Secondary battery

Abstract

The present invention suppresses deterioration in cycle characteristics of a secondary battery. A secondary battery (1) is provided with a negative electrode (3) and a positive electrode (4) that are immersed in an electrolyte, and a separator (33) that separates the negative electrode and the positive electrode, the negative electrode having a collector (negative electrode collector (31)) and a multi-layer material part (negative electrode multi-layer material part (32)), the multi-layer material part having a main surface (34) that faces the positive electrode with the separator therebetween, and a side surface (first side surface (35)) that is connected between the main surface and the collector. The separator covers at least the multilayer material portion of the negative electrode in a state of being in contact with the main surface and the side surface.

Description

Technical Field

[0001] The technology disclosed herein relates to a secondary battery. Background Art

[0002] Patent document 1 describes a conventional lithium secondary battery. Conventional lithium secondary batteries have a space retaining member between the exposed portion of the negative electrode current collector and the separator. The space retaining member ensures the space required for the expansion / contraction of the negative electrode composite material accompanying the charge and discharge of the secondary battery. The expansion / contraction of the negative electrode composite material is not hindered, and the capacity reduction accompanying the repeated charge and discharge is suppressed.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-242262

[0006] Technical problem to be solved by the invention

[0007] According to the research of the inventors of the present application, it was found that if the positive electrode composite material and the negative electrode composite material repeatedly expand / contract with repeated charge and discharge of the secondary battery, the electrolyte contained in the positive electrode composite material and the negative electrode composite material will seep out, and the amount of electrolyte contained in the positive electrode composite material and the negative electrode composite material will decrease. If the amount of electrolyte contained in the positive electrode composite material and the negative electrode composite material decreases, the capacity of the secondary battery will decrease. Summary of the invention

[0008] The technology disclosed herein suppresses the reduction in cycle characteristics of a secondary battery.

[0009] The technology disclosed herein relates to a secondary battery. The secondary battery has:

[0010] A negative electrode and a positive electrode, the negative electrode and the positive electrode are immersed in an electrolyte; and

[0011] a separator, the separator separating the negative electrode from the positive electrode,

[0012] The negative electrode comprises a current collector and a composite material portion on the current collector.

[0013] The composite material portion has a main surface and a side surface, the main surface facing the positive electrode via the separator, and the side surface connected between the main surface and the current collector.

[0014] The separator covers at least the composite material portion of the negative electrode in a state of being in contact with the main surface and the side surface.

[0015] The separator of the above-mentioned secondary battery covers at least the composite material portion of the negative electrode. In more detail, the composite material portion has a main surface and a side surface, and the separator covers the composite material portion in a state of contact with the main surface and the side surface. The separator suppresses the expansion / contraction of the composite material portion during the charge and discharge of the secondary battery. The suppression of the expansion / contraction of the composite material portion suppresses the seepage of the electrolyte from the composite material portion. In addition, the separator suppresses the outflow of the electrolyte seeping from the composite material portion. Since the reduction in the amount of the electrolyte contained in the composite material portion is suppressed, the reduction in the cycle characteristics of the secondary battery is suppressed.

[0016] In addition, the separator may also cover the composite material portion of the positive electrode. The separator covering the composite material portion of the positive electrode suppresses the reduction in the amount of electrolyte contained in the composite material portion. Generally, when comparing the positive electrode with the negative electrode, the expansion / contraction degree of the composite material portion of the negative electrode is greater. The reduction in the amount of electrolyte may be more significant at the negative electrode. The separator covering the composite material portion of the negative electrode is effective in suppressing the reduction in the cycle characteristics of the secondary battery.

[0017] Here, the separator can be formed by, for example, applying a slurry containing a resin and a solvent to the main surface and the side surface of the multi-layer material part, and then drying the applied slurry. By evaporation of the solvent, a porous separator can be realized that covers the multi-layer material part in a state of contact with the main surface and the side surface of the multi-layer material part.

[0018] In addition, the separator may be, for example, an insulating material including ceramics. In this case, a slurry including a ceramic material and a solvent may be applied to the main surface and the side surface of the composite material portion, and then the applied slurry may be dried to form the separator. Alumina, boehmite, aromatic polyamide, polyvinylidene fluoride, etc. may be used as the ceramic material. The size when using a ceramic material may be, for example, about 1.0 to 5.0 μm.

[0019] In the separator between the current collector and the main surface and in contact with the side surface, the thickness on the current collector side may be thicker than the thickness on the main surface side.

