Battery pack

Abstract

To improve design flexibility of a battery pack.SOLUTION: A battery module 3 comprises a laminate obtained by laminating a plurality of battery cells 8 each of which has a negative electrode containing lithium metal or lithium-containing metal. Each of the battery cells 8 has a positive electrode tab 7A and a negative electrode tab 7B protruding therefrom. The positive electrode tab 7A of one of the adjacent battery cells 8 and the negative electrode tab 7B of the other one of the battery cells face each other in a lamination direction, while the negative electrode tab 7B of the former one of the adjacent battery cells and the positive electrode tab 7A of the latter one of the battery cells also face each other in the lamination direction. The adjacent battery cells 8 are connected in series to each other, with the positive electrode tab 7A of one of the adjacent battery cells connected to the negative electrode tab 7B of the other one of the battery cells via an extendable / contractible inter-cell bus bar 13. The inter-cell bus bar 13 is contractibly extendable from an inter-electrode-tab distance in a fully charged state up to the inter-electrode-tab distance in a fully discharged state. The laminate is configured such that: any one of the battery cells 8, excluding those on both ends in the lamination direction, is fixed; and the unfixed ones of the battery cells 8 are movable in the lamination direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a battery module including a stack formed by stacking a plurality of flat battery cells in the thickness direction of the battery cells. [Background technology]

[0002] Patent Document 1 discloses a lithium-ion battery in which an electrode assembly, which uses a lithium-containing composite oxide as a positive electrode active material and a silicon-containing compound as a negative electrode active material, is housed in a metal case. Patent Document 1 also discloses the use of multiple lithium-ion batteries in a battery pack. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-13752 Summary of the Invention [Problem to be solved by the invention]

[0004] When lithium-ion batteries are used as a power source for vehicles such as electric vehicles, a battery pack consisting of a number of lithium-ion batteries that meets the required performance is installed in the vehicle, but it is desirable to avoid sacrificing livability and cargo space in order to install the battery pack. A known battery pack that satisfies these requirements is one in which multiple battery modules formed with a predetermined number of batteries are prepared, and these battery modules are arranged and electrically connected to fit the shape of a space that has minimal impact on livability, etc. This allows the battery modules to be arranged in a variety of shapes.

[0005] However, because lithium-ion batteries undergo volumetric changes during charging and discharging, it is necessary to ensure space to accommodate this volumetric change when designing a battery pack. In particular, in the case of lithium-ion batteries that use lithium metal or lithium-containing metals as the negative electrode, which experience large volumetric changes during charging and discharging, the shape of the battery pack may be limited depending on how the space is allocated to accommodate the volumetric change. In other words, the design freedom of the battery pack may be reduced depending on how the space is allocated to accommodate the volumetric change of the battery module.

[0006] However, the above document does not disclose the relationship between the space required to accommodate volume changes and the degree of freedom in design when using a lithium-ion battery as a battery pack, nor does it disclose a configuration for increasing the degree of freedom in design. In the first place, the lithium-ion battery in the above document, which uses a silicon material for the negative electrode, experiences a smaller amount of volume change during charging and discharging than one that uses lithium metal or the like for the negative electrode, so the space required to accommodate volume changes has little impact on the degree of freedom in design of the battery pack.

