JP7822981B2 - Energy storage devices - Google Patents

Description

This disclosure relates to an electricity storage device.

In the flat prismatic battery disclosed in Patent Document 1, the main case is formed as a half-shell made of processed metal plate with a flange around the opening of the recess. A plate assembly is housed in the recess. A metal cover plate is disposed with its peripheral portion overlapping the flange and welded to the flange. In this battery, a recess is formed in the main case and/or cover plate in a direction that reduces the battery's thickness. According to the publication, the recess presses against the plate assembly housed in the recess, compressing it, thereby suppressing expansion of the plate assembly. The publication also describes how forming the recess so that its depth is greater than or equal to the expected amount of expansion results in outward bulging within the depth of the recess. This prevents changes in the thickness of the battery even if the recess bulges, thereby suppressing the impact of battery bulging on the device.

The publication also proposes making the deformation strength of the cover plate with the recess lower than the deformation strength of the main case. It states that this makes it easier for pressure from inside the battery in the direction of expansion to reach the cover plate, making it less likely for expansion to occur on the main case side.

Japanese Patent Application Laid-Open No. 2004-103368

By the way, the inventor wants to improve the safety of electricity storage devices.

The electricity storage device disclosed herein includes a flat electrode assembly having a pair of opposing rectangular surfaces, and a hexahedral case housing the electrode assembly. The case includes a case body having a first surface, which is the widest of the six surfaces, and an opening facing the first surface, and a sealing plate, shaped to match the shape of the opening, that seals the opening. Inside the case, the electrode assembly is sandwiched between the first surface and the sealing plate so that the first surface faces one of the pair of rectangular surfaces, and the sealing plate faces the other of the pair of rectangular surfaces. The case is provided with a discharge valve that ruptures when the internal pressure of the case reaches a first threshold value P1. At least one of the first surface and the sealing plate is provided with a protruding portion that protrudes toward the rectangular surface. The protruding portion is configured to invert and protrude toward the outside of the case when the internal pressure of the case reaches a second threshold value P2, which is smaller than the first threshold value P1. An electricity storage device with this configuration has enhanced safety.

In one preferred embodiment of the energy storage device disclosed herein, the protruding portion protrudes in a dome shape toward the opposing rectangular surface when not inverted. This configuration can further improve the safety of the energy storage device.

In another preferred embodiment of the energy storage device disclosed herein, a protruding portion is provided on only one of the first surface and the sealing plate. With this configuration, the surface without the protruding portion can be made flat. This allows a certain degree of confining pressure to be constantly applied to the entire rectangular surface of the electrode body facing the flat surface.

In another preferred embodiment of the energy storage device disclosed herein, the protruding portion contacts the opposing rectangular surface when not inverted. This configuration not only improves the safety of the energy storage device, but also suppresses expansion of the electrode body.

In another preferred embodiment of the power storage device disclosed herein, the ratio (P2/P1) of the first threshold value P1 to the second threshold value P2 is 0.5 or greater and 0.8 or less. By setting the ratio (P2/P1) within this range, the safety of the power storage device can be more effectively improved.

FIG. 1 is a perspective view of an electricity storage device 1. FIG. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3 is a cross-sectional view taken along line III-III of FIG. FIG. 4 is an exploded perspective view of the case 10. As shown in FIG. FIG. 5 is a cross-sectional view of the electricity storage device 1. FIG. 6 is a schematic diagram of the electrode body 20.

An embodiment of the technology disclosed herein is described below. The embodiment described herein is not intended to limit the technology disclosed herein. Unless otherwise specified, the technology disclosed herein is not limited to the embodiment described herein. The drawings are schematic and do not necessarily reflect the actual product. Furthermore, components and parts that perform the same function are appropriately designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, the notation "A to B" indicating a numerical range means "greater than or equal to A and less than B" unless otherwise specified, and also encompasses the meaning of "greater than A and less than B."

