Secondary battery module

Abstract

To provide a secondary battery module having excellent cycle characteristics even when using a secondary battery whose volume varies with charging and discharging.SOLUTION: A secondary battery module includes a battery stack in which a number of secondary batteries are stacked, and a pair of end plates arranged at both ends in the stacking direction of the battery stack, and further includes a cushioning material arranged at least either between adjacent secondary batteries or between the battery stack and the end plates, and, in a first direction perpendicular to the stacking direction of the battery stack, one end of the cushioning material is a thick portion whose length in the stacking direction is greater, and the other end is a thin portion whose length in the stacking direction is smaller than that of the thick portion.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, research and development has been conducted on secondary battery modules that contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. A secondary battery module is a modularized combination of multiple secondary batteries, and generally includes a cell stack in which multiple secondary batteries are stacked, and a pair of end plates arranged at both ends in the stacking direction of the cell stack. Secondary battery modules are used in applications that require high current and high voltage, such as for driving the motors of electric vehicles and hybrid electric vehicles.

[0003] In a secondary battery module, it is being considered to place a cushioning material between the secondary batteries or between the cell stack and the end plate to apply a load (constraining force) in the stacking direction of the battery cells. As the cushioning material, a spring elastic body such as a leaf spring or a liquid spring is known (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-96974 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology related to the secondary battery module, the improvement of the electric capacity is an issue. In order to improve the electric capacity of the secondary battery, it has been considered to use an electrode laminate in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween, and an electrolyte solution housed in an exterior body as the secondary battery, and to use lithium metal or silicon particles as the negative electrode active material of the negative electrode. However, in a lithium secondary battery using lithium metal or silicon particles, the volume of the negative electrode increases significantly during charging, and the volume of the negative electrode decreases significantly during discharging. For this reason, when the charge / discharge cycle is repeated, the electrolyte solution flows out from inside the electrode laminate between the electrode laminate and the exterior body, causing a shortage of electrolyte solution in the electrode laminate, which may result in a decrease in cycle characteristics.

[0006] In order to solve the above problems, the present application aims to provide a secondary battery module that has excellent cycle characteristics even when using a secondary battery whose volume varies with charging and discharging, thereby contributing to energy efficiency. [Means for solving the problem]

[0007] The present inventors have found that the above-mentioned problems can be solved by disposing a cushioning material between secondary batteries or between a cell stack and an end plate, the cushioning material having one end portion made of a thick portion that is thicker and the other end portion made of a thin portion that is thinner than the thick portion, and have thus completed the present invention. Accordingly, the present invention provides the following.

[0008] (1) A secondary battery module having a battery stack in which a number of secondary batteries are stacked, and a pair of end plates arranged at both ends of the battery stack in a stacking direction, further comprising a cushioning material arranged at least either between adjacent secondary batteries or between the battery stack and the end plates, wherein, in a first direction perpendicular to the stacking direction of the battery stack, one end of the cushioning material is a thick portion whose length in the stacking direction is greater, and the other end is a thin portion whose length in the stacking direction is smaller than that of the thick portion.

[0009] According to the secondary battery module of (1), since the cushioning material has a thick portion and a thin portion, the amount of crushing of the cushioning material changes according to the amount of change in the volume of the secondary battery, and this makes it possible to control the binding force applied to the secondary battery, and therefore to adjust the flow of the electrolyte in the secondary battery during charging and discharging. Therefore, according to the secondary battery module of (1), even if a secondary battery whose volume changes due to charging and discharging is used, the electrolyte is unlikely to dry up, and the cycle characteristics are excellent.

[0010] (2) The secondary battery module according to (1), wherein the volume of the secondary battery varies with charging and discharging.

[0011] According to the secondary battery module (2), even if the volume of the secondary battery changes due to charging and discharging, the buffer material is crushed according to the amount of change in volume, and the direction of movement of the electrolyte in the secondary battery can be adjusted. As a result, the electrolyte is less likely to run out, and the cycle characteristics are excellent.

