Secondary battery module

Abstract

The problem to be solved by the present invention is to provide a secondary battery module having excellent cycle characteristics even when a secondary battery, the volume of which varies due to charge and discharge, is used. In order to solve the problem, this secondary battery module is provided with a battery laminate in which a plurality of secondary batteries are laminated, and a pair of end plates disposed at both ends of the battery laminate in the lamination direction, and is also provided with: a buffer material that is provided between the battery laminate and the pair of end plates; a plurality of second electrodes disposed between adjacent secondary batteries and / or between the battery stack and the end plate; in a first direction orthogonal to the stacking direction of the battery stack, one end of the buffer material is formed as a thick portion having a greater length in the stacking direction, and the other end is formed as a thin portion having a smaller length in the stacking direction than the thick portion.

Description

Technical Field

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

[0002] In recent years, research and development of secondary battery modules that help improve energy efficiency are being conducted to make them affordable, trustworthy, and ensure access to sustainable and advanced energy for many people. A secondary battery module is a combination of multiple secondary batteries and modularized. Generally speaking, it includes a single stack formed by stacking multiple secondary batteries, and a pair of end plates arranged at both ends of the stacking direction of the single stack. Secondary battery modules are used for applications that require large current and high voltage, such as motor driving of electric vehicles and hybrid electric vehicles.

[0003] In a secondary battery module, a buffer material is arranged between secondary batteries and between a single-cell stack and an end plate, etc., to apply a load (restraint force) in the stacking direction of the battery cells. As a buffer material, spring elastic bodies such as leaf springs and liquid springs are known (Patent Document 1).

[0004] [Prior Technical Literature]

[0005] (Patent Document)

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-96974 Summary of the invention

[0007] [Problems to be solved by the invention]

[0008] In addition, in the technology related to the secondary battery module, the improvement of electrical capacity has become a problem to be solved. In order to improve the electrical capacity of the secondary battery, it is being explored to use an electrode stack formed by stacking the positive electrode and the negative electrode with a separator in an outer body, and a battery formed by an electrolyte as a secondary battery, and to use lithium metal and silicon particles as negative electrode active materials for the negative electrode. However, the volume of the negative electrode of a lithium secondary battery using lithium metal and silicon particles will increase significantly during charging, and the volume of the negative electrode will decrease significantly during discharge. Therefore, when the charge and discharge cycle is repeated, it is possible that the electrolyte flows out from the inside of the electrode stack to between the electrode stack and the outer body, resulting in insufficient liquid depletion of the electrolyte in the electrode stack, and a decrease in the cycle characteristics.

[0009] The purpose of this case is to provide a secondary battery module that has excellent cycle characteristics even when using a secondary battery whose volume changes due to charge and discharge, so as to solve the above-mentioned problems and further contribute to improving energy efficiency.

[0010] [Technical means to solve the problem]

[0011] The inventors of the present invention have found that the above-mentioned problems can be solved by configuring a buffer material having a thick wall portion at one end and a thin wall portion having a smaller thickness than the thick wall portion at the other end between secondary batteries and between a single layer stack and an end plate, thereby completing the present invention. Therefore, the present invention provides the following invention.

[0012] (1) A secondary battery module comprising a battery stack formed by stacking a plurality of secondary batteries, and a pair of end plates arranged at both ends of the battery stack in a stacking direction, and further comprising: a buffer material arranged between adjacent secondary batteries and at least one of the battery stack and the end plates; in a first direction orthogonal to the stacking direction of the battery stack, one end of the buffer material is formed as a thick-walled portion having a greater length in the stacking direction, and the other end is formed as a thin-walled portion having a smaller length in the stacking direction than the thick-walled portion.

[0013] According to the secondary battery module of (1), since the buffer material has a thick wall portion and a thin wall portion, the amount of collapse of the buffer material changes according to the amount of change in the volume of the secondary battery, thereby being able to control the restraining force applied to the secondary battery, so that the flow of the electrolyte in the secondary battery during charge and discharge can be adjusted. Therefore, according to the secondary battery module of (1), even if a secondary battery whose volume changes due to charge and discharge is used, the electrolyte is not easily depleted, and the cycle characteristics are excellent.

[0014] (2) The secondary battery module according to (1) above, wherein the volume of the secondary battery changes due to charge and discharge.

