Battery system

Abstract

A battery system (1) comprises: a laminate (21) that includes a plurality of battery cells (211a-211e) each having a negative electrode containing lithium metal or a lithium alloy, and elastic bodies (213a-211d) disposed between the plurality of battery cells (211a-211e); a binding unit (22) that binds the laminate (21) and applies a restraint pressure to the laminate (21); a distance detection unit (3) that indirectly or directly detects the distances (d1-d4) between the plurality of battery cells (211a-211e); and a control unit (6) that determines an abnormality in the battery cells (211a-211e) on the basis of the distances (d1-d4) detected by the distance detection unit (3).

Description

Battery system

[0001] This invention relates to a battery system.

[0002] A solid-state battery is known that comprises a battery cell having a negative electrode containing lithium metal, a restraining mechanism for restraining the battery cell, a discharge mechanism for discharging the battery cell, a temperature detection mechanism for detecting the temperature of the battery cell and generating temperature data, and a control mechanism for controlling the operation of the restraining mechanism and the discharge mechanism based on the temperature data (see, for example, Patent Document 1). In this solid-state battery, if an abnormality in the battery cell is detected based on the temperature of the battery cell, the operation of the solid-state battery is controlled to prevent leakage of molten lithium metal.

[0003] International Publication No. 2024 / 079493

[0004] The all-solid-state battery described in Patent Document 1 above is equipped with an abnormality detection means in an active mechanism that can actively control the restraint pressure by a control mechanism that controls the operation of the restraint mechanism. However, from the viewpoint of energy density, it may be preferable to employ a passive mechanism that does not have a control mechanism that controls the operation of the restraint mechanism. However, in a passive mechanism, the abnormality detection method described in Patent Document 1 cannot be used.

[0005] The problem that this invention aims to solve is to provide a battery system that can detect abnormalities in battery cells using a passive mechanism.

[0006] The present invention solves the above problem by providing a battery system comprising a laminate containing a plurality of battery cells and an elastic body, and a binding part for binding the laminate, wherein the system includes a distance detection unit for detecting the distance between the plurality of battery cells, and an abnormality determination unit for determining an abnormality in a battery cell based on the distance detected by the distance detection unit.

[0007] According to the present invention, the distance between battery cells can be detected, and the presence or absence of abnormalities in the battery cells can be determined based on the detected distance.

[0008] Figure 1 is a block diagram of a battery system in an embodiment of the present invention. Figure 2 is a cross-sectional view showing a battery module in an embodiment of the present invention. Figure 3 is a flowchart showing a control method by the battery system in an embodiment of the present invention. Figure 4 is a graph illustrating an example of an abnormality detection method in an embodiment of the present invention. Figure 5 is a graph illustrating another example of an abnormality detection method in an embodiment of the present invention. Figure 6 is a schematic diagram showing the relationship between the control content of the battery system, the SOC, and the temperature of the battery cell in an embodiment of the present invention. Figure 7 is an enlarged cross-sectional view showing a battery cell in an embodiment of the present invention. Figure 8 is an enlarged cross-sectional view showing a modified example of the battery module in an embodiment of the present invention.

[0009] Embodiments of the present invention will be described below with reference to the drawings.

[0010] Figure 1 is a block diagram of the battery system 1 in this embodiment. Figure 2 is a cross-sectional view showing the battery module 2 in this embodiment.

[0011] As shown in Figure 1, the battery system 1 in this embodiment includes a battery module 2, a distance detection unit 3, a temperature detection unit 4, a SOC (state of charge) detection unit 5, a control unit 6, and a discharge mechanism 7.

[0012] As shown in Figure 2, the battery module 2 comprises a laminate 21 and a binding portion 22. In this embodiment, the laminate 21 includes a plurality (five in this example) of battery cells 211a to 211e and a plurality (four in this example) of elastic bodies 213a to 213d. However, the number of battery cells and elastic bodies is not limited to those shown above.

