Battery module

Abstract

In a battery module, surface pressure fluctuations on the battery cells are suppressed. [Solution] The battery module 11 comprises a plurality of battery cells 12 and a restraining member 13. The plurality of battery cells 12 are stacked. The restraining member 13 applies pressure to the battery cells 12 in the stacking direction. The restraining member 13 includes a tensioning member 16 made of a superelastic alloy.

Description

Technical Field

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

Background Art

[0002] In the battery module disclosed in Patent Document 1, a plurality of stacked battery cells are constrained in a state of being pressurized in the stacking direction by a metal tension band. Since the battery cells expand and contract during charge and discharge, the tension band is formed with concavo-convex portions that enable elastic deformation.

Prior Art Documents

Patent Documents

[0003] [[ID=!23]]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the metal tension band has a high Young's modulus, the stress change rate is larger than the strain change rate due to the stress-strain relationship. Therefore, when large expansion and contraction occur in the battery cells, a large surface pressure is applied to the battery cells, which may affect the battery cell characteristics. An object of the present invention is to suppress fluctuations in the surface pressure applied to battery cells in a battery module.

Means for Solving the Problems

[0005] According to one aspect of the present invention, a battery module includes a plurality of stacked battery cells and a restraining member that pressurizes the battery cells in the stacking direction. The restraining member includes a tension member made of a superelastic alloy.

Effects of the Invention

[0006] According to the present invention, since the battery cells are pressurized by a superelastic alloy, fluctuations in the surface pressure applied to the battery cells can be suppressed. [Brief explanation of the drawing]

[0007] [Figure 1] This is a diagram showing a battery module according to the first embodiment. [Figure 2] This is a stress-strain diagram. [Figure 3] This is a schematic diagram showing the crystal structure of a common metallic material. [Figure 4] This is a schematic diagram showing the crystal structure of a superelastic alloy. [Figure 5] This is a diagram showing a cross-section of a battery module. [Figure 6] This is a stress-strain diagram of a tension member. [Figure 7] This is a diagram showing a modified example. [Figure 8] This figure shows a battery module according to the second embodiment. [Figure 9] This figure shows a battery module according to the third embodiment. [Figure 10] This figure shows a battery module according to the fourth embodiment. [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 of the first embodiment. 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. The restraining member 13 modularizes multiple battery cells 12 by applying pressure in the stacking direction. The restraining member 13 comprises a tensioning member 16 and a pair of end plates 17.

[0010] The tension member 16 is a superelastic alloy exhibiting superelastic properties. Superelastic properties are characteristics that allow a material to return to its original shape after being deformed by a load, with a recoverable strain range of approximately 5-6%. Superelastic alloys are one of the following: titanium (Ti)-nickel (Ni) alloy, copper-based alloy, or iron-based alloy. Examples of copper-based alloys include copper (Cu)-aluminum (Al)-manganese (Mn) alloy and copper (Cu)-zinc (Zn)-aluminum (Al) alloy. Examples of iron-based alloys include iron (Fe)-nickel (Ni)-cobalt (Co) alloy and iron (Fe)-manganese (Mn)-aluminum (Al)-nickel (Ni) alloy. The tension member 16 is formed in a strip shape extending in the stacking direction, with one provided on each side in the height direction. The pair of end plates 17 are, for example, flat metal plates, and the ends of the tension members 16 are fixed to both sides in the height direction by any method such as welding, fastening, or bonding. The pair of end plates 17 sandwich the battery cell 12 from both sides in the stacking direction and restrain the battery cell 12 under pressure by the tension of the tension members 16.

[0011] Next, we will discuss superelastic alloys. Figure 2 is a stress-strain diagram. (a) in the figure shows the relationship between stress and strain in a general metal material. A general metal material has a linear elastic region. When deformed beyond this region, permanent strain remains even after unloading. The recoverable strain is in the range of about 0.2 to 0.3%. (b) in the figure shows the relationship between stress and strain in a superelastic alloy. When the temperature T is higher than the reverse transformation end temperature Af, the superelastic alloy can return to its original shape even after being loaded and deformed, 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 cell 12. The lower limit value T MIN of the operating temperature range in the battery cell 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.

[0012] Figure 3 is a diagram schematically showing the crystal of a general metal material. (a) in the figure shows the state before loading. (b) in the figure shows the state where slip starts on a specific plane due to loading. (c) in the figure shows the state where slip progresses and shear strain ε occurs. In this plastic deformation, the crystal structure does not change. Figure 4 is a diagram schematically showing the crystal of a superelastic alloy. (a) in the figure shows the state before loading. (b) in the figure shows the state where deformation starts due to loading. At this time, deformation occurs while the martensite phase is induced. (c) in the figure shows the state where shear strain ε occurs without the adjacent atoms breaking. When the temperature T is higher than the reverse transformation end temperature Af, after unloading, it can reverse transform from the unstable martensite phase to the parent phase and return to its original shape.

