Battery module

Abstract

A battery module includes a plurality of battery cells each having a flat shape, a plurality of elastic spacers alternately stacked with the plurality of battery cells, and a restraining member that restrains the plurality of battery cells and the plurality of elastic spacers in a stacking direction of the plurality of battery cells. The elastic spacer has a tab portion that expands between two adjacent battery cells, and a plurality of protrusions that protrude from one surface of the tab portion. The plurality of protrusions are arranged equidistantly at least along a first direction. When a distance between the plurality of protrusions in the first direction is x, and a dimension of each protrusion in the first direction is y, the following relationships are satisfied: 4 mm ≤ y ≤ 18 mm, y ≥ 4 / 9x - 10 / 3, and y ≤ x - 2.

Description

Technical Field

[0001] This invention relates to battery modules. Background Technology

[0002] Japanese Patent Application Publication No. 2020-004556 discloses a battery module. In the battery module, multiple battery cells, each having a flat shape, and elastic spacers equipped with plates and multiple protrusions are stacked and arranged, and constrained by a constraint member. Summary of the Invention

[0003] In a flat battery cell, positive and negative electrodes are stacked together with a separator between them, and electrolyte fills the space between the positive and negative electrodes. When configured this way, the battery cell expands in the stacking direction during charging and contracts in the stacking direction during discharging. Since the stacking direction of the two electrodes within the battery cell is the same as the stacking direction of multiple battery cells, the expansion of the battery cell is limited by the restraining members and the elastic spacers. Therefore, the increase in the distance between the two electrodes within the battery cell is suppressed, thus preventing a decrease in the battery cell's capacity. However, for example, there is a possibility that the expansion of the battery cell may be unnecessarily restricted due to factors such as the size or shape of the protrusions of the elastic spacers. In this case, there is a possibility that electrolyte may leak out between the two electrodes, causing an unexpected increase in the battery cell's resistance.

[0004] In this invention, a technique is provided to suppress or avoid the increase in the resistance value of a battery cell and to suppress the decrease in the capacity of the battery cell.

[0005] A first aspect of the present invention relates to a battery module. The battery module includes: a plurality of battery cells, each having a flat shape; a plurality of elastic spacers alternately stacked with the plurality of battery cells; and a constraint member constraining the plurality of battery cells and the plurality of elastic spacers in a stacking direction of the plurality of battery cells. Each elastic spacer has a sheet extending between two adjacent battery cells and a plurality of protrusions projecting from a surface of the sheet. The plurality of protrusions are arranged at equal intervals at least along a first direction. When the interval between the plurality of protrusions in the first direction is x, and the dimension of each protrusion in the first direction is y, the relationships 4mm ≤ y ≤ 18mm, y ≥ 4 / 9x - 10 / 3, and y ≤ x - 2 are satisfied.

[0006] In a first embodiment of the invention, the plurality of protrusions may also be arranged at equal intervals along a second direction perpendicular to the first direction, wherein the interval between the plurality of protrusions in the second direction is equal to the interval between the plurality of protrusions in the first direction, and the size of each protrusion in the second direction is equal to the size of each protrusion in the first direction.

[0007] In the first embodiment of the invention, each protrusion may also have a cylindrical shape.

[0008] In a first aspect of the invention, in the naturally shaped elastic spacer removed from the battery module, when the surface that contacts the front end of the plurality of protrusions and extends parallel to the sheet portion is defined as a cross section, the volume fraction of the area occupied by the plurality of protrusions in the region between the sheet portion and the cross section is greater than or equal to 14% and less than or equal to 38%.

[0009] A second aspect of the invention relates to a battery module. The battery module includes: a plurality of battery cells, each having a flat shape; a plurality of elastic spacers alternately stacked with the plurality of battery cells; and a constraint member constraining the plurality of battery cells and the plurality of elastic spacers in the stacking direction of the plurality of battery cells. The elastic spacers have a sheet extending between two adjacent battery cells and a plurality of protrusions projecting from a surface of the sheet. In the naturally shaped elastic spacers removed from the battery module, when a surface that contacts the front ends of the plurality of protrusions and extends parallel to the sheet is defined as a cross-section, the volume fraction of the area occupied by the plurality of protrusions in the region between the sheet and the cross-section is greater than or equal to 14% and less than or equal to 38%.

