Energy storage devices

Abstract

To provide a power storage device in which lithium salt is less likely to deposit in the vicinity of an electrode tab group.SOLUTION: A power storage device 100 disclosed herein includes an electrode assembly 20 including a first electrode 22 and a second electrode 24, an electrolyte 80, and a case 10 that accommodates them. The electrode assembly 20 includes a first electrode tab group and a second electrode tab group. The case 10 includes a case body 12 including a bottom wall 12a, a pair of first side walls 12b, a pair of second side walls 12c, and an opening 12h, and a sealing plate 14 that seals the opening 12h. When the power storage device 100 is in a fully charged state, the power storage device 100 has an excess electrolyte 80 which is an electrolyte present between the case body 12 and the electrode assembly 20 in a state in which a direction perpendicular to the bottom wall 12a is the vertical direction, and a liquid level 80H of the excess electrolyte 80 is located closer to the sealing plate 14 than a portion of the first electrode tab group 23 closest to the bottom wall 12a.SELECTED DRAWING: Figure 3

Description

Technical Field

[0005]

[0001] The present disclosure relates to a power storage device.

Background Art

[0002] Patent Document 1 discloses a battery including a wound electrode body. A positive electrode tab group is provided at one end of the wound electrode body, and a negative electrode tab group is provided at the other end. In this battery, the wound electrode body is housed in a battery case such that the positive electrode tab group and the negative electrode tab group protrude toward the side wall of the battery case (a so-called horizontal tab type battery).

[0003] Patent Document 2 discloses a lithium ion secondary battery in which the lower end of a wound electrode body is immersed in an electrolytic solution. In this battery, by defining the position of the liquid surface of the electrolytic solution with respect to the height of the electrolytic solution of the wound electrode body and the position of the joint portion between the electrode body and the current collector terminal, a lithium ion secondary battery excellent in cycle durability is realized. Further, Patent Document 3 discloses a technique for shortening the time required for the step of injecting the electrolytic solution into the battery case.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in a power storage device including an electrolytic solution containing a lithium salt and an electrode body having an electrode tab group (positive electrode tab group or negative electrode tab group), lithium precipitation tends to occur in the vicinity of the electrode tab group.

[0006] Therefore, the main objective of this technology is to provide an energy storage device in which lithium salt is less likely to be deposited near the electrode tab group. [Means for solving the problem]

[0007] The energy storage device disclosed herein comprises an electrode body including a first electrode and a second electrode, an electrolyte containing an organic solvent and a lithium salt, and a case housing the electrode body and the electrolyte. The electrode body comprises a group of first electrode tabs including a plurality of first electrode tabs protruding from a first end, and a group of second electrode tabs including a plurality of second electrode tabs protruding from a second end. The case comprises a case body including a bottom wall, a pair of first side walls extending from the bottom wall and facing each other, a pair of second side walls extending from the bottom wall and facing each other, and an opening facing the bottom wall, and a sealing plate sealing the opening. The group of first electrode tabs is arranged on one side of the pair of second side walls in the electrode body, and the group of second electrode tabs is arranged on the other side of the pair of second side walls in the electrode body. Furthermore, when the energy storage device is fully charged, the energy storage device has excess electrolyte between the case body and the electrode body in a state where the direction perpendicular to the bottom wall is the vertical direction, and the liquid level of the excess electrolyte is located closer to the sealing plate than the part of the first electrode tab group closest to the bottom wall.

[0008] In an energy storage device with this configuration, at least a portion of the first electrode tab group is immersed in the excess electrolyte. This makes it easier to homogenize the lithium salt concentration near the first electrode tab group. As a result, lithium salt is less likely to precipitate near the electrode tab group. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the current density distribution at the positive and negative electrodes of a wound electrode body. [Figure 2] This is a perspective view of an energy storage device according to one embodiment. [Figure 3] This is a cross-sectional view taken along line III-III in Figure 2. [Figure 4] This is a cross-sectional view taken along line IV-IV in Figure 2. [Figure 5] Cross-sectional view of line VV in Figure 2 [Figure 6] This is a schematic perspective view showing the group of electrodes attached to the sealing plate. [Figure 7] This is a schematic perspective view showing the electrode body 20. [Figure 8] This is a schematic diagram showing the configuration of the electrode body 20. [Figure 9] This is a diagram corresponding to Figure 3 of the energy storage device according to the second embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, with reference to the drawings, several preferred embodiments of the technology disclosed herein will be described. Matters other than those specifically mentioned herein but necessary for the implementation of this disclosure (e.g., general battery configurations and manufacturing processes not characterizing this disclosure) can be understood as design matters for those skilled in the art based on the prior art. This disclosure can be implemented based on the content disclosed herein and common technical knowledge in the art. Furthermore, the following description is not intended to limit the technology disclosed herein to the following embodiments. In this specification, the notation "A to B" (where A and B are arbitrary numbers) means "A or greater and B or less," and also encompasses the meanings of "greater than A and less than B," "greater than A and less than or equal to B," and "A or greater and less than B."

[0011] In this specification, "energy storage device" refers to a device capable of charging and discharging. Energy storage devices include batteries such as secondary batteries (non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries) and capacitors (physical batteries) such as electric double-layer capacitors.

[0012] According to the inventors' research, lithium deposition near the electrode tab group is presumed to occur through the following mechanism. Note that this mechanism is not limited in any way to the present technology. First, when a power storage device is rapidly charged, the lithium salt concentration at the ends of the electrode body where the electrode tabs are located becomes lower than that in the center of the electrode body and in the excess electrolyte (more specifically, the lithium salt concentration in the excess electrolyte is lower than that in the center of the electrode body). Near the electrode tabs, electrolyte exchange is less likely to occur, making it difficult to equalize the lithium salt concentration, and the lithium salt concentration near the electrode tabs remains relatively low. As a result, the reaction resistance increases in areas with low lithium salt concentration, making it easier for current to concentrate near the electrode tabs, and thus easier for lithium deposition to occur (low high-rate resistance). Figure 1 shows the current density distribution at the positive and negative electrodes of a wound electrode body. As shown in Figure 1, it can be seen that the current density is high near the positive and negative electrode tabs. Based on these findings, the inventors have completed this technology.