In this specification, the term "electricity storage device" refers to a device in which charge and discharge reactions occur as charge carriers move between a pair of electrodes (positive and negative electrodes) via an electrolyte. Such electricity storage devices include secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium-ion capacitors and electric double-layer capacitors. Below, we will explain an embodiment in which the electricity storage device is an electricity storage module equipped with a lithium-ion secondary battery.

Figure 1 is a perspective view of the energy storage device 1. Figure 2 is a cross-sectional view taken along line II-II of Figure 1. Figure 2 shows a cross-sectional view along the first surface 12a of the case 10. Figure 3 is a cross-sectional view taken along line III-III of Figure 1. Figure 3 shows a cross-sectional view along the second surfaces 12b and 12c of the case 10. Figure 4 is an exploded perspective view of the case 10. Figure 4 shows the case body 12 and the sealing plate 14 removed from the opening 12h of the case body 12.

<Electricity storage device 1>
The technology disclosed herein provides an electricity storage device 1. As shown in Figures 1 and 2, the electricity storage device 1 includes a case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collecting member 50, a negative electrode current collecting member 60, an electrolyte (not shown), and various insulating members.

-Case 10-
The case 10 is, for example, a hexahedron-shaped member that houses the electrode assembly 20. As shown in FIGS. 1 to 4 , the case 10 includes a case body 12 and a sealing plate 14. The case body 12 is, for example, the main body of the case 10 that houses the electrode assembly 20 therein. As shown in FIGS. 1 to 4 , the case body 12 has an opening 12h, a first surface 12a, a pair of opposing second surfaces 12b and 12c, and a pair of opposing third surfaces 12d and 12e. In this embodiment, the first surface 12a has a wide rectangular shape and is the widest of the six surfaces of the case 10. The first surface 12a faces the opening 12h. The pair of second surfaces 12b and 12c extend from a pair of opposing long sides of the first surface 12a. As shown in FIGS. 1 to 3 , the lower second surface 12c forms the bottom surface of the electricity storage device 1. The upper second surface 12b is the top surface opposite the bottom surface and is a mounting surface for electrode terminals. The pair of third surfaces 12d, 12e extend from a pair of opposing short sides of the first surface 12a. In this specification, the term "rectangular" includes shapes in which linear long and short sides are joined to each other via curves, shapes in which at least one of the long and short sides is not linear but is curved, uneven, or bent and composed of multiple straight or curved lines, etc.

Opening 12h is, for example, a location where sealing plate 14 is attached. Here, opening 12h is formed by being surrounded by the upper edges of the pair of second surfaces 12b, 12c and the upper edges of the pair of third surfaces 12d, 12e, and has a wide rectangular shape. As shown in Figures 3 and 4, opening 12h has a recessed step 121 along its inner edge. Here, sealing plate 14 is fitted into step 121. Furthermore, by joining (e.g., welding) sealing plate 14 to step 121, the case body 12 and sealing plate 14 are integrated, and the case 10 is hermetically sealed.

In the embodiment shown in Figures 3 and 4, the first surface 12a is a flat surface without any irregularities, through holes, etc. By making the first surface 12a a flat surface, it is possible to apply a confining pressure to the entire rectangular surface 20a of the electrode body 20.

As shown in Figures 1 to 4, the second surface 12b is provided with a discharge valve 123, a first mounting portion 124, and a second mounting portion 125. The discharge valve 123 is, for example, a thin-walled portion. Here, the discharge valve 123 is configured to burst open when the internal pressure of the case 10 reaches a first threshold P1, thereby discharging gas inside the case 10 to the outside. For this reason, the thickness of the discharge valve 123 is, for example, smaller than the thickness of other portions of the case body 12. Furthermore, the discharge valve 123 is provided with a recess, such as a groove or depression, that has a locally smaller thickness to facilitate bursting when necessary. The first mounting portion 124 is, for example, a portion where the positive terminal 30 is attached. In the embodiment shown in Figures 2 and 4, the first mounting portion 124 is a step recessed from the second surface 12b. A through-hole 18 through which the positive terminal 30 is inserted is provided at the bottom of the first mounting portion 124. The second mounting portion 125 is, for example, a portion where the negative electrode terminal 40 is attached. In the embodiment shown in FIG. 4, the second mounting portion 125 is a step recessed from the second surface 12b. A through-hole 19 through which the negative electrode terminal 40 is inserted is provided at the bottom of the second mounting portion 125.

