Secondary battery

Abstract

To suppress a deterioration of cycle characteristics of a secondary battery.SOLUTION: A secondary battery 1 includes: a negative electrode 3 and a positive electrode 4 which are immersed in an electrolyte; and a separator 33 which separates the negative electrode and positive electrode. The negative electrode has a current collector (negative electrode current collector 31) and a composite portion (negative electrode composite portion 32). The composite portion has a main surface 34 which faces the positive electrode via the separator, and a side surface (first side surface 35) which connects the main surface and the current collector. The separator covers at least the composite portion of the negative electrode in a state of being in contact with the main surface and the side surface.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Patent Document 1 describes a conventional lithium secondary battery. The conventional lithium secondary battery includes a spacer between an exposed portion of a negative electrode current collector and a separator. The spacer secures a space required for expansion / contraction of the negative electrode composite material accompanying charging / discharging of the secondary battery. Not impeding the expansion / contraction of the negative electrode composite material suppresses the capacity reduction accompanying repeated charging / discharging. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-242262 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the study of the present inventors, it was found that when the positive electrode mixture and the negative electrode mixture repeatedly expand and contract as the secondary battery is repeatedly charged and discharged, the electrolyte contained in the positive electrode mixture and the negative electrode mixture seeps out, and the amount of the electrolyte contained in the positive electrode mixture and the negative electrode mixture decreases. When the amount of the electrolyte contained in the positive electrode mixture and the negative electrode mixture decreases, the capacity of the secondary battery decreases.

[0005] The technique disclosed herein suppresses deterioration of the cycle characteristics of a secondary battery.

[0006] The technology disclosed herein relates to a secondary battery. a negative electrode and a positive electrode immersed in an electrolyte; A separator separating the negative electrode and the positive electrode, The negative electrode has a current collector and a mixture portion on the current collector, The mixture portion has a main surface facing the positive electrode via the separator and a side surface connecting the main surface and the current collector, The separator covers at least the mixture portion of the negative electrode in a state of contact with the main surface and the side surface.

[0007] The separator of the secondary battery covers at least the composite part of the negative electrode. More specifically, the composite part has a main surface and a side surface, and the separator covers the composite part while contacting the main surface and the side surface. The separator suppresses expansion / contraction of the composite part during charging / discharging of the secondary battery. The suppression of expansion / contraction of the composite part suppresses the electrolyte from seeping out of the composite part. In addition, the separator suppresses the electrolyte seeping out of the composite part from flowing out. Since the reduction in the amount of electrolyte contained in the composite part is suppressed, the deterioration of the cycle characteristics of the secondary battery is suppressed.

[0008] The separator may cover the composite part of the positive electrode. The separator covering the composite part of the positive electrode suppresses the decrease in the amount of electrolyte contained in the composite part. In general, the composite part of the negative electrode has a greater degree of expansion / contraction when compared with the positive electrode. The decrease in the amount of electrolyte may be more significant in the negative electrode. Covering the composite part of the negative electrode with the separator is effective in suppressing the decrease in the cycle characteristics of the secondary battery.

[0009] Here, the separator may be formed by, for example, applying a slurry containing a resin and a solvent to the main surface and side surfaces of the composite part, and then drying the applied slurry. By evaporating the solvent, a porous separator is realized that covers the composite part while being in contact with the main surface and side surfaces of the composite part.

[0010] The separator may be an insulating material containing, for example, ceramic. In this case, a slurry containing a ceramic material and a solvent is applied to the main surface and side surface of the composite part, and then the applied slurry is dried to form the separator. The ceramic material may be alumina, boehmite, aramid, polyvinylidene fluoride, or the like. When a ceramic material is used, the size may be, for example, about 1.0 to 5.0 μm.

[0011] In the separator in contact with the side surface between the current collector and the main surface, the thickness of the current collector side may be greater than the thickness of the main surface side.

