Battery module assembly method

Abstract

The goal is to improve the volumetric energy density in the assembly method of battery modules. [Solution] In the molding process, a superelastic alloy restraining member 13 is molded to pressurize and restrain a plurality of stacked battery cells 12 in the stacking direction, so that it takes on a pressurized shape relative to the battery cells 12 when the temperature is above the reverse transformation completion temperature Af. In the cooling and expansion process, the molded restraining member 13 is cooled to below the reverse transformation start temperature As, which is lower than the reverse transformation completion temperature Af, and the restraining member 13 is expanded until it takes on a non-pressurized shape relative to the battery cells 12. In the restoration process, the expanded restraining member 13 is heated to above the reverse transformation completion temperature Af, thereby restoring the restraining member 13 to its pressurized shape.

Description

Technical Field

[0001] The present invention relates to a method for assembling a battery module.

Background Art

[0002] 11> In all-solid-state batteries disclosed in Patent Document 1, since a laminate including a positive electrode, a solid electrolyte layer, and a negative electrode contracts during discharge, a piston device is controlled by a motor according to the discharge voltage to adjust the restraint pressure on the laminate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If a mechanism for pressurizing the battery module, such as a piston device controlled by a motor, is large, the volumetric energy density of the battery module will decrease. The problem of the present invention is to improve the volumetric energy density in the method for assembling a battery module.

Means for Solving the Problems

[0005] According to one aspect of the present invention, a method for assembling a battery module includes a forming step, a temperature-lowering expansion step, and a restoring step. In the forming step, a restraining member made of a superelastic alloy that becomes a pressurized shape is formed on the battery cell when the temperature is equal to or higher than the end temperature of reverse transformation in order to pressurize and restrain a plurality of stacked battery cells in the stacking direction. In the temperature-lowering expansion step, the formed restraining member is cooled to a temperature lower than the end temperature of reverse transformation and lower than the start temperature of reverse transformation, and the restraining member is expanded until it becomes a non-pressurized shape with respect to the battery cell. In the restoring step, the expanded restraining member is heated to a temperature equal to or higher than the end temperature of reverse transformation, so that the restraining member is restored until it becomes a pressurized shape. [Effects of the Invention]

[0006] According to the present invention, since multiple battery cells are pressurized by a superelastic alloy, a mechanism such as a piston device is not required. Therefore, it is possible to improve the volumetric energy density in the battery module. [Brief explanation of the drawing]

[0007] [Figure 1] This is a diagram showing a battery module. [Figure 2] This diagram shows how to assemble a battery module. [Figure 3] This is a stress-strain diagram. [Figure 4] This diagram shows the cooling process in the extended cooling step. [Figure 5] This diagram shows the extended processing of the cooling extension step. [Figure 6] This is a diagram showing the restoration process. [Figure 7] This figure shows the cooling extension process of the second embodiment. [Figure 8] This figure shows the cooling extension process of the third embodiment. [Figure 9] This figure shows the cooling extension process of the fourth embodiment. [Figure 10] This figure shows the heating time of the restraining member. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings. Note that the drawings are schematic and may differ from actual examples. Furthermore, the following embodiments are illustrative examples of devices and methods for realizing the technical concept of the present invention, and do not limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0009] 《First Embodiment》 "composition" Figure 1 shows a battery module 11. Here, the three orthogonal directions are defined as the stacking direction, the height direction, and the width direction, and the battery module 11 is shown as viewed from the width direction. The battery module 11 is installed in electric vehicles and hybrid vehicles as a vehicle power source and comprises multiple battery cells 12 and a restraining member 13. The battery cell 12 has a thin laminate structure with excellent cooling properties, and is constructed by stacking multiple cells perpendicular to the surface, resulting in a rectangular shape that is longer in the stacking direction when viewed from the width direction. The battery cell 12 expands and contracts mainly in the stacking direction during charging and discharging. Expansion occurs during charging, and contraction occurs during discharging.

[0010] The restraining member 13 is formed into an endless rectangular shape that surrounds the battery cell 12 when viewed from the width direction, and multiple battery cells 12 are bundled together into a module while being pressed from the stacking direction and the height direction. When viewed from the width direction, the four corners of the restraining member 13 are rounded to prevent stress concentration. The restraining member 13 is a superelastic alloy exhibiting superelastic properties. Superelastic properties are the characteristic that even if deformed by a load, it returns to its original shape when the load is removed, and the recoverable strain is in the range of about 5-6%. Superelastic alloys are either titanium (Ti)-nickel (Ni) alloys or copper-based alloys. Examples of copper-based alloys include copper (Cu)-aluminum (Al)-manganese (Mn) alloys and copper (Cu)-zinc (Zn)-aluminum (Al) alloys. The restraining member 13 sandwiches the battery cell 12 from both sides in the stacking direction and both sides in the height direction, and restrains the battery cell 12 while pressing it with the tension of the superelastic alloy.