By having the exhaust valve 123 configured as described above, when gas is generated inside the case 10 and the internal pressure of the case 10 increases, the exhaust valve 123 opens to release the gas outside the case 10, thereby reducing the internal pressure. However, with the recent widespread use of electricity storage devices, there is an increasing demand for improved safety in electricity storage devices. The inventors therefore considered the configuration of the case 10, believing that if an abnormality occurs in the electricity storage device and the internal case pressure increases, the safety of the electricity storage device could be improved if the internal case pressure could be reduced, for example, before the exhaust valve 123 opens.

The sealing plate 14 is, for example, a flat plate-like member that seals the opening 12h. Therefore, the shape of the sealing plate 14 may correspond to the shape of the opening 12h. In this embodiment, the sealing plate 14 is a wide rectangle. Here, when the sealing plate 14 is attached to the opening 12h, the sealing plate 14 faces the first surface 12a. As shown in FIG. 4, the sealing plate 14 has a pair of opposing long sides 14a, 14b and a pair of opposing short sides 14c, 14d. Here, the long side 14a rests on the bottom of the step 121 on the second surface 12b side. The long side 14b rests on the bottom of the step 121 on the second surface 12c side. The short side 14c rests on the bottom of the step 121 on the third surface 12d side. Additionally, the short side 14d rests on the bottom of the step 121 on the third surface 12e side.

1, 3, and 4, the sealing plate 14 has a flat portion 141 and a protruding portion 142. The flat portion 141 is, for example, a flat portion without irregularities, through holes, etc. Here, the flat portion 141 is the portion excluding the protruding portion 142. The protruding portion 142 is, for example, a portion protruding toward the rectangular surface 20a of the electrode body 20. In this embodiment, the protruding portion 142 is configured to reverse and protrude toward the outside of the case 10 when the internal pressure of the case 10 reaches a second threshold P2 that is lower than the first threshold P1 of the exhaust valve 123. The protruding portion 142 protrudes from the base end 142B toward the rectangular surface 20a, but when necessary, it reverses around the base end 142B as an axis and protrudes toward the outside of the case 10. The base end 142B is located, for example, at the edge of the flat portion 141 on the center side of the sealing plate 14 (here, the boundary between the flat portion 141 and the protruding portion 142).

As shown in Figures 1 to 3, when not inverted, the protruding portion 142 protrudes in a dome shape toward the opposing rectangular surface 20a. By configuring the protruding portion 142 in a dome shape, it can be more easily inverted when the internal pressure of the case 10 reaches the second threshold value P2. This improves the effectiveness of enhancing the safety of the power storage device. In this embodiment, the protruding portion 142 is elliptical in plan view, but is not limited to this. In other embodiments, the shape of the protruding portion 142 in plan view may be a perfect circle, an elongated hole, a substantially rectangular shape, etc.

In the embodiment shown in Figures 1 to 3, the power storage device 1 has a protruding portion 142 only on the sealing plate 14. By providing a protruding portion 142 only on the sealing plate 14, the first surface 12a can be made flat. This allows a certain degree of confining pressure to be constantly applied to the entire rectangular surface 20a facing the first surface 12a (flat surface) of the pair of rectangular surfaces 20a.

