Non-aqueous electrolyte secondary battery and method for manufacturing non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery comprises an electrode assembly comprising a plurality of positive electrodes and a plurality of negative electrodes alternately stacked one on top of the other with separators interposed therebetween, a non-aqueous electrolyte, and an outer casing for storing the electrode assembly and the non-aqueous electrolyte. The outer casing is provided with an injection port for injecting the electrolyte, and at least one of the positive electrode composite material layer of the positive electrode or the negative electrode composite material layer of the negative electrode constituting the electrode assembly has a first region distal to the injection port having a lower density than a second region proximal to the injection port.

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery and a method for manufacturing the non-aqueous electrolyte secondary battery. Background Art

[0002] Non-aqueous electrolyte secondary batteries, which include an electrode assembly comprising a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte solution, and an outer casing for housing these components, have long been known. For example, Patent Document 1 discloses a cylindrical non-aqueous electrolyte secondary battery comprising a wound electrode assembly in which a positive electrode and a negative electrode are spirally wound with a separator. In the non-aqueous electrolyte secondary battery of Patent Document 1, grooves are formed in the composite material layer of at least one of the positive electrode and the negative electrode in order to improve the permeability of the non-aqueous electrolyte solution in the electrode assembly and thereby improve the charge and discharge cycle characteristics of the battery.

[0003] Patent Document 2 discloses a cylindrical nonaqueous electrolyte secondary battery having a composite material layer of at least one of the positive and negative electrodes, and a low-density portion having a lower density than other regions formed along the axial direction of a wound electrode body. Patent Document 2 describes that providing the low-density portion in a portion of the composite material layer improves the permeability of the nonaqueous electrolyte.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-176558

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-137187 Summary of the Invention

[0008] However, for non-aqueous electrolytes, after the electrode body is housed inside the outer body, the outer body is usually injected into the outer body by a liquid injection portion provided on the outer body. However, in this case, it is an important issue to impregnate the entire electrode body with non-aqueous electrolyte. In this regard, the technology disclosed in patent documents 1 and 2 still has room for improvement. It should be noted that in the non-aqueous electrolyte secondary battery of patent document 1, the amount of active material in the composite material layer is reduced by forming a groove in the composite material layer, so there is a problem with the high capacity of the battery.

[0009] The non-aqueous electrolyte secondary battery disclosed herein is characterized in that it comprises: an electrode body formed by alternately stacking a plurality of positive electrodes and a plurality of negative electrodes one by one with the aid of separators, a non-aqueous electrolyte, and an outer body for accommodating the aforementioned electrode body and the aforementioned non-aqueous electrolyte, the aforementioned outer body being provided with an injection portion for injecting the aforementioned non-aqueous electrolyte, the aforementioned plurality of positive electrodes comprising: a positive electrode core body and a positive electrode composite material layer formed on the surface of the aforementioned positive electrode core body, the aforementioned plurality of negative electrodes comprising: a negative electrode core body and a negative electrode composite material layer formed on the surface of the aforementioned negative electrode core body, and in at least one of the aforementioned positive electrode composite material layer and the aforementioned negative electrode composite material layer, the density of a first region away from the aforementioned injection portion is lower than the density of a second region close to the aforementioned injection portion.

[0010] The manufacturing method of the non-aqueous electrolyte secondary battery disclosed in the present invention is characterized in that the non-aqueous electrolyte secondary battery includes an electrode body formed by alternately stacking a plurality of positive electrodes and a plurality of negative electrodes one by one via separators, a non-aqueous electrolyte, and an outer body. The manufacturing method includes: a step of forming the positive electrode composite material layer on the surface of the positive electrode core body to thereby produce the positive electrode; a step of forming the negative electrode composite material layer on the surface of the negative electrode core body to thereby produce the negative electrode; a step of using the plurality of positive electrodes and the plurality of negative electrodes to thereby produce the electrode body; and a step of accommodating the electrode body inside the outer body and then injecting the non-aqueous electrolyte. In the step of forming at least one of the positive electrode composite material layer and the negative electrode composite material layer, the composite material layer is formed in such a manner that the density of the region located on the first end side of the composite material layer is lower than the density of the region located on the second end side opposite to the first end side. In the step of injecting the non-aqueous electrolyte, the non-aqueous electrolyte is injected into the interior of the outer body from the second end side.

[0011] The nonaqueous electrolyte secondary battery disclosed herein allows the entire electrode body to be impregnated with the nonaqueous electrolyte when the nonaqueous electrolyte is injected into the interior of the outer casing, enabling the nonaqueous electrolyte to be evenly dispersed throughout the entire electrode body. For example, if the amount of electrolyte within the electrode body varies, the battery reaction becomes uneven, potentially leading to performance degradation. However, the nonaqueous electrolyte secondary battery disclosed herein can prevent such problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a perspective view showing the appearance of a nonaqueous electrolyte secondary battery as an example of an embodiment.

[0013] Figure 2 It is a perspective view of an electrode assembly and a sealing plate as an example of an embodiment.

[0014] Figure 3 This is an exploded perspective view of an electrode assembly as an example of an embodiment.

[0015] Figure 4 It is a cross-sectional view showing a portion of an electrode body and a front view of a positive electrode as an example of an embodiment.

[0016] Figure 5 It is a diagram for explaining a manufacturing process of a positive electrode as an example of an embodiment. DETAILED DESCRIPTION

[0017] Below, an example of an embodiment of the present disclosure is described in detail with reference to the accompanying drawings. It should be noted that it was initially envisioned that the multiple embodiments and modifications illustrated below could be selectively combined. Furthermore, in this specification, the phrase "value A to value B" means "greater than value A and less than value B," unless otherwise specified.

