Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to the present invention comprises a non-aqueous electrolyte secondary battery body and a restraining jig. The non-aqueous electrolyte secondary battery body has a laminated structure including, laminated in the following order: a positive electrode active material layer containing a positive electrode active material, a conduction assistant, and an electrolyte; a separator; and a negative electrode active material layer containing a negative electrode active material, a conduction assistant, and an electrolyte. A restraining pressure is applied by the restraining jig to the non-aqueous electrolyte secondary battery body in the lamination direction of the laminated structure. The yield stress of the positive electrode active material layer is 2 kPa or greater, the yield stress of the negative electrode active material layer is 2 kPa or greater, and the restraining pressure is 2-48 kPa.

Description

Nonaqueous electrolyte secondary battery

[0001] The present invention relates to a non-aqueous 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] Japanese Patent Application Laid-Open No. 2017-147222

[0005] Quasi-solid-state secondary batteries utilize the coating film of the electrode-forming slurry (electrode slurry) as the electrode active material layer. This eliminates the need for processes such as drying the coating film formed from the electrode slurry or injecting an electrolyte solution after forming the electrode active material layer, resulting in superior mass productivity (production efficiency). On the other hand, attempts have been made to increase the capacity (energy density) of batteries by increasing the content of electrode active material in the slurry-like electrode active material layer, or to increase the electronic conductivity by increasing the content of conductive additives. In these cases, electrode slurries containing high amounts of solid particles, such as electrode active material and conductive additives, tend to harden, resulting in poor coatability and making the resulting coating brittle and prone to crumbling. Conversely, reducing the content of solid particles in the electrode slurry in favor of coatability not only reduces energy density or electronic conductivity, but also leads to problems such as poor dimensional stability of the resulting coating due to its softness. The reduced dimensional stability of the electrode active material layer leads to reduced battery performance, such as battery capacity and cycle characteristics.

[0006] An object of the present invention is to provide a nonaqueous electrolyte secondary battery that has excellent shape stability in an electrode active material layer formed from a coating of electrode slurry, can achieve a higher energy density (higher capacity), and has excellent cycle characteristics.

[0007] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that the above-mentioned problems can be solved to a high degree by controlling the relationship between the yield stress of an electrode active material layer formed by a coating of an electrode slurry and the pressure applied in the stacking direction of each layer constituting a battery cell. The present invention was completed through further research based on this finding. The present invention provides the following nonaqueous electrolyte secondary battery. (1) A nonaqueous electrolyte secondary battery comprising a nonaqueous electrolyte secondary battery main body and a restraining jig, wherein the nonaqueous electrolyte secondary battery main body has a laminated structure in which a positive electrode active material layer containing a positive electrode active material, a conductive additive, and an electrolyte, a separator, and a negative electrode active material layer containing a negative electrode active material, a conductive additive, and an electrolyte are laminated in this order, and a restraining pressure is applied to the nonaqueous electrolyte secondary battery main body in a stacking direction of the laminated structure by the restraining jig, wherein the positive electrode active material layer has a yield stress of 2 kPa or more, the negative electrode active material layer has a yield stress of 2 kPa or more, and the restraining pressure is 2 to 48 kPa. (2) The nonaqueous electrolyte secondary battery according to (1), wherein the positive electrode active material layer has a yield stress of 2 to 30 kPa. (3) The nonaqueous electrolyte secondary battery according to (1) or (2), wherein the positive electrode active material layer has a yield stress of 2 to 20 kPa. (4) The nonaqueous electrolyte secondary battery according to any one of (1) to (3), wherein the negative electrode active material layer has a yield stress of 2 to 65 kPa. (5) The nonaqueous electrolyte secondary battery according to any one of (1) to (4), wherein the negative electrode active material layer has a yield stress of 2 to 55 kPa. (6) The nonaqueous electrolyte secondary battery according to any one of (1) to (5), wherein the confining pressure is 15 to 40 kPa. (7) The nonaqueous electrolyte secondary battery according to any one of (1) to (6), wherein the content of the positive electrode active material in the positive electrode active material layer is 70 mass % or more. (8) The nonaqueous electrolyte secondary battery according to any one of (1) to (7), wherein the content of the positive electrode active material in the positive electrode active material layer is 70 mass % to 85 mass %. (9) The nonaqueous electrolyte secondary battery according to any one of (1) to (8), wherein the content of the negative electrode active material in the negative electrode active material layer is 60% by mass or more. (10) The nonaqueous electrolyte secondary battery according to any one of (1) to (9), wherein the content of the negative electrode active material in the negative electrode active material layer is 60 to 75% by mass.

[0008] 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 practice, it is difficult to make a non-aqueous solvent completely anhydrous, and it usually contains 1 ppm or more of water. In the present invention, the "nonaqueous electrolyte" is a solution. That is, the non-aqueous electrolyte is composed of a non-aqueous solvent and various components such as an electrolyte dissolved in the solvent. Therefore, the "nonaqueous electrolyte" itself does not contain any substance insoluble in the solvent that constitutes the non-aqueous electrolyte. In the present invention, the "collapse" of the slurry electrode active material layer means that at least a portion of the slurry electrode active material layer is missing, crumbles, or cracks.

[0009] The nonaqueous electrolyte secondary battery of the present invention has excellent shape stability of the electrode active material layer formed from a coating of electrode slurry, can realize a higher energy density, and also has excellent cycle characteristics.

[0010] Fig. 1 is a longitudinal cross-sectional view showing a schematic diagram of a basic stacking configuration of an embodiment of a nonaqueous electrolyte secondary battery. Fig. 2 is a schematic diagram showing the arrangement relationship between a nonaqueous electrolyte secondary battery body and a restraining jig in an embodiment of the nonaqueous electrolyte secondary battery of the present invention. Fig. 2A is a top view of the nonaqueous electrolyte secondary battery as seen from the stacking direction. Fig. 2B is a side view of the nonaqueous electrolyte secondary battery as seen from a direction perpendicular to the stacking direction.

[0011] 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.

