Non-aqueous secondary battery and manufacturing method thereof

Abstract

To provide a non-aqueous secondary battery that suppresses deterioration of a positive electrode and a manufacturing method for the non-aqueous secondary battery.SOLUTION: A non-aqueous secondary battery includes a positive electrode sheet 21, a negative electrode sheet 24, and a non-aqueous electrolyte. A positive electrode mixture layer 23 constituting the positive electrode sheet 21 includes a positive electrode active material, a fibrous conductive material, a hydroxy NMP, and a positive electrode binder. The amount of hydroxy NMP present per surface area of the positive electrode active material is 0.0026 μg / cm2 or more and 0.0150 μg / cm2 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous secondary battery and a method for manufacturing a non-aqueous secondary battery. [Background technology]

[0002] The nonaqueous secondary battery includes an electrode assembly in which a positive electrode sheet and a negative electrode sheet are laminated with a separator interposed therebetween, and an electrolyte. The positive electrode sheet is formed by coating a positive electrode substrate with a positive electrode mixture containing a positive electrode active material. The positive electrode mixture of the nonaqueous secondary battery described in Patent Document 1 contains a positive electrode active material, a binder, a fibrous conductive material, a nonionic polymer dispersant, lithium hydroxide, and at least one additive selected from a lithium salt of a weak acid as a conductive material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-163626 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in nonaqueous secondary batteries that contain a fibrous carbon material in the positive electrode composite, a small amount of fibrous conductive material is required, which increases the side reaction between the positive electrode active material and the electrolyte when the nonaqueous secondary battery is energized, and HF generated as a by-product may accelerate deterioration of the positive electrode. [Means for solving the problem]

[0005] The nonaqueous secondary battery that solves the above-mentioned problems is a nonaqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a nonaqueous electrolyte, wherein the positive electrode mixture that constitutes the positive electrode sheet contains a positive electrode active material, a fibrous conductive material, a hydroxy NMP, and a positive electrode binder, and the amount of the hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0026 μg / cm 2 More than 0.0150μg / cm 2 The following is the result.

[0006] According to the above configuration, the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0026 μg / cm 2 More than 0.0150μg / cm 2 Since the fibrous conductive material contains hydroxy NMP, which is described below, it is possible to react the acid generated in the decomposition reaction of the non-aqueous electrolyte with the hydroxy NMP. Therefore, by including the fibrous conductive material, it is possible to improve the capacity and input / output while suppressing deterioration of the positive electrode due to the acid generated in the decomposition reaction of the non-aqueous electrolyte.

[0007] In the nonaqueous secondary battery, it is preferable that the average fiber length of the fibrous conductive material is 100 nm or more and 1000 nm or less, and the proportion of the fibrous conductive material contained in the positive electrode mixture is 0.5 wt % or more and 1.0 wt % or less.

[0008] According to the above configuration, the average fiber length of the fibrous conductive material is 100 nm or more and 1000 nm or less, thereby suppressing thickening of the positive electrode composite due to re-aggregation of the fibrous conductive material. Since the proportion of the fibrous conductive material in the positive electrode composite is 0.5 wt% or more and 1.0 wt% or less, a decrease in the proportion of the positive electrode active material due to a high content of conductive material is suppressed, thereby ensuring capacity. Therefore, productivity and battery performance can be achieved at the same time.

[0009] In the nonaqueous secondary battery, the specific surface area of ​​the positive electrode active material is 1.7 m 2 / g or more 2.5m 2 / g or less is preferable. According to the above configuration, the specific surface area of ​​the positive electrode active material is 1.7 m 2 / g or more 2.5m 2 / g or less, deterioration due to side reactions between the positive electrode active material and the non-aqueous electrolyte can be suppressed, while the reaction area can be secured and an increase in reaction resistance due to a decrease in the reaction area can be suppressed.

[0010] A method for manufacturing a nonaqueous secondary battery that solves the above-described problems is a method for manufacturing a nonaqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a nonaqueous electrolyte, wherein the positive electrode composite that constitutes the positive electrode sheet includes a positive electrode active material, a fibrous conductive material, a hydroxy NMP, and a positive electrode binder, and the proportion of the hydroxy NMP contained in the NMP solvent is 215 ppm or more and 1300 ppm or less, and a paste of the positive electrode composite that has been liquefied by the solvent is applied to a positive electrode substrate that constitutes the positive electrode sheet and then dried.

[0011] According to the above method, since the NMP solvent contains hydroxy NMP at a ratio of 215 ppm to 1300 ppm, the hydroxy NMP can react with the acid generated in the decomposition reaction of the non-aqueous electrolyte, thereby improving the capacity and input / output of the fibrous conductive material and suppressing deterioration of the positive electrode due to the acid generated in the decomposition reaction of the non-aqueous electrolyte.