[0018] Figure 1 1 is a perspective view showing the appearance of a non-aqueous electrolyte secondary battery 10 as an example of an embodiment. Figure 2 It is a perspective view of the electrode body 11 and the sealing plate 15 constituting the non-aqueous electrolyte secondary battery 10 (showing a state where the outer can 14 is removed). Figure 1 The illustrated nonaqueous electrolyte secondary battery 10 includes a rectangular container including an exterior can 14 and a sealing plate 15 as an exterior body. However, the exterior body is not limited thereto and may be, for example, an exterior body composed of a laminate sheet including a metal layer and a resin layer.

[0019] like Figure 1 and Figure 2 As shown, the non-aqueous electrolyte secondary battery 10 includes an electrode body 11, a non-aqueous electrolyte solution, a bottomed cylindrical outer can 14 that contains the electrode body 11 and the non-aqueous electrolyte solution, and a sealing plate 15 that seals the opening of the outer can 14. The non-aqueous electrolyte secondary battery 10 is a so-called square battery. The electrode body 11 is a stacked type electrode body in which a plurality of positive electrodes 20 and a plurality of negative electrodes 30 are alternately stacked one by one via separators 40 (see the following for details). Figure 3 The outer can 14 is a flat, substantially rectangular metal container with one axial end open, and the sealing plate 15 has an elongated rectangular shape. The outer can 14 and the sealing plate 15 are made of a metal material mainly composed of aluminum, for example.

[0020] For convenience of explanation, the height direction of the outer can 14 is referred to as the "upper and lower directions" of the non-aqueous electrolyte secondary battery 10, the sealing plate 15 side is referred to as the "upper direction," and the bottom side of the outer can 14 is referred to as the "lower direction." Furthermore, the direction along the longitudinal direction of the sealing plate 15 is referred to as the "lateral direction" of the non-aqueous electrolyte secondary battery 10.

[0021] The non-aqueous electrolyte solution comprises, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may also contain a halogen-substituted form in which at least a portion of the hydrogen atoms in these solvents are substituted with a halogen atom such as fluorine. Examples of the electrolyte salt include lithium salts such as LiPF6.

[0022] The non-aqueous electrolyte secondary battery 10 includes a positive terminal 12 electrically connected to the positive electrode 20 via a positive electrode current collector (not shown), and a negative terminal 13 electrically connected to the negative electrode 30 via a negative electrode current collector (not shown). In this embodiment, the positive terminal 12 is disposed at one end in the longitudinal direction of the sealing plate 15, and the negative terminal 13 is disposed at the other end in the longitudinal direction of the sealing plate 15. The positive terminal 12 and the negative terminal 13 are external connection terminals for electrical connection to other non-aqueous electrolyte secondary batteries 10, circuits, devices, etc., and are attached to the sealing plate 15 via an insulating member.

[0023] The sealing plate 15 constituting the outer body is provided with an injection portion 16 for injecting a non-aqueous electrolyte into the interior of the outer can 14 that accommodates the electrode body 11. The details will be described later, but after the electrode body 11 is accommodated in the outer can 14 and the opening of the outer can 14 is sealed with the sealing plate 15, the non-aqueous electrolyte is injected by the injection portion 16. The injection portion 16 is composed of, for example, a through hole formed on the sealing plate 15 and a rubber sealing member that seals the through hole. In addition, the sealing plate 15 is provided with a gas discharge valve 17 that opens the valve to discharge gas when an abnormality occurs in the battery, and a current cut-off mechanism 18 that cuts off the current flow when an abnormality occurs.

[0024] Figure 1 In the example shown, a liquid injection portion 16 and a gas discharge valve 17 are provided between the positive electrode terminal 12 and the negative electrode terminal 13. The gas discharge valve 17 is located in the longitudinal center of the sealing plate 15, and the liquid injection portion 16 is located between the positive electrode terminal 12 and the gas discharge valve 17. A current interruption mechanism 18 is located inside the positive electrode terminal 12.

[0025] like Figure 2 As shown, the electrode body 11 is divided into a first electrode group 11A and a second electrode group 11B. The first electrode group 11A and the second electrode group 11B have, for example, the same stacking structure and size, and are stacked in the thickness direction of the electrode body 11. A plurality of positive electrode tabs 23 and a plurality of negative electrode tabs 33 extending on the side of the sealing plate 15 are formed at the upper end of each electrode group. Each tab does not form a composite material layer described later and is a convex portion exposed on the surface of the core body. The positive electrode tab 23 is electrically connected to the positive terminal 12 via the positive electrode collector, and the negative electrode tab 33 is electrically connected to the negative terminal 13 via the negative electrode collector. It should be noted that the outer peripheral surface of each electrode group is covered by a separator 40.

[0026] Figure 3 FIG is an exploded perspective view of the electrode body 11. Figure 3 As shown, the electrode assembly 11 includes a plurality of positive electrodes 20 and a plurality of negative electrodes 30. Each electrode group constituting the electrode assembly 11 includes, for example, one more negative electrode 30 than positive electrode 20, and the negative electrodes 30 are arranged on both sides in the thickness direction of each electrode group. Figure 3 , a plurality of separators 40 are shown arranged one by one between the positive electrode 20 and the negative electrode 30, but each electrode group may include a single separator 40. In this case, the long separator 40 is folded into a zigzag shape and arranged between the positive electrode 20 and the negative electrode 30.

