Power storage element and power storage device

Abstract

This power storage element comprises: an electrode body in which electrode plates are wound; a container accommodating the electrode body; and a pair of terminals disposed on the container. The electrode body has a flat shape including a pair of curved portions facing each other, and a flat portion connecting the pair of curved portions. The container includes a pair of curved wall portions respectively facing the pair of curved portions, and flat wall portions respectively facing both surfaces of the flat portion of the electrode body. The pair of curved wall portions are a first curved wall portion and a second curved wall portion. The inner surface of the first curved wall portion and the inner surface of the second curved wall portion have a curved shape that follows the curved portions of the electrode body. The inner surfaces of the flat wall portions have a flat shape that follows the flat portion of the electrode body. The pair of terminals are disposed on one or a plurality of wall portions, among the wall portions constituting the container, of which the direction from the second curved wall portion toward the first curved wall portion is aligned with a direction penetrating the container from the inner surface to the outer surface thereof, and protrude in the direction from the second curved wall portion toward the first curved wall portion.

Description

Energy storage element and energy storage device

[0001] The present invention relates to an energy storage element and an energy storage device.

[0002] Conventionally, as disclosed in Patent Document 1, there has been known a nonaqueous electrolyte battery in which an electrode group is housed in a rectangular cylindrical container, the electrode group including a positive electrode including a positive electrode current collector and a positive electrode active material-containing layer, and a negative electrode including a negative electrode current collector and a negative electrode active material-containing layer, the positive electrode being wound in a flat spiral shape with a separator interposed therebetween.

[0003] JP 2010-73580 A

[0004] The container of the nonaqueous electrolyte battery (hereinafter referred to as "energy storage element") disclosed in Patent Document 1 is a rectangular cylindrical (prismatic) container 100z as shown in FIG. 1 of the present application, which is shown as a comparative example. As shown in FIG. 2 of the present application, the internal space of the container 100z is rectangular parallelepiped. As a result, even when an electrode group (hereinafter referred to as "electrode assembly") is housed in the container 100z, the inner wall of the container does not conform to the outer surface of the curved portion of the electrode assembly 700, and a gap (excess space) is generated between the curved portion of the wound (hereinafter referred to as "wound") electrode assembly 700 and the inner surface of the container 100z. Specifically, as shown in FIG. 3 of the present application, a gap (volume loss within the container due to excess space) is generated between the curved portion 711 of the electrode assembly 700 and the corner formed by the inner surface of the container parallel to the flat portion 712 of the electrode assembly 700 and the inner surface of the container 100z facing the curved portion 711 of the electrode assembly 700. This has been a factor in reducing the volumetric energy density inside the energy storage element. On the other hand, with a non-wound, laminated electrode body, even when housed in a rectangular cylindrical (square) container, there is little excess space inside the container, making it difficult for the volumetric energy density inside the energy storage element to decrease. However, from the standpoints of productivity and manufacturing costs, wound electrode bodies are superior to laminated electrode bodies, and there is a demand for an energy storage element that can house a flat wound electrode body without compromising the volumetric energy density.

[0005] An object of the present invention is to provide an electric storage element that houses a wound electrode body and has an increased volumetric energy density within the electric storage element container, and an electric storage device that has an increased volumetric energy density.

[0006] An energy storage element according to one aspect of the present invention comprises an electrode body having wound electrode plates, a container for accommodating the electrode body, and a pair of terminals disposed in the container, wherein the electrode body has a flat shape with a pair of opposing curved portions and a flat portion connecting the pair of curved portions, the container has a pair of curved wall portions each facing the pair of curved portions, and flat wall portions each facing both sides of the flat portion of the electrode body, the pair of curved wall portions being a first curved wall portion and a second curved wall portion, the inner surfaces of the first curved wall portion and the second curved wall portion having curved shapes that follow the curved portions of the electrode body, the inner surface of the flat wall portion having a flat shape that follows the flat portion of the electrode body, and the pair of terminals are disposed in one or more wall portions among the wall portions constituting the container, the direction approaching the first curved wall portion from the second curved wall portion being a direction penetrating from the inner surface to the outer surface of the container, and protrudes from the second curved wall portion in a direction approaching the first curved wall portion.

[0007] According to the present invention, it is possible to provide an energy storage element that can accommodate a wound electrode body with reduced volume loss within a container and that has an increased volumetric energy density within the energy storage element container, and an energy storage device that has an increased volumetric energy density.

[0008] FIG. 1 is a perspective view showing the appearance of an energy storage element in a prismatic container according to a comparative example. FIG. 2 is an exploded perspective view showing each component of an energy storage element in a prismatic container according to a comparative example. FIG. 3 is a cross-sectional view showing a state in which an electrode body is housed in a prismatic container according to a comparative example. FIG. 4 is a perspective view showing the appearance of an energy storage element according to an embodiment. FIG. 5 is an exploded perspective view showing each component of an energy storage element according to an embodiment. FIG. 6 is a perspective view showing the configuration of an electrode body according to an embodiment. FIG. 7 is a cross-sectional view showing the positional relationship between a container and an electrode body according to an embodiment. FIG. 8 is a cross-sectional view showing the positional relationship between a container and an electrode body according to a first modification. FIG. 9 is a perspective view showing the appearance of an energy storage element according to a second modification. FIG. 10 is a perspective view showing the appearance of an energy storage element according to a third modification. FIG. 11 is a plan view showing the appearance of energy storage elements according to fourth and fifth modifications. FIG. 12 is a perspective view showing the appearance of an energy storage element according to a sixth modification. FIG. 13 is a perspective view showing the appearance of an energy storage element according to a seventh modification. FIG. 14 is a plan view showing the appearance of an energy storage element according to an eighth modification. Fig. 15 is a perspective view showing the appearance of the energy storage device according to the embodiment. Fig. 16 is an exploded perspective view showing each component of the energy storage device according to the embodiment. Fig. 17 is an explanatory diagram showing a holding unit, a case, and each energy storage element according to the embodiment.

[0009] The inventors conceived of reducing the excess space between the electrode body and the container in the energy storage element container and improving the volumetric energy density inside the container of the energy storage element by aligning the inner surface of the wall portion (flat wall portion) facing the flat portion of the electrode body with the flat shape of the flat portion and the inner surface of the wall portion (curved wall portion) facing the curved portion of the electrode body with the curved shape of the curved portion. Furthermore, they conceived of incorporating a configuration in which a pair of terminals is disposed on one or more of the wall portions constituting the container, such that the direction from the second curved wall portion toward the first curved wall portion penetrates from the inner surface to the outer surface of the container, and the terminals protrude from the second curved wall portion toward the first curved wall portion. Furthermore, by providing terminals on the top of the energy storage element, wiring such as bus bars can be connected from above when assembling the energy storage elements, improving productivity.

[0010] The present invention is a groundbreaking invention that deviates from the conventional wisdom of similar conventional energy storage elements, which have traditionally been considered difficult to provide terminals for. It combines a configuration in which a pair of terminals are arranged on one or more wall portions that constitute the container, the direction from the second curved wall portion approaching the first curved wall portion being a direction that penetrates from the inner surface to the outer surface of the container, and the pair of terminals protrude in the direction from the second curved wall portion approaching the first curved wall portion.

[0011] (1) An energy storage element according to one aspect of the present invention comprises an electrode body having wound electrode plates, a container for accommodating the electrode body, and a pair of terminals disposed in the container, the electrode body having a flat shape with a pair of opposing curved portions and a flat portion connecting the pair of curved portions, the container having a pair of curved wall portions each facing the pair of curved portions and a flat wall portion each facing both sides of the flat portion of the electrode body, the pair of curved wall portions being a first curved wall portion and a second curved wall portion, the inner surfaces of the first curved wall portion and the second curved wall portion having curved shapes that follow the curved portions of the electrode body, the inner surface of the flat wall portion having a flat shape that follows the flat portion of the electrode body, the pair of terminals being disposed in one or more wall portions constituting the container, the direction from the second curved wall portion to the first curved wall portion being a direction that penetrates from the inner surface to the outer surface of the container, and the pair of terminals protrude from the second curved wall portion in a direction that follows the first curved wall portion.

