Method and device for inspecting battery module

Abstract

An inspection device (10) inspects a battery module (20) in which a binding pressure is applied to a laminate in which one or more battery cells (21) having an electrolyte layer containing a solid electrolyte, a positive electrode layer, and a negative electrode layer are laminated. A capacity measurement unit (102) measures a lower limit time capacity, which is the capacity of a battery module (20), when a charge / discharge control unit (101) discharges the battery module (20) to a predetermined lower limit charge rate for inspection after charging the battery module (20) to a predetermined upper limit charge rate for inspection, the charge rate being lower than the maximum charge rate during actual use of the battery module (20). A determination unit (103) determines that the battery module (20) is defective when the capacity retention rate of a lower limit time capacity, which is measured by repeatedly charging and discharging, with respect to the lower limit time capacity at the beginning of measurement is equal to or less than a threshold value.

Description

Battery module inspection method and inspection device

[0001] The present invention relates to a method and apparatus for inspecting a battery module.

[0002] All-solid-state batteries have been used that include battery modules in which battery cells containing solid electrolytes are stacked and constrained by pressure applied in the stacking direction (see, for example, Patent Document 1). The method for manufacturing an all-solid-state battery described in Patent Document 1 is a method for manufacturing an all-solid-state battery by arranging unit laminate bodies with insulating layers, each unit laminate body including an insulating layer and a unit laminate body including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, at both ends inside a housing, and assembling constraining members on the outside of the housing to apply constraining pressure.

[0003] Japanese Patent Application Laid-Open No. 2022-20241

[0004] In all-solid-state batteries manufactured by the manufacturing method described in Patent Document 1, in-plane distribution of the confining pressure may occur. If the in-plane distribution of the confining pressure is large, problems such as a decrease in durability as a battery module and short-circuiting of electrodes during charging may occur. To address such problems, a charge-discharge test may be performed to screen out batteries with large in-plane distribution as defective, but this has the problem of requiring a long time for the charge-discharge test.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a battery module inspection method and inspection device that can shorten the time required for inspection.

[0006] To achieve the above object, the present invention provides a battery module inspection method that applies a confining pressure to a stack of one or more battery cells, each having an electrolyte layer containing a solid electrolyte, a positive electrode layer, and a negative electrode layer, and measures a lower-limit capacity, which is the capacity of the battery module when the battery module is charged to an upper limit charge rate predetermined for inspection, which is lower than the maximum charge rate during actual use of the battery module, and then discharged to a lower limit charge rate predetermined for inspection. If the capacity retention rate of the lower-limit capacity measured by repeating such charging and discharging to the initial lower-limit capacity is equal to or less than a threshold, the battery module is determined to be defective.

[0007] According to the present invention, the inspection is performed based on the capacity retention rate when charging and discharging are repeated with a predetermined charge rate as the upper limit, so that the time required for the inspection can be shortened.

[0008] FIG. 1 is a block diagram showing an example of a functional configuration of a battery module inspection system according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a battery module to which a clamping pressure is applied. FIG. 3 is a diagram schematically showing a battery module to which a clamping pressure is applied. FIG. 4 is a diagram showing an example of a hardware configuration of an inspection device according to an embodiment. FIG. 5 is a diagram schematically showing an operation when a battery module is charged and discharged. FIG. 6 is a diagram showing the pressure dependency of internal resistance when a battery module is charged and discharged. FIG. 7 is a diagram showing a change in capacity when a battery module is charged and discharged. FIG. 8 is a diagram showing a change in capacity when a battery module is charged and discharged. FIG. 9 is a diagram showing the pressure dependency of internal resistance when a battery module is charged and discharged. FIG. 10 is a flowchart showing the procedure of a battery module inspection method according to an embodiment. FIG. 11 is a diagram showing a change in capacity maintenance rate. FIG. 12 is a block diagram showing an example of a functional configuration of a battery module inspection system according to a modified example.

[0009] A battery module inspection method and an inspection device according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or equivalent parts are designated by the same reference numerals.

[0010] A battery module inspection method according to an embodiment of the present invention is a method for inspecting an all-solid-state battery module. The battery module to be inspected is an all-solid-state battery module configured by applying a confining pressure to a stack of one or more battery cells, each having an electrolyte layer containing a solid electrolyte, a positive electrode layer, and a negative electrode layer. For example, a plurality of battery modules constitute a vehicle drive battery, and the battery module is installed in vehicles such as electric vehicles and hybrid vehicles.

