Battery pack

Abstract

To provide a battery pack with a simple structure that can suppress the decrease in cooling performance and the snake phenomenon of battery cells. [Solution] The battery pack 10P comprises a plurality of battery cells 10 constituting a secondary battery ND, each having an electrode body 2, a metal battery can 1 comprising a rectangular cylindrical extruded case body 11 that houses the electrode body and has a pair of long side portions 111 extending in the axial direction (Z direction), an upper short side portion 112a and a lower short side portion 112b perpendicular to the long side portions, with both axial ends 11T open, and a pair of lids 12 that seal the ends, and a restraining mechanism 5 that restrains the battery cells by applying pressure from both ends in the stacking direction (X direction) while the battery cells are stacked with an intervening member 51 sandwiched between the long side portions. The restraining mechanism includes a cooling section 54 that contacts the lower short side portion to cool the battery cell, and both ends 115 in the width direction of the lower short side portion are formed to be able to fit from above with projections 55 formed on the upper surface of the cooling section.

Description

Technical Field

[0001] The technology disclosed herein relates to a battery pack formed by assembling battery cells that constitute secondary batteries used as driving sources for hybrid vehicles, electric vehicles, and the like.

Background Art

[0002] Generally, secondary batteries used as driving sources for hybrid vehicles, electric vehicles and the like require high voltage and large current, so battery packs formed by assembling a plurality of battery cells are used. For example, such a battery pack is provided with a restraining mechanism in which rectangular battery cells are arranged and stacked in a column, and the outermost battery cells are pressurized and restrained inward in the stacking direction. In many cases, this restraining mechanism is provided with a cooling section that abuts against the bottom surface of the battery cells to cool each battery cell (see, for example, Patent Document 1).

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] However, since the above restraining mechanism generally does not restrain the upper end portion of the battery cell, when the pressure inside the case rises along with the temperature increase of the battery cell during rapid charging of the battery cell or the like, the bottom surface portion of the battery cell expands downward in an arc shape, reducing the contact area between the bottom surface portion of the battery cell and the cooling section, which causes a problem that the cooling performance of the battery cell decreases. Further, even when the electrode body volume-expands along with the aging deterioration of the battery cell, the bottom surface portion of the battery cell expands downward in an arc shape, reducing the contact area between the bottom surface portion of the battery cell and the cooling section, resulting in the problem that the cooling performance of the battery cell decreases.

[0005] Furthermore, when assembling a battery pack by arranging and stacking the battery cells in a vertical row, a snake phenomenon can occur where the stacked battery cells gradually shift position relative to the restraining mechanism, causing them to curve in the stacking direction. In this case, there was a problem in that defects were likely to occur at the connection point between the conductor (busbar) connecting the current collection terminals of each battery cell and the current collection terminal itself.

[0006] This disclosed technology has been made in view of the aforementioned problems, and aims to provide a battery pack with a simple structure that can suppress the reduction in cooling performance and the snake phenomenon of battery cells. [Means for solving the problem]

[0007] (1) One aspect of the present invention for solving the above problems is a battery pack comprising: an electrode body; a plurality of battery cells constituting a secondary battery comprising a metal battery can comprising: an electrode body; a rectangular cylindrical extruded case body for housing the electrode body, having a pair of long side portions extending in the axial direction and an upper short side portion and a lower short side portion perpendicular to the long side portions, with both ends in the axial direction open; and a pair of lids for sealing the ends; and a restraining mechanism for restraining the battery cells by applying pressure from both ends in the stacking direction while the battery cells are stacked with an intervening member sandwiched between the long side portions, wherein the restraining mechanism is provided with a cooling portion that contacts the lower short side portion to cool the battery cell, and both ends in the width direction of the lower short side portion are formed to be able to fit from above with projections formed on the upper surface of the cooling portion.

[0008] (2) In the battery pack described in (1), it is preferable that the thickness of the lower short side portion is greater than the thickness of the upper short side portion.

[0009] (3) In the battery pack described in (1) or (2), it is preferable that arcuate surfaces projecting outward in the width direction are provided along the axial direction at both ends in the width direction, and that the projections are formed to be elastically deformable and fit with respect to the arcuate surfaces.

[0010] (4) In the battery pack described in (1) or (2), it is preferable that elastically deformable locking claws are provided along the axial direction on the inner wall surface recessed upward from the lower end surface at both ends in the width direction, and that the projection is formed to be able to engage with the locking claw from below.