[0012] The thickness of the separator is relatively thick on the current collector side of the composite part. The expansion / contraction of the composite part is further suppressed on the current collector side. Suppressing the expansion / contraction of the composite part on the current collector side suppresses the composite part from peeling off from the current collector. Increasing the thickness of the separator on the current collector side relatively more effectively suppresses the deterioration of the cycle characteristics of the secondary battery.

[0013] The negative electrode may have a holding portion that is joined to the current collector with a gap between the side surface of the mixture portion and faces the side surface.

[0014] The retaining portion joined to the current collector faces the separator covering the side surface of the composite portion and prevents the separator from separating from the side surface of the composite portion. The retaining portion prevents the separator from separating from the side surface of the composite portion by interfering with the separator made of, for example, a porous membrane.

[0015] In addition, when the separator is formed by applying a slurry to the composite part, the retaining part prevents the slurry applied to the side surface from flowing out of the composite part along the surface of the current collector, and prevents the separator from coming off the side surface of the composite part during the manufacture of the secondary battery.

[0016] The separator is maintained in contact with the composite material portion during or after the secondary battery is manufactured.

[0017] the secondary battery further includes a container that contains a power generating element including the negative electrode, the positive electrode, and the separator, and the electrolyte; the current collector protrudes outside the container through an opening of the container, The holding portion may be a resin that seals the opening of the container.

[0018] 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.

[0019] The negative electrode current collector may have a recess between the mixture portion and the holding portion, the recess being recessed from a surface of the current collector.

[0020] The recess prevents the separator from coming off the side surface of the composite material. For example, a separator made of a porous film interferes with the recess. The separator is prevented from coming off the side surface of the composite material.

[0021] Furthermore, when the separator is formed by applying a slurry to the composite part, the recesses prevent the slurry applied to the side surface from flowing out of the composite part along the surface of the current collector.The recesses prevent the separator from being separated from the side surface of the composite part during the manufacture of the separator. Effect of the Invention

[0022] In the secondary battery, the expansion / contraction of at least the composite material portion of the negative electrode during charging and discharging of the secondary battery is suppressed, so that deterioration of cycle characteristics can be suppressed. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a cross-sectional view of a secondary battery. [Diagram 2] FIG. 2 is a cross-sectional view of the negative electrode. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view of the negative electrode and the positive electrode of a secondary battery according to a modified example. [Diagram 5] FIG. 5 is a cross-sectional view of a negative electrode of a secondary battery according to a modified example. [Figure 6] FIG. 6 is a cross-sectional view of a secondary battery according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of a secondary battery will be described with reference to the drawings. The secondary battery described here is merely an example.

[0025] (Overall structure of secondary battery) FIG. 1 shows a schematic diagram of the overall structure of a secondary battery 1. The secondary battery 1 in FIG. 1 is a battery cell in which a power generating element 2 is housed in a container 14. The secondary battery 1 is, for example, a lithium ion battery. The container 14 is formed into a bag shape by folding one laminate material 11 or by overlapping two laminate materials 11. The laminate material 11 has, for example, a three-layer structure in which a metal layer is sandwiched between resin layers on both sides. 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 while housing the power generating element 2 and an electrolyte. The secondary battery 1 is a so-called pouch-type battery.

[0026] The power generating element 2 has a negative electrode 3 and a positive electrode 4. The negative electrodes 3 and the positive electrodes 4 are immersed in an electrolyte inside a container 14. The negative electrodes 3 and the positive electrodes 4 are alternately stacked. The number of the negative electrodes 3 and the positive electrodes 4 is arbitrary. The number of the negative electrodes 3 may be greater than the number of the positive electrodes 4, for example. The power generating element 2 is an electrode laminate. In the following, the direction in which the negative electrodes 3 and the positive electrodes 4 are stacked may be referred to as the Y direction.

