Nonaqueous electrolyte secondary battery and method for manufacturing electrode for nonaqueous electrolyte secondary battery

Abstract

A positive electrode (11) comprises: a positive electrode core body (30); a positive electrode mixture layer (32) formed on the surface of the positive electrode core body (30); a positive electrode core body exposed part (31) where the positive electrode core body (30) is exposed; a protective layer (50) formed on the surface of the positive electrode core body exposed part (31); and a positive electrode tab (20) disposed on the surface of the protective layer (50). The protective layer (50) has a lower elastic modulus than the positive electrode tab (20), and the positive electrode tab (20) and the positive electrode core body exposed part (31) are connected via a connection part (51) formed in the protective layer (50).

Description

Non-aqueous electrolyte secondary battery and method for manufacturing an electrode for a non-aqueous electrolyte secondary battery

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

[0002] In recent years, in order to reduce the resistance of a battery, a non-aqueous electrolyte secondary battery including an electrode with a reduced thickness of a mixture layer has been developed. However, in such a non-aqueous electrolyte secondary battery, since the relative thickness of the electrode tab with respect to the thickness of the mixture layer becomes large, when charge and discharge are repeated, the pressure accompanying the expansion and contraction of the electrode concentrates on the electrode tab. The electrode tab is directly welded to the core body by ultrasonic welding or the like, but the welding is generally performed spotwise rather than over the entire electrode tab, so there is an electrode tab edge that is not welded to the core body on the outer periphery of the electrode tab. As the electrode expands and contracts during charge and discharge, the electrode tab is pressed against the core body, and the electrode tab edge may pierce the core body, causing minute cracks in the core body. When cracks occur in the core body, the current collecting efficiency of the electrode tab decreases, leading to deterioration of battery performance.

[0003] Patent Document 1 discloses an electrode tab in which the edge portion is cut out and only the central portion in the width direction protrudes toward the core body side. In this case, it is described that by interposing a protective layer made of a resin layer or the like between the cut-out portion of the electrode tab and the core body, it is possible to suppress cracks in the core body caused by the electrode tab edge accompanying the expansion and contraction of the electrode during charge and discharge.

[0004] Japanese Unexamined Patent Application Publication No. 2014 - 089856

[0005] However, in the configuration of the electrode tab disclosed in Patent Document 1, the outer periphery of the portion protruding toward the core body side newly becomes the edge of the electrode tab. When the electrode tab is strongly pressed against the core body as the electrode expands and contracts during charge and discharge, the edge generated by forming the cut-out portion may contact the core body, causing cracks in the core body. Therefore, it is necessary to more reliably prevent cracks in the core body caused by the electrode tab.

[0006] The non-aqueous electrolyte secondary battery according to this disclosure is a non-aqueous electrolyte secondary battery comprising an electrode body in which electrodes with opposite polarities are stacked and arranged via a separator, and an outer casing that houses the electrode body, wherein at least one of the electrodes comprises a core body, a composite layer formed on the surface of the core body, a core body exposed portion in which the core body is exposed, a protective layer formed on the surface of the core body exposed portion, and an electrode tab disposed on the surface of the protective layer, wherein the protective layer has a lower modulus of elasticity than the electrode tab, and the electrode tab and the core body exposed portion are connected via a connecting portion formed in the protective layer.

[0007] A method for manufacturing an electrode for a non-aqueous electrolyte secondary battery according to the present disclosure includes a first step of forming a protective layer on the core exposed portion, a second step of arranging an electrode tab on the core exposed portion via the protective layer, and a third step of joining the electrode tab to the core exposed portion, wherein in the third step, a connecting portion including at least one component of the electrode tab and the core exposed portion is formed in the protective layer, and the electrode tab and the core exposed portion are electrically connected via the connecting portion.

[0008] According to one aspect of this disclosure, it is possible to provide a non-aqueous electrolyte secondary battery that suppresses core cracking and has excellent durability. The non-aqueous electrolyte secondary battery according to this disclosure has excellent charge-discharge cycle characteristics, for example.