[0011] (5) In a battery pack described in any one of (1) to (4), the extruded case body is preferably provided with a partition wall that extends axially between the lower short side portion and the lower end of the electrode body, connecting the long side portions to each other, or the long side portion and the lower short side portion, and a coolant flow path is formed between the partition wall, the long side portion and the lower short side portion. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view of a battery pack according to one aspect of this embodiment. [Figure 2] Figure 1 is a side view of the battery cells that make up the battery pack shown. [Figure 3] This is an enlarged cross-sectional view of part A of the battery pack shown in Figure 1. [Figure 4] This is an enlarged cross-sectional view of part A in modified example 1 of the battery pack shown in Figure 1. [Figure 5] This is an enlarged cross-sectional view of part A in modified example 2 of the battery pack shown in Figure 1. [Figure 6] This is an enlarged cross-sectional view of part A in modified example 3 of the battery pack shown in Figure 1. [Figure 7] This is an enlarged cross-sectional view of part A in modified example 4 of the battery pack shown in Figure 1. [Figure 8] This is an enlarged cross-sectional view of part A in modified example 5 of the battery pack shown in Figure 1. [Modes for carrying out the invention]

[0013] <Detailed description of this battery pack> Next, the overall configuration of a battery pack according to one embodiment of the disclosed technology described above will be explained in detail with reference to the drawings. Figure 1 shows a schematic cross-sectional view of a battery pack according to one embodiment of this embodiment. Figure 2 shows a side view of the battery cells constituting the battery pack shown in Figure 1. Figure 3 shows an enlarged cross-sectional view of part A of the battery pack shown in Figure 1. In Figures 1 to 8, the X direction indicates the stacking direction of the battery cells in the battery pack, the Y direction indicates the vertical direction of the battery cells (extruded case body), and the Z direction indicates the axial direction of the extruded case body. The X direction is also the width direction of the upper short side portion and the lower short side portion, the Y direction is also the width direction of the long side portion, and the Z direction is also the axial direction of the electrode body.

[0014] A battery pack 10P according to one embodiment of the disclosed technology, as shown in Figures 1 to 3, comprises an electrode body 2, a metal battery can 1 comprising a battery cell 10 that constitutes a secondary battery ND having an electrode body 2, a rectangular cylindrical extruded case body 11 that houses the electrode body 2 and has a pair of long side portions 111 extending in the axial direction (Z direction), an upper short side portion 112a and a lower short side portion 112b perpendicular to the long side portions 111, and both ends 11T in the axial direction (Z direction) open, and a pair of lids 12 that seal the ends 11T, and a restraining mechanism 5 that restrains the battery cell 10 by applying pressure from both ends in the stacking direction (X direction) while the battery cell 10 is stacked with an intervening member 51 sandwiched between the long side portions 111.

[0015] Here, the electrode body 2 is formed by winding and laminating a strip-shaped positive electrode foil 2a, a strip-shaped negative electrode foil 2b, and a strip-shaped separator 2c sandwiched between the two electrode foils 2a and 2b in a flattened shape. However, it is not necessarily limited to this. For example, an electrode body formed by laminating multiple sheet-shaped positive electrode foils, sheet-shaped negative electrode foils, and sheet-shaped separators sandwiched between the two electrode foils may also be used. An insulating film (not shown) is interposed between the electrode body 2 and the battery can 1 to prevent short circuits between the electrode body 2 and the battery can 1. For example, polypropylene (PP) resin can be used for the insulating film.

[0016] Further, the battery cells 10 constituting the secondary battery ND may be, for example, lithium ion secondary batteries. In this case, for example, an aluminum foil is used as the positive electrode foil 2a, and the active material fixed thereto is, for example, a lithium transition metal oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O₂, LiNiO₂, etc.) can be used. For example, a copper foil is used as the negative electrode foil 2b, and graphite, hard carbon, soft carbon, or the like can be used as the active material fixed to the negative electrode foil 2b. Further, for the separator 2c, for example, a porous sheet made of polypropylene, polyethylene or the like can be used.

[0017] The metal battery can 1 is made of, for example, aluminum or an aluminum alloy, but is not necessarily limited thereto. The extruded case body 11 is formed into a square cylindrical body having a substantially rectangular cross section including a pair of wide long side portions 111 extending in the axial direction (Z direction), and a narrow upper short side portion 112a and a narrow lower short side portion 112b. The extruded case body 11 is a cylindrical body extrusion-molded in the axial direction (Z direction), and both end portions 11T in the axial direction (Z direction) are opened. A safety valve 113 that cleaves when the pressure inside the battery can 1 rises above a predetermined value and an injection port 114 for injecting an electrolyte are formed in the upper short side portion 112a.