[0015] According to the secondary battery module of (2), even if the volume of the secondary battery changes due to charge and discharge, the movement direction of the electrolyte in the secondary battery can be adjusted by crushing the buffer material according to the amount of volume change, so that the electrolyte is less likely to be depleted and the cycle characteristics are excellent.

[0016] (3) The secondary battery module according to (1) or (2) above, wherein the thin-walled portion of the buffer material is inclined so as to taper along the first direction, and an inclination angle of the thin-walled portion relative to the thick-walled portion is 0.057 to 1.15 degrees.

[0017] According to the secondary battery module of (3), the amount of collapse of the thin-walled portion of the buffer material can be continuously adjusted, and thus the restraining force applied to the secondary battery can be adjusted to more reliably avoid the depletion of the electrolyte solution.

[0018] (4) The secondary battery module according to any one of (1) to (3) above, wherein the thick portion of the buffer material is formed into an arc shape with a center as a vertex in a second direction perpendicular to the stacking direction and the first direction.

[0019] 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. In addition, when the volume of the secondary battery decreases, the electrolyte penetrates into 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.

[0020] (5) A secondary battery module according to any one of (1) to (4) above, wherein the buffer material is provided with a groove along a second direction orthogonal to the stacking direction and the first direction, and along a surface along the first direction, wherein the length of the surface in the first direction is set to A, and the length in the second direction is set to C, and the groove is a curved line connecting the center point in the second direction of the end portion of the thick-walled portion on the first direction and two points at a length position of 2 / 3A from the two ends of the second direction of the end portion of the thin-walled portion on the first direction toward the thick-walled portion side, or is a curved line connecting the center point and two points at a length position of 1 / 5C from the two ends of the thin-walled portion on the first direction toward the second direction.

[0021] According to the secondary battery module of (5), a groove is provided on the surface of the buffer material connected to the secondary battery. When the volume of the secondary battery increases, the pressure applied to the electrode in the secondary battery from the portion of the buffer material without the groove increases, so the electrolyte in the secondary battery easily moves to the portion opposite to the portion of the buffer material with the groove. In addition, when the volume of the secondary battery decreases, the electrolyte penetrates into the electrode of the secondary battery from the portion opposite to the portion of the buffer material with the groove, so that the electrolyte can be evenly supplied to the electrode of the secondary battery.

[0022] (6) The secondary battery module according to any one of (1) to (5) above, wherein the buffer material is arranged so that the thin-walled portion is located above the thick-walled portion in the gravity direction.

[0023] According to the secondary battery module of (6), when the volume of the secondary battery increases, the restraining force applied to the secondary battery increases from the bottom to the top, so the electrolyte can be anisotropically moved to the top of the secondary battery. On the other hand, when the volume of the secondary battery decreases, the restraining force applied to the secondary battery decreases from the top to the bottom, so the electrolyte can be moved from the top to the bottom of the secondary battery by the weight of the electrolyte. Therefore, even if the charge and discharge are repeated, the electrolyte is not easily liquefied and exhausted, and the cycle characteristics are excellent.

[0024] (7) A secondary battery module according to any one of (1) to (6) above, wherein the secondary battery comprises an electrode stack formed by stacking a positive electrode and a negative electrode with a separator therebetween, an electrolyte, and a packaging body for containing the electrode stack and the electrolyte, and the secondary battery is arranged in such a way that the stacking direction of the electrode stack is consistent with the stacking direction of the battery stack.

[0025] According to the secondary battery module of (7), the stacking direction of the electrode stack, which has a large volume change of the secondary battery, is consistent with the stacking direction of the battery stack, so a fixed pressure can be applied to the secondary battery regardless of the charge and discharge state of the secondary battery. Therefore, the charge and discharge capacity of the secondary battery is stable.

[0026] (8) The secondary battery module according to (7) above, wherein the volume of the negative electrode increases due to charge and decreases due to discharge.

[0027] According to the secondary battery module of (8), lithium metal or silicon particles can be used as the negative electrode active material, so the capacity of the secondary battery is increased.

[0028] (Effects of the Invention)

[0029] 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 charge and discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a front view showing a discharge state of a secondary battery module according to one embodiment of the present invention.

[0031] Figure 2 yes Figure 1 The bottom view of the secondary battery module is shown.

