Battery pack

Abstract

A battery pack P includes a battery module M in which a plurality of battery cells C are arranged between a pair of end plates 1, and a case 2 that accommodates the battery module M, the battery pack also having a structure in which the end plates 1 are fixed to a bottom wall 3 of the case 2. At least the bottom wall 3 and fixing portions 4 for the end plates 1 in the case 2 are covered by insulators 5, 6 having waterproofing and electrical insulation properties, and thus when water enters the case 2, the formation of a short circuit due to ion conduction in the water is prevented.

Description

Battery pack

[0001] The present invention relates to a battery pack comprising a battery module in which a plurality of battery cells are arranged and housed in a case, and more particularly to a battery pack having a function for suppressing short-circuit current when submerged in water.

[0002] An example of a conventional battery pack as described above is described in Patent Document 1. The battery pack described in Patent Document 1 has a structure in which multiple battery modules are arranged vertically and held between a pair of metal mounting members (end plates), and each mounting member is fixed to the bottom wall of the case with a bolt. Between the mounting members and the bolts, an annular insulator is interposed, which has an upper cylindrical portion that accommodates the bolt head and a lower cylindrical portion through which the bolt threads pass. This not only insulates the battery pack from direct electrical connection between the mounting members and the bolts, but also prevents a short circuit between the mounting members and the bolts due to condensation in the gap between them.

[0003] WO2014 / 155995

[0004] However, in the conventional battery packs described above, if water gets inside the case, there is a problem in that the mounting members (end plates) and the bolt heads may short-circuit due to ionic conduction in the water, creating a short circuit throughout the entire battery pack, including the battery module. Therefore, solving this problem was an issue.

[0005] The present invention has been made in response to the above-mentioned conventional problems, and aims to provide a battery pack that includes a battery module in which multiple battery cells are arranged between a pair of end plates, and a case that houses the battery module, with the end plates fixed to the bottom wall of the case, and that can prevent the formation of a short circuit due to ionic conduction in the water when water enters the case.

[0006] The battery pack according to the present invention comprises a battery module in which a plurality of battery cells are arranged between a pair of end plates, a case for accommodating the battery module, and the end plates fixed to the bottom wall of the case. The battery pack is characterized in that at least the areas inside the case where the bottom wall and the end plates are fixed are covered with an insulator that is waterproof and electrically insulating.

[0007] By adopting the above-described configuration, the battery pack of the present invention includes a battery module in which multiple battery cells are arranged between a pair of end plates, and a case that houses the battery module, with the end plates fixed to the bottom wall of the case.In the event that water enters the case, the insulators maximize the resistance of the water between the end plates and the fixed parts of the bottom wall and the case, thereby preventing the formation of a short circuit due to ionic conduction in the water.

[0008] FIG. 1 is a diagram illustrating a first embodiment of a battery pack, and is a side cross-sectional view illustrating a battery module together with an enlarged view of a main part. FIG. 2 is a plan view illustrating the arrangement of battery modules in a battery pack. The upper part is a cross-sectional view showing a short circuit that occurs between modules, and the lower part is a plan view showing a short circuit that occurs in the entire battery pack. FIG. 3 is a side cross-sectional view illustrating a second embodiment of a battery pack. FIG. 4 is a side cross-sectional view illustrating a main part of a third embodiment of a battery pack.

[0009] 1 includes a battery module M in which a plurality of battery cells C are arranged between a pair of end plates 1, 1, and a case 2 that houses the battery module M, with the end plates 1, 1 fixed to a bottom wall 3 of the case 2. In the battery pack P, at least the portions of the case 2 where the bottom wall 3 and the end plates 1, 1 are fixed are covered with an insulating grommet 5 and an insulating resin potting 6, which serve as insulators that have waterproof and electrical insulating properties.

[0010] The battery cells C are formed by winding or stacking a positive electrode foil and a negative electrode foil with a separator interposed therebetween, and then housing this wound or stacked body together with a negative electrode active material, etc. in a flat metal exterior body 11 (shown in an enlarged view in Figure 1 ). There are no restrictions on the number or connection method of the battery cells C in the battery module M, but in the illustrated example, eight battery cells C are provided, and external terminals provided on the top of each battery cell C are connected in series by bus bars B.

[0011] Each end plate 1 is made of metal and has a vertical wall 1A facing the battery cell C and a horizontal fixed wall 1B extending from the lower end of the vertical wall 1A to the outside of the battery module M. Although not shown in its entirety, the case 2 has a structure including, for example, a flat, box-shaped lower case that is open upward and an upper case that closes the top of the lower case. The bottom wall 3 of the case 2 has a two-layer structure including an insulating resin layer 3A on the inside of the case and a metal layer 3B on the outside of the case.

[0012] The fixing portion between the bottom wall 3 and the end plates 1, 1 includes a bolt 4 that penetrates the fixing wall 1B and insulating resin layer 3A of the end plates 1, 1 and screws into the metal layer 3B. The insulator covering this fixing portion includes an insulating grommet 5 that covers the outer periphery of the head of the bolt 4 and is interposed between the bolt 4 and the end plate 1, and an insulating resin potting 6 that seals the upper end of the insulating grommet 5 and covers the top surface of the bolt 4 head.