[0010] In a second embodiment of the invention, the plurality of protrusions may also have shapes that are equal to each other.

[0011] In a second embodiment of the invention, the plurality of protrusions may also be arranged at equal intervals at least along a first direction.

[0012] In a second embodiment of the invention, the surface of the battery cell contacted by the plurality of protrusions of the elastic spacer is rectangular in shape, having four corners, a pair of short sides, and a pair of long sides. When 5% of the length of the short side is taken as a first length, and for each of the four corners, a triangular region with the corner, a point on the short side at a distance of the first length from the corner, and a point on the long side at a distance of the first length from the corner as vertices is defined as a corner adjacency region, none of the plurality of protrusions of the elastic spacer contacts the corner adjacency region of the surface of the battery cell.

[0013] In the aforementioned battery module, battery cells and elastic spacers equipped with multiple protrusions are alternately stacked, and the battery cells and elastic spacers are constrained by constraint members in their stacking direction. Thus, the expansion of the battery cells is limited by the constraint members and elastic spacers. Furthermore, the multiple protrusions provided on the elastic spacers are configured to be equally spaced at least along a first direction, and satisfy predetermined relationships. These predetermined relationships mean that when the interval between the multiple protrusions in the first direction is x, and the dimension of each protrusion in the first direction is y, the relationships 4mm ≤ y ≤ 18mm, y ≥ 4 / 9x - 10 / 3, and y ≤ x - 2 are satisfied. With this configuration, unnecessary restriction on the expansion of the battery cells can be avoided, and the increase in the distance between the two electrodes within the battery cell can be suppressed. This can suppress the leakage of electrolyte to the outside between the two electrodes, suppress or prevent an unexpected increase in the resistance value of the battery cell, and also suppress the reduction in the capacity of the battery cell. Attached Figure Description

[0014] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which similar reference numerals denote similar parts, wherein:

[0015] Figure 1 This is a schematic diagram illustrating the structure of the battery module in an embodiment.

[0016] Figure 2 This diagram illustrates the elastic spacer positioned between two adjacent battery cells. The two adjacent battery cells are indicated by dashed lines.

[0017] Figure 3 This is a side view of the elastic spacer.

[0018] Figure 4 This is a plan view of the elastic spacer.

[0019] Figure 5 This is a table representing the results of cyclic experiments.

[0020] Figure 6 This is a table representing the results of cyclic experiments.

[0021] Figure 7 This is a graph representing the results of a cyclic test.

[0022] Figure 8 It is a side view of an elastic spacer that represents the volume ratio of the cross-section and the area occupied by multiple protrusions located in the region between the sheet and the cross-section.

[0023] Figure 9 This is a plan view of the elastic spacer. Additionally, the blank areas represent the volume fraction of the area occupied by the multiple protrusions in the region located between the sheet and the cut surface.

[0024] Figure 10 This is a table representing the results of cyclic experiments.

[0025] Figure 11 This is a graph representing the results of a cyclic test.

[0026] Figure 12 This is a diagram illustrating the corner adjacent areas of a battery cell. Detailed Implementation

[0027] In one embodiment of the invention, the plurality of protrusions may also be arranged at equal intervals along a second direction perpendicular to the first direction. In this case, the interval between the plurality of protrusions in the second direction may also be equal to the interval between the plurality of protrusions in the first direction, and the dimension of each protrusion in the second direction may also be equal to the dimension of each protrusion in the first direction. According to this structure, when the battery cell expands, the load applied from the protrusions of the elastic spacer to the adjacent battery cell can be avoided from being locally concentrated. Thus, it is possible to more reliably avoid unnecessarily restricting the expansion of the battery cell.

[0028] In one embodiment of the invention, each protrusion may also have a cylindrical shape. With this configuration, for each protrusion, the contact area between the protrusion of the elastic spacer and the adjacent battery cell is constant regardless of the amount of expansion of the battery cell. This avoids the localized concentration of load applied from each protrusion to the adjacent battery cell. However, as another embodiment, each protrusion does not necessarily have to be cylindrical; for example, it may be hemispherical, trapezoidal, prismatic, etc.