[0032] Figure 3A yes Figure 1 A front view of a buffer material used in the secondary battery module shown.

[0033] Figure 3B yes Figure 1 A perspective view of a buffer material used in the secondary battery module shown.

[0034] Figure 4A It is a cross-sectional view showing a discharge state of a secondary battery used in a secondary battery module according to an embodiment of the present invention.

[0035] Figure 4B It is a cross-sectional view showing a charging state of a secondary battery used in a secondary battery module according to an embodiment of the present invention.

[0036] Figure 5 It is shown Figure 1 A front view of the secondary battery module showing the charging state.

[0037] Figure 6 yes Figure 5 The bottom view of the secondary battery module is shown.

[0038] Figure 7 This is a bottom view of a secondary battery module in a modified example of the present invention in a discharged state.

[0039] Figure 8 yes Figure 7 The bottom view of the secondary battery module shown is in a charged state.

[0040] Fig. 9 This is a perspective view for explaining a modified example of the shape of a buffer material used in the secondary battery module of the present invention. DETAILED DESCRIPTION

[0041] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In addition, in the following drawings, the X direction is a stacking direction for stacking the secondary batteries, the Y direction is a first direction orthogonal to the X direction, and the Z direction refers to a second direction orthogonal to the X direction and the Y direction. The Y direction is also the direction of gravity. In addition, in the present embodiment, the secondary battery 10 is formed as a battery whose volume decreases in a discharge state and increases in a charge state. In addition, the discharge state includes the state of the secondary battery just after it is manufactured.

[0042] A secondary battery module 1a according to one embodiment of the present invention is as follows Figure 1 , 2 As shown, there is a battery stack 100 formed by stacking three secondary batteries 10, and a pair of end plates 20 arranged at both ends of the stacking direction (X direction) of the battery stack 100. A buffer material 30a is arranged between adjacent secondary batteries 10, and a buffer material 30b is arranged between the battery stack 100 and the end plate 20. The secondary battery 10 is in a discharged state and has a reduced volume.

[0043] The pair of end plates 20 are restrained by a fastening member (not shown). The pair of end plates 20 restrain the battery stack 100 in the X direction by transmitting the restraining force applied by the fastening member to the battery stack 100. The material of the end plates 20 is not particularly limited, and various materials used in end plates for battery modules can be used.

[0044] The buffer materials 30a and 30b have the function of relaxing the restraining force applied to the secondary battery 10. The buffer materials 30a and 30b are as follows. Figure 3AAs shown in FIG. 1 and FIG. 2 , in the Y direction (first direction), there is a thick wall portion 31 having a large length in the X direction (stacking direction) and a thin wall portion 32 having a smaller length in the X direction than the thick wall portion 31. The thick wall portion 31 is always in contact with the secondary battery. The thin wall portion 32 is inclined in a manner that the front end becomes thinner along the Y direction, forming a gap 50 that is separated from the secondary battery 10. The secondary battery module 1a is configured in a manner that the thin wall portion 32 of the buffer material 30a, 30b is located at the top and the thick wall portion 31 is located at the bottom in the Y direction (gravity direction).

[0045] The cushioning material 30b is the same as the cushioning material 30a except that it is formed in a shape obtained by taking a half of the cushioning material 30a in the Y direction, and therefore, the cushioning material 30a will be described in detail as an example.

[0046] The inclination angle θ of the thin-walled portion 32 of the buffer material 30a relative to the thick-walled portion 31 (see Figure 3A ) is not particularly limited but is in the range of 0.057 to 1.15 degrees.

[0047] The length A of the buffer material 30a in the Y direction (first direction) (see Figure 3A ) may be the same as the secondary battery 10. The length As of the thick portion 31 in the Y direction (see Figure 3A ) For example, the length A of the Y direction relative to the buffer material 30a may be in the range of 20% to 80%. If the length As of the Y direction of the thick wall portion 31 is 20% or more, even if the volume of the secondary battery 10 increases or decreases, the positional displacement between the secondary battery 10 and the buffer material 30a is unlikely to occur. In addition, if the length As of the Y direction of the thick wall portion 31 is 80% or less, the range of the thin wall portion 32 becomes wider, so when the volume of the secondary battery 10 is reduced, the area of ​​the gap 50 formed between the secondary battery 10 and the buffer material 30a becomes larger.