[0011] Figure 2 shows the assembly method of the battery module 11. (a) in the figure shows the forming process. In the forming process, in order to press and restrain a plurality of stacked battery cells 12 in the stacking direction, a restraining member 13 made of a superelastic alloy that takes a pressurized shape is formed on the battery cells 12 when the temperature reaches above the reverse transformation end temperature Af. (b) in the figure shows the temperature reduction and expansion process. In the temperature reduction and expansion process, the formed restraining member 13 is cooled to a temperature below the reverse transformation start temperature As, which is lower than the reverse transformation end temperature Af, and the restraining member 13 is expanded until it takes a non-pressurized shape with respect to the battery cells 12. (c) in the figure shows the restoration process. In the restoration process, the expanded restraining member 13 is heated to a temperature above the reverse transformation end temperature Af, and the restraining member 13 is restored to the pressurized shape by the shape memory effect.

[0012] Figure 3 is a stress-strain diagram. (a) in the figure shows the relationship between stress and strain when the temperature T of the superelastic alloy is below the reverse transformation start temperature As. The superelastic alloy has a linear elastic region, and when deformed beyond it, strain remains even after unloading. The recoverable strain is in the range of about 0.2 to 0.3%. When the superelastic alloy is heated to a temperature above the reverse transformation end temperature Af, it is restored to its original shape by the shape memory effect. (b) in the figure shows the relationship between stress and strain when the temperature T of the superelastic alloy is above the reverse transformation end temperature Af. When the superelastic alloy is above the reverse transformation end temperature Af, even if it is loaded and deformed, it can return to its original shape by superelasticity when unloaded, which is a non-linear elastic deformation. The reverse transformation end temperature Af can be adjusted according to the composition of the superelastic alloy, and it needs to be set lower than the lower limit value T MIN of the operating temperature range in the battery cells 12. The lower limit value T MIN of the operating temperature range in the battery cells 12 is, for example, about -15°C. Therefore, the composition of the superelastic alloy is adjusted so that the reverse transformation end temperature Af is, for example, less than -20°C. In the case of a Ti-Ni alloy, as the Ni concentration increases, the reverse transformation end temperature Af decreases.

[0013] Figure 4 is a diagram showing the temperature reduction treatment in the temperature reduction and expansion process. Here, by sending cold air from the cold air blower 16 to the restraint member 13, the temperature is lowered below the reverse transformation start temperature As. The cold air blower 16 is a fan that supplies cold air to the entire restraint member 13, and for example, nitrogen gas is used for the cold air. If the battery cell 12 is disposed inside the restraint member 13, the cold air is prevented from hitting the battery cell 12. For example, the cold air is supplied only to the outside of the restraint member 13, or a partition is provided between the restraint member 13 and the battery cell 12 to control the flow path of the cold air.

[0014] FIG. 5 is a diagram showing the expansion process of the temperature lowering expansion process. Here, the restraint member 13 is expanded by the robot hand 17. The robot hand 17 expands the restraint member 13 by pulling the portions other than the four corners when viewed in the width direction. In (a) in the figure, each side extending in the longitudinal direction is pulled from both sides in the extending direction. In (b) in the figure, each side extending in the short side direction is pulled from both sides in the extending direction. Here, the case of executing in the order from (a) to (b) is shown, but it is not limited thereto. That is, it may be executed in the order from (b) to (a), or (a) and (b) may be executed simultaneously.

[0015] FIG. 6 is a diagram showing the restoration process. Here, the battery cell 12 is disposed inside the restraint member 13, and by sending warm air from the warm air blower 18 to the restraint member 13, the temperature is raised to the reverse transformation end temperature Af or higher. The warm air blower 18 is a fan that supplies warm air to the entire restraint member 13, and for example, a PTC heater is used as the heat source. Since the battery cell 12 is disposed inside the restraint member 13, the warm air is prevented from hitting the battery cell 12. For example, the warm air is supplied only to the outside of the restraint member 13 to control the flow path of the warm air.