[0029] In the above embodiment, in the naturally shaped elastic spacer removed from the battery module, when the surface that contacts the front ends of the multiple protrusions and extends parallel to the sheet is defined as a cross-section, the volume fraction of the area occupied by the multiple protrusions in the region between the sheet and the cross-section can be greater than or equal to 14% and less than or equal to 38%. According to this structure, both unnecessarily restricting the expansion of the battery cell can be more reliably avoided, and the increase in the distance between the two electrodes within the battery cell can be suppressed. Furthermore, the term "natural shape" refers to the shape of the elastic spacer after it has been restored to its original shape by a restoring force after being removed from the battery module. The term "natural shape" can also refer to the shape of the elastic spacer after it has been restored to its original shape by a restoring force immediately after being removed from the battery module following assembly.

[0030] The present invention also relates to a battery module comprising: a plurality of battery cells, each having a flat shape; a plurality of elastic spacers alternately stacked with the plurality of battery cells; and a constraint member constraining the plurality of battery cells and the plurality of elastic spacers in the stacking direction of the plurality of battery cells. The elastic spacers have a sheet extending between two adjacent battery cells and a plurality of protrusions projecting from a surface of the sheet. In the naturally shaped elastic spacer removed from the battery module, when a sectional surface is defined as the surface that contacts the front ends of the plurality of protrusions and extends parallel to the sheet, the volume fraction of the area occupied by the plurality of protrusions in the region between the sheet and the sectional surface is greater than or equal to 14% and less than or equal to 38%.

[0031] In the aforementioned battery module, battery cells and elastic spacers with multiple protrusions are alternately stacked, and the battery cells and elastic spacers are constrained by constraint members in their stacking direction. Thus, the expansion of the battery cells is limited by the constraint members and elastic spacers. Furthermore, the elastic spacers are configured to satisfy a predetermined relationship in their natural shape when removed from the battery module. This predetermined relationship refers to a situation where, when a sectional surface is defined as the surface that contacts the front ends of the multiple protrusions and extends parallel to the sheet portion, the volume fraction of the area occupied by the multiple protrusions in the region between the sheet portion and the sectional surface is greater than or equal to 14% and less than or equal to 38%. With this structure, unnecessary restriction on the expansion of the battery cells can be avoided, and the increase in the distance between the two electrodes within the battery cell can be suppressed. This suppresses the leakage of electrolyte to the outside between the two electrodes, suppresses or prevents an unexpected increase in the resistance value of the battery cell, and also suppresses a decrease in the capacity of the battery cell.

[0032] In the above embodiment, the multiple protrusions may also have shapes that are equal to each other. With this structure, for each protrusion, the contact area between the protrusion of the elastic spacer and the adjacent battery cell becomes equal when the battery cell expands. Therefore, when the battery cell expands, the load applied from the protrusion of the elastic spacer to the adjacent battery cell can be prevented from becoming locally concentrated.

[0033] In the above embodiment, the multiple protrusions can also be arranged at equal intervals at least along a first direction. With this structure, when the battery cell expands, the load applied from the protrusions of the elastic spacer to the adjacent battery cell can be prevented from becoming locally concentrated. Furthermore, the multiple protrusions only need to be arranged at equal intervals along the first direction. However, the multiple protrusions can also be arranged at equal intervals along a second direction in addition to the first direction.

[0034] In the embodiments described above, the surface of the battery cell contacted by the multiple protrusions of the elastic spacer can also be rectangular, having four corners, a pair of short sides, and a pair of long sides. In this case, when 5% of the length of the short side is used as the first length, and for each of the four corners, a triangular region with the corner, a point on the short side a first length away from the corner, and a point on the long side a first length away from the corner as vertices is defined as the corner adjacency region, none of the multiple protrusions of the elastic spacer contacts the corner adjacency region of the battery cell surface. Within the surface of the battery cell, the corner adjacency region has relatively high rigidity, while the region outside the corner adjacency region has relatively low rigidity. Therefore, when the battery cell expands, the load applied to the battery cell from the protrusions of the elastic spacer can be effectively transmitted within the battery cell, suppressing the increase in distance between the two electrodes within the battery cell. This suppresses or prevents a decrease in the battery cell's capacity.