[0007] Therefore, an object of the present invention is to increase the degree of freedom in design when a lithium ion battery using lithium metal or the like for the negative electrode is used as a battery pack. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a stacked body in which a plurality of flat battery cells each having a negative electrode containing lithium metal or a lithium-containing metal, a solid electrolyte, and a positive electrode are stacked in the thickness direction of the battery cells. a fixing member provided at the center of the stacked body in the stacking direction; A battery module comprising: and a case whose interior is partitioned by a partition member, and whose fixing member is fixed to the floor surface of the partitioned space.The battery cells have positive and negative electrode tabs as electrode tabs that protrude in a direction perpendicular to the thickness direction of the battery cell, and the positive electrode tab of one of the adjacent battery cells faces the negative electrode tab of the other battery cell, and the negative electrode tab of one battery cell faces the positive electrode tab of the other battery cell, respectively, in the stacking direction, and the adjacent battery cells are connected in series by an expandable inter-cell bus bar between the positive electrode tab of one battery cell and the negative electrode tab of the other battery cell. Each inter-cell bus bar is expandable from the distance between the electrode tabs in a fully charged state to the distance between the electrode tabs in a fully discharged state, and the stack is The battery cells located on both sides of the fixing member in the stacking direction are fixed to the fixing member. The battery cell stack includes a pair of end plates disposed at both ends of the battery cell stack in the stacking direction, and a plurality of connecting members formed of an elastic material that can absorb volumetric changes of the battery cells in the stacking direction and that connect the pair of end plates, and a restraining mechanism that applies restraining pressure to the stack from both sides in the stacking direction, so that the pair of end plates are movable in response to volumetric changes of the battery cells in the stacking direction. The gap dimensions Δt1 and Δt2, which are the dimensions in the stacking direction of the gap between the stacking direction end faces of the battery modules in a fully discharged state and the opposing case and partition member, are set as follows: Δt1 ≧ (the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the case wall in a fully charged state) - (the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the case wall in a fully discharged state) Δt2 ≧ (the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the partition member in a fully charged state) - (the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the partition member in a fully discharged state) [Effects of the Invention]

[0009] According to the above aspect, it is possible to increase the degree of freedom in design when a plurality of battery modules are used as a battery pack. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view illustrating the appearance of a battery pack according to a first embodiment. [Figure 2] FIG. 2 is a perspective view of the battery module according to the first embodiment. [Figure 3] FIG. 3 is a side view of the battery module according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the direction of action of the confining pressure. [Figure 5]FIG. 5 is a diagram showing the arrangement and connection state of the battery modules according to the first embodiment. [Figure 6] FIG. 6 is a stress-strain diagram of the solid electrolyte. [Figure 7] FIG. 7 is a diagram showing voltage characteristics during charging of a lithium ion battery. [Figure 8] FIG. 8 is a diagram showing the arrangement and connection state of battery modules according to a modified example. [Figure 9] FIG. 9 is a perspective view of a battery module according to the second embodiment. [Figure 10] FIG. 10 is a side view of a battery module according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0012] [First embodiment] A first embodiment of the present invention will be described with reference to FIGS.

[0013] FIG. 1 is a perspective view showing a battery pack 1 according to this embodiment.

[0014] The battery pack 1 is configured to include a plurality of battery modules 3A to 3D and a case 2 that houses them. Note that while Fig. 1 shows a portion housing four battery modules 3A to 3D, this is only a portion of the battery pack 1, and the actual battery pack 1 houses many more battery modules. The specific configuration of the battery modules 3A to 3D will be described later.

[0015] [case] The interior of the case 2 is divided into multiple spaces by partition members 2A, and battery modules 3A to 3D are fixed in each space. The battery modules 3A to 3D are electrically connected by first inter-module bus bars 5A, 5B and second inter-module bus bars 6A, 6B. In the following description, when there is no need to particularly distinguish between the battery modules 3A to 3D, the first inter-module bus bars 5A to 5C, and the second inter-module bus bars 6A, 6B, they will be referred to as battery modules 3, first inter-module bus bars 5, and second inter-module bus bars 6, respectively.

[0016] [Battery module] Fig. 2 is a perspective view of the battery module 3, and Fig. 3 is a side view of the battery module 3. Here, the first battery module 3A will be described, but the other battery modules 3B to 3D are basically the same.

[0017] The battery module 3 includes a plurality of battery cells 8 (eight in this embodiment), a fixing mechanism 9 that fixes the battery cells 8, and a restraining mechanism 12 that restrains the battery cells 8. The restraining mechanism 12 will be described later.

[0018] The battery cell 8 is a laminated electrode body in which a predetermined number of flat-shaped unit cells, each made by stacking a positive electrode, an electrolyte, and a negative electrode, are stacked in the thickness direction and housed in an exterior material such as a laminate film. The battery of this embodiment is an all-solid-state lithium-ion battery that uses a solid electrolyte for the electrolyte and lithium metal or a lithium-containing alloy for the negative electrode.