[0020] On the side surface of the composite material part, the thickness of the separator is relatively thicker than that on the collector side. The composite material part further suppresses its expansion / contraction on the collector side. Suppressing the expansion / contraction of the composite material part on the collector side suppresses the separation of the composite material part from the collector. Making the thickness of the separator on the collector side relatively thicker more effectively suppresses the reduction of the cycle characteristics of the secondary battery.

[0021] The negative electrode may include a holding portion that is joined to the current collector with a gap therebetween with respect to the side surface of the composite material portion and that faces the side surface.

[0022] The retaining portion joined to the current collector faces the separator covering the side surface of the multilayer material portion, and inhibits the separator from separating from the side surface of the multilayer material portion. The retaining portion inhibits the separator from separating from the side surface of the multilayer material portion by interfering with the separator, for example, a porous film.

[0023] In addition, when the separator is formed by applying slurry to the composite material part, the retaining part prevents the slurry applied to the side surface from flowing out of the composite material part along the surface of the collector. The retaining part prevents the separator from separating from the side surface of the composite material part during the manufacture of the secondary battery.

[0024] The separator is held in contact with the clad material portion during or after manufacturing the secondary battery.

[0025] The secondary battery may further include a container that accommodates a power generation element and the electrolyte, wherein the power generation element includes the negative electrode, the positive electrode, and the separator.

[0026] The current collector protrudes outward from the opening of the container.

[0027] The holding portion is a resin that closes the opening of the container.

[0028] If the holding portion is used for both holding the separator and sealing the container, the number of components of the secondary battery can be reduced.

[0029] The negative electrode current collector may include a recessed portion sunken from a surface of the current collector between the composite material portion and the retaining portion.

[0030] The recessed portion prevents the separator from separating from the side surface of the multi-layer material portion. For example, the separator made of a porous film interferes with the recessed portion. The separator is prevented from separating from the side surface of the multi-layer material portion.

[0031] In addition, when the separator is formed by applying slurry to the multilayer material part, the recessed portion prevents the slurry applied to the side surface from flowing out of the multilayer material part along the surface of the current collector. The recessed portion prevents the separator from separating from the side surface of the multilayer material part during the manufacture of the separator.

[0032] Effects of the Invention

[0033] Since the secondary battery described above suppresses expansion and contraction of at least the cladding material portion of the negative electrode during charge and discharge of the secondary battery, it is possible to suppress a decrease in cycle characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a cross-sectional view of a secondary battery.

[0035] Figure 2 It is a cross-sectional view of the negative electrode.

[0036] Figure 3 yes Figure 2 Cross-sectional view along line III-III.

[0037] Figure 4 It is a cross-sectional view of a negative electrode and a positive electrode of a secondary battery according to a modification.

[0038] Figure 5 It is a cross-sectional view of a negative electrode of a secondary battery according to a modification.

[0039] Figure 6 It is a cross-sectional view of a secondary battery according to a modification.

[0040] Explanation of symbols

[0041] 1 Secondary battery

[0042] 10 Secondary batteries

[0043] 12, 13 opening

[0044] 14 Container

[0045] 2 Power generation element

[0046] 3 Negative electrode

[0047] 31. Negative electrode collector

[0048] 32 Negative electrode composite material department

[0049] 33 Divider

[0050] 34 Main surface

[0051] 35 first side surface

[0052] 36 Second side surface

[0053] 37 recess

[0054] 4 Positive electrode

[0055] 41. Positive electrode collector

[0056] 42 Positive electrode composite material department

[0057] 43 Divider

[0058] 44 Main surface

[0059] 45 Side surface

[0060] 5. Resin

[0061] 51. Maintaining part

[0062] 52. Maintaining part

[0063] 53. Maintaining department. DETAILED DESCRIPTION

[0064] Hereinafter, embodiments of the secondary battery will be described with reference to the drawings. The secondary battery described here is an example.

[0065] (Overall structure of secondary battery)

[0066] Figure 1 The overall structure of the secondary battery 1 is schematically shown. Figure 1 The secondary battery 1 is a battery unit in which a power generation element 2 is housed in a container 14. The secondary battery 1 is, for example, a lithium-ion battery. The container 14 is a component in which a sheet of laminated material 11 is folded or two sheets of laminated material 11 are overlapped to form a bag. The laminated material 11 is, for example, a three-layer structure in which a metal layer is sandwiched on both sides by a resin layer. The metal layer is, for example, aluminum or stainless steel. The resin layer is, for example, polypropylene (PP) or polyethylene (PE). The container 14 is sealed in a state in which the power generation element 2 and the electrolyte are housed. The secondary battery 1 is a so-called soft-pack battery.