[0035] Hereinafter, with reference to the accompanying drawings, a battery module 10 as an embodiment of the present invention will be described. The battery module 10 is used, for example, as a power source for an electric vehicle. Figure 1 As shown, the battery module 10 is equipped with multiple battery cells 12. Each battery cell 12 is, for example, a rechargeable battery cell capable of repeated charging and discharging, such as a lithium-ion rechargeable battery cell. Each battery cell 12 has a flat shape and is arranged parallel to the X and Y directions. The multiple battery cells 12 are arranged along the Z direction. Here, the X, Y, and Z directions are orthogonal to each other. Furthermore, there is no particular limitation on the specific number of multiple battery cells 12, which can be appropriately varied according to the required output voltage of the battery module 10.

[0036] Although omitted in the figure, inside each battery cell 12, the positive electrode and the negative electrode are stacked in the Z direction separated by a separator and an electrolyte. In this case, although there are no particular limitations, inside each battery cell 12, multiple sheets constituting the positive electrode and multiple sheets constituting the negative electrode can also be stacked alternately separated by a separator. Alternatively, the long strips constituting the positive electrode and the long strips constituting the negative electrode can also be wound into a flat shape separated by a separator.

[0037] like Figure 1 , Figure 2 As shown, the battery module 10 is also equipped with a plurality of elastic spacers 14. The plurality of elastic spacers 14 are stacked alternately with the plurality of battery cells 12 along the Z direction. That is, an elastic spacer 14 is disposed between each pair of adjacent battery cells. The plurality of elastic spacers 14 can elastically deform according to the load from the battery cells 12. In one example, the plurality of elastic spacers 14 are made of elastic materials such as rubber or resin.

[0038] like Figure 2 As shown, each elastic spacer 14 is equipped with a sheet portion 20 and a plurality of protrusions 22. The sheet portion 20 is configured to extend between two adjacent battery cells 12. The plurality of protrusions 22 protrude from a surface 20a of the sheet portion 20 and abut against the adjacent battery cell 12. According to this structure, the elastic spacer 14 can more flexibly deform elastically according to the load from the battery cell 12. In addition, there is no particular limitation on the specific number of the plurality of elastic spacers 14, which can be appropriately varied according to the number of battery cells 12.

[0039] like Figure 3 , Figure 4 As shown, a plurality of protrusions 22 are arranged at equal intervals of x along the X and Y directions. That is, two adjacent protrusions 22 in the X direction are arranged with an interval of x, and two adjacent protrusions 22 in the Y direction are also arranged with an interval of x. Furthermore, in this invention, the interval x between two protrusions 22 refers to the distance between the centers of the two protrusions 22. Each protrusion 22 has a cylindrical shape with a diameter of y. That is, the dimension of the protrusion 22 in the first direction is y, and the dimension of the protrusion 22 in the second direction is also y.

[0040] Here, the X direction in this embodiment is an example of a first direction in this invention. The Y direction in this embodiment is an example of a second direction in this invention. The Z direction in this embodiment is an example of a stacking direction in this invention.

[0041] return Figure 1The battery module 10 is also equipped with a constraint member 16. The constraint member 16 has a generally cuboid shape and an upwardly opening 18. Stacked battery cells 12 and elastic spacers 14 are disposed within the opening 18. Thus, the constraint member 16 constrains multiple battery cells 12 and multiple elastic spacers 14 in the stacking direction (i.e., the Z direction) of the battery cells 12 and elastic spacers 14. Therefore, in the event that multiple battery cells 12 expand, the expansion of the battery cells 12 is limited by the constraint member 16. Furthermore, there are no particular limitations on the specific shape and structure of the constraint member 16.

[0042] As described above, in the battery module 10 of this embodiment, a plurality of battery cells 12 and a plurality of elastic spacers 14 are alternately stacked along the Z direction. Here, inside each battery cell 12, the positive electrode and the negative electrode are stacked in the same Z direction. Thus, each battery cell 12 expands in the stacking direction (i.e., the Z direction) during charging and contracts in the stacking direction (i.e., the Z direction) during discharging. When the battery cell 12 expands, the expansion of the battery cell 12 is suppressed by the elastic force of the elastic spacers 14 because the elastic spacers 14 adjacent to the battery cell 12 are compressed. As a result, the reduction in the capacity of the battery cell 12 is suppressed because the increase in the distance between the two electrodes within the battery cell 12 is suppressed. However, when the elastic force generated by the elastic spacers 14 is too strong, there is a possibility that the expansion of the battery cell 12 is unnecessarily restricted. In this case, there is a possibility that the electrolyte will leak out to the outside between the two electrodes, and the resistance value of the battery cell 12 will unexpectedly increase.