[0019] Positive electrode tabs 7A that are electrically connected to the positive electrodes in the battery cell 8 and negative electrode tabs 7B that are electrically connected to the negative electrodes are attached to the side of the battery cell 8. Although the positive electrode tabs 7A and negative electrode tabs 7B are attached to the same side in FIG. 2, they may be attached to different side surfaces. The above-described battery cells 8 are used in a state where multiple cells are stacked in the thickness direction. In the following description, the direction in which the battery cells 8 are stacked is also referred to as the stacking direction. In the following description, when it is not necessary to distinguish between the positive electrode tabs 7A and negative electrode tabs 7B, they will be referred to as electrode tabs 7.

[0020] The fixing mechanism 9 includes a base 9B made of a rectangular plate-like member, and a fixed wall 9A made of a rectangular plate-like member provided on the base 9B in a direction perpendicular to the stacking direction. Note that the fixed wall 9A and the base 9B do not need to be separate members, and may be formed from a single member.

[0021] In this embodiment, battery cells 8 are fixed to both sides of the fixed wall 9A in the stacking direction, and three battery cells 8 are stacked on each fixed battery cell 8 so that they can move in the stacking direction relative to the base 9B. In other words, four battery cells 8 are stacked using one surface of the fixed wall 9A as the reference, and four battery cells 8 are stacked using the other surface as the reference. In other words, in this embodiment, the fixed wall 9A is provided in the center in the stacking direction.

[0022] The battery cells 8 are stacked such that the positive electrode tab 7A of one of the adjacent battery cells 8 and the negative electrode tab 7B of the other battery cell 8 face each other in the stacking direction. The stacked battery cells 8 are connected in series using inter-cell bus bars 13. That is, electrodes of opposite polarity that face each other in the stacking direction are connected by the inter-cell bus bars 13. The negative electrode tab 7B of the battery cell 8 at one end of the stack and the positive electrode tab 7A of the battery cell 8 at the other end are connected to first inter-module bus bars 5A, 5B, respectively.

[0023] The inter-cell bus bars 13 are flexible in the stacking direction. The reason for this is as follows: In a lithium-ion battery that uses lithium metal or the like for the negative electrode, the volume of the negative electrode decreases when the battery is discharged due to the dissolution of lithium, and increases when the battery is charged due to the deposition of lithium. This change in volume causes a change in the thickness of the battery cells 8 (i.e., the dimension in the stacking direction). If the dimension of the battery cells 8 in the stacking direction changes, the distance between adjacent electrode tabs 7 also changes. Therefore, to accommodate the volume change of the lithium-ion battery that occurs during charging and discharging, the inter-cell bus bars 13 connecting adjacent electrodes are made flexible. Note that if the volume of each battery cell 8 changes, the dimension of the entire module in the stacking direction also changes, and this changes the distance between other battery modules 3. Therefore, the first inter-module bus bars 5A, 5B that connect the battery modules 3 to each other in the stacking direction are also made flexible. 1 connects battery modules 3 arranged in a direction perpendicular to the stacking direction, it does not need to be flexible like the first inter-module bus bars 5 and inter-cell bus bars 13. However, it does need to have enough elasticity to accommodate changes in the distance between the battery modules due to differences in the amount of volume change between the two connected battery modules.

[0024] Here, the lengths of the inter-cell bus bar 13 and the first inter-module bus bar 5 will be described.

[0025] As described above, the inter-cell bus bar 13 must connect adjacent electrode tabs 7 to each other in all states from the fully discharged state to the fully charged state. In other words, the inter-cell bus bar 13 must be able to extend to at least the distance between the electrode tabs in the fully charged state. In other words, the inter-cell bus bar 13 must have a length at least equal to or greater than the distance between the electrode tabs in the fully discharged state, and be able to extend to a length equal to or greater than the sum of the distance between the electrode tabs in the fully discharged state and the change in the dimension of one battery cell 8 in the stacking direction until it reaches the fully charged state.