[0011] Fig. 1 is a diagram showing the configuration of an inspection system 1 that uses a battery module inspection method according to the present embodiment. As shown in Fig. 1, the inspection system 1 includes an inspection device 10, a battery module 20 to be inspected, a temperature sensor 70, and a charger 80 that charges the battery module 20. The battery module 20 includes output terminals 30 for measuring the charging rate, capacity, and resistance.

[0012] The battery module 20 includes a plurality of battery cells 21. The battery cells 21 are all-solid-state secondary batteries and include at least a positive electrode, a solid electrolyte, and a negative electrode. The positive electrode contains at least a positive electrode active material capable of absorbing and releasing lithium (Li), such as LiCoO ２ , LiMnO ２ , LiNiO ２ , LiVO ２ , and Li(Ni—Mn—Co)O ２ Layered rock salt compounds such as LiMn ２ O ４ , and LiNi ０．５ Mn １．５ spinel-type compounds such as LiFePO ４ , and LiMnPO ４ Olivine type compounds such as Li ２ FeSiO and LiMnSiO ４ The battery module 20 contains a lithium metal composite oxide, such as a Si-containing compound, and a positive electrode active material containing sulfur. Examples of the solid electrolyte include a sulfide solid electrolyte and an oxide solid electrolyte. The negative electrode may contain lithium, such as lithium metal or a lithium alloy. In this embodiment, a battery module 20 containing lithium metal will be described.

[0013] The battery cells 21 are sealed in an exterior member with tabs connected to a laminate having a positive electrode, a solid electrolyte, and a negative electrode. The battery cells 21 are formed in a flat shape, with multiple battery cells 21 stacked in a direction perpendicular to the flat surface. Elastic bodies 25 may be provided between the multiple battery cells 21. The battery cells 21 of the battery module 20 expand when charged and contract when discharged, so providing the elastic bodies 25 can absorb displacement due to charging and discharging. The elastic bodies 25 do not necessarily have to be provided between all of the battery cells 21.

[0014] Fixing plates 22 are installed on the top and bottom surfaces of a stack formed by stacking multiple battery cells 21, and the position of the stack is maintained by the fixing plates 22 and fixing posts 26 connecting the fixing plates 22, and the stack is fixed in place with a constraining pressure applied to it in the stacking direction. Figures 2A and 2B are schematic diagrams showing the battery module 20 with a constraining pressure applied.

[0015] Here, as shown in FIG. 2A , it is desirable that the confinement pressure (surface pressure) be uniformly applied to the battery cells 21 by the fixing plate 22 and the fixing posts 26. However, as shown in FIG. 2B , if the fixing plate 22 is installed at an angle, the in-plane distribution of the confinement pressure (surface pressure distribution) on the battery cells 21 may become large. The in-plane distribution of the confinement pressure indicates the degree of variation in the surface to which the confinement pressure is applied, and is expressed, for example, as the in-plane variance or in-plane fluctuation of the confinement pressure. A large in-plane distribution of the confinement pressure may cause problems such as a decrease in the durability of the battery module 20 and electrode short-circuiting during charging. The inspection system 1 according to this embodiment inspects the battery module 20 and determines that a battery module 20 with a large in-plane distribution of the confinement pressure is defective. Note that if elastic bodies 25 are installed between multiple battery cells 21, the in-plane distribution of the confinement pressure can be suppressed by inserting the elastic bodies 25. In such a case, the in-plane distribution of the confinement pressure is evaluated for the configuration including the elastic bodies 25.

[0016] The charger 80 is connected to the battery module 20 via a charging cable and charges the battery module 20. The charger 80 is controlled by the inspection device 10 so that the battery module 20 reaches a target charging rate. The temperature sensor 70 measures the temperature of the environment in which the battery module 20 is installed and outputs temperature information to the inspection device 10.

[0017] The inspection device 10 controls the charger 80 to charge the battery module 20. Thereafter, the inspection device 10 discharges the battery module 20, measures the charge rate, capacity, and resistance of the battery module 20 at that time, and determines whether the battery module 20 is in a good condition based on the measurement results. FIG. 3 is a diagram showing an example of the hardware configuration of the inspection device 10. In the example of FIG. 3, the inspection device 10 includes a processor 1011, a storage unit 1012, a communication interface (indicated as communication I / F in the figure) 1013, and a measurement unit 1014.