[0043] Regarding the aforementioned problems, the inventors, in order to optimize the elastic spacer 14, examined the relationship between the structure of the elastic spacer 14 and the degradation occurring in the battery cell 12. In this examination, a cyclic test was conducted to quantitatively evaluate the degradation of the battery module 10, using the spacing x and diameter y of the protrusions 22 in the elastic spacer 14 as parameters. Specifically, the battery module 10 was subjected to 500 charge-discharge cycles, and the changes in its internal resistance and charging capacity before and after the cycles were measured. Figures 5-7 The first verification result is shown in the figure. In the cyclic test, constant current, constant voltage (CCCV) charging was used. The charging conditions were 4.25V, 0.5C, and a cutoff current of 0.1C. On the other hand, the discharging conditions were 2.8V and 0.5C.

[0044] about Figures 5-7The resistance rise rate represents the ratio of the internal resistance after the cycle test to the internal resistance before the cycle test. If the resistance rise rate is less than or equal to 100%, the resistance value of battery cell 12 is considered to be maintained. Figure 5 , Figure 6 The value is represented by "A". On the other hand, if the rate of increase in resistance is greater than 100%, it is determined that the resistance value of battery cell 12 has increased. Figure 5 , Figure 6 The term "B" is used to represent this. Capacity retention rate indicates the ratio of the charged capacity after a cycle test to the charged capacity before the cycle test. A capacity retention rate greater than or equal to 80% is considered to be within the allowable range. Figure 5 , Figure 6 In this context, "A" is used to represent it. On the other hand, if the capacity retention rate is less than 80%, it is considered to be outside the allowable range. Figure 5 , Figure 6 In Chinese, it is represented by "B".

[0045] like Figure 6 As shown in levels 53-57, when the diameter y of the protrusion 22 is greater than or equal to 19 mm, it is determined that the resistance value of the battery cell 12 has increased. This is considered to be because the diameter y of the protrusion 22 of the elastic spacer 14 is too large, excessively restricting the expansion of the battery cell 12, thereby causing the electrolyte inside the battery cell 12 to be discharged to the outside between the two electrodes. Therefore, it is understood that when the diameter y of the protrusion 22 of the elastic spacer 14 is less than or equal to 18 mm, unnecessary restriction on the expansion of the battery cell 12 can be avoided. Here, the relationship that the diameter y of the protrusion 22 is less than or equal to 18 mm is represented by "y≤18mm", corresponding to... Figure 7 The straight line (a) and the region below it.

[0046] like Figure 5 As shown in levels 6, 9, 20-24, when the diameter y of the protrusion 22 is less than or equal to 3 mm, the capacity retention rate is considered to be outside the allowable range. This is believed to be because the diameter y of the protrusion 22 of the elastic spacer 14 is too small to adequately restrict the expansion of the battery cell 12, thus increasing the distance between the two electrodes within the battery cell 12. Therefore, it is understood that when the diameter y of the protrusion 22 of the elastic spacer 14 is greater than or equal to 4 mm, the increase in the distance between the two electrodes within the battery cell 12 can be suppressed. Here, the relationship that the diameter y of the protrusion 22 is greater than or equal to 4 mm is represented by "4 mm ≤ y", corresponding to... Figure 7 The straight line (b) and the area above it.

[0047] In addition to the results above, even when the diameter y of the protrusion 22 is in the range of 4 mm to 18 mm, the resistance value of the battery cell 12 increases or the capacity retention rate decreases, depending on the spacing x of the protrusions 22. Therefore, regarding the spacing x of the protrusions 22, like the diameter y of the protrusions 22, both upper and lower limits are supported. This will be explained in detail below.