[0026] When the first inter-module bus bar 5B is integrated as shown in FIG. 1 , the first inter-module bus bar 5 must be able to expand and contract from the electrode tab distance between the electrode tab 7 at the end of the first battery module 3A and the electrode tab 7 at the end of the second battery module 3B in a fully discharged state to the same electrode tab distance in a fully charged state. In other words, the expansion range must be equal to or greater than the sum of the following two factors. The first factor is the cumulative value of the amount of change in the stacking direction dimension of each battery cell 8 on the first inter-module bus bar 5 side from the fixing wall 9A, among the battery cells 8 constituting the first battery module 3A. The second factor is the cumulative value of the amount of change in the stacking direction dimension of each battery cell 8 on the first inter-module bus bar 5 side from the fixing wall 9A, among the battery cells 8 constituting the second battery module 3B.

[0027] The first inter-module bus bar 5 may be configured such that a first member connected to the first battery module 3A and a second member connected to the second battery module 3B are connected by a connecting portion provided between the first battery module 3A and the second battery module 3B. In this case, the expansion and contraction width required for the first member is equal to or greater than the first factor, and the expansion and contraction width required for the second member is equal to or greater than the third factor.

[0028] As described above, by providing the inter-cell bus bars 13 and the first inter-module bus bars 5 with flexibility, even if the dimensions of the battery cells 8 change in the stacking direction, excessive stress is not generated at the adhesive joints between each bus bar and each electrode tab 7 and the welds between each electrode tab 7 and the electrode of each cell. In other words, tearing of the electrode tabs due to repeated charging and discharging can be prevented. As a result, a high-energy-density negative electrode using lithium metal or a lithium-containing alloy can be used.

[0029] [Restraint mechanism] FIG. 4 is a diagram showing the direction of action of the restraining pressure applied by the restraining mechanism 12. As shown in FIG.

[0030] The restraint mechanism 12 has the function of applying a restraint pressure, which is a compressive load along the stacking direction, to the stack of battery cells 8, as indicated by the white arrow in Fig. 4. Specifically, it comprises a pair of end plates 10 arranged at both ends of the stack of battery cells 8, and multiple (four in this embodiment) connecting members 11 that connect the end plates 10. The connecting members 11 are elastic bodies (e.g., springs) that can absorb volumetric changes in the stack of battery cells 8. The elastic force of the connecting members 11 acts in a direction that brings the end plates 10 closer to each other.

[0031] The reason for applying the confining pressure is to ensure contact between the positive electrode and the electrolyte and between the negative electrode and the electrolyte even if the volume of the battery cell 8 changes.

[0032] Alternatively, a mechanism capable of arbitrarily controlling the confining pressure may be used. For example, a mechanism may be considered that includes a pair of end plates 10, a connecting member 11 that exerts an elastic force in a direction that moves the end plates 10 toward each other and whose elastic force changes depending on the temperature, and a heater (not shown) that adjusts the temperature of the elastic member. With this mechanism, the magnitude of the confining pressure can be controlled by operating the heater depending on the expansion state of the battery module 3.

[0033] [Battery pack] 5 is a top view of the battery pack 1 in FIG. 1. As shown in the figure, the case 2 is divided into four spaces by partition members 2A. A battery module 3 is housed in each space by fixing a base 9B of the fixing mechanism 9 to the floor of the case 2. The four battery modules 3 are connected in series via the first inter-module bus bar 5 and the second inter-module bus bar 6. That is, as shown by the white arrows in FIG. 4, current flows from the first battery module 3A to the second battery module 3B, the third battery module 3C, and the fourth battery module 3D in this order, and then from the fourth battery module 3D to another battery module 3 (not shown) via the second inter-module bus bar 6B.

[0034] When setting up the battery pack 1, the dimensions in the stacking direction of each space that houses the battery modules 3 must be determined taking into consideration the volumetric changes of the battery modules 3. In other words, it is necessary to ensure space for the battery modules 3 to expand upon charging. This is because (1) without expansion space, lithium deposition during charging becomes difficult, which could result in overvoltage, and (2) without expansion space, lithium deposition could cause excessive compressive stress to act on the battery modules 3, which could deteriorate the solid electrolyte.