[0027] As described above, the electrode body 11 has a structure in which a plurality of positive electrodes 20 and a plurality of negative electrodes 30 are alternately stacked one by one via a separator 401. The positive electrode 20 and the negative electrode 30 respectively include a positive electrode tab 23 and a negative electrode tab 33 protruding from above. In other words, the positive electrode 20 and the negative electrode 30 are stacked in such a manner that the tabs face the same direction. In addition, the positive electrode tab 23 is located on one lateral end side of the electrode body 11, and the negative electrode tab 33 is located on the other lateral end side of the electrode body 11, and the plurality of positive electrode tabs 23 are arranged in the thickness direction of the electrode body 11, and the plurality of negative electrode tabs 33 are arranged in the thickness direction of the electrode body 11.

[0028] Figure 4 1 is a cross-sectional view showing a portion of the electrode body 11 and a front view of the positive electrode 20. Figure 4 As shown, the positive electrode 20 includes a positive electrode core 21 and a positive electrode composite material layer 22 formed on the surface of the positive electrode core 21. The positive electrode composite material layer 22 is formed on both surfaces of the positive electrode core 21. Similarly, the negative electrode 30 includes a negative electrode core 31 and a negative electrode composite material layer 32 formed on the surface of the negative electrode core 31. The negative electrode composite material layer 32 is formed on both surfaces of the negative electrode core 31. The negative electrode 30 is slightly larger than the positive electrode 20, and the positive electrode composite material layer 22 of the positive electrode 20 is arranged opposite the negative electrode composite material layer 32 within the formed area.

[0029] Hereinafter, the structures of the positive electrode 20 and the negative electrode 30 , particularly the positive electrode composite material layer 22 and the negative electrode composite material layer 32 , will be described in detail.

[0030] [positive electrode]

[0031] The positive electrode 20 has a structure in which a positive electrode composite material layer 22 is formed on the entire surface of the positive electrode core 21 except for the positive electrode tab 23 (hereinafter referred to as the "base"). The positive electrode core 21 can use a foil of a metal that is stable within the operating voltage range of the battery, such as aluminum, or a film in which the metal is arranged on the surface. The thickness of the positive electrode core 21 is, for example, 5μm to 20μm, preferably 8μm to 15μm. The base of the positive electrode core 21 has a square shape when viewed from above, and the positive electrode tab 23 protrudes from one side of the square. Usually, a metal foil is processed to obtain a positive electrode core 21 in which the base and the positive electrode tab 23 are integrally formed.

[0032] The positive electrode composite material layer 22 includes, for example, a positive electrode active material, a conductive material, and a binding material, and is formed on both sides of the base of the positive electrode core 21. It should be noted that the positive electrode composite material layer 22 can also be formed at the root of the positive electrode tab 23. The thickness of the positive electrode composite material layer 22 on one side of the positive electrode core 21 is, for example, 40 μm to 120 μm, preferably 50 μm to 80 μm. The positive electrode 20 can be manufactured as follows: a positive electrode composite material slurry including a positive electrode active material, a conductive material, and a binding material is applied to the positive electrode core 21, the coating is dried, and the positive electrode composite material layer 22 is formed on both sides of the positive electrode core 21 by compression, and then cut into a specified shape to thereby manufacture.

[0033] A lithium transition metal composite oxide can be used as the positive electrode active material. Examples of the metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among them, it is preferred to contain at least one of Ni, Co, and Mn. As an example of a preferred composite oxide, a lithium transition metal composite oxide containing Ni, Co, and Mn and a lithium transition metal composite oxide containing Ni, Co, and Al can be mentioned.

[0034] The volume-based median diameter (hereinafter referred to as "D50") of the positive electrode active material is, for example, 2 μm to 30 μm. The volume-based D50 refers to the particle size at which the cumulative frequency of the volume-based particle size distribution, from the smallest particle size, reaches 50%, also known as the median diameter. D50 can be measured using a laser diffraction particle size distribution analyzer (e.g., MicrotracBEL HRA, manufactured by Nikkiso Co., Ltd.) using water as the dispersion medium.

[0035] As the conductive material included in the positive electrode composite material layer 22, carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be exemplified. As the binding material included in the positive electrode composite material layer 22, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins can be exemplified. In addition, these resins can also be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), and the like.

[0036] The positive electrode core 21 of the positive electrode 20 is adjacent to the positive electrode composite material layer, and a protective layer not shown in the figure may also be provided. The protective layer extends in a strip shape along the length direction of the positive electrode core 21. The protective layer has the function of preventing the negative electrode 30 and the positive electrode core 21 from short-circuiting when the positive electrode 20 is opposite to the negative electrode 30 with the aid of the separator 40 to form an electrode body. The protective layer includes, for example, inorganic material particles such as ceramics and a resin binder. The thickness of the protective layer formed on both sides of the positive electrode core 21 is, for example, 70 μm. In this embodiment, the positive electrode core 21 of the positive electrode 20 includes a positive electrode core 21 formed with a protective layer. It should be noted that non-essential components may also be omitted in the protective layer of this embodiment.

[0037] The density of the positive electrode composite material layer 22 may be non-uniform, and may include high-density regions and low-density regions. Specifically, the density of the first region away from the liquid injection portion 16 is lower than the density of the second region near the liquid injection portion 16. In other words, a low-density region is formed in the portion of the positive electrode composite material layer 22 away from the liquid injection portion 16, and a high-density region is formed in the portion near the liquid injection portion 16. When the density of the positive electrode composite material layer is uniform, it is difficult for the non-aqueous electrolyte to penetrate the first region away from the liquid injection portion 16. However, by reducing the density of the first region, the non-aqueous electrolyte can more easily penetrate the first region.