[0009] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure. This is a plan view of the longitudinal center of the positive electrode, which is an example of an embodiment. This is a cross-sectional view taken along line AA in Figure 2. This shows a cross-sectional view of the positive electrode before joining the positive electrode tab to the positive electrode core (a) and a cross-sectional view of the positive electrode after joining the positive electrode tab (b), illustrating the process of joining the positive electrode tab to the positive electrode core.

[0010] Hereinafter, embodiments of the non-aqueous electrolyte secondary battery according to this disclosure will be described in detail with reference to the drawings.

[0011] It is intended from the outset that new embodiments can be constructed by appropriately combining the characteristic features of the embodiments and modifications described below. In the following embodiments, the same reference numerals are used for the same components in the drawings, and redundant explanations are omitted. In addition, multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. Furthermore, among the components described below, components that are not described in the independent claim indicating the highest-level concept are optional components and are not essential components. Moreover, this disclosure is not limited to the embodiments and modifications described below, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0012] Figure 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment.

[0013] As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 has a positive electrode 11 and a negative electrode 12 with opposite polarities, and a separator 13, and comprises a wound electrode body 14 in which the positive electrode 11 and the negative electrode 12 are wound around the separator 13. The non-aqueous electrolyte secondary battery 10 also comprises a bottomed cylindrical outer casing 16 that houses the electrode body 14, and a sealing body 17 that closes the opening of the outer casing 16. The outer casing 16 houses the electrode body 14 together with the non-aqueous electrolyte.

[0014] The outer casing 16 is a bottomed cylindrical metal container having a cylindrical portion 16a and a bottom portion 16b provided at one axial end of the cylindrical portion 16a. The outer casing 16 has a grooved portion 22, described later, formed on the other axial end side of the cylindrical portion 16a, which is the open end side, and the sealing body 17 is supported by the grooved portion 22 and closes the opening of the outer casing 16. For the sake of explanation, in the following, the sealing body 17 side of the non-aqueous electrolyte secondary battery 10 will be considered the top, and the bottom portion 16b side of the outer casing 16 will be considered the bottom.

[0015] The non-aqueous electrolyte has ionic conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (non-aqueous electrolyte solution), but may also be a solid electrolyte using a gel-like polymer or the like. The non-aqueous electrolyte secondary battery 10 is preferably a lithium-ion battery. The electrolyte salt may be, for example, LiBF ４ LiPF ６ Lithium salts such as the above are used. Non-aqueous solvents include, for example, esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), as well as ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain halogen-substituted products in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.

[0016] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP). In terms of suppressing the deterioration of the charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries or improving the output characteristics, the non-aqueous electrolyte preferably contains 5% by mass or more of FEC relative to the mass of the non-aqueous electrolyte, and more preferably contains 5% to 15% by mass of FEC.

[0017] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0018] As described above, the electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strips, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and short-side directions of the electrode plate. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0019] The positive electrode 11 and negative electrode 12 constituting the electrode body 14 include a positive electrode tab 20 and a negative electrode tab 21. The positive electrode tab 20 electrically connects the electrode plate of the positive electrode 11 to the sealing body 17. The positive electrode tab 20 is located in the longitudinal center of the electrode plate of the positive electrode 11, away from the winding start end and winding end of the electrode body 14. The positive electrode tab 20 corresponds to the electrode tab. The positive electrode tab 20 is a strip-shaped conductive member and has a thickness greater than the thickness of the positive electrode core body described later. The constituent material of the positive electrode tab is not particularly limited, but it is preferable that the positive electrode tab 20 is made of a metal mainly composed of aluminum.

[0020] The negative electrode tab 21 is joined to the winding end of the negative electrode 12. The negative electrode tab 21 is a strip-shaped conductive member and has a thickness greater than the thickness of the negative electrode core body described later. The constituent material of the negative electrode tab 21 is not particularly limited. Preferably, the negative electrode tab 21 is made of a metal mainly composed of nickel or copper, or a metal containing both nickel and copper. In the example shown in Figure 1, the positive electrode tab 20 extends through the opening of the upper insulating plate 18 toward the sealing body 17 and is joined to the lower surface of the sealing body 17, so that the sealing body 17 becomes the positive electrode terminal. The negative electrode tab 21 passes outside the lower insulating plate 19 and is bent along the inner surface of the bottom of the outer casing 16, and is connected to the inner surface of the bottom of the outer casing 16 by welding or the like, so that the outer casing 16 becomes the negative electrode terminal.

