows. (Method for measuring the viscosity of the electrolyte solution) An E-type viscometer (TV-35, manufactured by Toki Sangyo Co., Ltd.) and a standard cone rotor (1°34' x R24) were used. A sample cup was adjusted to 25°C, and 1.1 mL of the obtained electrolyte solution was poured into it. The sample cup was then set in the main body and maintained for 5 minutes until the temperature became constant. The viscosity was then measured at a rotation speed of 50 rpm and used as the viscosity value.

[0076] <Preparation of Electrode-Forming Slurry> (1) Preparation of Positive Electrode Slurry 70% by mass of LFP1 as the positive electrode active material, 1% by mass of acetylene black (manufactured by Denka Company, Denka Black (trade name)) as a conductive additive, and 29% by mass of each of the electrolyte solutions prepared above as the electrolyte solution were mixed in a mixer to obtain a positive electrode slurry (electrode-forming slurry). (2) Preparation of Negative Electrode Slurry 60% by mass of artificial graphite (manufactured by Showa Denko K.K., UF-G30 (trade name)) as the negative electrode active material, 1.5% by mass of acetylene black (manufactured by Denka Company, Denka Black (trade name)) as a conductive additive, and 38.5% by mass of each of the electrolyte solutions prepared above as the electrolyte solution were mixed in a mixer to obtain a negative electrode slurry (electrode-forming slurry).

[0077] [Preparation of Nonaqueous Electrolyte Secondary Battery] (1) Preparation of Quasi-Solid Secondary Battery Each positive electrode slurry was applied to a 4 cm long x 3 cm wide aluminum current collector to a thickness of 300 μm to form a slurry positive electrode active material layer, which served as a positive electrode. Each negative electrode slurry was applied to a 4 cm long x 3 cm wide copper current collector to a thickness of 300 μm to form a slurry negative electrode active material layer, which served as a negative electrode. A separator (made of polyethylene, 6 cm long x 5 cm wide x 20 μm thick) was then placed on the negative electrode active material layer of the negative electrode, and the positive electrode was then placed on the separator so that the positive electrode active material layer was in contact with the separator. An aluminum tab was attached to the end of the aluminum current collector, and a nickel tab was attached to the end of the copper current collector by ultrasonic welding to form an electrode assembly. This electrode assembly was sandwiched between two aluminum laminate films, three sides were heat-sealed, and the remaining side was vacuum-sealed to prepare a laminated battery (quasi-solid secondary battery).

[0078] (2) Preparation of a conventional non-aqueous electrolyte secondary battery (non-slurry electrode active material layer non-aqueous electrolyte secondary battery) (Experiment No. 29 (Comparative Example)) (2-1) Preparation of the positive electrode The LFP1 as the positive electrode active material, acetylene black (manufactured by Denka Corporation, Denka Black (trade name)) as a conductive additive, and polyvinylene difluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium were mixed in a mass ratio of positive electrode active material: conductive additive: binder: NMP = 70: 1: 2: 27 to prepare a positive electrode slurry. The positive electrode slurry was applied to the entire surface of one side of a 12 μm thick positive electrode current collector (aluminum foil) (length 4 cm, width 3 cm) and dried at 120 ° C. until the dispersion medium was completely evaporated. Thereafter, the mixture was pressed using a roll press to obtain a sheet-like positive electrode (positive electrode sheet) having a positive electrode current collector and a positive electrode active material layer. The thickness of the positive electrode active material layer of the positive electrode sheet was approximately 300 μm. (2-2) Preparation of Negative Electrode Artificial graphite (Showa Denko K.K., UF-G30 (trade name)) as the negative electrode active material, styrene-butadiene copolymer (SBR) as the binder, carboxymethyl cellulose (CMC) as the thickener, and solvent (water) were mixed in a mass ratio of negative electrode active material:SBR:CMC:water=60:1.5:0.5:38 to obtain a negative electrode slurry. The negative electrode slurry was applied to one side of a 12 μm thick negative electrode current collector (copper foil) and dried at 150 °C until the solvent completely evaporated. Thereafter, the mixture was pressed using a roll press to obtain a sheet-like negative electrode (negative electrode sheet) having a negative electrode current collector and a negative electrode active material layer. The thickness of this negative electrode active material layer was approximately 300 μm. (2-3) Preparation of Secondary Battery Each positive electrode sheet and the negative electrode sheet obtained above were stacked with a separator (made of polyethylene, 6 cm long, 5 cm wide, 20 μm thick) interposed between them to form a laminate consisting of a positive electrode collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode collector, thereby obtaining an electrode laminate. An aluminum tab was attached to the end of the positive electrode collector, and a nickel tab was attached to the end of the negative electrode collector by ultrasonic welding. A battery assembly was produced by housing this electrode laminate in a laminate container. The electrolyte solution shown in Table 1 was poured into the case with the inlet open, and the inlet was then sealed to seal the case, producing a laminate battery.