[0012] The nonaqueous electrolyte secondary battery of the present invention (hereinafter also referred to as "secondary battery of the present invention") includes a nonaqueous electrolyte secondary battery main body and a restraining jig. The nonaqueous electrolyte secondary battery main body (hereinafter also referred to as "secondary battery main body") includes a positive electrode active material layer containing a positive electrode active material, a conductive additive, and an electrolyte solution, a negative electrode active material layer containing a negative electrode active material, a conductive additive, and an electrolyte solution, and a separator disposed between the positive electrode active material layer and the negative electrode active material layer. The secondary battery main body functions as a battery by itself. The secondary battery main body typically includes an exterior body. In the secondary battery of the present invention, pressure (restraining pressure) is applied to the secondary battery main body by the restraining jig in the stacking direction (stacking direction of "positive electrode active material layer / separator / negative electrode active material layer"). In the secondary battery of the present invention, the yield stress of the positive electrode active material layer is 2 kPa or more, the yield stress of the negative electrode active material layer is 2 kPa or more, and the restraining pressure by the restraining jig is 2 to 48 kPa.

[0013] 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 operating parts when the battery is in operation. 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 non-aqueous electrolyte, and electrons are supplied to the operating part 6. In the example shown, a light bulb is used as the operating part 6, and it is lit by discharge. Note that the restraining jig is not shown in Fig. 1.

[0014] 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 formed in the form of a slurry containing an electrode active material and an 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 layer using a slurry (suspension, dispersion) in which the electrode active material is dispersed in a non-aqueous electrolyte. That is, in a typical non-aqueous electrolyte secondary battery, a coating liquid is prepared in which the electrode active material is dispersed 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 that is soluble in the solvent in the coating liquid. The binder solidifies upon drying, forming 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, not a slurry layer. In contrast, in a typical 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 an electrolyte such as a lithium salt 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 .

[0015] FIG. 2 schematically illustrates one embodiment of a secondary battery of the present invention. FIG. 2A is a top view of the nonaqueous electrolyte secondary battery as viewed from above in the stacking direction. In FIG. 2A, the nonaqueous electrolyte secondary battery body 101 of the nonaqueous electrolyte secondary battery 100 has a flat, rectangular shape, and tabs 101a and 101b for extracting power from its ends extend from the positive electrode current collector and the negative electrode current collector (neither of which is shown), respectively. In FIG. 2A, the nonaqueous electrolyte secondary battery body 101 is sandwiched between two plate-shaped restraining jigs 102, and is restrained by tightening four screws 103 to adjust the spacing between the restraining jigs 102, with pressure being applied in the stacking direction. FIG. 2B is a side view of the nonaqueous electrolyte secondary battery as viewed in a direction perpendicular to the stacking direction (the lower side of the paper in FIG. 2A).

[0016] The yield stress of the positive electrode active material layer is 2 kPa or more, preferably 5 kPa or more, and more preferably 7 kPa or more. The upper limit of the yield stress of the positive electrode active material layer is not particularly limited, and a practical value is about 30 kPa. The yield stress of the positive electrode active material layer is preferably 2 to 30 kPa, more preferably 2 to 27 kPa, even more preferably 2 to 20 kPa, even more preferably 5 to 20 kPa, even more preferably 7 to 20 kPa, even more preferably 10 to 20 kPa, even more preferably 12 to 18 kPa, even more preferably 12 to 17 kPa, and even more preferably 14 to 16 kPa. The yield stress of the negative electrode active material layer is 2 kPa or more, preferably 5 kPa or more, and more preferably 8 kPa or more. The upper limit of the yield stress of the negative electrode active material layer is not particularly limited, and a practical value is about 65 kPa. The yield stress of the negative electrode active material layer is preferably 2 to 65 kPa, more preferably 2 to 60 kPa, even more preferably 2 to 55 kPa, even more preferably 2 to 50 kPa, even more preferably 4 to 40 kPa, even more preferably 6 to 35 kPa, even more preferably 8 to 35 kPa, even more preferably 10 to 35 kPa, even more preferably 10 to 30 kPa, even more preferably 10 to 20 kPa, even more preferably 10 to 18 kPa, even more preferably 10 to 16 kPa. The yield stresses of the positive electrode active material layer and the negative electrode active material layer can be controlled, for example, by the content, material, size, specific surface area, etc. of solid particles such as the electrode active material and the conductive additive. These preferred ranges will be described later. The yield stress of the positive electrode active material layer and the negative electrode active material layer can be determined by measuring the yield stress of a slurry having the same composition as the slurry constituting these layers. More specifically, it can be measured by the method described in the Examples.

[0017] The confining pressure in the secondary battery of the present invention is lower than the confining pressure (e.g., 100 kPa) employed in conventional nonaqueous electrolyte secondary batteries. As described above, by setting the yield stress of each of the positive electrode active material layer and the negative electrode active material layer within the above-described range, the shape stability of the formed layers themselves can be improved. Furthermore, by controlling the confining pressure applied to a secondary battery body including electrode active material layers having these yield stresses within the above-described specific low range, the energy density and cycle characteristics of the resulting secondary battery can both be significantly improved. The confining pressure applied by the confining jig in the stacking direction is preferably 2 to 46 kPa, more preferably 5 to 46 kPa, more preferably 7 to 46 kPa, even more preferably 10 to 44 kPa, even more preferably 10 to 40 kPa, even more preferably 15 to 40 kPa, and even more preferably 20 to 35 kPa. The confining pressure applied by the confining jig can be measured by the method described in the Examples. The influence of the restraining pressure applied by the restraining jig on the deformation of the electrode active material layer caused by charge and discharge is small, and this influence is at a level that can be practically ignored.

[0018] The secondary battery of the present invention may have one or more of the above-described secondary battery bodies. When having a plurality of secondary battery bodies, the plurality of secondary battery bodies can be stacked along the stacking direction of the electrode active material layers. Also, the plurality of secondary battery bodies can be arranged in parallel in a direction perpendicular to the stacking direction of the electrode active material layers.

[0019] The secondary battery body, restraining jig, and the like that constitute the secondary battery of the present invention will be described in more detail.