[0038] In this embodiment, a liquid injection portion 16 is provided between the positive electrode terminal 12 of the sealing plate 15 and the gas discharge valve 17, at a position that overlaps with the positive electrode tab 23 in the vertical direction. Therefore, the density of the positive electrode composite material layer 22 can be highest near the positive electrode tab 23 and decrease as it moves away from the positive electrode tab 23. However, from the perspective of the productivity of the positive electrode 20, the density of the positive electrode composite material layer 22 is preferably substantially constant in the horizontal direction. In other words, the density of the positive electrode composite material layer 22 preferably varies in the vertical direction, with a high density at the upper end side of the positive electrode composite material layer 22 close to the liquid injection portion 16 and a low density at the lower end side of the positive electrode composite material layer 22 away from the liquid injection portion 16.

[0039] When the positive electrode composite material layer 22 is divided into three equal parts from the sealing plate 15 side to the bottom side of the outer can 14 (the positive electrode composite material layer 22 formed on the base of the positive electrode core 21 is divided into three equal parts in the vertical direction), and is defined as the second region 22B, the middle region 22C, and the first region 22A in sequence from the sealing plate 15 side, the density of the positive electrode composite material layer 22 preferably satisfies the following relationship.

[0040] Density ρ of the second region 22B 22B >Density ρ of the middle region 22C 22C >Density ρ of the first region 22A 22A

[0041] Density ρ 22A Specific density ρ 22C Low, density ρ 22C Specific density ρ 22B By forming such a density pattern in the positive electrode mixture layer 22 , the nonaqueous electrolyte can be uniformly dispersed throughout the entire electrode body 11 when the nonaqueous electrolyte is injected from the injection portion 16 provided in the sealing plate 15 .

[0042] The density of the positive electrode composite material layer 22 can be calculated by subtracting the mass of the positive electrode core 21 from the mass of the positive electrode 20 of a specified area. The density of the positive electrode composite material layer 22 can be calculated based on the specified area, the mass of the positive electrode composite material layer 22, and the average thickness of the positive electrode composite material layer 22 (the density of the negative electrode composite material layer 32 is also the same). 22B , ρ 22C , ρ 22A When the positive electrode composite material layer 22 formed on the base of the positive electrode core 21 is used, it is possible to divide the positive electrode composite material layer 22 into three equal parts in the vertical direction and use them as sample pieces for density measurement.

[0043] The density of the positive electrode composite material layer 22 can be gradually reduced from the upper end to the lower end of the positive electrode composite material layer 22. For example, the density can change steeply at the boundary between the second region 22B, the middle region 22C, and the first region 22A. In this case, the density of each region can be constant throughout the region. It should be noted that the thickness of the positive electrode composite material layer 22 can be gradually changed along with the density of the positive electrode composite material layer 22. For example, the thickness can be gradually increased from the upper end to the lower end of the positive electrode composite material layer 22 within a range that does not affect battery performance.

[0044] The density of the positive electrode composite material layer 22 can be changed in stages as described above, but it is preferably gradually reduced from the upper end to the lower end of the positive electrode composite material layer 22. That is, it is preferred that there is no boundary in the positive electrode composite material layer 22 where the density changes steeply. For example, there is no steep density difference at the boundary between the second region 22B, the middle region 22C, and the first region 22A, and the density of each region gradually decreases from the upper end to the lower end of each region. By forming a gentle density change in the upper and lower directions of the positive electrode composite material layer 22, the electrolyte moves more smoothly. In addition, within the range that does not affect the battery performance, the thickness can be gradually increased from the upper end to the lower end of the positive electrode composite material layer 22.

[0045] The above-described density pattern of the positive electrode composite material layer 22 may be applied only to the positive electrode composite material layer 22 formed on one surface of the positive electrode core 21. However, from the perspective of uniformity of the battery reaction, it is preferably applied to each positive electrode composite material layer 22 formed on both surfaces of the positive electrode core 21. In addition, the density pattern of the two positive electrode composite material layers 22 is preferably the same. The above-described density pattern of the positive electrode composite material layer 22 is preferably applied to all positive electrodes 20 constituting the electrode body 11.

[0046] [negative electrode]

[0047] The negative electrode 30 has a structure in which a negative electrode composite material layer 32 is formed on the entire surface of the negative electrode core 31, excluding the negative electrode tab 33, i.e., the base. The negative electrode core 31 can be made of a foil of a metal that is stable within the battery operating voltage range, such as copper, or a thin film having the metal disposed on the surface. The thickness of the negative electrode core 31 is, for example, 3 μm to 15 μm, preferably 5 μm to 10 μm. As in the case of the positive electrode 20, the base of the negative electrode core 31 has a square shape when viewed from the front, and the negative electrode tab 33 protrudes from one side of the square.

[0048] The negative electrode composite material layer 32 contains, for example, a negative electrode active material and a binder, and is formed on both sides of the base of the negative electrode core 31. It should be noted that the negative electrode composite material layer 32 can also be formed at the root of the negative electrode tab 33. The thickness of the negative electrode composite material layer 32 on one side of the negative electrode core 31 is, for example, 40 μm to 120 μm, and preferably 50 μm to 80 μm. The negative electrode 30 can be manufactured as follows: a negative electrode composite material slurry containing a negative electrode active material and a binder is applied to the negative electrode core 31, the coating is dried, and the negative electrode composite material layer 32 is formed on both sides of the negative electrode core 31 by compression, and then cut into a predetermined shape.

[0049] As the negative electrode active material, for example, a carbon-based active material that reversibly stores and releases lithium ions can be used. Preferred carbon-based active materials include natural graphites such as flaky graphite, bulk graphite, and earthy graphite, and artificial graphites such as bulk artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB). In addition, the negative electrode active material can be a Si-based active material composed of at least one of Si and a Si-containing compound, or a carbon-based active material and a Si-based active material can be used in combination.