[0021] A separator 13 is positioned on the outermost surface of the electrode body 14 and is in contact with the inner surface of the outer casing 16. The separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0022] The positive electrode 11 has a strip-shaped positive electrode core 30 and positive electrode mixture layers 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. A preferred positive electrode core 30 is a metal foil mainly composed of aluminum or an aluminum alloy. The thickness of the positive electrode core 30 is, for example, 10 μm to 30 μm.

[0023] The positive electrode composite layer preferably comprises a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVDF), and is formed on both sides of the positive electrode core. The thickness of the positive electrode composite layer is, for example, 40 μm to 200 μm. For the positive electrode active material, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, etc. is used. As described later, the positive electrode tab 20 is joined to the positive electrode core 30 by ultrasonic welding or the like.

[0024] The negative electrode 12 comprises a negative electrode core and negative electrode composite layers formed on both sides of the negative electrode core. The negative electrode core can be made of a metal foil that is stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode composite layer contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR). The thickness of the negative electrode composite layer is, for example, 40 μm to 100 μm. The negative electrode active material can be, for example, graphite or a Si-containing material. The negative electrode tab 21 is preferably joined to the negative electrode core by ultrasonic welding or the like.

[0025] An annular gasket 28 is interposed between the outer casing 16 and the sealing body 17. The sealing body 17 is crimped and fixed to the upper end, which is the open end of the outer casing 16, via the gasket 28. Specifically, the upper end of the outer casing 16 is crimped to the peripheral edge of the sealing body 17 via the gasket 28. This seals the inside of the battery.

[0026] Furthermore, the outer casing 16 has grooves 22 that support the sealing body 17, which are formed, for example, by pressing the side surface from the outside. The grooves 22 are preferably formed in an annular shape along the circumferential direction of the outer casing 16, and their upper surface supports the sealing body 17.

[0027] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The cap 27 has an annular flange on its outer circumference and is hat-shaped with a cylindrical portion in the center whose upper end is closed. The internal terminal plate 23 has a central hole that penetrates vertically. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective central portions, and the insulating member 25 is interposed between their respective peripheral portions. The components constituting the sealing body 17 are stacked axially on the flange portion of the sealing body 17.

[0028] When the internal pressure of the battery increases, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure increases further, the upper valve body 26 breaks, and gas is released from the opening 27a of the cap 27.

[0029] The positive electrode tab 20, the exposed portion 31 of the positive electrode core, and the protective layer 50 constituting the positive electrode 11 will be described in detail using Figures 2 and 3. Figure 2 is a plan view of the longitudinal center of the positive electrode 11. Figure 3 is a cross-sectional view taken along line AA in Figure 2.

[0030] As shown in Figures 2 and 3, the positive electrode 11 includes a positive electrode core exposed portion 31 in which the positive electrode core 30 is exposed. The positive electrode core exposed portion 31 has a predetermined width in the longitudinal direction of the positive electrode 11 and is formed in a strip shape so as to extend parallel to the width direction of the positive electrode 11. The positive electrode core exposed portion 31 is the portion to which the positive electrode tab 20 is connected and is provided by not forming a positive electrode mixture layer 32 on the positive electrode core 30. The positive electrode core exposed portion 31 can be made, for example, by intermittently applying a positive electrode slurry containing positive electrode active material, conductive agent, binder, etc., to both sides of the positive electrode core 30, leaving the portion that will become the positive electrode core exposed portion 31 untouched.

[0031] A protective layer 50 is formed on the surface of the exposed positive electrode core portion 31 to protect the positive electrode core 30, and a positive electrode tab 20 is placed on the surface of the protective layer 50. The protective layer 50 is, for example, a resin layer, and examples include a resin layer coated with a resin such as polyvinylidene fluoride (PVDF). The protective layer 50 may be conductive from the viewpoint of current collection efficiency. A conductive protective layer 50 can be made, for example, by adding a highly conductive filler such as carbon black or carbon nanotubes to the resin.