[0012] According to the energy storage element of one aspect of the present invention described in (1) above, the inner surface of the container of the energy storage element follows both the flat portion and the curved portion, which are the outer surface of the electrode body, so that the excess space within the container of the energy storage element can be made smaller than in the case of a rectangular container, and a decrease in the volumetric energy density within the energy storage element container can be suppressed.

[0013] (2) In the energy storage element described in (1) above, the pair of terminals may protrude from the outer surface of the first curved wall portion in a direction from the second curved wall portion toward the first curved wall portion.

[0014] According to the energy storage element described in (2) above, the pair of terminals are located at the ends of the energy storage element in the direction from the second curved wall portion toward the first curved wall portion, so that the terminals can be easily accessed from the outside even after the plurality of energy storage elements are unitized, facilitating electrical connection (such as welding) between the terminals and the bus bar or the like.

[0015] (3) In the energy storage element described in (1) above, the container may include a pair of notches positioned relative to each other in the winding axis direction of the electrode body, the pair of notches being positioned to sandwich the first curved wall portion of the container in the winding axis direction, the pair of terminals being positioned within the pair of notches and on a surface on which the direction from the second curved wall portion to the first curved wall portion is a direction penetrating from the inner surface of the container to the outer surface of the container, and protruding from the second curved wall portion in a direction approaching the first curved wall portion.

[0016] According to the energy storage element described in (3) above, the pair of terminals are arranged on a surface within the pair of notches, the direction from the second curved wall portion toward the first curved wall portion being a direction penetrating from the inner surface of the container to the outer surface of the container, and further, are arranged so as to protrude from the second curved wall portion toward the first curved wall portion, thereby reducing the amount of protrusion of the terminals in the opposing direction of the pair of curved portions. In other words, by arranging the terminals within the notches, the volume of the energy storage element including the terminals is reduced, and the volumetric energy density is higher than when the terminals are arranged on the curved wall portions.

[0017] (4) The energy storage element described in (1) above may include a pair of first terminals and a pair of second terminals arranged in the container, and the pair of first terminals may be the pair of terminals that protrude from the outer surface of the first curved wall portion in a direction from the second curved wall portion toward the first curved wall portion, and the pair of second terminals may protrude from the outer surface of the second curved wall portion in a direction from the first curved wall portion toward the second curved wall portion.

[0018] According to the energy storage element described in (4) above, a pair of terminals (a pair of first terminals and a pair of second terminals) protrude from the outer surfaces of each curved wall portion (first curved wall portion, second curved wall portion) of the container. This allows for a higher volumetric energy density of the energy storage element than when a pair of terminals protrudes from each end of the container in the winding axis direction. Furthermore, the pair of first terminals are located at the end of the energy storage element in the direction from the second curved wall portion toward the first curved wall portion, and the pair of second terminals are located at the end of the energy storage element in the direction from the first curved wall portion toward the second curved wall portion. This makes it easy to approach the terminals from the outside after unitizing multiple energy storage elements. This facilitates electrical connection (e.g., welding) between the terminals and bus bars, etc. Furthermore, since the energy storage element includes two pairs of terminals (a pair of first terminals and a pair of second terminals), current can be efficiently extracted from the energy storage element. In other words, the four-terminal structure of the energy storage element reduces resistance, resulting in an energy storage element with excellent output performance.

[0019] (5) The energy storage element described in (1) above may include a pair of first terminals and a pair of second terminals disposed in the container, the pair of first terminals being the pair of terminals, and the container may include a pair of first notches and a pair of second notches, the pair of first notches being disposed at positions sandwiching the first curved wall portion of the container in the winding axis direction of the electrode body, the pair of second notches being disposed at positions sandwiching the second curved wall portion of the container in the winding axis direction, the pair of first terminals being disposed within the pair of first notches and on a surface on which a direction from the second curved wall portion to the first curved wall portion penetrates from the inner surface of the container to the outer surface of the container, and protruding from the second curved wall portion in a direction approaching the first curved wall portion, and the pair of second terminals being disposed within the pair of second notches and on a surface on which a direction from the first curved wall portion to the second curved wall portion penetrates from the inner surface of the container to the outer surface of the container, and protruding from the first curved wall portion in a direction approaching the second curved wall portion.

[0020] According to the energy storage element described in (5) above, the pair of first terminals are provided within the pair of first notches so as to protrude from the second curved wall portion toward the first curved wall portion, thereby reducing the amount of protrusion of the pair of first terminals outward from the container in the direction from the second curved wall portion toward the first curved wall portion. Similarly, the pair of second terminals are provided within the pair of second notches so as to protrude from the first curved wall portion toward the second curved wall portion, thereby reducing the amount of protrusion of the pair of second terminals outward from the container in the direction from the first curved wall portion toward the second curved wall portion. Because of this configuration, the energy storage element includes two pairs of terminals (a pair of first terminals and a pair of second terminals), allowing for efficient extraction of current from the energy storage element. In other words, by providing the energy storage element with a four-terminal structure, resistance can be reduced, resulting in an energy storage element with excellent output performance. Furthermore, by arranging the terminals within the notches (a pair of first notches and a pair of second notches), the volume of the energy storage element including the terminals can be reduced, thereby increasing the volumetric energy density of the energy storage element compared to when the terminals are arranged on the curved wall portions.

[0021] (6) In the energy storage element according to any one of (1) to (5), the electrode plate contains a positive electrode active material, and the positive electrode active material is α-NaFeO containing nickel element. ２ The lithium transition metal composite oxide may include a lithium transition metal composite oxide having a type crystalline structure, and the content of nickel element relative to the transition metal element contained in the lithium transition metal composite oxide may be 50 mol % or more.

[0022] The positive electrode active material of the wound electrode body is α-NaFeO containing nickel element. ２It is known that a wound electrode assembly using an electrode plate containing a lithium transition metal composite oxide having a crystalline structure and in which the nickel content relative to the transition metal elements contained in the lithium transition metal composite oxide is 50 mol% or more exhibits a high volumetric energy density of the positive electrode active material, while the curved portion of the electrode assembly undergoes significant expansion during charging and discharging. In an energy storage device in which a flat-shaped wound electrode assembly containing such a positive electrode active material is housed in a rectangular cylindrical (square) container, the excess space between the curved portion of the electrode assembly and the inner surface of the container is relatively large, making the expansion of the curved portion of the electrode assembly more likely to proceed. In particular, energy storage devices incorporating multiple energy storage elements generally constrain the flat portion of the electrode assembly, and in batteries in which the flat portion is constrained, expansion of the flat portion is suppressed. As a result, the boundary between the flat portion with suppressed expansion and the curved portion of the electrode assembly using an electrode with a nickel content of 50 mol% or more, which exhibits high expansion, can form high strain, potentially damaging the electrode and significantly reducing safety. In contrast, the energy storage element described in (6) above can reduce the excess space within the container compared to a rectangular container, and can suppress expansion of the electrode body at the curved portion of the electrode body even when a positive electrode active material with a high volumetric energy density is used. Therefore, the energy storage element described in (6) above significantly improves the volumetric energy density within the container of the energy storage element, and furthermore, exhibits the effects of excellent safety.

[0023] (7) The present invention may be an electricity storage device including the electricity storage element according to any one of (1) to (6) above.

[0024] According to the electricity storage device described in (7) above, the electricity storage device includes the above-described electricity storage element, and thus the electricity storage device can have an increased volumetric energy density.

[0025] (Embodiments) Hereinafter, with reference to the drawings, an energy storage element and an energy storage device according to embodiments of the present invention (including modified examples thereof) will be described. The embodiments described below all show comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, manufacturing processes, and the order of manufacturing processes shown in the following embodiments are examples and are not intended to limit the present invention. In each drawing, dimensions and the like are not strictly illustrated. In each drawing, the same or similar components are assigned the same reference numerals. The names of the components (each component) in this embodiment are those used in this embodiment and may differ from the names of the components (each component) in the background art.