[0050] As with the positive electrode 20, the binder included in the negative electrode composite material layer 32 can be a fluororesin, PAN, polyimide, acrylic resin, polyolefin, or the like, preferably styrene-butadiene rubber (SBR). Furthermore, the negative electrode composite material layer 32 preferably further includes CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), or the like. The combined use of SBR, CMC or its salt, and PAA or its salt is preferred.

[0051] Similar to the positive electrode composite material layer 22, the negative electrode composite material layer 32 may have a high-density region and a low-density region. When the negative electrode composite material layer 32 formed at the base of the negative electrode core 31 is divided into three equal parts in the vertical direction and defined as the second region, the middle region, and the first region, starting from the sealing plate 15 side, the density of the negative electrode composite material layer 32 preferably satisfies the following relationship.

[0052] Density ρ of the second region 32B 32B >Density ρ of the middle region 32C 32C >Density ρ of the first region 32A 32A

[0053] The density of the negative electrode mixture layer 32 may be changed in stages, but preferably decreases gradually from the upper end to the lower end of the negative electrode mixture layer 32 .

[0054] The density pattern of the positive electrode composite material layer 22 can also be applied to the negative electrode composite material layer 32 (as described above, the preferred density value is different). Regarding the negative electrode composite material layer 32, the above description is cited and repeated description is omitted below. In order to improve the permeability of the non-aqueous electrolyte relative to the electrode body 11, in at least one of the positive electrode composite material layer 22 and the negative electrode composite material layer 32, the density of the first region away from the liquid injection portion 16 is lower than the density of the second region close to the liquid injection portion 16. Therefore, the above density pattern can be applied only to the positive electrode composite material layer 22, or only to the negative electrode composite material layer 32. In addition, the above density pattern can also be applied to both the positive electrode composite material layer 22 and the negative electrode composite material layer 32.

[0055] The following describes an example method for manufacturing the nonaqueous electrolyte secondary battery 10 having the above-described structure. The manufacturing process for the nonaqueous electrolyte secondary battery 10 includes: a step for fabricating the positive electrode 20; a step for fabricating the negative electrode 30; a step for fabricating the electrode assembly 11 using the positive electrode 20 and the negative electrode 30; and a step for housing the electrode assembly 11 within an exterior body and then injecting a nonaqueous electrolyte solution into the exterior body. It should be noted that the materials constituting the electrode assembly 11, such as the positive electrode active material, negative electrode active material, and separator 40, can be the same as those conventionally used.

[0056] In this manufacturing process, in at least one of the steps of forming the positive electrode composite material layer 22 and the negative electrode composite material layer 32, the composite material layer is formed so that the density of the region located on the first end side of the composite material layer is lower than the density of the region located on the second end side opposite to the first end side. Furthermore, in the step of injecting the non-aqueous electrolyte, the non-aqueous electrolyte is injected into the interior of the outer body from the second end side of the composite material layer. In other words, the non-aqueous electrolyte is injected so that the non-aqueous electrolyte moves from the high-density side to the low-density side of the composite material layer.

[0057] It should be noted that when the outer body is a square metal container consisting of an outer can 14 and a sealing plate 15, the injection portion 16 is present even after the non-aqueous electrolyte is injected. However, after the non-aqueous electrolyte is injected, the position of the injection portion may not be clear. In either case, the non-aqueous electrolyte needs to be injected so that it moves from the high-density side to the low-density side of the composite material layer.

[0058] As described above, the positive electrode 20 is produced by forming the positive electrode composite material layer 22 on the surface of the positive electrode core 21. Similarly, the negative electrode 30 is produced by forming the negative electrode composite material layer 32 on the surface of the negative electrode core 31. Furthermore, the electrode body 11 is produced by alternately stacking a plurality of positive electrodes 20 and a plurality of negative electrodes 30 one by one through the separator 40. At this time, the positive electrode 20 and the negative electrode 30 are formed in a manner that is consistent with the embodiment of the present invention. Figure 3 The separator 40 may be an insulating porous sheet folded into a zigzag shape.

[0059] Figure 5 : is a diagram showing the manufacturing process of the positive electrode 20. Figure 5 As shown, the positive electrode 20 is produced by coating a positive electrode composite material slurry containing a positive electrode active material, etc., on a long metal foil 50 serving as the positive electrode core 21, drying and rolling the coating, forming the positive electrode composite material layer 22 on both sides of the metal foil 50, and then cutting the metal foil 50 into a predetermined shape. The metal foil 50 can be cut using conventionally known methods such as laser irradiation or die punching. Figure 5The long metal foil 50 has a width that can form two positive electrodes 20 in the width direction, and has a width slightly larger than the vertical length of the two positive electrodes 20 .

[0060] The positive electrode composite material slurry is applied to the portion of the metal foil 50 extending from both ends in the width direction to the portion excluding the region of a predetermined width. Exposed portions 51 are provided at both ends in the width direction of the metal foil 50, where the surface of the metal foil 50 is exposed. The metal foil 50, having the positive electrode composite material layer 22 formed on both surfaces by the application of the positive electrode composite material slurry, is cut lengthwise at the center of the width direction, and is then cut widthwise at predetermined intervals corresponding to the transverse length of the positive electrode 20. Furthermore, the metal foil 50 is cut lengthwise along the boundary between the positive electrode composite material layer 22 and the exposed portion 51, and the exposed portion 51 is cut at predetermined intervals to form the positive electrode tab 23.

[0061] The positive electrode composite material slurry is applied to the surface of the metal foil 50 using a known coating device such as a gravure coater, a slit coater, or a die coater. As described above, the second region 22B is formed with a density of p 22B >Density ρ of the middle region 22C 22C >Density ρ of the first region 22A 22A The method of forming the positive electrode composite material layer 22 with a density pattern is not particularly limited. As an example, the density pattern can be formed by changing the amount of the positive electrode composite material slurry applied along the width direction of the metal foil 50 .

