Secondary battery and battery pack

Abstract

To prevent a distance between a positive electrode sheet and a negative electrode sheet at the bent portion from increasing in the event of abnormal heat generation.SOLUTION: A battery cell 10 includes a wound body 30 formed in a flat shape having a flat portion F and a bent portion C by winding a positive electrode sheet 50, a negative electrode sheet 40, and a separator 45 arranged between the positive electrode sheet 50 and the negative electrode sheet 40, a heat-shrinkable sheet 55 which is arranged on the outermost periphery of the wound body 30 and which shrinks at a predetermined temperature, and an adhesive layer 56 interposed between the heat-shrinkable sheet 55 and the flat portion F and not interposed between the heat-shrinkable sheet 55 and the bent portion C.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a secondary battery and a battery pack. [Background technology]

[0002] It is known that a secondary battery includes a wound body in which a positive electrode sheet, a negative electrode sheet, and a separator are wound in a stacked state (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a secondary battery in which a positive electrode, a separator, and a negative electrode are laminated and wound to form an oval cross section, an electrode assembly, a side spacer, and an insulating sheet are wound around the electrode assembly, which prevents misalignment between the electrode assembly and the side spacer.

[0004] In a secondary battery, it is preferable to prevent the distance between the positive electrode sheet and the negative electrode sheet at the bent portion from increasing when abnormal heat is generated. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-056081 A Summary of the Invention [Problem to be solved by the invention]

[0006] In consideration of the above, an object of the present invention is to prevent the distance between the positive electrode sheet and the negative electrode sheet at the bent portion from increasing during abnormal heat generation. [Means for solving the problem]

[0007] A secondary battery according to a first aspect of the present invention includes a wound body formed by winding a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet into a flat shape having a flat portion and a curved portion, a heat-shrinkable sheet disposed on the outermost periphery of the wound body and which shrinks at a predetermined temperature, and an adhesive layer interposed between the heat-shrinkable sheet and the flat portion and not interposed between the heat-shrinkable sheet and the curved portion.

[0008] In a secondary battery according to a second aspect of the present invention, in the secondary battery according to the first aspect of the present invention, the adhesive layer is provided on the entire surface of the flat portion.

[0009] A secondary battery of a third aspect of the present invention is a secondary battery of the first or second aspect of the present invention, wherein the thickness of the heat-shrinkable sheet arranged in the bent portion is made thicker than that of the heat-shrinkable sheet arranged in the flat portion.

[0010] A battery pack according to a fourth aspect of the present invention is a battery pack equipped with a secondary battery according to any one of the first to third aspects of the present invention, and includes a stack in which the secondary batteries are stacked, and a case in which the stack is housed and compressed in the stacking direction. Effect of the Invention

[0011] In the secondary battery of the first embodiment of the present invention, the adhesive layer is interposed between the heat shrinkable sheet and the flat portion, but not between the heat shrinkable sheet and the bent portion, so that the heat shrinkable sheet arranged at the bent portion shrinks during abnormal heat generation. On the other hand, the heat shrinkable sheet arranged at the flat portion is bonded to the flat portion, so that the shrinkage is suppressed. Therefore, a force acts toward the inside of the bent portion due to the shrinkage of the heat shrinkable sheet arranged at the bent portion. As a result, the distance between the positive electrode sheet and the negative electrode sheet at the bent portion can be suppressed from increasing during abnormal heat generation. This can suppress a short circuit caused by Li deposition.

[0012] In the secondary battery according to the second embodiment of the present invention, the adhesive layer is provided on the entire surface of the flat portion, so that the heat shrinkable sheet is prevented from shrinking in the flat portion during abnormal heat generation. This prevents the shrinkage of the heat shrinkable sheet arranged in the flat portion from affecting the shrinkage of the heat shrinkable sheet arranged in the bent portion. As a result, the distance between the positive electrode sheet and the negative electrode sheet in the bent portion can be effectively prevented from increasing during abnormal heat generation.

[0013] In the secondary battery according to the third aspect of the present invention, the heat-shrinkable sheet disposed at the bent portion is thicker than the heat-shrinkable sheet disposed at the flat portion, so that the heat-shrinkable sheet disposed at the bent portion shrinks by a larger amount during abnormal heat generation, and therefore the distance between the positive electrode sheet and the negative electrode sheet at the bent portion can be further prevented from increasing during abnormal heat generation.