As shown in Figure 3, the protruding portion 142 contacts the opposing rectangular surface 20a when not inverted. This allows a confining pressure to be applied to the rectangular surface 20a, thereby suppressing expansion of the electrode body 20. The protruding portion 142 also fixes the electrode body 20 within the case 10. This prevents the electrode body 20 from moving within the case 10 when vibrations, shocks, etc. are applied to the energy storage device 1, thereby preventing the electrode tabs from tearing, etc.

For example, the protruding portion 142 applies a relatively greater pressing force to the central region 20CR of the rectangular surface 20a of the electrode body 20 than to the edge regions 20PR (see FIG. 2). Here, the central region 20CR is a region whose center is the intersection CP of a first center line CL1 passing through the midpoint A of a pair of opposing long sides of the rectangular surface 20a and a second center line CL2 passing through the midpoint B of a pair of opposing short sides of the rectangular surface 20a. When the area of the rectangular surface 20a is 1, the area of the central region 20CR should be approximately 1/8 to 1/2 (e.g., 1/6 to 1/3). Here, the edge regions 20PR are the area of the rectangular surface 20a excluding the central region 20CR. In the embodiment shown in FIG. 2, the central region 20CR is the area of the rectangular surface 20a surrounded by a dotted line. The end region 20PR is the region outside the dotted line on the rectangular surface 20a.

Considering that only the protruding portion 142 inverts when the internal pressure of the case 10 reaches the second threshold P2, the thickness of the protruding portion 142 should be smaller than, for example, the thickness of the flat portion 141 and the thickness of the case body 12. Also, considering that the second threshold P2 (inversion pressure) of the protruding portion 142 is smaller than the first threshold P1 (rupture pressure) of the discharge valve 123, the thickness of the protruding portion 142 should be smaller than the thickness of the discharge valve 123.

From the perspective of appropriately achieving the effect of enhancing the safety of the power storage device 1, the ratio (P2/P1) of the first threshold value P1 to the second threshold value P2 can be set to approximately 0.2 to 0.9. The ratio (P2/P1) is preferably 0.5 to 0.8. This more preferably achieves the effect of enhancing the safety of the power storage device 1.

Figure 5 is a cross-sectional view of the energy storage device 1. Figure 5 shows the protruding portion 142 protruding outward. In this embodiment, the energy storage device 1 includes the exhaust valve 123 and the protruding portion 142 as components that are activated when the internal pressure of the case 10 increases. When the internal pressure of the case 10 does not reach either the threshold of the exhaust valve 123 or the threshold of the protruding portion 142, the exhaust valve 123 does not burst, and the protruding portion 142 does not invert (see Figure 3). When the internal pressure of the case 10 increases and reaches the second threshold P2, the protruding portion 142 bursts outward from the case 10, centering around the base end 142B (see Figure 5). Here, as described above, the second threshold P2 is smaller than the first threshold P1, which is the bursting pressure of the exhaust valve, and therefore the case 10 continues to expand outward until the internal pressure of the case 10 increases and reaches the first threshold P1. When the internal pressure of the case 10 reaches the first threshold value P1, the exhaust valve 123 opens.

-Electrode body 20-
The electrode assembly 20 is a power generating element of the electricity storage device 1, for example, having a positive electrode and a negative electrode. FIG. 6 is a schematic diagram of the electrode assembly 20. As shown in FIG. 6, the electrode assembly 20 is a wound electrode assembly in which a long sheet-like positive electrode 22 and a long sheet-like negative electrode 24 are wound in the sheet longitudinal direction LD with a separator 23 interposed therebetween. The electrode assembly 20 can be produced, for example, by winding the positive electrode 22, the negative electrode 24, and the separator 23 into a cylindrical body and press-molding the cylindrical body. Therefore, the electrode assembly 20 has a flat shape and a pair of rectangular faces 20a (see FIGS. 2 and 3).