[0018] The processor 1011 includes, for example, a CPU (Central Processing Unit) and its peripheral circuits, and executes various types of arithmetic processing. The processor 1011 executes control programs stored in the storage unit 1012. The processor 1011 may include a volatile semiconductor memory such as a RAM (Random Access Memory) that functions as a working memory for the CPU. The processor 1011 may also include an arithmetic circuit such as a logical arithmetic unit or a numerical arithmetic unit.

[0019] The storage unit 1012 includes, for example, a non-volatile semiconductor memory such as an EEPROM (Electrically Erasable and Programmable Read Only Memory), a flash memory, etc. The storage unit 1012 stores the control program executed by the processor 1011 and various data used in the arithmetic processing of the processor 1011.

[0020] The communication interface 1013 is an interface for communicating with the temperature sensor 70 and the charger 80. The communication interface 1013 acquires a sensor signal from the temperature sensor 70 and passes it to the processor 1011, and also outputs a control signal for the charger 80 generated by the processor 1011.

[0021] The measuring unit 1014 is connected to the output terminal 30 of the battery module 20 and includes a measuring instrument for measuring the charging rate, capacity, and resistance of the battery module 20. The measuring unit 1014 may be configured separately and independently from the inspection device 10. In this case, the measuring unit 1014 may be connected to the communication interface 1013 of the inspection device 10.

[0022] The processor 1011 executes a control program stored in the storage unit 1012, thereby functioning as a charge / discharge control unit 101, a capacity measurement unit 102, and a determination unit 103, as shown in Fig. 1. Note that although the inspection device 10 in Fig. 1 shows only the functional units according to this embodiment, the inspection device 10 may have other control, determination, or inspection functions.

[0023] The charge / discharge control unit 101 controls charging of the battery module 20 by the charger 80 and discharging of the battery module 20. Here, the charging rate of the battery module 20 indicates the charging state of the battery module 20, with the maximum charging rate when mounted on a vehicle and used in practice being 100% and the minimum charging rate being 0%. The charge / discharge control unit 101 sets a predetermined charging rate (e.g., 25%) lower than the maximum charging rate when used in practice as an upper limit charging rate for testing, and controls the battery module 20 to be charged up to the upper limit charging rate. After the battery module 20 has been charged up to the upper limit charging rate, the charge / discharge control unit 101 controls the battery module 20 to be discharged down to a lower limit charging rate (e.g., 0%) predetermined for testing.

[0024] The capacity measurement unit 102 measures the capacity of the battery module 20 when charging and discharging are repeated by the charge / discharge control unit 101. Specifically, a decrease in capacity when the in-plane distribution of the confining pressure of the battery module 20 is large becomes noticeable when the battery module 20 is discharged and the charging rate approaches 0%, so the capacity measurement unit 102 measures the lower limit capacity, which is the capacity of the battery module 20 when the charging rate reaches the lower limit charging rate after discharging.

[0025] The determination unit 103 determines whether the battery module 20 is good or bad based on the lower limit capacity measured by the capacity measurement unit 102. Specifically, if the capacity maintenance rate, which is the ratio of the lower limit capacity measured by repeating charge and discharge to the lower limit capacity at the start of measurement, is equal to or less than a threshold value, the battery module is determined to be defective.

[0026] Below, a detailed description is given of the decrease in capacity retention rate of the battery module 20 that occurs when the in-plane distribution of the confining pressure is large. Fig. 4 is a schematic diagram showing the operation of the battery module 20 when charging and discharging, and Fig. 5 is a diagram showing the pressure dependency of direct current resistance (DCR) when charging and discharging the battery module 20. Hereinafter, the resistance when charging may be referred to as the charging DCR, and the resistance when discharging may be referred to as the discharging DCR.

[0027] 4, the battery module 20 is charged from a state of charge (SOC) of 0% (SOC 0%), and when the state of charge reaches 25% (SOC 25%), a large amount of lithium metal (LiM) is deposited on the high-voltage side. This is because the internal resistance of the all-solid-state battery module 20 decreases as the voltage increases, resulting in a larger charging current.

[0028] The battery is then discharged. The higher the pressure, the lower the resistance and the larger the discharge current, resulting in a significant decrease in the amount of lithium metal. At a charge rate of 0-25% (SOC 0-25%), the in-plane distribution of the amount of lithium metal is moderated. As shown in FIG. 5, the discharge DCR has a higher pressure dependency than the charge DCR. In other words, the discharge DCR is more sensitive to pressure differences than the charge DCR. This means that the current distribution ratio, which indicates the ratio of the ease of current flow on the high-pressure side to the low-pressure side, is larger during discharge.