[0020] [Restraining Jig] The restraining jig applies a pressure of 2 to 48 kPa in the stacking direction of the secondary battery body. Originally, a restraining jig primarily restrains the secondary battery body with high pressure to suppress deformation of the electrode active material layer associated with charging and discharging of the secondary battery body. However, in the present invention, as described above, the yield stress of the electrode active material layer is controlled within a specific range, and the secondary battery body is restrained with a specific low pressure. The restraining jig is not particularly limited as long as it is capable of applying the above-mentioned pressure in the stacking direction (thickness direction) of the battery body. A typical restraining jig can be used. For example, a combination of a plate-shaped member and a connecting member can be used. Examples of the connecting member include screws, elastic bodies, etc. For example, the plate-shaped member may be fixed with screws, or may be tightened with an elastic body. The plate-shaped member may also be fixed from the outside with a spring or the like. The restraining jig preferably applies pressure evenly to the main surfaces of the secondary battery body (the entire upper and lower surfaces of the stacked structure). From this viewpoint, it is preferable that the restraining jig includes a plate-shaped member. When the restraining jig includes a plate-shaped member, the restraining pressure applied to the secondary battery main body by the restraining jig can be controlled by adjusting the distance between the plate-shaped members. The material of the plate-shaped members is not particularly limited, but stainless steel, aluminum, etc. can be used. For example, as shown in FIG. 2 , the restraining jig can be a combination of a pair of plate-shaped members and four screws. By connecting the pair of plate-shaped members with the screws and adjusting the tightening of the screws, the spacing between the plate-shaped members can be adjusted to control the restraining pressure.

[0021] [Non-aqueous electrolyte secondary battery body (secondary battery body)] The secondary battery body has a positive electrode active material layer exhibiting the above-mentioned specific yield stress, a negative electrode active material layer exhibiting the above-mentioned specific yield stress, and a separator disposed therebetween. Except for controlling the yield stresses of the positive electrode active material layer and the negative electrode active material layer, the secondary battery body can adopt the configuration of a typical quasi-solid secondary battery (cell).

[0022] The secondary battery body usually has an exterior. The exterior can be an exterior of a normal secondary battery, such as a laminate film or a can. From the viewpoint of applying pressure using a restraining jig, a laminate film is preferable for the exterior. When the battery is enclosed in the exterior, the pressure inside the exterior may be reduced, which may apply pressure to the electrode active material layer, separator, etc. However, the pressure from the exterior is significantly smaller than the restraining pressure applied by the restraining jig, and does not substantially affect the manifestation of the effects of the present invention.

[0023] Each component constituting the secondary battery body will now be described in more detail.

[0024] <Positive electrode slurry and positive electrode active material layer> The positive electrode active material layer is a layer composed of a positive electrode slurry containing a positive electrode active material, a conductive additive, and an electrolyte. The following description of the components and component contents in the positive electrode slurry applies directly to the components and component contents in the positive electrode active material layer. The same applies to the description of the negative electrode active material layer and the negative electrode slurry.

[0025] (Positive Electrode Active Material) The positive electrode active material is preferably one that can reversibly insert and release lithium ions. There are no particular limitations on the material, and it 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 lithium-containing transition metal oxide as the positive electrode active material, and a transition metal element M ａ A transition metal oxide containing at least one element 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: ａ The amount of Li / M is preferably 0 to 30 mol % relative to the amount of Li / M (100 mol %). ａMore preferably, the lithium-containing transition metal oxide is synthesized by mixing the above-mentioned components so that the molar ratio of the above-mentioned components is 0.3 to 2.2. Specific examples of the lithium-containing transition metal oxide include (MA) a lithium-containing transition metal oxide having a layered rock salt structure, (MB) a lithium-containing transition metal oxide having a spinel structure, (MC) a lithium-containing transition metal phosphate compound, (MD) a lithium-containing transition metal halide phosphate compound, and (ME) a ​​lithium-containing transition metal silicate compound.

[0026] (MA) Specific examples of lithium-containing 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 lithium-containing 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.

[0027] The shape of the positive electrode active material is not particularly limited, but particulate form is preferred. The average particle diameter (average particle diameter 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 diameter. 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.

[0028] When a commercially available positive electrode active material is used, the average particle diameter of the positive electrode active material is the value listed in the manufacturer's catalog. When the manufacturer's average particle diameter information is unavailable or when a synthesized positive electrode active material is used, the positive electrode active material is dispersed in water and the particle diameter value (volume-based median diameter D50 in water) obtained by measuring with a laser diffraction / scattering particle size distribution measurement device (e.g., HORIBA Particle LA-960V2) is used. This also applies to the average particle diameter of solid particles other than the positive electrode active material.

[0029] 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.

[0030] The surface of the positive electrode active material may be coated with an oxide such as another metal oxide, a carbon-based material, or the like. These surface coating layers can function as an interface resistance stabilizing layer. Examples of surface coating materials include metal oxides containing Ti, Nb, Ta, W, Zr, Al, Si, or Li. Specific examples include titanate spinel, tantalum-based oxides, niobium-based oxides, and lithium niobate-based compounds, such as Li ４ Ti ５ O １２ , Li ２ Ti ２ O ５ , LiTaO ３ , LiNbO ３ , LiAlO ２ , Li ２ ZrO ３ , Li ２ WO ４ , Li ２ TiO ３ , Li ２ B ４ O ７ , Li ３ P.O. ４ , Li ２ MoO ４ , Li ３ BO ３ , LiBO ２ , Li ２ CO ３ , Li ２ SiO ３, SiO ２ , TiO ２ , ZrO ２ , Al ２ O ３ , B ２ O ３ , and Li ３ AlF ６ Carbon-based materials such as C, SiC, and SiOC (carbon-doped silicon oxide) can also be used as the surface coating material.

[0031] The positive electrode active material may be surface-coated with a carbon-based material in order to increase the electronic conductivity to a desired level. The positive electrode active material is preferably surface-coated with carbon (C). The carbon surface coating can be formed by baking the positive electrode active material in the presence of an additive (organic substance) that serves as a carbon source. Examples of the additive that can be used include styrene-maleic anhydride copolymer, polystyrene, and polycarbonate.

[0032] 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.

