Battery module

Abstract

This battery module (1) comprises: a stack (40) that is configured by alternately stacking a plurality of battery cells (41-45), which each have a negative electrode that contains lithium metal or a lithium alloy, and a plurality of elastic bodies (51-54); and a fastening member (60) that fastens the stack (40). The number of the battery cells is equal to or greater than the number of the elastic bodies. In cases where the center-to-center distance (d1 to d4) between the battery cells (41-45) is less than a specific value, tabs (46-49) for connecting the battery cells come into contact with the fastening member (60).

Description

Battery module

[0001] This invention relates to a battery module.

[0002] A film-cased battery equipped with a safety mechanism is known (see, for example, Patent Document 1). This safety mechanism electrically connects the electrode tabs to release energy from the cell when the film casing expands beyond a predetermined level. This safety mechanism includes a first conductor connected to the positive electrode tab, a second conductor connected to the negative electrode tab, and an insulator fixed to the outer surface of the film casing and interposed between the first and second conductors.

[0003] Japanese Patent Publication No. 2016-110959

[0004] When the above safety mechanism is applied to a battery in which lithium metal or lithium alloy is deposited on the negative electrode, there is a problem in that even normal cells in such batteries undergo large volume changes due to expansion and contraction, making it difficult to detect and process abnormal cells effectively.

[0005] The problem that this invention aims to solve is to provide a battery module capable of detecting or handling abnormalities in a battery cell having a negative electrode containing lithium metal or a lithium alloy.

[0006] The present invention solves the above problem by ensuring that when the distance between the centers of the battery cells in a laminated structure where the number of battery cells is equal to or greater than the number of elastic bodies falls below a predetermined value, the tabs connecting the battery cells come into contact with the fastening member.

[0007] According to the present invention, when the distance between the centers of battery cells falls below a predetermined value, the tabs connecting the battery cells come into contact with the fastening member, making it possible to detect or process abnormalities in battery cells equipped with a negative electrode containing lithium metal or a lithium alloy.

[0008] Figure 1 is a block diagram of a battery system in an embodiment of the present invention. Figure 2(a) is a cross-sectional view showing a battery module in an embodiment of the present invention when there are no abnormal battery cells, and Figure 2(b) is a cross-sectional view showing a battery module in an embodiment of the present invention when there are abnormal battery cells. Figure 3 is a graph showing the difference in thickness between normal and abnormal battery cells. Figure 4 is a graph showing the relationship between SOC and the distance between the centers of battery cells, with Figure 4(a) showing the relationship when the number of battery cells is less than the number of elastic bodies, Figure 4(b) showing the relationship when the number of battery cells is the same as the number of elastic bodies, and Figure 4(c) showing the relationship when the number of battery cells exceeds the number of elastic bodies. Figure 5(a) is a cross-sectional view showing a first modified example of a battery module in an embodiment of the present invention, and Figure 5(b) is a cross-sectional view showing a second modified example of a battery module in an embodiment of the present invention. Figure 6 is a cross-sectional view showing a third modified example of a 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(a) is a cross-sectional view showing the battery module 4 in this embodiment when there are no abnormal battery cells.

[0011] The battery system 1 comprises a controller 2, a DC-DC converter 3, a battery module 4, and a discharge unit 8. The controller 2 is a battery control unit (BCU). The controller 2 determines the SOC usage range of the multiple battery cells 41 to 45 contained in the battery module 4 according to the state of the battery cells 41 to 45. The controller 2 is composed of memory such as ROM or RAM, and a processor such as a CPU.

[0012] The DC-DC converter 3 is a power conversion device that converts the voltage input from the battery module 4 into a predetermined voltage and outputs power to a load such as a motor. The DC-DC converter 3 also converts the voltage input from a load such as a motor or a charging device into a predetermined voltage and outputs power to the battery module 4. The DC-DC converter 3 is controlled by the controller 2. The battery module 4 is connected to the input side of the DC-DC converter 3, and the load is connected to the output side of the DC-DC converter 3. The load is a power grid, etc. In other words, the battery module 4 is electrically connected to the load via the DC-DC converter 3.