[0012] (3) The secondary battery module according to (1) or (2), wherein the thin portion of the cushioning material is tapered in the first direction, and the inclination angle of the thin portion relative to the thick portion is 0.057 to 1.15 degrees.

[0013] (3) According to the secondary battery module, the amount of crushing of the thin portion of the cushioning material can be continuously adjusted, and therefore the restraining force applied to the secondary battery can be adjusted to more reliably prevent the electrolyte from drying up.

[0014] (4) A secondary battery module described in any one of (1) to (3) above, wherein in a second direction perpendicular to the stacking direction and the first direction, the thick portion of the cushioning material is arc-shaped with a vertex at the center.

[0015] According to the secondary battery module of (4), when the volume of the secondary battery increases, the electrolyte in the secondary battery easily flows in the second direction. Also, when the volume of the secondary battery decreases, the electrolyte enters the electrodes in the secondary battery from the second direction, so that the electrolyte can be evenly supplied to the electrodes of the secondary battery.

[0016] (5) A secondary battery module according to any one of (1) to (4), wherein the cushioning material has a groove on a surface along a second direction perpendicular to the stacking direction and the first direction and along the first direction, and the length of the surface in the first direction is A and the length of the surface in the second direction is C, and the groove is curved between a center point of the thick portion side end in the first direction and two points located at a length of 2 / 3A from both ends of the thin portion side end in the first direction in the second direction toward the thick portion side, or is curved between the center point and two points located at a length of 1 / 5C from both ends of the thin portion side end in the first direction toward the second direction.

[0017] According to the secondary battery module of (5), a groove is provided on the surface of the cushioning material that contacts the secondary battery, and when the volume of the secondary battery increases, the pressure applied to the electrodes in the secondary battery increases from the part of the cushioning material where the groove is not provided, so that the electrolyte in the secondary battery tends to move to the part opposite the part of the cushioning material where the groove is provided. Also, when the volume of the secondary battery decreases, the electrolyte penetrates into the electrode of the secondary battery from the part opposite the part of the cushioning material where the groove is provided, so that the electrolyte can be evenly supplied to the electrode of the secondary battery.

[0018] (6) The secondary battery module according to any one of (1) to (5) above, wherein the cushioning material is arranged such that the thin portion is located higher in the direction of gravity than the thick portion.

[0019] According to the secondary battery module of (6), when the volume of the secondary battery increases, the binding force applied to the secondary battery increases from the bottom to the top, so that the electrolyte can be moved anisotropically to the top of the secondary battery. On the other hand, when the volume of the secondary battery decreases, the binding force applied to the secondary battery decreases from the top to the bottom, so that the electrolyte can be moved from the top to the bottom of the secondary battery by its own weight. Therefore, even if the battery is repeatedly charged and discharged, the electrolyte is unlikely to dry up, and the cycle characteristics are excellent.

[0020] (7) A secondary battery module according to any one of (1) to (6), wherein the secondary battery includes an electrode stack in which a positive electrode and a negative electrode are stacked with a separator therebetween, an electrolytic solution, and a packaging body that contains the electrode stack and the electrolytic solution, and the secondary battery is arranged such that the stacking direction of the electrode stack coincides with the stacking direction of the battery stack.

[0021] According to the secondary battery module of (7), the stacking direction of the electrode stack, which has a large volume fluctuation in the secondary battery, coincides with the stacking direction of the battery stack, so that a constant pressure can be applied to the secondary battery regardless of the charge / discharge state of the secondary battery, thereby stabilizing the charge / discharge capacity of the secondary battery.

[0022] (8) The secondary battery module according to (7) above, wherein the negative electrode increases in volume when charged and decreases in volume when discharged.