2 and 6, the electrode body 20 is housed in the case body 12 so that the winding axis direction WD and the vertical direction of the energy storage device 1 are approximately parallel. In this embodiment, the winding axis WL of the electrode body 20 is approximately parallel to the first surface 12a, the third surfaces 12d and 12e, and the sealing plate 14, and is approximately perpendicular to the second surfaces 12b and 12c. Furthermore, within the case 10, the electrode body 20 is sandwiched between the first surface 12a and the sealing plate 14 so that the first surface 12a faces one of the pair of rectangular surfaces 20a, and the sealing plate 14 faces the other of the pair of rectangular surfaces 20a. Furthermore, one end face of the electrode body 20 in the winding axis direction WD faces the second surface 12b, and the other end face faces the second surface 12c. In this case, the end surface of the electrode assembly 20 is the laminated surface of the positive electrode 22, negative electrode 24, and separator 23, and is an open surface.

As shown in FIG. 6, the positive electrode 22 has a long, strip-shaped positive electrode current collector foil 22c (e.g., aluminum foil) and a positive electrode active material layer 22a adhered to at least one surface of the positive electrode current collector foil 22c. Although not particularly limited, a protective layer 22p may be provided on one side edge of the positive electrode 22 in the winding axis direction WD, as needed. Note that the constituent materials of the positive electrode active material layer 22a and the protective layer 22p may be any materials used in this type of electricity storage device (in this embodiment, a lithium-ion secondary battery) without any particular restrictions.

A plurality of positive electrode tabs 22t are provided at one end of the positive electrode current collector foil 22c in the winding axis direction WD (the upper end in Figure 6). The plurality of positive electrode tabs 22t protrude toward one end of the winding axis direction WD (the upper end in Figure 6). The plurality of positive electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction LD of the positive electrode 22. The positive electrode tabs 22t are part of the positive electrode current collector foil 22c and are portions of the positive electrode current collector foil 22c where the positive electrode active material layer 22a is not formed (active material layer unformed portion). In the embodiment shown in Figure 6, a protective layer 22p is provided on the base end side of the positive electrode tab 22t. In this embodiment, the plurality of positive electrode tabs 22t protrude further in the winding axis direction WD than the separator 23. The plurality of positive electrode tabs 22t are stacked at one end of the winding axis direction WD (the upper end in Figure 6) to form a positive electrode tab group. For this reason, the height (length in the winding axis direction WD) and the width (length in the longitudinal direction LD) of each positive electrode tab 22t do not need to be the same. As shown in Figure 2, a positive electrode current collecting member 50 is joined to the stacked positive electrode tabs 22t (positive electrode tab group).

As shown in FIG. 6, the negative electrode 24 has a long, strip-shaped negative electrode current collector foil 24c (e.g., copper foil) and a negative electrode active material layer 24a adhered to at least one surface of the negative electrode current collector foil 24c. Note that the constituent materials of the negative electrode active material layer 24a may be any materials used in this type of electricity storage device (in this embodiment, a lithium-ion secondary battery) without any particular restrictions.

A plurality of negative electrode tabs 24t are provided at one end of the negative electrode current collector foil 24c in the winding axis direction WD (the upper end in Figure 6). The plurality of negative electrode tabs 24t protrude toward one end of the winding axis direction WD (the upper end in Figure 6). The plurality of negative electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction LD of the negative electrode 24. The negative electrode tabs 24t are part of the negative electrode current collector foil 24c and are portions of the negative electrode current collector foil 24c where the negative electrode active material layer 24a is not formed (active material layer unformed portions). In this embodiment, the plurality of negative electrode tabs 24t protrude further in the winding axis direction WD than the separator 23. For example, the plurality of negative electrode tabs 24t are stacked at one end of the winding axis direction WD (the upper end in Figure 6) to form a negative electrode tab group. For this reason, the height (length in the winding axis direction WD) and the width (length in the longitudinal direction LD) of each negative electrode tab 24t do not need to be the same. As shown in Figure 2, a negative electrode current collecting member 60 is joined to the stacked negative electrode tabs 24t (negative electrode tab group).

The separator 23 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. In this embodiment, the separator 23 forms the outer surface of the electrode assembly 20. The separator 23 is, for example, a porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP).