[0012] In the method for manufacturing the nonaqueous secondary battery, it is preferable that the average fiber length of the fibrous conductive material is 100 nm or more and 1000 nm or less, and the proportion of the fibrous conductive material contained in the positive electrode mixture is 0.5 wt% or more and 1.0 wt% or less.

[0013] According to the above method, the average fiber length of the fibrous conductive material is 100 nm or more and 1000 nm or less, thereby suppressing thickening of the positive electrode composite due to re-aggregation of the fibrous conductive material. Since the proportion of the fibrous conductive material in the positive electrode composite is 0.5 wt% or more and 1.0 wt% or less, a decrease in the proportion of the positive electrode active material due to a high content of conductive material is suppressed, thereby ensuring capacity. Therefore, productivity and battery performance can be achieved at the same time.

[0014] In the method for producing the nonaqueous secondary battery, the specific surface area of ​​the positive electrode active material is 1.7 m 2 / g or more 2.5m 2 / g or less is preferable. According to the above method, the specific surface area of ​​the positive electrode active material is 1.7 m 2 / g or more 2.5m 2 / g or less, deterioration due to side reactions between the positive electrode active material and the non-aqueous electrolyte can be suppressed, while the reaction area can be secured and an increase in reaction resistance due to a decrease in the reaction area can be suppressed. [Effects of the Invention]

[0015] According to the present invention, by including a fibrous conductive material, it is possible to improve the capacity and input / output while suppressing deterioration of the positive electrode. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a perspective view showing a schematic configuration of a cell battery of an embodiment of a nonaqueous secondary battery. [Figure 2] FIG. 2 is a view showing a part of the electrode body of the embodiment in an expanded state. [Figure 3] FIG. 1 shows an NMR spectrum of a positive electrode mixture containing no hydroxy-NMP. [Figure 4] FIG. 1 is a model diagram of a positive electrode active material that does not contain hydroxy NMP. [Figure 5] FIG. 1 is a model diagram of a positive electrode active material that does not contain hydroxy NMP. [Figure 6] FIG. 2 is a diagram showing an NMR spectrum of a positive electrode composite material containing hydroxy NMP according to the same embodiment. [Figure 7] FIG. 2 is a model diagram of a positive electrode active material containing hydroxy NMP according to the embodiment. [Figure 8] FIG. 2 is a model diagram of a positive electrode active material containing hydroxy NMP according to the embodiment. [Figure 9] 1 is a graph showing the relationship between the amount of hydroxy NMP and the rate of deterioration. [Figure 10] 1 is a graph showing the relationship between the amount of hydroxy NMP and the rate of deterioration. [Figure 11] 1 is a table showing examples and comparative examples of nonaqueous secondary batteries. DETAILED DESCRIPTION OF THE INVENTION

[0017] [Present embodiment] An embodiment of a nonaqueous secondary battery and a method for manufacturing a nonaqueous secondary battery will be described below with reference to Figures 1 to 8. As an example of a nonaqueous secondary battery, a lithium ion secondary battery will be described.

[0018] [Lithium-ion secondary battery 10] As shown in Figure 1, a lithium-ion secondary battery 10 is a cell battery that is combined with a plurality of lithium-ion secondary batteries 10 and sealed in a resin or metal case to form a battery pack. The battery pack is used in hybrid vehicles and electric vehicles.

[0019] The lithium-ion secondary battery 10 includes a battery case 11 and a lid 12. The battery case 11 has a rectangular parallelepiped shape with an opening on the upper side. The lid 12 seals the opening of the battery case 11. The battery case 11 and the lid 12 are made of a metal such as aluminum or an aluminum alloy. The lithium-ion secondary battery 10 forms a sealed battery container by attaching the lid 12 to the battery case 11.

[0020] The lid 12 is provided with two external terminals, a positive electrode terminal 13A and a negative electrode terminal 13B. The positive electrode external terminal 13A and the negative electrode external terminal 13B are used for charging and discharging power. An electrode assembly 20 is housed inside the battery case 11. An inserting film (not shown) is inserted between the battery case 11 and the electrode assembly 20. The positive electrode side current collector 20A, which is the end of the electrode assembly 20 on the positive electrode side, is electrically connected to the positive electrode external terminal 13A via a positive electrode side current collector 14A. The negative electrode side current collector 20B, which is the end of the electrode assembly 20 on the negative electrode side, is electrically connected to the negative electrode external terminal 13B via a negative electrode side current collector 14B. A nonaqueous electrolyte is injected into the battery case 11 through an inlet (not shown). The shapes of the positive electrode external terminal 13A and the negative electrode external terminal 13B are not limited to those shown in FIG. 1 and may be any shape.