[0033] The specific surface area (BET specific surface area) of the positive electrode active material is 0.01 to 100 m ２ / g is preferred. The specific surface area of ​​the positive electrode active material can be calculated by the BET (single point) method using a nitrogen adsorption method in which the positive electrode active material is packed into a sample tube, dried by flowing nitrogen, and measured using a specific surface area / pore distribution measuring device (e.g., BELSORP MINI manufactured by Microtrac-Bell). Note that the specific surface area of ​​commercially available positive electrode active materials may be listed in the manufacturer's catalog. The same applies to the specific surface areas of the conductive additive and negative electrode active material described below.

[0034] The positive electrode active materials may be used alone or in combination of two or more.

[0035] The content of the positive electrode active material in the positive electrode slurry is preferably 70% by mass or more, more preferably 75% by mass or more, preferably 70 to 85% by mass, more preferably 70 to 80% by mass, even more preferably 75 to 79% by mass, and still more preferably 76 to 78% by mass.

[0036] The content of the positive electrode active material in the positive electrode slurry solids 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.

[0037] (Conductive Aid) The conductive aid is not particularly limited, and any known conductive aid can be used. For example, it may be an electron-conductive material such as graphites (e.g., natural graphite, artificial graphite), carbon blacks (e.g., acetylene black, ketjen black, furnace black), amorphous carbon (e.g., needle coke), carbon fibers (e.g., vapor-grown carbon fiber or carbon nanotube), or carbonaceous materials (e.g., graphene or fullerene). It may also be a metal powder or metal fiber (e.g., copper or nickel), or a conductive polymer (e.g., polyaniline, polypyrrole, polythiophene, polyacetylene, or polyphenylene derivative). When an electrode active material and a conductive aid are used in combination, those conductive aids that do not intercalate or deintercalate Li during charging and discharging the battery and do not function as an active material are considered conductive aids. Therefore, among conductive aids, those that can function as an active material in the active material layer during charging and discharging the battery are classified as active materials rather than conductive aids. Whether or not a conductive aid functions as an active material during charging and discharging the battery is not uniquely determined, but is determined by its combination with the active material. The conductive additive may be used alone or in combination of two or more.

[0038] The shape of the conductive additive is not particularly limited, but is preferably particulate. The average particle diameter (average particle diameter in equivalent sphere form) of the conductive additive is 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.

[0039] The specific surface area (BET specific surface area) of the conductive additive is 10 to 2000 m ２ / g is preferred.

[0040] The content of the conductive additive in the positive electrode slurry is preferably 0.1 to 3 mass %, more preferably 0.3 to 2 mass %, even more preferably 0.5 to 1.5 mass %, and still more preferably 0.5 to 1 mass %.

[0041] The content of the conductive additive in the solid content of the positive electrode slurry 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 %.

[0042] (Electrolyte) The electrolyte is composed of an electrolyte (electrolyte salt) and a non-aqueous solvent that dissolves the electrolyte.

[0043] As the electrolyte, any electrolyte that can be used in a non-aqueous electrolyte solution for a quasi-solid secondary battery can be used. The electrolyte is preferably a metal salt, such as lithium salt, potassium salt, sodium salt, calcium salt, or magnesium salt. As the lithium salt, lithium salts that are commonly used in electrolytes for lithium ion secondary batteries are preferred, such as the following lithium salts:

[0044] (L-1) Inorganic lithium salt: LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF ６ Inorganic fluoride salts such as LiClO ４ , LiBrO ４ , LiIO ４ perhalogenates such as LiAlCl ４ Inorganic chloride salts, etc.

[0045] (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 (lithium bis(fluorosulfonyl)imide, also known as LiFSI), LiN(CF ３SO 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 ) ３ perfluoroalkyl fluorophosphates such as

[0046] (L-3) Oxalatoborate salts: lithium bis(oxalato)borate, lithium difluorooxalatoborate, etc.

[0047] 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 is particularly preferred. ｆ１ and R ｆ２ represents a perfluoroalkyl group, preferably having 1 to 6 carbon atoms.

[0048] The non-aqueous electrolyte may contain one electrolyte alone or two or more electrolytes in any combination.

[0049] In the positive electrode slurry, the electrolyte concentration in the electrolytic solution is not particularly limited as long as it functions as an electrolytic solution. For example, it can be 10.0 to 50.0 mass %, preferably 15.0 to 30.0 mass %. The molar concentration is preferably 0.5 to 1.5 M.

[0050] The non-aqueous solvent serving as the medium for the electrolyte solution is preferably an aprotic organic solvent, and more preferably an aprotic organic solvent having 2 to 10 carbon atoms. Examples of such non-aqueous solvents include linear or cyclic carbonate compounds, lactone compounds, linear or cyclic ether compounds, ester compounds, nitrile compounds, amide compounds, oxazolidinone compounds, nitro compounds, linear or cyclic sulfone or sulfoxide compounds, and phosphate ester compounds. Compounds having an ether bond, carbonyl bond, ester bond, or carbonate bond are preferred. These compounds may have a substituent.

[0051] Examples of non-aqueous solvents include ethylene carbonate, fluorinated ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and methyl acetate. , ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidone (NMP), N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, etc. These may be used alone or in combination of two or more. Among these, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone is preferred, and a combination of a high-viscosity (high-dielectric constant) solvent (e.g., relative dielectric constant ε≧30) such as ethylene carbonate or propylene carbonate with a low-viscosity solvent (e.g., viscosity≦1 mPa s) such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate is more preferred. Using a mixed solvent with such a combination improves the dissociation properties of the electrolyte and the mobility of ions. A particularly preferred nonaqueous solvent is a combination of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0052] The content of the non-aqueous electrolyte solution in the positive electrode slurry is an amount such that the total of the solid particles constituting the positive electrode slurry and the non-aqueous electrolyte solution becomes 100 mass %, and is usually an amount such that the total of the positive electrode active material, the conductive additive, and the non-aqueous electrolyte solution becomes 100 mass %.

[0053] (Other Components) The positive electrode slurry 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. When the positive electrode slurry contains the other components, the amount of the other components is preferably 0.05 to 1.5 parts by mass, more preferably 0.1 to 1.0 parts by mass, per 100 parts by mass of the total content of the positive electrode active material and the conductive additive.