[0029] Because the current distribution ratio differs between charging and discharging, the battery module 20 does not return to its original state of charge after repeated charging and discharging. When the high-pressure side is discharged to a charge rate of approximately 0% (SOC 0%), lithium metal remains on the low-pressure side. Repeated charging and discharging in this manner causes lithium metal to accumulate on the low-pressure side, reducing the overall capacity of the battery module 20. Therefore, by detecting the reduction in capacity during discharge after repeated charging and discharging, it is possible to predict whether the in-plane distribution of the confining pressure is large and, furthermore, to determine whether the battery module 20 is defective.

[0030] 6A and 6B are diagrams showing examples of changes in the capacity of the battery module 20 during charging and discharging. In Figures 6A and 6B, the vertical axis represents charging voltage, and the horizontal axis represents capacity. The plot lines represent values ​​at the first, tenth, twentieth, and thirtieth cycles of charging and discharging, with the upward-sloping lines representing values ​​during charging and the downward-sloping lines representing values ​​during discharging. The plot lines during discharging represent values ​​at the first, tenth, twentieth, and thirtieth cycles, starting from the right.

[0031] Figure 6A shows the measurement results for a battery module 20 with a small in-plane distribution of confinement pressure (surface pressure distribution). Near the lower limit of the post-discharge charge voltage (charge rate), surrounded by the dashed-dotted box in Figure 6A, the difference between the first and 30th cycles is small. Figure 6B shows the measurement results for a battery module 20 with a large in-plane distribution of confinement pressure (surface pressure distribution). Near the lower limit of the post-discharge charge voltage (charge rate), surrounded by the dashed-dotted box in Figure 6B, the difference between the first and 30th cycles is large compared to the case of a small in-plane distribution of confinement pressure in Figure 6A.

[0032] 6B , in battery module 20 with a large in-plane distribution of confining pressure, the lower-limit capacity, which is the capacity when the charge voltage (charge rate) reaches the lower limit after discharge, decreases with repeated charge and discharge, resulting in a lower capacity retention rate. For example, in FIG. 6B , when the battery module is discharged in the first cycle at the start of measurement and the charge voltage reaches the lower limit of 2.5 V, the capacity is approximately 135 mAh / g, and when the battery module is discharged in the 30th cycle and the charge voltage reaches 2.5 V, the capacity is approximately 110 mAh / g, and the capacity retention rate is approximately 81% (110 / 135).

[0033] In this way, the determination unit 103 of the inspection device 10 may calculate the capacity maintenance rate of the lower limit capacity when charging and discharging are repeated relative to the lower limit capacity at the start of measurement, and may determine that the battery module 20 is defective when the capacity maintenance rate is equal to or less than a predetermined threshold. Alternatively, when the capacity maintenance rate is equal to or less than the threshold, it may determine that the in-plane distribution of the confining pressure of the battery module 20 is equal to or greater than a certain level. Note that the start of measurement may be the first time, or may be the second time or later if it is an early period.

[0034] Next, conditions for improving the accuracy of capacity retention rate measurement will be described. Figures 5 and 7 are diagrams showing the pressure dependence of direct current resistance (DCR) when charging and discharging the battery module 20. Figure 5 shows the case of charging and discharging with a maximum charge rate of 25%, while Figure 7 shows the case of charging and discharging with a maximum charge rate of 50%. It can be seen that the difference between the discharge DCR and the charge DCR is larger when the maximum charge rate is 25% in Figure 5 compared to Figure 7, which clearly shows the influence of the in-plane distribution of the confining pressure.

[0035] In other words, repeating charge and discharge in a low charge rate region makes it easier to detect large in-plane distributions of confinement pressure, thereby improving the accuracy of detecting defects in the battery module 20. Furthermore, setting the upper limit charge rate at 25% shortens the time required for charge and discharge, thereby shortening the inspection time. The upper limit charge rate is a charge rate lower than the maximum charge rate during actual use of the battery module 20, and is a charge rate that is predetermined depending on the type, performance, required specifications, inspection time, etc. of the battery module 20. The upper limit charge rate is, for example, a value of 50% or less, and preferably 25%.

[0036] On the other hand, as is clear from Figures 6A and 6B, the lower limit of the charge rate during discharge is such that the closer it is to 0%, the greater the change in capacity. Therefore, the lower limit of the charge rate is a predetermined value equal to or greater than 0%, and is preferably 0%.