[0013] As shown in Figure 2(a), the battery module 4 includes a laminate 40, a binding member 60, and a voltage detection unit 70. The laminate 40 is located inside the binding member 60. The laminate 40 comprises a plurality of (five in this example) battery cells 41-45, a plurality of (four in this example) tabs 46-49, and a plurality of (four in this example) elastic bodies 51-54.

[0014] In this embodiment, a plurality of battery cells 41 to 45 and a plurality of elastic bodies 51 to 54 are stacked alternately along the stacking direction (a direction perpendicular to the main surfaces of the battery cells 41 to 45 or a direction perpendicular to the main surfaces of the elastic bodies 51 to 54).

[0015] In this embodiment, the number of battery cells is greater than the number of elastic bodies, but the number of battery cells may be the same as the number of elastic bodies. Although not specifically shown, in this case, unlike in this embodiment, the elastic body is located at one end of the laminate 40.

[0016] The battery cells 41-45 are lithium-ion secondary batteries. Although not specifically shown, the battery cells 41-45 include a positive electrode, a negative electrode, and an electrolyte. The negative electrode contains lithium metal. In the battery cells 41-45, 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 41-45. 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 41-45. The negative electrode may also contain a lithium metal alloy. Furthermore, this lithium-ion secondary battery is not particularly limited, but a solid-state battery can be given as an example. This solid-state battery has an electrolyte layer containing a solid electrolyte. This electrolyte layer may also contain a polymer electrolyte or a liquid electrolyte.

[0017] Each of the battery cells 41 to 46 is electrically connected by tabs 46 to 49. These tabs 46 to 49 are inter-cell tabs that connect the positive terminals (positive lead tabs) 41a to 45a and the negative terminals (negative lead tabs) 41b to 45b of the battery cells 41 to 46. The tabs 46 to 49 are plate-shaped members made of a metal material and extend along the stacking direction of the tabs 46 to 49.

[0018] Tabs 46-49 represent the distance d between the centers of battery cells 41-46. １ ~d ４ The tabs are designed to buckle and bend outward when the distance between the centers of the battery cells 41 and 46 is less than a predetermined value. Such tabs 46 to 49 are not particularly limited, but can be manufactured by adjusting the thickness, length, width, and material type of the tabs 46 to 49. Alternatively, the tabs 46 to 49 may be provided with grooves, slits, etc., to control the distance between the centers of the battery cells 41 to 46 d １ ~d ４ It may be designed to buckle if the value is below a predetermined value.

[0019] The elastic bodies 51 to 54 are elastic sheet members. When no load is applied, this sheet member has a substantially constant thickness over substantially the entire area of the sheet member. The elastic bodies 51 to 54 are interposed between the battery cells 41 to 45, and press the battery cells 41 to 45 by elastic force.

[0020] The fastening member 60 accommodates the laminated body 40 and fastens the laminated body 40. The fastening member 60 in the present embodiment presses the laminated body 40 toward the lamination direction of the laminated body 40 to apply a binding pressure. The fastening member 60 is not particularly limited, but a laminate film including a metal foil can be exemplified. This laminate film may be an exterior body of a battery. Alternatively, the fastening member 60 may be a conductive member accommodated inside the exterior body.

[0021] As described above, the battery module 4 according to the present embodiment pressurizes and restrains the battery cells 41 to 45 by means of the aforementioned elastic bodies 51 to 54 and the fastening member 60. That is, the battery module 4 according to the present embodiment is a battery module including a passive mechanism that does not actively control the binding pressure on the battery cells 41 to 45 using power (for example, electric energy, etc.). In other words, in this battery module 4, the binding pressure passively changes along with the expansion and contraction of the battery cells 41 to 45.