[0032] The protective layer 50 is formed on the surface of the exposed positive electrode core 31, at least in the portion that overlaps with the positive electrode tab 20, and excluding the connecting portion 51 described later. The positive electrode tab 20 and the positive electrode core 30 are electrically connected via the connecting portion 51. The protective layer 50 prevents the edges E1 and E2 of the positive electrode tab 20 from directly contacting the positive electrode core 30. Furthermore, because the protective layer 50 has a lower elastic modulus than the positive electrode tab 20, cracking of the positive electrode core 30 caused by the edges of the positive electrode tab 20 is suppressed.

[0033] The thickness of the protective layer 50 is preferably 1 μm or more and 4 μm or less, and more preferably 1 μm or more and 2 μm or less. The thickness of the protective layer 50 is determined, for example, based on the portion of the protective layer 50 that is interposed between the positive electrode tab 20 and the positive electrode core exposed portion 31 and does not face the edges E1 and E2. If the thickness of the protective layer 50 is less than 1 μm, the positive electrode core 30 cannot be adequately protected. If the thickness of the protective layer 50 is greater than 4 μm, it becomes difficult to ensure sufficient bonding strength between the positive electrode tab 20 and the positive electrode core exposed portion 31.

[0034] The protective layer 50 and the positive electrode tab 20 may be placed on either the outer or inner surface of the winding of the positive electrode core 30 of the positive electrode 11, but it is preferable that they be placed on the inner surface. When the electrode tab is placed on the inner surface of the core of a wound electrode body, the pressure associated with the expansion and contraction of the electrode during charging and discharging tends to concentrate on the edge of the electrode tab compared to when the electrode tab is placed on the outer surface. For this reason, when the positive electrode tab 20 is placed on the inner surface of the winding of the positive electrode core 30, the crack suppression effect of the positive electrode core 30 is significantly enhanced.

[0035] The positive electrode tab 20 and the positive electrode core exposed portion 31 are connected via a connecting portion 51. The connecting portion 51 is joined to the positive electrode core exposed portion 31 at the portion that contacts the positive electrode core exposed portion 31, and is integrated with the positive electrode core exposed portion 31. Therefore, the connecting portion 51 will not damage the positive electrode core 30. In addition, a protective layer 50 is interposed between the edges E1 and E2 of the positive electrode tab 20 and the positive electrode core exposed portion 31, so that the edges E1 and E2 of the positive electrode tab 20 and the positive electrode core 30 do not come into direct contact. Therefore, when the protective layer 50 is formed on the surface of the positive electrode core exposed portion 31, even if the positive electrode tab 20 is pressed against the positive electrode core exposed portion 31 by the pressure associated with the expansion and contraction of the electrode, the edges E1 and E2 of the positive electrode tab 20 do not come into direct contact with the positive electrode core 30, thus suppressing cracks in the positive electrode core 30 and achieving a good charge-discharge cycle.

[0036] In this embodiment, the connecting portions 51 are provided at eight locations in a plan view (see Figure 2) of the portion where the positive electrode tab 20 and the positive electrode core exposed portion 31 overlap, arranged in four rows in the width direction of the positive electrode 11 and two columns in the longitudinal direction of the positive electrode 11. However, the positions where the connecting portions 51 are provided are not limited to these. In this embodiment, each of the multiple connecting portions 51 has a circular shape in a plan view, but the shape of the connecting portions 51 is not limited to this. In a plan view, the connecting portions 51 can have various shapes depending on the shape of the ultrasonic horn described later and the welding method of the positive electrode tab 20 and the positive electrode core exposed portion 31. It is preferable that the connecting portions 51 are arranged at multiple locations within the protective layer 50.

[0037] Next, a method for manufacturing a positive electrode 11, in which a protective layer 50 is formed on the exposed positive electrode core portion 31 and the positive electrode tab 20 is joined, will be described in detail using Figure 4. Figure 4 shows the process of joining the positive electrode tab 20 to the positive electrode core 30, with a cross-sectional view of the positive electrode before joining the positive electrode tab (a) and a cross-sectional view of the positive electrode after joining the positive electrode tab (b).