[0067] The power generation element 2 has a negative electrode 3 and a positive electrode 4. The negative electrode 3 and the positive electrode 4 are immersed in the electrolyte inside the container 14. The negative electrode 3 and the positive electrode 4 are alternately stacked. The number of negative electrodes 3 and positive electrodes 4 is arbitrary. For example, the number of negative electrodes 3 and positive electrodes 4 may be more than the number of negative electrodes 3. The power generation element 2 is an electrode stack. In addition, hereinafter, the direction in which the negative electrode 3 and the positive electrode 4 are stacked is sometimes referred to as the Y direction.

[0068] The negative electrode 3 has a negative electrode collector 31. The negative electrode collector 31 is a thin plate extending in the X direction orthogonal to the Y direction. Figure 1 The left end of the secondary battery 1 protrudes outward from the first opening 12 of the container 14. In addition, the X direction is the direction in which the negative electrode collector 31 and the positive electrode collector 41 described later protrude in the secondary battery 1. In addition, the direction orthogonal to the X direction and the Y direction is called the Z direction. In other words, the Z direction is the direction orthogonal to the direction in which the negative electrode collector 31 and the positive electrode collector 41 protrude.

[0069] A negative electrode active material is applied to the upper and lower surfaces of a negative electrode current collector 31 located inside the container 14 . The negative electrode active material forms a negative electrode composite material portion 32 on the negative electrode current collector 31 .

[0070] The negative electrode 3 has a separator 33. The separator 33 separates the negative electrode composite material portion 32 of the negative electrode 3 and the positive electrode composite material portion 42 of the positive electrode 4. The separator 33 covers the surfaces of the two negative electrode composite material portions 32. The details of the structure of the separator 33 will be described later.

[0071] The positive electrode 4 has a positive electrode collector 41. The positive electrode collector 41 is a thin plate extending in the X direction. Figure 1 The right end of the positive electrode current collector 41 protrudes outward from the second opening 13 of the container 14. The second opening 13 is an opening opposite to the first opening 12 in the X direction. In addition, the protruding direction of the positive electrode current collector 41 is not limited to the opposite side to the negative electrode current collector 31.

[0072] The positive electrode active material is applied to the upper and lower surfaces of the positive electrode collector 41 located inside the container 14 . The positive electrode active material forms a positive electrode composite material portion 42 connected to the positive electrode collector 41 .

[0073] As described above, the negative electrodes 3 and the positive electrodes 4 are alternately stacked. The negative electrode composite material portion 32 and the positive electrode composite material portion 42 are stacked in the stacking direction via the separator 33 inside the container 14. The area of ​​the negative electrode composite material portion 32 may be larger than that of the positive electrode composite material portion 42, for example. In the protruding direction of the positive electrode current collector 41, the negative electrode composite material portion 32 may also protrude more than the positive electrode composite material portion 42.

[0074] The first opening 12 of the container 14 is sealed by the resin 5. The resin 5 is located between the laminate 11 and the negative electrode collector 31 and between the negative electrode collectors 31. Similarly, the second opening 13 is sealed by the resin 5. The resin 5 is located between the laminate 11 and the positive electrode collector 41 and between the positive electrode collectors 41.

[0075] The plurality of negative electrode current collectors 31 are not connected inside the container 14, but protrude outside the container 14 respectively. The plurality of positive electrode current collectors 41 are also not connected inside the container 14, but protrude outside the container 14 respectively. In the container 14, the connection space between the negative electrode current collector 31 and the positive electrode current collector 41 can be omitted, so the area of ​​the negative electrode composite material part 32 and the positive electrode composite material part 42 can be increased. Therefore, the energy density of the secondary battery 1 can be improved.

[0076] (Structure of the separator)

[0077] Next, refer to Figure 2 and Figure 3 The structure of the separator 33 will be described in detail. Figure 2 The cross section of one negative electrode 3 included in the power generating element 2 is shown. Figure 3 yes Figure 2 Cross-sectional view along line III-III.