[0026] In the following description and drawings, the longitudinal direction of the energy storage element and the winding axis direction of the electrode body provided in the energy storage element are defined as the X-axis direction. The arrangement direction of the multiple energy storage elements, the thickness direction of the container of the energy storage element, the opposing direction of the pair of flat portions of the electrode body, and the opposing direction of the pair of flat wall portions of the container are defined as the Y-axis direction. The arrangement direction of the case lid and case body of the energy storage device, the opposing direction of the pair of curved portions of the electrode body, the opposing direction of the pair of curved wall portions of the container, or the up-down direction are defined as the Z-axis direction. These X-axis, Y-axis, and Z-axis directions intersect each other (orthogonal in this embodiment). Depending on the usage mode, the Z-axis may not be the up-down direction, but for convenience of explanation, the following description will be made assuming that the Z-axis direction is the up-down direction.

[0027] In the following description, the term "insulation" means "electrical insulation." An insulating material has a volume resistivity of 1×10 １０ It is preferable that the material be made of a material with a resistance of Ωm or more.

[0028] In the following description, the positive X-axis direction refers to the direction of the X-axis arrow, and the negative X-axis direction refers to the direction opposite to the positive X-axis direction. The same applies to the Y-axis and Z-axis directions. The positive Z-axis direction can be exemplified as the direction from the second curved wall portion of the container toward the first curved wall portion, and the negative Z-axis direction can be exemplified as the direction from the second curved wall portion of the container toward the first curved wall portion. Furthermore, expressions indicating relative directions or attitudes, such as parallel and perpendicular, also include cases where the directions or attitudes are not strictly those of the same kind. "Two directions are perpendicular" does not only mean that the two directions are completely perpendicular, but also means that the two directions are substantially perpendicular, i.e., there is a difference of about a few percent.

[0029] [Description of Energy Storage Element] An overall description of the energy storage element 10 according to the embodiment will be given using Fig. 4 and Fig. 5. Fig. 4 is a perspective view showing the appearance of the energy storage element 10 according to the embodiment. Fig. 5 is an exploded perspective view showing the components of the energy storage element 10 according to the embodiment.

[0030] The energy storage element 10 is an energy storage element that can charge electricity from an external source or discharge electricity to an external source. The energy storage element 10 is not limited to a nonaqueous electrolyte secondary battery, but may be a secondary battery other than a nonaqueous electrolyte secondary battery, or may be a capacitor. The energy storage element 10 may not be a secondary battery, but may be a primary battery that can use stored electricity without the user having to charge it. Furthermore, the energy storage element 10 may be an all-solid-state battery using a solid electrolyte or a polymer battery. The energy storage element 10 may also be a pouch-type energy storage element. In this embodiment, the energy storage element 10 is illustrated based on a flat, oval cylindrical shape, but the shape of the energy storage element 10, i.e., the shape of the container 100, is not limited to a shape based on a flat, oval cylindrical shape. As long as the inner surface of the container 100 conforms to the outer surface of the electrode assembly 700 described below, the container 100 may have a shape based on a polygonal prism, an elliptical cylinder, a cylindrical shape, or the like.

[0031] 4 and 5 , in this embodiment, the energy storage element 10 includes a container 100, a pair of terminals 300, and a pair of external gaskets 400. Furthermore, the energy storage element 10 includes a pair of internal gaskets 500, a pair of current collectors 600, and an electrode assembly 700 inside the container 100. The container 100 includes a lid 170 that covers the end facing the positive direction of the X-axis, and a lid 170 that covers the end facing the negative direction of the X-axis. The outer surface of the lid 170 facing the positive direction of the X-axis is referred to as a first side surface portion 110, and the outer surface of the lid 170 facing the negative direction of the X-axis is referred to as a second side surface portion 120.

[0032] An electrolyte solution (nonaqueous electrolyte) is sealed inside the container 100, but is not shown in the figure. The type of electrolyte solution is not particularly limited as long as it does not impair the performance of the energy storage element 10. In addition to the above components, spacers may be disposed on the sides, above, or below the electrode body 700, or an insulating film or the like that encases the electrode body 700 or the like may be disposed.

[0033] The container 100 is a case having an oval cylindrical shape that is long in the X-axis direction and flattened in the Y-axis direction. In this embodiment, the length of the container 100 in the X-axis direction is three times or more the length of the container 100 in the Z-axis direction, and the length of the container 100 in the X-axis direction is five times or more the length of the container 100 in the Y-axis direction.

[0034] The container 100 includes a container body 160 and a pair of lids 170. The container body 160 and each lid 170 are assembled together to form the container 100 in a cylindrical shape that is long in the X-axis direction. The container body 160 includes a pair of flat wall portions 131 and a pair of curved wall portions 141, 151 (a first curved wall portion 141 and a second curved wall portion 151). The pair of flat wall portions 131 and the pair of curved wall portions 141, 151 form a cylindrical shape that is long in the X-axis direction and penetrates the container body 160 in the X-axis direction. Each lid 170 of the pair of lids 170 is a plate-shaped member that closes each end of the container body 160 in the X-axis direction, and is included in the wall portion of the container 100. The lid 170 located in the negative X-axis direction closes the end of the container body 160 in the negative X-axis direction, and the lid 170 located in the positive X-axis direction closes the end of the container body 160 in the positive X-axis direction.

[0035] A gas exhaust valve 800 (see FIGS. 4 and 5) is disposed on the lid 170 in the positive direction of the X axis. Specifically, the gas exhaust valve 800 is disposed on the lid 170 in the positive direction of the X axis at a position in the negative direction of the Z axis. The gas exhaust valve 800 is a safety valve that releases pressure inside the container 100 when the pressure inside the container 100 rises excessively.

[0036] With this configuration, the container 100 is configured such that the electrode assembly 700 and the like are housed inside the container body 160, and then the container body 160 and the lid 170 are joined by welding or the like, thereby sealing the interior. The material of the container 100 (container body 160 and lid 170) is not particularly limited, but a weldable metal such as stainless steel, aluminum, aluminum alloy, iron, or plated steel sheet is preferred.

[0037] Although not shown here, a liquid injection portion is formed in the container body 160 or the lid 170. The liquid injection portion is a portion for injecting an electrolyte into the container 100 when manufacturing the energy storage element 10.

[0038] Each curved wall portion of the pair of curved wall portions 141, 151 is elongated in the X-axis direction and faces the curved portion 711 of the electrode body 700. That is, it can be said that the pair of curved wall portions 141, 151 face the pair of curved portions 711, respectively. The inner surfaces of each curved wall portion 141, 151 are curved to fit along the curved portion 711 of the electrode body 700. Specifically, the inner surface of the first curved wall portion 141, which is the curved wall portion 141 located in the positive direction of the Z axis, is curved so as to be concave in the positive direction of the Z axis, and the inner surface of the second curved wall portion 151, which is the curved wall portion 151 located in the negative direction of the Z axis, is curved so as to be concave in the negative direction of the Z axis. In this embodiment, the outer surfaces of each curved wall portion 141, 151 are also curved, with the first curved wall portion 141 formed in a curved shape that protrudes in the positive direction of the Z axis and the second curved wall portion 151 formed in a curved shape that protrudes in the negative direction of the Z axis. Each of the pair of flat wall portions 131 is elongated in the X-axis direction and faces the flat portion 712 of the electrode body 700 in the Y-axis direction. In other words, it can be said that the flat wall portions 131 face both sides of the flat portion 712. Each flat wall portion 131 is formed in the shape of a flat plate parallel to the XZ plane, and the inner surface of the flat wall portion 131 has a flat shape that fits along the flat portion 712 of the electrode body 700.