[0079] (3) Battery initialization These laminated batteries were charged and discharged under the following conditions to complete the battery initialization. The initial discharge capacity was in the range of 90 to 110 mAh. <Charge and discharge conditions for initialization> Temperature: 25°C Constant current-constant voltage (CC-CV) charging: Current value 15 mA, upper limit voltage 3.6 V, end current value 0.5 mA Constant current (CC) discharging: Current value 15 mA, end voltage 2.0 V

[0080] [Low-Temperature Cycle Characteristics] The cycle characteristics of the laminated batteries at low temperatures were evaluated by repeatedly charging and discharging under the following conditions. Specifically, each initialized nonaqueous electrolyte secondary battery was charged and discharged under the following <charge and discharge conditions of 0°C and 0.1 C>, and the discharge capacity during this discharge was defined as the initial discharge capacity at 0°C and 0.1 C. Furthermore, 200 cycles of charge and discharge were performed under the following <charge and discharge conditions of 0°C and 0.1 C>, and the discharge capacity during the 200th cycle was defined as the discharge capacity at 0°C and 0.1 C after 200 cycles. From the obtained discharge capacities, the discharge capacity retention rate at 0°C was calculated using the following formula. The obtained discharge capacity retention rate was applied to the following evaluation criteria to evaluate the cycle characteristics at 0°C. <Charge / discharge conditions at 0°C, 0.1C> Temperature: 0°C CC-CV charge: Current value 10mA, upper limit voltage 3.6V, final current value 0.5mA CC discharge: Current value 10mA, final voltage 2.0V (Discharge capacity retention rate at 0°C) = (Discharge capacity at 0°C, 0.1C after 200 cycles) / (Initial discharge capacity at 0°C, 0.1C) x 100 (%) - Evaluation criteria - A: 95% or more B: 93% or more, less than 95% C: 90% or more, less than 93% D: 87% or more, less than 90% E: 85% or more, less than 87% F: Less than 85%

[0081] [Room Temperature Cycle Characteristics] The cycle characteristics of the laminated batteries at room temperature were evaluated by repeatedly charging and discharging under the following conditions. Specifically, each initialized nonaqueous electrolyte secondary battery was charged and discharged under the following <charge and discharge conditions of 25°C and 0.1 C>, and the discharge capacity during this discharge was defined as the initial discharge capacity at 25°C and 0.1 C. Furthermore, 200 cycles of charge and discharge were performed under the following <charge and discharge conditions of 25°C and 0.1 C>, and the discharge capacity during the 200th cycle was defined as the discharge capacity at 25°C and 0.1 C after 200 cycles. From the obtained discharge capacities, the discharge capacity retention rate was calculated using the following formula. The obtained discharge capacity retention rate was applied to the following evaluation criteria to evaluate the cycle characteristics at 25°C. Compared to the above 0°C, 25°C is a condition where the discharge capacity retention rate is more likely to decrease. <Charge / discharge conditions at 25°C, 0.1C> Temperature: 25°C CC-CV charge: Current value 10mA, upper limit voltage 3.6V, final current value 0.5mA CC discharge: Current value 10mA, final voltage 2.0V (Discharge capacity retention rate at 25°C) = (Discharge capacity at 25°C, 0.1C after 200 cycles) / (Initial discharge capacity at 25°C, 0.1C) x 100 (%) - Evaluation criteria - A: 95% or more B: 93% or more, less than 95% C: 90% or more, less than 93% D: 87% or more, less than 90% E: 85% or more, less than 87% F: Less than 85%