[0013] Figure 2 is a perspective view of the energy storage device 100. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a cross-sectional view taken along line IV-IV in Figure 2. Figure 5 is a cross-sectional view taken along line VV in Figure 2. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, back, up, and down, respectively, and the symbols X, Y, and Z in the drawings represent the short side direction, the long side direction perpendicular to the short side direction, and the up and down direction of the energy storage device 100, respectively. However, these are merely directions for the convenience of explanation and do not limit the installation configuration of the energy storage device 100 in any way. Note that each drawing is schematically drawn, and the dimensional relationships (length, width, thickness, etc.) do not necessarily reflect the actual dimensional relationships. In addition, in the drawings described below, the same symbols are used for members and parts that perform the same function, and redundant explanations may be omitted or simplified.

[0014] As shown in FIG. 3, the power storage device 100 includes a case 10, an electrode body 20, and an electrolytic solution 80. Further, the power storage device 100 according to the present embodiment further includes a first electrode terminal 30, a first electrode external conductive member 32, a second electrode terminal 40, a second electrode external conductive member 42, a gasket 90, an external insulating member 92, a first electrode current collector 50, a second electrode current collector 60, and an internal insulating member 70. Here, the power storage device 100 is a lithium ion secondary battery.

[0015] The case 10 is a housing that houses the electrode body 20. Here, the case 10 has an outer shape of a flat and bottomed rectangular parallelepiped (rectangular shape). The material of the case 10 may be the same as that conventionally used, and there is no particular limitation. The case 10 is preferably made of a metal having a predetermined strength. Examples of such metal materials include aluminum, aluminum alloy, iron, iron alloy, and the like.

[0016] The case 10 includes a case body 12, a sealing plate 14, and a gas discharge valve 17. The case body 12 is a flat rectangular (hexahedron shape) container with one surface being an opening 12h. Specifically, as shown in FIG. 2, the case body 12 includes a substantially rectangular bottom wall 12a, a pair of first side walls 12b that extend upward in a U shape from the short sides of the bottom wall 12a and face each other, and a pair of second side walls 12c that extend upward in a U shape from the long sides of the bottom wall 12a and face each other. The area of the second side wall 12c is smaller than the area of the first side wall 12b. The opening 12h is formed on the upper surface of the case body 12 surrounded by the pair of first side walls 12b and the pair of second side walls 12c. The sealing plate 14 is attached to the case body 12 so as to seal the opening 12h of the case body 12. The sealing plate 14 is a plate material having a substantially rectangular shape in plan view. The sealing plate 14 faces the bottom wall 12a of the case body 12. The case 10 is formed by joining (for example, welding) the sealing plate 14 to the periphery of the opening 12h of the case body 12. The joining of the sealing plate 14 can be performed by welding such as laser welding.

[0017] As shown in FIGS. 2 and 3, the gas discharge valve 17 is formed in the sealing plate 14. The gas discharge valve 17 is configured to open when the pressure in the case 10 reaches or exceeds a predetermined value and discharge the gas in the case 10.

[0018] In addition to the gas discharge valve 17, the sealing plate 14 is provided with a liquid injection hole 15 and two terminal insertion holes 18 and 19. The liquid injection hole 15 communicates with the internal space of the case body 12 and is an opening provided for injecting electrolyte during the manufacturing process of the power storage device 100. The liquid injection hole 15 is sealed by a sealing member 16. As such a sealing member 16, for example, a blind rivet is suitable. Thereby, the sealing member 16 can be firmly fixed inside the case 10.

[0019] FIG. 6 is a perspective view schematically showing the electrode body 20 attached to the sealing plate 14. In the present embodiment, a plurality (here, three) of electrode bodies 20 are housed inside the case 10. The number of electrode bodies 20 housed inside one case 10 is not particularly limited and may be one or two or more (plural). As shown in FIG. 3, a first electrode current collector 50 is disposed on one side (the left side in FIG. 3) in the long side direction Y of each electrode body 20, and a second electrode current collector 60 is disposed on the other side (the right side in FIG. 3) in the long side direction Y. Each of the plurality of electrode bodies 20 is connected in parallel. However, the plurality of electrode bodies 20 may be connected in series. The electrode body 20 may be housed inside the case body 12 of the case 10 such that the winding shaft WL is along the bottom wall 12a while being covered with an insulating sheet made of a resin sheet. The insulating sheet may be, for example, in a bag shape or a box shape, or may be formed into a box shape by folding one or a plurality of sheets.

[0020] Figure 7 is a schematic perspective view of the electrode body 20. Figure 8 is a schematic diagram showing the configuration of the electrode body 20. As shown in Figure 8, the electrode body 20 has a first electrode 22, a second electrode 24, and a separator 26. The electrode body 20 is a wound electrode body in which a strip-shaped first electrode 22 and a strip-shaped second electrode 24 are stacked with two strip-shaped separators 26 in between, and wound around a winding axis WL. However, the structure of the electrode body is not limited to the technology disclosed herein. For example, the electrode body may be a laminated electrode body in which a plurality of rectangular first electrodes and a plurality of rectangular second electrodes are stacked in an insulated state.

[0021] The first electrode 22 and the second electrode 24 can each be either a positive or negative electrode. For example, the first electrode 22 may be a negative electrode and the second electrode 24 may be a positive electrode, but preferably the first electrode 22 is a positive electrode and the second electrode 24 is a negative electrode. The first electrode 22 and the second electrode 24 are different electrodes. In this embodiment, the first electrode 22 is a positive electrode and the second electrode 24 is a negative electrode.

[0022] The electrode body 20 has a flattened shape. The electrode body 20 is positioned inside the case body 12 with its winding axis WL oriented substantially parallel to the long side direction Y. That is, the electrode body 20 is positioned inside the case body 12 with the thickness direction X of the energy storage device 100 (the direction perpendicular to the first side wall 12b of the case 10) coinciding with the thickness direction of the electrode body 20. Specifically, as shown in Figure 4, the electrode body 20 has a pair of curved portions (R portions) 20r facing the bottom wall 12a and sealing plate 14 of the case body 12, and a flat portion 20f connecting the pair of curved portions 20r and facing the first side wall 12b of the case body 12. The flat portion 20f extends along the first side wall 12b.

