Secondary battery

Abstract

To make the reaction site of a secondary battery uniform.SOLUTION: A secondary battery 100 includes a laminate 101 in which a flat positive electrode 110 having a positive electrode tab 113 (current collecting tab), a flat negative electrode 120 having a negative electrode tab 123 (current collecting tab), and a separator 130 that holds an electrolyte are stacked. The secondary battery 100 is provided with a cooling unit 140 that has a refrigerant flow path 142 and cools the laminate 101 by a heat flow in a direction perpendicular to the laminate 101, and the cooling unit 140 is configured such that the cooling capacity is lower in an area away from the current collecting tab than in the vicinity of the current collecting tab.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a battery pack that includes a stack of flat batteries with wide and narrow sides, stacked with the wide sides facing each other, a heating means provided from the outside of the stack opposite the wide sides, and a cooling means provided from the outside of the stack opposite the narrow sides, as a technology for uniformly heating the inside of the battery during cold start-up and uniformly cooling the batteries during high-temperature use, thereby improving temperature variations within the battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 039116 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] However, it was not necessarily easy to make the reaction within the battery uniform, even when a heating means was provided facing the wide surface and a cooling means was provided facing the narrow surface, as in Patent Document 1. This is thought to be because the current density distribution within the battery cell is not uniform, and when the temperature rises locally in areas where the current density is high, the electrical resistance in those areas decreases, creating a positive feedback effect that further increases the current density.

[0005] The present invention has been made in view of the above points, and has as its object to easily achieve uniformity of reaction sites. [Means for solving the problem]

[0006] To achieve the above objectives, The present invention provides a flat positive electrode having a current collecting tab; a flat negative electrode having a current collecting tab; a separator for holding an electrolyte; and a laminate in which the separator and the separator are stacked, a cooling unit having a coolant flow path and configured to cool the stack by a heat flow in a direction perpendicular to the stack, The cooling portion is configured so that the cooling capacity is lower in an area distant from the current collecting tab than in an area close to the current collecting tab.

[0007] This reduces the temperature near the current collecting tab, relatively increasing the electrical resistance, reducing and uniforming the current density, dispersing the reaction sites and uniforming the temperature rise. [Effects of the Invention]

[0008] In the present invention, the reaction sites can be easily made uniform. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an exploded perspective view schematically showing the configuration of a secondary battery 100 according to a reference example. [Figure 2] FIG. 2 is a front view showing an example of the refrigerant flow path 142 according to the first embodiment. [Figure 3] FIG. 3 is a front view showing an example of a refrigerant channel 142 according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, modifications, and reference examples, components having the same functions as those in other embodiments will be designated by the same reference numerals, and their description will be omitted.

[0011] (Overall composition) First, for convenience, the overall configuration of the reference example will be described.

[0012] 1 is a schematic exploded perspective view showing the configuration of a secondary battery 100 (battery cell) according to a reference example. The secondary battery 100 may be, for example, a lithium-ion battery or a nickel-metal hydride battery.

[0013] The secondary battery 100 includes a laminate 101 and a cooling unit 140. As shown in Fig. 1, the laminate 101 may be a stacked battery formed by stacking a plurality of rectangular sheet-shaped positive electrodes 110, a plurality of rectangular sheet-shaped negative electrodes 120, and a plurality of rectangular sheet-shaped separators 130. In this case, the size of the laminate 101 may be a rectangle, for example, 5 cm to 11 cm in length and 10 cm to 200 cm in width.

[0014] The positive electrode 110 includes a positive electrode foil 111, a positive electrode composite 112, a positive electrode tab 113 (current collecting tab), and an electrolyte. The positive electrode 110 has a sheet shape. The positive electrode 110 may have, for example, a rectangular shape. The positive electrode 110 may be formed to have the same size as the negative electrode 120, for example.