[0021] [Electrode body 20] 2, the electrode assembly 20 is a flat wound body obtained by winding a laminate in which a long positive electrode sheet 21 and a negative electrode sheet 24 are stacked with a separator 27 interposed therebetween. The positive electrode sheet 21, the negative electrode sheet 24, and the separator 27 are stacked so that their respective longitudinal directions coincide with the longitudinal direction D1. In the laminate before winding, the positive electrode sheet 21, the separator 27, the negative electrode sheet 24, and the separator 27 are stacked in this order.

[0022] [Positive electrode sheet 21] The positive electrode sheet 21 includes a positive electrode current collector 22 and a positive electrode composite layer 23. The positive electrode current collector 22 is a foil-like positive electrode base material formed in a long shape. The positive electrode composite layer 23 is provided on each of two opposing surfaces of the positive electrode current collector 22. The positive electrode current collector 22 includes, at one end in the width direction D2, a positive electrode-side uncoated portion 22A where the positive electrode composite layer 23 is not formed and the positive electrode current collector 22 is exposed.

[0023] A metal foil made of aluminum or an alloy containing aluminum as a main component is used for the positive electrode current collector 22. The positive electrode current collector 22 functions as a current collector for the positive electrode. In the wound state, the positive electrode-side uncoated portion 22A of the positive electrode current collector 22 has opposing surfaces that are pressed against each other to form the positive electrode-side current collecting portion 20A.

[0024] The positive electrode mixture layer 23 is a hardened product of a liquid positive electrode mixture paste. The positive electrode mixture paste includes a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. The positive electrode mixture layer 23 is formed by drying the positive electrode mixture paste and evaporating the positive electrode solvent. Therefore, the positive electrode mixture layer 23 includes a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0025] The positive electrode active material is a lithium-containing composite oxide capable of absorbing and releasing lithium ions, which are charge carriers in the lithium-ion secondary battery 10. The lithium-containing composite oxide is an oxide containing lithium and a metal element other than lithium. The metal element other than lithium is at least one selected from the group consisting of, for example, nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained in the lithium-containing composite oxide as iron phosphate.

[0026] For example, the lithium-containing composite oxide is lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or lithium manganese oxide (LiMn2O4). For example, the lithium-containing composite oxide is a ternary lithium-containing composite oxide containing nickel, cobalt, and manganese, such as lithium nickel cobalt manganese oxide (LiNiCoMnO2). For example, the lithium-containing composite oxide is lithium iron phosphate (LiFePO4).

[0027] The positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent. The positive electrode solvent NMP contains hydroxy NMP. The ratio of hydroxy NMP contained in the NMP solvent is 215 ppm or more and 1300 ppm or less. The positive electrode conductive material contains a fibrous conductive material. For example, carbon nanotubes are used as the fibrous conductive material. The positive electrode binder is an example of a resin component contained in the positive electrode mixture paste. For example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), etc. are used as the positive electrode binder.

[0028] In the positive electrode mixture layer 23 in which the positive electrode mixture paste is dried and the positive electrode solvent is evaporated, the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2 ] is as follows.

[0029] The positive electrode sheet 21 may have an insulating layer at the boundary between the positive electrode uncoated portion 22A and the positive electrode composite layer 23. The insulating layer contains an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0030] [Negative electrode sheet 24] The negative electrode sheet 24 includes a negative electrode current collector 25 and a negative electrode composite layer 26. The negative electrode current collector 25 is a foil-like negative electrode base material formed in a long strip. The negative electrode composite layer 26 is provided on each of two opposing surfaces of the negative electrode current collector 25. The negative electrode current collector 25 includes a negative electrode-side uncoated portion 25A at one end in the width direction D2, opposite the positive electrode-side uncoated portion 22A, where the negative electrode composite layer 26 is not formed and the negative electrode current collector 25 is exposed.

[0031] A metal foil made of copper or an alloy mainly containing copper is used for the negative electrode current collector 25. The negative electrode current collector 25 functions as a current collector for the negative electrode. When the negative electrode uncoated portion 25A is wound, opposing surfaces of the negative electrode uncoated portion 25A are pressed against each other to form the negative electrode current collector 20B.

[0032] The negative electrode mixture layer 26 is a hardened product of a liquid negative electrode mixture paste. The negative electrode mixture paste includes a negative electrode active material, a negative electrode solvent, a negative electrode thickener, and a negative electrode binder. The negative electrode mixture layer 26 is formed by drying the negative electrode mixture paste and evaporating the negative electrode solvent. Therefore, the negative electrode mixture layer 26 includes the negative electrode active material, and further includes a negative electrode thickener and a negative electrode binder as additives. The negative electrode mixture layer 26 may further include an additive such as a conductive material.