[0027] The negative electrode 3 has a negative electrode current collector 31. The negative electrode current collector 31 is a thin plate material extending in the X direction perpendicular to the Y direction. A first end of the negative electrode current collector 31, that is, a left end in FIG. 1, protrudes outward from a first opening 12 of the container 14. The X direction is a direction in which the negative electrode current collector 31 and a positive electrode current collector 41, which will be described later, protrude in the secondary battery 1. The direction perpendicular to the X direction and the Y direction is called the Z direction. In other words, the Z direction is a direction perpendicular to the direction in which the negative electrode current collector 31 and the positive electrode current collector 41 protrude.

[0028] 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 mixture portion 32 on the negative electrode current collector 31.

[0029] The negative electrode 3 has a separator 33. The separator 33 separates the negative electrode mixture portion 32 of the negative electrode 3 from the positive electrode mixture portion 42 of the positive electrode 4. The separator 33 covers the surface of each of the two negative electrode mixture portions 32. The structure of the separator 33 will be described in detail later.

[0030] The positive electrode 4 has a positive electrode current collector 41. The positive electrode current collector 41 is a thin plate material extending in the X direction. A second end of the positive electrode current collector 41, i.e., the right end in FIG. 1 , protrudes outward from a second opening 13 of the container 14. The second opening 13 is an opening opposite to the first opening 12 in the X direction. Note that the protruding direction of the positive electrode current collector 41 is not limited to the opposite side with respect to the negative electrode current collector 31.

[0031] A positive electrode active material is applied to the upper and lower surfaces of a positive electrode current collector 41 located inside the container 14. The positive electrode active material forms a positive electrode mixture portion 42 to which the positive electrode current collector 41 is connected.

[0032] As described above, the negative electrodes 3 and the positive electrodes 4 are stacked alternately. The negative electrode mixture portion 32 and the positive electrode mixture portion 42 are stacked in the stacking direction inside the container 14 with the separator 33 interposed therebetween. The area of ​​the negative electrode mixture portion 32 may be larger than the area of ​​the positive electrode mixture portion 42, for example. In the protruding direction of the positive electrode current collector 41, the negative electrode mixture portion 32 may protrude beyond the positive electrode mixture portion 42.

[0033] The first opening 12 of the container 14 is sealed with resin 5. The resin 5 is located between the laminate material 11 and the negative electrode current collector 31, and between the negative electrode current collectors 31. Similarly, the second opening 13 is sealed with resin 5. The resin 5 is located between the laminate material 11 and the positive electrode current collector 41, and between the positive electrode current collectors 41.

[0034] The multiple negative electrode current collectors 31 are not connected inside the container 14, and each protrude to the outside of the container 14. Similarly, the multiple positive electrode current collectors 41 are not connected inside the container 14, and each protrude to the outside of the container 14. Since the connection space between the negative electrode current collectors 31 and the positive electrode current collectors 41 inside the container 14 can be omitted, the areas of the negative electrode composite portion 32 and the positive electrode composite portion 42 can be increased accordingly. This allows the energy density of the secondary battery 1 to be increased.

[0035] (Separator structure) Next, the structure of the separator 33 will be described in detail with reference to Fig. 2 and Fig. 3. Fig. 2 shows a cross section of one negative electrode 3 included in the power generating element 2. Fig. 3 is a cross section taken along line III-III in Fig. 2.

[0036] As described above, the negative electrode mixture portion 32 is located on the negative electrode current collector 31. In order to facilitate understanding, Fig. 2 only shows the negative electrode mixture portion 32 and separator 33 on the upper surface of the negative electrode current collector 31. The negative electrode mixture portion 32 and separator 33 on the lower surface of the negative electrode current collector 31 have the same structure as the negative electrode mixture portion 32 and separator 33 on the upper surface.

[0037] The negative electrode mixture portion 32 has a main surface 34 and side surfaces 35, 36. The main surface 34 faces the positive electrode mixture portion 42 via the separator 33. The side surfaces 35, 36 connect the main surface 34 and the negative electrode current collector 31. The side surfaces include a first side surface 35 (see FIG. 2) facing in the X direction and a second side surface 36 (see FIG. 3) facing in the Z direction.