[0022] FIG. 3 is a graph showing the difference in thickness between a normal battery cell and an abnormal battery cell. According to the findings of the inventors of the present invention, when a battery cell is normal, as shown in FIG. 3, the thickness t for each SOC of the battery cells 41 to 45 included in the laminated body 40 １ to t ５ have substantially the same thickness as each other (t １ =t ２ =t ３ =t ４ =t ５ ). On the other hand, as shown in FIG. 3, the thickness of a battery cell in which an abnormality has occurred differs from that of a normal battery cell in how the thickness changes, and becomes thinner than the thickness of a normal battery cell (t １ =t ２ =t ４ =t ５ >t ３ ).

[0023] Furthermore, based on the findings described above, the inventors of the present invention have found that a difference occurs in the change of the center-to-center distance between battery cells depending on the magnitude relationship between the number of battery cells and the number of elastic bodies. FIG. 4 is a graph showing the relationship between SOC and the center-to-center distance between battery cells. FIG. 4(a) is a graph showing the above relationship when the number of battery cells is less than the number of elastic bodies, FIG. 4(b) is a graph showing the above relationship when the number of battery cells is equal to the number of elastic bodies, and FIG. 4(c) is a graph showing the above relationship when the number of battery cells exceeds the number of elastic bodies. In these graphs, the stacked body includes five battery cells, and the center-to-center distance between the battery cells when an abnormality occurs in the third battery cell from the end is shown.

[0024] As shown in FIG. 4(a), when an abnormality occurs in the third battery cell from the end (hereinafter, the third battery cell from the end is referred to as an abnormal cell), the thickness of the abnormal cell becomes relatively thin, so that d at 100% SOC ２ and d ３ have smaller values than those in a normal state. However, when the number of battery cells is less than the number of elastic bodies, d at 100% SOC in an abnormal state ２ and d ３ have larger values than d at 0% SOC and 50% SOC in a normal state ２ and d ３ .

[0025] In contrast, as shown in FIG. 4(b) and FIG. 4(c), when the number of battery cells is greater than or equal to the number of elastic bodies, d at 100% SOC in an abnormal state ２ and d ３ have smaller values than d at 0% SOC and 50% SOC in a normal state ２ and d ３ . Therefore, when the number of battery cells is greater than or equal to the number of elastic bodies and the center-to-center distance between the battery cells is less than a predetermined value, by designing the tabs connecting adjacent battery cells such that the tabs contact the fastening member, an abnormality of a battery cell can be detected.

[0026] It should be noted that the predetermined value referred to herein is not particularly limited, and is, for example, the inter-center distance A (predetermined value A) shown in the graphs of FIG. 4(b) and FIG. 4(c). This predetermined value A is d when charging and discharging the laminated body 40 in which all battery cells are normal １ to d ４ may be the minimum value. More specifically, the predetermined value is the inter-center distance between adjacent battery cells when the SOC of the battery cell is at the maximum usage value ("SOC 100%" in FIG. 3 and FIGS. 4(a) to 4(c)), and the maximum usage value may be the maximum value in the usage range of the SOC of the battery cell defined by the controller 2.

[0027] Based on the above findings, as described above, the tabs 46 to 49 are arranged such that the inter-center distance d between adjacent battery cells 41 to 45 １ to d ４ is set to buckle and bend to protrude outward when the distance is less than the predetermined value A. FIG. 2(b) is a cross-sectional view showing the battery module 4 according to the present embodiment when there is an abnormal battery cell 43. In FIG. 2(b), for convenience of explanation, the case where the battery cell 43 is an abnormal cell is illustrated, but the present invention is not limited thereto.