[0033] The negative electrode active material is a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, graphitizable carbon, and carbon nanotubes. One example of the negative electrode solvent is water. One example of the negative electrode thickener is CMC (carboxymethyl cellulose), which contains a sodium salt. One example of the negative electrode binder is the same as the positive electrode binder. One example of the negative electrode binder is SAR (styrene-acrylic acid copolymer), which contains a sodium salt.

[0034] [Separator 27] The separator 27 prevents contact between the positive electrode sheet 21 and the negative electrode sheet 24, and also holds the nonaqueous electrolyte between the positive electrode sheet 21 and the negative electrode sheet 24. When the electrode assembly 20 is immersed in the nonaqueous electrolyte, the nonaqueous electrolyte permeates from the ends of the separator 27 in the width direction D2 toward the center.

[0035] The separator 27 is a nonwoven fabric made of polypropylene, etc. Examples of the separator 27 that can be used include porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, and ion-conductive polymer electrolyte membranes.

[0036] [Nonaqueous electrolyte] The nonaqueous electrolyte is a composition containing a supporting salt in a nonaqueous solvent. The nonaqueous solvent may be one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. The supporting salt may be one or more lithium compounds (lithium salts) selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, LiBOB (lithium bis(oxalatoborate)), etc.

[0037] In this embodiment, ethylene carbonate is used as the nonaqueous solvent. LiBOB is added to the nonaqueous electrolyte as a lithium salt of the film-forming agent. For example, LiBOB is added to the nonaqueous electrolyte so that the concentration of LiBOB in the nonaqueous electrolyte is 0.001 mol / L or more and 0.1 mol / L or less.

[0038] Here, a case where the positive electrode solvent does not contain hydroxy NMP will be described. Figure 3 shows the NMR spectrum in the absence of hydroxy-NMP. In the absence of hydroxy-NMP, the chemical shifts in the range of 1.1 ppm to 1.6 ppm, indicated by the dashed line, are not obtained.

[0039] 4 shows a state in which fibrous conductive material 32 is present on the surface of positive electrode active material 31 in the positive electrode mixture layer constituting the positive electrode sheet, but hydroxy NMP is not present. Fibrous conductive material 32 adheres to the surface of positive electrode active material 31 and connects the positive electrode active material 31 between adjacent pieces of positive electrode active material 31.

[0040] As shown in Figure 5, when a non-aqueous secondary battery is energized and the non-aqueous electrolyte decomposes, acid is generated. When this acid reacts with the positive electrode active material 31, a deteriorated layer is formed on the surface of the positive electrode sheet. For example, if the acid generated by the decomposition of the non-aqueous electrolyte is hydrofluoric acid (HF) and the positive electrode active material 31 is lithium nickel oxide (LiNiO), the decomposition reaction shown in the following formula (1) occurs. NiO in formula (1) is the deteriorated layer. HF+LiNiO2→LiF+NiO+0.5H2+0.5O2···(1)

[0041] Next, the case where the positive electrode solvent contains hydroxy NMP will be described. Figure 6 shows the NMR spectrum in the presence of hydroxy-NMP, where chemical shifts are observed in the range of 1.0 ppm to 1.6 ppm, as indicated by the dashed line.

[0042] 7 shows a state in which fibrous conductive material 32 and hydroxy NMP 33 are present on the surface of positive electrode active material 31 in the positive electrode composite layer that constitutes the positive electrode sheet. Fibrous conductive material 32 adheres to the surface of positive electrode active material 31 and connects the positive electrode active material 31 together. Hydroxy NMP 33 adheres to the surface of positive electrode active material 31.

[0043] As shown in Figure 8, when a non-aqueous secondary battery is energized and the non-aqueous electrolyte decomposes, an acid is generated. This acid reacts with hydroxy NMP, which can prevent a deterioration layer from forming on the surface of the positive electrode sheet. For example, if the acid generated by the decomposition of the non-aqueous electrolyte is hydrofluoric acid (HF) and the hydroxy group is represented as R-OH, the decomposition reaction shown in the following formula (2) occurs. HF+R-OH→R-F+H2O (2)

[0044] [Manufacturing method] Next, a method for manufacturing the lithium ion secondary battery 10 will be described. A method for manufacturing the positive electrode sheet 21 will be described.