[0038] The separator 33 is, for example, a porous body through which an ionic substance can permeate. The separator 33 is formed by, for example, 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 part 32, and then drying the slurry. When the solvent evaporates, the separator 33 becomes a porous body, and the separator 33 covers the negative electrode composite part 32 in a state in which the separator 33 is in contact with the main surface 34, the first side surface 35, and the second side surface 36 of the negative electrode composite part 32. Examples of resins for forming the separator 33 include polyethylene, polypropylene, aromatic polyamide resin, and liquid crystal polyester resin. Examples of solvents include water, methyl ethyl ketone, acetone, and alcohols (e.g., ethanol). The method for forming the separator 33 is not limited to applying a slurry.

[0039] Here, holding portions 51 and 52 are joined to the surface of negative electrode current collector 31. Holding portion 51 faces first side surface 35 of negative electrode composite portion 32 with a predetermined gap therebetween. Holding portion 52 faces second side surface 36 with a predetermined gap therebetween.

[0040] The retaining portions 51, 52 prevent the slurry applied to the first side surface 35 and the second side surface 36 of the negative electrode mixture portion 32 from flowing out of the negative electrode mixture portion 32 along the surface of the negative electrode current collector 31 when the separator 33 is formed. The retaining portions 51, 52 prevent the separator 33 from being separated from the side surfaces 35, 36 of the negative electrode mixture portion 32 when the secondary battery 1 is manufactured.

[0041] 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 generating element 2 in which the negative electrode 3 and the positive electrode 4 are laminated, the retaining portions 51 are arranged in the stacking direction. When the secondary battery 1 is manufactured, the laminate material 11 is placed on the power generating element 2, and then the retaining portions 51 arranged in the stacking direction are pressurized and heated from the outside toward the center in the stacking direction. The retaining portions 51 are welded to the negative electrode current collector 31, or the retaining portions 51 are welded to each other, thereby sealing the edge of the laminate material 11. A retaining portion that seals the second opening 13 of the container 14 is joined to the positive electrode current collector 41 of the positive electrode 4.

[0042] The separator 33 covers the negative electrode mixture portion 32 in contact with the main surface 34, the first side surface 35, and the second side surface 36 of the negative electrode mixture 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.

[0043] The thickness ty of the separator 33 in contact with the main surface 34, i.e., the thickness ty in the Y direction, is greater than the thickness tx1 or tz1 of the separator 33 in contact with the first side surface 35. The thickness ty may be, for example, 5 μm or more and 30 μm or less. The thickness tx1 or tz1 may be, for example, 1 μm or more and 15 μm or less.

[0044] 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 greater than the thickness tx1 or tz1 on the main surface 34 side.

[0045] As described above, the separator 33 of the secondary battery 1 covers the negative electrode mixture portion 32. More specifically, the separator 33 covers the negative electrode mixture portion 32 in a state of contacting the main surface 34, the first side surface 35, and the second side surface 36 of the negative electrode mixture portion 32. The separator 33 suppresses the expansion / contraction of the negative electrode mixture portion 32 during charging / discharging of the secondary battery 1. The suppression of the expansion / contraction of the negative electrode mixture portion 32 suppresses the electrolyte from seeping out from the negative electrode mixture portion 32. The separator 33 also suppresses the electrolyte seeping out from the negative electrode mixture portion 32 from flowing out. The negative electrode mixture portion 32 retains the electrolyte even if the secondary battery 1 is repeatedly charged and discharged. The secondary battery 1 is suppressed from decreasing in capacity. That is, the secondary battery 1 is suppressed from decreasing in cycle characteristics.

[0046] In a lithium ion battery, the expansion / contraction of the negative electrode mixture portion 32 is generally greater than the expansion / contraction of the positive electrode mixture portion 42. The suppression of the expansion / contraction of the negative electrode mixture portion 32 by the separator 33 is particularly effective in suppressing deterioration of the cycle characteristics of the lithium ion battery.