[0048] First, the relationship between the resistance value of the battery cell 12 and the spacing x of the protrusions 22 will be explained. For example, when the diameter y of the protrusions 22 is 18 mm, the resistance value of the battery cell 12 increases when the spacing x of the protrusions 22 is 18 mm (refer to level 37), while the resistance value of the battery cell 12 is maintained when the spacing x of the protrusions 22 is greater than or equal to 20 mm (refer to levels 25, 31, etc.). These results show that even when the diameter y of the protrusions 22 is in the range of 4 mm to 18 mm, if the spacing x of the protrusions 22 is too small, it will excessively restrict the expansion of the battery cell 12. Therefore, to avoid an increase in the resistance value of the battery cell 12, it is necessary to determine a lower limit for the spacing x of the protrusions 22, just as it is for the diameter y of the protrusions 22. Specifically, the spacing x of the protrusions 22 must satisfy "y ≤ x - 2". This relationship corresponds to... Figure 7 The straight line (c) and the region below it.

[0049] Secondly, the relationship between capacity retention rate and the spacing x of the protrusions 22 is explained. For example, when the diameter y of the protrusions 22 is 16 mm, the capacity retention rate is outside the allowable range when the spacing x of the protrusions 22 is 48 mm (refer to level 11), and is within the allowable range when the spacing x of the protrusions 22 is less than or equal to 40 mm (refer to levels 44-47, etc.). These results show that even when the diameter y of the protrusions 22 is in the range of 4 mm to 18 mm, the expansion of the battery cell 12 cannot be sufficiently limited when the spacing x of the protrusions 22 is larger than necessary. Therefore, it is necessary to determine an upper limit for the spacing x of the protrusions 22, just like the diameter y of the protrusions 22. Specifically, the spacing x of the protrusions 22 must satisfy "y ≥ 4 / 9x - 10 / 3". This relationship corresponds to... Figure 7 The straight line (d) and the region above it.

[0050] The above results show that when the spacing x of the protrusions 22 and the diameter y of the protrusions 22 satisfy a specified relationship, it is possible to avoid unnecessarily restricting the expansion of the battery cell 12 and suppress the increase in the distance between the two electrodes within the battery cell 12. Here, the specified relationship, related to the spacing x of the protrusions 22 and the diameter y of the protrusions 22, refers to the relationships 4mm ≤ y ≤ 18mm, y ≥ 4 / 9x - 10 / 3, and y ≤ x - 2. This is consistent with the relationship between... Figure 7 The regions enclosed by straight lines (a)-(d) are consistent. In the battery module 10 equipped with an elastic spacer 14 that satisfies the above relationship, the leakage of electrolyte to the outside between the two electrodes is suppressed, the unexpected increase in the resistance value of the battery cell 12 is suppressed or avoided, and the capacity reduction of the battery cell 12 is also suppressed.

[0051] In addition to the first verification, the inventors also conducted a second verification to optimize the elastic spacer 14, verifying the relationship between the structure of the elastic spacer 14 and the degradation that occurs in the battery 12. In this verification, as... Figure 8 , Figure 9 As shown, in the naturally shaped elastic spacer 14 removed from the battery module 10, the surface that contacts the front ends of the plurality of protrusions 22 and extends parallel to the sheet portion is defined as the sectional surface P. At this time, the volume fraction V (hereinafter sometimes referred to as "volume fraction V of protrusions 22") of the area occupied by the plurality of protrusions 22 in the region located between the sheet portion 20 and the sectional surface P is obtained. Using this volume fraction V as a parameter, a cycle test is performed to quantitatively evaluate the degradation of the battery module 10. Similar to the first verification, the battery module 10 is subjected to 500 charge-discharge cycles, and the changes in internal resistance and charging capacity before and after these cycles are measured. Figure 10 , Figure 11 The value in the middle represents the result of the second verification. Figure 11 In the diagram, curve (a) represents the rate of increase in resistance, and curve (b) represents the rate of capacity retention. Furthermore, the methods for determining the internal resistance and charging capacity of the battery module 10, as well as the charging and discharging conditions in the cycle test, are the same as in the first verification; therefore, repeated descriptions are omitted.