[0016] <<Function and Effect>> Next, the main function and effect of the first embodiment will be described. (1) The assembly method for the battery module 11 includes a molding step, a cooling and expansion step, and a restoration step. In the molding step, a superelastic alloy restraint member 13 is molded to pressurize and restrain a plurality of stacked battery cells 12 in the stacking direction, so that when the temperature is above the reverse transformation completion temperature Af, it takes on a pressurized shape relative to the battery cells 12. In the cooling and expansion step, the molded restraint member 13 is cooled to below the reverse transformation start temperature As, which is lower than the reverse transformation completion temperature Af, and the restraint member 13 is expanded until it takes on a non-pressurized shape relative to the battery cells 12. In the restoration step, the expanded restraint member 13 is heated to above the reverse transformation completion temperature Af, thereby restoring the restraint member 13 to its pressurized shape. In this way, since the plurality of battery cells 12 are pressed by a superelastic alloy, a mechanism such as a piston device is not required. Therefore, the volumetric energy density in the battery module 11 can be improved.

[0017] (2) In the cooling extension process, cold air is sent to the restraining member 13 to cool it down to below the reverse transformation start temperature As. This makes it possible to easily cool only the restraining member 13 by controlling the flow path. In other words, it is possible to prevent the battery cell 12 from being cooled unintentionally and to maintain the proper charge and discharge characteristics of the battery cell 12. (3) The restraining member 13 is formed into an endless rectangular shape that surrounds the battery cells 12 when viewed from a direction perpendicular to the stacking direction of the battery cells 12. In the cooling expansion process, the restraining member 13 is expanded by pulling on parts other than the four corners when viewed from a direction perpendicular to the stacking direction of the battery cells 12. This suppresses deformation of the four corners of the restraining member 13. The four corners of the restraining member 13 affect the perpendicularity of the corners and the parallelism of the sides, so high precision is required. In other words, by suppressing deformation of the four corners, the battery cells 12 can be uniformly pressurized, and the appropriate charge and discharge characteristics of the battery cells 12 can be maintained.

[0018] (4) In the cooling expansion process, each side of the battery cell 12 is pulled from both sides in the extension direction when viewed from a direction perpendicular to the stacking direction. This reliably prevents deformation of the four corners of the restraining member 13. (5) The superelastic alloy has a reverse transformation completion temperature Af that is lower than the operating temperature range T in the battery cell 12. MIN It is set to less than this value. This makes it possible to achieve superelasticity of the restraining member 13 within the normal operating temperature range. (6) The superelastic alloy is either a titanium-nickel alloy or a copper-based alloy. By selecting an appropriate alloy in this way, the proper charge and discharge characteristics of the battery cell 12 can be maintained.

[0019] 《Second Embodiment》 "composition" The second embodiment has the same configuration as the first embodiment described above, except that it shows another aspect of the cooling extension process. Therefore, common parts are denoted by the same reference numerals, and a detailed explanation is omitted. Figure 7 shows the cooling extension process of the second embodiment. Here, a restraining member 13 is placed inside the mold 21, and the restraining member 13 is expanded while its temperature is lowered by pushing it out from the inside with a cooled fluid. The mold 21 is formed into an endless rectangular shape that surrounds the restraining member 13 when viewed from the width direction, and its internal dimensions in the stacking direction and height direction correspond to its external dimensions in the stacking direction and height direction when the restraining member 13 is expanded. For example, liquid nitrogen or nitrogen gas is used as the cooled fluid. If a battery cell 12 is placed inside the restraining member 13, a partition is provided to prevent the cooled fluid from coming into contact with the battery cell 12.

[0020] Effects and Benefits Next, the main effects and advantages of the second embodiment will be described. (1) The restraining member 13 is formed in an endless shape that surrounds the battery cell 12 when viewed from a direction perpendicular to the stacking direction of the battery cell 12. In the cooling and expansion process, the restraining member 13 is expanded while being cooled by pushing it out from the inside with a cooled fluid. This allows the cooling and expansion processes for the restraining member 13 to be performed simultaneously, thereby shortening the cycle time. By using a fluid, the restraining member 13 can be uniformly pushed out from the inside. By controlling the flow path, only the restraining member 13 can be easily cooled. In other words, it is possible to prevent the battery cell 12 from being cooled unintentionally and to maintain the proper charge and discharge characteristics of the battery cell 12. (2) In the cooling expansion process, the restraining member 13 is placed inside the mold 21, and the restraining member 13 is pushed out from the inside with the cooled fluid. This makes it possible to arbitrarily set the dimensions of the restraining member 13 after expansion. Other effects and benefits resulting from the common configuration are the same as those of the first embodiment described above.