[0078] As described above, the negative electrode composite material portion 32 is located above the negative electrode current collector 31. Figure 2In the figure, for ease of understanding, only the negative electrode composite material portion 32 and the separator 33 on the upper surface of the negative electrode current collector 31 are shown. The structures of the negative electrode composite material portion 32 and the separator 33 on the lower surface of the negative electrode current collector 31 are also the same as those of the negative electrode composite material portion 32 and the separator 33 on the upper surface.

[0079] The negative electrode composite material portion 32 has a main surface 34 and side surfaces 35 and 36. The main surface 34 is a surface facing the positive electrode composite material portion 42 via the separator 33. The side surfaces 35 and 36 are surfaces connected between the main surface 34 and the negative electrode current collector 31. The side surfaces include a first side surface 35 (see Figure 2 ) and a second side surface 36 facing the Z direction (refer to Figure 3 ).

[0080] The separator 33 is, for example, a porous body that can be permeated by ionic substances. The separator 33 is formed, for example, by applying a slurry containing a resin and a solvent to the main surface 34, the first side surface 35, and the second side surface 36 of the negative electrode composite material part 32, and then drying the slurry. The solvent evaporates, so that the separator 33 becomes a porous body, and the separator 33 covers the negative electrode composite material part 32 in a state of contact with the main surface 34, the first side surface 35, and the second side surface 36 of the negative electrode composite material part 32. As a resin for forming the separator 33, polyethylene, polypropylene, aromatic polyamide resin, or liquid crystal polyester resin can be exemplified. As a solvent, water, methyl ethyl ketone, acetone, or alcohols (such as ethanol) can be exemplified. In addition, the method for forming the separator 33 is not limited to the application of the slurry.

[0081] Here, the holding portions 51 and 52 are joined to the surface of the negative electrode current collector 31. The holding portion 51 is spaced a predetermined distance from the first side surface 35 of the negative electrode composite material portion 32 and faces the first side surface 35. The holding portion 52 is spaced a predetermined distance from the second side surface 36 and faces the second side surface 36.

[0082] When forming the separator 33, the retaining portions 51 and 52 prevent the slurry applied to the first side surface 35 and the second side surface 36 of the negative electrode composite material portion 32 from flowing out of the negative electrode composite material portion 32 along the surface of the negative electrode current collector 31. When manufacturing the secondary battery 1, the retaining portions 51 and 52 prevent the separator 33 from leaving the side surfaces 35 and 36 of the negative electrode composite material portion 32.

[0083] The retaining portion 51 also constitutes the resin 5 that seals the first opening 12 of the container 14 in the secondary battery 1. That is, in the power generation element 2 in which the negative electrode 3 and the positive electrode 4 are stacked, the retaining portion 51 is arranged in the stacking direction. When the secondary battery 1 is manufactured, after the laminated material 11 covers the power generation element 2, the retaining portion 51 arranged in the stacking direction is pressurized and heated from the outside toward the center side in the stacking direction. The edge of the laminated material 11 is sealed by welding the retaining portion 51 and the negative electrode collector 31 or the retaining portions 51 to each other. In addition, the positive electrode collector 41 of the positive electrode 4 is joined to the retaining portion that seals the second opening 13 of the container 14.

[0084] The separator 33 covers the negative electrode composite material portion 32 in a state of being in contact with the main surface 34, the first side surface 35, and the second side surface 36 of the negative electrode composite material portion 32. There is no gap or substantially no gap between the separator 33 and the main surface 34, the first side surface 35, and the second side surface 36.

[0085] The thickness ty of the spacer 33 in contact with the main surface 34, that is, the thickness ty in the Y direction, is thicker than the thickness tx1 or tz1 of the spacer 33 in contact with the first side surface 35. The thickness ty can be set to, for example, 5 μm to 30 μm. The thickness tx1 or tz1 can be set to, for example, 1 μm to 15 μm.

[0086] In addition, in the separator 33 in contact with the first side surface 35 or the second side surface 36 , the thickness tx2 or tz2 on the negative electrode current collector 31 side is thicker than the thickness tx1 or tz1 on the main surface 34 side.

[0087] As described above, the separator 33 of the secondary battery 1 covers the negative electrode composite material portion 32. More specifically, the separator 33 covers the negative electrode composite material portion 32 in a state of being in contact with the main surface 34, the first side surface 35 and the second side surface 36 of the negative electrode composite material portion 32. The separator 33 suppresses the expansion / contraction of the negative electrode composite material portion 32 during the charge and discharge of the secondary battery 1. The suppression of the expansion / contraction of the negative electrode composite material portion 32 suppresses the electrolyte from seeping out of the negative electrode composite material portion 32. The separator 33 also suppresses the outflow of the electrolyte seeping from the negative electrode composite material portion 32. Even if the secondary battery 1 is repeatedly charged and discharged, the negative electrode composite material portion 32 retains the electrolyte. The reduction in the capacity of the secondary battery 1 is suppressed. That is, the reduction in the cycle characteristics of the secondary battery 1 is suppressed.

