Power storage device

Abstract

To provide a power storage device which can prolong its life.SOLUTION: A power storage device 10 comprises: a pair of electrodes including a positive electrode 17 and a negative electrode 18; a separator 14 provided between the pair of electrodes; and a seal part 11 which is provided to surround the pair of electrodes and the separator, thereby forming a sealed space SP for housing a liquid electrolyte. In the power storage device, power storage modules 12 each consisting of the pair of electrodes, the separator, and the seal part are laminated. Viewing from a lamination direction, an outer periphery and an inner periphery of corners of the seal part are chamfered. The seal part has a constant width.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electricity storage device. [Background technology]

[0002] Patent Document 1 discloses an electricity storage device in which bipolar electrodes and separators are alternately stacked and the periphery is welded with a seal. In the electricity storage device, a space is formed between the bipolar electrodes and the seal. An uncoated portion is provided on the current collector of the bipolar electrode located on the inner periphery of the seal to form the space. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-094745 Summary of the Invention [Problem to be solved by the invention]

[0004] In the electricity storage device disclosed in Patent Document 1, volume changes in the sealed portion during the manufacture and use of the electricity storage device cause uneven stress to be applied to the uncoated portion, which causes damage to the uncoated portion and makes it difficult to extend the life of the electricity storage device.

[0005] The present disclosure has been made in consideration of the above circumstances, and provides a power storage device that can be made to have a longer lifespan. [Means for solving the problem]

[0006] The power storage device according to the present disclosure comprises: a pair of electrodes including a positive electrode and a negative electrode; a separator provided between the pair of electrodes; and a seal portion provided so as to surround the pair of electrodes and the separator, thereby forming an enclosed space for accommodating a liquid electrolyte; a power storage device in which a power storage module including the pair of electrodes, the separator, and the seal portion is stacked, The corners of the sealing portion are chamfered on the outer and inner peripheries when viewed from the stacking direction, The width of the seal portion is constant. [Effects of the Invention]

[0007] The present disclosure makes it possible to provide a power storage device that can be made to have a longer lifespan. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view (xz cross-sectional view) of the electricity storage device according to the first embodiment. [Figure 2] 1 is a cross-sectional view (xy cross-sectional view) of a power storage device according to a first embodiment. [Figure 3] FIG. 1 is a cross-sectional view (xy cross-sectional view) of a power storage device according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and for clarity of explanation, duplicate explanations are omitted as necessary. In addition, some reference numerals are omitted to avoid cluttering the drawings. Naturally, the right-handed xyz Cartesian coordinate system shown in the drawings is for the convenience of explaining the positional relationships of the components. Normally, the positive direction of the z axis is vertically upward, and the xy plane is the horizontal plane.

[0010] (Embodiment 1) <Configuration of the power storage device> First, an example of the configuration of a power storage device will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view (xz cross-sectional view) of the power storage device. Fig. 1 shows only the parts of the power storage device that are related to charging and discharging, and omits components such as restraining plates. The power storage device 10 is, for example, a secondary battery such as a lithium-ion secondary battery. The power storage device 10 is used as a battery for various vehicles such as forklifts, hybrid vehicles, and electric vehicles.

[0011] As shown in Fig. 1, the energy storage device 10 is configured by stacking a plurality of energy storage modules 12. In the example shown in Fig. 1, the energy storage device 10 is configured by stacking a plurality of energy storage modules 12 in the z-axis direction. Hereinafter, the z-axis direction in the drawing will be referred to as the stacking direction.

[0012] The electricity storage module 12 includes a pair of electrodes including a positive electrode 17 and a negative electrode 18, a separator 14 provided between the pair of electrodes, and a seal portion 11. The seal portion 11 is provided to surround the pair of electrodes including the positive electrode 17 and the negative electrode 18 and the separator 14, thereby forming a sealed space SP. A liquid electrolyte is filled (contained) in the sealed space SP.

[0013] In other words, in the energy storage device 10, the energy storage modules 12 adjacent to each other in the stacking direction are welded together by the seal portions 11. This prevents the liquid electrolyte filled in the sealed space SP from leaking out of the energy storage device 10.

[0014] Here, it can be said that the power storage device 10 is configured by alternately stacking bipolar electrodes 13 and separators 14. In the example shown in Fig. 1, the power storage device 10 has a plurality of bipolar electrodes 13 and a plurality of separators 14 stacked alternately in the stacking direction.

[0015] The bipolar electrode 13 will now be described. The bipolar electrode 13 has a positive electrode current collector 15a, a negative electrode current collector 15b, a positive electrode 17 provided on one surface of the positive electrode current collector 15a, and a negative electrode 18 provided on one surface of the negative electrode current collector 15b. The bipolar electrode 13 has a structure in which the positive electrode 17, the positive electrode current collector 15a, the negative electrode current collector 15b, and the negative electrode 18 are stacked in this order.