[0013] Note that Figure 2 illustrates a case where an abnormality has occurred in battery cell 211c for the sake of explanation. According to the inventors' findings, the thickness of each SOC of battery cells 211a to 211e included in the laminate 21 is approximately equal when the battery cells are normal. On the other hand, the thickness of a battery cell with an abnormality changes in a different way than that of a normal battery cell, and has a difference of a certain amount or more compared to the thickness of a normal battery cell. For example, in Figure 2, the thicknesses of battery cells 211a, 211b, 211d, and 211e are approximately equal, while the thickness of battery cell 211c is thinner. Therefore, the inventors have found that it is possible to detect a battery cell with an abnormality based on the distance between battery cells, which allows for evaluation of the difference in battery cell thickness.

[0014] Each battery cell 211a to 211e in this embodiment has a charge-discharge function. Although not specifically shown, each battery cell 211a to 211e comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode contains lithium metal. In the battery cells 211a to 211e, during charging, lithium ions move from the positive electrode to the negative electrode via the solid electrolyte, and lithium metal is deposited on the negative electrode. This charging increases the thickness of the battery cells 211a to 211e. On the other hand, during discharge, the lithium metal from the negative electrode moves to the positive electrode side as lithium ions and is absorbed into the positive electrode. That is, lithium metal is lost from the negative electrode during discharge. This discharge decreases the thickness of the battery cells 211a to 211e.

[0015] Furthermore, the electrolyte includes at least a solid electrolyte. This electrolyte may also include a polymer electrolyte or a liquid electrolyte.

[0016] Furthermore, each battery cell 211a to 211e is electrically connected to each other by tabs 212a to 212d. Tabs 212a to 212d are plate-shaped members made of a metal material and extend along the stacking direction of the battery cells 211a to 211e.

[0017] The elastic bodies 213a to 213d are elastic sheet members. The elastic bodies 213a to 213d are interposed between the battery cells 211a to 211e and press against the battery cells 211a to 211e with elastic force.

[0018] The securing portion 22 houses the laminate 21 and secures the laminate 21. In this embodiment, the securing portion 22 applies restraining pressure by pressing the laminate 21 in the stacking direction (Z direction in the figure).

[0019] Thus, in this embodiment, the battery module 2 restrains the battery cells 211a to 211e by applying pressure with the elastic bodies 213a to 213d and the restraining portion 22. In other words, the battery module 2 in this embodiment is a battery module equipped with a passive mechanism that does not actively control the restraining pressure on the battery cells 211a to 211e using power (e.g., electrical energy). In this battery module 2, the restraining pressure changes passively in accordance with the expansion and contraction of the battery cells 211a to 211e.

[0020] As shown in Figures 1 and 2, the distance detection unit 3 detects the distance between battery cells 211a to 211e. As shown in Figure 2, the distance detection unit 3 in this embodiment is not particularly limited, but includes a plurality of strain gauges 31a to 31d. Each strain gauge 31a to 31d is attached to tabs 212a to 212d. The strain gauges 31a to 31d can measure the amount of displacement (i.e., elongation or contraction) of tabs 212a to 212d due to the expansion or contraction of battery cells 211a to 211e. Since the initial length of tabs 212a to 212d is a known value, the distance d between battery cells 211a to 211e can be measured based on the initial length and the amount of displacement. １ ~d ４ The distance d between battery cells 211a to 211e can be calculated based on the displacement of the tab. １ ~d ４ When calculating this, the configuration of existing battery modules can be effectively utilized for distance measurement.

[0021] Furthermore, although not particularly limited, the distance detection unit 3 may include a distance sensor capable of measuring the distance between cells instead of a strain gauge.

[0022] As shown in FIG. 1, the temperature detection unit 4 detects the temperatures of the battery cells 211a to 211e. Then, the temperature detection unit 4 outputs the detected temperature data to the control unit 6. The temperature detection unit 4 is not particularly limited, but includes a temperature sensor or the like. The temperature detection unit 4 may be configured to directly measure the temperature of the battery cell, or may be configured to indirectly estimate it.

[0023] The SOC detection unit 5 detects the SOCs of the battery cells 211a to 211e. Then, the SOC detection unit 5 outputs the detected SOC data to the control unit 6. The SOC detection unit 5 is not particularly limited, but may detect the charge amount by estimating the SOCs of the battery cells 211a to 211e from the voltage or the like.