[0037] Fig. 8 is a diagram showing the pressure dependency of direct current resistance (DCR) when charging and discharging the battery module 20. Fig. 5 shows the case where the ambient temperature of the space in which the battery module 20 to be measured is placed is 25°C, while Fig. 7 shows the case where the ambient temperature is 60°C. Compared to Fig. 8, when the ambient temperature in Fig. 5 is 25°C, the difference between the discharge DCR and the charge DCR is larger, and it can be seen that the influence of the in-plane distribution of the confinement pressure is significantly expressed.

[0038] In other words, repeating charge and discharge at an environmental temperature close to room temperature (e.g., 25°C) makes it easier to detect a large in-plane distribution of confinement pressure than at a high temperature, thereby improving the accuracy of determining whether the battery module 20 is good or bad. The environmental temperature is a temperature determined in advance depending on the type, performance, required specifications, inspection time, etc. of the battery module 20, and is, for example, a temperature below room temperature, preferably 25°C. For example, the environmental temperature may be set based on the temperature characteristics of the charge DCR and discharge DCR shown in Figures 5 and 8.

[0039] The procedure of the inspection method using the inspection device 10 configured as above will be described in detail with reference to the flowchart of Fig. 9. Fig. 9 is a flowchart of the inspection process executed by the processor 1011 of the inspection device 10.

[0040] First, the processor 1011 of the inspection device 10 acquires parameters to be used in the inspection (step S101). The parameters include an ambient temperature, a charging range, and a threshold value for the capacity retention rate. For example, the processor 1011 acquires 25°C as the ambient temperature, a lower limit of the charging rate of 0% and an upper limit of the charging rate of 25% as the charging range, and an upper limit of 92% as the threshold value for the capacity retention rate. Furthermore, the parameters may include a parameter related to the number of charge / discharge cycles. Specifically, in determining the capacity retention rate, a reference number n at the start of measurement, which is used as a reference for the capacity retention rate, may be acquired. ０ , the upper limit number of judgments N(n ０ , N is a natural number, 1≦n ０ <N). The parameters acquired in step S101 are parameters that are determined in advance depending on the type, performance, required specifications, inspection time, etc. of the battery module 20. In step S101, other parameters necessary for the inspection may also be acquired.

[0041] Next, the environmental temperature of the battery module 20 is set to the temperature acquired in step S101 (step S102). After the environmental temperature has stabilized at the set temperature, the charge / discharge control unit 101 of the inspection device 10 sets the value of n, which is the number of charge / discharge cycles, to 1 (n is a natural number, step S103), and charges the battery module 20 to the upper limit of the charging rate acquired in step S101 (step S104). The charge / discharge control unit 101 measures the charging rate of the battery module 20, and after the charging rate reaches the upper limit, discharges the battery module 20 to the lower limit of the charging rate (step S105).

[0042] After the charging rate of the battery module 20 reaches the lower limit, the capacity measurement unit 102 measures and records the capacity (step S106). That is, the capacity measured and recorded in step S106 is the lower limit capacity. After that, the capacity measurement unit 102 measures and records the capacity at the reference number n, where n is the number of times set at the start of measurement. ０ It is determined whether n is greater than the reference number n (step S107). ０ If it is equal to or less than n (step S107: No), 1 is added to n (step S111), and the process returns to step S104. Thereafter, charging / discharging and capacity measurement are repeated (steps S104 to S106).

[0043] n is the reference number n ０ When the capacity maintenance rate is greater than the predetermined threshold (step S107: Yes), the determination unit 103 calculates the capacity maintenance rate, and when the capacity maintenance rate is equal to or less than the predetermined threshold (step S108: Yes), the determination unit 103 determines that an abnormality has occurred (step S109). ０ If the capacity maintenance rate, which is the ratio of the capacity measured the second time to the lower limit capacity, is equal to or less than the threshold set in step S101, the battery module 20 is determined to be defective. Then, the process ends.

[0044] On the other hand, if the determination unit 103 determines that the capacity maintenance rate is greater than the predetermined threshold value (step S108: No), or if the number of cycles n is smaller than the upper limit number of cycles N for determination set in step S101 (step S110: No), the charge / discharge control unit 101 increments n by 1 (step S111) and returns to step S104. Thereafter, charge / discharge and capacity measurement are repeated (steps S104 to S106).