[0047] Separator 33 may be elastically deformable. Elastically deformable separator 33 can suppress damage when negative electrode mixture portion 32 attempts to expand / contract.

[0048] On the first side surface 35 or the second side surface 36 of the negative electrode mixture portion 32, the thickness (tx1, tz2) of the separator 33 on the current collector side is relatively thicker. The negative electrode mixture portion 32 is joined to the negative electrode current collector 31, and the separator 33 further suppresses the expansion / contraction of the negative electrode mixture portion 32 on the current collector side. By suppressing the expansion / contraction of the negative electrode mixture portion 32 on the current collector side, peeling of the negative electrode mixture portion 32 from the negative electrode current collector 31 is suppressed. Increasing the thickness of the separator 33 on the current collector side relatively is advantageous for suppressing deterioration of the secondary battery 1.

[0049] Furthermore, the above-described holding portions 51, 52 not only hold the separator 33 during the manufacture of the secondary battery 1, but also prevent the separator 33 from being separated from the negative electrode mixture portion 32 even after the manufacture of the secondary battery 1 by interfering with the separator 33. The separator 33 is held in contact with the negative electrode mixture portion 32 during or after the manufacture of the secondary battery 1.

[0050] The separator 33 on the second side surface 36 may be omitted.

[0051] (Variation 1) 4 shows a modified example of the separator. The separator may be formed on each of the negative electrode 3 and the positive electrode 4.

[0052] The separator 43 of the positive electrode 4 covers the positive electrode mixture portion 42. More specifically, the positive electrode mixture portion 42 has a main surface 44 and a side surface 45. The separator 43 covers the positive electrode mixture portion 42 in a state of contact with the main surface 44 and the side surface 45.

[0053] 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 portion 42 and the negative electrode composite 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 each thinner than the thickness ty of the separator 33 in FIG. 2. The sum of the thickness ty1 and the thickness ty2 is equal to or substantially equal to the thickness ty of the separator 33 in FIG. 2. Note that the thickness ty1 and the thickness ty2 may be the same or different.

[0054] Furthermore, in the separator in contact with side surface 45 of positive electrode mixture portion 42, thickness tx4 on the positive electrode current collector 41 side is greater than thickness tx3 on the main surface 44 side.

[0055] Since the separator 43 covers the positive electrode mixture portion 42, expansion / contraction of the positive electrode mixture portion 42 during charging / discharging of the secondary battery 1 is suppressed. The electrolyte is suppressed from seeping out from the positive electrode mixture portion 42. In the secondary battery 1, a decrease in the amount of electrolyte is suppressed in each of the positive electrode mixture portion 42 and the negative electrode mixture portion 32. Both the positive electrode mixture portion 42 and the negative electrode mixture portion 32 can retain the electrolyte even if the secondary battery 1 is repeatedly charged and discharged. The secondary battery 1 is suppressed from decreasing in capacity even if it is repeatedly charged and discharged. That is, the secondary battery 1 is suppressed from decreasing in cycle characteristics.

[0056] Similarly to the negative electrode mixture portion 32, the thickness of the separator 43 on the side surface 45 of the positive electrode mixture portion 42 is relatively greater on the current collector side. This prevents the positive electrode mixture portion 42 from peeling off from the positive electrode current collector 41.

[0057] Separator 43 of positive electrode 4 can be formed in the same manner as separator 33 of negative electrode 3. Positive electrode 4 has a holding portion 53. Holding portion 53 faces side surface 45 of positive electrode mixture portion 42 with a predetermined distance therebetween.

[0058] Holding portion 53 prevents the slurry applied to side surface 45 of positive electrode mixture portion 42 from flowing out of positive electrode mixture portion 42 along the surface of positive electrode current collector 41 during the formation of separator 43. Holding portion 53 also prevents separator 43 from being separated from positive electrode mixture portion 42 by interfering with separator 43 even after secondary battery 1 is manufactured.