[0039] In the container body 160, the outer surface of each flat wall portion 131 comprises a long side surface 130, the outer surface of the first curved wall portion 141, which is a curved wall portion 141 in the positive direction of the Z axis, comprises a top surface 140, and the outer surface of the second curved wall portion 151, which is a curved wall portion 151 in the negative direction of the Z axis, comprises a bottom surface 150. The long side surfaces 130 are surfaces that are elongated in the X axis direction and parallel to the XZ plane, and the pair of long side surfaces 130 face each other in the Y axis direction. The top surface 140 is a surface that is elongated in the X axis direction and curved so as to be recessed in the positive direction of the Z axis along the curved portion 711 of the electrode body 700, and is located in the positive direction of the Z axis relative to the long side surfaces 130. The bottom surface 150 is a surface that is elongated in the X axis direction and curved so as to be recessed in the negative direction of the Z axis along the curved portion 711 of the electrode body 700, and is located in the negative direction of the Z axis relative to the long side surfaces 130.

[0040] Of the pair of lid bodies 170, the lid body 170 in the positive direction of the X axis has a first side surface 110 which is an outer surface parallel to the YZ plane. Of the pair of lid bodies 170, the lid body 170 in the negative direction of the X axis has a second side surface 120 which is an outer surface parallel to the YZ plane.

[0041] The terminals 300 are terminals (positive electrode terminal and negative electrode terminal) electrically connected to the electrode body 700 via the current collector 600. In other words, the terminals 300 are metal members for conducting electricity stored in the electrode body 700 to the external space of the energy storage element 10, or for introducing electricity into the internal space of the energy storage element 10 in order to store electricity in the electrode body 700. The material of the terminals 300 is not particularly limited, but the terminals 300 are formed of a conductive material such as aluminum, an aluminum alloy, copper, or a copper alloy. The terminals 300 are connected (joined) to the current collector 600 by crimping, welding, or the like, and are attached to the lid body 170.

[0042] The energy storage device 10 of this embodiment includes a pair of terminals 300. Each terminal 300 includes a terminal body 330 and a shaft 340 protruding from the terminal body 330. The terminal body 330 is a portion that protrudes outward from the terminal installation surface of the container 100. In this embodiment, the outer surface of the first curved wall 141 includes the terminal installation surface, and each terminal 300 of the pair of terminals 300 and each external gasket 400 are disposed on the outer surface of the first curved wall 141 of the container 100. Each terminal 300 protrudes in the positive direction of the Z axis from the outer surface of the first curved wall 141 of the container 100. Here, the first curved wall 141 is one of the wall portions that constitute the container 100, and the direction approaching the first curved wall 141 from the second curved wall 151 is a direction that penetrates from the inner surface to the outer surface of the container 100.

[0043] Through holes 112a, 122a through which shank 340 passes are formed in the terminal installation surface of first curved wall portion 141. Shank 340 is crimped in a state in which it passes through first curved wall portion 141, outer gasket 400, inner gasket 500, and current collector 600, thereby connecting (joining) terminal 300 and current collector 600.

[0044] In this embodiment, the terminal main body portion 330 protrudes outward from the container 100 in the positive direction of the Z axis from the terminal installation surface; in other words, the terminal main body portion 330 protrudes from the second curved wall portion 151 of the container 100 in a direction approaching the first curved wall portion 141.

[0045] The current collectors 600 are arranged one at each end of the electrode body 700 in the X-axis direction. The current collectors 600 are connected (joined) to the electrode body 700 and the terminal 300, and are conductive members (positive electrode current collector and negative electrode current collector) that electrically connect the electrode body 700 and the terminal 300. The current collector 600 integrally includes a first joint portion 630 and a second joint portion 640. Specifically, the first joint portion 630 of the current collector 600 is connected (joined) to a tab portion 720 of the electrode body 700 (described later) by welding, crimping, or the like, and the second joint portion 640 of the current collector 600 is connected (joined) to the terminal 300 by crimping, welding, or the like. The first joint portion 630 and the second joint portion 640 are each flat-plate-shaped portions formed by bending a single piece of sheet metal. The material of the current collector 600 is not particularly limited, but in this embodiment, the positive electrode current collector is formed of a conductive material such as aluminum or an aluminum alloy, and the negative electrode current collector is formed of a conductive material such as copper or a copper alloy.

[0046] The external gasket 400 is disposed between the first curved wall portion 141 of the container 100 and the terminal 300, and is a member that insulates between the first curved wall portion 141 and the terminal 300 and seals the interior of the container 100. In this embodiment, the external gasket 400 is a plate-shaped, rectangular insulating member. The internal gasket 500 is disposed between the lid 170 and the current collector 600, and is a member that insulates between the first curved wall portion 141 and the current collector 600 and seals the interior of the container 100. In this embodiment, both the external gasket 400 and the internal gasket 500 are plate-shaped, rectangular insulating members. The material of the external gasket 400 and the internal gasket 500 may be an electrically insulating resin such as polypropylene (PP), polyethylene (PE), polystyrene (PS), ABS resin, or a composite material thereof.

[0047] The electrode body 700 is an electricity storage element (power generating element) formed by winding electrode plates. The electrode body 700 has a long, elongated cylindrical shape extending in the X-axis direction. In this embodiment, the length of the electrode body 700 in the Y-axis direction is shorter than the lengths of the electrode body 700 in the X-axis direction and the Z-axis direction, so the electrode body 700 has a flat shape (a flat shape) in the Y-axis direction. The length of the electrode body 700 in the X-axis direction is 300 mm or more, specifically, approximately 500 mm to 1500 mm. The length of the electrode body 700 in the X-axis direction is longer than the length of the electrode body 700 in the Z-axis direction, and the length of the electrode body 700 in the X-axis direction is three times or more the length of the electrode body 700 in the Z-axis direction. The electrode body 700 includes a main body portion 710 and a plurality of tab portions 720 protruding from the main body portion 710. As described above, the tab portions 720 are connected (joined) to the current collector 600.

[0048] In this embodiment, the multiple tab portions 720 protrude one by one from both end faces in the X-axis direction of the main body portion 710. A positive electrode tab portion 721 is provided on the end face (one end face) of the main body portion 710 in the positive X-axis direction, and a negative electrode tab portion 722 is provided on the end face (the other end face) of the main body portion 710 in the negative X-axis direction.

[0049] Such an energy storage element 10 is manufactured by the following manufacturing method. First, the container body 160 is formed by extrusion molding, or by rolling a metal sheet and welding the ends in the Z-axis direction together. The container body 160 may be formed by welding together multiple segments divided in the XY plane. Next, the electrode body 700 is inserted into the container body 160. After insertion, the current collectors 600 are connected to each tab portion 720. Next, the external gasket 400, the internal gasket 500, the first curved wall portion 141, and the terminals 300 are assembled to each current collector 600, and then each lid 170 is welded to both ends of the container body 160. Thereafter, the electrolyte is injected into the container 100 through the injection port, and the injection port is sealed.

[0050] [Explanation of the configuration of the electrode assembly] Fig. 6 is a perspective view showing the configuration of an electrode assembly 700 according to an embodiment. Specifically, Fig. 6 shows a partially unfolded state of the winding of the electrode plates in the electrode assembly 700. As shown in Fig. 6, the electrode assembly 700 includes a positive electrode plate 740, a negative electrode plate 750, and separators 761 and 762.

[0051] The positive electrode plate 740 is an electrode plate in which a positive electrode active material layer 742 is disposed on the surface of a positive electrode current collector foil 741, which is a long strip of metal foil. Aluminum, an aluminum alloy, or the like is used for the positive electrode current collector foil 741. The negative electrode plate 750 is an electrode plate in which a negative electrode active material layer 752 is disposed on the surface of a negative electrode current collector foil 751, which is a long strip of metal foil. Copper, a copper alloy, or the like is used for the negative electrode current collector foil 751. As the positive electrode active material used in the positive electrode active material layer 742 and the negative electrode active material used in the negative electrode active material layer 752, any known material can be used as long as it is capable of absorbing and releasing lithium ions.