As shown in Figure 6, in the electrode assembly 20, the lower end P3 of the separator 23 is the lowest, followed by the lower end P2 of the negative electrode 24, and the lower end P1 of the positive electrode 22 is the highest. The widths of each sheet (in Figure 6, this is the length in the winding direction WD, excluding the positive electrode tab 22t and negative electrode tab 24t) are largest in the order of separator 23, negative electrode 24, and positive electrode 22.

- Positive electrode terminal 30 -
The positive electrode terminal 30 is, for example, a member electrically connected to the positive electrode 22 of the electrode body 20. As shown in FIG. 2 , the positive electrode terminal 30 is inserted through the through hole 18 and exposed to the outside of the case body 12. Here, the positive electrode terminal 30 has a first conductive member 31 and a second conductive member 32. In this embodiment, the first conductive member 31 has a shaft portion 31 a and a base portion 31 b. The shaft portion 31 a is, for example, cylindrical and is inserted into the through hole 18 and the through hole of the second conductive member 32. The base portion 31 b is, for example, flat and is disposed along the outer surface (here, the second surface 12 b) of the case body 12. The second conductive member 32 is, for example, flat and is connected to a bus bar when constructing the energy storage module. In this embodiment, the second conductive member 32 is rectangular. The first conductive member 31 and the second conductive member 32 are connected to each other outside the case 10. The first conductive member 31 is made of, for example, aluminum or an aluminum alloy. The second conductive member 32 is made of, for example, aluminum, an aluminum alloy, copper, a copper alloy, or the like.

-Negative terminal 40-
The negative electrode terminal 40 is, for example, a member electrically connected to the negative electrode 24 of the electrode body 20. As shown in FIG. 2 , the negative electrode terminal 40 is inserted into the through-hole 19 and exposed to the outside of the case body 12. Here, the negative electrode terminal 40 has a first conductive member 41 and a second conductive member 42. The first conductive member 41 is made of, for example, copper or a copper alloy. The negative electrode terminal 40 may have a configuration similar to that of the positive electrode terminal 30, for example. Therefore, a description of the configuration of the negative electrode terminal 40 will be omitted here.

--Positive electrode current collecting member 50--
The positive electrode current collecting member 50 is, for example, a member that electrically connects the positive electrode tab 22t and the positive electrode terminal 30. The positive electrode current collecting member 50 is, for example, a plate-shaped conductive member. As shown in FIG. 2 , the positive electrode current collecting member 50 extends along the inner surface of the case body 12 (here, the inside of the second surface 12b) in the direction of the long side of the second surface 12b. The positive electrode tab 22t (here, a group of positive electrode tabs) is connected to one end (the right end in FIG. 2 ) of the positive electrode current collecting member 50. The lower end of the shaft portion 31a of the positive electrode terminal 30 is inserted into a through-hole 50h at the other end (the left end in FIG. 2 ) of the positive electrode current collecting member 50 and crimped. The positive electrode current collecting member 50 is, for example, made of aluminum or an aluminum alloy.

-Negative electrode current collecting member 60-
The negative electrode current collecting member 60 is, for example, a member that electrically connects the negative electrode tab 24t and the negative electrode terminal 40. The negative electrode current collecting member 60 is, for example, a plate-shaped conductive member. As shown in FIG. 2 , the negative electrode current collecting member 60 extends along the inner surface of the case body 12 (here, the inside of the second surface 12b) in the direction of the longer side of the second surface 12b. The negative electrode tab 24t (here, a group of negative electrode tabs) is connected to one end (the left end in FIG. 2 ) of the negative electrode current collecting member 60. The lower end of the negative electrode terminal 40 is inserted into a through-hole 60h at the other end (the right end in FIG. 2 ) of the negative electrode current collecting member 60 and crimped. The negative electrode current collecting member 60 is, for example, made of copper or a copper alloy.