[0045] The method for manufacturing lithium-ion secondary battery 10 includes a coating step of coating a positive electrode mixture paste onto positive electrode current collector 22 and a drying step of drying the positive electrode mixture paste. The positive electrode mixture paste includes a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. In the drying step, the positive electrode mixture paste is dried and the positive electrode solvent is evaporated, thereby forming positive electrode mixture layer 23.

[0046] 7, the positive electrode composite layer constituting the positive electrode sheet contains positive electrode active material 31, fibrous conductive material 32, and hydroxy NMP 33. Fibrous conductive material 32 and hydroxy NMP 33 are attached to the surface of positive electrode active material 31.

[0047] The average fiber length of the fibrous conductive material is 100 nm or more and 1000 nm or less. If the average fiber length of the fibrous conductive material is shorter than 100 nm, sufficient conductivity cannot be obtained. If the average fiber length of the fibrous conductive material is longer than 1000 nm, the fibrous conductive material will aggregate due to intermolecular forces and hydrogen bonds between the fibrous conductive material, making it difficult to ensure sufficient conductivity.

[0048] The proportion of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 wt% or more and 1.0 wt% or less. If the proportion of the fibrous conductive material contained in the positive electrode mixture layer 23 is less than 0.5 wt%, reaction resistance is ensured, but the active surface of the positive electrode active material is exposed to a large extent, and the effect of suppressing deterioration is not sufficiently obtained. If the proportion of the fibrous conductive material contained in the positive electrode mixture layer 23 is more than 1.0 wt%, deterioration is suppressed by the coating, but the reaction area is reduced, and sufficient input and output are not obtained.

[0049] The specific surface area of ​​the positive electrode active material is 1.7 m 2 / g] or more 2.5[m 2 / g] or less. The specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g], sufficient input and output cannot be obtained due to an increase in reaction resistance caused by a decrease in the reaction area. 2 / g], deterioration due to side reactions cannot be suppressed sufficiently, and a sufficient effect cannot be obtained. Preferably, the specific surface area of ​​the positive electrode active material is 2.0 [m 2 / g] or more 2.4[m 2 / g or less.

[0050] The average fiber length of the fibrous conductive material 32 is determined as follows: The positive electrode composite paste is centrifuged, and the positive electrode active material 31 is precipitated. The supernatant is recovered and further diluted. The fibrous conductive material 32 contained in the diluted supernatant is dispersed, and SEM images of the fibrous conductive material 32 are obtained at multiple locations. Each of the fibrous conductive material 32 contained in the SEM images is traced, and their lengths are quantified by image analysis. Therefore, measurement is possible even if the fibrous conductive material 32 is bent. The parameter for calculating the average is the average number of traced fibrous conductive material 32. Note that when determining the fiber length from a stock solution of the fibrous conductive material 32, the stock solution of the fibrous conductive material 32 is diluted, and SEM images of the fibrous conductive material 32 contained in the stock solution are obtained at multiple locations, and measurement is performed in the same manner as above. Furthermore, to determine the fiber length of the fibrous conductive material 32 contained in the positive electrode composite, the positive electrode composite is dissolved in a solvent such as NMP, the dissolved positive electrode composite is centrifuged, and the positive electrode active material precipitates. The supernatant is then recovered and further diluted. The fibrous conductive material 32 contained in the diluted supernatant is dispersed, and SEM images of the fibrous conductive material 32 are obtained at multiple locations and measured in the same manner as above. For example, the centrifugation is performed at a rotation speed of 15,000 rpm, a centrifugal force of 21,500 g, and a processing time of 10 min. If the fibrous conductive material 32 is not easily broken, the average fiber length of the fibrous conductive material 32 will be the same whether it is measured using the original solution of the fibrous conductive material 32, the positive electrode composite paste, or the positive electrode composite.

[0051] As shown in Figure 9, when hydroxy NMP is added to the NMP solvent, the degradation rate decreases. In particular, when the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0100 [μg / cm 2 If the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is small, the deterioration rate is not sufficiently suppressed.

[0052] 10, when hydroxy NMP is added to the NMP solvent, the reaction resistance increases in proportion to the amount of hydroxy NMP present per unit surface area of ​​the positive electrode active material. That is, if the amount of hydroxy NMP present per unit surface area of ​​the positive electrode active material is large, the desorption and insertion of Li from and into the surface of the positive electrode active material is inhibited, thereby increasing the reaction resistance.

[0053] Therefore, the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2

[0043] or less. That is, the amount of hydroxy NMP present in the NMP solvent is desirably within a range that satisfies the degradation rate of less than 90% and the reaction resistance of less than 110%. Therefore, by including a fibrous conductive material in the positive electrode mixture layer, it is possible to improve the capacity and input / output while suppressing the degradation of the positive electrode due to the acid generated in the decomposition reaction of the nonaqueous electrolyte.