[0015] The positive electrode foil 111 is a member for transferring electrons to the positive electrode composite 112. The positive electrode foil 111 is made of a conductive material. The positive electrode foil 111 may be made of, for example, copper, nickel, or zinc. The positive electrode foil 111 is in a sheet shape. The positive electrode foil 111 may be, for example, rectangular. In this case, the size of the positive electrode foil 111 may be, for example, 4.5 cm to 10.5 cm in length and 9.5 cm to 190 cm in width.

[0016] The positive electrode composite 112 is a member for causing a charge / discharge reaction on the positive electrode side. The positive electrode composite 112 is provided on the positive electrode foil 111. For example, the positive electrode composite 112 may be provided on both sides of the positive electrode foil 111. The material of the positive electrode composite 112 may be LiFePO4 or a ternary material that is a mixture of Li, Mn, Co, and Ni.

[0017] The positive electrode tab 113 is provided to transfer electrons between the positive electrode foil 111 and the positive electrode composite 112, between the inside and outside of the positive electrode 110. The positive electrode tab 113 is provided on the outer periphery of the positive electrode foil 111. For example, in the case of a rectangular positive electrode foil 111, the positive electrode tab 113 may be provided on one side of the positive electrode foil 111.

[0018] The positive electrode tab 113 may be formed of, for example, the same material as the positive electrode foil 111. The positive electrode tab 113 may be formed of, for example, a material different from that of the positive electrode foil 111. The positive electrode tab 113 may be provided by extending from the outer periphery of the positive electrode foil 111. In other words, the positive electrode tab 113 may be provided continuously from the outer periphery of the positive electrode foil 111. The positive electrode tab 113 may be provided by attaching a member separate from the positive electrode foil 111. The size of the positive electrode tab 113 may be, for example, 2.5 cm to 5.5 cm in length and 1.5 cm to 3.5 cm in width.

[0019] The negative electrode 120 includes a negative electrode foil 121, a negative electrode composite 122, a negative electrode tab 123 (current collecting tab), and an electrolyte. The negative electrode 120 has a sheet shape. The negative electrode 120 may have, for example, a rectangular shape. The negative electrode 120 may be formed to have the same size as the positive electrode 110, for example.

[0020] The negative electrode foil 121 is a member for transferring electrons to the negative electrode composite material 122. The negative electrode foil 121 is made of a conductive material. The negative electrode foil 121 may be made of, for example, aluminum, titanium, or stainless steel. The negative electrode foil 121 is in a sheet shape. The negative electrode foil 121 may be, for example, rectangular. In this case, the size of the negative electrode foil 121 may be, for example, 4.5 cm to 10.5 cm in length and 9.5 cm to 190 cm in width.

[0021] The negative electrode composite 122 is a member for causing a charge / discharge reaction on the negative electrode side. The negative electrode composite 122 is provided on the negative electrode foil 121. The negative electrode composite 122 may be provided on both sides of the negative electrode foil 121, for example. The material of the negative electrode composite 122 may be a carbon-based compound such as graphite or a silicon-based compound.

[0022] The negative electrode tab 123 is provided to transfer electrons between the negative electrode foil 121 and the negative electrode composite 122, between the inside and outside of the negative electrode 120. The negative electrode tab 123 is provided on the outer periphery of the negative electrode foil 121. For example, in the case of a rectangular negative electrode foil 121, the negative electrode tab 123 may be provided on one side of the negative electrode foil 121.

[0023] The negative electrode tab 123 may be formed of, for example, the same material as the negative electrode foil 121. The negative electrode tab 123 may be formed of, for example, a material different from that of the negative electrode foil 121. The negative electrode tab 123 may be provided by extending from the outer periphery of the negative electrode foil 121. In other words, the negative electrode tab 123 may be provided continuously from the outer periphery of the negative electrode foil 121. The negative electrode tab 123 may be provided by attaching a member separate from the negative electrode foil 121. The size of the negative electrode tab 123 may be, for example, 2.5 cm to 5.5 cm in length and 1.5 cm to 3.5 cm in width.