[0052] As a positive electrode active material, LiMPO ４ , LiMSiO ４ , LiMBO ３ (M is one or more transition metal elements selected from Fe, Ni, Mn, Co, etc.), polyanion compounds such as lithium titanate, LiMn ２ O ４ and LiMn １．５ Ni ０．５ O ４ Lithium transition metal composite oxides having a spinel-type crystal structure, such as LiMO ２ (M is one or more transition metal elements selected from Fe, Ni, Mn, Co, etc.) ２ Examples of the negative electrode active material include lithium metal, an alloy capable of absorbing and releasing lithium, a carbon material (graphite, non-graphitizable carbon, easily graphitizable carbon, low-temperature fired carbon, amorphous carbon, etc.), and silicon oxide.

[0053] The positive electrode active material layer may contain optional components such as other positive electrode active materials, conductive agents, binders, thickeners, and fillers, as needed. ２A lithium transition metal composite oxide having a crystalline structure of the type α-NaFeO is preferred. ２ The lithium transition metal composite oxide having a crystalline structure preferably contains at least one of nickel, cobalt, and manganese, and more preferably contains nickel. The lithium transition metal composite oxide also preferably contains nickel and manganese, and more preferably contains nickel, cobalt, and manganese. Here, the positive electrode active material is α-NaFeO containing nickel. ２ When the electrode assembly 700 includes a lithium transition metal composite oxide having a crystalline structure, it is preferable to set the content of nickel to 50 mol % or more relative to the transition metal elements contained in the lithium transition metal composite oxide in order to increase the volumetric energy density of the electrode assembly 700. By using such a lithium transition metal composite oxide, it is possible to further increase the volumetric energy density of the energy storage device 10. The lithium transition metal composite oxide may contain only nickel, only nickel and manganese, or only nickel, cobalt, and manganese as transition metal elements. The lithium transition metal composite oxide may further contain other metal elements such as aluminum. The positive electrode active material layer is made of α-NaFeO ２ The positive electrode active material layer may further contain a positive electrode active material other than the lithium transition metal composite oxide having a crystalline structure. As the positive electrode active material, various conventionally known positive electrode active materials can be used. However, the content of the lithium transition metal composite oxide relative to the total positive electrode active materials contained in the positive electrode active material layer is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass. Thus, by primarily using the lithium transition metal composite oxide as the positive electrode active material, it is possible to further increase the volumetric energy density of the nonaqueous electrolyte storage element.

[0054] Separators 761 and 762 are microporous sheets made of resin. Any known material can be used as the material for separators 761 and 762 as long as it does not impair the performance of energy storage element 10. Separators 761 and 762 may be made of a woven fabric or nonwoven fabric that is insoluble in organic solvents, a synthetic resin microporous film made of a polyolefin resin such as polyethylene, or the like.

[0055] The electrode assembly 700 is formed by winding a positive electrode plate 740, a negative electrode plate 750, and separators 761 and 762. The electrode assembly 700 is formed by stacking the negative electrode plate 750, the separator 761, the positive electrode plate 740, and the separator 762 in this order and winding them. In this embodiment, the positive electrode plate 740, the negative electrode plate 750, and the separators 761 and 762 are wound around a winding axis L extending in the X-axis direction, thereby forming the wound electrode assembly 700. The winding axis L is an imaginary axis that serves as the central axis when winding the positive electrode plate 740, the negative electrode plate 750, and the separators 761 and 762. In this embodiment, the winding axis is a straight line that passes through the center of the electrode assembly 700, is parallel to the X-axis direction, and is perpendicular to the Y-axis and Z-axis directions.

[0056] A plurality of protruding pieces 743 protruding outward are arranged at intervals on the edge of the positive electrode plate 740 in the X-axis positive direction. Similarly, a plurality of protruding pieces 753 protruding outward are arranged at intervals on the edge of the negative electrode plate 750 in the X-axis negative direction. Each of the plurality of protruding pieces 743 is a portion where no positive electrode active material layer is disposed and the positive electrode current collector foil 741 is exposed (a portion where no positive electrode active material layer is formed). Each of the plurality of protruding pieces 753 is a portion where no negative electrode active material layer is disposed and the negative electrode current collector foil 751 is exposed (a portion where no negative electrode active material layer is formed). In FIG. 6 , the portions where no active material layer is formed (portions where no positive electrode active material layer is formed, portions where no negative electrode active material layer is formed) are indicated by diagonal lines.

[0057] When the positive electrode plate 740, the negative electrode plate 750, and the separators 761, 762 are wound, the multiple protruding pieces 743 of the positive electrode plate 740 overlap at the end face (one end face) of the main body portion 710 in the positive direction of the X axis, and the multiple protruding pieces 753 of the negative electrode plate 750 overlap at the end face (the other end face) in the negative direction of the X axis. The portion of the positive electrode plate 740 where the multiple protruding pieces 743 overlap is the positive electrode tab portion 721. In other words, the positive electrode tab portion 721 is a portion where the multiple pieces (protruding pieces 743) of the electrode plates (positive electrode plate 740 and negative electrode plate 750) of the same polarity are stacked.

[0058] Similarly, the portion of the negative electrode plate 750 where the multiple protruding pieces 753 overlap is the negative electrode tab portion 722. In other words, the negative electrode tab portion 722 is a portion where the multiple pieces (protruding pieces 753) provided on the electrode plate of the same polarity (negative electrode plate 750) among the multiple electrode plates (positive electrode plate 740 and negative electrode plate 750) are stacked.

[0059] As described above, the electrode body 700 includes a main body portion 710 that constitutes the main body of the electrode body 700, and tab portions 720 (positive electrode tab portion 721 and negative electrode tab portion 722) that protrude from each end face in the X-axis direction of the main body portion 710. In other words, the electrode body 700 includes a pair of tab portions that are composed of the positive electrode tab portion 721 and the negative electrode tab portion 722.

[0060] The main body portion 710 is an elongated cylindrical portion formed by winding together a portion of the positive electrode plate 740 where the positive electrode active material layer 742 is disposed (formed, coated), a portion of the negative electrode plate 750 where the negative electrode active material layer 752 is disposed (formed, coated), and separators 761 and 762. The region of the main body portion 710 where at least one of the positive electrode active material layer 742 and the negative electrode active material layer 752 is laminated is referred to as the active material layer formation portion. The outer surface of the main body portion 710 includes curved portions 711 at both ends in the Z-axis direction and flat portions 712 at both ends in the Y-axis direction. In other words, the outer surface of the main body portion 710 includes a pair of curved portions 711 and a pair of flat portions 712. Each flat portion 712 of the pair of flat portions 712 is located between the pair of curved portions 711 in the Z-axis direction, resulting in an overall flat shape. It can also be said that the pair of curved portions 711 are arranged at positions sandwiching each flat portion 712 in the Z-axis direction.

[0061] The curved portion 711 is a portion that extends in the X-axis direction and protrudes in the Z-axis direction. When viewed from the X-axis direction, the curved portion 711 is curved in a semicircular arc shape (curved shape). The curved portion 711 located in the positive direction of the Z-axis and the first curved wall portion 141 of the container body 160 directly face each other in the Z-axis direction, and the curved portion 711 located in the negative direction of the Z-axis and the second curved wall portion 151 of the container body 160 directly face each other in the Z-axis direction. In other words, the curved portion 711 and the curved wall portion 141 face each other in the Z-axis direction, and the curved portion 711 and the curved wall portion 151 face each other in the Z-axis direction.

[0062] The flat portion 712 is a flat portion that extends in the X-axis direction and is parallel to the XZ plane, connecting the ends of the pair of curved portions 711. The flat portion 712 has a surface that is perpendicular to the Y-axis direction. Each flat portion 712 is disposed opposite a corresponding flat wall portion 131 of the container body 160. In the portion of the electrode body 700 sandwiched between the flat portions 712, multiple wound electrode plates (positive electrode plates 740 and negative electrode plates 750) are stacked in the Y-axis direction. In this description, the main stacking direction of the multiple electrode plates is defined as the Y-axis direction.