[0023] This technology is also particularly effective in energy storage devices equipped with wide electrodes, which are prone to uneven salt concentration in the electrolyte. In wide electrodes, electrolyte exchange between the inside and outside of the electrode becomes difficult, leading to uneven salt concentration. Therefore, the aspect ratio of the electrode 20 (width (length in the long side direction Y) / height (length in the vertical direction Z)) may be, for example, 2 or more, or 2.3 or more.

[0024] The first electrode 22 (here referred to as the positive electrode), as shown in Figure 8, comprises a first electrode current collector 22c, a first electrode active material layer 22a fixed to at least one surface of the first electrode current collector 22c, and a first electrode protective layer 22p. However, the first electrode protective layer 22p is not essential and can be omitted in other embodiments. The first electrode current collector 22c is strip-shaped. The first electrode current collector 22c is made of a conductive metal such as aluminum, aluminum alloy, nickel, or stainless steel. Here, the first electrode current collector 22c is a metal foil, specifically an aluminum foil.

[0025] Multiple first electrode tabs 22t are provided on one axial end of the winding shaft WL of the first electrode current collector 22c (the first end 20a of the electrode body 20; the left end in Figure 8). The multiple first electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction of the strip-shaped first electrode 22. The multiple first electrode tabs 22t protrude outward from the separator 26 toward one axial side of the winding shaft WL (the side of the first end 20a of the electrode body 20; the left side in Figure 8). The first electrode tabs 22t are part of the first electrode current collector 22c and are made of metal foil (aluminum foil). However, the first electrode tabs 22t may be made of a different component from the first electrode current collector 22c. At least a portion of the first electrode tab 22t is formed in which the first electrode active material layer 22a and the first electrode protective layer 22p are not formed, and the first electrode current collector 22c is exposed.

[0026] As shown in Figure 5, multiple first electrode tabs 22t are stacked at one end in the axial direction of the winding axis WL (the left end in Figure 5) to form a first electrode tab group 23. As shown in Figure 3, the first electrode tab group 23 protrudes from the first end 20a of the electrode body 20. Inside the case 10, the first electrode tab group 23 is located on one side of the second side wall 12c of the case body 12 (the left side in Figure 1). Each of the multiple first electrode tabs 22t is connected to the first electrode current collector 50 in a bent state. This allows the size of the main body of the electrode body 20 housed in the case 10 to be increased, thereby enabling a higher energy density for the energy storage device 100. Note that each of the multiple first electrode tabs 22t does not necessarily have to be bent.

[0027] This technology is more effective in energy storage devices equipped with electrode bodies in which the portion for electrical connection to the electrode terminals is tab-shaped (electrode tab) than in electrode bodies in which the exposed current collector portion for electrical connection to the electrode terminals is provided in a strip shape (i.e., electrode bodies in which the exposed current collector portion is provided along the entire height direction of the electrode body). This is because the provision of electrode tabs makes it easier for current to concentrate near the electrode tabs, which makes lithium deposition more likely.

[0028] As shown in Figure 3, in the direction perpendicular to the bottom wall 12a of the case body 12 (up and down direction Z), the ratio of the length L3 of the first electrode tab group 23 to the length L1 of the first end 20a of the electrode body 20 (L3 / L1) is, for example, 0.1 or more, preferably 0.2 or more. Furthermore, the above ratio (L3 / L1) is 0.5 or less, preferably 0.4 or less. Note that the length L3 of the first electrode tab group 23 refers to the longest length of the first electrode tab group 23 in the up and down direction Z.

[0029] As shown in Figure 3, the first electrode tab group 23 is electrically connected to the first electrode terminal 30 via the first electrode current collector 50. The first electrode current collector 50 here comprises a first electrode first current collector 51 and a first electrode second current collector 52. The first electrode first current collector 51 and the first electrode second current collector 52 are preferably made of the same metal type as the first electrode current collector 22c, and may be made of a conductive metal such as aluminum or an aluminum alloy. The first electrode tab group 23 and the first electrode second current collector 52 are connected at a connection part J (see Figure 5). The connection part J may be, for example, an ultrasonic joint or a laser welding part. The first electrode second current collector 52 and the first electrode first current collector 51 are electrically connected (see Figure 3). The first electrode first current collector 51 is electrically connected to the first electrode terminal 30 (see Figure 3).

[0030] In this embodiment, as shown in Figure 3, the first electrode first current collector 51 has a first region extending along the inner surface of the sealing plate 14 and a second region extending along the inner surface of the second side wall 12c of the case 10. The first region is electrically connected to the first electrode terminal 30. The second region is electrically connected to the first electrode second current collector 52. The first electrode first current collector 51 may be constructed by bending a single member, for example by press working, or by integrating multiple members by welding. Here, the first electrode first current collector 51 is fixed to the sealing plate 14 by crimping.

[0031] In this embodiment, as shown in Figure 3, the second current collector portion 52 of the first electrode extends along the inner surface of the second side wall 12c of the case 10 (in the vertical direction Z). In this embodiment, the second current collector portion 52 of the first electrode has an inclined portion between its upper end, which is connected to the first current collector portion 51 of the first electrode, and its lower end, which is connected to the first electrode tab group 23. However, the second current collector portion 52 of the first electrode does not have to have the inclined portion.

[0032] As shown in Figure 3, the first electrode terminal 30 is inserted into a terminal insertion hole 18 formed at one end (the left end in Figure 3) of the sealing plate 14 in the long side direction Y. The first electrode terminal 30 is fixed to the sealing plate 14. The first electrode terminal 30 is preferably made of metal, and more preferably of aluminum or an aluminum alloy. At least a portion of the first electrode terminal 30 is exposed on the outer surface of the case 10. In this case, the first electrode terminal 30 is electrically connected to the first electrode current collector 51 inside the case 10. In this case, the first electrode terminal 30 is crimped to the peripheral portion of the terminal insertion hole 18 by a crimping process or the like.