[0054] The positive electrode slurry can be obtained by uniformly mixing the components constituting the slurry. For example, a non-aqueous solvent and an electrolyte are mixed to obtain a non-aqueous electrolyte solution, and this non-aqueous electrolyte solution is mixed with an electrode active material and a conductive additive to obtain a slurry in which the electrode active material and the conductive additive are dispersed in the solvent. The mixing method is not particularly limited, and a method commonly used in this technical field can be appropriately adopted.

[0055] The thickness of the positive 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 40 to 400 μm, and even more preferably 80 to 350 μm.

[0056] <Negative Electrode Slurry and Negative Electrode Active Material Layer> The negative electrode active material layer is a layer made of a negative electrode slurry containing a negative electrode active material, a conductive additive, and an electrolyte solution.

[0057] (Negative electrode active material) The negative electrode active material is preferably one that can reversibly absorb and release lithium ions. There are no particular limitations on the material, 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.

[0058] 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.

[0059] 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 O８ 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.

[0060] 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:

[0061] The negative electrode active material preferably contains titanium atoms. More specifically, TiNb ２ O ７ (Niobium titanate oxide [NTO]), Li ４ Ti ５ O1 ２ 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.

[0062] 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.

[0063] 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 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., LaSi2 / Si), as well as 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:

[0064] The shape of the negative electrode active material is not particularly limited, but a particulate form is preferred. The average particle diameter of the negative electrode active material is preferably 0.1 to 60 μm. To achieve the desired particle diameter, 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 preferably performed to achieve the desired particle diameter. 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 method or a wet method.

[0065] The above-mentioned negative electrode active materials may be used singly or in combination of two or more. Among them, a combination of a silicon atom-containing active material and a carbonaceous material is preferred, and a combination of SiOx (0<x≦1) and graphite is particularly preferred. When SiOx (0<x≦1) and graphite are combined, the mass ratio (SiOx / graphite) is preferably 2 or less, more preferably 1 or less, and even more preferably 0.5 or less. When forming a negative electrode active material layer, the 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.

[0066] The specific surface area (BET specific surface area) of the negative electrode active material is 0.1 to 100 m ２ / g is preferred.

[0067] The content of the negative electrode active material in the negative electrode slurry is preferably 60% by mass or more, more preferably 62% by mass or more, preferably 60 to 75% by mass, more preferably 62 to 73% by mass, even more preferably 60 to 70% by mass, still more preferably 62 to 70% by mass, and even more preferably 64 to 70% by mass.

[0068] The content of the negative electrode active material in the negative electrode slurry solids 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.

[0069] (Conductive Aid) As the conductive aid contained in the negative electrode slurry, the conductive aids exemplified as the conductive aid for the positive electrode slurry can be used.

[0070] The content of the conductive additive in the negative electrode slurry is preferably 0.1 to 3 mass %, more preferably 0.3 to 2 mass %, even more preferably 0.5 to 1.5 mass %, and still more preferably 0.5 to 1 mass %.

[0071] The content of the conductive additive in the solid content of the negative electrode slurry 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 %.

[0072] (Electrolyte) The electrolyte contained in the negative electrode slurry may be any of the electrolytes listed as the electrolyte for the positive electrode slurry.

[0073] The content of the nonaqueous electrolyte solution in the negative electrode slurry is an amount that, when combined with the solid particles constituting the negative electrode slurry, makes up 100% by mass, and is usually an amount that, when combined with the negative electrode active material and the conductive additive, makes up 100% by mass.

[0074] (Other Components) The negative electrode slurry may contain "(other components)" as desired, similarly to the positive electrode slurry. When the negative electrode slurry contains other components, the amount of the other components is preferably 0.05 to 1.5 parts by mass, and more preferably 0.1 to 1.0 part by mass, relative to 100 parts by mass of the total content of the negative electrode active material and the conductive additive.

[0075] The negative electrode slurry can be prepared in the same manner as the positive electrode slurry.

[0076] The thickness of the negative 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 40 to 400 μm, and even more preferably 80 to 350 μm.

[0077] <Current Collectors, Separators, etc.> The materials and components of the secondary battery body, such as the positive electrode current collector, negative electrode current collector, and separator, are not particularly limited. These materials and components can be appropriately selected from those used in conventional nonaqueous electrolyte secondary batteries. For details on the components and manufacturing methods typically used in these secondary batteries, see, for example, JP 2016-201308 A, JP 2005-108835 A, JP 2012-185938 A, and WO 2018 / 135395. The separator is preferably made of polypropylene or polyethylene, and more preferably polyethylene. The secondary battery body typically includes a positive electrode current collector and a negative electrode current collector. Aluminum, aluminum alloys, and the like are preferred materials for the positive electrode current collector. Copper, nickel, carbon, and the like are preferred materials for the negative electrode current collector. The secondary battery body typically includes tabs for extracting power from the positive and negative electrodes.

[0078] [Other Components] In the secondary battery of the present invention, a cushioning material may be disposed between the restraining jig and the secondary battery body, or between a plurality of secondary battery bodies. Examples of the cushioning material include rubber, urethane foam, and a gel sheet.

[0079] The nonaqueous electrolyte secondary battery body can be manufactured by a manufacturing method including forming an electrode active material layer using a positive electrode slurry and a negative electrode slurry exhibiting the above-described yield stress. For example, the manufacturing method can include applying a positive electrode slurry containing a positive electrode active material onto a positive electrode current collector and applying a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector. The method for applying the slurry is not particularly limited, and can include, for example, application 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 by placing it within a frame of a specified thickness and stretching it. The method for manufacturing the secondary battery of the present invention can also be appropriately adopted using conventional methods, except for forming the electrode active material layer using the positive electrode slurry and a negative electrode slurry exhibiting the above-described specific yield stress and restraining the secondary battery body using a restraining jig. 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.

[0080] The secondary battery of the present invention can be installed in electronic devices such as notebook computers, pen-input PCs, mobile PCs, electronic book players, mobile phones, cordless phone handsets, pagers, handheld terminals, portable fax machines, portable copiers, portable printers, headphone stereos, video camcorders, LCD televisions, handheld vacuum cleaners, portable CD players, mini-discs, electric shavers, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, and memory cards. It can also be installed in consumer 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.