[0062] When the coating amount of the positive electrode composite material slurry is changed to form the above-mentioned density pattern, the slurry is applied in a manner such that the coating amount gradually increases from the exposed portion 51 side to the central side in the width direction of the metal foil 50. At this time, if the coating is applied in a manner such that the coating amount gradually increases from the central side in the width direction of the metal foil 50 to the exposed portion 51 side, the composite material slurry will be retained at the boundary between the exposed portion 51 and the positive electrode composite material layer, so that the composite material layer will float up, resulting in the so-called "warping (Japanese: ear stand)". If the positive electrode sheet with warping is wound and production continues, there is a concern that the warping part will wrinkle and eventually break, so it is not preferred. Then, the coating film of the positive electrode composite material slurry is heated and dried to evaporate and remove the solvent in the slurry.

[0063] After the coating is dried by heating, the coating is compressed using rollers or the like. The rolling load of the rollers is increased from the center of the width of the metal foil 50 where the coating is formed toward the ends. For example, a method can be used in which a large load is applied to both ends of the roller in the width direction, the roller is bent into an inverted crown shape, and compression is performed. Alternatively, a method can be used in which the rollers are compressed using inverted crown-shaped rollers. Using these methods, when the metal foil 50 coated with the slurry is compressed so that the coating amount gradually increases from the exposed portion 51 side toward the center of the width of the metal foil 50, a positive electrode composite material layer 22 is formed on both sides of the metal foil 50, with the density gradually increasing from the center of the width of the metal foil 50 toward the exposed portion 51 side.

[0064] Next, the metal foil 50 on which the positive electrode mixture layer 22 is formed is cut at a predetermined position to obtain the positive electrode 20 including the positive electrode mixture layer 22 having the above-described density pattern on both surfaces of the metal foil 50 .

[0065] During the manufacturing process of the non-aqueous electrolyte secondary battery 10, the electrode body 11 is housed within the outer can 14 such that the second region 22B, serving as a high-density region, is located on the upper end of the positive electrode composite material layer 22 near the sealing plate 15, and the first region 22A, serving as a low-density region, is located on the lower end of the positive electrode composite material layer 22 near the bottom of the outer can 14. When the above-described density pattern is applied to the negative electrode composite material layer 32, the negative electrode 30 is also arranged such that the second region, serving as a high-density region, is located on the sealing plate 15 side, and the first region, serving as a low-density region, is located on the bottom side of the outer can 14. In this case, the negative electrode 30 can be manufactured by applying substantially the same process as that described above for the positive electrode 20. It should be noted that after the positive electrode tabs 23 of the plurality of positive electrodes 20 are connected to the positive electrode current collector, and the negative electrode tabs 33 of the plurality of negative electrodes 30 are connected to the negative electrode current collector, respectively, by welding or the like, the electrode body 11 is housed within the outer can 14.

[0066] The electrode body 11 is housed in the outer can 14, and after the opening of the outer can 14 is sealed with a sealing plate 15, a non-aqueous electrolyte is injected from the liquid injection portion 16 provided in the sealing plate 15. As a result, the non-aqueous electrolyte penetrates from the upper end of the positive electrode composite material layer 22 into the electrode body 11 and permeates the second region 22B, which is a high-density region. It then rapidly permeates toward the lower end of the positive electrode composite material layer 22, in the order of the intermediate region 22C and the first region 22A, and permeates the entire positive electrode composite material layer 22.

[0067] The following description will refer to the experimental example of the present disclosure, but the present disclosure is not limited to this experimental example. It is sufficient as long as the density of the first region away from the liquid injection part in at least one of the positive electrode composite material layer of the positive electrode and the negative electrode composite material layer of the negative electrode constituting the electrode body is lower than the density of the second region close to the liquid injection part.

[0068] First, for the positive electrode 20, the density ρ of the second region 22B is 22B , the density ρ of the middle region 22C 22C , and the density ρ of the first region 22A 22A The following experimental examples are provided. The following values ​​are examples of average values ​​of the densities when lithium nickel cobalt manganese oxide (NCM) is used as the positive electrode active material. The preferred range of each density varies depending on the type of the positive electrode active material.

[0069] (Experimental Example 1)

[0070] The density ρ of the second region 22B 22B becomes 3.72g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.62g / cm 3 , the density ρ of the first region 22A 22A becomes 3.52g / cm 3 The positive electrode 20 is manufactured in this way.

[0071] (Experimental Example 2)

[0072] The density ρ of the second region 22B 22B becomes 3.67g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.57g / cm 3 , the density ρ of the first region 22A 22A becomes 3.47g / cm 3 The positive electrode 20 is manufactured in this way.

[0073] (Experimental Example 3)

[0074] The density ρ of the second region 22B 22B becomes 3.62g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.52g / cm 3 , the density ρ of the first region 22A 22A becomes 3.42g / cm 3 The positive electrode 20 is manufactured in this way.

[0075] (Experimental Example 4)

[0076] The density ρ of the second region 22B 22B becomes 3.59g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.57g / cm 3 , the density ρ of the first region 22A 22A becomes 3.55g / cm 3The positive electrode 20 is manufactured in this way.

[0077] (Experimental Example 5)

[0078] The density ρ of the second region 22B 22B becomes 3.57g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.47g / cm 3 , the density ρ of the first region 22A 22A becomes 3.37g / cm 3 The positive electrode 20 is manufactured in this way.

[0079] (Experimental Example 6)

[0080] The density ρ of the second region 22B 22B becomes 3.52g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.42g / cm 3 , the density ρ of the first region 22A 22A becomes 3.32g / cm 3 The positive electrode 20 is manufactured in this way.