[0013] The insulating grommet 5 has a large diameter portion 5A that receives the head of the bolt 4 and a small diameter portion 5B through which the threads of the bolt 4 pass, with its lower end reaching the insulating resin layer 3A of the bottom wall 3. The insulating grommet 5 secures the end plate 1 to the bottom wall 3 by tightly fitting the continuous portion between the large diameter portion 5A and the small diameter portion 5B to the end plate 1 and applying the fastening force of the bolt 4, while also tightly fitting the lower end of the small diameter portion 5B to the insulating resin layer 3A, ensuring watertightness between the two. The insulating resin potting 6 fits snugly inside the upper part of the large diameter portion 5A of the insulating grommet 5, and its outer periphery is tightly fitted to the large diameter portion 5A, ensuring watertightness between the two.

[0014] There are no restrictions on the material of the insulating resin potting 6 as long as it is waterproof and electrically insulating, but more preferably, one of urethane resin potting, silicone resin potting, and epoxy resin potting can be used.

[0015] The battery pack P can be configured to include a plurality of battery modules M, as shown in Fig. 2. In the illustrated example, four battery modules M are arranged vertically and horizontally, with the battery cells C, C at the ends of the upper and lower battery modules M on the left side of the figure being connected to each other by a first bus bar B1, the battery cells C, C of the upper left and right battery modules M, M in the figure being connected to each other by a second bus bar B2, and the battery cells C, C of the upper right battery modules M, M in the figure being connected to each other by a third bus bar B3.

[0016] As a result, the battery modules M are connected in series in a clockwise direction from the bottom left battery module M to the bottom right battery module M in the drawing. The battery cells C, C at the center of the battery pack P in the bottom left and right battery modules M, M in the drawing are connected to an external connector via a bus bar and harness (not shown).

[0017] In the battery module M of the battery pack P having the above configuration, if water enters the case 2 as shown by the water surface F in FIG. 1, and if the insulating resin potting 6 is absent and the heads of the bolts 4 are exposed, a short circuit will occur due to ionic conduction of water (including salt water) W interposed between the end plate 1 and the bolts 4.

[0018] In the battery module M, a short circuit occurs due to ionic conduction of water W between the end plate 1 and the adjacent battery cell C, resulting in a short circuit (shown by a dotted line in FIG. 1 ) extending from one bolt 4 on the right side in FIG. 1 through the water W, one end plate 1, water W, the battery cell C at one end, the bus bar B and the battery cells C, C connected by the bus bar B, the battery cell C at the other end, water W, the other end plate 1, water W, the other bolt 4, and the metal layer 3B of the bottom wall 3, before reaching one of the bolts 4. In this case, a short circuit occurs between the battery cells C, C at both ends via their respective metal exterior bodies 11, but this is not directly related to the present invention and will not be described in detail here.

[0019] Furthermore, since the battery pack P of this embodiment has a structure in which four battery modules M are arranged vertically and horizontally as shown in Fig. 2, a short circuit (dotted line) occurs through all of the modules M, as shown in the lower part of Fig. 3. In this case, as shown in the upper part of Fig. 3, a short circuit path (dotted line) occurs between the lower left and right modules M, M in the figure, from one bolt 4 through the metal layer 3B of the bottom wall 3 to the other bolt 4.

[0020] In contrast, in the battery module M of the above embodiment, at least the bolts 4, which are the fixing points between the bottom wall 3 and the end plates 1 inside the case 2, are covered with insulating grommets 5 and insulating resin potting 6, which are insulators, so that short circuits caused by ionic conduction in water are blocked between each end plate 1 and each bolt 4.

[0021] That is, the battery module M uses the insulators (insulating grommets 5 and insulating resin potting 6) that cover the fixing portions to maximize the ionic conduction resistance R in the water between the end plates 1 and the bolts 4. This allows the entire battery pack P to block short circuits caused by ionic conduction in the water.

[0022] In this way, the battery pack P includes a battery module M in which a plurality of battery cells C are arranged between a pair of end plates 1, 1, and a case 2 that houses the battery module M, and in a structure in which the end plate 1 is fixed to the bottom wall 3 of the case 2, it is possible to prevent the formation of a short circuit due to ionic conduction in the water when water enters the case 2. As a result, the battery pack P not only naturally prevents short circuits due to condensation water, but also improves the function of suppressing short-circuit current when water enters the battery pack P.

[0023] Furthermore, the above-mentioned battery pack P has a fixing portion that includes a bolt 4 that penetrates the end plate 1 and the insulating resin layer 3A and screws into the metal layer 3B, and by adopting an insulating grommet 5 and an insulating resin potting 6, it is possible to completely block ionic conduction in the water between the end plate 1 and the bolt 4 with a relatively simple configuration, thereby reliably preventing the formation of a short circuit.