[0038] The method for manufacturing the positive electrode 11 includes the following steps. (1) A step of forming a protective layer 50 on the exposed portion 31 of the positive electrode core. (2) A step of disposing the positive electrode tab 20 on the exposed portion 31 of the positive electrode core through the protective layer 50. (3) A step of joining the positive electrode tab 20 to the exposed portion 31 of the positive electrode core. In the third step, a connecting portion 51 containing at least one component of the positive electrode tab 20 and the exposed portion 31 of the positive electrode core is formed in the protective layer 50, and the positive electrode tab 20 and the exposed portion 31 of the positive electrode core are electrically connected through the connecting portion 51.

[0039] As shown in FIG. 4(a), as the first step, a protective layer 50 is formed on the exposed portion 31 of the positive electrode core, which is a portion where the positive electrode active material layer 32 is not formed on the positive electrode core 30. Before joining the positive electrode tab 20, the protective layer 50 is formed by applying a resin to at least a portion of the surface of the exposed portion 31 of the positive electrode core that overlaps with the positive electrode tab 20 to be disposed in the second step described later. The protective layer 50 may be formed by attaching a resin sheet to the exposed portion 31 of the positive electrode core.

[0040] As the second step, the positive electrode tab 20 is disposed on the exposed portion 31 of the positive electrode core through the protective layer 50. At this point, the positive electrode tab 20 and the exposed portion 31 of the positive electrode core are not electrically connected.

[0041] As shown in FIG. 4(b), as the third step, the positive electrode tab 20 is joined to the exposed portion 31 of the positive electrode core through the protective layer 50. In the third step, the connecting portion 51 is formed in the protective layer 50, and the connecting portion 51 is joined to the positive electrode tab 20. Thereby, the positive electrode tab 20 and the exposed portion 31 of the positive electrode core are electrically connected through the connecting portion 51. In the process of joining the positive electrode tab 20 to the connecting portion 51, the protective layer 50 between the positive electrode tab 20 and the connecting portion 51 disappears. That is, the protective layer 50 is formed on at least a portion of the surface of the exposed portion 31 of the positive electrode core that overlaps with the positive electrode tab 20 and is other than the connecting portion 51.

[0042] Various methods can be used to join the positive electrode tab 20 to the positive electrode core exposed portion 31 via the protective layer 50, but ultrasonic welding using an ultrasonic welding machine is preferred, for example. Ultrasonic welding is a joining method characterized by sandwiching the members to be joined between an ultrasonic horn and an anvil, applying ultrasonic vibration to the ultrasonic horn while applying pressure, and pushing the sandwiched members toward the anvil to apply a load, thereby generating strong frictional heat at the joining surfaces of the members, melting and joining them.

[0043] In the ultrasonic welding process for joining the positive electrode tab 20 to the positive electrode core exposed portion 31, first, an ultrasonic horn is placed on the side of the positive electrode tab 20 that is positioned on the surface of the protective layer 50, and an anvil is placed on the side of the positive electrode core exposed portion 31 where the positive electrode tab 20 is not placed. Next, the positive electrode tab 20 and the positive electrode core exposed portion 31 are welded together by applying ultrasonic vibration to the ultrasonic horn while the positive electrode core 30, protective layer 50, and positive electrode tab 20 are sandwiched between the ultrasonic horn and the anvil and pressure is applied. At this time, the portion of the positive electrode core exposed portion 31 that is pressed by the anvil has the shape of the anvil transferred onto it and has a shape that protrudes toward the positive electrode tab 20. This forms a connecting portion 51. Alternatively, the portion of the positive electrode tab 20 that is pressed by the ultrasonic horn may protrude toward the positive electrode core exposed portion 31 to form the connecting portion 51. The connecting portion 51 may be formed so that the protruding portion of the positive electrode core exposed portion 31 and the protruding portion of the positive electrode tab 20 are joined together. It is preferable that the positive electrode tab 20 and the positive electrode core exposed portion 31 be welded by ultrasonic welding because the formation of the connecting portion 51 is easy and the protective layer 50 is less susceptible to thermal damage. However, the welding method is not limited to ultrasonic welding, and laser welding or resistance welding can also be used. For example, when welding the positive electrode tab 20 and the positive electrode core exposed portion 31 by laser welding, a molten and solidified portion consisting of components derived from the positive electrode tab 20 and the positive electrode core exposed portion 31 is formed as the connecting portion 51 within the protective layer 50. In any welding method, the connecting portion 51 is formed to include at least one component of the positive electrode tab 20 and the positive electrode core exposed portion 31.