[0045] When the number of cycles n is equal to or greater than the upper limit number N of determinations set in step S101 (step S110: Yes), the determination unit 103 determines that the battery module 20 is normal (step S112). Specifically, if the capacity maintenance rate of the lower limit capacity measured in step S106 remains greater than the threshold value set in step S101 for a certain number of times (N times) or more, the battery module 20 is determined to be good. Then, the process ends.

[0046] 10 is a diagram showing an example of the capacity maintenance rate of the battery module 20 measured using the inspection method shown in FIG. 9. In the example of FIG. 10, the capacity maintenance rate of the battery module 20 with a small in-plane distribution of the confining pressure (surface pressure distribution) is about 97% after 20 cycles, as shown by the black circles. In contrast, the capacity maintenance rate of the battery module 20 with a large in-plane distribution of the confining pressure (surface pressure distribution) is 91% after 20 cycles, as shown by the white circles. In this example, among the parameters acquired in step S101 of FIG. 9, the reference number of times n ０ is set to 1, the upper limit number of judgments N is set to 20, and the threshold value of the capacity maintenance rate is set to 92%, the battery module 20 indicated by the black circle is judged to be good, and the battery module 20 indicated by the white circle is judged to be bad when the capacity maintenance rate falls below 92%.

[0047] As described above, the inspection method according to this embodiment is a method for inspecting a battery module 20 in which a confining pressure is applied to a stack of one or more battery cells, each having an electrolyte layer containing a solid electrolyte, a positive electrode layer, and a negative electrode layer. In the inspection method according to this embodiment, the battery module 20 is charged to a predetermined upper limit charging rate for inspection, which is lower than the maximum charging rate during actual use of the battery module 20, and then discharged to a predetermined lower limit charging rate for inspection, and the lower limit capacity is measured. If the capacity maintenance rate of the lower limit capacity measured after repeated charging and discharging is equal to or less than a threshold value relative to the initial lower limit capacity, the battery module 20 is determined to be defective. This allows the inspection to be performed based on the capacity measured after charging and discharging within a narrower range of charging rates than the range during actual use of the battery module 20, thereby shortening the time required for the inspection.

[0048] (Modification) The above embodiment can be modified in various ways. Fig. 11 is a diagram showing an inspection system 2 according to a modification. The battery module 60 that is the target of the inspection method according to this modification is, like the above embodiment, an all-solid-state battery module having a configuration in which a confining pressure is applied to a stack of one or more battery cells 21, each having an electrolyte layer containing a solid electrolyte, a positive electrode layer, and a negative electrode layer. However, this modification differs from the above embodiment in that it has a function that makes it possible to change the average value of the confining pressure by controlling the load applied to the stack.

[0049] As shown in Fig. 11 , an inspection system 2 according to this modification includes an inspection device 11, a battery module 60 to be inspected, a temperature sensor 70, and a charger 80 that charges the battery module 60. The configurations and functions of the temperature sensor 70 and the charger 80 are the same as those of the above embodiment. The inspection system 2 also includes a load controller 90 that controls the load applied to the stack of battery modules 60. In addition to the functions of the above embodiment, the inspection device 11 also includes a pressure control unit 104 that controls the average value of the restraint pressure applied to the battery cells 21 by controlling the load controller 90. The hardware configuration of the inspection device 11 and the functions of the charge / discharge control unit 101, capacity measurement unit 102, and determination unit 103 are the same as those of the above embodiment.

[0050] The battery module 60 includes a stack of multiple battery cells 21 similar to those in the above embodiment, and a mechanism for applying a load to the battery cells 21 is provided by fixing plates 22, pressure plates 23, and elastic bodies 24 provided above and below the stack. The fixing plates 22 are provided at positions above and below the stack of battery cells 21. The pressure plates 23 apply a load in the stacking direction of the battery cells 21 included in the battery module 60 based on a control signal transmitted from a load controller 90.

[0051] The pressure plates 23 are provided on top of the stack of battery cells 21. The pressure plates 23 are connected to an actuator (not shown) and can move up and down using power from the actuator. Elastic members 24 are provided between the multiple pressure plates 23 and are members that transmit the load received from the pressure plates 23 to the stack of battery cells 21.

[0052] When applying confinement pressure to the battery cells 21, the position of the upper pressure plate 23 of the pair of pressure plates 23 moves down along the fixed posts 26 so that the upper pressure plate 23 approaches the multiple battery cells 21. As the upper pressure plate 23 moves, the load from the pressure plate 23 is transmitted to the stack of multiple battery cells 21 via the elastic body 24 and the lower pressure plate 23. When reducing the confinement pressure of the battery cells 21, the position of the upper pressure plate 23 moves up along the fixed posts 26 so that the upper pressure plate 23 moves away from the multiple battery cells 21.