[0063] The curved shape of the curved portion 711 as viewed from the X-axis direction is not limited to a semicircular arc shape, but may be a shape like a part of an ellipse, a rectangular shape with rounded corners, etc. The outer surface of the flat portion 712 is not limited to being completely flat, but may be slightly concave or slightly bulged.

[0064] Fig. 7 is a cross-sectional view showing the positional relationship between the container 100 and the electrode assembly 700 according to the embodiment. Fig. 7 shows a state in which the outer surface of the main body 710 is in complete contact with the inner surface of the container 100. Immediately after the energy storage device 10 is manufactured, a portion of the outer surface of the main body 710 of the electrode assembly 700 may not be in complete contact with the inner surface of the container 100. However, as charge / discharge cycles are repeated, the main body 710 of the electrode assembly 700 expands, and the outer surface of the main body 710 comes into complete contact with the inner surface of the container 100.

[0065] Specifically, the inner surface of each flat wall portion 131 of the container 100 has a flat shape that conforms to the flat portion 712 of the main body portion 710 of the opposing electrode body 700, and each flat portion 712 of the main body portion 710 is in contact with the inner surface of each flat wall portion 131. In Fig. 7, the flat portion 712 of the main body portion 710 and the inner surface of the flat wall portion 131 that directly face each other are in contact overall, but there may be a portion where there is no contact between the flat portion 712 of the main body portion 710 and the inner surface of the flat wall portion 131 due to distortion of a portion of the flat portion 712 of the main body portion 710, for example.

[0066] The inner surface of the first curved wall portion 141 of the container 100 has a curved shape that follows the curved portion 711 of the main body portion 710 of the electrode body 700, and the curved portion 711 of the main body portion 710 is in contact with the inner surface of the first curved wall portion 141. In Fig. 7, the curved portion 711 of the main body portion 710 and the inner surface of the first curved wall portion 141, which directly face each other, are in contact overall, but there may be a portion where the curved portion 711 of the main body portion 710 and the inner surface of the first curved wall portion 141 do not contact due to, for example, partial distortion of the curved portion 711 of the main body portion 710. The second curved wall portion 151 of the container 100 has a similar configuration to that described above, and therefore is not shown or described here.

[0067] Although the outer surfaces of the curved wall portions 141 and 151 in the embodiment are curved along the curved shape of the inner surfaces of the curved wall portions 141 and 151, the outer surfaces of the curved wall portions 141 and 151 do not have to be curved. At least a portion of the outer surfaces of the curved wall portions 141 and 151 may have a curved shape with a different curvature than the inner surfaces of the curved wall portions 141 and 151 and / or a shape with one or more corners. FIG. 8 is a cross-sectional view showing the positional relationship between the container 100b and the electrode assembly 700 of an energy storage element 10b according to Modification 1. The energy storage element 10b has a similar configuration to that shown in FIG. 7 in that the outer surface of the main body 710 of the electrode assembly 700 is shown in a state in which the entire outer surface of the main body 710 is in contact with the inner surface of the container 100b. The energy storage element 10b differs from the energy storage element 10 according to the embodiment in that the outer surface of the curved wall portion 141b of the container 100b has a polygonal shape with multiple corners when viewed from the winding axis direction.

[0068] In the energy storage element 10 of this embodiment, the inner surface of the flat wall portion 131 of the container 100 contacts the flat portion 712 of the electrode body 700, and the inner surfaces of the curved wall portions 141, 151 contact the curved portion 711 of the electrode body 700. Therefore, the surplus space within the container 100 of the energy storage element 10 can be made smaller than in the case of a rectangular container (see FIG. 3), thereby suppressing a decrease in the volumetric energy density within the container 100 of the energy storage element 10. Since the energy storage element 10b of Modification 1 has a similar configuration, the surplus space within the container 100b of the energy storage element 10b can be made smaller than in the case of a rectangular container (see FIG. 3), thereby suppressing a decrease in the volumetric energy density within the container 100b of the energy storage element 10b.

[0069] The BOL (Beginning of Life) of the energy storage element 10 includes the time of shipment or immediately after manufacture. Immediately after manufacture, it is also assumed that the number of charge / discharge cycles since the energy storage element 10 was first charged after manufacture may be less than a predetermined number. The predetermined number is the number of times that the main body portion 710 of the electrode assembly 700 expands and the outer surface of the main body portion 710 can come into contact with the inner surface of the container 100 as a whole. The predetermined number is preferably 10 times, more preferably 5 times, and even more preferably 3 times. Even if the number of charge / discharge cycles of the energy storage element 10 is less than the predetermined number, this is included in the present invention as long as the main body portion 710 of the electrode assembly 700 expands as the energy storage element 10 is used and the outer surface of the main body portion 710 can come into contact with the inner surface of the container 100 as a whole.

[0070] [Explanation of Effects] As described above, according to the energy storage element 10 of the embodiment of the present invention, the curved wall portions 141, 151 on the inner surface of the container 100 have a curved shape that follows the curved portion 711 of the electrode body 700 and face the curved portion 711, and the flat wall portion 131 on the inner surface of the container 100 has a flat shape that follows the flat portion 712 of the electrode body 700 and faces the flat portion 712.Therefore, the excess space within the container 100 of the energy storage element 10 can be made smaller than in the case of a rectangular container, and a decrease in the volumetric energy density within the container 100 of the energy storage element 10 can be suppressed.

[0071] In the above-described configuration, the excess space generated between the outer surface of the electrode body 700 and the inner surface of the container 100 of the energy storage element 10 is generally small, making it easier to release heat generated in the electrode body 700 to the outside than in the case of a rectangular container in which the outer surface of the curved portion of the electrode body does not fit the inner surface of the container, creating an excess space (gap). This improves the cooling performance of the energy storage element 10. Furthermore, because the excess space generated between the outer surface of the electrode body 700 and the inner surface of the container 100 of the energy storage element 10 is generally small, the detection depth (thickness) can be reduced when using a device to detect contamination such as metal pieces in the excess space. This makes it easier to detect contamination using the device.

[0072] Since the pair of terminals 300 protrude from the outer surface of the first curved wall portion 141 of the container 100, the pair of terminals 300 are located at the end of the energy storage element 10 in the direction from the second curved wall portion 151 toward the first curved wall portion 141. This makes it easy to approach the terminals 300 from the outside even after a plurality of energy storage elements 10 are unitized. This facilitates electrical connection (welding, etc.) between the terminals 300 and a bus bar or the like.

[0073] The positive electrode active material of the wound electrode body 700 is α-NaFeO ２It is known that a wound electrode assembly using an electrode plate containing a lithium transition metal composite oxide having a crystalline structure and in which the nickel content relative to the transition metal elements contained in the lithium transition metal composite oxide is 50 mol % or more has a high volumetric energy density of the positive electrode active material, but the curved portion of the electrode assembly undergoes significant expansion during charging and discharging. In an energy storage device in which a flat, wound electrode assembly containing such a positive electrode active material is housed in a prismatic container, the excess space between the curved portion of the electrode assembly and the inner surface of the container is relatively large, and the expansion of the curved portion of the electrode assembly is more likely to proceed significantly. In contrast, the energy storage device 10 according to the embodiment houses a flat, wound electrode assembly 700 containing such a positive electrode active material in a container 100 having an inner surface curved along the outer surface of the curved portion 711. This reduces the excess space within the container 100 compared to a prismatic container, and can suppress expansion of the electrode assembly at the curved portion of the electrode assembly even when a positive electrode active material with a high volumetric energy density is used. As a result, the effect of improving the volumetric energy density inside the container 100 of the energy storage element 10 is significantly achieved.

[0074] The effects of the energy storage device 10 according to the above-described embodiment are similarly obtained by the energy storage device 10b according to the first modified example.

[0075] [Explanation of Modifications] The following describes each of the modifications (Modifications 2 to 9) of the above embodiment. In the following description, parts that are the same as those in the above embodiment or other modifications will be given the same reference numerals, and their description may be omitted.