[0081] 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.

[0082] [Preparation of active materials] (1) Preparation of LFP1 and LFP2 ４ ) powder raw material (Gelon, particle size 2.5 μm) 10 parts by mass was mixed with 90 parts by mass of water, and the following amount of styrene-maleic anhydride copolymer was added as an additive, followed by stirring and mixing for 3 hours. Then, the mixture was baked at 700°C for 10 hours in a nitrogen atmosphere. In this way, cathode active materials LFP1 and LFP2, each surface-coated with a carbon-based material, were obtained. The electronic conductivities of the respective cathode active materials were as follows: LFP1: additive amount = 0.1 parts by mass, electronic conductivity = 1.4 mS / cm LFP2: additive amount = 0.2 parts by mass, electronic conductivity = 3.0 mS / cm (2) Preparation of NMC1 NMC (LiNi １／３ Co １／３ Mn １／３ O ２ 10 parts by mass of powder raw material (NCM111, particle size 8 μm) was mixed with 90 parts by mass of water, and the following amount of styrene-maleic anhydride copolymer was added as an additive, followed by stirring and mixing for 3 hours. The mixture was then fired at 700°C for 10 hours in a nitrogen atmosphere. In this way, a positive electrode active material NMC1 coated with a carbon-based material was obtained. The electronic conductivity of NMC1 was as follows: NMC1: additive amount = 0.1 parts by mass, electronic conductivity = 1.3 mS / cm

[0083] [Preparation of Electrolyte Solution] (1) Preparation of Electrolyte Solution EL1 Ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) were mixed in a mass ratio of 3 / 4 / 3 to prepare a non-aqueous solvent. ６ and LiPF ６ The concentration of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) was adjusted to 1M (mol / L) to prepare electrolyte solution EL1. (2) Preparation of electrolyte solution EL2: Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 3 / 4 / 3 to prepare a non-aqueous solvent. Lithium bis(fluorosulfonyl)imide (LiFSI) was added to this non-aqueous solvent to prepare electrolyte solution EL2. The LiFSI concentration was adjusted to 1M.

[0084] [Preparation of Positive Electrode Slurry] (1) Positive Electrode Slurry Used in Example 1 Positive electrode slurry was prepared by mixing 79% by mass of LFP1 as a positive electrode active material and acetylene black (Denka Black (trade name), manufactured by Denka Co., Ltd., specific surface area: 68 m) as a conductive additive. ２ 1% by mass of the ionic liquid (Ionic Liquid) containing 1% by mass of ionic liquid EL1 / g) and 20% by mass of the electrolyte solution EL1 were mixed in a centrifugal planetary mixer (Thinky Corporation, Awatori Rentaro (trade name)) to obtain a positive electrode slurry used in Example 1. (2) Positive electrode slurries used in Examples 2 to 29 and Comparative Examples 1 to 9 Positive electrode slurries used in Examples 2 to 29 and Comparative Examples 1 to 9 were obtained in the same manner as the positive electrode slurry used in Example 1, except that the positive electrode active material and conductive additive shown in Table 1 were used in the proportions (% by mass) shown in Table 1, with the remainder being the electrolyte solution shown in Table 1. The conductive additive used in Example 28 was Ketjenblack (Lion Corporation, Carbon ECP (trade name), specific surface area = 890 m) ２ / g) (ECP).

[0085] [Preparation of Negative Electrode Slurry] (1) Negative Electrode Slurry Used in Example 1 68% by mass of artificial graphite (UF-G30 (trade name) manufactured by Showa Denko K.K.) as the negative electrode active material, 1.5% by mass of acetylene black (Denka Black (trade name) manufactured by Denka Co., Ltd.) as the conductive aid, and 30.5% by mass of the above-described electrolytic solution EL1 as the electrolytic solution were mixed in a centrifugal planetary mixer (Awatori Rentaro (trade name) manufactured by Thinky Corporation) to obtain the negative electrode slurry used in Example 1. (2) Negative Electrode Slurries Used in Examples 2 to 29 and Comparative Examples 1 to 9 Negative electrode slurries used in Examples 2 to 29 and Comparative Examples 1 to 9 were obtained in the same manner as the negative electrode slurry used in Example 1, except that the negative electrode active materials and conductive aids shown in Table 1 were used in the proportions shown in Table 1, with the remainder being the electrolytic solution shown in Table 1.

[0086] [Method for measuring yield stress] The dynamic viscoelasticity of each electrode slurry was measured at a temperature of 25°C and a shear rate of 1 / sec using a rheometer (ARES rheometer (AR-2000 (trade name)), manufactured by TA Instruments). The first maximum value obtained from the shear stress-strain curve was taken as the yield stress of the electrode slurry.

[0087] [Method for Evaluating Shape Stability of Electrode Active Material Layer] The shape stability of the electrode active material layer was evaluated using the area change rate of the coating film formed by coating the electrode slurry on the current collector as an index. Each positive electrode slurry was applied to an aluminum current collector to a thickness of 300 μm and an area of ​​4 cm square (16 cm ２ ) to form a square, and a positive electrode having the resulting coating film (positive electrode active material layer) on an aluminum current collector was fabricated. Thereafter, the positive electrode was placed on a horizontally arranged adsorption plate so that the aluminum current collector was in contact with the positive electrode, and in this state, the adsorption plate was rotated 90° so that the square surface of the positive electrode active material layer was perpendicular to the horizontal direction. After maintaining this state for 1 minute, the adsorption plate was returned to a horizontal position so that the positive electrode active material layer was facing up, and the area of ​​the positive electrode active material layer was measured. The area (Y cm) of the positive electrode active material layer ２ The measurement of the area change rate (%) was performed by taking an image of the positive electrode active material layer using a digital microscope imaging device (VHX-7000 (product name), manufactured by Keyence Corporation) and calculating the area of ​​the positive electrode active material layer using the same device. From the obtained measured values, the area change rate before and after the vertical holding was calculated using the following formula. The obtained area change rate was evaluated by applying it to the following evaluation criteria. In the formula below, the value between two "|"s is an absolute value. When the positive electrode active material layer collapses, a portion of it sags in the vertical direction, increasing the area of ​​the positive electrode active material layer, or the sagging portion of the positive electrode active material layer falls, causing defects in the positive electrode active material layer, resulting in an increase in the area change rate. Area change rate (%) = 100 × |(Y) - 16| / 16 For each negative electrode slurry, shape stability was evaluated in the same manner as for the positive electrode slurry, except that a copper current collector was used instead of an aluminum current collector. -Evaluation criteria- A: Less than 0.5% B: 0.5% or more, less than 1% C: 1% or more, less than 2% D: 2% or more, less than 3% E: 3% or more, less than 4% F: 4% or more