[0028] As shown in FIG. 2(b), in this laminated body 40, the thickness of the abnormal battery cell 43 is smaller than that of the other battery cells 41, 42, 44, and 45. Therefore, the inter-center distance d between the center of the battery cell 41 and the center of the battery cell 42 １ , the inter-center distance d between the center of the battery cell 42 and the center of the battery cell 43 ２ is smaller. Similarly, compared to the inter-center distance d １ , the inter-center distance d between the center of the battery cell 43 and the center of the battery cell 44 ３ is smaller. Further, compared to the inter-center distance d between the center of the battery cell 44 and the center of the battery cell 45 ４ , the inter-center distance d ２ , d ３ are smaller. It should be noted that in the present embodiment, the center of a battery cell refers to the center of the battery cell in the thickness direction. The inter-center distance is the distance between straight lines that pass through the aforementioned centers and are parallel to the main surface of the battery cell.

[0029] In this way, if an abnormality occurs in battery cell 43, the distance d between the centers of battery cell 43 and the adjacent battery cells 42 and 44 is... ２ d ３ It becomes smaller. And the distance d between centers ２ However, for example, when the value falls below the predetermined value A mentioned above, the tab 47 buckles, and the distance d between centers buckles. ３ However, when the value falls below a predetermined value A, the tab 48 buckles. In this embodiment, the buckled tab 48 comes into contact with the fastening member 60 and is electrically connected to the fastening member 60. For example, if the fastening member 60 is an exterior body made of laminate film, the buckled tab 48 comes into contact with the metal foil of the laminate film.

[0030] When the tab 48 comes into contact with the securing member 60, an abnormality in the battery cell can be detected, for example, by utilizing the voltage difference as described below. In this embodiment, the voltage detection unit 70 detects the voltage difference between the positive terminal 43a of the battery cell 43 and the securing member 60. The voltage detection unit 70 outputs the detected voltage to the controller 2. The voltage detection unit 70 may also detect the voltage difference between the positive and negative terminals other than the positive terminal 43a of the battery cell 43 and the securing member 60.

[0031] Here, for example, let's assume the voltage of one battery cell is 4V. As shown in Figure 2(a), when the tab 48 is not in contact with the fixing member 60, the voltage detected by the voltage detection unit 70 is 0V. On the other hand, as shown in Figure 2(b), when the tab 48 is in contact with the fixing member 60, the voltage detected by the voltage detection unit 70 is 8V. Therefore, based on this voltage detection result, the controller 2 can determine that there is an abnormality in either the battery cell 43 or the battery cell 44.

[0032] Furthermore, the controller 2 discharges the battery cell 43 or battery cell 44 that may be experiencing an abnormality using the discharge unit 8 shown in Figure 1. By discharging the battery cell, the state of the battery cell can be changed from a state in which lithium is easily moved to a safe state in which lithium is less easily moved. Such a discharge unit 8 includes a load circuit that is electrically connected to each of the battery cells 41 to 45.

[0033] With the battery system 1 described above, it is possible to detect abnormalities in the battery cells 41 to 45 and perform processing (discharge processing) in response to such abnormalities.

[0034] Furthermore, in the above-described embodiment, the voltage of the positive terminal 43a of the battery cell 43 is used, but as shown in Figure 5(a), abnormalities may also be detected by using the voltage of the terminal of a battery cell located at the end of the stacked body 40. Figure 5(a) is a cross-sectional view showing a first modified example of the battery module 4 in this embodiment. As shown in Figure 5(a), the voltage detection unit 70 is connected to the positive terminal 45a of the battery cell 45. This positive terminal 45a is a module terminal for connecting to the outside of the battery module 4. Since such a module terminal is connected to a busbar (not shown), the voltage can be easily extracted by detecting the voltage near the busbar.

[0035] Furthermore, although the above-described embodiment uses one voltage difference to detect abnormalities, as shown in Figure 5(b), two voltage differences may be used to detect abnormalities. Figure 5(b) is a cross-sectional view showing a second modified example of the battery module 4 in this embodiment. As shown in Figure 5(b), this battery module 4 is equipped with two voltage detection units 70a and 70b. The voltage detection unit 70a in this embodiment corresponds to an example of the "first detection unit" in the present invention, and the voltage detection unit 70b in this embodiment corresponds to an example of the "first detection unit" in the present invention.