[0018] The end portion 11T of the extruded case body 11 is connected to the flat cover body 12 by welding or the like. Current collector terminals 3 connected to tab portions 2T formed at both ends of the electrode body 2 in the axial direction (Z direction) are fixed to the cover body 12 via an insulating material 4. Of the pair of cover bodies 12, a positive current collector terminal 3a is fixed to one cover body 12, and a negative current collector terminal 3b is fixed to the other cover body 12.

[0019] The interposed member 51 is composed of an elastically deformable elastic member 51a and an insulating member 51b to prevent the restraining load P1 from increasing excessively when the pressure inside the battery can 1 rises. However, the interposed member 51 is not limited to this, and a member having both elasticity and insulation properties, such as ethylene propylene rubber (EPDM), can be used. The restraining mechanism 5 includes a pair of side pressure plates 52 that press the long side surface portion 111 of the outermost battery cell 10 with the insulating member 51b interposed therebetween, a base 53 that supports the lower end portions of the side pressure plates 52, and a connecting plate (not shown) that connects the left and right side pressure plates 52. Further, in the plurality of battery cells 10 restrained by the restraining mechanism 5, each current collecting terminal 3 (the positive electrode current collecting terminal 3a and the negative electrode current collecting terminal 3b) is electrically connected via a bus bar (not shown).

[0020] Further, the restraining mechanism 5 is provided with a cooling portion 54 that abuts against the lower short side surface portion 112b to cool the battery cell 10, and both widthwise end portions 115 of the lower short side surface portion 112b are formed so as to be fittable from above with protrusions 55 formed on the upper surface of the cooling portion 54. The cooling portion 54 is fixed to the base 53, and a coolant flow path 541 having substantially the same width as the battery cell 10 is formed along the axial direction (Z direction) at a position facing each battery cell 10. The cooling portion 54 may be formed by extrusion molding along the axial direction (Z direction). Further, the cooling portion 54 may be divided corresponding to each battery cell 10, and the protrusions 55 may be formed at both widthwise end portions of the divided cooling portions.

[0021] The protrusion 55 is formed between adjacent coolant flow paths 541 and between both widthwise end portions 115 of the lower short side surface portion 112b in adjacent battery cells 10, being divided into two left and right protrusions 55a and 55b. A gap 116 that allows the protrusions 55a and 55b to flex during fitting is formed between the two left and right protrusions 55a and 55b. Here, the protrusion 55 (55a, 55b) is formed integrally with the cooling portion 54, but may be formed as a separate member.

[0022] Due to the above configuration, even when the pressure inside the battery can 1 increases due to the temperature rise of the battery cells 10 during rapid charging of the battery pack 10P, or when the electrode body 2 expands in volume due to the aging of the battery cells 10 constituting the battery pack 10P, the lower short side portion 112b of the extruded case body 11, which is fitted with the projection portion 55 of the cooling portion 54 and both ends 115 in the width direction, is less likely to deform downward in an arc shape and is more likely to maintain contact with the cooling portion 54. Therefore, the reduction in the contact area between the lower short side portion 112b and the cooling portion 54 can be suppressed, more heat can be dissipated through the lower short side portion 112b in contact with the cooling portion 54, and the battery cells 10 of the battery pack 10P can be effectively cooled.

[0023] Furthermore, by pressing both ends 115 in the width direction of the lower short side portion 112b of each battery cell 10 from above (Q direction) and engaging them with the projection 55 formed on the upper surface of the cooling portion 54 from above, even when pressure is applied from both ends in the stacking direction (X direction), displacement of each battery cell 10 relative to the restraining mechanism 5 can be avoided, and the snake phenomenon of curvature in the stacking direction (X direction) can be suppressed. Thus, a battery pack 10P can be provided that suppresses the deterioration of the cooling performance of the battery cells 10 and the snake phenomenon with a simple structure.

[0024] Furthermore, in this battery pack 10P, it is preferable that the plate thickness d2 of the lower short side portion 112b is formed to be thicker than the plate thickness d1 of the upper short side portion 112a. In this case, even if the upper short side portion 112a, which has a thin plate thickness d1, deforms due to an increase in pressure inside the battery can 1 or an increase in the volume of the electrode body 2, the lower short side portion 112b, which has a thick plate thickness d2, is less likely to deform. Therefore, even when the pressure inside the battery can 1 increases or when the electrode body 2 expands in volume due to the aging of the battery cell 10, heat can be reliably dissipated by the cooling unit 54 via the less deformable lower short side portion 112b, and the battery cell 10 constituting the battery pack 10P can be cooled more effectively.