[0082]

[0083] <Notes for Table 1> "Ester compound of formula (I)" means an ester compound represented by formula (I). For convenience, compounds in which the number of carbon atoms of the ester compound is outside the range of formula (2) are also listed in the same row as the ester compound of formula (I). All of the ester compounds in the table are R ２ is a straight-chain hydrocarbon group. １ "," "R ２ " and "R １ +R ２"In the above formulas, C1 means 1 carbon atom, C2 means 2 carbon atoms, C3 means 3 carbon atoms, C4 means 4 carbon atoms, C5 means 5 carbon atoms, C6 means 6 carbon atoms, C7 means 7 carbon atoms, C8 means 8 carbon atoms, and C9 means 9 carbon atoms. "Content" means the content in a non-aqueous solvent. "EC / 50" means that 50% by mass (wt%) of ethylene carbonate (EC) is contained. "EC / 97" means that 97% by mass of EC is contained. "EC / 95" means that 95% by mass of EC is contained. "EC / 20" means that 20% by mass of EC is contained. "EC / 15" means that 15% by mass of EC is contained. "EC / 30" means that 30% by mass of EC is contained. "EC / 30, EMC / 50" means that the composition contains 30 mass% EC and 50 mass% ethyl methyl carbonate (EMC). "PC / 50" means that the composition contains 50 mass% propylene carbonate (PC). "PC / 30" means that the composition contains 30 mass% PC. "EMC / 50" means that the composition contains 50 mass% EMC. "EMC / 30" means that the composition contains 30 mass% EMC. "GBL / 20" means that the composition contains 20 mass% γ-butyrolactone. "DBE / 50" means that the composition contains 50 mass% dibutyl ether (DBE). "DBE / 30" means that the composition contains 30 mass% DBE.

[0084]