[0024] The control unit 6 receives the data related to the distances d １ ~d ４ received by the distance detection unit 3, and determines whether or not an abnormality has occurred in the battery cells 211a to 211e based on the received data. Note that the control unit 6 in the present embodiment corresponds to an example of the "abnormality determination unit" in the present invention.

[0025] Further, when the control unit 6 determines that an abnormality has occurred in a specific battery cell, it determines the method of processing to be performed on the specific battery cell based on the temperature data detected by the temperature detection unit 4 and the SOC data detected by the SOC detection unit 5. The control unit 6 in the present embodiment has a function of discharging a specific battery cell by controlling the discharge mechanism 7, although details will be described later. Note that the control unit 6 in the present embodiment also corresponds to an example of the "processing method determination unit" in the present invention.

[0026] The control unit 6 may have a processor, although not particularly shown. The processor includes a ROM (Read Only Memory) storing a program for performing abnormality determination, a CPU (Central Processing Unit) for executing the program stored in the ROM, and a RAM (Random Access Memory) functioning as an accessible storage device. The processor executes the functions of the control unit 6 by causing the CPU to execute the program stored in the ROM.

[0027] The discharge mechanism 7 can discharge each of the battery cells 211a to 211e. The discharge mechanism 7 includes, for example, a load circuit connected to each of the battery cells 211a to 211e.

[0028] FIG. 3 is a flowchart showing a control method by the battery system 1 in the present embodiment. Hereinafter, the control method by the battery system 1 in the present embodiment will be described while referring to FIG. 3.

[0029] First, in step S101, the distance detection unit 3 detects the distance d between the battery cell 211a and the battery cell 211b, １ the distance d between the battery cell 211b and the battery cell 211c, ２ the distance d between the battery cell 211c and the battery cell 211d, ３ and the distance d between the battery cell 211d and the battery cell 211e. ４ In the present embodiment, using the above-described strain gauge, the displacement amounts of the tabs 212a to 212d in the stacking direction are measured, and the distances d １ to d ４ are calculated from the measurement values.

[0030] Next, in step S102, the control unit 6 determines whether or not an abnormality has occurred in the battery cells 211a to 211e based on the distances d １ to d ５ received from the distance detection unit 3. A specific abnormality determination method in the present embodiment will be described while referring to FIG. 4.

[0031] Figure 4 is a graph illustrating an example of the abnormality detection method in this embodiment. Figure 4 shows the relationship between the distance between cells and the SOC. Also, the line L in Figure 4 ｒｅｆ This indicates a reference value, which specifically represents a distance map for each State of Center (SOC) between normal battery cells. For example, this distance map can be created by pre-measuring the distance between battery cells while charging and discharging a stack containing multiple normal battery cells.

[0032] In this step S102, each distance d １ ~d ４ Straight line L ｒｅｆ The amount of deviation from is a predetermined threshold (d in the figure). ｔ１ or d ｔ２ If the value is greater than d, it is determined that there is an abnormality in the battery cell. The SOC of battery cells 211a to 211e is the distance d mentioned above. １ ~d ４ When this is detected, it is recorded by the SOC detection unit 5.

[0033] For example, in the battery module 2 shown in Figure 2, an abnormality has occurred in battery cell 211c, but in this example, the thickness of battery cell 211c is thinner than the thickness of the other battery cells 211a, 211b, 211d, and 211e. Therefore, as shown in Figure 4, the distance d ２ d ３ Reference value L ｒｅｆ Deviation amount Δd from １ The threshold d ｔ１ It has become larger. Therefore, it can be determined that there is an abnormality in battery cell 211c.

[0034] In this embodiment, the example given is that the thickness of battery cell 211c is thinner than the thickness of the other battery cells 211a, 211b, 211d, and 211e. However, the thickness of battery cell 211c may be thicker than the thickness of the other battery cells 211a, 211b, 211d, and 211e. In this case, as shown in Figure 4, the distance d ２ ', d ３ ' is the reference value L ｒｅｆ The value becomes smaller than Δd. ２ is the threshold d ｔ２It becomes larger. In this case as well, it can be determined that there is an abnormality in the battery cell 211c.