[0035] In the battery module 3 of this embodiment, the battery cells 8 are fixed to a fixing wall 9A provided in the center of the stack of battery cells 8, and the battery module 3 expands and contracts with the fixing wall 9A as the fixed end. Therefore, it is necessary to secure space for the battery module 3 to expand on both sides of the stacking direction of the battery module 3. Therefore, the gap dimensions Δt1 and Δt2, which are the dimensions in the stacking direction of the gaps between the end faces of the battery module 3 in the stacking direction and the case 2 and partition member 2A facing them in a fully discharged state, are set as follows: Δt1≧(the dimension in the stacking direction of the four battery cells 8 stacked on one surface of the fixing wall 9A in a fully charged state)−(the dimension in the stacking direction of the four battery cells 8 in a fully discharged state) Δt2≧(the dimension in the stacking direction of the four battery cells 8 stacked on the other surface of the fixing wall 9A in a fully charged state)−(the dimension in the stacking direction of the four battery cells 8 in a fully discharged state) In the above formula, "one surface" is the surface facing the wall surface of the case 2, and "the other surface" is the surface facing the partition member 2A.

[0036] Incidentally, when one end of a stack of battery cells 8 is used as the fixed end, for example, when a battery cell 8 is fixed to one end plate 10, no gap is required between the end plate 10 (which serves as the fixed end) and the case 2 or the partition member 2A. A gap is then provided between the other end plate 10 and the case 2 or the partition member 2A to accommodate volumetric changes of all stacked battery cells 8. In this case, if the number of stacked battery cells is eight, the gap is the sum of the gap Δt1 and the gap Δt2. In other words, the gap required for one battery module 3 is the same regardless of the position of the fixed end, as long as the number of stacked battery cells is the same. However, when comparing the amount of movement due to expansion and contraction of the battery cell 8 farthest from the fixed end, the amount of movement is smaller when the fixed end is located at the center of the stacking direction than when the fixed end is located at an end.

[0037] As described above, when the fixed end is located in the center of the stacking direction, gaps Δt1 and Δt2 are provided at both ends of the stacking direction, whereas when the fixed end is located at one end, a large gap, the sum of gaps Δt1 and Δt2, is provided at the other end. Therefore, when the fixed end is located in the center of the stacking direction, space efficiency in the stacking direction can be improved compared to when the fixed end is located at an end. Furthermore, improved space efficiency increases the design freedom of the battery pack 1.

[0038] The fixing mechanism 9 in this embodiment is configured to fix the battery cell 8 at the center in the stacking direction, but this is to improve space efficiency by making the gap Δt1 and the gap Δt2 the same. However, if any of the battery cells 8 except for the battery cells 8 at both ends in the stacking direction are fixed, space efficiency can be improved compared to when the ends are fixed.

[0039] [Confining Pressure] Next, the magnitude of the restraining pressure applied by the restraining mechanism 12 will be described.

[0040] The magnitude of the confining pressure is determined by the elastic force of the connection members 11. That is, the confining pressure is greatest when the battery module 3 is fully charged, when the dimension in the stacking direction is greatest, and is smallest when the battery module 3 is fully discharged, when the dimension in the stacking direction is smallest.

[0041] It is necessary to set an upper limit for the confining pressure so that the battery cell 8 will not be broken due to yield deformation of the components even after repeated charging and discharging. The component for which yield deformation is particularly problematic is the solid electrolyte. Therefore, in this embodiment, the confining pressure in the fully charged state (i.e., the maximum confining pressure) is set to be smaller than the minimum yield stress of the solid electrolyte.

[0042] Figure 6 shows the stress-strain curve of the solid electrolyte. Based on this stress-strain curve, the minimum yield stress of the solid electrolyte is found and the maximum confining pressure is determined. In Figure 6, yielding begins at stress σ1, so the minimum yield stress is σ1. Therefore, the maximum confining pressure is set to a value smaller than σ1. This prevents the solid electrolyte from cracking due to excessive compressive stress, which can lead to a decrease in ionic conductivity and the generation of lithium dendrites from the cracks.