[0013] Next, the cross-sectional area St of the tension member 16 will be described. Figure 5 is a diagram showing the cross-section of the battery module 11. Let St be the cross-sectional area of ​​the two tension members 16, and Sc be the cross-sectional area of ​​the battery cell 12. If σt is the stress when the tension member 16 deforms by a strain ε, and F is the load, then Equation 1 can be derived. F = σt × St St = F / σt ………(1) The surface pressure σc applied to the battery cell 12 is given by Equation 2. σc = F / Sc F = σc × Sc ………(2) From equations 1 and 2, the following equation (3) is obtained. St = σc × Sc / σt ………(3) From Equation 3, it can be seen that the larger the stress σt, the smaller the cross-sectional area St of the tension member 16 can be.

[0014] Figure 6 is a stress-strain diagram of the tension member 16. The region A enclosed by the dotted line represents the stress σt at which martensitic transformation begins, which is, for example, about 160-200 MPa. Thus, by constructing the tension member 16 from a superelastic alloy, the stress σt at which large deformation begins becomes large, and therefore the cross-sectional area St of the tension member 16 can be reduced according to equation (3). In contrast, when the tension member is made of rubber, the stress at which deformation begins is 0.5 N / mm². 2 It is less than that. Therefore, when made of a superelastic alloy, the thickness can be reduced to less than 1 / 100th of that when made of rubber. The region B enclosed by the dotted line is a region where even a slight change in stress σt causes a large change in strain ε. Therefore, when the tension member 16 deforms in conjunction with the expansion and contraction of the battery cell 12, a nearly constant surface pressure σc can be applied to the battery cell 12.

[0015] Effects and Benefits Next, the main effects and advantages of the first embodiment will be described. (1) The battery module 11 comprises a plurality of battery cells 12 and a restraining member 13. The plurality of battery cells 12 are stacked. The restraining member 13 applies pressure to the battery cells 12 in the stacking direction. The restraining member 13 comprises a tensioning member 16 made of a superelastic alloy. When the battery cells 12 expand and contract due to charging and discharging, the superelastic alloy undergoes a phase transformation and deforms while maintaining pressure on the battery cells 12. This suppresses fluctuations in surface pressure on the battery cells 12 and maintains appropriate charging and discharging characteristics. Since the superelastic alloy has a high stress σt when large deformation begins, the cross-sectional area St of the tensioning member 16 can be reduced.

[0016] (2) The restraining member 13 is equipped with a pair of end plates 17. The pair of end plates 17 sandwich the battery cell 12 from both sides in the stacking direction and pressurize the battery cell 12 with the tension of the tension member 16. This allows the battery cell 12 to be pressed uniformly and maintain the proper charge and discharge characteristics of the battery cell 12. (3) The superelastic alloy is one of the following: a titanium-nickel alloy, a copper-based alloy, or an iron-based alloy. By selecting an appropriate alloy in this way, the proper charge and discharge characteristics of the battery cell 12 can be maintained. (4) 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 tension member 16 within the normal operating temperature range.

[0017] Variant form In the first embodiment, a configuration in which the restraining member 13 is equipped with an end plate 17 was described, but the invention is not limited to this, and the end plate 17 may be omitted. Figure 7 shows a modified example. This configuration is the same as the first embodiment described above, except that the end plate 17 is omitted and another form of the tension member 16 is shown. The restraining member 13 includes one tension member 19. The tension member 19 is formed into an endless rectangular shape that surrounds the battery cell 12 when viewed from the width direction, and pressurizes the battery cell 12 from the stacking direction and the height direction. This makes it possible to obtain the same effects as the first embodiment and further reduce the number of parts.

[0018] 《Second Embodiment》 "composition" The second embodiment has the same configuration as the first embodiment described above, except that it shows a different aspect of the restraining member 13. Therefore, common parts are denoted by the same reference numerals, and detailed descriptions are omitted. Figure 8 shows the battery module 11 of the second embodiment. The restraining member 13 is equipped with a pressure adjustment mechanism 21. The pressure adjustment mechanism 21 is supported by one end plate 17 and is capable of adjusting the pressure on the battery cell 12. It comprises a pressure screw 22 and a pressure plate 23. The pressure screw 22 extends in the stacking direction and fits into a screw hole in the end plate 17. The pressure plate 23 is interposed between the tip of the pressure screw 22 and the battery cell 12. Therefore, by tightening the pressure screw 22, the battery cell 12 is pressurized via the pressure plate 23. Note that there may be multiple pressure screws 22 in the width direction.