[0016] A positive electrode current collector 15a and a negative electrode current collector 15b are provided between the positive electrode 17 and the negative electrode 18 in the bipolar electrode 13. One surface of the positive electrode current collector 15a and one surface of the negative electrode current collector 15b are in contact with each other. The other surface of the positive electrode current collector 15a is in contact with the positive electrode 17, and the other surface of the negative electrode current collector 15b is in contact with the negative electrode 18.

[0017] The positive electrode current collector 15a and the negative electrode current collector 15b are made of, for example, conductive metal foil. The positive electrode current collector 15a is, for example, copper foil. The negative electrode current collector 15b is, for example, aluminum foil. In the example shown in FIG. 1, the stacking end of the electricity storage device 10 is the negative electrode current collector 15b on the positive side of the z-axis, and the positive electrode current collector 15a on the negative side of the z-axis.

[0018] The power storage module 12 is electrically connected to a conductive plate (not shown), and charging and discharging of the power storage device 10 is performed via the positive electrode 17 and the negative electrode 18.

[0019] <Uncoated area> Next, the uncoated portion will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view (xy cross-sectional view) of the energy storage device according to embodiment 1. Fig. 2 is a cross-sectional view from the direction (stacking direction) indicated by the arrow in Fig. 1. Fig. 2 is an xy cross-sectional view showing a part of the energy storage device 10 according to embodiment 1. The following description focuses on the positive electrode side, but the same applies to the negative electrode side.

[0020] The power storage device 10 will be described. As shown in FIG. 2, the positive electrode current collector 15a has a contact portion 171 with the positive electrode 17, an uncoated portion SP1, and a contact portion 111 with the seal portion 11. An uncoated portion SP1 is provided on the outer periphery of the contact portion 171. Further, a contact portion 111 is provided on the outer periphery of the uncoated portion SP1. That is, in the power storage device 10, the contact portion 171, the uncoated portion SP1, and the contact portion 111 are configured in this order from the inner periphery to the outer periphery.

[0021] As shown in FIG. 2, in the power storage device 10, the contact portion 111 (seal portion 11) has chamfers on the outer periphery and the inner periphery of the corner portion G1 of the contact portion 111 (seal portion 11) when viewed from the stacking direction (z-axis direction). In other words, the corner portion G1 of the contact portion 111 (seal portion 11) has a certain curvature.

[0022] More specifically, the width of the corner portion G1 of the contact portion 111 (seal portion 11) is the width a1. Further, the widths of the straight portions ST1 and ST2 are the width a1. That is, the width of the contact portion 111 (seal portion 11) is constant.

[0023] <Power storage device according to the comparative example> Here, the power storage device according to the comparative example will be described while referring to FIG. 3. FIG. 3 is a cross-sectional view (xy cross-sectional view) of the power storage device according to the comparative example. FIG. 3 is an xy cross-sectional view showing a part of the power storage device 50 according to the comparative example.

[0024] As shown in the lower part of FIG. 2, the contact portion 111 (seal portion 11) has right-angled shapes on the outer periphery and the inner periphery of the corner portion G2 when viewed from the stacking direction (z-axis direction). More specifically, the width of the corner portion G2 of the contact portion 111 (seal portion 11) is the width b1. Further, the widths of the straight portions ST1 and ST2 are the width a1 (<b1). That is, the width of the corner portion G2 of the contact portion 111 (seal portion 11) is larger than the widths of the straight portions ST1 and ST2. The power storage device 50 has the same other configuration as the power storage device 10.

[0025] <Generation of wrinkles (power storage device according to the comparative example)> Next, with reference to FIGS. 2 and 3, the occurrence of wrinkles in the uncoated sections SP1 of the electricity storage device 10 and the electricity storage device 50 will be described.

[0026] First, a power storage device 50 according to a comparative example will be described with reference to Fig. 3. In the uncoated portion SP1, wrinkles are generated due to stress from the positive electrode 17 and due to stress accompanying a change in the volume of the seal portion 11.

[0027] Wrinkles caused by stress from the positive electrode 17 will be described. The positive electrode 17 is in contact with the contact portion 171. Therefore, due to the weight of the positive electrode 17, stress is applied from the contact portion 171 to the uncoated portion SP1 in the outer circumferential direction. In other words, stress is applied to the uncoated portion SP1 from the positive electrode 17, causing wrinkles.

[0028] Wrinkles caused by stress due to volumetric changes in the sealed portion 11 will now be described. The sealed portion 11 is in contact with the contact portion 111. Here, the volume of the sealed portion 11 changes with the manufacture and use of the electricity storage device 10. More specifically, during manufacture, the sealed portion 11 expands and contracts due to the heat generated when welding the sealed portion. During use, the sealed portion 11 expands and contracts due to the heat generated when the electricity storage device 10 is used. The amount of elongation of the sealed portion 11 is expressed by the following equation (1).