-Electrolyte-
The electrolyte solution contains, for example, an electrolyte salt and a non-aqueous solvent. Examples of the electrolyte salt include _LiPF6 . The concentration of the electrolyte salt in the electrolyte solution is, for example, 0.7 mol/L to 1.3 mol/L. The non-aqueous solvent may be, for example, a carbonate. Examples of carbonates include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), and the like. These may be used alone or in combination of two or more.

-Insulating materials-
Various insulating members are used in the power storage device 1. In the embodiment shown in Fig. 2, a first insulating member 91 and a second insulating member 92 are used. In this embodiment, the first insulating member 91 insulates the positive electrode terminal 30 or the negative electrode terminal 40 from the second surface 12b at the outside of the case 10 and the inner wall of the through hole 18 or the through hole 19. Furthermore, the second insulating member insulates the positive electrode terminal 30 or the negative electrode terminal 40 from the second surface 12b inside the case 10.

The electricity storage device 1 can be used for a variety of purposes, but is particularly suitable as a power source (driving power source) for motors mounted on vehicles such as passenger cars and trucks. While there are no particular limitations on the type of vehicle, suitable examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

As described above, the energy storage device 1 includes a flat electrode assembly 20 and a hexahedral case 10 that houses the electrode assembly 20. The electrode assembly 20 has a pair of opposing rectangular surfaces 20a. The case 10 includes a case body 12 having a first surface 12a, which is the widest of the six surfaces, and an opening 12h facing the first surface 12a. The case body 12 also includes a sealing plate 14 that has a shape corresponding to the shape of the opening 12h and seals the opening 12h. Inside the case 10, the electrode assembly 20 is sandwiched between the first surface 12a and the sealing plate 14 so that the first surface 12a faces one of the pair of rectangular surfaces 20a and the sealing plate 14 faces the other rectangular surface 20a. The case 10 is provided with a discharge valve 123 that ruptures when the internal pressure of the case 10 reaches a first threshold value P1. The sealing plate 14 has a protruding portion 142 that protrudes toward the rectangular surface 20a. The protruding portion 142 is configured to reverse and protrude outward from the case 10 when the internal pressure of the case 10 reaches a second threshold P2 that is lower than the first threshold P1.

In the electricity storage device 1, the protruding portion 142 inverts outward at a second threshold P2 that is smaller than the first threshold P1 at which the discharge valve 123 ruptures. In the electricity storage device 1, when the internal pressure of the case 10 reaches the second threshold P2, the protruding portion 142 inverts and bulges outward, increasing the volume of the case 10. Therefore, when the internal pressure of the case 10 increases, the internal pressure can be reduced before the discharge valve 123 opens. Furthermore, as the protruding portion 142 bulges outward, the confining pressure exerted by the protruding portion 142 on the electrode assembly 20 is no longer applied. This widens the inter-electrode distance in the electrode assembly 20, increasing resistance. This suppresses the progression of excessive reactions in the electricity storage device 1. Therefore, the safety of the electricity storage device 1 having the above-described configuration is enhanced.

In the above embodiment, the protruding portion 142 of the energy storage device 1 is provided only on the sealing plate 14. However, this is not limited to this. The protruding portion 142 may be provided only on the first surface 12a. This configuration can also improve the safety of the energy storage device 1. Alternatively, the protruding portion 142 may be provided on both the sealing plate 14 and the first surface 12a. In this way, when the protruding portion 142 protrudes outward, the volume of the case 10 can be increased, thereby efficiently reducing the internal pressure of the case 10.