[0052] like Figure 10 As shown in Level 1-4, when the volume fraction V of the protrusion 22 is less than or equal to 13%, the capacity retention rate is considered to be outside the allowable range. This is believed to be because the volume fraction V of the protrusion 22 of the elastic spacer 14 is too small to adequately restrict the expansion of the battery cell 12, resulting in an increase in the distance between the two electrodes within the battery cell 12. Therefore, it is understood that when the volume fraction V of the protrusion 22 of the elastic spacer 14 is greater than or equal to 14%, the increase in the distance between the two electrodes within the battery cell 12 can be suppressed.

[0053] like Figure 10As shown in levels 30-41, when the volume fraction V of the protrusion 22 is greater than or equal to 39%, it is determined that the resistance value of the battery cell 12 has increased. This is considered to be because the volume fraction V of the protrusion 22 of the elastic spacer 14 is too large, excessively restricting the expansion of the battery cell 12, thereby causing the electrolyte inside the battery cell 12 to drain to the outside between the two electrodes. Thus, it is understood that when the volume fraction V of the protrusion 22 of the elastic spacer 14 is less than or equal to 38%, unnecessarily restricting the expansion of the battery cell 12 can be avoided.

[0054] Based on the above results, when the volume fraction V of the protrusion 22 of the elastic spacer 14 is greater than or equal to 14% and less than or equal to 38%, it can both avoid unnecessarily restricting the expansion of the battery cell 12 and suppress the increase in the distance between the two electrodes within the battery cell 12. In this case, the outflow of electrolyte to the outside between the two electrodes is suppressed, an unexpected increase in the resistance value of the battery cell 12 is suppressed or avoided, and the capacity reduction of the battery cell 12 is also suppressed.

[0055] Although there are no particular limitations, in the battery module 10 of this embodiment, the elastic spacer 14 can also satisfy both the relationship specified from the first verification result and the relationship specified from the second verification result. That is, the spacing x and diameter y of the protrusions 22 of the elastic spacer 14 can also satisfy the relationships 4mm≤y≤18mm, y≥4 / 9x-10 / 3, and y≤x-2, and the volume fraction V of the protrusions 22 is greater than or equal to 14% and less than or equal to 38%. According to this structure, both the unnecessary restriction on the expansion of the battery cell 12 can be avoided more reliably, and the increase in the distance between the two electrodes within the battery cell 12 can be suppressed.

[0056] In one example, in the battery module 10 of this embodiment, such as Figure 12As shown, the surface 12a of the battery cell 12, which is contacted by the plurality of protrusions 22 of the elastic spacer 14, has a rectangular shape, having four corners 24, a pair of short sides, and a pair of long sides. Let 5% of the length of the short sides be a first length L. For each of the four corners 24, the region of a triangle with the corner 24, a point 24a on the short side of the corner 24 at a distance of the first length L from the corner 24, and a point 24b on the long side of the corner 24 at a distance of the first length L from the corner 24 as vertices is defined as the corner abutment region 26. In this case, none of the plurality of protrusions 22 of the elastic spacer 14 contacts the corner abutment region 26 of the surface 12a of the battery cell 12. Within the surface 12a of the battery cell 12, the corner abutment region 26 has relatively high rigidity, while the region outside the corner abutment region 26 has relatively low rigidity. Therefore, when the battery cell 12 expands, the load applied to the battery cell 12 from the protrusion 22 of the elastic spacer 14 can be effectively transferred within the battery cell 12, thus suppressing the increase in the distance between the two electrodes within the battery cell 12. This suppresses or prevents a decrease in the capacity of the battery cell 12.

[0057] In the battery module 10 of this embodiment, each protrusion 22 does not necessarily have a cylindrical shape. In other embodiments, each protrusion 22 may be, for example, hemispherical, trapezoidal, or prismatic. Furthermore, the protrusions 22 may have shapes in which the dimensions in the X direction and the Y direction are different. Regardless of the shape of each protrusion 22, by satisfying the relationship determined by the first verification and / or by satisfying the relationship determined by the second verification, it is desirable to effectively suppress the degradation of the battery cell 12.