[0081] (Experimental Example 7)

[0082] The density ρ of the second region 22B 22B becomes 3.44g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.34g / cm 3 , the density ρ of the first region 22A 22A becomes 3.23g / cm 3 The positive electrode 20 is manufactured in this way.

[0083] (Experimental Example 8)

[0084] The density ρ of the second region 22B 22B becomes 3.37g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.27g / cm 3 , the density ρ of the first region 22A 22A becomes 3.16g / cm 3 The positive electrode 20 is manufactured in this way.

[0085] (Experimental Example 9)

[0086] The density ρ of the second region 22B 22B becomes 3.30g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.20g / cm3 , the density ρ of the first region 22A 22A becomes 3.08g / cm 3 The positive electrode 20 is manufactured in this way.

[0087] (Experimental Example 10)

[0088] The density ρ of the second region 22B 22B becomes 3.23g / cm 3 , the density ρ of the middle region 22C 22C becomes 3.13g / cm 3 , the density ρ of the first region 22A 22A becomes 3.01g / cm 3 The positive electrode 20 is manufactured in this way.

[0089] Next, for the negative electrode 30, the density ρ of the second region 32B is 32B , the density ρ of the middle region 32C 32C , and the density ρ of the first region 32A 32A The following experimental examples are provided. The following values ​​are examples of average values ​​of the densities when graphite is used as the negative electrode active material. The preferred range of each density varies depending on the type of the negative electrode active material.

[0090] (Experimental Example 11)

[0091] The density ρ of the second region 32B 32B becomes 1.70g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.68g / cm 3 , the density ρ of the first region 32A 32A becomes 1.66g / cm 3 The negative electrode 30 is manufactured in this manner.

[0092] (Experimental Example 12)

[0093] The density ρ of the second region 32B 32B becomes 1.63g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.57g / cm 3 , the density ρ of the first region 32A 32A becomes 1.52g / cm 3 The negative electrode 30 is manufactured in this manner.

[0094] (Experimental Example 13)

[0095] The density ρ of the second region 32B 32B becomes 1.58g / cm 3 , the density ρ of the middle region 32C32C becomes 1.52g / cm 3 , the density ρ of the first region 32A 32A becomes 1.47g / cm 3 The negative electrode 30 is manufactured in this manner.

[0096] (Experimental Example 14)

[0097] The density ρ of the second region 32B 32B becomes 1.53g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.47g / cm 3 , the density ρ of the first region 32A 32A becomes 1.42g / cm 3 The negative electrode 30 is manufactured in this manner.

[0098] (Experimental Example 15)

[0099] The density ρ of the second region 32B 32B becomes 1.48g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.47g / cm 3 , the density ρ of the first region 32A 32A becomes 1.46g / cm 3 The negative electrode 30 is manufactured in this manner.

[0100] (Experimental Example 16)

[0101] The density ρ of the second region 32B 32B becomes 1.48g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.42g / cm 3 , the density ρ of the first region 32A 32A becomes 1.37g / cm 3 The negative electrode 30 is manufactured in this manner.

[0102] (Experimental Example 17)

[0103] The density ρ of the second region 32B 32B becomes 1.43g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.37g / cm 3 , the density ρ of the first region 32A 32A becomes 1.32g / cm 3 The negative electrode 30 is manufactured in this manner.

[0104] (Experimental Example 18)

[0105] The density ρ of the second region 32B 32B becomes 1.39g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.35g / cm 3 , the density ρ of the first region 32A 32A becomes 1.30g / cm 3 The negative electrode 30 is manufactured in this manner.

[0106] (Experimental Example 19)

[0107] The density ρ of the second region 32B 32B becomes 1.36g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.31g / cm 3 , the density ρ of the first region 32A 32A becomes 1.26g / cm 3 The negative electrode 30 is manufactured in this manner.

[0108] (Experimental Example 20)

[0109] The density ρ of the second region 32B 32B becomes 1.32g / cm 3 , the density ρ of the middle region 32C 32C becomes 1.28g / cm 3 , the density ρ of the first region 32A 32A becomes 1.22g / cm 3 The negative electrode 30 is manufactured in this manner.

[0110] (Evaluation of the impregnation rate of non-aqueous electrolyte)

[0111] The nonaqueous electrolyte impregnation rate was measured for the positive electrodes 20 and negative electrodes 30 of Experimental Examples 1 to 20. A fixed amount (1 μml) of nonaqueous electrolyte was dripped onto the compressed positive electrode plates. The time required for complete impregnation was measured using a stopwatch. The results are shown in Tables 1 and 2.

[0112] [Table 1]

[0113]

[0114] [Table 2]

[0115]

[0116] According to the results of Experimental Examples 1 to 20, it was found that in the high-density region and the low-density region of the positive electrode composite material layer and the negative electrode composite material layer, the low-density region had a shorter impregnation time. 22A , ρ32A Lower than density ρ 22C , ρ 32C , density ρ 22C , ρ 32C Lower than density ρ 22B , ρ 32B The density pattern indicates that the nonaqueous electrolyte injected from the injection port 16 provided on the sealing plate 15 can be smoothly transferred to the tank bottom opposite the injection port. In other words, it is possible to uniformly disperse the nonaqueous electrolyte throughout the electrode assembly.