As described above, specific aspects of the technology disclosed herein include those described in the following sections.
Item 1:
An electricity storage device,
a flat electrode body having a pair of opposing rectangular surfaces;
a hexahedral case for accommodating the electrode assembly, the case having a case body having a first surface that is the widest of the six surfaces and an opening facing the first surface, and a sealing plate that seals the opening and has a shape corresponding to the shape of the opening;
It is equipped with
Within the case, the electrode body is sandwiched between the first surface and the sealing plate such that the first surface faces one of the pair of rectangular surfaces and the sealing plate faces the other of the pair of rectangular surfaces,
The case is provided with a discharge valve that opens when the internal pressure of the case reaches a first threshold value P1,
a protruding portion that protrudes toward the rectangular surface is provided on at least one of the first surface and the sealing plate,
The power storage device is configured such that the protruding portion reverses and protrudes outward from the case when the internal pressure of the case reaches a second threshold value P2 that is lower than the first threshold value P1.
Item 2:
Item 2. The power storage device according to item 1, wherein the protruding portion protrudes in a dome shape toward the opposing rectangular surface when the protruding portion is not inverted.
Item 3:
Item 3. The power storage device according to item 1 or 2, wherein the protruding portion is provided on only one of the first surface and the sealing plate.
Item 4:
Item 4. The power storage device according to any one of Items 1 to 3, wherein the protruding portion is in contact with the opposing rectangular surface when the protruding portion is not inverted.
Item 5:
Item 5. The power storage device according to any one of items 1 to 4, wherein a ratio (P2/P1) of the first threshold value P1 to the second threshold value P2 is 0.5 or more and 0.8 or less.

The above describes embodiments of the technology disclosed herein, but it is not intended that the technology disclosed herein be limited to the above embodiments. The technology disclosed herein may also be implemented in other embodiments. The technology described in the claims includes various modifications and variations of the embodiments exemplified above. For example, it is possible to replace part of the above embodiments with other modified embodiments, and it is also possible to add other modified embodiments to the above embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

1 Electricity storage device 10 Case 12 Case body 123 Discharge valve 12a First surface 12h Opening 14 Sealing plate 142 Projecting portion 20 Electrode body 20a Rectangular surface 22 Positive electrode 23 Separator 24 Negative electrode 30 Positive electrode terminal 40 Negative electrode terminal 50 Positive electrode current collector 60 Negative electrode current collector 91 First insulating member 92 Second insulating member

Claims (2)

An electricity storage device,
a flat electrode body having a pair of opposing rectangular surfaces, the electrode body being a wound electrode body in which a long sheet-like positive electrode and a long sheet-like negative electrode are wound in the sheet longitudinal direction with a separator interposed therebetween ;
a hexahedral case for accommodating the electrode assembly, the case having a case body having a first surface that is the widest of the six surfaces and an opening facing the first surface, and a sealing plate that seals the opening and has a shape corresponding to the shape of the opening;
It is equipped with
Within the case, the electrode body is sandwiched between the first surface and the sealing plate such that the first surface faces one of the pair of rectangular surfaces and the sealing plate faces the other of the pair of rectangular surfaces,
The case is provided with a discharge valve that opens when the internal pressure of the case reaches a first threshold value P1,
a protruding portion that protrudes toward the rectangular surface is provided on at least one of the first surface and the sealing plate,
the protruding portion is configured to reverse and protrude outward from the case when the internal pressure of the case reaches a second threshold value P2 that is lower than the first threshold value P1,
the protruding portion is provided on only one of the first surface and the sealing plate,
the first surface and the sealing plate, whichever surface is not provided with the protruding portion, has a flat surface;
When the protruding portion is not inverted,
It protrudes in a dome shape toward the opposing rectangular surface,
the pressing force is greater in a central region of the rectangular surface than in an end region of the rectangular surface, and
The central region is a region having a center point at the intersection of a first center line passing through the midpoints of a pair of opposing long sides of the rectangular surface and a second center line passing through the midpoints of a pair of opposing short sides of the rectangular surface, and having an area of 1/6 to 1/3 of the area of the rectangular surface .
Energy storage device. The power storage device according to claim 1 , wherein a ratio (P2/P1) of the first threshold value P1 to the second threshold value P2 is equal to or greater than 0.5 and equal to or less than 0.8.