[0043] On the other hand, it is necessary to determine the lower limit of the confining pressure so that contact at the interface between the positive electrode and the solid electrolyte and between the negative electrode and the solid electrolyte is ensured during repeated charge and discharge. Ensuring contact here means achieving a contact state that allows stable battery reactions to occur and prevents excessive voltage increases. The contact state becomes particularly problematic when the confining pressure is at its lowest in the fully discharged state.

[0044] Figure 7 shows the relationship between charging time and voltage when a fully discharged battery module 3 is charged at a constant current. If contact is not ensured, for example, if separation occurs at the interface between the negative electrode and the solid electrolyte, the voltage will increase excessively over time, as indicated by the dashed line P1 in the figure. On the other hand, if contact is ensured, the voltage will remain constant, as indicated by the solid line P1 in the figure.

[0045] Therefore, the minimum confining pressure that gives the result of the solid line P2 is determined by experiment, etc., and set as the minimum confining pressure. This applies a confining pressure greater than the stress necessary to ensure contact, making it possible to suppress excessive voltage increases due to poor contact between the positive electrode and solid electrolyte and between the negative electrode and solid electrolyte, and ensuring output characteristics that can handle rapid charging.

[0046] [Variations] This modification, like the above embodiment, is also included in the scope of the present invention.

[0047] 8 is a perspective view of a battery pack 1 according to a modified example, which differs from the above embodiment in the order in which the four battery modules 3 are connected.

[0048] In the battery pack 1 of the above embodiment, the first battery module 3A is connected in series, followed by the second battery module 3B, the third battery module 3C, and the fourth battery module 3D. In contrast, in the battery pack 1 of this modified example, the first battery module 3A is connected in series, followed by the fourth battery module 3D, the third battery module 3C, and the second battery module 3B. Due to this difference, the arrangement, required number, and dimensions of the first inter-module bus bar 5 and the second inter-module bus bar 6 also differ. However, the required extensible length of the first inter-module bus bar 5 is the same as in the above embodiment.

[0049] As described above, this embodiment provides a battery module 3 including a stack formed by stacking a plurality of flat battery cells 8, each having a negative electrode containing lithium metal or a lithium-containing metal, a solid electrolyte, and a positive electrode, in the thickness direction of the battery cells. The battery cells 8 have, as electrode tabs 7, positive electrode tabs 7A and negative electrode tabs 7B that protrude in a direction perpendicular to the thickness direction of the battery cells. The positive electrode tab 7A of one of adjacent battery cells 8 faces the negative electrode tab 7B of the other battery cell 8, and the negative electrode tab 7B of one battery cell 8 faces the positive electrode tab 7A of the other battery cell 8, respectively, in the stacking direction. Adjacent battery cells 8 are connected in series by an expandable inter-cell bus bar 13, with the positive electrode tab 7A of one battery cell 8 and the negative electrode tab 7B of the other battery cell 8 being connected by an expandable inter-cell bus bar 13. Each inter-cell bus bar 13 is expandable from the distance between the electrode tabs in a fully charged state to the distance between the electrode tabs in a fully discharged state. The stack is characterized in that all battery cells 8 except for those at both ends in the stacking direction are fixed, and the unfixed battery cells 8 are movable in the stacking direction. By fixing the battery cells 8 other than those at the ends in this way, the amount of movement caused by expansion and contraction of the battery cells 8 arranged at the ends during charging and discharging is reduced compared to when the battery cells 8 at the ends are fixed, improving the space efficiency in the stacking direction of the battery pack 1. Furthermore, improved space efficiency increases the degree of freedom in the design of the battery pack 1.

[0050] In this embodiment, a fixing wall (fixing member) 9A is provided in the center in the stacking direction, and the battery cells 8 located on both sides of the fixing wall 9A in the stacking direction are fixed to the fixing wall 9A. This increases the degree of freedom in designing the battery pack 1.

[0051] In this embodiment, a restraining mechanism 12 is provided that applies restraining pressure from both sides in the stacking direction, and when fully charged, the restraining mechanism 12 applies a restraining pressure that is smaller than the minimum yield stress of the battery cells 8. This makes it possible to prevent malfunctions such as a decrease in ionic conductivity due to yield deformation of the battery cells 8.