[0088] In lithium ion batteries, the expansion / contraction of the negative electrode composite material portion 32 is generally greater than that of the positive electrode composite material portion 42. The separator 33 suppresses the expansion / contraction of the negative electrode composite material portion 32, which is particularly effective in suppressing the reduction in the cycle characteristics of the lithium ion battery.

[0089] In addition, the separator 33 may be elastically deformable. The elastically deformable separator 33 can suppress damage when the negative electrode composite material portion 32 attempts to expand or contract.

[0090] On the first side surface 35 or the second side surface 36 of the negative electrode composite material portion 32, the thickness of the separator 33 is relatively thick as the thickness (tx1, tz2) on the collector side. The negative electrode composite material portion 32 is bonded to the negative electrode collector 31, but the separator 33 further suppresses the expansion / contraction of the negative electrode composite material portion 32 on the collector side. By suppressing the expansion / contraction of the negative electrode composite material portion 32 on the collector side, the negative electrode composite material portion 32 is suppressed from peeling off from the negative electrode collector 31. Making the thickness of the separator 33 on the collector side relatively thick is advantageous for suppressing the deterioration of the secondary battery 1.

[0091] In addition, the above-mentioned holding parts 51 and 52 not only hold the separator 33 during the manufacture of the secondary battery 1, but also interfere with the separator 33 after the manufacture of the secondary battery 1 to prevent the separator 33 from being separated from the negative electrode composite material part 32. The separator 33 is held in contact with the negative electrode composite material part 32 during or after the manufacture of the secondary battery 1.

[0092] In addition, the partition 33 of the second side surface 36 can be omitted.

[0093] (Variant 1)

[0094] Figure 4 A modified example of the separator is shown. The separator may be formed on each of the negative electrode 3 and the positive electrode 4 .

[0095] The separator 43 of the positive electrode 4 covers the positive electrode mixed layer material portion 42. More specifically, the positive electrode mixed layer material portion 42 has a main surface 44 and a side surface 45. The separator 43 covers the positive electrode mixed layer material portion 42 in a state of being in contact with the main surface 44 and the side surface 45.

[0096] Here, the separator 43 of the positive electrode 4 and the separator 33 of the negative electrode 3 overlap in the Y direction between the positive electrode composite material portion 42 and the negative electrode composite material portion 32. The thickness ty1 of the separator 33 of the negative electrode 3 and the thickness ty2 of the separator 43 of the positive electrode 4 are respectively greater than Figure 2 The thickness ty of the separator 33 is thin. The sum of the thickness ty1 and the thickness ty2 is equal to or substantially equal to Figure 2 The thickness ty of the separator 33. In addition, the thickness ty1 and the thickness ty2 may be the same or different.

[0097] In addition, in the separator in contact with the side surface 45 of the positive electrode composite material portion 42 , the thickness tx4 on the positive electrode current collector 41 side is greater than the thickness tx3 on the main surface 44 side.

[0098] Since the separator 43 covers the positive electrode composite material portion 42, the expansion / contraction of the positive electrode composite material portion 42 during the charge and discharge of the secondary battery 1 is suppressed. The electrolyte is suppressed from leaking out of the positive electrode composite material portion 42. The secondary battery 1 suppresses the reduction in the amount of electrolyte in the positive electrode composite material portion 42 and the negative electrode composite material portion 32, respectively. Even if the secondary battery 1 is repeatedly charged and discharged, the positive electrode composite material portion 42 and the negative electrode composite material portion 32 can retain the electrolyte together. Even if the secondary battery 1 is repeatedly charged and discharged, the reduction in capacity can be suppressed. That is, the secondary battery 1 suppresses the reduction in cycle characteristics.

[0099] On the side surface 45 of the positive electrode composite material portion 42, the thickness of the separator 43 is relatively thick on the collector side, similarly to the negative electrode composite material portion 32. This prevents the positive electrode composite material portion 42 from peeling off from the positive electrode collector 41.