[0024] The separator 130 is a member that holds an electrolyte between the positive electrode 110 and the negative electrode 120. The separator 130 is provided to reduce the possibility of short-circuiting between the positive electrode 110 and the negative electrode 120 while allowing the movement of lithium ions. The separator 130 may be in a sheet shape. The separator 130 may be formed using a porous material. The separator 130 may be formed using a non-conductive material. The separator 130 may be made of, for example, polypropylene, polyethylene, nonwoven fabric, or the like. The size of the separator 130 may be, for example, 4.7 cm to 10.7 cm in length and 9.7 cm to 195 cm in width.

[0025] The electrolyte is a material for transferring lithium ions required for causing charge-discharge reactions between the positive electrode 110 and the negative electrode 120. The electrolyte is a non-aqueous electrolyte. The electrolyte may be, for example, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), or a mixture of the above organic solvents. The electrolyte may contain, for example, a lithium salt. The lithium salt may be, for example, LiPF6 (lithium hexafluorophosphate) or LiFSI (lithium bis(fluorosulfonyl)imide).

[0026] The cooling section 140 is a member for cooling the laminate 101. The cooling section 140 is provided at a position where it contacts the main surface of the laminate 101. The cooling section 140 has a thermal resistor 141 and a refrigerant flow path 142. The cooling section 140 is shaped to cover substantially the entire main surface of the laminate 101. Here, "substantially the entire surface" means that it covers 80% or more of the area of ​​the main surface of the laminate 101.

[0027] The cooling section 140 may be rectangular, for example. The size of the cooling section 140 may be, for example, 5 cm to 10 cm in length and 10 cm to 200 cm in width. The cooling section 140 may be, for example, the same shape as the main surface of the laminate 101. The cooling section 140 may be, for example, larger than the main surface of the laminate 101. This makes it difficult for the area of ​​the main surface of the laminate 101 that is in contact with the cooling section 140 to decrease even if the cooling section 140 is misaligned from the main surface of the laminate 101. As a result, it is possible to make it difficult for the cooling efficiency of the cooling section 140 to decrease.

[0028] The cooling unit 140 is made of a thermally conductive material, which may be, for example, a metal material, such as aluminum, an aluminum alloy, copper, or another metal alloy.

[0029] The thermal resistor 141 is provided between the cooling unit 140 and the laminate 101. The thermal resistor 141 is provided to locally reduce the cooling efficiency of the cooling unit 140. The thermal resistor 141 may be, for example, substantially rectangular. Here, the term "substantially rectangular" refers not only to a rectangle with four right-angled corners, but also to a rectangle with rounded corners.

[0030] The thermal resistor 141 may be made of a thermally resistant material. Examples of the thermally resistant material include resin, glass, and rubber. The thermal resistor 141 may be in the form of a sheet. The thermal resistor 141 may be formed by directly coating the surface of the cooling unit 140, for example.

[0031] The thermal resistor 141 covers an approximately central portion of the laminate 101. Here, the approximately central portion refers to covering an area excluding a position that is approximately 20% of the width of the laminate 101 from the positive electrode tab 113 or the negative electrode tab 123 toward the center of the laminate 101.

[0032] The size of the thermal resistor 141 may be, for example, 3 cm to 10 cm in length and 6 cm to 120 cm in width if it is rectangular. The thermal resistor 141 may have, for example, a plurality of grooves (not shown). This allows the grooves to absorb shape changes even when the thermal resistor 141 repeatedly expands and contracts due to heat, making it less likely to peel off.

[0033] The thermal resistor 141 may be formed, for example, from a resin material molded into a plurality of circles (not shown). In this case, the size of each circle may be, for example, 2 cm to 10 cm in diameter. The thermal resistor 141 may have various shapes other than those described above, as long as it covers approximately the center of the laminate 101.