[0044] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0045] <Example 1> [Preparation of Positive Electrode] As the positive electrode active material, lithium nickel cobalt aluminate represented by LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ was used. The positive electrode active material, acetylene black (AB) as a conductive agent, and PVDF as a binder were mixed at a mass ratio of 98:1:1, and N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode slurry. Further, PVDF as a resin and NMP as a dispersion medium were mixed at a mass ratio of 100:5 to prepare a protective layer slurry. First, leaving a predetermined positive electrode core body exposed portion at the central portion in the longitudinal direction of the positive electrode, the positive electrode slurry was applied to both surfaces of the positive electrode core body made of aluminum foil (thickness: 15 μm), and the coating film was dried and compressed to obtain a composite layer with a thickness of 111 μm. Next, the protective layer slurry was applied to the surface of the positive electrode core body exposed portion, and the coating film was dried on a hot plate at 80 °C for 1 minute to form a protective layer with a thickness of 1 μm, and the positive electrode core body was cut to a predetermined electrode size. Using an ultrasonic welder, an aluminum tab (thickness: 100 μm) was welded to the positive electrode core body exposed portion through the protective layer to obtain a positive electrode. The ultrasonic welding was carried out under the conditions of an applied energy of 1.5 J and a hold time of 0.01 s.

[0046] [Preparation of Negative Electrode] As the negative electrode active material, a mixture of graphite and silicon oxide mixed at a mass ratio of 95:5 was used. The negative electrode active material, a dispersion of styrene butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na) were mixed at a solid content mass ratio of 98:1:1, and water was used as a dispersion medium to prepare a negative electrode slurry. Next, leaving a predetermined negative electrode core body exposed portion on both surfaces of the negative electrode core body made of copper foil, the negative electrode slurry was applied, the coating film was dried and compressed, and then the negative electrode core body was cut to a predetermined electrode size. A nickel tab was welded to the negative electrode core body exposed portion to obtain a negative electrode.

[0047] [Preparation of Non-aqueous Electrolyte] In a mixed solvent of ethylene carbonate and ethyl methyl carbonate mixed at a volume ratio of 3:7 (25 °C), LiPF ６ was dissolved to obtain a non-aqueous electrolyte.

[0048] [Battery Fabrication] The positive electrode and the negative electrode were wound in a spiral shape via a separator to create a wound electrode body. This electrode body was housed in a bottomed cylindrical outer casing, the non-aqueous electrolyte was injected, and the opening of the outer casing was sealed with a sealing body via a gasket to obtain battery X1.

[0049] <Example 2> In the preparation of the positive electrode, the thickness of the protective layer formed on the surface of the exposed portion of the positive electrode core was adjusted to 2 μm, except that the positive electrode and battery X2 were obtained in the same manner as in Example 1.

[0050] <Example 3> In the preparation of the positive electrode, the thickness of the protective layer formed on the surface of the exposed portion of the positive electrode core was adjusted to 4 μm, except that the positive electrode and battery X3 were obtained in the same manner as in Example 1.

[0051] <Comparative Example> In the preparation of the positive electrode, a positive electrode and battery Y were obtained in the same manner as in Example 1, except that a protective layer was not formed on the surface of the exposed portion of the positive electrode core.

[0052] [Confirmation of the presence or absence of cracks in the positive electrode core] For each battery in the examples and comparative examples, the presence or absence of cracks in the positive electrode core after the charge-discharge cycle test was confirmed by the following method. First, the prepared batteries were charged with a constant current of 1C until the battery voltage reached 4.2V, then rested for 30 minutes, and then discharged with a constant current of 5C until the battery voltage reached 2.5V, followed by a rest for 60 minutes. After repeating this charge-discharge cycle 200 times, each battery was disassembled, and the removed positive electrode core was visually inspected. At this time, batteries in which light transmission was confirmed were judged to have a "crack," and those in which light transmission was not confirmed were judged to be "no crack." The confirmation results are shown in Table 1.

[0053]

[0054] As shown in Table 1, no cracks were observed in the positive electrode core of any of the batteries X1 to X3 in the examples. In contrast, a crack was observed in the positive electrode core of battery Y in the comparative example because no protective layer was provided on the surface of the exposed portion of the positive electrode core.