[0014] In the battery pack according to the fourth aspect of the present invention, the flat portion of the wound body is compressed in the stacking direction, and therefore a restraining force acts on the flat portion. Meanwhile, since no adhesive layer is interposed between the heat shrinkable sheet and the bent portion, the heat shrinkable sheet is contracted at the bent portion during abnormal heat generation. Therefore, the distance between the positive electrode sheet and the negative electrode sheet can be prevented from increasing at the flat portion and the bent portion during abnormal heat generation. This can prevent a short circuit caused by Li deposition. [Brief description of the drawings]

[0015] [Figure 1] 1 is an exploded perspective view showing a battery pack according to a first embodiment. [Diagram 2] FIG. 2 is an exploded perspective view showing a battery cell according to the first embodiment. [Diagram 3] FIG. 2 is a perspective view showing a partially developed state of the wound body according to the first embodiment. [Figure 4] 4 is a cross-sectional view showing a schematic view of a wound body according to the first embodiment, showing a cross section taken along the line AA in FIG. [Diagram 5] 4 is a graph showing the relationship between the internal pressure and temperature of a battery cell. [Figure 6]FIG. 2 is a perspective view showing a state in which the heat-shrinkable sheet according to the first embodiment is unfolded. [Figure 7] 4 is a cross-sectional view showing a wound body according to the first embodiment, showing the cross section BB of FIG. 3. [Figure 8] FIG. 3 is a cross-sectional view showing a state in which the heat-shrinkable sheet according to the first embodiment has shrunk. [Figure 9] FIG. 11 is a cross-sectional view showing a wound body according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [First embodiment] Hereinafter, a battery pack according to a first embodiment will be described with reference to the drawings. The battery pack according to the first embodiment is a combination of battery cells 10 as lithium ion secondary batteries, and is used, for example, as an on-board power source for electric vehicles, hybrid vehicles, and the like. In each drawing, the arrow UP indicates the upper side in the vertical direction of the battery pack 1, the arrow FR indicates the front side in the front-rear direction of the battery pack 1, the arrow LH indicates the left side in the left-right direction of the battery pack 1, the arrow D indicates the stacking direction D of the battery stack 5, and the arrow G indicates the width direction G of the battery cells 10. In the first embodiment, the stacking direction D of the battery stack 5 coincides with the front-rear direction of the battery pack 1.

[0017] [Battery pack 1 configuration] As shown in FIG. 1, the battery pack 1 includes a battery stack 5 as a laminate, and a case 80 for accommodating the battery stack 5 therein.

[0018] <Battery stack 5> The battery stack 5 includes a plurality of battery cells (single cells) 10, a plurality of intermediate members 70 arranged in contact with wide surfaces of the battery cells 10, and bus bars 15 that electrically connect the battery cells 10. In the battery stack 5, the battery cells 10 and the intermediate members 70 are arranged alternately in the stacking direction D.

[0019] <Battery cell 10> As shown in FIG. 2, the battery cell 10 includes a lid assembly 20, a winding body 30, and a battery case 70.

[0020] (Lid Assembly 20) The lid assembly 20 has a negative external terminal 22 and a positive external terminal 23 on the upper surface of the lid member 21. The lid assembly 20 has a negative current collector terminal 24 and a positive current collector terminal 25 on the lower surface of the lid member 21.

[0021] (Wound body 30) As shown in FIG. 2, the wound body 30 has a power generating section 31 , a negative electrode current collecting section 32 , and a positive electrode current collecting section 33 .

[0022] 3, the wound body 30 is formed in a flat shape having a flat portion F and a bent portion C by winding a negative electrode sheet 40 as an electrode sheet, a positive electrode sheet 50 as an electrode sheet, and two separators 45 in a stacked state, as shown in FIG. 3. A heat shrinkable sheet 55 is disposed on the outermost periphery of the wound body 30.

[0023] The flat portion F is a portion formed in the vertical middle portion of the wound body 30, and has a flat outer surface. The bent portion C is a portion formed on the top and bottom of the wound body 30, and has an arc-shaped vertical cross section, and is the bent portion with the largest curvature.

[0024] The power generation section 31 is formed by laminating an area of ​​the positive electrode sheet 50 coated with the positive electrode active material 52, an area of ​​the negative electrode sheet 40 coated with the negative electrode active material 42, and a separator 45. A heat shrinkable sheet 55 is disposed on the outermost periphery of the power generation section 31. The power generation section 31 has the function of storing electrical energy of the battery cells 10.

