Battery module

Abstract

To eliminate uneven concentration of the electrolyte solution within the electrode body. [Solution] The battery module comprises a plurality of battery cells stacked in a first direction and spacers positioned between adjacent battery cells, wherein each battery cell has a rectangular battery case containing an electrode body and an electrolyte, and each spacer has a pressing portion that contacts a predetermined pressing region on the outer surface of the battery case and presses the battery cell in a first direction, wherein the pressing region is a region that overlaps with the central part of the electrode body when viewed from the first direction and does not overlap with both ends of the electrode body in the width direction of the battery cell, and the pressing portion is formed in a shape such that the portion that overlaps with the portion of the electrode body below the central part is larger than the portion that overlaps with the portion of the electrode body above the central part when viewed from the first direction.

Description

Technical Field

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

Background Art

[0002] The Patent Document 1 discloses that in a battery module in which a plurality of battery cells are stacked, a spacer is disposed between adjacent battery cells, and a convex rib provided on the spacer is brought into contact with the outer surface of the battery case to apply a restraint load to the battery cells. The long side surface of the outer surface of the battery case that contacts the rib includes a restraint region where the rib contacts and a non-restraint region where the rib does not contact.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a secondary battery, expansion and contraction of the electrode body due to charge and discharge and volume expansion of the electrolytic solution occur. Therefore, the electrolytic solution may be extruded from the inside of the electrode body due to a pumping action caused by the expansion and contraction of the electrode body and the volume expansion of the electrolytic solution. In this case, there is a risk that the resistance of the battery cell increases due to unevenness in the concentration of the electrolytic solution inside the electrode body.

[0005] In the configuration described in the Patent Document 1, inside the battery case that houses the electrode body and the electrolytic solution, the movement of the electrolytic solution is restricted in the portion of the electrode body corresponding to the restraint region, and the electrolytic solution is allowed to stay in the portion of the electrode body corresponding to the non-restraint region. Thereby, outflow of the electrolytic solution inside the electrode body is suppressed, and unevenness in the concentration of the electrolytic solution inside the electrode body is suppressed. However, in the configuration described in the Patent Document 1, it is impossible to cope with the elimination of the unevenness in the concentration of the electrolytic solution that has once occurred inside the electrode body, and there is room for improvement.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a battery module that can eliminate uneven concentration of the electrolyte when uneven concentration occurs inside the electrode body. [Means for solving the problem]

[0007] The present invention relates to a battery module comprising a plurality of battery cells stacked in a first direction and spacers disposed between adjacent battery cells, wherein each battery cell has a rectangular battery case containing an electrode body and an electrolyte, and each spacer has a pressing portion that contacts a predetermined pressing region on the outer surface of the battery case and presses the battery cell in the first direction, wherein the pressing region is a region that overlaps with the central part of the electrode body when viewed from the first direction and does not overlap with both ends of the electrode body in the width direction of the battery cell, and the pressing portion is formed such that, when viewed from the first direction, the portion of the electrode body that overlaps with the portion below the central part is larger than the portion of the electrode body that overlaps with the portion above the central part. [Effects of the Invention]

[0008] In this invention, it is possible to eliminate uneven concentration of the electrolyte solution when uneven concentration occurs within the electrode body. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing a battery module in an embodiment. [Figure 2] This is a diagram to explain spacers. [Figure 3] This is a diagram illustrating the pressure area. [Figure 4] This diagram illustrates the positional relationship between the pressing area and the electrode body. [Figure 5] This is a diagram illustrating the electrode body and electrolyte. [Figure 6]This diagram illustrates the concentration variations in the electrolyte solution that occur inside the electrode body. [Figure 7] This is a diagram to explain the concentration of the electrolyte. [Figure 8] This diagram illustrates the state in which the battery module is air-cooled. [Figure 9] This diagram illustrates how to create a temperature difference between the central and end portions of an electrode by partially cooling the electrode body. [Figure 10] This diagram illustrates how reducing the concentration unevenness of the electrolyte lowers the resistance of the battery cell. [Modes for carrying out the invention]

[0010] The following describes in detail the battery module in the embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

[0011] Figure 1 is a schematic diagram showing a battery module in an embodiment. The battery module 1 is a battery pack in which a plurality of battery cells 10 are stacked. The battery module 1 comprises a plurality of battery cells 10 and spacers 20 arranged between adjacent battery cells 10. The battery cells 10 are prismatic cells. The battery cells 10 have a prismatic battery case 11 and terminals 12.

[0012] The battery module 1 includes a laminate in which battery cells 10 and spacers 20 are alternately stacked in a first direction X. A restraining load acts on this laminate, compressing it in the first direction X by a restraining member or the like. For example, the restraining member includes a pair of end plates and a restraining band. This restraining load causes the spacers 20 to press the battery cells 10 in the first direction X. The first direction X is the same direction as the stacking direction of the battery module 1 and the same direction as the thickness direction of the battery cells 10.