[0034] The thickness of the thermal resistor 141 may be, for example, approximately uniform. Here, "approximately uniform" means that the thickness includes manufacturing errors of the resin film, in other words, the thickness is uniform if there is an error of about 5% of the total thickness.

[0035] The thickness of the thermal resistor 141 may be thinner, for example, at a position closer to the positive electrode tab 113 or the negative electrode tab 123 than at the central portion. This creates a gradient in the cooling capacity even in the approximately central portion of the laminate 101, making it easier to uniformize the overall reaction of the secondary battery 100. The thickness of the thermal resistor 141 may be, for example, about 0.1 mm to 10 mm.

[0036] The cooling flow path 142 is a member for introducing a cooling medium into the cooling unit 140 from an inlet 142a, circulating the cooling medium within the cooling unit 140 along the cooling flow path 142 in a plane parallel to the stack 101, and discharging the cooling medium from an outlet 142b to the outside of the cooling unit 140, thereby cooling the stack 101 by a heat flow perpendicular to the stack 101, i.e., in a direction from the stack toward the cooling unit 140. The cooling medium may be, for example, water or an alternative chlorofluorocarbon (R32, R410A). The heat exchanger and circulation flow path, which exchange heat between the cooling refrigerant and the stack 101 and exchange the heat gained by the cooling refrigerant with outside air so that the cooling refrigerant can be cooled again, are not the focus of the present invention, and therefore will not be described here for convenience.

[0037] The cooling flow channels 142 are a plurality of flow channels provided in the cooling unit 140. The cooling flow channels 142 may be formed, for example, by extrusion molding when forming the cooling unit 140. The cooling flow channels 142 may be formed, for example, by a hollow member. The cross section of the cooling flow channels 142 may be, for example, rectangular. The cross section of the cooling flow channels 142 may be circular.

[0038] The cooling channels 142 are arranged so that the density of the channels is higher in the vicinity of the positive electrode tab 113 or the negative electrode tab 123 than in the approximate center portion of the laminate 101. In this case, the cooling channels 142 may be provided so as to curve in the up-down direction of the laminate 101 in the approximate center portion of the laminate 101, for example, as shown in FIG.

[0039] (Reference example) In Fig. 1, 110 is a sheet-shaped positive electrode, 120 is a sheet-shaped negative electrode, and a plurality of positive electrodes 110 and a plurality of negative electrodes 120 are alternately stacked one by one with separators 130 for holding an electrolyte interposed therebetween. The positive electrode 110 is a rectangular sheet-shaped positive electrode foil 111 (conductive material) with a positive electrode composite 112 formed on both sides. The negative electrode 120 is a rectangular sheet-shaped negative electrode foil 121 (conductive material) with a negative electrode composite 122 formed on both sides.

[0040] The positive electrode tab 113 (current collecting tab) of the positive electrode 110 extends laterally from one side of the positive electrode foil 111, and the negative electrode tab 123 (current collecting tab) of the negative electrode 120 extends laterally from the other side of the negative electrode foil 121 that faces the side of the positive electrode foil 111. That is, the positive electrode tab 113 and the negative electrode tab 123 extend in opposite directions. In other words, they are arranged to face each other on both sides of the portion where the positive electrode 110 and the negative electrode 120 are stacked with the separator 130 interposed therebetween.

[0041] A cooling unit 140 having a refrigerant flow path 142 is provided on at least one side of the laminate 101 formed by stacking the positive electrode 110, the negative electrode 120, and the separator 130 as described above. A thermal resistor 141 such as a predetermined thermal resistance film or coating is interposed between the laminate 101 and the cooling unit 140 and between the positive electrode tab 113 and the negative electrode tab 123, for example, in a region of approximately half the length of the laminate 101 at the center in the longitudinal direction of the laminate 101, forming a cooling capacity distribution in which the cooling capacity of the cooling unit 140 is lower in regions away from the positive electrode tab 113 and the negative electrode tab 123 than in the vicinity of these tabs.