[0021] Third Embodiment "composition" The third embodiment has the same configuration as the first embodiment described above, except that it shows another aspect of the cooling extension process. Therefore, common parts are denoted by the same reference numerals, and a detailed explanation is omitted. Figure 8 shows the cooling extension process of the third embodiment. Figure (a) shows a jig 31 with a truncated pyramidal tip. Figure (b) shows the cooled jig 31 and restraining member 13 viewed from the width direction. In the third embodiment, the cooled jig 31 is inserted inside the restraining member 13 and the restraining member 13 is pushed out from the inside, thereby expanding the restraining member 13 while cooling it down. It is desirable to have the battery cell 12 waiting behind the jig 31 so that when it passes through the jig 31, the battery cell 12 is positioned inside the restraining member 13.

[0022] Effects and Benefits Next, the main effects and advantages of the third embodiment will be described. (1) The restraining member 13 is formed in an endless shape that surrounds the battery cell 12 when viewed from a direction perpendicular to the stacking direction of the battery cell 12. In the cooling and expansion process, a cooled jig with a frustoconical tip is inserted into the inside of the restraining member 13 and the restraining member 13 is pushed out from the inside, thereby expanding the restraining member 13 while cooling it. This allows the cooling and expansion processes for the restraining member 13 to be performed simultaneously, shortening the cycle time. By using the jig 31, the restraining member 13 can be uniformly pushed out from the inside. By using the jig 31, only the restraining member 13 can be reliably cooled. In other words, the battery cell 12 is prevented from cooling down, and the proper charge and discharge characteristics of the battery cell 12 can be maintained. Other effects and benefits resulting from the common configuration are the same as those of the first embodiment described above.

[0023] 《Fourth Embodiment》 "composition" The fourth embodiment has the same configuration as the first embodiment described above, except that it shows another aspect of the cooling extension process. Therefore, common parts are denoted by the same reference numerals, and a detailed explanation is omitted. Figure 9 shows the cooling extension process of the fourth embodiment. Here, the battery cell 12 is kept warm while the restraining member 13 is cooled. Figure (a) shows a hot air blower 41 as a warming mechanism. The hot air blower 41 keeps the battery cell 12 warm above its cold resistance temperature Tc by blowing warm air. The cold resistance temperature Tc of the battery cell 12 is, for example, around -20°C. Figure (b) shows a heating coil 42 as a warming mechanism. When energized, the heating coil 42 keeps the battery cell 12 warm above its cold resistance temperature Tc by electromagnetic induction heating.

[0024] Effects and Benefits Next, the main effects and advantages of the fourth embodiment will be described. (1) In the cooling expansion process, the battery cells 12 are placed inside the restraining member 13, and the battery cells 12 are kept warm above the cold resistance temperature Tc using a hot air fan 41 or heating coil 42, and the restraining member 13 is cooled to below the reverse transformation start temperature As. This reliably prevents the battery cells 12 from being cooled unintentionally and maintains the proper charge and discharge characteristics of the battery cells 12. Other effects and benefits resulting from the common configuration are the same as those of the first embodiment described above.

[0025] 《Fifth Embodiment》 "composition" The fifth embodiment has the same configuration as the first embodiment described above, except that it shows another aspect of the restoration process. Therefore, common parts are denoted by the same reference numerals, and a detailed explanation is omitted. Here, the process of sending hot air from the hot air fan 18 to the restraining member 13 is omitted, and instead, the cooling capacity that cools the restraining member 13 in the cooling extension process is gradually weakened, thereby raising the temperature of the restraining member 13 to above the reverse transformation completion temperature Af.

[0026] Figure 10 shows the heating time of the restraining member 13. The graph shows the time elapsed since the restraint member 13 was heated on the horizontal axis and the temperature of the restraint member 13 on the vertical axis. Characteristic line L1 shows the case where the restraint member 13 is heated using the hot air blower 18 during the restoration process. When the hot air blower 18 is used, the restraint member 13 is heated to above the reverse transformation completion temperature Af in the shortest time. Characteristic line L2 shows the case where the restraint member 13 is expanded and then left at room temperature during the cooling and expansion process. When left at room temperature, it reaches the reverse transformation completion temperature Af relatively quickly, though not as quickly as when using the hot air blower 18. Characteristic line L3 shows the case where the cooling capacity used to cool the restraint member 13 is gradually reduced during the cooling and expansion process. When the cooling capacity is reduced, the restraint member 13 is heated to above the reverse transformation completion temperature Af in the longest time.