[0023] According to the secondary battery module of (8), lithium metal or silicon particles can be used as the negative electrode active material, so that the capacity of the secondary battery is increased. Effect of the Invention

[0024] According to the present invention, it is possible to provide a secondary battery module having excellent cycle characteristics even when using a secondary battery whose volume varies due to charging and discharging. [Brief description of the drawings]

[0025] [Figure 1]FIG. 2 is a front view showing a discharging state of the secondary battery module according to the embodiment of the present invention. [Diagram 2] 2 is a bottom view of the secondary battery module shown in FIG. 1. [Figure 3A] 2 is a front view of a cushioning material used in the secondary battery module shown in FIG. [Figure 3B] 2 is a perspective view of a cushioning material used in the secondary battery module shown in FIG. [Figure 4A] 4 is a cross-sectional view showing a discharged state of a secondary battery used in the secondary battery module according to the embodiment of the present invention; FIG. [Figure 4B] 4 is a cross-sectional view showing a charging state of a secondary battery used in the secondary battery module according to one embodiment of the present invention. FIG. [Diagram 5] 2 is a front view showing a charging state of the secondary battery module shown in FIG. 1. [Figure 6] 6 is a bottom view of the secondary battery module shown in FIG. 5. [Figure 7] FIG. 13 is a bottom view of a secondary battery module in a discharged state according to a modified example of the present invention. [Figure 8] 8 is a bottom view of the secondary battery module shown in FIG. 7 in a charged state. [Figure 9] 11 is a perspective view illustrating a shape of a modified example of a cushioning material used in the secondary battery module of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the X direction is the stacking direction of the secondary batteries, the Y direction is a first direction perpendicular to the X direction, and the Z direction is a second direction perpendicular to the X direction and the Y direction. The Y direction is also the direction of gravity. In this embodiment, the secondary battery 10 is assumed to decrease in volume in a discharged state and increase in volume in a charged state. The discharged state includes the state of the secondary battery immediately after its manufacture.

[0027] 1 and 2, a secondary battery module 1a according to one embodiment of the present invention has a battery stack 100 in which three secondary batteries 10 are stacked, and a pair of end plates 20 arranged at both ends of the stacking direction (X direction) of the battery stack 100. A cushioning material 30a is arranged between adjacent secondary batteries 10, and a cushioning material 30b is arranged between the battery stack 100 and the end plate 20. The secondary batteries 10 are in a discharged state, and their volume has been reduced.

[0028] The pair of end plates 20 are restrained by fastening members (not shown). The pair of end plates 20 transmit the restraining force applied by the fastening members to the battery stack 100, thereby restraining the battery stack 100 in the X direction. There are no particular limitations on the material of the end plates 20, and various materials used for end plates for battery modules can be used.

[0029] The cushioning materials 30a and 30b have the effect of reducing the binding force applied to the secondary battery 10. As shown in Figs. 3A and 3B, the cushioning materials 30a and 30b have, in the Y direction (first direction), a thick portion 31 that is longer in the X direction (stacking direction) and a thin portion 32 that is shorter in the X direction than the thick portion 31. The thick portion 31 is always in contact with the secondary battery. The thin portion 32 is inclined so as to taper along the Y direction, forming a gap 50 that separates it from the secondary battery 10. In the Y direction (gravity direction), the secondary battery module 1a is arranged so that the thin portions 32 of the cushioning materials 30a and 30b are located above and the thick portions 31 are located below. The cushioning material 30b is the same as the cushioning material 30a except that it has a shape that is half the size of the cushioning material 30a along the Y direction, so the cushioning material 30b will be described in detail using the cushioning material 30a as an example.

[0030] The inclination angle θ (see FIG. 3A) of the thin portion 32 with respect to the thick portion 31 of the cushioning material 30a is not particularly limited, but is within the range of 0.057 to 1.15 degrees. The length A (see FIG. 3A) of the cushioning material 30a in the Y direction (first direction) may be the same as that of the secondary battery 10, for example. The length As (see FIG. 3A) of the thick portion 31 in the Y direction may be within a range of 20 to 80% of the length A of the cushioning material 30a in the Y direction, for example. When the length As of the thick portion 31 in the Y direction is 20% or more, the secondary battery 10 and the cushioning material 30a are less likely to be displaced from each other even if the volume of the secondary battery 10 increases or decreases. When the length As of the thick portion 31 in the Y direction is 80% or less, the range of the thin portion 32 becomes wider, and therefore the area of ​​the gap 50 formed between the thick portion 31 and the cushioning material 30a becomes wider when the volume of the secondary battery 10 is reduced.