[0025] The negative electrode current collecting part 32 is not coated with an active material, and is formed by winding a negative electrode sheet 40. The positive electrode current collecting part 33 is not coated with an active material, and is formed by winding a positive electrode sheet 50.

[0026] 4, the negative electrode sheet 40 is formed by coating both sides of a long strip-shaped negative electrode body 41 with a negative electrode active material 42. The negative electrode active material 42 has an outer periphery-side negative electrode active material 42A arranged on the outer periphery side, and an inner periphery-side negative electrode active material 42B arranged on the inner periphery side.

[0027] At the other end in the width direction G of the negative electrode sheet 40, the negative electrode active material 42 is not applied, and the negative electrode body 41 is exposed.

[0028] The positive electrode sheet 50 is formed by coating both sides of a long strip-shaped positive electrode body 51 with a positive electrode active material 52. The positive electrode active material 52 has an outer periphery side positive electrode active material 52A arranged on the outer periphery side, and an inner periphery side positive electrode active material 52B arranged on the inner periphery side.

[0029] At one end in the width direction G of the positive electrode sheet 50, the positive electrode active material 52 is not applied, and the positive electrode body 51 is exposed.

[0030] The separator 45 is formed of an insulating material such as polypropylene, polyethylene, etc. The separator 45 is disposed between the positive electrode sheet 50 and the negative electrode sheet 40, and insulates the positive electrode sheet 50 from the negative electrode sheet 40.

[0031] (battery case 70) The battery case 70 is made of aluminum, for example, and is formed in the shape of a rectangular box that is long in the left-right direction and has an open top.

[0032] With the wound body 30, the negative electrode current collector terminal 24, and the positive electrode current collector terminal 25 housed inside the battery case 70, the lid member 21 is attached, for example, by laser welding, so as to cover the opening of the battery case 70.

[0033] <Intermediate member 70> The intermediate member 70 is made of, for example, insulating resin. This suppresses heat transfer between the battery cells 10 and insulates the battery cells 10 from each other. The intermediate member 70 may be formed with comb-like ribs for forming an air passage between the intermediate member 70 and the battery cells 10.

[0034] As shown in Fig. 1, the intermediate member 70 includes a spacer 71 and an end plate 72. The spacer 71 is disposed between the battery cells 10 in the stacking direction D. The spacer 71 is formed into a rectangular plate shape with its plate thickness direction extending in the front-rear direction. The end plate 72 is disposed at both ends of the battery stack 5 in the stacking direction D. The end plate 72 is formed into a rectangular plate shape with its plate thickness direction extending in the front-rear direction.

[0035] <Busbar 15> 1, bus bar 15 is formed, for example, in a rectangular plate shape with its plate thickness direction extending in the up-down direction in the stacking direction D. Bus bar 15 electrically connects the external terminals of adjacent battery cells 10.

[0036] <Case 80> 1, the case 80 is formed by, for example, aluminum die casting. The case 80 is formed into a rectangular box shape with an open top, and is made up of a bottom plate 81, side plates 82, a front plate 83, and a rear plate 84. The battery stack 5 is accommodated in the case 80 in a state compressed in the stacking direction D.

[0037] [Relationship between internal pressure and temperature of battery cells] 5, it can be seen that when the temperature of the battery cell 10 rises, the internal pressure of the battery cell 10 also rises. Here, the rise in internal pressure of the battery cell 10 is caused by gas generation within the battery cell 10 due to abnormal heat generation. Furthermore, when gas is generated within the battery cell 10, the inter-electrode distance (the distance between the positive electrode sheet 50 and the negative electrode sheet 40) increases. Therefore, in the first embodiment, a heat-shrinkable sheet 55 is provided on the outer periphery of the wound body 30.

[0038] [Composition of Heat Shrink Sheet 55] 7, the heat shrinkable sheet 55 is wound around the outermost circumference of the wound body 30. The heat shrinkable sheet 55 may be a sheet that shrinks at a predetermined temperature (e.g., 70° C.). The heat shrinkable sheet 55 may be, for example, an insulating resin sheet such as an electron beam cross-linked soft polyolefin resin.

[0039] 6 and 7, the heat-shrinkable sheet 55 is formed in a rectangular sheet shape. An adhesive layer 56 is interposed between the heat-shrinkable sheet 55 and the flat portion F. On the other hand, no adhesive layer 56 is interposed between the heat-shrinkable sheet 55 and the bent portion C. The adhesive layer 56 can be formed of, for example, an acrylic adhesive.