[0036] The voltage detection unit 70a detects the voltage difference between the positive terminal 56a of the battery cell 56 and the securing member 60. On the other hand, the voltage detection unit 70b detects the voltage difference between the negative terminal 41b of the battery cell 41 and the securing member 60. In other words, in this embodiment, abnormalities are detected by utilizing the voltage of the module terminals of the battery cells located at both ends within the battery cells of the laminate 40.

[0037] For example, suppose the voltage of one battery cell is 4V. Then, if the voltage difference detected by the voltage detection unit 70a is 8V, the controller 2 can determine that there is a possibility of an abnormality in battery cell 45 or battery cell 55. At the same time, if the voltage difference detected by the voltage detection unit 70b is 4V, the controller 2 can determine that there is a possibility of an abnormality in battery cell 42 or battery cell 41. In this way, it is possible to detect multiple abnormal cells and process those abnormalities.

[0038] Furthermore, although the above-described embodiment uses the discharge unit 8 to handle abnormalities, discharge may also be performed by short-circuiting the battery cell and the securing member externally, as shown in Figure 6. Figure 6 is a cross-sectional view showing a third modified example of the battery module in this embodiment. In this third modified example, unlike the above-described embodiment, when an abnormality occurs in the battery cell 43, not only the buckled tab 48 but also the buckled tab 47 is set to come into contact with the securing member 60.

[0039] In other words, when both the positive and negative electrode tabs 47 and 48 connected to the malfunctioning battery cell 43 come into contact with the securing member 60, an external short circuit occurs between the battery cell 43 and the securing member 60. As a result, a current I flows through the securing member 60, allowing the malfunctioning cell to be discharged. In this way, the malfunction can be resolved by discharging the malfunctioning cell using an external short circuit with the securing member 60.

[0040] 1...Battery system 2...Controller 3...DC-DC converter 4...Battery module 40...Laminate 41-45, 55, 56...Battery cells 41a-45a...Positive terminal (positive lead tab) 41b-45b...Negative terminal (negative lead tab) 46-49...Tabs (inter-cell tabs) 51-54...Elastic body 60...Binding part 70...Voltage detection part 8...Discharge part

Claims

1. A battery module comprising: a laminate formed by alternately stacking a plurality of battery cells having a negative electrode containing lithium metal or a lithium alloy, and a plurality of elastic bodies; and a fastening member for fastening the laminate, wherein the number of battery cells is equal to or greater than the number of elastic bodies, and tabs connecting the battery cells to each other contact the fastening member when the distance between the centers of the battery cells is less than a predetermined value.

2. A battery module according to claim 1, wherein the battery module comprises a positive electrode tab attached to the positive electrode terminal of the battery cell and a negative electrode tab attached to the negative electrode terminal of the battery cell, wherein the positive electrode tab and the negative electrode tab contact the fixing member when the distance between the centers is less than a predetermined value.

3. A battery module according to claim 1, wherein the battery module includes a voltage detection unit that detects a first voltage at one terminal of the battery cell and a second voltage at the fixing member, and the presence or absence of an abnormality in the battery cell is determined based on the difference between the first and second voltages detected by the voltage detection unit.

4. A battery module according to claim 3, wherein the voltage detection unit detects the voltage at the terminal of a battery cell located at one end among the plurality of battery cells as the first voltage.

5. A battery module according to claim 3 or 4, wherein a battery cell determined to be abnormal based on the detection result of the voltage detection unit is discharged.

6. A battery module according to claim 3 or 4, wherein the voltage detection unit includes a first detection unit that detects the voltage at the terminal of a battery cell located at one end of the plurality of battery cells as the first voltage, and a second detection unit that detects the voltage at the terminal of a battery cell located at the other end of the plurality of battery cells as the first voltage.

7. A battery module according to any one of claims 1 to 6, wherein the predetermined value is the distance between the centers of the battery cells when the SOC of the battery cells is at its maximum usage value, and the maximum usage value is the maximum value within the usage range of the SOC of the battery cells.

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