[0024] Furthermore, in the above-mentioned battery pack P, the lower end of the insulating grommet 5 reaches the insulating resin layer 3A, so that in the event of water intrusion, watertightness can be ensured between the end plate 1 and the bolt 4, and between the end plate 1 and the bottom wall 3, and the bolt 4, which is generally made of metal, can be protected from water.

[0025] Furthermore, in the battery pack P, the insulating resin potting 6 serving as an insulator is one of urethane resin potting, silicone resin potting, and epoxy resin potting, which further improves watertightness and electrical insulation, and the insulating resin potting 6 adheres tightly to the insulating grommet 5 without any gaps, ensuring sufficient watertightness between the two.

[0026] 4 is a diagram illustrating a second embodiment of a battery pack according to the present invention. In the following embodiments, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0027] The illustrated battery pack P has the same basic configuration as the first embodiment, and also includes an insulating ring 7 that is disposed between the end plate 1 and the bottom wall 3, centered on the bolt 4, and compressed between the lower end of the end plate 1 and the bottom wall 3. The material of the insulating ring 7 is not limited, but the same material as the insulating grommet 5 can be used, for example.

[0028] Similar to the previous embodiment, the battery pack P having the above configuration can prevent the formation of a short circuit due to ionic conduction in the water when water enters the case 2. Furthermore, in particular, by employing the insulating ring 7, the battery pack P can simultaneously achieve both fixing and ensuring watertightness between the end plate 1 and the bottom wall 3, and between the insulating grommet 5 and the end plate 1, between the end plate 1 and the insulating ring 7, and between the insulating ring 7 and the bottom wall 3, as the bolts 4 are tightened to the metal layer 3B of the bottom wall 3.

[0029] In the above embodiment, the lower end of the small diameter portion 5B of the insulating grommet 5 is located lower than the underside of the fixed wall 1B of the end plate 1, thereby ensuring insulation and watertightness between the fixed wall 1B and the bolt 4. Furthermore, in the above embodiment, the inner diameter of the insulating ring 7 is made larger than the outer diameter of the small diameter portion 5B, so that the insulating ring 7 is crushed between the fixed wall 1B and the bottom wall 3 and pressed against both, thereby improving the watertightness between the fixed wall 1B and the bottom wall 3. By adopting a crushable structure in this way, it is possible to prevent the dimensional tolerances of parts such as the insulating grommet 5 from becoming extremely small.

[0030] 5 is a diagram illustrating a third embodiment of a battery pack according to the present invention. The battery pack P, the main part of which is shown in FIG. 5, includes the insulating ring 7 described in the second embodiment, and the lower end of the small diameter portion 5B of the insulating grommet 5 reaches the insulating resin layer 3A of the bottom wall 3.

[0031] According to the above configuration, the insulating ring 7 is crushed between the fixed wall 1B and the bottom wall 3 of the end plate 1, and at the same time, the small diameter portion 5B of the insulating grommet 5 is crushed in the axial direction. A double sealing structure is obtained by the small diameter portion 5B and the insulating ring 7, thereby further improving both the insulation and watertightness between the fixed wall 1B, bolt 4, and bottom wall 3.

[0032] The configuration of the battery pack according to the present invention is not limited to the above-described embodiments, and can be modified as appropriate within the scope of the gist of the present invention. For example, by making the end plates out of insulating resin, it is possible to further enhance the function of preventing short circuits due to ionic conduction in water.

[0033] C Battery cell M Battery module 1 End plate 2 Case 3 Bottom wall of case 3A Insulating resin layer 3B Metal layer 4 Bolt (fixing portion) 5 Insulating grommet (insulator) 6 Insulating resin potting (insulator) 7 Insulating ring 11 Metallic exterior body

Claims

1. A battery pack having a structure including a battery module in which a plurality of battery cells are arranged between a pair of end plates, and a case that houses the battery module, and the end plates are fixed to a bottom wall of the case, At least the fixing portions of the bottom wall and the end plates in the case are covered with an insulator having waterproof and electrical insulating properties, the bottom wall includes an insulating resin layer on the inside of the case and a metal layer on the outside of the case, the fixing portion includes a bolt that penetrates the end plate and the insulating resin layer and is screwed into the metal layer, a battery pack characterized in that the insulator comprises an insulating grommet that covers the outer periphery of the head of the bolt and is interposed between the bolt and the end plate, and an insulating resin potting that seals the upper end of the insulating grommet and covers the top surface of the head of the bolt.

2. (delete)

3. 2. The battery pack according to claim 1, further comprising an insulating ring disposed between the end plate and the bottom wall, the insulating ring being centered around the bolt and compressed between the end plate and the bottom wall.

4. 4. The battery pack according to claim 1, wherein a lower end of the insulating grommet reaches the insulating resin layer.

5. 2. The battery pack according to claim 1, wherein the insulating resin potting is one of a urethane resin potting, a silicone resin potting, and an epoxy resin potting.