[0117] As described above, with the nonaqueous electrolyte secondary battery 10 having the above-described structure, comprising an electrode body 11 in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked with separators, when the nonaqueous electrolyte is injected into the interior of the external can 14, the nonaqueous electrolyte can be impregnated throughout the electrode body 11, enabling uniform distribution of the nonaqueous electrolyte throughout the entire electrode body 11. Furthermore, while the nonaqueous electrolyte is squeezed out of the electrode body 11 by the expansion of the electrode body 11 during battery charging and discharging, the electrode body 11 has a structure in which the positive electrodes 20 and the negative electrodes 30 are alternately stacked with separators 40, resulting in improved nonaqueous electrolyte permeability compared to wound-type electrode bodies. Specifically, the nonaqueous electrolyte penetrates the electrode body 11 from the top, bottom, left, and right. By using the non-aqueous electrolyte secondary battery 10, the above-mentioned density pattern of the composite material layer and the synergistic effect of the stacked structure of the electrode body 11 are utilized to greatly improve the permeability of the non-aqueous electrolyte relative to the electrode body 11, thereby suppressing the performance degradation caused by the deviation of the non-aqueous electrolyte amount in the electrode body.

[0118] The above embodiments can be appropriately modified in design without compromising the purpose of the present disclosure. For example, Figure 2 While the electrode assembly 11 includes the first electrode group 11A and the second electrode group 11B, the electrode assembly 11 may not be divided into multiple electrode groups. Furthermore, a configuration in which the composite material layer having the above-described density pattern is formed only on a portion of the plurality of positive electrodes 20 or only on a portion of the plurality of negative electrodes 30 is also envisioned.

[0119] Description of Reference Numerals

[0120] 10Non-aqueous electrolyte secondary battery

[0121] 11 electrode body

[0122] 11A 1st electrode group

[0123] 11B 2nd electrode group

[0124] 12 Positive terminal

[0125] 13 Negative terminal

[0126] 14 outer cans

[0127] 15 Sealing plate

[0128] 16 Liquid injection department

[0129] 17 Gas discharge valve

[0130] 18 Current cut-off mechanism

[0131] 20 positive electrode

[0132] 21 positive electrode core

[0133] 22 positive electrode composite material layer

[0134] 22A Area 1

[0135] 22B Area 2

[0136] 22C middle area

[0137] 23 positive electrode tab

[0138] 30 negative electrode

[0139] 31 negative electrode core

[0140] 32 negative electrode composite material layer

[0141] 33 negative electrode tab

[0142] 40 dividers

[0143] 50 metal foil

[0144] 51 exposed part

Claims

1. A non-aqueous electrolyte secondary battery comprising: An electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked one by one via separators, Non-aqueous electrolyte, and an outer casing for housing the electrode assembly and the non-aqueous electrolyte, The outer body is provided with a liquid injection portion for injecting the non-aqueous electrolyte. The plurality of positive electrodes include a positive electrode core and a positive electrode composite material layer formed on the surface of the positive electrode core. The plurality of negative electrodes include a negative electrode core and a negative electrode composite material layer formed on the surface of the negative electrode core. The density of at least one of the positive electrode composite material layer and the negative electrode composite material layer is lower in a first region away from the liquid injection portion than in a second region close to the liquid injection portion, and decreases in stages or gradually from an upper end close to the liquid injection portion to a lower end away from the liquid injection portion. The density of the positive electrode composite material layer is obtained by subtracting the mass of the positive electrode core from the mass of the positive electrode of a specified area as the mass of the positive electrode composite material layer, and calculating it based on the specified area, the mass of the positive electrode composite material layer, and the average thickness of the positive electrode composite material layer; the density of the negative electrode composite material layer is obtained by subtracting the mass of the negative electrode core from the mass of the negative electrode of a specified area as the mass of the negative electrode composite material layer, and calculating it based on the specified area, the mass of the negative electrode composite material layer, and the average thickness of the negative electrode composite material layer.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The outer body includes an outer can having a square cylindrical bottom and a sealing plate for sealing an opening of the outer can. The liquid injection portion is provided on the sealing plate, When at least one of the positive electrode composite material layer and the negative electrode composite material layer is divided into three equal parts from the sealing plate side to the bottom side of the outer can, and defined as the second region, the middle region, and the first region in sequence from the sealing plate side, the density of each region satisfies the relationship of the density of the second region > the density of the middle region > the density of the first region.

3. A method for manufacturing a non-aqueous electrolyte secondary battery, wherein: The non-aqueous electrolyte secondary battery comprises an electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked one by one via separators, a non-aqueous electrolyte solution, and an outer body. The manufacturing method comprises: A process for manufacturing the positive electrode by forming a positive electrode composite material layer on the surface of the positive electrode core; forming a negative electrode composite material layer on the surface of the negative electrode core to produce the negative electrode; a step of manufacturing the electrode assembly using the plurality of positive electrodes and the plurality of negative electrodes; and After housing the electrode assembly in the outer casing, injecting the non-aqueous electrolyte solution, In the step of forming at least one of the positive electrode composite material layer and the negative electrode composite material layer, the composite material layer is formed in such a manner that the density of the region located on the first end side of the composite material layer is lower than the density of the region located on the second end side opposite to the first end, and the density decreases in stages or gradually decreases from the second end toward the first end. In the step of injecting the non-aqueous electrolyte, the non-aqueous electrolyte is injected into the interior of the outer body from the second end side; The density of the positive electrode composite material layer is obtained by subtracting the mass of the positive electrode core from the mass of the positive electrode of a specified area as the mass of the positive electrode composite material layer, and calculating it based on the specified area, the mass of the positive electrode composite material layer, and the average thickness of the positive electrode composite material layer; the density of the negative electrode composite material layer is obtained by subtracting the mass of the negative electrode core from the mass of the negative electrode of a specified area as the mass of the negative electrode composite material layer, and calculating it based on the specified area, the mass of the negative electrode composite material layer, and the average thickness of the negative electrode composite material layer.

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