[0076] (Modification 2) A description will be given of an energy storage device 10c according to Modification 2. Fig. 9 is a perspective view showing the appearance of an energy storage device 10c according to Modification 2, in which an elongated cylindrical region that serves as a reference for the outer shape of a container 100c is shown by a two-dot chain line L1.

[0077] As shown in FIG. 9 , the container 100c of the energy storage device 10c includes a lid 170c covering the end portion in the positive direction of the X-axis and a lid 170c covering the end portion in the negative direction of the X-axis. The energy storage device 10c differs from the energy storage device 10 according to the embodiment in that each lid 170c of the container 100c has a bent shape. Specifically, the region of the lid 170c from the center in the Z-axis direction to the end portion in the negative direction of the Z-axis is bent so as to protrude in the X-axis direction. Furthermore, at the end portion in the X-axis direction, the region of the flat wall portion 131c from the center in the Z-axis direction to the curved wall portion 151 protrudes in the X-axis direction beyond the remaining portion of the flat wall portion 131c and the curved wall portion 141. The positive electrode components are disposed on a first side surface portion 110c that constitutes the outer surface of the lid 170c in the positive direction of the X-axis. The negative electrode components are disposed on the second side surface portion 120c that constitutes the outer surface of the lid body 170c in the negative X-axis direction. Examples of the positive electrode components include a terminal 300c, an external gasket 400c, an internal gasket 500c, and a current collector 600c, while examples of the negative electrode components include a terminal 300c, an external gasket 400c, an internal gasket 500c, and a current collector 600c. In the second modification, the first side surface portion 110c and the second side surface portion 120c are located within a range of 1% to 10% of the length of the container 100c in the X-axis direction from the end face of the container 100c in the X-axis direction, although the range of the length of the container 100c in the X-axis direction may be greater than 10%.

[0078] Energy storage element 10c has one notch at the end of container 100c in the positive Z-axis direction, one at the end in the positive X-axis direction, and one at the end in the negative X-axis direction. That is, energy storage element 10c has a pair of notches (a pair of first notches). In other words, container 100c has a pair of notches (a pair of first notches) at the end in the positive Z-axis direction, which are mutually positioned in the winding axis direction of electrode body 700.

[0079] The pair of first notches are positioned to sandwich the first curved wall portion 141c in the X-axis direction (winding axis direction). Each notch is a portion where a corner (end) of the container 100c is cut out, and is rectangular when viewed from the Y-axis direction. In other words, the container 100c has an outer shape that is elongated in the X-axis direction and flattened in the Y-axis direction, with rectangular notches formed at both ends and the top of the container 100c in the X-axis direction (ends in the positive Z-axis direction) when viewed from the Y-axis direction. Each notch can also be considered to form a recess by recessing a portion of the oval cylindrical shape that serves as a reference. Of the multiple notches, each of the pair of notches (pair of first notches) located at the top of the container 100c is the first recess 101c. Each notch may have any shape. At least a portion of each notch may be curved, may have one or more corners, or may not necessarily penetrate the container 100c in the Y-axis direction. The shape of each notch in the energy storage element described below is also not particularly limited.

[0080] The first side surface portion 110c includes a first upper side surface 111c and a first upper surface 112c. The first upper side surface 111c is a surface parallel to the YZ plane and facing in the positive direction of the X axis. The first upper surface 112c is a surface parallel to the XY plane and facing in the positive direction of the Z axis. The first upper side surface 111c is continuous with the first upper surface 112c and is the surface of the outer surface of the lid body 170c in the positive direction of the X axis that is located furthest in the positive direction of the Z axis. The first upper surface 112c is a surface continuous with the first upper side surface 111c and a surface of the lid body 170c that is further in the negative direction of the Z axis than the first upper surface 112c.

[0081] The second side surface portion 120c includes a second upper side surface 121c and a second upper surface 122c. The configuration of the outer surface of the cover 170c in the negative X-axis direction is the same as the configuration of the outer surface of the cover 170c in the positive X-axis direction, and therefore a description thereof will be omitted.

[0082] One terminal 300c is arranged on the first upper surface 112c of the first side surface portion 110c, and one terminal 300c is arranged on the second upper surface 122c of the second side surface portion 120c.

[0083] A gas exhaust valve 800c is disposed at the end of the cover 170c in the positive Z-axis direction. The gas exhaust valve 800c is disposed on the cover 170c covering the end in the positive X-axis direction and / or the cover 170c covering the end in the negative X-axis direction.

[0084] The terminal installation surface is a surface that forms each first recess 101c and faces the positive direction of the Z axis. Specifically, the terminal installation surface located on the outer surface of the lid 170c in the positive direction of the X axis is the first top surface 112c, and the terminal installation surface located on the outer surface of the lid 170c in the negative direction of the X axis is the second top surface 122c. The first top surface 112c and the second top surface 122c are outer surfaces of the wall portions that make up the container 100c, and the direction from the second curved wall portion 151c to the first curved wall portion 141c penetrates from the inner surface to the outer surface of the container 100c. Thus, in this embodiment, one terminal 300c and one external gasket 400c are arranged on the surface of the lid 170c in the positive direction of the X axis and the surface of the lid 170c in the negative direction of the X axis. It can also be said that the pair of terminals 300c and the pair of external gaskets 400c are arranged on a plurality of wall portions (two wall portions) of the container 100c.

[0085] In the energy storage device 10c according to the second modification, the terminal body 330c protrudes outward from the terminal installation surface toward the positive Z-axis direction of the container 100c, protruding from the second curved wall 151c of the container 100c toward the first curved wall 141c. In the energy storage device 10c, a pair of terminals 300c are disposed within a pair of notches. The terminal body 330c is located within the space S1 created by the notches and does not protrude beyond the space S1. Each lid 170c has a through-hole formed in a wall portion (in this embodiment, the first upper surface 112c and the second upper surface 122c) including the terminal installation surface, through which the shaft 340c passes. Each lid 170c may be bent to conform to the shape of the end of the container body 160c in the X-axis direction during or after connection between the terminal 300c and the current collector 600c.

[0086] The pair of terminals 300c are arranged on a surface such that the direction from the second curved wall portion 151c toward the first curved wall portion 141c is the direction penetrating from the inner surface of the container 100c to the outer surface of the container 100c, and further, are arranged to protrude from the second curved wall portion 151c in the direction toward the first curved wall portion 141c, thereby reducing the amount of protrusion of the terminals 300c in the opposing direction of the pair of curved portions 711. In other words, by arranging the terminals 300c in the cutouts, the volume of the energy storage element 10c is reduced and the volumetric energy density is higher than when the terminals 300c are arranged on the curved wall portion 141c.

[0087] (Modification 3) An energy storage device 10d according to Modification 3 will be described. FIG. 10 is a perspective view showing the appearance of an energy storage device 10d according to Modification 3. An elongated cylindrical region that serves as a reference for the outer shape of the container 100d is illustrated by a two-dot chain line L1. As shown in FIG. 10, the container 100d of the energy storage device 10d has, at its end in the positive Z-axis direction, one notch at its end in the positive X-axis direction and one notch at its end in the negative X-axis direction. That is, the energy storage device 10d has a pair of first notches that are a pair of notches. Furthermore, the container 100d of the energy storage device 10d has, at its end in the negative Z-axis direction, one notch at its end in the positive X-axis direction and one notch at its end in the negative X-axis direction. That is, the energy storage device 10d has a pair of second notches that are a pair of notches. In other words, the container 100d has a pair of notches (a pair of first notches) at its end in the positive direction of the Z axis, which are mutually positioned in the direction of the winding axis of the electrode body 700, and a pair of notches (a pair of second notches) at its end in the negative direction of the Z axis, which are mutually positioned in the direction of the winding axis of the electrode body 700.

[0088] Of the multiple cutouts, each of a pair of cutouts (a pair of first cutouts) located in the upper part of the container 100d is a first recess 101d. The first recess 101d is one of the multiple cutouts that make up the pair of cutouts located in the upper part of the container 100d. The pair of first cutouts are positioned to sandwich the first curved wall portion 141d in the X-axis direction (winding axis direction). An outer gasket 400d and a terminal 300d are installed in each first recess 101d.