[0059] The holder for the positive electrode 4 may also constitute the resin 5 that seals the second opening 13 (see FIG. 1) of the container 14 in the secondary battery 1.

[0060] (Variation 2) 5 shows a modification regarding the current collector, which may be formed with a recess 37 for holding the separator.

[0061] The recess 37 is recessed from the surface of the negative electrode current collector 31. The recess 37 is located between the negative electrode mixture portion 32 and the holder 51.

[0062] The recessed portion 37 prevents the slurry applied to the first side surface 35 from flowing out of the negative electrode mixture portion 32 along the surface of the negative electrode current collector 31 when the slurry is applied to the negative electrode mixture portion 32. The recessed portion 37 prevents the separator 33 from being separated from the side surface of the negative electrode mixture portion 32 when the secondary battery 1 is manufactured.

[0063] Recess 37 also interferes with separator 33 after secondary battery 1 is manufactured, thereby preventing separator 33 from being separated from first side surface 35 of negative electrode mixture portion 32.

[0064] (Variation 3) Fig. 6 shows a modified example of the structure of the secondary battery. In the secondary battery 1 of Fig. 1, a plurality of negative electrode current collectors 31 and a plurality of positive electrode current collectors 41 individually protrude outward from openings 12, 13 of the container 14. In the secondary battery 10 of Fig. 6, a plurality of negative electrode current collectors 31 are connected to each other inside the container 14. A tab 15 connected to a collective portion of the negative electrode current collectors 31 protrudes outward from the container 14. That is, the tab 15 is joined to an edge of the laminate material 11 via a resin 54. In the secondary battery 10, the holding portion 51 has a function of holding the separator 33, but does not seal the opening of the container 14.

[0065] 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, similar to the case where the negative electrode current collector 31 and the positive electrode current collector 41 are connected to each other inside the container 14.

[0066] (Other embodiments) The separators 33 and 44 may be formed by using a porous membrane other than by applying a slurry as described above. That is, the composite part may be covered with the porous membrane in a state where the porous membrane is in contact with the main surface and the side surface of the composite part. The retaining parts 51, 52, and 53 or the recessed part 37 interfere with the separator made of the porous membrane, thereby preventing the separator from being separated from the side surface of the composite part.

[0067] Furthermore, the features of the above-mentioned configurations can be combined to the extent possible. [Explanation of symbols]

[0068] 1 Secondary battery 10 Secondary battery 12, 13 aperture 14 Container 2 Power generation elements 3 negative electrode 31 Negative electrode current collector 32 Negative electrode composite part 33 Separator 34 Main Surface 35 First aspect 36 Second aspect 37 Recess 4 Positive electrode 41 Positive electrode current collector 42 Positive electrode mixture section 43 Separator 44 Main Surface 45 Side 5. Resin 51 Holding part 52 Holding part 53 Holding part

Claims

1. a negative electrode and a positive electrode immersed in an electrolyte; A separator separating the negative electrode and the positive electrode, The negative electrode has a current collector and a mixture portion on the current collector, The mixture portion has a main surface facing the positive electrode via the separator and a side surface connecting the main surface and the current collector, The separator covers at least the mixture portion of the negative electrode in a state of contact with the main surface and the side surface.

2. 2. The secondary battery according to claim 1, A secondary battery, wherein the separator, which is in contact with the side surface between the current collector and the main surface, has a thickness on the current collector side greater than a thickness on the main surface side.

3. 3. The secondary battery according to claim 1, The negative electrode is joined to the current collector with a gap between the side surface of the composite portion and has a holding portion facing the side surface.

4. 4. The secondary battery according to claim 3, a container that contains a power generating element including the negative electrode, the positive electrode, and the separator, and the electrolyte; the current collector protrudes outside the container through an opening of the container, The holding portion is a resin that seals the opening of the container.

5. 4. The secondary battery according to claim 3, the negative electrode current collector has a recess between the mixture portion and the holding portion that is recessed from a surface of the current collector.

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