[0033] The first electrode terminal 30 is insulated from the sealing plate 14 by an internal insulating member 70 and a gasket 90. The internal insulating member 70 comprises a base portion 70a interposed between the first electrode current collector 51 and the sealing plate 14, and a protruding portion 70b projecting from the base portion 70a toward the electrode body 20. The protruding portion 70b restricts the movement of the electrode body 20, preventing contact between the sealing plate 14 and the electrode body 20. On the other hand, outside the case 10, the first electrode terminal 30 is connected to the first electrode external conductive member 32. The first electrode external conductive member 32 is a member to which external members such as busbars may be attached. An external insulating member 92 is positioned between the first electrode external conductive member 32 and the outer surface of the sealing plate 14. The external insulating member 92 insulates the first electrode external conductive member 32 from the sealing plate 14. Note that the first electrode external conductive member 32 and the external insulating member 92 are not essential components and may be omitted as appropriate. The internal insulating member 70, gasket 90, and external insulating member 92 may be made of, for example, fluororesins such as perfluoroalkoxyalkanes (PFA) and polytetrafluoroethylene (PTFE), or synthetic resin materials such as polyphenylene sulfide (PPS).

[0034] As shown in Figure 8, the first electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped first electrode current collector 22c. The first electrode active material layer 22a contains an active material (for example, a lithium transition metal composite oxide such as lithium nickel cobalt manganese composite oxide) that can reversibly intercept and release charge carriers. When the total solid content of the first electrode active material layer 22a is taken as 100% by mass, the active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The first electrode active material layer 22a may contain optional components other than the active material, such as conductive materials, binders, and various additives. As a conductive material, for example, a carbon material such as acetylene black (AB) may be used. As a binder, for example, polyvinylidene fluoride (PVdF) may be used.

[0035] This technology is also suitably effective in energy storage devices (high-capacity energy storage devices) equipped with wide electrode bodies that are prone to uneven salt concentration in the electrolyte. Therefore, the width of the first electrode active material layer 22a (the axial length of the winding axis WL) may be, for example, 10 cm or more, 20 cm or more, or 25 cm or more.

[0036] As shown in Figure 8, the first electrode protective layer 22p is provided at the boundary between the first electrode current collector 22c and the first electrode active material layer 22a in the long side direction Y. Here, the first electrode protective layer 22p is provided at one end (the left end in Figure 8) in the axial direction of the winding axis WL of the first electrode current collector 22c. The first electrode protective layer 22p is provided in a strip shape along the first electrode active material layer 22a. The first electrode protective layer 22p contains an inorganic filler (e.g., alumina). The first electrode protective layer 22p may also contain optional components other than the inorganic filler, such as conductive materials, binders, various additives, etc. The conductive material and binder may be the same as those exemplified as those that may be included in the first electrode active material layer 22a.

[0037] The second electrode 24 (the negative electrode in this case), as shown in Figure 8, comprises a second electrode current collector 24c and a second electrode active material layer 24a fixed to at least one surface of the second electrode current collector 24c. The second electrode current collector 24c is strip-shaped. The second electrode current collector 24c is made of a conductive metal such as copper, copper alloy, nickel, or stainless steel. In this case, the second electrode current collector 24c is a metal foil, specifically a copper foil.

[0038] Multiple second electrode tabs 24t are provided on one axial end of the winding shaft WL of the second electrode current collector 24c (the second end 20b of the electrode body 20; the right end in Figure 8). The second electrode tabs 24t are provided on the side of the winding shaft WL opposite to the side on which the first electrode tab 22t is provided, in the axial direction of the winding shaft WL. The multiple second electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction of the strip-shaped second electrode 24. The multiple second electrode tabs 24t protrude outward from the separator 26 toward one side of the winding shaft WL in the axial direction (the side of the second end 20b of the electrode body 20; the right side in Figure 8). The second electrode tabs 24t are part of the second electrode current collector 24c and are made of metal foil (copper foil). However, the second electrode tabs 24t may be made of a different component from the second electrode current collector 24c. At least a portion of the second electrode tab 24t is provided with a region where the second electrode active material layer 24a is not formed, and the second electrode current collector 24c is exposed.

[0039] As shown in Figure 5, multiple second electrode tabs 24t are stacked at one end of the winding axis WL in the axial direction (the right end in Figure 5) to form a second electrode tab group 25. In the height direction (up and down direction Z) of the energy storage device 100, the second electrode tab group 25 may be located at the same height as the first electrode tab group 23 or higher on the sealing plate 14 side (upper side) than the first electrode tab group 23 (i.e., the first electrode tab group 23 is located lower on the bottom wall 12a side (lower side) than the second electrode tab group 25). Preferably, the first electrode tab group 23 and the second electrode tab group 25 are provided at the same height (symmetrical positions).

[0040] As shown in Figure 3, the second electrode tab group 25 protrudes from the second end 20b of the electrode body 20. Inside the case 10, the second electrode tab group 25 is located on one side of the second side wall 12c of the case body 12 (the right side in Figure 1, opposite to the side where the first electrode tab group 23 is located). Each of the multiple second electrode tabs 24t is connected to the second electrode current collector 60 in a bent state. This allows the size of the main body of the electrode body 20 housed in the case 10 to be increased, thereby enabling a higher energy density for the energy storage device 100. Note that each of the multiple second electrode tabs 24t does not necessarily have to be bent.

[0041] As shown in Figure 3, in the direction perpendicular to the bottom wall 12a of the case body 12 (up and down direction Z), the ratio (L4 / L2) of the length L4 of the second electrode tab group 25 to the length L2 of the second end 20b of the electrode body 20 is, for example, 0.1 or more, preferably 0.2 or more. Also, the above ratio (L4 / L2) is 0.5 or less, preferably 0.4 or less. Here, the length L4 of the second electrode tab group 25 refers to the longest length of the second electrode tab group 25 in the up and down direction Z. Note that the length L1 of the first end 20a and the length L2 of the second end 20b may be different lengths, but preferably they are the same length (the same or a difference of 5% or less). Also, the length L3 of the first electrode tab group 23 and the length L4 of the second electrode tab group 25 may be different lengths, but preferably they are the same length (the same or a difference of 5% or less).

[0042] As shown in Figure 3, the second electrode tab group 25 is electrically connected to the second electrode terminal 40 via the second electrode current collector 60. The second electrode current collector 60 here comprises a second electrode first current collector 61 and a second electrode second current collector 62. The second electrode first current collector 61 and the second electrode second current collector 62 are preferably made of the same metal type as the second electrode current collector 24c, and may be made of a conductive metal such as copper or a copper alloy. The second electrode tab group 25 and the second electrode second current collector 62 are connected at connection part J (see Figure 5). The second electrode second current collector 62 and the second electrode first current collector 61 are electrically connected (see Figure 3). The second electrode first current collector 61 is electrically connected to the second electrode terminal 40 (see Figure 3).