[0054] Next, the effects of this embodiment will be described. (1) The amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2 Since the hydroxy NMP contains hydroxy NMP having a molecular weight of 100 or less, the acid generated in the decomposition reaction of the non-aqueous electrolyte can react with the hydroxy NMP. Therefore, by including the fibrous conductive material, the capacity and input / output can be improved, while deterioration of the positive electrode due to the acid generated in the decomposition reaction of the non-aqueous electrolyte can be suppressed.

[0055] (2) Because the average fiber length of the fibrous conductive material is 100 nm or more and 1,000 nm or less, thickening of the positive electrode composite due to re-aggregation of the fibrous conductive material can be suppressed. Because the proportion of the fibrous conductive material contained in the positive electrode composite is 0.5 wt% or more and 1.0 wt% or less, a decrease in the proportion of the positive electrode active material due to a high content of conductive material can be suppressed, thereby ensuring capacity. Therefore, productivity and battery performance can be achieved at the same time.

[0056] (3) The specific surface area of ​​the positive electrode active material is 1.7 m 2 / g] or more 2.5[m 2 / g] or less, deterioration due to side reactions between the positive electrode active material and the non-aqueous electrolyte can be suppressed, while the reaction area can be secured and an increase in reaction resistance due to a decrease in the reaction area can be suppressed.

[0057] (4) The hydroxy NMP solvent contains hydroxy NMP at a ratio of 215 ppm to 1300 ppm, which allows the hydroxy NMP to react with the acid generated during the decomposition reaction of the non-aqueous electrolyte. This improves the capacity and input / output performance of the fibrous conductive material, while suppressing deterioration of the positive electrode due to the acid generated during the decomposition reaction of the non-aqueous electrolyte.

[0058] [Other embodiments] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0059] In the above embodiment, carbon nanotubes are used as the fibrous conductive material 32. However, carbon nanofibers may also be used as the fibrous conductive material 32. In the above embodiment, the electrode body 20 is a wound body obtained by winding a laminate in which a positive electrode sheet 21 and a negative electrode sheet 24 are stacked with a separator 27 interposed therebetween. However, the electrode body may also be a laminate in which a plurality of positive electrode sheets 21 and a plurality of negative electrode sheets 24 are alternately stacked with a separator 27 interposed therebetween.

[0060] The lithium-ion secondary battery 10 may be installed in an automatic transport vehicle, a special-purpose vehicle for loading and unloading, an electric vehicle, a hybrid vehicle, a computer, or other electronic device, or may be part of other systems. For example, it may be installed in a moving object such as a ship or an aircraft, or it may be a power supply system that supplies power from a power plant via a substation to a building or home where a secondary battery is installed.

[0061] [Example] Next, examples and comparative examples of the lithium ion secondary battery 10 will be described with reference to Fig. 11. Note that these examples and comparative examples do not limit the nonaqueous secondary battery and the method for manufacturing the nonaqueous secondary battery.

[0062] As shown in Fig. 11, lithium ion secondary batteries 10 were prepared in examples and comparative examples in which the ratio of fibrous conductive material (CNT) 32 contained in the positive electrode composite, the specific surface area of ​​the positive electrode active material, the ratio of hydroxy NMP contained in NMP, and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material were changed. The degradation rate and reaction resistance were evaluated for each example and comparative example.

[0063] [Comparative Example 1] The ratio of fibrous conductive material contained in the positive electrode mixture is 0.4 wt%, and the specific surface area of ​​the positive electrode active material is 2.1 m 2 / g], the proportion of hydroxy NMP contained in NMP is 1294 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0155 [μg / cm 2 ].

[0064] Comparative Example 2 The ratio of fibrous conductive material contained in the positive electrode mixture is 1.2 wt%, and the specific surface area of ​​the positive electrode active material is 2.1 m 2 / g], the proportion of hydroxy NMP contained in NMP is 0 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0000 [μg / cm 2 ].

[0065] Comparative Example 3 The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 wt%, and the specific surface area of ​​the positive electrode active material is 2.0 m 2 / g], the proportion of hydroxy NMP contained in NMP is 0 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0000 [μg / cm 2 ].

[0066] Comparative Example 4 The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 wt%, and the specific surface area of ​​the positive electrode active material is 2.4 m 2 / g], the proportion of hydroxy NMP contained in NMP is 108 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0011 [μg / cm 2 ].

[0067] Comparative Example 5 The ratio of fibrous conductive material contained in the positive electrode mixture is 0.9 wt%, and the specific surface area of ​​the positive electrode active material is 2.4 m 2 / g], the proportion of hydroxy NMP contained in NMP is 1359 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0143 [μg / cm 2 ].