[0027] Effects and Benefits Next, the main effects and advantages of the fifth embodiment will be described. (1) In the restoration process, the cooling capacity used to cool the restraining member 13 in the cooling expansion process is gradually reduced, thereby raising the temperature of the restraining member 13 to above the reverse transformation completion temperature Af. This prevents the restraining member 13 from being subjected to shock due to abrupt restoration and maintains the proper charge and discharge characteristics of the battery cell 12. In other words, if a hot air fan 18 is used or the battery is left at room temperature, the temperature will quickly reach the reverse transformation completion temperature Af, which may cause the battery cell 12 to be subjected to shock due to the abrupt restoration of the restraining member 13. Other effects and benefits resulting from the common configuration are the same as those of the first embodiment described above.

[0028] Although the above description has been made with reference to a limited number of embodiments, the scope of the rights is not limited to these, and modifications of the embodiments based on the above disclosure will be obvious to those skilled in the art. Each embodiment and modification can be adopted in any combination. [Explanation of symbols]

[0029] 11...Battery module, 12...Battery cell, 13...Restraining member, 16...Air cooler, 17...Robot hand, 18...Hot air blower, 21...Mold, 31...Jig, 41...Hot air blower, 42...Heating coil

Claims

1. A molding step in which a restraining member made of a superelastic alloy is formed to apply pressure to multiple stacked battery cells in the stacking direction, in order to restrain the battery cells by applying pressure to them, when the temperature is above the reverse transformation completion temperature, A cooling and expansion step in which the molded restraint member is cooled to a temperature lower than the reverse transformation start temperature, which is lower than the reverse transformation completion temperature, and the restraint member is expanded until it is in a non-pressurized shape relative to the battery cell, A method for assembling a battery module, characterized by including a restoration step of restoring the restraint member to the pressurized shape by raising the temperature of the expanded restraint member to a temperature above the reverse transformation completion temperature.

2. The method for assembling a battery module according to claim 1, characterized in that the temperature is lowered to below the reverse transformation start temperature by sending cold air to the restraining member in the temperature reduction extension step.

3. The restraining member is formed into an endless rectangular shape that surrounds the battery cells when viewed from a direction perpendicular to the stacking direction of the battery cells. The battery module assembly method according to claim 1, characterized in that the restraining member is expanded in the cooling expansion step by pulling on parts other than the four corners when viewed from a direction perpendicular to the stacking direction of the battery cells.

4. The battery module assembly method according to claim 3, characterized in that, in the cooling expansion step, each side is pulled from both sides in the extension direction when viewed from a direction perpendicular to the stacking direction of the battery cells.

5. The restraining member is formed in an endless shape that surrounds the battery cell when viewed from a direction perpendicular to the stacking direction of the battery cell, The method for assembling a battery module according to claim 1, characterized in that the restraining member is expanded while its temperature is lowered by pushing it out from the inside with a cooled fluid during the cooling expansion step.

6. The method for assembling a battery module according to claim 5, characterized in that in the cooling and expanding step, the restraining member is placed inside the mold and the cooled fluid is used to push and expand the restraining member from the inside.

7. The restraining member is formed in an endless shape that surrounds the battery cell when viewed from a direction perpendicular to the stacking direction of the battery cell, The method for assembling a battery module according to claim 1, characterized in that in the cooling and expanding step, a cooled jig having a frustoconical tip is inserted into the inside of the restraining member and the restraining member is pushed open from the inside, thereby expanding the restraining member while cooling it down.

8. The method for assembling a battery module according to claim 1, characterized in that in the cooling expansion step, the battery cells are placed inside the restraining member, the battery cells are kept at a temperature above the cold resistance temperature using a heat retention mechanism, and the restraining member is cooled to a temperature below the reverse transformation start temperature.

9. The battery module assembly method according to claim 1, characterized in that, in the restoration step, the restorative step is performed by gradually weakening the cooling capacity that cools the restraining member in the cooling extension step, thereby raising the temperature of the restraining member to above the reverse transformation completion temperature.

10. The method for assembling a battery module according to claim 1, characterized in that the superelastic alloy has a reverse transformation completion temperature set to be less than the lower limit of the operating temperature range in the battery cell.

11. The method for assembling a battery module according to claim 1, characterized in that the superelastic alloy is either a titanium-nickel alloy or a copper-based alloy.

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