[0052] In this embodiment, during full discharge, the restraint mechanism 12 applies a restraint pressure greater than the stress required to ensure contact at the interface between the negative electrode and the solid electrolyte and at the interface between the solid electrolyte and the positive electrode, thereby preventing excessive voltage increases due to poor contact at these interfaces.

[0053] [Second embodiment] FIG. 9 is a perspective view of the battery module 3 according to this embodiment, and FIG. 10 is a side view of the battery module 3. As shown in FIG.

[0054] The configurations of the fixing mechanism 9 and the restraining mechanism 12, and the magnitude of the restraining pressure applied by the restraining mechanism 12 are the same as those in the first embodiment, and therefore a description thereof will be omitted.

[0055] The battery module 3 is similar to the battery module 3 of the first embodiment in that four battery cells 8 are stacked on each side of a fixed wall 9A, and a restraining pressure is applied from both sides in the stacking direction by a restraining mechanism 12. However, whereas the battery cells 8 are connected in series in the battery module 3 of the first embodiment, the battery cells 8 are connected in parallel in the battery module 3 of this embodiment. For this reason, the battery cells 8 are stacked so that all of the positive electrode tabs 7A and all of the negative electrode tabs 7B of the stack are aligned in a row in the stacking direction, and adjacent battery cells 8 are connected by an inter-cell bus bar 20 that allows the positive electrode tabs 7A and the negative electrode tabs 7B to extend and retract.

[0056] The inter-cell bus bar 20 is formed by integrating bus bars that connect the electrode tabs 7 of adjacent battery cells 8 together in the stacking direction.

[0057] In this case, the inter-cell bus bar 20 must be able to expand and contract from the integrated length of the inter-electrode tab distances when adjacent electrode tabs 7 are in a fully discharged state to the integrated length of the inter-electrode tab distances when adjacent electrode tabs 7 are in a fully charged state. In other words, the expansion range required of the inter-cell bus bar 20 is the integrated value of the amount of change in the inter-electrode tab distance due to the expansion and contraction of the battery cells 8. However, the amount of change in the inter-electrode tab distance must be uniform.

[0058] Note that, instead of the inter-cell bus bar 20 integrated by connection as described above, an inter-cell bus bar 20 formed from a single member and having connection portions with each electrode tab may be used. Even in this case, the length and expansion width of the inter-cell bus bar 20 are the same as when the inter-cell bus bar 20 is integrated by connection.

[0059] The first inter-module bus bar 5 is the same as in the first embodiment, and therefore a description thereof will be omitted.

[0060] As described above, in this embodiment, all positive electrode tabs 7A and all negative electrode tabs 7B of the stack are aligned in a row in the stacking direction, and adjacent battery cells 8 are connected in parallel by the extendable inter-cell bus bar 20, connecting the positive electrode tabs 7A and the negative electrode tabs 7B to each other. The inter-cell bus bar 20 is a single component that connects the electrode tabs 7 of adjacent battery cells 8 in the stacking direction, or connects the electrode tabs 7 of all battery cells 8 from one end to the other in the stacking direction. The inter-cell bus bar 20 is extendable from the integrated length between adjacent electrode tabs in a fully charged state to the integrated length between adjacent electrode tabs in a fully discharged state. The stack is characterized in that all battery cells 8 except for those at both ends in the stacking direction are fixed, and the unfixed battery cells are movable in the stacking direction. This also achieves the same effects as the first embodiment.

[0061] It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical concept described in the claims. [Explanation of symbols]

[0062] 1 battery pack 2 cases 3 Battery Module 5 First inter-module bus bar 6 Second inter-module bus bar 7 electrodes 8 battery cells 9 Fixing member 12 Restraint mechanism 13 Inter-cell bus bar 20 Inter-cell bus bar