[0053] In this way, the battery module 60 can adjust the load applied to the battery cells 21 using a control signal from the load controller 90 based on a control command output by the inspection device 11. In other words, the fixing plate 22, pressure plate 23, elastic body 24, and fixing column 26 form a mechanism that can vary the average value of the confinement pressure in the plane to which the load is applied by adjusting the load. Note that the mechanism that varies the load or the mechanism that varies the average value of the confinement pressure is not limited to the mechanism shown in FIG. 11 , and other mechanisms may be used.

[0054] The battery module 60 further includes a load sensor 50 below the stack, and by monitoring the output of the load sensor 50, the average value of the restraint pressure (surface pressure) applied to the battery cells 21 can be measured.

[0055] The battery module 60 has the same characteristics as those of the above-described embodiment, and has, for example, the pressure dependency of the internal resistance shown in Fig. 5. As shown in Fig. 5, when charging and discharging are performed at an ambient temperature of 25°C with a maximum charge rate of 25%, the charge DCR and discharge DCR have different pressure dependencies, but the difference between the charge DCR and discharge DCR increases as the pressure decreases.

[0056] Therefore, in the inspection method according to this modification, charging and discharging are performed with the average value of the confinement pressure set to a predetermined pressure or less, and if the capacity maintenance rate is equal to or less than a predetermined threshold, it is determined that the battery module 60 is defective or that the in-plane distribution of the confinement pressure of the battery module 60 is equal to or greater than a certain level. This improves the accuracy of determining whether the battery module 60 is good or bad. The average value of the confinement pressure is determined in advance depending on the type, performance, required specifications, inspection time, etc. of the battery module 60, but is preferably a predetermined pressure of 0.1 MPa or more and 2 MPa or less.

[0057] The procedure of the inspection method according to this modification is the same as that of the above embodiment, and follows the flowchart of Fig. 9. In step S101, the processor 1011 of the inspection device 11 acquires parameters to be used in the inspection, such as the ambient temperature, the charging range, the threshold value of the capacity maintenance rate, the reference number of times n, ０ In addition to the upper limit number of judgments N, a set pressure, which is the average value of the restraining pressure, is acquired (step S101). Thereafter, the pressure control unit 104 of the inspection device 11 controls the load controller 90 to set the average value of the restraining pressure to a set pressure of 0.1 MPa or more and 2 MPa or less, and then performs the processes from step S102 onwards. The processes from step S102 onwards are the same as those in the above embodiment.

[0058] As described above, the inspection method according to this modification involves repeating charge and discharge while applying a confining pressure having an average value equal to or less than a predetermined pressure to the battery cells 21 of a battery module 60 having a mechanism for varying the average value of the confining pressure of the battery cells 21, and judging the battery module 60 to be defective if the capacity maintenance rate of the lower limit capacity when the charge rate reaches the lower limit after discharge is equal to or less than a threshold value. This allows for inspection within a low pressure range where the influence of the in-plane distribution of the confining pressure is significant, thereby improving inspection accuracy.

[0059] The hardware configurations and flowcharts shown in the above-described embodiments and modifications are merely examples and can be modified or applied as desired. For example, in the above-described embodiments and modifications, the inspection device 10, 11 repeatedly charges the battery module 20, 60 to the upper limit and discharges it to the lower limit to measure the lower limit capacity, and determines that the battery module 20, 60 is defective when the capacity maintenance rate of the lower limit capacity becomes equal to or less than a predetermined threshold. However, this is not limited to this. For example, there may be multiple thresholds, and the pass / fail of the battery module 20, 60 may be determined using thresholds that decrease depending on the number n of repeated cycles (98%, 96%, etc.).

[0060] Alternatively, the determining unit 103 of the inspection device 10, 11 may determine whether the battery module 20, 60 is good or bad based on the rate (slope) of decrease in the capacity maintenance rate.

[0061] Alternatively, the inspection devices 10 and 11 may be configured to ０ The lower limit capacity measured by charging and discharging the battery for the first time is compared with the predetermined fixed number of times, M (M is n ０ The capacity retention rate may be calculated as the ratio of the upper limit charging rate and the lower limit charging rate measured after charging and discharging the battery (a natural number greater than or equal to M), and this capacity retention rate may be used to determine whether the battery is good or bad. In this case, the upper limit charging rate and the lower limit charging rate do not need to be constant during the number of repetitions M, and multiple upper limit charging rates or multiple lower limit charging rates may be present and may be changed during the repetition.