[0043] In this embodiment, as shown in Figure 3, the second electrode first current collector 61 has a first region extending along the inner surface of the sealing plate 14 and a second region extending along the inner surface of the second side wall 12c of the case 10. The first region is electrically connected to the second electrode terminal 40. The second region is electrically connected to the second electrode second current collector 62. The second electrode first current collector 61 may be constructed by bending a single member, for example by press working, or by integrating multiple members by welding. In this embodiment, the second electrode first current collector 61 is fixed to the sealing plate 14 by crimping.

[0044] In this embodiment, as shown in Figure 3, the second electrode second current collector 62 extends along the inner surface of the second side wall 12c of the case 10 (in the vertical direction Z). In this embodiment, the second electrode second current collector 62 has an inclined portion between its upper end, which is connected to the second electrode first current collector 61, and its lower end, which is connected to the second electrode tab group 25. However, the second electrode second current collector 62 does not have to have the inclined portion.

[0045] As shown in Figure 3, the second electrode terminal 40 is inserted into a terminal insertion hole 19 formed at one end (the right end in Figure 3) of the sealing plate 14 in the long side direction Y. The second electrode terminal 40 is fixed to the sealing plate 14. The second electrode terminal 40 is preferably made of metal, and more preferably of copper or a copper alloy. At least a portion of the second electrode terminal 40 is exposed on the outer surface of the case 10. In this case, the second electrode terminal 40 is electrically connected to the second electrode first current collector 61 inside the case 10. In this case, the second electrode terminal 40 is crimped to the peripheral portion of the terminal insertion hole 19 by a crimping process or the like.

[0046] The second electrode terminal 40 is insulated from the sealing plate 14 by an internal insulating member 70 and a gasket 90. Details of the internal insulating member 70 are the same as those described above for the first electrode terminal 30, so they are omitted here. Outside the case 10, the second electrode terminal 40 is connected to the second electrode external conductive member 42. The second electrode external conductive member 42 is a member to which external members such as busbars may be attached. An external insulating member 92 is placed between the second electrode external conductive member 42 and the outer surface of the sealing plate 14. The external insulating member 92 insulates the second electrode external conductive member 42 from the sealing plate 14. Note that the second electrode external conductive member 42 and the external insulating member 92 are not essential components and may be omitted as appropriate.

[0047] As shown in Figure 8, the second electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped second electrode current collector 24c. The second electrode active material layer 24a contains an active material (for example, a carbon material such as graphite) that can reversibly intercept and release charge carriers. When the total solid content of the second electrode active material layer 24a is taken as 100% by mass, the active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The second electrode active material layer 24a may contain optional components other than the active material, such as a binder, a dispersant, various additives, etc. As a binder, for example, rubbers such as styrene-butadiene rubber (SBR) can be used. As a dispersant, for example, celluloses such as carboxymethylcellulose (CMC) can be used.

[0048] This technology is also suitably effective in energy storage devices (high-capacity energy storage devices) equipped with wide electrode bodies that are prone to uneven salt concentration in the electrolyte. Therefore, the width of the second electrode active material layer 24a (the axial length of the winding axis WL) may be, for example, 10 cm or more, 20 cm or more, or 25 cm or more.

[0049] As shown in Figure 8, the separator 26 is a component that insulates the first electrode 22 and the second electrode 24. For the separator 26, a porous sheet made of polyolefin resin such as polyethylene (PE) or polypropylene (PP) is preferred. The separator 26 may have a base material made of a porous sheet made of resin, and a heat-resistant layer (HRL) containing an inorganic filler, provided on at least one surface of the base material. Examples of inorganic fillers include alumina, boehmite, aluminum hydroxide, and titania.

[0050] The electrolyte 80 is, for example, a non-aqueous electrolyte containing an organic solvent and a supporting salt. As the organic solvent, aprotic solvents such as carbonates, esters, and ethers can be used. Among these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be suitably used. Alternatively, fluorinated solvents such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC) can be suitably used. Such organic solvents can be used individually or in appropriate combinations of two or more. As the supporting salt, lithium salts such as LiPF6, LiBF4, and LiClO4 can be suitably used. The concentration of the supporting salt is not particularly limited, but it is preferably, for example, between 0.7 mol / L and 1.3 mol / L. Furthermore, the electrolyte 80 may contain components other than the organic solvent and supporting salt mentioned above, as long as they do not significantly impair the effects of this technology. For example, it may contain various additives such as gas generators, film-forming agents, dispersants, and thickeners.

[0051] The energy storage device 100 is typically used with the direction perpendicular to the bottom wall 12a of the case 10 (up / down direction Z) being vertical (the bottom wall 12a being on the bottom). In this specification, this usage state is also referred to as the "normal usage state." As shown in Figure 3, in the energy storage device 100, electrolyte 80 exists between the case body 12 and the electrode body 20 (hereinafter also referred to as "excess electrolyte 80"). When the energy storage device 100 is in a charging state, the negative electrode plate (e.g., negative electrode active material) expands, and the electrolyte 80 is discharged from inside the electrode body 20. When the energy storage device 100 is in a discharging state, the negative electrode plate (e.g., negative electrode active material) contracts, and the electrolyte enters the inside of the electrode body 20. Therefore, the amount of excess electrolyte 80 fluctuates depending on the charging and discharging state of the energy storage device 100. The presence of excess electrolyte 80 prevents the electrolyte from running out inside the electrode body 20, which is advantageous from the viewpoint of extending the lifespan of the energy storage device 100.

[0052] As shown in Figure 3, in the normal operating state, when the energy storage device 100 is fully charged, the liquid level 80H of the excess electrolyte 80 is located on the sealing plate 14 side (upper side) of the portion of the first electrode tab group 23 closest to the bottom wall 12a of the case body 12 (lower end portion 23b). That is, at least a portion of the first electrode tab group 23 is immersed in the excess electrolyte 80. This makes it easier to equalize the lithium salt concentration near the first electrode tab group 23 with the lithium salt concentration of the excess electrolyte 80. As a result, lithium deposition near the first electrode tab group 23 is suppressed. From a similar viewpoint, it is even more preferable that the liquid level 80H of the excess electrolyte 80 is located on the sealing plate 14 side (upper side) of the second electrode tab group 25 closest to the bottom wall 12a of the case body 12 (lower end portion 25b). In this specification, the state of charge (SOC) of the energy storage device 100 is defined as "fully charged" when the device is at "100% charge".