Claims

1. A battery pack including: a battery module including a stack of flat battery cells stacked in a thickness direction of the battery cells, the flat battery cells having a negative electrode containing lithium metal or a lithium-containing metal, a solid electrolyte, and a positive electrode; and a fixing member provided at the center of the stack in the stacking direction; and a case whose interior is partitioned by a partition member, and the fixing member is fixed to a floor surface of the partitioned space, the battery cell has, as electrode tabs, a positive electrode tab and a negative electrode tab that protrude in a direction perpendicular to the thickness direction of the battery cell, The positive electrode tab of one of the adjacent battery cells faces the negative electrode tab of the other battery cell, and the negative electrode tab of one battery cell faces the positive electrode tab of the other battery cell, in the stacking direction, Adjacent battery cells are connected in series, with the positive electrode tab of one battery cell and the negative electrode tab of the other battery cell connected by an expandable inter-cell bus bar, each inter-cell bus bar is expandable from a distance between electrode tabs in a fully charged state to a distance between electrode tabs in a fully discharged state; In the stack, the battery cells located on both sides of the fixing member in the stacking direction are fixed to the fixing member, and the unfixed battery cells are movable in the stacking direction, a restraint mechanism that applies restraint pressure to the stack from both sides in the stacking direction, the restraint mechanism including a pair of end plates arranged at both ends of the stack of battery cells in the stacking direction, and a plurality of connecting members that connect the pair of end plates and are formed of an elastic material that can absorb volume changes in the stacking direction of the battery cells; and the pair of end plates are movable in response to a change in volume of the battery cells in the stacking direction; A battery pack in which gap dimensions Δt1 and Δt2, which are the dimensions in the stacking direction of the gap between the stacking direction end faces of the battery modules in a fully discharged state and the opposing case and partition member, are set as follows. Δt1≧(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the case wall in a fully charged state)−(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the case wall in a fully discharged state) Δt2≧(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the partition member in a fully charged state)−(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the partition member in a fully discharged state)

2. A battery pack including: a battery module including a stack of flat battery cells stacked in a thickness direction of the battery cells, the flat battery cells having a negative electrode containing lithium metal or a lithium-containing metal, a solid electrolyte, and a positive electrode; and a fixing member provided at the center of the stack in the stacking direction; and a case whose interior is partitioned by a partition member, and the fixing member is fixed to a floor surface of the partitioned space, the battery cell has, as electrode tabs, a positive electrode tab and a negative electrode tab that protrude in a direction perpendicular to the thickness direction of the battery cell, all positive electrode tabs and all negative electrode tabs of the stack are aligned in a row in the stacking direction, Adjacent battery cells are connected in parallel, with their positive electrodes and negative electrodes connected by expandable inter-cell bus bars. the inter-cell bus bar is an integrated member formed by connecting the inter-cell bus bars connecting the electrode tabs of adjacent battery cells in the stacking direction, or is a single member connecting the electrode tabs of all battery cells from one end to the other end in the stacking direction, and is extendable from a length obtained by integrating the distances between adjacent electrode tabs in a fully charged state to a length obtained by integrating the distances between adjacent electrode tabs in a fully discharged state, In the stack, the battery cells located on both sides of the fixing member in the stacking direction are fixed to the fixing member, and the unfixed battery cells are movable in the stacking direction, a restraint mechanism that applies restraint pressure to the stack from both sides in the stacking direction, the restraint mechanism including a pair of end plates arranged at both ends of the stack of battery cells in the stacking direction, and a plurality of connecting members that connect the pair of end plates and are formed of an elastic material that can absorb volume changes in the stacking direction of the battery cells; and the pair of end plates are movable in response to a change in volume of the battery cells in the stacking direction; A battery pack in which gap dimensions Δt1 and Δt2, which are the dimensions in the stacking direction of the gap between the stacking direction end faces of the battery modules in a fully discharged state and the opposing case and partition member, are set as follows. Δt1≧(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the case wall in a fully charged state)−(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the case wall in a fully discharged state) Δt2≧(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the partition member in a fully charged state)−(the dimension in the stacking direction of the battery cells stacked on the surface of the fixing member facing the partition member in a fully discharged state)

3. The battery module according to claim 1 or 2, When fully charged, the restraint mechanism applies a restraint pressure to the stack that is less than the minimum yield stress of the battery cells.

4. The battery module according to claim 3, During full discharge, the restraint mechanism applies a restraint pressure to the stack that is greater than the stress required to ensure contact at the interface between the negative electrode and the solid electrolyte and at the interface between the solid electrolyte and the positive electrode.

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