[0013] The spacer 20 has a flat plate portion 21 and a pressing portion 22 that protrudes from the flat plate portion 21 in the first direction X. Between adjacent battery cells 10, the flat plate portion 21 abuts on one battery cell 10, and the pressing portion 22 abuts on the other battery cell 10. The flat plate portion 21 is formed in a shape corresponding to the battery case 11, abuts on the long side surface 13a of the battery case 11 in one battery cell 10, and faces the long side surface 13a of the battery case 11 in the other battery cell 10.

[0014] As shown in FIG. 2, the flat plate portion 21 is formed in a rectangular shape having the second direction Y as the longitudinal direction and the third direction Z as the short-side direction. The pressing portion 22 is formed in a trapezoidal shape in which the upper base 22a is shorter than the lower base 22b. The upper base 22a and the lower base 22b extend along the second direction Y. In the spacer 20, the pressing portion 22 is formed at the central position of the flat plate portion 21. Note that the second direction Y is the same direction as the width direction of the battery cell 10. The third direction Z is the same direction as the height direction of the battery cell 10 and the same direction as the height direction of the trapezoid in the pressing portion 22.

[0015] As shown in FIG. 3, the outer surface of the battery case 11 includes a pair of long side surfaces 13a formed on both sides in the first direction X, a pair of short side surfaces 13b formed on both sides in the second direction Y, an upper surface 13c, and a lower surface 13d. The long side surface 13a is a surface that faces the flat plate portion 21 in the first direction X and abuts on the pressing portion 22. The long side surface 13a includes a pressing region 14 where the pressing portion 22 abuts and a region where the pressing portion 22 does not abut. The pressing region 14 has the same trapezoidal shape as the pressing portion 22. For the sake of convenience of explanation, in FIG. 3, the flat plate portion 21 is omitted, and only the pressing portion 22 of the spacer 20 is shown.

[0016] The pressing region 14 is a portion where the pressing portion 22 abuts and is a region pressed in the first direction X by the pressing portion 22. The pressing portion 22 abuts on the pressing region 14 of the long side surface 13a and presses the battery cell 10 in the first direction X. By pressing the pressing region 14, the pressing portion 22 can press the electrode body 15 in the battery case 11.

[0017] As shown in FIG. 4, the pressing region 14 is a region that overlaps with the central portion 15a of the electrode body 15 when viewed from the first direction X and does not overlap with both end portions 15b, 15b of the electrode body 15 in the width direction of the battery cell 10. The central portion 15a is the central portion in the second direction Y and the central portion in the third direction Z. The end portion 15b is the end portion in the second direction Y. As shown in FIG. 5, the electrode body 15 and the electrolytic solution are accommodated inside the battery case 11.

[0018] The electrode body 15 is a wound electrode body in which the upper and lower sides in the height direction of the battery cell 10 are sealed. In the electrode body 15, one end portion 15b is a positive electrode connection portion in which only the portion where the positive electrode current collector is exposed is wound, and the other end portion 15b is a negative electrode connection portion in which only the portion where the negative electrode current collector is exposed is wound. The positive electrode side terminal 12 is connected to the positive electrode connection portion, and the negative electrode side terminal 12 is connected to the negative electrode connection portion. Both end portions 15b are open in the width direction of the battery cell 10, and the electrolytic solution can move between the inside and the outside of the electrode body 15 through the end portion 15b. The electrolytic solution exists inside the electrode body 15 and also exists as an excess liquid 16 outside the electrode body 15. Most of the electrolytic solution has penetrated inside the electrode body 15. The excess liquid 16 that does not penetrate inside the electrode body 15 accumulates on the lower surface 13d side inside the battery case 11.

[0019] As the battery cell 10 undergoes repeated charging and discharging, the electrolyte is pushed out from inside the electrode body 15 due to a pumping action caused by the expansion and contraction of the electrode body 15 and the volume expansion of the electrolyte due to charging and discharging. Since both ends 15b of the electrode body 15 are open, the electrolyte inside the electrode body 15 flows out from the ends 15b. As a result, as shown in Figure 6, the electrolyte concentration is higher in the central part 15a and lower at both ends 15b, resulting in uneven electrolyte concentration inside the electrode body 15. Since the lower edge of the electrode body 15 is immersed in the excess liquid 16, the area with a higher electrolyte concentration is larger in the lower part of the electrode body 15 than in the upper part. When uneven electrolyte concentration occurs inside the electrode body 15, the internal resistance of the battery cell 10 increases. As shown in Figure 7, when analyzing the concentration of the electrolyte in the battery cell 10 during a transient increase in resistance, as viewed from the first direction X, using electrolyte analysis (XRF analysis), it was found that the central part 15a was the most concentrated, and the area of ​​higher concentration became wider towards the bottom, resulting in a trapezoidal shape.