[0031] Length B (see FIG. 3A) in the X direction (stacking direction) of bottom 31a of thick portion 31 of cushioning material 30a may be within a range of 10 to 40% of the X direction length of secondary battery 10. In addition, the ratio of the X direction length of thin portion 32 to length B in the X direction of bottom 31a of thick portion 31 is determined by inclination angle θ of thin portion 32, length A in the Y direction of cushioning material 30a, and length As of thick portion 31 in the Y direction.

[0032] The materials for the buffer members 30a and 30b may be rubber materials or a combination of springs and plastics. Examples of the rubber materials include natural rubber, diene rubber, and non-diene rubber. The Young's modulus of the buffer members 30a and 30b may be within a range of 0.002 to 4 GPa, for example.

[0033] 4A, the secondary battery 10 includes an electrode stack 18 in which a positive electrode 11 and a negative electrode 14 are stacked with a separator 17 between them, an electrolyte (not shown), and a packaging body 19 that contains the electrode stack 18 and the electrolyte. The secondary battery 10 is a lithium metal secondary battery that uses lithium metal as the negative electrode active material. The secondary battery 10 is arranged such that the stacking direction of the electrode stack 18 coincides with the X direction (stacking direction) of the battery stack 100.

[0034] The positive electrode 11 has a positive electrode current collector 12 and a positive electrode active material layer 13. The positive electrode current collector 12 is extended to the outside by a positive electrode lead terminal (not shown). The material of the positive electrode current collector 12 may be, for example, Al.

[0035] The positive electrode active material layer 13 includes a positive electrode active material. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNi p Mn q Co r O2(p+q+r=1), LiNi p Al q Co r O2(p+q+r=1), lithium manganese oxide (LiMn2O4), Li 1+x Mn 2-x-y M y Examples of the positive electrode active material layer 13 include a different element-substituted Li-Mn spinel represented by O4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (an oxide containing Li and Ti), and lithium metal phosphate (LiMPO4, M=at least one selected from Fe, Mn, Co, and Ni). The positive electrode active material layer 13 may contain various additives used as materials for positive electrode active material layers, such as a binder and a conductive assistant.

[0036] The negative electrode 14 has a negative electrode current collector 15. The negative electrode current collector 15 is drawn to the outside by a negative electrode lead terminal (not shown). The material of the negative electrode current collector 15 may be, for example, Cu. A Li foil may be laminated on the surface of the negative electrode current collector 15.

[0037] 4B, a negative electrode active material layer 16 (lithium metal layer) is formed in the negative electrode 14 by charging. Therefore, the negative electrode 14 of the secondary battery 10b after charging becomes thicker in the stacking direction of the electrode laminate 18, and the volume increases. After charging, the secondary battery 10b loses the negative electrode active material layer 16 by discharging, and the volume decreases.

[0038] The electrolytic solution includes an organic solvent and an electrolyte. Examples of the organic solvent include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers, aromatic ethers, sulfones, cyclic esters, chain carboxylates, and nitriles. Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 4-methyl1,3-dioxolane. Examples of the chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, and diethyl ether. Examples of hydrofluoroethers include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl)ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, and the like. Examples of aromatic ethers include anisole. Examples of sulfones include sulfolane and methylsulfolane. Examples of cyclic esters include γ-butyrolactone, and the like. Examples of chain carboxylates include acetates, butyrates, and propionates. Examples of nitriles include acetonitrile and propionitrile. The organic solvents may be used alone or in combination of two or more.

[0039] The electrolyte is a source of lithium ions, which are charge transfer media, and includes a lithium salt. Examples of the lithium salt include LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(CF3SO2)2(LiTFSI), LiN(FSO2)2(LiFSI), and LiBC4O8. The lithium salt may be used alone or in combination of two or more. The concentration of the electrolyte is, for example, within the range of 1.0 mol / L to 4.0 mol / L.