[0035] Furthermore, in the above abnormality detection method, the reference value L measured in advance is used. ｒｅｆ Anomaly detection was performed using this method, but it is not limited to this. Anomaly detection of a battery cell may also be performed by comparing multiple distances detected by the distance detection unit 3, as shown in the anomaly detection method described below. Figure 5 is a graph illustrating another example of the anomaly detection method in this embodiment, showing the inter-cell distances when the SOC is 100%, when the SOC is 50%, and when the SOC is 0%. Also, in Figure 5, unlike the battery module 2 shown in Figure 2, an example is shown where the stacked body has nine battery cells.

[0036] As described above, the change in thickness of a faulty battery cell differs from that of a normal battery cell, allowing for the identification of faulty battery cells based on the inter-cell distance. For example, in the example shown in Figure 5, the distance between the fourth and fifth battery cells, and the distance between the fifth and sixth battery cells, differ from the distances between other battery cells. Therefore, it can be determined that the fifth battery cell is faulty. In this way, faulty battery cells can also be identified by comparing the inter-cell distances detected by the distance detection unit 3.

[0037] Returning to Figure 3, if it is determined in step S102 that an abnormal battery cell exists, in step S103 the control unit 6 determines whether the SOC of the abnormal battery cell is greater than or equal to a predetermined SOC value A.

[0038] Figure 6 is a schematic diagram showing the relationship between the control contents of the battery system 1 in this embodiment, the SOC, and the temperature of the battery cell. As shown in Figures 3 and 6, in step S103, if the SOC of an abnormal battery cell is less than a predetermined SOC value A, in step S104, the control unit 6 discharges the abnormal battery cell using the discharge mechanism 7 and terminates control of the battery module 2. By discharging the abnormal battery cell in this way, the state of the abnormal battery cell can be changed from a state in which lithium is easily moved to a state in which lithium is not easily moved, thus enabling a safe response to the abnormality of the battery cell.

[0039] In this embodiment, the predetermined SOC value A is such that, when the lithium metal present at the negative electrode melts, the amount of molten lithium metal can be contained within the buffer space of the outer casing. Such a buffer space will be described with reference to Figure 6.

[0040] Figure 7 is an enlarged cross-sectional view showing the battery cell 211 in this embodiment. Here, battery cells 211a to 211e are collectively referred to as battery cell 211. As shown in Figure 7, the battery cell 211 comprises a film-like outer casing 214 and an electrode stack 215 housed within the outer casing 214. Inside the outer casing 214, a buffer space 216 is provided between the outer casing 214 and the electrode stack 215.

[0041] With this configuration, even if some lithium metal melts, the melted lithium metal is contained in the buffer space 216 and does not reach the outside of the outer casing 214. Here, the amount of lithium metal that can melt, that is, the amount of lithium metal contained in the negative electrode, changes depending on the charge and discharge state of the battery cell 211. Specifically, the amount of lithium metal contained in the negative electrode increases during charging and decreases during discharge. Therefore, the predetermined SOC value A is set so that the amount of lithium metal contained in the negative electrode is such that it can be contained in the buffer space 216.

[0042] If the predetermined SOC value A is such that, if the battery cell 211 overheats abnormally, the discharge in step S104 reduces the charge of the battery cell 211 so that the amount of lithium metal contained in the negative electrode is within a range that can be accommodated in the buffer space 216. Therefore, even if the temperature at which the lithium metal melts is reached afterward, the molten lithium metal can be contained in the buffer space 216, preventing leakage to the outside.

[0043] Returning to Figure 3, in step S105, if the SOC of the abnormal battery cell is greater than or equal to a predetermined SOC value A, the control unit 6 determines that the temperature T of the abnormal cell detected by the temperature detection unit 4 is greater than or equal to the predetermined temperature T １ It is determined whether or not the above is true. １ This is a temperature below the melting point of lithium metal or lithium alloy.

[0044] In step S105, the abnormal temperature T of the battery cell is set to a predetermined temperature T. １ If the value is less than the specified value, in step S106, the abnormal battery cell is discharged and control of the battery module 2 is terminated. This allows for a safe response to battery cell abnormalities, as described above.