[0020] In order to reduce the internal resistance of the battery cell 10, which has increased due to the uneven concentration of the electrolyte, it is necessary to eliminate the uneven concentration of the electrolyte inside the electrode body 15. To eliminate the uneven concentration of the electrolyte that has occurred inside the electrode body 15, it is conceivable to make the electrolyte flow inside the electrode body 15 so that the concentration of the electrolyte becomes uniform. The inventors focused on the fact that the electrolyte diffuses inside the electrode body 15 due to the temperature difference inside the electrode body 15. The higher the temperature of the electrolyte, the easier it diffuses. In the battery module 1, by pressing only the part 15c of the electrode body 15 where the electrolyte concentration is high with the pressing part 22, the part of the electrode body 15 where the electrolyte concentration is low is actively cooled, and a temperature difference is created between the central part 15a side and both end parts 15b side of the electrode body 15. This moves the concentrated electrolyte present in the central region of the electrode body 15, promoting the mitigation of uneven electrolyte concentration inside the electrode body 15.

[0021] Specifically, as shown in Figure 4, the pressing area 14 is set such that, when viewed from the first direction X, the area pressing the portion of the electrode body 15 below the central portion 15a is larger than the area pressing the portion of the electrode body 15 above the central portion 15a. In other words, the pressing portion 22 is formed such that, when viewed from the first direction X, the portion overlapping with the portion of the electrode body 15 below the central portion 15a is larger than the portion overlapping with the portion of the electrode body 15 above the central portion 15a.

[0022] For example, the pressing portion 22 is positioned to contact the center of the long side surface 13a. The upper base 22a of the pressing portion 22 is formed to be 60-65% of the width of the battery cell 10. The lower base 22b of the pressing portion 22 is formed to be 70-80% of the width of the battery cell 10. The trapezoidal height of the pressing portion 22 is formed to be 70-80% of the height of the battery cell 10.

[0023] As shown in Figure 8, since the battery module 1 is air-cooled, cooling air can be circulated between adjacent battery cells 10 in areas of the long side surface 13a where the pressing portion 22 does not come into contact. In this case, as shown in Figure 9, the portion of the electrode body 15 not pressed by the pressing portion 22 is cooled by the cooling air, but the portion pressed by the pressing portion 22 is not actively cooled by the cooling air, resulting in a temperature difference in the width direction of the battery cell 10. As a result, the central portion 15a side is hotter, and the end portion 15b side is hotter. Since the electrolyte diffuses from the hotter portion to the colder portion, the concentrated electrolyte diffuses from the central portion 15a side to the end portion 15b side, mitigating the electrolyte concentration gradient inside the electrode body 15. In this way, the temperature difference in the electrode body 15 can promote the mitigation of electrolyte concentration unevenness. As shown in Figure 10, when the mitigation of electrolyte concentration unevenness inside the electrode body 15 is promoted, the internal resistance of the battery cell 10 decreases. As a result, the battery module 1 can eliminate any concentration unevenness that may have occurred inside the electrode body 15, allowing it to perform at its full potential.

[0024] As described above, according to the embodiment, the temperature difference of the electrode body 15 between the portion pressed by the pressing portion 22 and the portion not pressed by the pressing portion 22 promotes the diffusion of the electrolyte inside the electrode body 15, thereby eliminating any unevenness in concentration that may have occurred.

[0025] Furthermore, the pressing portion 22 is not limited to cases where the upper base 22a, lower base 22b, and hypotenuse are all straight lines. The pressing portion 22 may, for example, have an upper base 22a that is curved, or a hypotenuse that is curved. In short, the pressing portion 22 only needs to be formed in a substantially trapezoidal shape. [Explanation of symbols]

[0026] 1 Battery Module 10 battery cells 11 Battery case 13a long side 15 Electrode body 15a central part 15b End 20 Spacers 22 Pressing part

Claims

1. Multiple battery cells stacked in the first direction, A spacer is placed between adjacent battery cells, Equipped with, The aforementioned battery cell has a rectangular battery case containing an electrode body and an electrolyte inside, The spacer is a battery module having a pressing portion that contacts a predetermined pressing area on the outer surface of the battery case and presses the battery cell in the first direction, The pressing region is a region that, when viewed from the first direction, overlaps with the central part of the electrode body and does not overlap with both ends of the electrode body in the width direction of the battery cell. The pressing portion is formed such that, when viewed from the first direction, the portion of the electrode body that overlaps with the portion below the central part is larger than the portion of the electrode body that overlaps with the portion above the central part. A battery module characterized by the following features.

2. The pressing portion is formed in a substantially trapezoidal shape, with the lower base being longer than the upper base when viewed from the first direction. The battery module according to feature 1.

3. The upper base is formed to a length of 60-65% of the width of the battery cell. The lower base is formed to be 70-80% of the width of the battery cell. The height of the aforementioned roughly trapezoidal shape is formed to be 70-80% of the height of the battery cell. The battery module according to feature 2.

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