[0088] [Battery Fabrication] The nonaqueous electrolyte secondary batteries shown in FIG. 2 were fabricated using the positive electrode and negative electrode slurries described above. Each positive electrode slurry shown in Table 1 was applied to a 300 μm thickness on an aluminum current collector measuring 4 cm in length and 3 cm in width to form a positive electrode active material layer, thereby fabricating a positive electrode. Each negative electrode slurry shown in Table 1 was applied to a 300 μm thickness on a copper current collector measuring 4 cm in length and 3 cm in width to form a negative electrode active material layer, thereby fabricating a negative electrode. A separator (made of polyethylene, 6 cm in length, 5 cm in width, 20 μm thick) was then placed on the negative electrode active material layer of the negative electrode in contact with the negative electrode active material layer, and the positive electrode was placed on the separator so that the positive electrode active material layer was in contact with the separator. The positive electrode and negative electrode were arranged so that the positive electrode and negative electrode were overlapping at the same position, sandwiching the separator between them. 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 group. This electrode group was sandwiched between two aluminum laminate films, three sides were heat-sealed, and the remaining side was vacuum-sealed to produce a laminated battery (non-aqueous electrolyte secondary battery body). A pressure measurement film (5 cm x 4 cm) was placed on the resulting laminated battery to cover the electrode portion, and the battery was sandwiched between two stainless steel plates (SUS plates) (6 cm long x 10 cm wide x 10 mm thick), and screws were tightened at the four corners. The battery was left in this state for 3 minutes. The screws were then loosened to remove the pressure measurement film, and the restraining pressure applied to the electrode portion was read from the discoloration of the pressure measurement film at the restraining portion using a pressure image analysis system (FPD-8010J (trade name), manufactured by Fujifilm Corporation). Next, the loosened screws were retightened to obtain a nonaqueous electrolyte secondary battery in which the nonaqueous electrolyte secondary battery body was constrained at the constraining pressure shown in Table 1 (see FIG. 2 ). In this way, a nonaqueous electrolyte secondary battery was produced in which pressure was applied to the nonaqueous electrolyte secondary battery body in the stacking direction by the constraining jig including the SUS plate. The obtained nonaqueous electrolyte secondary battery was charged and discharged under the following charge and discharge conditions to complete battery initialization. <Charge and discharge conditions for initialization> (Temperature) 25°C (Charge conditions) Constant current-constant voltage (CC-CV) charge: Current value 10 mA, upper limit voltage 3.6 V, end current value 0.5 mA (Discharge conditions) Constant current (CC) discharge: Current value 10 mA, end voltage 2.0 V

[0089] [Battery Performance (Energy Density)] The above-described initialized non-aqueous electrolyte secondary battery was charged and discharged under the following conditions, and the discharge energy (Wh) was calculated from the discharge capacity (Ah) and average voltage (V). In addition, the total thickness (m) of the laminate consisting of the positive electrode current collector, the positive electrode active material layer, the separator, the negative electrode active material layer, and the negative electrode current collector, and the area (m) of the positive electrode active material layer were also calculated. ２ ) and calculated the volume (L) of the laminate (power generating element). The volume energy density was calculated as (discharge energy (Wh)) / (volume (L) of the power generating element). The obtained volume energy density was evaluated according to the following evaluation criteria. It is known that when a lithium ion secondary battery is discharged at a high rate, the output is generally significantly reduced compared to when it is discharged at a low rate. In order to understand the initial performance, in this evaluation, the battery was discharged at a high rate (50 mA, 0.5 C). <Charge and discharge conditions at 0.5C> (Temperature) 25°C (Charge conditions) CC-CV charge: Current value 10mA, upper limit voltage 3.6V, final current value 0.5mA (Discharge conditions) CC discharge: Current value 50mA, final voltage 2.0V - Evaluation criteria - A: 380Wh / L or more B: 370Wh / L or more, less than 380Wh / L C: 360Wh / L or more, less than 370Wh / L D: 350Wh / L or more, less than 360Wh / L E: Less than 350Wh / L

[0090] [Battery Performance (Cycle Characteristics)] The nonaqueous electrolyte secondary batteries were subjected to charge / discharge measurements under the following conditions to evaluate their cycle characteristics at 45°C. The initial discharge capacity at 25°C and 0.1 C was used as a reference, and the capacity retention rate was calculated from the discharge capacity at 25°C and 0.1 C after 200 cycles of charge / discharge at 45°C. Specifically, each initialized nonaqueous electrolyte secondary battery was charged / discharged under the following <charge / discharge conditions at 25°C and 0.1 C>, and the discharge capacity during this discharge was taken as the initial discharge capacity at 25°C and 0.1 C. Furthermore, 200 cycles of charge / discharge were performed under the following <cycle charge / discharge conditions at 45°C>. After this cycle, the battery was charged / discharged again under the following <charge / discharge conditions at 25°C and 0.1 C>, and the discharge capacity after this discharge was measured. The discharge capacity retention rate was calculated from the obtained discharge capacity using the following formula. The obtained discharge capacity retention rate was evaluated according to the following evaluation criteria. <Charge-discharge conditions at 25°C, 0.1C> (Temperature) 25°C (Charge conditions) CC-CV charge: Current value 10mA, upper limit voltage 3.6V, final current value 0.5mA (Discharge conditions) CC discharge: Current value 10mA, final voltage 2.0V <Cycle charge-discharge conditions at 45°C> (Temperature) 45°C (Charge conditions) CC-CV charge: Current value 10mA, upper limit voltage 3.6V, final current 0.5mA (Discharge conditions) CC discharge: Current value 10mA, final voltage 2.0V Discharge capacity retention rate (%) = 100 x (discharge capacity at 25°C, 0.1C after cycle charge-discharge at 45°C) / (initial discharge capacity at 25°C, 0.1C) - 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%