[0048] The length B of the bottom 31a of the thick portion 31 of the buffer material 30a in the X direction (stacking direction) (see Figure 3A ) For example, it may be in the range of 10% to 40% relative to the length in the X direction of the secondary battery 10. In addition, the ratio of the length in the X direction of the thin-walled portion 32 to the length B in the X direction of the bottom 31a of the thick-walled portion 31 is determined by the inclination angle θ of the thin-walled portion 32, the length A in the Y direction of the buffer material 30a, and the length As in the Y direction of the thick-walled portion 31.

[0049] As the material of the buffer material 30a, 30b, a rubber material or a combination of a spring and a plastic can be used. Examples of the rubber material include natural rubber, diene rubber, non-diene rubber and the like. The Young's modulus of the buffer material 30a, 30b can also be within the range of 0.002 GPa to 4 GPa, for example.

[0050] Secondary battery 10 Figure 4A As shown, the secondary battery 10 comprises: an electrode stack 18 formed by stacking a positive electrode 11 and a negative electrode 14 via a separator 17; an electrolyte (not shown); and a package 19 that contains the electrode stack 18 and the electrolyte. The secondary battery 10 is formed as a lithium metal secondary battery using lithium metal as a negative electrode active material. The secondary battery 10 is configured in such a way that the stacking direction of the electrode stack 18 coincides with the X direction (stacking direction) of the battery stack 100.

[0051] The positive electrode 11 includes a positive electrode current collector 12 and a positive electrode active material layer 13. The positive electrode current collector 12 is led out to the outside via a positive electrode lead terminal (not shown).

[0052] As the material of the positive electrode current collector 12 , for example, Al can be used.

[0053] The positive electrode active material layer 13 contains a positive electrode active material. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and LiNiO2. p Mn q Co r O2(p+q+r=1), LiNi p Al q Co r O2 (p + q + r = 1), lithium manganate (LiMn2O4), Li 1+x Mn 2－x－y M y O4 (x+y=2, M is selected from at least one of Al, Mg, Co, Fe, Ni and Zn) represented by a heterogeneous element substituted Li-Mn spinel, lithium titanate (comprising an oxide of Li and Ti), lithium metal phosphate (LiMPO4, M is selected from at least one of Fe, Mn, Co and Ni), etc. The positive electrode active material layer 13 may also include various additives such as a binder and a conductive aid used as a material of the positive electrode active material layer.

[0054] The negative electrode 14 has a negative electrode collector 15. The negative electrode collector 15 is led out to the outside through a negative electrode lead terminal (not shown). As a material of the negative electrode collector 15, for example, Cu can be used. Li foil may be stacked on the surface of the negative electrode collector 15.

[0055] Negative electrode 14 Figure 4B As shown, the negative electrode active material layer 16 (lithium metal layer) is generated by charging. Therefore, in the negative electrode 14 of the secondary battery 10b after charging, the thickness of the electrode stack 18 in the stacking direction becomes thicker, and the volume increases. In the secondary battery 10b after charging, the negative electrode active material layer 16 dissolves and disappears due to discharge, and the volume decreases.

[0056] The electrolyte solution includes an organic solvent and an electrolyte. As an organic solvent, for example, cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers, aromatic ethers, sulfones, cyclic esters, chain carboxylates, and nitriles can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 4-methyl 1,3-dioxolane. Examples of 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, and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane. Examples of aromatic ethers include anisole. Examples of sulfones include cyclopentane sulfone and methylcyclopentane sulfone. Examples of cyclic esters include γ-butyrolactone. Examples of chain carboxylates include acetate, butyrate, and propionate. Examples of nitriles include acetonitrile and propionitrile. The organic solvent may be used alone or in combination of two or more.

[0057] The electrolyte is a source of lithium ions that serve as a charge transfer medium and includes lithium salts. Examples of lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(CF3SO2)2(LiTFSI), LiN(FSO2)2(LiFSI), and LiBC4O8. Lithium salts can be used alone or in combination of two or more. The concentration of the electrolyte is, for example, in the range of 1.0 mol / L to 4.0 mol / L.