[0100] The separator 43 of the positive electrode 4 can also be formed by the same method as the separator 33 of the negative electrode 3. The positive electrode 4 has a holding portion 53. The holding portion 53 faces the side surface 45 of the positive electrode composite material portion 42 at a predetermined distance.

[0101] The retaining portion 53 prevents the slurry applied to the side surface 45 of the positive electrode composite material portion 42 from flowing out from the positive electrode composite material portion 42 along the surface of the positive electrode current collector 41 when the separator 43 is formed. The retaining portion 53 also prevents the separator 43 from being separated from the positive electrode composite material portion 42 by interfering with the separator 43 after the secondary battery 1 is manufactured.

[0102] In addition, the holding portion of the positive electrode 4 may also be formed by closing the second opening 13 of the container 14 in the secondary battery 1 (see Figure 1 ) of resin 5.

[0103] (Variant 2)

[0104] Figure 5 A modification example of the current collector is shown. A recess 37 for holding a separator may be formed in the current collector.

[0105] The recessed portion 37 is recessed from the surface of the negative electrode current collector 31 . The recessed portion 37 is located between the negative electrode composite material portion 32 and the holding portion 51 .

[0106] When the slurry is applied to the negative electrode composite material portion 32, the recessed portion 37 prevents the slurry applied to the first side surface 35 from flowing out of the negative electrode composite material portion 32 along the surface of the negative electrode current collector 31. The recessed portion 37 prevents the separator 33 from separating from the side surface of the negative electrode composite material portion 32 when the secondary battery 1 is manufactured.

[0107] Furthermore, even after the secondary battery 1 is manufactured, the recessed portion 37 interferes with the separator 33 , thereby preventing the separator 33 from being separated from the first side surface 35 of the negative electrode composite material portion 32 .

[0108] (Variant 3)

[0109] Figure 6 Modifications of the structure of the secondary battery are shown. Figure 1 The plurality of negative electrode current collectors 31 and the plurality of positive electrode current collectors 41 of the secondary battery 1 protrude outward from the openings 12 and 13 of the container 14 , respectively. Figure 6 The plurality of negative electrode current collectors 31 of the secondary battery 10 are connected to each other inside the container 14. The tab 15 connected to the collective portion of the negative electrode current collectors 31 protrudes outward from the container 14. That is, the tab 15 is joined to the edge of the laminate 11 via the resin 54. In the secondary battery 10, the retaining portion 51 has the function of retaining the separator 33, but the opening of the container 14 is not closed.

[0110] In the secondary battery 10 , the positive electrode current collector 41 and the negative electrode current collector 31 are also connected to each other inside the container 14 , similarly to the negative electrode current collector 31 .

[0111] (Other embodiments)

[0112] In addition, the separators 33 and 44 can be formed by applying the slurry as described above, or by using a porous film. That is, the multi-layer material part can be covered by the porous film in a state where the porous film is in contact with the main surface and the side surface of the multi-layer material part. The retaining portion 51, 52, 53 or the recessed portion 37 can prevent the separator from being separated from the side surface of the multi-layer material part by interfering with the separator composed of the porous film.

[0113] Furthermore, the features of the above-mentioned multiple components can be combined within a possible range.

Claims

1. A secondary battery, characterized in that: have: A negative electrode and a positive electrode, the negative electrode and the positive electrode are immersed in an electrolyte; and a separator, the separator separating the negative electrode from the positive electrode, The negative electrode comprises a current collector and a composite material portion on the current collector. The composite material portion has a main surface and a side surface, the main surface facing the positive electrode via the separator, and the side surface connected between the main surface and the current collector. The separator covers at least the composite material portion of the negative electrode in a state of being in contact with the main surface and the side surface.

2. The secondary battery according to claim 1, characterized in that: In the separator between the current collector and the main surface and in contact with the side surface, the thickness on the current collector side is thicker than the thickness on the main surface side.

3. The secondary battery according to claim 1 or 2, characterized in that: The negative electrode includes a holding portion that is joined to the current collector with a gap therebetween with respect to the side surface of the composite material portion and that faces the side surface.

4. The secondary battery according to claim 3, characterized in that: A container is further provided, the container accommodating a power generation element and the electrolyte, the power generation element including the negative electrode, the positive electrode and the separator, The current collector protrudes outward from the opening of the container. The holding portion is a resin that closes the opening of the container.

5. The secondary battery according to claim 3, characterized in that: The current collector of the negative electrode has a recessed portion recessed from a surface of the current collector between the multilayer material portion and the retaining portion.

Images