[0029]

number

[0030] where ΔL is the amount of elongation of the seal portion 11, L is the width of the seal portion, α is the linear expansion coefficient, and ΔT is the temperature difference.

[0031] In the electricity storage device 50, the width (b1) of the corner G2 of the seal portion 11 is larger than the width (a1) of the straight portions ST1 and ST2. Therefore, according to formula (1), the expansion and contraction of the seal portion 11 causes the expansion amount of the corner G1 to be larger than the expansion amounts of the straight portions ST1 and ST2.

[0032] As a result, expansion and contraction of the seal portion 11 causes non-uniform repeated stress to be applied to the uncoated portion SP1 from the contact portion 111 in the outer and inner circumferential directions. In other words, non-uniform repeated stress is applied to the uncoated portion SP1 from the seal portion 11, causing wrinkles. Note that the greater the difference in the linear expansion coefficient between the positive electrode current collector 15a and the seal portion 11, the greater the repeated stress applied to the uncoated portion SP1.

[0033] Therefore, in the electricity storage device 50 according to the comparative example, wrinkles caused by stress from the positive electrode 17 and wrinkles caused by stress accompanying volumetric changes in the seal portion 11 overlap with each other, causing localized stress concentration in the uncoated portion SP1, which may result in damage to the uncoated portion SP1.

[0034] <Occurrence of Wrinkles (Power Storage Device According to Embodiment 1)> Next, the electricity storage device 10 according to the first embodiment will be described with reference to Fig. 2. Wrinkles occur in the uncoated section SP1 due to stress from the contact section 171, similar to the electricity storage device 50 according to the comparative example.

[0035] However, in the energy storage device 10, the width of the sealed portion 11 is constant. Therefore, according to formula (1), the amount of elongation of the sealed portion 11 is equal at the corner portion G1 and the straight portions ST1 and ST2. As a result, as the sealed portion 11 expands and contracts, uniform repeated stress is applied from the contact portion 111 to the uncoated portion SP1 in the outer and inner circumferential directions.

[0036] Therefore, the energy storage device 10 according to the first embodiment can prevent wrinkles from occurring in the uncoated portion SP1 due to stress caused by volumetric changes in the sealed portion 11. Therefore, the energy storage device 10 according to the first embodiment can prevent wrinkles caused by stress from the contact portion 171 and wrinkles caused by stress caused by volumetric changes in the sealed portion 11 from overlapping with each other. This prevents localized stress concentration from occurring in the uncoated portion SP1, and prevents damage to the uncoated portion SP1.

[0037] As described above, in the energy storage device 10, the outer and inner peripheries of the corners G1 of the seal portion 11 are chamfered when viewed from the stacking direction (z-axis direction). Also, in the energy storage device 10, the width of the seal portion 11 is constant. This configuration can prevent damage to the uncoated portion SP1, thereby reducing electrolyte leakage and improving the lifespan and safety of the energy storage device.

[0038] For the sake of simplicity, we have focused on the two-dimensional change (amount of expansion) as in Equation (1), but the same can be said for the three-dimensional change (amount of volume change). Note that the expansion in Equation (1) includes expansion indicating the amount of expansion and expansion indicating the amount of contraction. The expansion indicating the amount of expansion has a positive value, and the expansion indicating the amount of contraction has a negative value.

[0039] In addition, if the amount of expansion and contraction (volume change) of the sealed portion 11 is reduced, the uniform repeated stress on the uncoated portion SP1 is reduced, and the occurrence of wrinkles can be suppressed. Therefore, in order to reduce the amount of expansion and contraction (volume change), it is preferable that the sealed portion 11 has a small linear expansion coefficient. The sealed portion 11 is preferably made of, for example, polyethylene.

[0040] The present invention is not limited to the above-described embodiment, and can be appropriately modified without departing from the spirit of the present invention. In other words, the above description has been omitted or simplified as appropriate for the sake of clarity, and a person skilled in the art can easily modify, add, or convert each element of the embodiment within the scope of the present invention. [Explanation of symbols]

[0041] 10, 50 Energy storage device 11 Seal part 12 Energy storage module 13 Bipolar electrodes 14 Separator 15a Positive electrode current collector 15b Negative electrode current collector 17 Positive electrode 18 negative electrode 111, 171 contact parts a1, b1 width G1, G2 corner SP closed space SP1 Uncoated area Straight section ST1, ST2

Claims

[Claim 1] a pair of electrodes including a positive electrode and a negative electrode; a separator provided between the pair of electrodes; and a seal portion provided so as to surround the pair of electrodes and the separator, thereby forming an enclosed space for accommodating a liquid electrolyte; a power storage device in which a power storage module including the pair of electrodes, the separator, and the seal portion is stacked, The corners of the sealing portion are chamfered on the outer and inner peripheries when viewed from the stacking direction, The width of the seal portion is constant. Energy storage device.

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