[0085] When the electrode-forming slurries containing the electrolyte solutions containing a carboxylic acid ester compound other than the ester compound represented by formula (I) (Nos. 1, 6, 17, 19, 21, 23, 25, and 27) or the electrolyte solutions containing the ester compound represented by formula (I) in a content of less than 5 to 80 mass % (Nos. 7 and 10) were used to form electrode active material layers for quasi-solid secondary batteries, the discharge capacity retention rate was less than 85% both at low temperature and at room temperature, and the cycle characteristics were poor. In contrast, when electrode-forming slurries containing electrolyte solutions containing 5 to 80 mass % of the ester compound represented by formula (I) (Nos. 2 to 5, 8, 9, 11 to 14, 18, 20, 22, 24, 26, and 28) were used to form electrode active material layers for quasi-solid secondary batteries, the discharge capacity retention rate at low temperatures was 87% or higher and the discharge capacity retention rate at room temperature was 85% or higher, resulting in improved cycle characteristics. It can be seen that the use of the electrode-forming slurries of the present invention makes it possible to obtain nonaqueous electrolyte secondary batteries that exhibit excellent cycle characteristics. It can also be seen that carbonate compounds are more preferable than ether compounds as the nonaqueous solvent to be combined with the ester compound represented by formula (I) (comparison of Nos. 3, 18, and 22 with No. 26). Furthermore, by combining an ester compound represented by formula (I), a carbonate compound, and a cyclic ester compound, the cycle characteristics can be further improved (compare No. 3 with No. 12, No. 18 with No. 20, and No. 22 with No. 24). Conventionally, the use of a relatively volatile solvent such as dimethyl carbonate (boiling point 90°C) causes fluctuations in the electrolyte composition due to solvent evaporation during battery production. Therefore, relatively low-volatility solvents, such as ethylene carbonate (boiling point 248°C), have been used as the nonaqueous solvent for the electrolyte. However, as shown in the above examples, it can be seen that the cycle characteristics can be further improved by intentionally mixing a relatively volatile ester compound such as butyl acetate (boiling point 126°C).Furthermore, comparing Experiments No. 2 and No. 15, even when ethyl methyl carbonate (boiling point 107°C), which has a boiling point close to propyl acetate (boiling point 102°C), was used, the cycle characteristics were poor (for example, the discharge capacity retention rate at low temperatures was 87% or more in Experiment No. 2, but less than 85% in Experiment No. 15). This result demonstrates that the cycle characteristics improvement effect of the cyclic ester compound is effectively manifested not in combination with a carbonate compound, but in combination with the ester compound represented by formula (I). Furthermore, when an electrolyte solution having the same components as the electrolyte solution used in Experiment No. 11 was used as the electrolyte solution for a conventional nonaqueous electrolyte secondary battery (not a quasi-solid secondary battery) (Experiment No. 29), the cycle characteristics improvement effect was not obtained. This demonstrates that the cycle characteristics improvement effect achieved by using the electrolyte solution specified in the present invention is an effect unique to quasi-solid secondary batteries.

[0086] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0087] This application claims priority based on Japanese Patent Application No. 2024-041138, filed on March 15, 2024, the contents of which are incorporated herein by reference as part of the present specification.

[0088] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery 1 Negative electrode current collector 2 Negative electrode active material layer 3 Separator 4 Positive electrode active material layer 5 Positive electrode current collector 6 Operating part (light bulb)

Claims

1. A slurry for forming an electrode of a non-aqueous electrolyte secondary battery, comprising an electrode active material, a conductive additive, and an electrolyte, wherein the electrolyte comprises an electrolyte and a non-aqueous solvent, the non-aqueous solvent contains an ester compound represented by the following formula (I), and the content of the ester compound in the non-aqueous solvent is 5 to 80 mass %: R １ and R ２ represents a hydrocarbon group, and the number of carbon atoms in the ester compound satisfies the following formula (2): 4≦(R １ (number of carbon atoms in R ２ (number of carbon atoms)≦8... Formula (2) 2. The electrode-forming slurry according to claim 1, wherein the number of carbon atoms in the ester compound satisfies the following formula (3): 5≦(R １ (number of carbon atoms in R ２ (number of carbon atoms)≦6... Formula (3) 3. The electrode-forming slurry according to claim 1, wherein the non-aqueous solvent contains a carbonate compound.

4. The electrode-forming slurry according to claim 3, wherein the non-aqueous solvent contains a cyclic ester compound.

5. The electrode-forming slurry according to claim 1, wherein the electrolyte contains a lithium salt, and the content of the lithium salt in the electrolytic solution is 0.9 to 1.5M.

6. The electrode-forming slurry according to claim 1, wherein the viscosity of the electrolyte is 2.8 to 7.5 mPa·s.

7. A non-aqueous electrolyte secondary battery having a positive electrode, a separator, and a negative electrode in this order, wherein the electrode-forming slurry according to any one of claims 1 to 6 is used as a positive electrode active material layer constituting the positive electrode and / or a negative electrode active material layer constituting the negative electrode.

8. A method for producing a non-aqueous electrolyte secondary battery, comprising applying the electrode-forming slurry according to any one of claims 1 to 6 onto an electrode current collector to form a slurry-like electrode active material layer.

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