[0040] The packaging body 19 is expandable and contractable in accordance with the increase and decrease in the volume of the negative electrode 14 due to charging and discharging. A laminate film can be used as the material of the packaging body 19. As the laminate film, a laminate film having a three-layer structure in which an inner resin layer, a metal layer, and an outer resin layer are laminated in this order from the inside can be used. The outer resin layer may be, for example, a polyamide layer, the metal layer may be, for example, an aluminum layer, and the inner resin layer may be, for example, a polypropylene layer.

[0041] When the volume of the secondary battery 10 in the battery stack 100 increases due to charging, the thick parts 31 of the cushioning materials 30a and 30b are crushed in the X direction by the compressive force caused by the increased volume. The crushing of the thick parts 31 generates a repulsive force against the compressive force, and the binding force applied from the thick parts 31 to the secondary battery 10 increases, so that the binding force inside the secondary battery 10 becomes large. Meanwhile, since there is a gap 50 between the thin parts 32 of the cushioning materials 30a and 30b and the secondary battery 10, no compressive force is applied to the thin parts 32 at the beginning of charging. Therefore, at the beginning of charging, a binding force is applied to the part of the electrode stack 18 of the secondary battery 10 facing the thick parts 31, and the electrolyte moves upward in the Y direction (gravity direction). Furthermore, when the thin parts 32 come into contact with the secondary battery 10 from below in the Y direction as the volume of the secondary battery 10 increases, the thin parts 32 are also crushed. When the thin portion 32 is crushed, a restraining force is applied from the thin portion 32 to the secondary battery 10, and the electrolyte in the electrode stack 18 inside the secondary battery 10 that faces the thin portion 32 moves upward in the Y direction. Then, when the entire thin portion 32 is crushed, it is pushed out of the electrode stack 18.

[0042] As shown in Fig. 5, when looking at the front (surface along the XY direction) of the secondary battery module 1b after charging is completed, the binding force applied from the cushioning materials 30a, 30b to the secondary battery 10b is strongest at the portion facing the thick portion 31, and becomes weaker at the portion facing the thin portion 32 (the thicker the arrow in Fig. 5, the stronger the binding force). On the other hand, as shown in Fig. 6, at the bottom surface of the secondary battery module 1b after charging is completed, the compressive force from the secondary battery 10b is applied evenly to the thick portions 31 of the cushioning materials 30a, 30b, so the amount of crushing is uniform. Therefore, the binding force applied from the thick portions 31 of the cushioning materials 30a, 30b to the secondary battery 10b is uniform.

[0043] When the secondary battery 10b is discharged after charging and the volume of the secondary battery 10b gradually decreases, the compressive force applied from the secondary battery 10b to the cushioning materials 30a, 30b decreases. As a result, the amount of crushing of the thick portion 31 and the thin portion 32 of the cushioning materials 30a, 30b decreases, and a gap 50 is formed between the thin portion 32 and the secondary battery 10b and the thin portion 32. When the gap 50 is formed, the electrolyte infiltrates into the electrode stack 18 through the gap 50. The electrolyte that has infiltrated into the electrode stack 18 flows downward from the upper end in the Y direction (gravity direction) due to its own weight, and is uniformly supplied to the positive electrode 11 and the negative electrode 14.

[0044] According to the secondary battery module 1 of this embodiment, since the cushioning material 30 has the thick portion 31 and the thin portion 32, it becomes possible to control the confining pressure applied to the secondary battery 10 when the volume of the secondary battery 10 increases, and therefore it is possible to adjust the flow of the electrolyte in the secondary battery 10 during charging and discharging. Therefore, the secondary battery module 1 of this embodiment is less likely to suffer from liquefaction and drying of the electrolyte, and has excellent cycle characteristics, even when using a secondary battery 10 whose volume fluctuates due to charging and discharging. In the secondary battery module 1 of this embodiment, the thin wall portions 32 of the cushioning materials 30a and 30b are inclined so as to taper along the Y direction (first direction), and the inclination angle of the thin wall portion 32 with respect to the thick wall portion 31 is set to 0.057 to 1.15 degrees, so that the crushing amount of the cushioning material in the contact area between the thin wall portion 32 of the cushioning materials 30a and 30b and the secondary battery 10 can be continuously adjusted. Therefore, the binding force applied to the secondary battery 10 can be adjusted so that the electrolyte does not run out more reliably. Furthermore, according to the secondary battery module 1 of this embodiment, the thin wall portions 32 of the cushioning materials 30a and 30b are arranged so as to be located higher in the gravity direction than the thick wall portion 31, so that when the volume of the secondary battery 10 increases, the electrolyte can be moved anisotropically to the upper side of the secondary battery 10. On the other hand, when the volume of the secondary battery 10 decreases, the electrolyte can be moved from the upper side to the lower side of the secondary battery 10 due to its own weight. Therefore, even when the battery is repeatedly charged and discharged, the electrolyte is less likely to liquefy and dry up, resulting in excellent cycle characteristics.