[0058] The package 19 can expand and contract according to the increase and decrease of the volume of the negative electrode 14 caused by charge and discharge. A laminated film can be used as a material for the package 19. As the laminated film, a laminated film having a three-layer structure in which an inner resin layer, a metal layer, and an outer resin layer are sequentially laminated from the inner side can be used. Optionally, the outer resin layer is, for example, a polyamide layer, the metal layer is, for example, an aluminum layer, and the inner resin layer is, for example, a polypropylene layer.

[0059] When the volume of the secondary battery 10 of the battery stack 100 increases due to charging, the thick-walled portion 31 of the buffer material 30a, 30b is crushed in the X direction due to the compressive force caused by the volume increase. Since the thick-walled portion 31 is crushed, a repulsive force against the compressive force is generated, and the restraining force applied to the secondary battery 10 from the thick-walled portion 31 increases, and the restraining force becomes larger inside the secondary battery 10. On the other hand, since there is a gap 50 between the thin-walled portion 32 of the buffer material 30a, 30b and the secondary battery 10, no compressive force is applied to the thin-walled portion 32 at the beginning of charging. Therefore, at the beginning of charging, a restraining force is applied to the portion of the secondary battery 10 that is opposite to the thick-walled portion 31 of the electrode stack 18, and the electrolyte moves upward in the Y direction (direction of gravity). Further, when the thin-walled portion 32 contacts the secondary battery 10 from the bottom of the Y direction as the volume of the secondary battery 10 increases, the thin-walled portion 32 is also crushed. When the thin portion 32 is crushed, a restraining force is applied to the secondary battery 10 from the thin portion 32, and the electrolyte in the electrode stack 18 inside the secondary battery 10 facing the thin portion 32 moves upward in the Y direction. Then, when the thin portion 32 is crushed as a whole, it is pushed out of the electrode stack 18.

[0060] like Figure 5 As shown in FIG. 1 , when observing the front side (the side along the XY direction) of the secondary battery module 1b after charging, the restraining force applied from the buffer materials 30a and 30b to the secondary battery 10b is the highest at the portion facing the thick wall portion 31, and the portion facing the thin wall portion 32 becomes weaker as it moves forward ( Figure 5 The arrow in the figure indicates that the greater the thickness, the greater the constraint force). On the other hand, Figure 6 As shown, at the bottom of the secondary battery module 1b after charging, the compressive force generated by the secondary battery 10b is evenly applied to the thick wall portions 31 of the buffer materials 30a and 30b, so the amount of crushing is uniform. As a result, the restraining force applied to the secondary battery 10b from the thick wall portions 31 of the buffer materials 30a and 30b is uniform.

[0061] When the charged secondary battery 10b is discharged and the volume of the secondary battery 10b is gradually reduced, the compressive force applied from the secondary battery 10b to the buffer materials 30a and 30b becomes lower. As a result, the amount of crushing of the thick-walled portion 31 and the thin-walled portion 32 of the buffer materials 30a and 30b becomes smaller, and a gap 50 is formed between the thin-walled portion 32, the secondary battery 10b, and the thin-walled portion 32. When the gap 50 is formed, the electrolyte penetrates into the interior of the electrode stack 18 from the gap 50. The electrolyte penetrated into the interior of the electrode stack 18 flows from the upper end in the Y direction (gravity direction) to the bottom due to its own weight, and is evenly supplied to the positive electrode 11 and the negative electrode 14.

[0062] According to the secondary battery module 1 of the present embodiment, since the buffer material 30 has the thick wall portion 31 and the thin wall portion 32, when the volume of the secondary battery 10 increases, the restraining pressure applied to the secondary battery 10 can be controlled, so that the flow of the electrolyte in the secondary battery 10 during charge and discharge can be adjusted. Therefore, even if the secondary battery module 1 of the present embodiment uses the secondary battery 10 whose volume changes due to charge and discharge, the electrolyte is not easily liquefied and exhausted, and the cycle characteristics are excellent.