[0053] In the normal operating state, when the energy storage device 100 is fully charged, it is preferable that the liquid level 80H of the excess electrolyte 80 is located closer to the bottom wall 12a of the case body 12 than half the height H (see Figure 3) of the second side wall 12c of the case body 12 (i.e., the height from the bottom wall 12a of the excess electrolyte 80 to the liquid level 80H is less than 1 / 2H), more preferably the height from the bottom wall 12a of the excess electrolyte 80 to the liquid level 80H is 1 / 3H or less, and even more preferably the height from the bottom wall 12a of the excess electrolyte 80 to the liquid level 80H is 1 / 4H or less. A smaller amount of excess electrolyte 80 is advantageous from the viewpoint of pressure resistance life because it increases the remaining space inside the case 10. However, if there is no excess electrolyte 80 or if there is too little, depletion of the electrolyte inside the electrode body 20 may occur. Therefore, the height from the bottom wall 12a of the excess electrolyte 80 to the liquid surface 80H is preferably, for example, 1 / 20H or more, and more preferably 1 / 10H or more.

[0054] In this embodiment, in the direction perpendicular to the bottom wall 12a of the case body 12 (up and down direction Z), the portion of the first electrode tab group 23 closest to the bottom wall 12a of the case body 12 (lower end portion 23b) is located on the bottom wall 12a side (lower side) than half the length L1 (height) of the first end portion 20a of the electrode body 20 (see Figure 3). Alternatively, the lower end portion 23b of the first electrode tab group 23 may be positioned on the bottom wall 12a side (lower side) than 1 / 3, 1 / 4, or 1 / 5 of the length L1 (height) of the first end portion 20a of the electrode body 20 from the bottom wall 12a side. This is advantageous from the viewpoint of pressure resistance life because, even when the amount of excess electrolyte 80 is reduced, the lower end portion 23b of the first electrode tab group 23 is more easily immersed in the excess electrolyte 80. The position of the lower end portion 25b of the second electrode tab group 25 is the same as that of the first electrode tab group 23 described above. In other words, the portion of the second electrode tab group 25 closest to the bottom wall 12a of the case body 12 (lower end portion 25b) is preferably located closer to the bottom wall 12a (lower side) than half the length L2 (height) of the second end portion 20b of the electrode body 20, and may be positioned closer to the bottom wall 12a (lower side) than 1 / 3, 1 / 4, or 1 / 5 of the length L2 (height) of the second end portion 20b of the electrode body 20 from the bottom wall 12a side.

[0055] Furthermore, in this embodiment, in the direction perpendicular to the bottom wall 12a of the case body 12 (vertical direction Z), the entirety of the first electrode tab group 23 (from the lower end to the upper end of length L3) is located on the bottom wall 12a side (lower side) than the position halfway through the length L1 (height) of the first end 20a of the electrode body 20 (see Figure 3). In other words, the part of the first electrode tab group 23 closest to the sealing plate 14 is located on the bottom wall 12a side (lower side) than the position halfway through the length L1 (height) of the first end 20a of the electrode body 20. Alternatively, the entirety of the first electrode tab group 23 may be positioned on the bottom wall 12a side (lower side) than the position 1 / 3, 1 / 4, or 1 / 5 of the length L1 (height) of the first end 20a of the electrode body 20 from the bottom wall 12a side. As a result, even when the amount of excess electrolyte 80 is reduced, the lower end portion 23b of the first electrode tab group 23 is more easily immersed in the excess electrolyte 80, which is advantageous from the viewpoint of pressure resistance life. The position of the lower end portion 25b of the second electrode tab group 25 is the same as the position of the first electrode tab group 23 described above. That is, the entirety of the second electrode tab group 25 is preferably located on the bottom wall 12a side (lower side) than half the length L2 (height) of the second end portion 20b of the electrode body 20, and may also be located on the bottom wall 12a side (lower side) than 1 / 3, 1 / 4, or 1 / 5 of the length L2 (height) of the second end portion 20b of the electrode body 20 from the bottom wall 12a side.

[0056] When the energy storage device 100 is fully charged under normal operating conditions, the proportion of the length L3 of the first electrode tab group 23 in the direction perpendicular to the bottom wall 12a of the case body 12 (up and down direction Z) that is immersed in the excess electrolyte 80 (i.e., the proportion located on the bottom wall 12a side of the liquid surface 80H of the excess electrolyte 80) may be, for example, 5% or more, 10% or more, or 20% or more. The higher this proportion, the easier it is to homogenize the lithium salt concentration near the first electrode tab group 23, and the more effectively lithium deposition can be suppressed near the first electrode tab group 23. Furthermore, this proportion may be 100% from the viewpoint of suppressing lithium deposition, but it may also be 80% or less, 60% or less, or 40% or less. Lowering this proportion reduces the amount of excess electrolyte 80, which is advantageous from the viewpoint of pressure resistance life. The same applies to the second electrode tab group 25. That is, when fully charged under normal operating conditions, the proportion of the length L3 of the second electrode tab group 25 in the direction perpendicular to the bottom wall 12a of the case body 12 (up and down direction Z) that is immersed in the excess electrolyte 80 may be, for example, 5% or more, 10% or more, or 20% or more. Furthermore, this proportion may be 100%, but may also be 80% or less, 60% or less, or 40% or less.

[0057] It is preferable that the energy storage device 100 has excess electrolyte 80 when the state of charge (SOC) is 15% under normal operating conditions. Generally, the SOC of energy storage devices when they are shipped is 15% to 30%, and the minimum SOC used in the market is 15%, so having excess electrolyte 80 in this state is preferable from the viewpoint of preventing depletion. Furthermore, under normal operating conditions and when the SOC is 15%, it is preferable that the liquid level 80H of the excess electrolyte 80 is located closer to the bottom wall 12a than the part of the bottom wall 12a of the first electrode tab group 23 that is closest to the bottom wall 12a (lower end 23b) in the direction perpendicular to the bottom wall 12a of the case body 12 (up and down direction Z). With this configuration, the amount of excess electrolyte 80 is reduced and the pressure resistance performance is improved.