[0068] Comparative Example 6 The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 [wt%], and the specific surface area of ​​the positive electrode active material is 1.8 [m 2 / g], the proportion of hydroxy NMP contained in NMP is 1186 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0166 [μg / cm 2 ].

[0069] Comparative Example 7 The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 [wt%], and the specific surface area of ​​the positive electrode active material is 2.2 [m 2 / g], the proportion of hydroxy NMP contained in NMP is 205 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0023 [μg / cm 2 ].

[0070] [Comparative Example 8] The ratio of fibrous conductive material contained in the positive electrode mixture is 0.4 wt%, and the specific surface area of ​​the positive electrode active material is 2.0 m 2 / g], the proportion of hydroxy NMP contained in NMP is 431 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0054 [μg / cm 2 ].

[0071] Comparative Example 9 The ratio of fibrous conductive material contained in the positive electrode mixture is 1.5 wt%, and the specific surface area of ​​the positive electrode active material is 2.0 m 2 / g], the proportion of hydroxy NMP contained in NMP is 410 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0052 [μg / cm 2 ].

[0072] [Comparative Example 10] The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 [wt%], and the specific surface area of ​​the positive electrode active material is 1.6 [m 2 / g], the proportion of hydroxy NMP contained in NMP is 431 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0068 [μg / cm 2 ].

[0073] [Example 1] The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 wt%, and the specific surface area of ​​the positive electrode active material is 2.1 m 2 / g], the proportion of hydroxy NMP contained in NMP is 216 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0026 [μg / cm 2 ].

[0074] [Example 2] The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 wt%, and the specific surface area of ​​the positive electrode active material is 2.3 m 2 / g], the proportion of hydroxy NMP contained in NMP is 647 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0071 [μg / cm 2 ].

[0075] [Example 3] The ratio of fibrous conductive material contained in the positive electrode mixture is 0.8 [wt%], and the specific surface area of ​​the positive electrode active material is 2.2 [m 2 / g], the proportion of hydroxy NMP contained in NMP is 1294 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0148 [μg / cm 2 ].

[0076] [Example 4] The ratio of fibrous conductive material contained in the positive electrode mixture is 0.5 wt%, and the specific surface area of ​​the positive electrode active material is 2.1 m 2 / g], the proportion of hydroxy NMP contained in NMP is 647 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0078 [μg / cm 2 ].

[0077] [Example 5] The ratio of fibrous conductive material contained in the positive electrode mixture is 1.0 [wt%], and the specific surface area of ​​the positive electrode active material is 2.1 [m 2 / g], the proportion of hydroxy NMP contained in NMP is 647 [ppm], and the amount of hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0078 [μg / cm 2 ].

[0078] [evaluation] The degradation rate and reaction resistance were evaluated for each of the above examples and comparative examples. The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 [wt %] or more and 1.0 [wt %] or less, and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less, and Comparative Example 3, in which the NMP does not contain hydroxy NMP, is used as a comparison standard for the degradation rate and reaction resistance.

[0079] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is less than 0.5 wt %, and the specific surface area of ​​the positive electrode active material is 1.7 m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is 215 [ppm] or more and 1300 [ppm] or less, and the amount of hydroxy NMP present in NMP is 0.0150 [μg / cm 2 In Comparative Example 1, where the amount of ZnO is greater than 1, the deterioration rate is slightly reduced, and the reaction resistance is unchanged.

[0080] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is more than 1.0 [wt %], and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less and in Comparative Example 2 where the NMP does not contain hydroxy NMP, the degradation rate is slightly reduced and the reaction resistance increases to 115[%].

[0081] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 [wt %] or more and 1.0 [wt %] or less, and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is less than 215 [ppm], and the amount of hydroxy NMP present in NMP is 0.0026 [μg / cm 2 In Comparative Example 4, where the difference is less than 1 / 2, the deterioration rate is slightly reduced and the reaction resistance remains almost unchanged.

[0082] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 [wt %] or more and 1.0 [wt %] or less, and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is more than 1300 [ppm], and the amount of hydroxy NMP present in NMP is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2 In Comparative Example 5, where the temperature is 0.1 to 1.0°C, the deterioration rate is slightly reduced and the reaction resistance is almost unchanged.

[0083] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 [wt %] or more and 1.0 [wt %] or less, and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is 215 [ppm] or more and 1300 [ppm] or less, and the amount of hydroxy NMP present in NMP is 0.0150 [μg / cm 2 In Comparative Example 6, where the ratio is greater than 1, the degradation rate is slightly reduced and the reaction resistance is almost unchanged.