[0045] In the secondary battery module 1a of this embodiment, the bottoms of the thick parts 31 of the cushioning materials 30a and 30b are rectangular, but the bottoms of the thick parts 31 of the cushioning materials 30a and 30b may be curved. Fig. 7 shows a modified example in which the bottoms of the cushioning materials 30a and 30b are curved.

[0046] In the secondary battery module 2a shown in FIG. 7, the bottoms of the cushioning materials 40a, 40b are arc-shaped with the center in the Z direction (second direction) as the apex. The center of the thick portion 31 in the Z direction contacts the secondary battery 10, which is in a discharged state and has a reduced volume, and both ends in the Z direction are separated from the secondary battery 10 to form a gap 50. When the volume of the secondary battery 10 increases in the X direction due to charging, the cushioning materials 30a, 30 are pressed in the X direction by the secondary battery 10, and the length of the thick portion 31 in the X direction gradually decreases and the interval of the gap 50 becomes narrower. In the secondary battery module 2b after charging, the secondary battery 10b contacts the thin portions 32 of the cushioning materials 30a, 30b in the Z direction as shown in FIG. 8. The secondary battery 10b after charging is subjected to pressure from the cushioning materials 30a, 30b. As shown in FIG. 8, the pressure applied by the cushioning materials 30a, 30b is highest at the center in the Z direction and becomes weaker toward both ends in the Z direction (the thicker the arrows in FIG. 8, the greater the restraining pressure).

[0047] According to the secondary battery module 2 of this modification, when the volume of the secondary battery 10 increases, the electrolyte in the electrode stack 18 is more likely to flow in the second direction. When the volume of the secondary battery 10 decreases, the electrolyte enters the electrode stack 18 from the second direction, so that the electrolyte can be more evenly supplied to the electrode stack 18 of the secondary battery 10.

[0048] In the secondary battery module 1a of this embodiment, the side surfaces of the cushioning materials 30a, 30b that come into contact with the secondary batteries 10 are flat, but grooves may be provided on the side surfaces of the cushioning materials 30a, 30b that come into contact with the secondary batteries 10.

[0049] In the cushioning material 40c shown in FIG. 9, grooves 41 and 42 are indicated by imaginary lines. The grooves 41 and 42 are provided on the side surface of the cushioning material 40c that contacts the secondary battery 10, i.e., on the YZ surface along the Y direction (first direction) and the Z direction (second direction). The length of this YZ surface in the Y direction is A and the length in the Z direction is C. The grooves 41 are located between the center point P0 in the Z direction of the thick-walled portion side end of the YZ surface in the Y direction and both ends P 10 , P 20Two points P located at a distance of 1 / 5C in the Z direction from 11 , P 21 The groove 42 is formed in a curved shape connecting the center point P0 in the Z direction of the thick-walled portion side end in the Y direction and two points P 12 , P 22 The groove 41 is formed in a curved shape connecting the center point P0 and the end point P 11 , P 21 The groove 42 is curved from the center point P0 to the end point P 12 , P 22 The grooves 41 and 42 have a curved shape that bulges outward toward the thick portion 31. The grooves may have an arc shape. The length of the grooves 41 and 42 in the X direction is within a range of 0.1 to 2.0 mm from the surface of the thick portion 31, for example.