[0058] The following describes an example of a method for manufacturing the energy storage device 100, but it is not limited to any particular method of manufacturing the energy storage device 100. The method for manufacturing the energy storage device 100 may include a forming step of forming the electrode body 20, a construction step of constructing the energy storage device assembly, an electrolyte injection step of injecting electrolyte, and a charging step of charging the battery assembly. Furthermore, the manufacturing method disclosed herein may include other steps at any stage, the order of the steps may be changed as appropriate, and steps may be omitted as appropriate.

[0059] The above forming process may be the same as that of a known method. A strip-shaped first electrode 22, a strip-shaped second electrode 24, and two strip-shaped separators 26 are prepared. Next, the first electrode 22 and the second electrode 24 are stacked so that the separators 26 are placed between them. At this time, the stacking is done so that the longitudinal directions of each are aligned. Then, the electrode body 20 is manufactured by winding the stack around the winding axis WL (see Figure 8). In the forming process, the arrangement of the first electrode tab group 23 and the second electrode tab group 25 can be adjusted as appropriate.

[0060] The above construction process may be the same as that of a known method. An example of construction is shown below, but the order of construction is not limited, and the construction described below can be performed before or after other steps. For example, first, the first electrode terminal 30 is attached to the terminal insertion hole 18 of the sealing plate 14. At this time, the gasket 90 is placed between the first electrode terminal 30 and the sealing plate 14. Next, the first electrode first current collector 51 and the internal insulating member 70 are placed on the inner surface of the sealing plate 14. At this time, the internal insulating member 70 is placed between the inner surface of the sealing plate 14 and the first electrode first current collector 51. Then, the end of the first electrode terminal 30 protruding from the inner surface of the sealing plate 14 is crimped (riveted) to fix the first electrode first current collector 51 and the internal insulating member 70 to the sealing plate 14. Similarly, the second electrode terminal 40 is inserted into the terminal insertion hole 19, and the gasket 90, the second electrode first current collector 61, and the internal insulating member 70 are fixed to the sealing plate 14. On the outer surface of the sealing plate 14, an external insulating member 92 is placed around the gasket 90 attached to the first electrode terminal 30. The first electrode external conductive member 32 is attached on the placed external insulating member 92, and the first electrode terminal 30 and the first electrode external conductive member 32 are electrically connected. The second electrode external conductive member 42 can be handled in the same manner as the first electrode external conductive member 32, so a description is omitted.

[0061] In the construction process, as shown in Figure 7, the first electrode second current collector 52 is joined to the first electrode tab group 23 of the electrode body 20, and the second electrode second current collector 62 is joined to the second electrode tab group 25. The joining method is not particularly limited and may be ultrasonic bonding, resistance welding, laser welding, etc. After that, the first electrode first current collector 51 and the first electrode second current collector 52 attached to the sealing plate 14 are joined, and the second electrode first current collector 61 and the second electrode second current collector 62 attached to the sealing plate 14 are joined to produce an assembly as shown in Figure 6. The joining method is not particularly limited and may be ultrasonic bonding, resistance welding, laser welding, etc.

[0062] Next, the assembly shown in Figure 6 is inserted into the case body 12. At this time, the first electrode tab group 23 is positioned on one side of the second side wall 12c, and the second electrode tab group 25 is positioned on the other side of the second side wall 12c. Then, the case body 12 and the sealing plate 14 are attached by joining (for example, laser bonding) the sealing plate 14 to the periphery of the opening 12h of the case body 12. In this way, the energy storage device assembly is manufactured.

[0063] In the electrolyte injection process, the electrolyte 80 is injected into the case 10 through the injection hole 15 of the sealing plate 14 according to a known method. At this time, the volume inside the case 10 and the volume of the electrode body 20 are taken into consideration. Under normal operating conditions, when the energy storage device 100 is fully charged, the liquid level 80H of the excess electrolyte 80 is adjusted so that it is closer to the sealing plate 14 than the lower end 23b of the first electrode tab group 23. Furthermore, by changing the amount of electrolyte 80 injected, the liquid level H of the excess electrolyte 80 and the positional relationship with the first electrode tab group 23 can be adjusted within the range described above. The amount of excess electrolyte 80 may be determined, for example, by X-ray detection or by installing a sensor inside the case 10. After injection, the injection hole 15 is sealed with the sealing member 16.

[0064] The energy storage device 100 can be used for various applications, for example, as a battery for vehicles. The type of vehicle is not particularly limited, but examples include plug-in hybrid vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). Furthermore, the energy storage device 100 can also be suitably used as a cell stack, in which multiple energy storage devices 100 are arranged in a predetermined arrangement direction and a load is applied from the arrangement direction by a restraining mechanism.

[0065] Although several embodiments of this disclosure have been described above, these embodiments are merely examples. This disclosure can be implemented in various other forms. This disclosure can be implemented based on the content disclosed herein and common technical knowledge in the art. The technology described in the claims includes various modifications and changes to the embodiments illustrated above. For example, it is possible to replace parts of the above embodiments with other modifications, and to add other modifications to the above embodiments. Furthermore, technical features that are not described as essential may be deleted as appropriate.

[0066] For example, in the above embodiment, as shown in Figure 3, in the direction perpendicular to the bottom wall 12a of the case body 12 (up and down direction Z), the lower end portion 23b of the first electrode tab group 23 was located on the bottom wall 12a side (downward) of the position halfway through the length L1 (height) of the first end portion 20a of the electrode body 20. However, the position of the first electrode tab group 23 is not limited to this. Figure 9 is a corresponding diagram of the energy storage device 100A according to the second embodiment, as shown in Figure 3. In the energy storage device 100A, the lower end portion 23b of the first electrode tab group 23 is located on the sealing plate 14 side (upward) of the position halfway through the length L1 (height) of the first end portion 20a of the electrode body 20. In this embodiment as well, under normal operating conditions, the liquid level 80H of the excess electrolyte 80 is located on the sealing plate 14 side of the lower end portion 23b of the first electrode tab group 23, thereby suppressing lithium deposition near the first electrode tab group 23.