[0084] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 [wt %] or more and 1.0 [wt %] or less, and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is less than 215 [ppm], and the amount of hydroxy NMP present in NMP is 0.0026 [μg / cm 2 In Comparative Example 7, where the difference is less than 1 / 2, the deterioration rate is slightly reduced and the reaction resistance is almost unchanged.

[0085] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is less than 0.5 wt %, and the specific surface area of ​​the positive electrode active material is 1.7 m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is 215 [ppm] or more and 1300 [ppm] or less, and the amount of hydroxy NMP present in NMP is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2 In Comparative Example 8, where the temperature is 0.1 to 1.0°C, the deterioration rate increases and the reaction resistance decreases.

[0086] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is more than 1.0 [wt %], and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is 215 [ppm] or more and 1300 [ppm] or less, and the amount of hydroxy NMP present in NMP is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2In Comparative Example 9, where the temperature is 0.1 to 1.0°C, the deterioration rate is slightly decreased and the reaction resistance is greatly increased.

[0087] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 [wt %] or more and 1.0 [wt %] or less, and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g], the proportion of hydroxy NMP contained in NMP is 215 [ppm] or more and 1300 [ppm] or less, and the amount of hydroxy NMP present in NMP is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2 In Comparative Example 10, which is below 100%, the deterioration rate remains unchanged and the reaction resistance remains almost unchanged.

[0088] The ratio of the fibrous conductive material contained in the positive electrode mixture layer 23 is 0.5 [wt %] or more and 1.0 [wt %] or less, and the specific surface area of ​​the positive electrode active material is 1.7 [m 2 / g] or more 2.5[m 2 / g] or less, the proportion of hydroxy NMP contained in NMP is 215 [ppm] or more and 1300 [ppm] or less, and the amount of hydroxy NMP present in NMP is 0.0026 [μg / cm 2 ] or more 0.0150[μg / cm 2 In Examples 1 to 5, where the degradation rate was 80% or less, the reaction resistance was less than 115%. In Examples 1 to 5, the degradation rate was reduced and the increase in reaction resistance was suppressed, so excellent results were obtained. [Explanation of symbols]

[0089] 10...Lithium-ion secondary battery 11...Battery case 12...lid body 13A...Positive external terminal 13B…Negative external terminal 14A...Positive electrode side current collecting member 14B...Negative electrode side current collecting member 20...Electrode body 20A...Positive electrode current collector 20B...Negative electrode side current collecting part 21...Positive electrode sheet 22...Positive electrode current collector 22A: Uncoated area on the positive electrode side 23...Positive electrode mixture layer 24...Negative electrode sheet 25...Negative electrode current collector 25A...Negative electrode uncoated area 26…Negative electrode composite material layer 27...Separator 31...Cathode active material 32...Fiber conductive material 33...Hydroxy NMP

Claims

1. A non-aqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte, The positive electrode mixture constituting the positive electrode sheet includes a positive electrode active material, a fibrous conductive material, a hydroxy NMP, and a positive electrode binder, The amount of the hydroxy NMP present per surface area of ​​the positive electrode active material is 0.0026 μg / cm ２ 0.0150μg / cm or more ２ Is less than or equal to Non-aqueous secondary battery.

2. The average fiber length of the fibrous conductive material is 100 nm or more and 1000 nm or less, The ratio of the fibrous conductive material contained in the positive electrode mixture is 0.5 wt % or more and 1.0 wt % or less. The nonaqueous secondary battery according to claim 1 .

3. The specific surface area of ​​the positive electrode active material is 1.7 m ２ / g or more 2.5m ２ / g or less The nonaqueous secondary battery according to claim 1 or 2.

4. A method for manufacturing a non-aqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte solution, comprising the steps of: The positive electrode mixture constituting the positive electrode sheet includes a positive electrode active material, a fibrous conductive material, a hydroxy NMP, and a positive electrode binder, The ratio of the hydroxy NMP contained in the NMP solvent is 215 ppm or more and 1300 ppm or less, The paste of the positive electrode mixture liquefied by the solvent is applied to a positive electrode substrate constituting the positive electrode sheet and dried. A method for manufacturing a non-aqueous secondary battery.

5. The average fiber length of the fibrous conductive material is 100 nm or more and 1000 nm or less, The ratio of the fibrous conductive material contained in the positive electrode mixture is 0.5 wt % or more and 1.0 wt % or less. The method for producing the nonaqueous secondary battery according to claim 4 .

6. The specific surface area of ​​the positive electrode active material is 1.7 m ２ / g or more 2.5m ２ / g or less The method for producing the nonaqueous secondary battery according to claim 4 or 5.

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