[0050] The secondary battery module using the cushioning material 40c has grooves 41, 42 on the YZ surface that contacts the secondary battery 10, and when the volume of the secondary battery 10 increases, the pressure applied to the secondary battery 10 from the portion of the cushioning material 40c where the grooves 41, 42 are not provided increases, so that the electrolyte in the electrode laminate 18 is more likely to move to the portion facing the portion where the grooves of the cushioning material 40c are provided. Also, when the volume of the secondary battery 10 decreases, the electrolyte enters the electrode laminate 18 from the portion facing the portion where the grooves of the cushioning material 40c are provided, so that the electrolyte can be evenly supplied to the electrode laminate 18 of the secondary battery 10. The end of the groove 41 is at point P 11 , P 21 The end of the groove 42 is at point P 12 , P 22 However, the position of the end is not limited to this. The end of the groove is P 10 ~P 11 Between and P 20 ~P 21 It may be between P 10 ~P 12 During 20 ~P 22 The positions of the ends of the groove may be symmetrical with respect to the central point P0.

[0051] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate. For example, in this embodiment, the thin-walled portions 32 of the cushioning materials 30a, 30b have a length in the X direction that continuously decreases so as to taper along the Y direction, but the shape of the thin-walled portions 32 is not limited to this. The length of the thin-walled portions 32 in the X direction may decrease in stages.

[0052] In the present embodiment, the secondary battery 10 is a lithium metal secondary battery using lithium metal as the negative electrode active material, but the secondary battery 10 is not limited to this. Silica particles may be used as the negative electrode active material of the secondary battery 10. The secondary battery 10 may be one whose volume does not change due to charging and discharging. [Explanation of symbols]

[0053] 1a, 1b, 2a, 2b Secondary battery module 10, 10b secondary battery 11 Positive electrode 12 Positive electrode current collector 13 Cathode active material layer 14 Negative electrode 15 Negative electrode current collector 16 Negative electrode active material layer 17 Separator 18 Electrode laminate 19 Packaging 20 End Plate 30a, 30b, 40a, 40b, 40c buffer material 31 Thick wall part 31a bottom 32 Thin section 32a Tip 41, 42 groove 50 Gap

Claims

1. A secondary battery module including a battery stack in which a plurality of secondary batteries are stacked, and a pair of end plates disposed on both ends of the battery stack in a stacking direction, a buffer material disposed between adjacent secondary batteries or between the battery stack and the end plate, a second end of the buffer material in a first direction perpendicular to the stacking direction of the battery stack, the second end of the buffer material being a thick portion whose length in the stacking direction is greater than that of the thick portion, and the third end of the buffer material being a thin portion whose length in the stacking direction is smaller than that of the thick portion.

2. The secondary battery module according to claim 1 , wherein the volume of the secondary battery varies with charging and discharging.

3. 2. The secondary battery module according to claim 1, wherein the thin portion of the buffer material is tapered in the first direction, and an inclination angle of the thin portion relative to the thick portion is 0.057 to 1.15 degrees.

4. The secondary battery module according to claim 1 , wherein in a second direction perpendicular to the stacking direction and the first direction, the thick portion of the cushioning material is formed in an arc shape having a vertex at a center.

5. The buffer material has a groove on a surface along the first direction and a second direction perpendicular to the stacking direction and the first direction, The length of the surface in the first direction is A, and the length of the surface in the second direction is C, 2. The secondary battery module of claim 1, wherein the groove is curved between a center point in the second direction of the thick portion side end in the first direction and two points located 2 / 3A in length from both ends of the thin portion side end in the first direction toward the thick portion side, or between the center point and two points located 1 / 5C in length from both ends of the thin portion side end in the first direction toward the second direction.

6. The secondary battery module according to claim 1 , wherein the buffer material is disposed such that the thin portion is located above the thick portion in a direction of gravity.

7. The secondary battery includes an electrode stack in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, an electrolytic solution, and a packaging body that contains the electrode stack and the electrolytic solution, The secondary battery module according to claim 1 , wherein the secondary batteries are arranged such that a stacking direction of the electrode stack coincides with a stacking direction of the battery stack.

8. The secondary battery module according to claim 7 , wherein the negative electrode increases in volume when charged and decreases in volume when discharged.

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