[0067] As described above, specific embodiments of the technology disclosed herein include those described in the following sections. Section 1: An electrode body including a first electrode and a second electrode, An electrolyte containing an organic solvent and a lithium salt, A case for housing the electrode body and the electrolyte solution. A power storage device comprising, The electrode body described above is A group of first electrode tabs including a plurality of first electrode tabs protruding from a first end, A group of second electrode tabs including a plurality of second electrode tabs protruding from the second end, Equipped with, The above case is, The bottom wall and, A pair of first side walls extending from the bottom wall and facing each other, A pair of second side walls extending from the bottom wall and facing each other, An opening facing the bottom wall mentioned above and The case body, including, A sealing plate that seals the above opening and Equipped with, The above-mentioned first electrode tab group is arranged inside the case on one side of the pair of second side walls. The above-mentioned second electrode tab group is arranged inside the case on the other side of the pair of second side walls. When the above energy storage device is fully charged, The above-mentioned energy storage device has excess electrolyte, which is the electrolyte, between the case body and the electrode body, in a state where the direction perpendicular to the bottom wall is the vertical direction. An energy storage device in which the liquid level of the excess electrolyte is located closer to the sealing plate than the portion of the first electrode tab group closest to the bottom wall. Section 2: In the direction perpendicular to the bottom wall, The ratio (L3 / L1) of the length L3 of the first electrode tab group to the length L1 of the first end of the electrode body is 0.1 to 0.5. The energy storage device according to item 1, wherein the ratio (L4 / L2) of the length L4 of the second electrode tab group to the length L2 of the second end of the electrode body is 0.1 to 0.5. Section 3: The energy storage device according to item 1 or 2, wherein the liquid level of the excess electrolyte is located on the bottom wall side of half the height H of the second side wall. Section 4: The energy storage device according to any one of items 1 to 3, wherein when the state of charge (SOC) of the energy storage device is 15%, the liquid level of the excess electrolyte is located closer to the bottom wall than the part of the first electrode tab group that is closest to the bottom wall. Section 5: The energy storage device according to any one of items 1 to 4, wherein, in a direction perpendicular to the bottom wall, the portion of the first electrode tab group closest to the bottom wall is located closer to the bottom wall than half the length of the first end. [Explanation of symbols]

[0068] 10 cases 12 Case body 12a Bottom wall 12b 1st side wall 12c 2nd side wall 14 Sealing plate 20 Electrode body 22 1st electrode 23 First electrode tab group 24 2nd electrode 25 Second electrode tab group 30 1st electrode terminal 40 2nd electrode terminal 80 Electrolyte (Excess Electrolyte) 80H liquid level 100, 100A energy storage device

Claims

1. An electrode body including a first electrode and a second electrode, An electrolyte containing an organic solvent and a lithium salt, A case for housing the electrode body and the electrolyte solution A power storage device comprising, The electrode body is A group of first electrode tabs including a plurality of first electrode tabs partially protruding from a first end, A group of second electrode tabs including a plurality of second electrode tabs partially protruding from the second end, Equipped with, The aforementioned case is, The bottom wall and, A pair of first side walls extending from the bottom wall and facing each other, A pair of second side walls extending from the bottom wall and facing each other, An opening opposite the bottom wall and The case body, including, A sealing plate that seals the opening and Equipped with, In a direction perpendicular to the bottom wall, The length L3 of the first electrode tab group is smaller than the length L1 of the first end of the electrode body. The length L4 of the second electrode tab group is smaller than the length L2 of the second end of the electrode body. The first electrode tab group is arranged inside the case on one side of the pair of second side walls. The second electrode tab group is arranged inside the case on the other side of the pair of second side walls. When the aforementioned energy storage device is fully charged, The energy storage device has excess electrolyte, which is the electrolyte, between the case body and the electrode body, with the direction perpendicular to the bottom wall being the vertical direction. The liquid level of the excess electrolyte is located closer to the sealing plate than the portion of the first electrode tab group closest to the bottom wall, The liquid level of the excess electrolyte is located closer to the bottom wall than half the height H of the second side wall. Energy storage device.

2. An electrode body including a first electrode and a second electrode, An electrolyte containing an organic solvent and a lithium salt, A case for housing the electrode body and the electrolyte solution A rechargeable battery equipped with a secondary battery, The electrode body is A group of first electrode tabs including a plurality of first electrode tabs partially protruding from a first end, A group of second electrode tabs including a plurality of second electrode tabs partially protruding from the second end, Equipped with, The aforementioned case is, The bottom wall and, A pair of first side walls extending from the bottom wall and facing each other, A pair of second side walls extending from the bottom wall and facing each other, An opening opposite the bottom wall and The case body, including, A sealing plate that seals the opening and Equipped with, In a direction perpendicular to the bottom wall, The length L3 of the first electrode tab group is smaller than the length L1 of the first end of the electrode body. The length L4 of the second electrode tab group is smaller than the length L2 of the second end of the electrode body. The first electrode tab group is arranged inside the case on one side of the pair of second side walls. The second electrode tab group is arranged inside the case on the other side of the pair of second side walls. When the aforementioned energy storage device is fully charged, The energy storage device has excess electrolyte, which is the electrolyte, between the case body and the electrode body, with the direction perpendicular to the bottom wall being the vertical direction. The liquid level of the excess electrolyte is located closer to the sealing plate than the portion of the first electrode tab group closest to the bottom wall, When the state of charge (SOC) of the energy storage device is 15%, the liquid level of the excess electrolyte is located closer to the bottom wall than the portion of the first electrode tab group that is closest to the bottom wall. Energy storage device.

3. In a direction perpendicular to the bottom wall, The ratio of the length L3 of the first electrode tab group to the length L1 of the first end of the electrode body (L3 / L1) is 0.1 to 0.

5. The ratio of the length L4 of the second electrode tab group to the length L2 of the second end of the electrode body (L4 / L2) is 0.1 to 0.

5. The energy storage device according to claim 1 or 2.

4. The aforementioned energy storage device is a secondary battery, The energy storage device according to claim 1, wherein when the state of charge (SOC) of the energy storage device is 15%, the liquid level of the excess electrolyte is located closer to the bottom wall than the portion of the first electrode tab group that is closest to the bottom wall.

5. The energy storage device according to claim 1 or 2, wherein, in a direction perpendicular to the bottom wall, the portion of the first electrode tab group closest to the bottom wall is located closer to the bottom wall than half the length of the first end.

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