[0045] In step S107, the abnormal battery cell temperature T is set to a predetermined temperature T. １ If the above conditions are met, in step S107, control of the battery module 2 is terminated without discharging the abnormal battery cell. Thus, if the SOC of the abnormal battery cell is A or higher, and the temperature T of the abnormal battery cell is a predetermined temperature T １ If the above conditions are met, performing a discharge procedure may cause a short circuit between the molten lithium and the positive electrode. Therefore, control of the battery module 2 is terminated without performing a discharge procedure. This allows for the detection of highly abnormal battery cells and enables safe subsequent handling of the abnormality.

[0046] With the battery system 1 described above, the passive mechanism can detect abnormalities in the battery cells 211a to 211e.

[0047] In the above embodiment, the distance between cells is calculated based on the displacement of the tab, but this is not limited to this. For example, by measuring or estimating the distance between the elastic bodies 213a to 213d shown in Figure 2, the distance d between multiple battery cells 211a to 211e can be calculated. １ ~d ４ It may also be detected. The distance between elastic bodies 213a to 213d is the distance d between multiple battery cells 211a to 211e. １ ~d ４ This can be considered as such. In this way, the distance between the elastic bodies 213a to 213d can be used to determine if there is an abnormality in the battery cell.

[0048] Figure 7 is an enlarged cross-sectional view showing a modified example of the battery module 2 in this embodiment. As shown in Figure 7, in this modified example, the battery cells 211a and 211b are directly stacked without an elastic body in between. Similarly, the battery cells 211c and 211d are directly stacked without an elastic body in between, and the battery cells 211e and 211f are directly stacked without an elastic body in between.

[0049] In this case, the distance d between the elastic body 213a and the binding portion 22 in the stacking direction ５ The distance d between the elastic bodies 213a and 213b in the stacking direction. ６ The distance d between the elastic body 213b and the binding portion 22 in the stacking direction. ７ You may also use this to determine if there is an abnormality in the battery cell.

[0050] 1...Battery system 2...Battery module 21...Laminate 211a-211e...Battery cell 212...Tab 213a-213e...Elastic body 22...Binding part 3...Distance detection part 4...Temperature detection part 5...SOC detection part 6...Control unit 7...Discharge mechanism

Claims

1. A battery system comprising: a laminate including a plurality of battery cells having a negative electrode containing lithium metal or a lithium alloy, and an elastic body disposed between the plurality of battery cells; a binding unit for binding the laminate and applying a binding pressure to the laminate; a distance detection unit for indirectly or directly detecting the distance between the plurality of battery cells; and an abnormality detection unit for determining an abnormality in the battery cells based on the distance detected by the distance detection unit.

2. A battery system according to claim 1, wherein the battery system further comprises a processing method determination unit that determines a method of processing to be performed on a specific battery cell based on the temperature and SOC of the specific battery cell when the abnormality determination unit determines that an abnormality has occurred in a specific battery cell.

3. A battery system according to claim 2, wherein the processing method determination unit determines whether or not to discharge the specific battery cell.

4. A battery system according to claim 2 or 3, wherein the processing method determination unit determines that the specific battery cell should be discharged when the temperature is below a predetermined temperature or the SOC is below a predetermined SOC.

5. A battery system according to claim 4, wherein the predetermined temperature is below the melting point of the lithium metal or the lithium alloy.

6. A battery system according to claim 4 or 5, wherein the battery cell has an outer casing for housing the negative electrode, the outer casing has a buffer space inside that can accommodate molten lithium metal when the lithium metal melts, and the predetermined SOC is such that when the lithium metal present in the negative electrode melts, the amount of molten lithium metal can be accommodated in the buffer space.

7. A battery system according to any one of claims 1 to 6, wherein the abnormality determination unit determines an abnormality based on the amount of deviation between the distance detected by the distance detection unit and the distance between normal battery cells acquired in advance for each SOC.

8. A battery system according to any one of claims 1 to 6, wherein the abnormality determination unit determines an abnormality based on the amount of deviation between the distance between specific battery cells detected by the distance detection unit and the distance between other battery cells other than the specific battery cells detected by the distance detection unit.

9. A battery system according to any one of claims 1 to 8, wherein the distance detection unit detects the distance by measuring or estimating the amount of displacement of tabs connecting the plurality of battery cells in the stacking direction of the stacked body.

10. A battery system according to any one of claims 1 to 8, wherein the distance detection unit detects the distance between a plurality of battery cells by measuring or estimating the distance between a plurality of elastic bodies.

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