[0055] From the above results, it can be seen that cracking of the positive electrode core can be prevented by providing a protective layer on the surface of the exposed portion of the positive electrode core, as in the batteries X1 to X3 of the examples.

[0056] The non-aqueous electrolyte secondary battery and the method for manufacturing an electrode for a non-aqueous electrolyte secondary battery according to the present disclosure may have the following configurations. Configuration 1: A non-aqueous electrolyte secondary battery comprising an electrode body in which electrodes of different polarities are stacked and arranged via a separator, and an outer casing for housing the electrode body, wherein at least one of the electrodes comprises: a core body; a composite layer formed on the surface of the core body; a core body exposed portion in which the core body is exposed; a protective layer formed on the surface of the core body exposed portion; and an electrode tab disposed on the surface of the protective layer, wherein the protective layer has a lower modulus of elasticity than the electrode tab, and the electrode tab and the core body exposed portion are connected via a connecting portion formed in the protective layer. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the electrode body is a wound-type electrode body in which the electrodes are wound via a separator. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 2, wherein the protective layer and the electrode tab are disposed on the inner surface of the wound core body. Configuration 4: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the thickness of the protective layer is 1 μm or more and 4 μm or less in the portion interposed between the core exposed portion and the electrode tab. Configuration 5: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the connecting portion is arranged at multiple positions within the protective layer. Configuration 6: A method for manufacturing an electrode for a non-aqueous electrolyte secondary battery, comprising: a first step of forming a protective layer on the core exposed portion; a second step of arranging an electrode tab on the core exposed portion via the protective layer; and a third step of joining the electrode tab to the core exposed portion, wherein in the third step, a connecting portion including at least one component of the electrode tab and the core exposed portion is formed within the protective layer, and the electrode tab and the core exposed portion are electrically connected via the connecting portion. Configuration 7: The method for manufacturing an electrode for a non-aqueous electrolyte secondary battery according to Configuration 6, wherein the third step is an ultrasonic welding step, in which the electrode tab and the exposed core are pressed together with an ultrasonic horn and an anvil to form a connecting portion, and the electrode tab and the exposed core are electrically connected.

[0057] 10 Battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18 Upper insulating plate, 19 Lower insulating plate, 20 Positive electrode tab, 21 Negative electrode tab, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 27a Opening, 28 Gasket, 30 Positive electrode core body, 31 Positive electrode core body exposed section, 32 Positive electrode mixture layer, 50 Protective layer, 51 Connecting section

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body in which electrodes of opposite polarities are stacked and arranged via a separator, and an outer casing for housing the electrode body, wherein at least one of the electrodes comprises: a core body; a composite layer formed on the surface of the core body; a core body exposed portion in which the core body is exposed; a protective layer formed on the surface of the core body exposed portion; and an electrode tab disposed on the surface of the protective layer, wherein the protective layer has a lower modulus of elasticity than the electrode tab, and the electrode tab and the core body exposed portion are connected via a connecting portion formed in the protective layer.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the electrode body is a wound-type electrode body in which the electrode is wound around a separator.

3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the protective layer and the electrode tab are arranged on the inner surface of the core body.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the protective layer is 1 μm or more and 4 μm or less in the portion interposed between the core body exposed portion and the electrode tab.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the connecting portion is arranged at multiple positions within the protective layer.

6. A method for manufacturing an electrode for a non-aqueous electrolyte secondary battery, comprising: a first step of forming a protective layer on a core body exposed portion; a second step of arranging an electrode tab on the core body exposed portion via the protective layer; and a third step of joining the electrode tab to the core body exposed portion, wherein in the third step, a connecting portion including at least one component of the electrode tab and the core body exposed portion is formed in the protective layer, and the electrode tab and the core body exposed portion are electrically connected via the connecting portion.

7. The method for manufacturing an electrode for a non-aqueous electrolyte secondary battery according to claim 6, wherein the third step is an ultrasonic welding step, wherein the electrode tab and the exposed core are pressed together with an ultrasonic horn and an anvil to form a connecting portion, and the electrode tab and the exposed core are electrically connected.

Images