[0042] The cooling capacity distribution described above allows the cooling capacity to be higher near the positive electrode tab 113 and the negative electrode tab 123 than in the region between them, thereby keeping the temperature lower. In this case, the electrical resistance between the positive electrode 110 and the negative electrode 120 is relatively higher near the positive electrode tab 113 and the negative electrode tab 123, thereby reducing the current density (the current flowing between them). Therefore, if the cooling capacity distribution described above is not formed, the current density tends to be higher near the positive electrode tab 113 and the negative electrode tab 123 than in the region between them. However, by utilizing the temperature dependence of the migration rate of, for example, lithium ions, the reaction rate can be locally controlled to uniformize the current density over the entire surface of the positive electrode 110 and the negative electrode 120. This disperses the reaction sites that were concentrated around the positive electrode tab 113 and the negative electrode tab 123, thereby uniforming the temperature rise. This suppresses the progression of partial degradation of the secondary battery 100, and is expected to extend its lifespan.

[0043] (Embodiment 1) In order to make the cooling capacity lower in regions away from the positive electrode tab 113 and the negative electrode tab 123 than in the vicinity thereof, it is not limited to providing the thermal resistor 141 as described above, but the refrigerant flow paths 142 may be dispersed and arranged as shown in Fig. 2. That is, in the regions near the positive electrode tab 113 and the negative electrode tab 123, the refrigerant flow paths 142 are densely arranged to set a high cooling capacity, while in the region between the positive electrode tab 113 and the negative electrode tab 123, the refrigerant flow paths 142 are sparsely arranged to set a relatively low cooling capacity. By doing so, similar to providing the thermal resistor 141 as described above, the current flowing between the positive electrode 110 and the negative electrode 120, and therefore the current density, can be reduced by utilizing the temperature dependency of the migration speed of lithium ions and the like, and the reaction sites can be dispersed, thereby suppressing the progress of partial deterioration of the secondary battery 100.

[0044] (Embodiment 2) Furthermore, in order to set the cooling capacity distribution, it is not limited to the above, but for example, as shown in Fig. 3, a refrigerant flow path 142 may be formed so that the refrigerant is discharged by bypassing the region between the positive electrode tab 113 and the negative electrode tab 123. Even when arranged in this manner, the current flowing between the positive electrode 110 and the negative electrode 120, and therefore the current density, can be reduced, and the reaction sites can be dispersed, thereby suppressing the progression of partial deterioration of the secondary battery 100. [Explanation of symbols]

[0045] 100 Secondary battery 101 laminate 110 positive electrode 111 Positive electrode foil 112 Positive electrode mixture 113 Positive electrode tab 120 negative electrode 121 Negative electrode foil 122 Negative electrode mixture 123 Negative electrode tab 130 Separator 140 Cooling section 141 Thermal resistor 142 refrigerant flow path 142a entrance 142b Outlet

Claims

1. a flat positive electrode having a current collecting tab; a flat negative electrode having a current collecting tab; a separator for holding an electrolyte; and a laminate in which the separator and the separator are stacked, a cooling unit having a coolant flow path and configured to cool the stack by a heat flow in a direction perpendicular to the stack, 10. The secondary battery according to claim 9, wherein the cooling portion is configured so that the cooling capacity is lower in an area distant from the current collecting tab than in an area close to the current collecting tab.

2. 2. The secondary battery of claim 1, The cooling section is configured such that the cooling capacity is lower in an area away from the current collecting tab than in an area near the current collecting tab by varying the density of the flow paths.

3. 2. The secondary battery of claim 1, The positive electrode and the negative electrode are each formed in a rectangular plate shape, A secondary battery, characterized in that the current collecting tab of the positive electrode and the current collecting tab of the negative electrode extend in opposite directions.

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