[0062] Furthermore, in the above embodiment and variant examples, examples have been described in which the processor 1011 executes a control program to realize each function, but the inspection devices 10, 11 may also be configured using dedicated hardware that realizes each function.

[0063] Furthermore, the control program for executing the operations of the above-described embodiments and modifications may be stored and distributed on a computer-readable recording medium such as a CD-ROM (Compact Disc Read-Only Memory), a DVD (Digital Versatile Disc), an MO (Magneto Optical Disc), or a memory card, and the program may be installed on a computer to configure the inspection devices 10 and 11 that can realize each function. When each function is realized by sharing the work between an OS (Operating System) and an application, or by cooperation between an OS and an application, only the parts other than the OS may be stored on the recording medium.

[0064] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. In other words, the scope of the present invention is defined by the claims, not by the embodiments. Various modifications made within the scope of the claims and the meaning of the disclosure equivalent thereto are considered to be within the scope of the present invention.

[0065] 1, 2 Inspection system, 10, 11 Inspection device, 20, 60 Battery module, 21 Battery cell, 22 Fixing plate, 23 Pressure plate, 24, 25 Elastic body, 26 Fixing column, 30 Output terminal, 50 Load sensor, 70 Temperature sensor, 80 Charger, 90 Load controller, 101 Charging / discharging control unit, 102 Capacity measurement unit, 103 Determination unit, 104 Pressure control unit, 1011 Processor, 1012 Memory unit, 1013 Communication interface, 1014 Measurement unit.

Claims

1. A method for inspecting a battery module in which a confining pressure is applied to a stack of one or more battery cells each having an electrolyte layer containing a solid electrolyte, a positive electrode layer, and a negative electrode layer, the method comprising: measuring a lower limit capacity, which is the capacity of the battery module when the battery module is charged to an upper limit charge rate predetermined for inspection, which is lower than the maximum charge rate during actual use of the battery module, and then discharging to a lower limit charge rate predetermined for inspection; and determining the battery module as defective if the capacity retention rate of the lower limit capacity measured by repeating the charging and discharging to the lower limit capacity at the start of measurement is equal to or less than a threshold value.

2. The battery module inspection method according to claim 1, wherein when the capacity maintenance rate is equal to or less than the threshold value, it is determined that the in-plane distribution of the confining pressure of the battery module is equal to or greater than a certain level.

3. The battery module inspection method according to claim 2, wherein if the capacity maintenance rate of the lower limit capacity measured after repeating the charging and discharging a predetermined number of times exceeds the threshold value, it is determined that the in-plane distribution of the confining pressure of the battery module is smaller than a certain value.

4. A battery module inspection method according to any one of claims 1 to 3, wherein, when the charge range during actual use of the battery module is from 0% to 100%, the lower limit charge rate is 0% or more and the upper limit charge rate is 50% or less.

5. The battery module inspection method according to claim 4, wherein the lower limit of the charging rate is 0%.

6. A battery module inspection method according to claim 1, wherein, when the battery module is equipped with a mechanism for varying the average value of the restraint pressure applied to the stack, the average value is set to a predetermined pressure or less, and the charging and discharging of the battery module are repeated.

7. The battery module inspection method according to claim 6, wherein the average value is set to a predetermined pressure of 0.1 MPa or more and 2 MPa or less.

8. The battery module inspection method according to claim 1, wherein the charging and discharging of the battery module is repeated in an environment at a temperature equal to or lower than a predetermined temperature.

9. An inspection device for inspecting a battery module in which a restraining pressure is applied to a stack of one or more battery cells each having an electrolyte layer containing a solid electrolyte, a positive electrode layer, and a negative electrode layer, the inspection device comprising: a measuring unit that measures a lower limit capacity, which is the capacity of the battery module when the battery module is charged to an upper limit charge rate predetermined for inspection, which is a charge rate lower than the maximum charge rate during actual use of the battery module, and then discharged to a lower limit charge rate predetermined for inspection; and a processor that determines the battery module to be defective when the capacity maintenance rate of the lower limit capacity measured by repeatedly charging and discharging, relative to the lower limit capacity at the start of measurement, is equal to or lower than a threshold value.

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