[0040] In other words, at the flat portion F, the heat shrinkable sheet 55 is fixed to the wound body 30 by the adhesive layer 56. On the other hand, at the bent portion C, the heat shrinkable sheet 55 is not fixed to the wound body 30. The adhesive layer 56 is provided at a position corresponding to the flat portion F of the wound body 30, but is not provided at a position corresponding to the bent portion C of the wound body 30. The adhesive layer 56 is provided on the entire surface of the flat portion F at the outermost periphery of the wound body 30.

[0041] [Operation of the winding body 30] As shown in FIG. 7, within the assumed operating temperature range of the battery pack 1, the heat-shrinkable sheet 55 does not shrink, and almost no force is applied from the heat-shrinkable sheet 55 to the bent portion C.

[0042] 8, when the assumed usage temperature of the battery pack 1 (for example, 70° C.) is exceeded, the heat-shrinkable sheet 55 shrinks at the bent portion C because the heat-shrinkable sheet 55 is not fixed to the wound body 30. When the heat-shrinkable sheet 55 shrinks at the bent portion C, a force acts toward the inside of the wound body 30.

[0043] On the other hand, since the heat shrinkable sheet 55 is fixed to the wound body 30 by the adhesive layer 56 in the flat portion F, the shrinkage of the heat shrinkable sheet 55 is suppressed.

[0044] [Effect] The battery cell 10 of the first embodiment includes a wound body 30 formed in a flat shape having a flat portion F and a bent portion C by winding a positive electrode sheet 50, a negative electrode sheet 40, and a separator 45 disposed between the positive electrode sheet 50 and the negative electrode sheet 40, a heat-shrinkable sheet 55 that is disposed on the outermost periphery of the wound body 30 and shrinks at a predetermined temperature, and an adhesive layer 56 that is interposed between the heat-shrinkable sheet 55 and the flat portion F and is not interposed between the heat-shrinkable sheet 55 and the bent portion C (see FIG. 7 ).

[0045] Since the adhesive layer 56 is interposed between the heat shrink sheet 55 and the flat portion F, and is not interposed between the heat shrink sheet 55 and the bent portion C, the heat shrink sheet 55 arranged at the bent portion C is contracted during abnormal heat generation. On the other hand, the heat shrink sheet 55 arranged at the flat portion F is bonded to the flat portion F, and thus contraction is suppressed. Therefore, a force acts toward the inside of the bent portion C due to the contraction of the heat shrink sheet 55 arranged at the bent portion C. As a result, the distance between the positive electrode sheet 50 and the negative electrode sheet 40 at the bent portion C can be suppressed from increasing during abnormal heat generation. This can suppress a short circuit caused by Li deposition.

[0046] In the battery cell 10 of the first embodiment, the adhesive layer 56 is provided on the entire surface of the flat portion F (see FIG. 7).

[0047] Since the adhesive layer 56 is provided on the entire surface of the flat portion F, the heat-shrinkable sheet 55 arranged on the flat portion F is prevented from shrinking during abnormal heat generation. This prevents the shrinkage of the heat-shrinkable sheet 55 arranged on the flat portion F from affecting the shrinkage of the heat-shrinkable sheet 55 arranged on the bent portion C. As a result, it is possible to effectively prevent the distance between the positive electrode sheet 50 and the negative electrode sheet 40 at the bent portion C from increasing during abnormal heat generation.

[0048] When a secondary battery (battery cell) is compressed in the stacking direction, a binding force acts on the flat portion F of each battery cell in the stacking direction of the battery cell. On the other hand, an external binding force is less likely to act on the bent portion C of each battery cell. Therefore, gas generated during abnormal heat generation may accumulate between the positive electrode sheet 50 and the negative electrode sheet 40 at the bent portion C, and the distance between the positive electrode sheet 50 and the negative electrode sheet 40 may increase at the bent portion C. If the distance between the positive electrode sheet 50 and the negative electrode sheet 40 increases, a bias in the current distribution occurs, making it easier for Li deposition to occur, which may lead to a short circuit.

[0049] The battery pack 1 of the first embodiment includes a battery stack 5 in which secondary batteries are stacked, and a case 80 in which the battery stack 5 is housed while being compressed in the stacking direction.