[0063] In the secondary battery module 1 of the present embodiment, the thin-walled portion 32 of the buffer material 30a, 30b is inclined in a manner that the front end tapers along the Y direction (first direction), and the inclination angle of the thin-walled portion 32 relative to the thick-walled portion 31 is 0.057 to 1.15 degrees, so the amount of collapse of the buffer material in the contact area between the thin-walled portion 32 of the buffer material 30a, 30b and the secondary battery 10 can be continuously adjusted. Therefore, the restraining force applied to the secondary battery 10 can be adjusted to more reliably avoid the occurrence of liquid depletion of the electrolyte. Furthermore, according to the secondary battery module 1 of the present embodiment, since the thin-walled portion 32 of the buffer material 30a, 30b is arranged in a manner that it is located on the upper side of the gravity direction than the thick-walled portion 31, when the volume of the secondary battery 10 increases, the electrolyte can be anisotropically moved 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 of the secondary battery 10 to the lower side by the dead weight of the electrolyte. Therefore, even if charge and discharge are repeated, liquefaction and depletion of the electrolyte solution are unlikely to occur, and the cycle characteristics are excellent.

[0064] In the secondary battery module 1 a of the present embodiment, the bottoms of the thick portions 31 of the buffer materials 30 a and 30 b are formed in a rectangular shape, but the bottoms of the thick portions 31 of the buffer materials 30 a and 30 b may be curved. Figure 7 FIG. 2 shows a modified example in which the bottoms of the buffer members 30 a and 30 b are curved.

[0065] exist Figure 7 In the secondary battery module 2a shown, the bottom of the buffer materials 40a, 40b is formed into an arc shape with the center in the Z direction (second direction) as the vertex. The center in the Z direction of the thick wall portion 31 is in contact with the secondary battery 10 which is in a discharged state and has a reduced volume, and the two 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 buffer materials 30a, 30 are pressed in the X direction by the secondary battery 10, and the length of the thick wall portion 31 in the X direction gradually decreases and the interval of the gap 50 becomes narrower. The secondary battery module 2b after charging is as shown. Figure 8As shown in FIG. 1 , the secondary battery 10b is in contact with the thin wall portion 32 of the buffer materials 30a and 30b in the Z direction. After charging, the secondary battery 10b is subjected to pressure from the buffer materials 30a and 30b. The pressure applied from the buffer materials 30a and 30b is as shown in FIG. Figure 8 As shown, the center of the Z direction is the highest, and the weaker it is towards the ends of the Z direction ( Figure 8 The arrow in the figure indicates that the greater the thickness, the greater the constraint pressure).

[0066] According to the secondary battery module 2 of this variation, when the volume of the secondary battery 10 increases, the electrolyte in the electrode stack 18 easily flows in the second direction. In addition, when the volume of the secondary battery 10 decreases, the electrolyte penetrates into the electrode stack 18 from the second direction, so that the electrolyte can be supplied to the electrode stack 18 of the secondary battery 10 more evenly.

[0067] In the secondary battery module 1 a of the present embodiment, the side surfaces of the buffer materials 30 a and 30 b in contact with the secondary battery 10 are formed into flat surfaces. However, grooves may be provided on the side surfaces of the buffer materials 30 a and 30 b in contact with the secondary battery 10 .

[0068] Fig. 9 In the illustrated buffer material 40c, the grooves 41 and 42 are indicated by imaginary lines.

[0069] The grooves 41 and 42 are provided on the side of the buffer material 40c that contacts the secondary battery 10, that is, on the YZ plane along the Y direction (first direction) and the Z direction (second direction). Let the length of the Y direction of the YZ plane be A, and the length of the Z direction be C, then the groove 41 is formed to connect the center point P0 of the thick wall side end in the Y direction of the YZ plane and the two ends P0 of the thin wall side end in the Y direction. 10 , P 20 Towards the Z direction to two points P at the length position of 1 / 5C 11 , P 12 The groove 42 is formed by connecting the center point P0 in the Z direction of the thick-walled portion side end in the Y direction and two points P0 at the length position of 2 / 3A from both ends of the thin-walled portion side end in the Y direction toward the thick-walled portion side. 12 , P 22 The groove 41 is a curve extending from the central point P0 toward the end point P 11 , P 21 The groove 42 is in the shape of a curve that bulges outward, and extends from the central point P0 toward the end point P 12 , P 22 The grooves 41 and 42 may be in the shape of a curve that bulges outward. The length of the grooves 41 and 42 in the X direction is, for example, within the range of 0.1 mm to 2.0 mm from the surface of the thick wall portion 31 .