[0019] Effects and Benefits Next, the main effects and advantages of the second embodiment will be described. (1) The restraining member 13 is equipped with a pressure adjustment mechanism 21. The pressure adjustment mechanism 21 is supported by one end plate 17 and can adjust the pressure on the battery cell 12. This allows the pressure on the battery cell 12 to be adjusted arbitrarily by the pressure adjustment mechanism 21 while the tension member 16 is pressurizing the battery cell 12. Therefore, 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.

[0020] Third Embodiment "composition" The third embodiment has the same configuration as the second embodiment described above, except that it shows another form of the restraining member 13. Therefore, common parts are denoted by the same reference numerals, and a detailed explanation is omitted. Figure 9 shows the battery module 11 of the third embodiment. The restraining member 13 includes a guide member 31. The guide member 31 is a substantially L-shaped frame that extends in the stacking direction at the four corners of the battery cell 12 when viewed from the stacking direction and contacts the corners of the battery cell 12, with its other end supported by the other end plate 17. The guide member 31 allows the battery cell 12 to be displaced in the stacking direction and restricts its displacement in the direction perpendicular to the stacking direction.

[0021] Effects and Benefits Next, the main effects and advantages of the third embodiment will be described. (1) The restraining member 13 includes a guide member 31. The guide member 31 extends in the stacking direction, and its other end is supported by the other end plate 17, allowing the battery cell 12 to be displaced in the stacking direction and restricting its displacement in the direction perpendicular to the stacking direction. This suppresses the application of uneven surface pressure to the battery cell 12 due to misalignment of the battery cell 12, and maintains proper charge and discharge characteristics. Other effects and benefits resulting from the common configuration are the same as those of the second embodiment described above.

[0022] 《Fourth Embodiment》 "composition" The fourth embodiment has the same configuration as the first embodiment described above, except that it shows another form of the tension member 16. Therefore, common parts are denoted by the same reference numerals and detailed descriptions are omitted. Figure 10 shows a battery module 11 of the fourth embodiment. The restraining member 13 includes a tension member 41. The tension member 41 is formed in an axial shape extending in the stacking direction and is configured to allow fasteners such as nuts to be fitted from one or both axial directions to tighten the end plate 17. The tension member 41 is positioned, for example, at the four corners of the battery cell 12 when viewed from the stacking direction.

[0023] Effects and Benefits Next, the main effects and advantages of the fourth embodiment will be described. (1) The tension member 41 is formed in an axial shape extending in the stacking direction, and the end plate 17 can be tightened by fitting a fastener from one or the other axial direction. This gives the tension member 41 a pressure adjustment function, allowing the pressure on the battery cell 12 to be adjusted as desired. Therefore, 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.

[0024] 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. Furthermore, each embodiment and modification can be adopted in any combination. [Explanation of Symbols]

[0025] 11...Battery module, 12...Battery cell, 13...Restraining member, 16...Tension member, 17...End plate, 19...Tension member, 21...Pressure adjustment mechanism, 23...Pressure plate, 31...Guide member, 41...Tension member

Claims

1. Multiple stacked battery cells, The battery cells are further equipped with a restraining member that applies pressure to them in the stacking direction, The restraining member is A battery module characterized by having a tension member made of a superelastic alloy.

2. The restraining member is The battery module according to claim 1, further comprising a pair of end plates that sandwich the battery cell from both sides in the stacking direction and pressurize the battery cell by the tension of the tension member.

3. The restraining member is The battery module according to claim 2, characterized in that it is supported by one of the end plates and includes a pressure adjustment mechanism capable of adjusting the pressure on the battery cell.

4. The restraining member is The battery module according to claim 3, characterized in that it includes a guide member that extends in the stacking direction, has its other end supported by the other end plate, allows the battery cell to be displaced in the stacking direction, and restricts its displacement in a direction perpendicular to the stacking direction.

5. The battery module according to claim 2, characterized in that the tension member is formed in an axial shape extending in the stacking direction, and the end plate can be tightened by fitting a fastener from one or the other in the axial direction.

6. The battery module according to claim 1, characterized in that the superelastic alloy is one of a titanium-nickel alloy, a copper-based alloy, and an iron-based alloy.

7. The battery module according to claim 1, characterized in that the superelastic alloy's reverse transformation completion temperature is set to be less than the lower limit of the operating temperature range in the battery cell.

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