[0025] Here, the plate thickness d2 of the lower short side portion 112b is formed to be constant overall and thicker than the plate thickness d1 of the upper short side portion 112a, but this is not necessarily the only option. For example, as shown by the dashed line KS in Figure 3, the plate thickness d2 may be made thicker than the plate thickness d1 of the upper short side portion 112a only at the corner where the long side portion 111 and the lower short side portion 112b intersect. In this case, the space for housing the electrode body 2 can be expanded, which can contribute to improving the energy density.

[0026] Furthermore, in this battery pack 10P, it is preferable that arcuate surfaces CS projecting outward in the width direction are provided along the axial direction (Z direction) at both ends 115 in the width direction, and that the projections 55 are formed to be elastically deformable and fit with respect to the arcuate surfaces CS. The projections 55 have a concave arcuate surface that contacts the arcuate surfaces CS. In this case, when the lower short side portion 112b of each battery cell 10 is brought into contact with the cooling portion 54 from above, the projections 55 of the cooling portion 54 are pressed by the arcuate surfaces CS of the lower short side portion 112b, elastically deform outward in the width direction, pass through the arcuate surfaces CS, and then return to their original state, allowing the projections 55 of the cooling portion 54 to be elastically fitted with both ends 115 in the width direction of the lower short side portion 112b. Therefore, in the fitted state between the widthwise ends 115 and the projections 55, the projections 55 of the cooling unit 54 grip the widthwise ends 115 of the lower short side portion 112b with their elastic force P2, making it difficult for the lower short side portion 112b to separate from the cooling unit 54. Consequently, the battery cells 10 constituting the battery pack 10P can be cooled more effectively.

[0027] <Variation> The embodiments described in detail above are merely illustrative and do not limit the disclosed technology in any way. Therefore, the disclosed technology can be improved and modified in various ways without departing from its gist. Figure 4 shows an enlarged cross-sectional view of part A in Modification 1 of the battery pack shown in Figure 1. Figure 5 shows an enlarged cross-sectional view of part A in Modification 2 of the battery pack shown in Figure 1. Figure 6 shows an enlarged cross-sectional view of part A in Modification 3 of the battery pack shown in Figure 1. Figure 7 shows an enlarged cross-sectional view of part A in Modification 4 of the battery pack shown in Figure 1. Figure 8 shows an enlarged cross-sectional view of part A in Modification 5 of the battery pack shown in Figure 1.

[0028] In this battery pack 10P, as shown in Figures 4, 5, 7, and 8, the extruded case bodies 11B, 11C, 11E, and 11F are provided with partition walls 113B, 113C, 113E, and 113F that extend axially (Z direction) between the lower short side portion 112b and the lower end portion 2K of the electrode body 2, connecting the long side portions 111 to each other, or the long side portion 111 and the lower short side portion 112b. Coolant flow paths 117B, 117C, 117E, and 117F are formed between the partition walls 113B, 113C, 113E, and 113F and the long side portion 111 and the lower short side portion 112b. These are also possible in modified versions 1, 2, 4, and 5 of the battery pack 10P.

[0029] In this case, the cooling performance of the battery cells 10B, 10C, 10E, and 10F constituting the battery pack 10P can be further improved by the refrigerant flowing through the refrigerant channels 117B, 117C, 117E, and 117F formed between the partition walls 113B, 113C, 113E, and 113F and the long side portion 111 and the lower short side portion 112b.

[0030] As a result, when rapidly charging the battery cells 10B, 10C, 10E, and 10F, the pressure inside the battery cans 1B, 1C, 1E, and 1F increases due to the temperature rise of the battery cells 10B, 10C, 10E, and 10F, or when the electrode body 2 expands in volume due to the aging of the battery cells 10B, 10C, 10E, and 10F, heat can be dissipated to the cooling section 54 via the lower short side portion 112b, which is less prone to deformation, and heat can also be dissipated via the refrigerant flowing through the refrigerant passages 117B, 117C, 117E, and 117F of the battery cans 1B, 1C, 1E, and 1F, thereby more effectively cooling the battery cells 10B, 10C, 10E, and 10F that constitute the battery pack 10P.

[0031] Furthermore, in the battery pack 10P, as shown in Figures 6, 7, and 8, elastically deformable locking claws KM are extended axially (Z-direction) along the inner wall surfaces 118D, 118E, and 118F that are recessed upward from the lower end surface at both ends 115D, 115E, and 115F in the width direction, and the projections 55D, 55E, and 55F are formed to be able to engage with the locking claws KM from below. These are also examples of modified battery packs 10P 3, 4, and 5.