[0070] The secondary battery module using the buffer material 40c is provided with grooves 41 and 42 on the surface in contact with the secondary battery 10, that is, the YZ surface. When the volume of the secondary battery 10 increases, the pressure applied to the secondary battery 10 from the portion of the buffer material 40c where the grooves 41 and 42 are not provided increases, so the electrolyte in the electrode stack 18 is easily moved to the portion opposite to the portion of the buffer material 40c where the grooves are provided. In addition, when the volume of the secondary battery 10 decreases, the electrolyte penetrates into the electrode stack 18 from the portion opposite to the portion of the buffer material 40c where the grooves are provided, so that the electrolyte can be evenly supplied to the electrode stack 18 of the secondary battery 10. The end of the groove 41 is set as P 11 , P 21 , the end of the groove 42 is set as point P 12 , P 22 , but the position of the end is not limited to this. The end of the groove can be at P 10 ~P 11 Between and P 20 ~P 21 Between, or between P 10 ~P 12 Between 20 ~P 22 The ends of the grooves may be located symmetrically with respect to the central point P0.

[0071] As mentioned above, although the preferred embodiment of the present invention has been described, the present invention is not limited to the above-mentioned embodiment, and can be modified appropriately.

[0072] For example, in this embodiment, the thin-walled portion 32 of the buffer material 30a, 30b continuously decreases in length in the X direction so as to taper along the Y direction, but the shape of the thin-walled portion 32 is not limited thereto. The length of the thin-walled portion 32 in the X direction may also decrease in stages.

[0073] In addition, in this embodiment, the secondary battery 10 is formed as a lithium metal secondary battery using lithium metal as the negative electrode active material, but the secondary battery 10 is not limited thereto. Silica particles may also be used as the negative electrode active material of the secondary battery 10. In addition, the secondary battery 10 may also be a battery whose volume does not change due to charge and discharge.

[0074] Reference numerals

[0075] 1a, 1b, 2a, 2b secondary battery modules

[0076] 10, 10b secondary battery

[0077] 11 Positive electrode

[0078] 12Positive electrode collector

[0079] 13 Positive electrode active material layer

[0080] 14 Negative electrode

[0081] 15 Negative electrode collector

[0082] 16 Negative electrode active material layer

[0083] 17 Diaphragm

[0084] 18-electrode stack

[0085] 19Packaging

[0086] 20 End Plate

[0087] 30a, 30b, 40a, 40b, 40c buffer material

[0088] 31 Thick wall part

[0089] 31a bottom

[0090] 32 Thin wall part

[0091] 32a front end

[0092] Slots 41 and 42

[0093] 50 gap

Claims

1. A secondary battery module comprising a battery stack formed by stacking a plurality of secondary batteries, and a pair of end plates disposed at both ends of the battery stack in a stacking direction, and further comprising: A buffer material is disposed at least one of between the adjacent secondary batteries and between the battery stack and the end plate; In a first direction orthogonal to the stacking direction of the battery stack, one end of the buffer material is formed as a thick portion having a greater length in the stacking direction, and the other end is formed as a thin portion having a smaller length in the stacking direction than the thick portion.

2. The secondary battery module according to claim 1, wherein: The volume of the secondary battery changes due to charge and discharge.

3. The secondary battery module according to claim 1, wherein: The thin-walled portion of the buffer material is inclined so as to become thinner along the first direction, and an inclination angle of the thin-walled portion relative to the thick-walled 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 buffer material is formed in an arc shape with the center as a vertex.

5. The secondary battery module according to claim 1, wherein: The buffer material is provided with grooves on a surface along a second direction orthogonal to the stacking direction and the first direction, and along the first direction. The length of the surface in the first direction is set to A, and the length in the second direction is set to C. The groove is in the shape of a curve connecting the center point in the second direction of the thick-walled portion side end in the first direction and two points at a length position of 2 / 3A from the two ends of the thin-walled portion side end in the first direction toward the thick-walled portion side, or is in the shape of a curve connecting the center point and two points at a length position of 1 / 5C from the two ends of the thin-walled 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 arranged such that the thin-walled portion is located above the thick-walled portion in a gravity direction.

7. The secondary battery module according to claim 1, wherein: The secondary battery comprises an electrode stack formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween, an electrolyte, and a package containing the electrode stack and the electrolyte. The secondary battery is 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 volume of the negative electrode increases due to charging and decreases due to discharging.

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