[0091]

[0092]

[0093] <Notes for Table 1> LFP1 and LFP2: LFP (LiFePO ４ ) with a carbon-based material. NMC1: The NMC (LiNi) prepared above １／３ Co １／３ Mn １／３ O ２) coated with a carbon-based material. AB: Acetylene black. ECP: Ketjen black. EL1: LiPF prepared above. ６ EL2: The electrolyte solution containing LiFSI prepared above

[0094] The secondary battery of Comparative Example 1, which had a positive electrode active material layer with a small amount of positive electrode active material and a yield stress of 1.5 kPa, had poor shape stability of the positive electrode active material layer itself, and even when the confining pressure was controlled within the range specified in the present invention, the secondary battery had low energy density and poor cycle characteristics. The secondary battery of Comparative Example 2, which had a negative electrode active material layer with a small amount of negative electrode active material and a yield stress of 1.5 kPa, also had poor shape stability of the negative electrode active material layer itself, and even when the confining pressure was controlled within the range specified in the present invention, the secondary battery had low energy density and poor cycle characteristics. The secondary batteries of Comparative Examples 3 to 5, in which the yield stress of the electrode active material layer was within the range specified in the present invention, all had good shape stability of the electrode active material layer itself. However, Comparative Examples 3 and 5, in which the confining pressure was higher than that specified in the present invention, had poor energy density and cycle characteristics, and Comparative Example 4, in which the confining pressure was lower than that specified in the present invention, also had poor energy density and cycle characteristics. The secondary batteries of Comparative Examples 6 to 9, which had a positive electrode active material layer with a small amount of positive electrode active material and a yield stress of 1.7 kPa or less, all had poor shape stability of the positive electrode active material layer itself, and even when the confining pressure was controlled within the range specified in the present invention, the secondary batteries had low energy density and poor cycle characteristics, similar to Comparative Example 1. In contrast to the results of each of the above Comparative Examples, the secondary batteries of the present invention, in which battery bodies having positive electrode active material layers and negative electrode active material layers formed from positive electrode slurries and negative electrode slurries with a yield stress of 2 kPa or more were confined at a confining pressure of 2 to 48 kPa, all had excellent shape stability of the electrode active material layers, and the secondary batteries were also excellent in energy density and cycle characteristics.

[0095] Here, a comparison between Comparative Example 3 (confining pressure 50 kPa) and Comparative Example 5 (confining pressure 100 kPa, a typical confining force for secondary batteries) shows that when the confining pressure is higher than the specified value of the present invention, no positive or negative correlation is observed between battery performance and confining pressure. In contrast, as shown in Example 17 (confining pressure 46 kPa), by setting the confining pressure within the specified value of the present invention, battery performance is significantly improved. In other words, controlling the yield stress of the electrode active material layer within the specified value of the present invention and then controlling the confining pressure to 48 kPa or less as specified in the present invention has been shown to have technical significance unexpected from conventional knowledge in improving battery performance. Furthermore, the technical significance of the lower limit of the confining pressure specified in the present invention can also be seen from a comparison between Example 22 and Comparative Example 4. Furthermore, with regard to yield stress, Example 9 (yield stress of the positive electrode active material layer: 3 kPa) and Example 8 (yield stress of the positive electrode active material layer: 5 kPa) show comparable results in both shape stability and battery performance. However, increasing the yield stress to Example 7 (yield stress of the positive electrode active material layer: 7 kPa) significantly improves shape stability and energy density. It can also be seen that secondary batteries satisfying the specifications of the present invention can achieve sufficiently high energy density even with a small amount of positive electrode active material (e.g., comparison with Examples 1 to 3). Comparisons between Example 26 and Comparative Example 6 (both using LFP2 as the positive electrode active material), Example 27 and Comparative Example 7 (both using NMC1 as the positive electrode active material), Example 28 and Comparative Example 8 (both using ECP as the conductive additive), and Example 29 and Comparative Example 9 (both using EL2 as the electrolyte) show that shape stability and battery performance are significantly improved when the specifications of the present invention are met, even when the types of positive electrode active material, conductive additive, and electrolyte are changed.

[0096] 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.

[0097] This application claims priority based on Japanese Patent Application No. 2024-012715, filed on January 31, 2024, the contents of which are incorporated herein by reference as part of the present specification.

[0098] 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) 100 Non-aqueous electrolyte secondary battery 101 Non-aqueous electrolyte secondary battery body 101a, 101b Tab 102 Holding jig 103 Screw

Claims

1. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte secondary battery body and a restraining jig, wherein the non-aqueous electrolyte secondary battery body has a layered structure in which a positive electrode active material layer containing a positive electrode active material, a conductive additive, and an electrolyte, a separator, and a negative electrode active material layer containing a negative electrode active material, a conductive additive, and an electrolyte are layered in this order, and a restraining pressure is applied to the non-aqueous electrolyte secondary battery body by the restraining jig in the stacking direction of the layered structure, and the positive electrode active material layer has a yield stress of 2 kPa or more, the negative electrode active material layer has a yield stress of 2 kPa or more, and the restraining pressure is 2 to 48 kPa.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material layer has a yield stress of 2 to 30 kPa.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material layer has a yield stress of 2 to 20 kPa.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material layer has a yield stress of 2 to 65 kPa.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material layer has a yield stress of 2 to 55 kPa.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the restraining pressure applied by the restraining jig is 15 to 40 kPa.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of said positive electrode active material in said positive electrode active material layer is 70 mass % or more.

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of said positive electrode active material in said positive electrode active material layer is 70 to 85 mass %.

9. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of said negative electrode active material in said negative electrode active material layer is 60 mass % or more.

10. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of said negative electrode active material in said negative electrode active material layer is 60 to 75 mass %.

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