[0032] In this case, when the lower short side portion 112b of each battery cell 10D, 10E, and 10F is brought into contact with the cooling unit 54 from above, the projections 55D, 55E, and 55F of the cooling unit 54 engage with the locking claws KM formed on the inner wall surfaces 118D, 118E, and 118F of both widthwise ends 115D, 115E, and 115F of the lower short side portion 112b, allowing the projections 55D, 55E, and 55F of the cooling unit 54 to fit with both widthwise ends 115D, 115E, and 115F of the lower short side portion 112b. Therefore, in this fitted state, the lower short side portion 112b comes into contact with the cooling unit 54 and is less likely to separate from the cooling unit 54. Consequently, the battery cells 10D, 10E, and 10F constituting the battery pack 10P can be cooled more reliably.

[0033] Furthermore, in the battery packs 10P of modified examples 3, 4, and 5, it is preferable that grooves 116 are formed at both ends 115D, 115E, and 115F in the width direction, adjacent to the inner wall surfaces 118D, 118E, and 118F in the width direction, extending upward from the lower end surface to a depth similar to that of the inner wall surfaces 118D, 118E, and 118F. In this case, the protrusions 55D, 55E, and 55F can engage with the locking claws KM from below more easily.

[0034] Furthermore, in the battery pack 10P of Modification 1, as shown in Figure 4, an inclined guide surface may be formed at the upper end of the projection 55B to guide both ends 115B in the width direction of the lower short side portion 112b. Also, in the battery pack 10P of Modification 4, as shown in Figure 7, an inverted V-shaped guide surface 542 may be formed on the upper surface of the cooling section 54 to guide both ends 115E in the width direction of the lower short side portion 112b of the adjacent battery cell 10E. In this case, both ends 115B and 115E in the width direction of the lower short side portion 112b of the battery cells 10B and 10E can be more easily fitted from above with the projections 55B and 55E formed on the upper surface of the cooling section 54.

[0035] Furthermore, in the battery packs 10P of modified examples 3, 4, and 5, as shown in Figures 6, 7, and 8, a cooling plate 51c that is elastically deformable and has multiple refrigerant flow paths 51e between the long side portions 111 may be provided. In this case, the cooling performance of the battery cells 10D, 10E, and 10F can be further improved. [Explanation of Symbols]

[0036] 1, 1B, 1C, 1D, 1E, 1F Battery cans 2 Electrode body 2K bottom end 5 Restraint mechanism 10, 10B, 10C, 10D, 10E, 10F battery cells 10-pack battery 11, 11B, 11C, 11D, 11E, 11F Extrusion case body 11T end 12 Lid 51 Intervening member 54 Cooling section 55, 55B, 55C, 55D, 55E, 55F protrusion 111 Long side part 112a Upper short side part 112b Lower short side part 113B, 113C, 113E, 113F Bulkhead 115, 115B, 115C: Both ends in the width direction 115D, 115E, 115F: Both ends in the width direction 117B, 117C, 117E, 117F Refrigerant flow path 118D, 118E, 118F Interior wall surface CS arc surface KM Locking Claw ND secondary battery

Claims

1. A plurality of battery cells comprising an electrode body, a metal battery can comprising a pair of axially extending long side portions and upper and lower short side portions perpendicular to the long side portions, with both ends in the axial direction open, and a pair of lids that seal the ends, thereby constituting a secondary battery, A battery pack comprising: a restraining mechanism that restrains the battery cells by applying pressure from both ends in the stacking direction while the battery cells are stacked with an intervening member sandwiched between their long side portions, The restraining mechanism includes a cooling section that contacts the lower short side portion to cool the battery cell. The widthwise ends of the aforementioned lower short side portion are formed to be able to fit from above with the projections formed on the upper surface of the cooling portion. Battery pack.

2. In the battery pack described in claim 1, The thickness of the lower short side portion is formed to be thicker than the thickness of the upper short side portion. Battery pack.

3. In the battery pack described in claim 1, At both ends in the width direction, arcuate surfaces projecting outward in the width direction are extended along the axial direction. The aforementioned projection is formed to be elastically deformable and fit with respect to the arcuate surface. Battery pack.

4. In the battery pack described in claim 1, At both ends in the width direction, elastically deformable locking claws are provided extending axially along the inner wall surface, which is recessed upward from the lower end surface. The projection is formed to be able to engage with the locking claw from below. Battery pack.

5. In the battery pack described in claim 1, The extrusion case body is provided with a partition wall that extends axially between the lower short side portion and the lower end of the electrode body, connecting the long side portions together, or the long side portion and the lower short side portion. A refrigerant flow path is formed between the partition wall, the long side surface, and the lower short side surface. Battery pack.

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