[0050] The flat portion F of the wound body 30 is compressed in the stacking direction, and therefore a restraining force acts on it. Meanwhile, since the heat shrinkable sheet 55 is not interposed between the heat shrinkable sheet 55 and the bent portion C, the heat shrinkable sheet 55 arranged at the bent portion C is contracted during abnormal heat generation. Therefore, the distance between the positive electrode sheet 50 and the negative electrode sheet 40 can be prevented from increasing at the flat portion F and the bent portion C during abnormal heat generation. This can prevent a short circuit caused by Li deposition.

[0051] Second Embodiment The secondary battery of the second embodiment differs from the secondary battery of the first embodiment in that the configuration of the heat shrink sheet is different. Note that the same or equivalent parts as those described in the first embodiment will be described using the same terms or symbols.

[0052] [composition] 9, the portion of heat-shrinkable sheet 155 arranged at bent portion C is doubled and thus formed thicker than the portion of heat-shrinkable sheet 155 arranged at flat portion F. Note that heat-shrinkable sheet 155 arranged at bent portion C may be formed thicker than the portion of heat-shrinkable sheet 155 arranged at flat portion F by making it thicker.

[0053] [Effect] In the battery cell 10 of the second embodiment, the heat-shrinkable sheet 155 arranged on the bent portion C is made thicker than the heat-shrinkable sheet 155 arranged on the flat portion F (see FIG. 9).

[0054] The thickness of the heat-shrinkable sheet 155 arranged at the bent portion C is formed to be thicker than that of the heat-shrinkable sheet 155 arranged at the flat portion F, so that the amount of shrinkage of the heat-shrinkable sheet 155 arranged at the bent portion C increases in the event of abnormal heat generation. Therefore, the distance between the positive electrode sheet 50 and the negative electrode sheet 40 at the bent portion C can be further prevented from increasing in the event of abnormal heat generation.

[0055] Other configurations and functions and effects are substantially the same as those of the first embodiment, and therefore description thereof will be omitted.

[0056] The secondary battery of the present invention has been described above based on the first and second embodiments. However, the specific configuration is not limited to these embodiments, and design changes and the like are permitted as long as they do not deviate from the gist of the invention according to each claim in the scope of the claims.

[0057] In the first and second embodiments, an example has been shown in which the heat shrinkable sheet is provided on the outer peripheral surface of the separator 45. However, the heat shrinkable sheet may be provided on the outer peripheral surface of the positive electrode sheet or the negative electrode sheet.

[0058] In the first and second embodiments, an example has been shown in which the adhesive layer 56 is provided on the entire surface of the flat portion F of the wound body 30. However, the adhesive layer may be provided near the boundary between the flat portion F of the wound body 30 and the bent portion C. In other words, the adhesive layer may be provided on the upper and lower end portions of the flat portion F of the wound body 30.

[0059] In the first and second embodiments, the adhesive layer 56 is formed of, for example, an acrylic adhesive. However, the adhesive layer may be formed of other adhesives.

[0060] In the first and second embodiments, an example has been shown in which the battery stack 5 includes the intermediate member 70. However, the battery stack 5 does not necessarily have to include the intermediate member 70.

[0061] In the first and second embodiments, an example has been shown in which one battery stack 5 is housed in the case 80. However, the case may house two battery stacks 5 with an intermediate plate therebetween. [Explanation of symbols]

[0062] 1 Battery pack 5 Battery stack (an example of a laminate) 10 Secondary battery 30 Wound body 40 Negative electrode sheet 45 Separator 50 Positive electrode sheet 55 Heat shrink sheet 56 Adhesive layer 80 cases C bent part F flat area

Claims

1. a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wound together to form a flat wound body having a flat portion and a curved portion; a heat shrinkable sheet disposed on the outermost periphery of the wound body and shrinking at a predetermined temperature; an adhesive layer interposed between the heat shrinkable sheet and the flat portion and not interposed between the heat shrinkable sheet and the bent portion; A secondary battery comprising:

2. The adhesive layer is provided on the entire surface of the flat portion. The secondary battery according to claim 1 .

3. The thickness of the heat shrinkable sheet disposed at the bent portion is formed to be thicker than that of the heat shrinkable sheet disposed at the flat portion.

2. The secondary battery according to claim 1.

4. A battery pack including the secondary battery according to any one of claims 1 to 3, a stack in which secondary batteries are stacked; a case in which the laminate is accommodated while being compressed in a lamination direction; Including battery pack.

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