[0058] Furthermore, the plurality of protrusions 22 need not necessarily be arranged at equal intervals along both the X and Y directions; they only need to be arranged at equal intervals along at least one of the X or Y directions. When the plurality of protrusions 22 are arranged at equal intervals along the X direction, the interval between the plurality of protrusions 22 in the X direction and the dimension of each protrusion 22 in the X direction preferably satisfy the relationship specified in the first verification. Based on this, or alternatively, when the plurality of protrusions 22 are arranged at equal intervals along the Y direction, the interval between the plurality of protrusions 22 in the Y direction and the dimension of each protrusion 22 in the Y direction preferably satisfy the relationship specified in the first verification.

[0059] In the battery module 10 of this embodiment, the plurality of protrusions 22 do not necessarily have the same shape as each other. Furthermore, or alternatively, the plurality of protrusions 22 do not necessarily have to be equally spaced in one or both of the X and Y directions. In this implementation, it is also desirable to effectively suppress the degradation of the battery cell 12 by having the plurality of protrusions 22 satisfy the relationship specified by the second verification.

[0060] Several specific examples have been described in detail above; however, these are merely illustrative and do not limit the scope of protection claimed in this application. The technology described in the claims includes various modifications and alterations to the specific examples illustrated above. The technical elements described in this specification or drawings can be individually or in combination to exert technical usefulness.

Claims

1. A battery module, characterized in that, include: Multiple battery cells, each of which has a flat shape; Multiple elastic spacers are alternately stacked with the multiple battery cells; as well as A constraint member constrains the plurality of battery cells and the plurality of elastic spacers in the stacking direction of the plurality of battery cells. The elastic spacer has a sheet portion that extends between two adjacent battery cells, and a plurality of protrusions that project from one surface of the sheet portion. The plurality of protrusions are arranged at equal intervals at least along a first direction. When the interval between the plurality of protrusions in the first direction is x, and the size of each protrusion in the first direction is y, the following relationships are satisfied: 4mm≤y≤18mm, y≥(4 / 9)x-10 / 3, and y≤x-2.

2. The battery module as described in claim 1, characterized in that, The plurality of protrusions are also arranged at equal intervals along a second direction perpendicular to the first direction. The spacing between the plurality of protrusions in the second direction is equal to the spacing between the plurality of protrusions in the first direction. The dimensions of each protrusion in the second direction are equal to the dimensions of each protrusion in the first direction.

3. The battery module as described in claim 1 or 2, characterized in that, Each protrusion has a cylindrical shape.

4. The battery module as described in claim 1 or 2, characterized in that, In the naturally shaped elastic spacer removed from the battery module, when the surface that contacts the front end of the plurality of protrusions and extends parallel to the sheet is defined as a cross-section, the volume fraction of the area occupied by the plurality of protrusions in the region between the sheet and the cross-section is greater than or equal to 14% and less than or equal to 38%.

5. A battery module, characterized in that, include: Multiple battery cells, each of which has a flat shape; Multiple elastic spacers are alternately stacked with the multiple battery cells; as well as A constraint member constrains the plurality of battery cells and the plurality of elastic spacers in the stacking direction of the plurality of battery cells. The elastic spacer has a sheet portion that extends between two adjacent battery cells, and a plurality of protrusions that project from one surface of the sheet portion. In the naturally shaped elastic spacer removed from the battery module, when the surface that contacts the front end of the plurality of protrusions and extends parallel to the sheet is defined as a cross-section, the volume fraction of the area occupied by the plurality of protrusions in the region between the sheet and the cross-section is greater than or equal to 14% and less than or equal to 38%.

6. The battery module as described in claim 5, characterized in that, The plurality of protrusions have the same shape as each other.

7. The battery module as described in claim 5 or 6, characterized in that, The plurality of protrusions are arranged at equal intervals at least along a first direction.

8. The battery module as described in claim 1 or 2, characterized in that, The surface of the battery cell that is in contact with the plurality of protrusions of the elastic spacer is rectangular in shape, having four corners, a pair of short sides, and a pair of long sides. When 5% of the length of the short side is taken as the first length, for each of the four corners, the region of the triangle with the corner, a point on the short side that is a distance of the first length from the corner, and a point on the long side that is a distance of the first length from the corner as its vertices is defined as the corner adjacency region. None of the plurality of protrusions of the elastic spacer comes into contact with the corner adjacent region of the surface of the battery cell.

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