[0089] Of the multiple cutouts, each of a pair of cutouts (a pair of second cutouts) located at the bottom of the container 100d is a second recess 102d. The second recess 102d is one of the multiple cutouts that make up the pair of cutouts located at the bottom of the container 100d. The pair of second cutouts are positioned to sandwich the second curved wall portion 151d in the X-axis direction (winding axis direction). Each of the pair of second cutouts has the same configuration as each of the pair of first cutouts. In other words, the container 100d has a pair of cutouts (a pair of first cutouts) located at its end in the positive Z-axis direction and mutually positioned in the winding axis direction of the electrode body 700, and a pair of cutouts (a pair of second cutouts) located at its end in the negative Z-axis direction and mutually positioned in the winding axis direction of the electrode body 700. As a result, the outer shape of the container 100d is an oval cylinder that is long in the X-axis direction and flattened in the Y-axis direction, with rectangular cutouts formed at the top and bottom of both ends in the X-axis direction when viewed from the Y-axis direction. It can also be said that each notch forms a recess by recessing a part of the oval cylindrical shape that serves as a reference.

[0090] The container 100d includes a pair of lids 170d. The lid 170d facing the positive X-axis direction is bent to match the positions of the ends of the curved wall portions 141d and 151d in the X-axis direction and the position of the end of the flat wall portion 131d in the X-axis direction. The first side surface portion 110d, which is the outer surface of the lid 170d facing the positive X-axis direction, includes a first upper surface 111d, a first upper surface 112d, a first middle surface 113d, a first lower surface 114d, and a first lower surface 115d. The first upper surface 112d and the first lower surface 114d are surfaces parallel to the XY plane. The first upper surface 112d faces in the positive Z-axis direction, and the first lower surface 114d faces in the negative Z-axis direction. The first upper surface 111d, the first middle surface 113d, and the first lower surface 115d are surfaces parallel to the YZ plane and can also be said to be surfaces facing the positive direction of the X axis. The first upper surface 111d is continuous with the first upper surface 112d and is the surface of the outer surface of the cover 170d in the positive direction of the X axis that is located furthest in the positive direction of the Z axis. The first lower surface 115d is continuous with the first lower surface 114d and is the surface of the outer surface of the cover 170d in the positive direction of the X axis that is located furthest in the negative direction of the Z axis. The first middle surface 113d is a surface continuous with the first upper surface 112d and the first lower surface 114d, and is positioned between the first upper surface 111d and the first lower surface 115d in the Z axis direction when viewed from the X axis direction. Of the pair of lid bodies 170, the lid body 170 in the negative X-axis direction is bent to match the positions of the ends of the curved wall portions 141d and 151d in the X-axis direction and the position of the end of the flat wall portion 131d in the X-axis direction, similar to the lid body 170 in the positive X-axis direction. The second side surface portion 120d, which is the outer surface of the lid body 170d in the negative X-axis direction, includes a second upper surface 121d, a second upper surface 122d, a second middle surface 123d, a second lower surface 124d, and a second lower surface 125d. The configuration of the outer surfaces of the lid body 170d in the negative X-axis direction is the same as the configuration of the outer surfaces of the lid body 170d in the positive X-axis direction, so a description thereof will be omitted.

[0091] As shown in Fig. 10 , in the container 100d of the energy storage device 10d, a gas exhaust valve 800d is arranged on a surface parallel to the YZ plane in each second recess 102d. Specifically, the gas exhaust valve 800d is arranged on a first lower surface 114d and a second lower surface 124d on the outer surfaces of the pair of lid bodies 170d. The gas exhaust valve 800d may be provided in the first recess 101d. The gas exhaust valve 800d may be provided in one second recess 102d. The other configuration of the energy storage device 10d is similar to that of the energy storage device 10c according to the second modification.

[0092] (Modifications 4 and 5) We will now describe a storage element 10e according to modification 4 and a storage element 10f according to modification 5. Fig. 11(a) is a plan view showing the appearance of the storage element 10e according to modification 4 when viewed from the positive direction of the X-axis, and Fig. 11(b) is a plan view showing the appearance of the storage element 10f according to modification 5 when viewed from the positive direction of the X-axis.

[0093] As shown in Fig. 11A, in the energy storage element 10e, the terminal body 330e of the terminal 300e is formed of a bolt. Although not shown, the same applies to the terminal 300e in the negative X-axis direction. The rest of the configuration is the same as that of the energy storage element 10d of the third modification shown in Fig. 10, and therefore description thereof will be omitted.

[0094] 11B, in the energy storage element 10f, the end portion in the positive X-axis direction of each flat wall portion 131f of the container 100f is positioned more inward in the Y-axis direction than each flat wall portion 131f in the central region in the X-axis direction. Here, the end portion in the positive X-axis direction refers to a region of the flat wall portion 131f that faces the multiple tab portions 720 of the electrode body 700 in the Y-axis direction. The central region in the X-axis direction refers to a region of the flat wall portion 131f that faces the main body portion 710 of the electrode body 700 in the Y-axis direction. That is, in the flat wall portion 131f located in the positive Y-axis direction, the position in the Y-axis direction of the end portion in the positive X-axis direction is further in the negative Y-axis direction than the position in the Y-axis direction of the flat wall portion 131f in the region that faces the outer surface of the main body portion 710 in the positive Y-axis direction. In the flat wall portion 131f located in the negative Y-axis direction, the position in the Y-axis direction at the end in the positive X-axis direction is further in the positive Y-axis direction than the position in the Y-axis direction of the flat wall portion 131f in the region facing the outer surface of the main body portion 710 in the negative Y-axis direction. Although not shown, the configuration of the flat wall portion 131f at the end in the negative X-axis direction is also similar. The other configurations are similar to those of the energy storage element 10d of Modification 3. With the above configuration, in the energy storage element 10f, a gap is generated in the Y-axis direction between the end in the X-axis direction and adjacent components (the energy storage element 10f and the case 2, etc.), and this gap can be used for heat dissipation from the energy storage element 10f, wiring, etc.

[0095] The energy storage element 10f may be manufactured by the following manufacturing method. First, a container body 160f is formed with aligned ends in the X-axis direction by extrusion molding or by rolling a metal sheet and welding the ends in the Z-axis direction. Next, the electrode body 700 is inserted into this container body 160f. After insertion, the current collectors 600 are connected to each tab portion 720. Next, the external gasket 400f, the internal gasket 500, the lid 170f, and the terminals 300f are assembled to each current collector 600, and then the lids 170f are welded to close the ends of the container body 160f from the X-axis direction. Then, electrolyte is injected into the container 100f through the injection port, and the injection port is sealed. The manufacturing method of the energy storage element 10i according to Modification 8, described below, is similar.

[0096] (Variation 6) An energy storage device 10g according to Variation 6 will be described. FIG. 12 is a perspective view showing the appearance of the energy storage device 10g according to Variation 6. The energy storage device 10g has a configuration in which terminals 300g and external gaskets 400g are arranged at each end of the first curved wall portion 141 in the X-axis direction and each end of the second curved wall portion 151 of the energy storage device 10 ( FIG. 4 ) according to the embodiment. That is, the energy storage device 10g includes four terminals 300g and four external gaskets 400g. Specifically, first terminals 301g are arranged at the end of the first curved wall portion 141g facing the positive direction of the X-axis and the end of the second curved wall portion 151g facing the negative direction of the X-axis, forming a pair of first terminals 301g. Furthermore, second terminals 302g are arranged at the end of the second curved wall portion 151g facing the positive direction of the X-axis and the end of the second curved wall portion 151g facing the negative direction of the X-axis, forming a pair of second terminals 302g. Here, the first curved wall portion 141g is one of the wall portions constituting the container 100g, and the direction from the second curved wall portion 151g to the first curved wall portion 141g is a direction penetrating from the inner surface to the outer surface of the container 100g. The second curved wall portion 151g is one of the wall portions constituting the container 100g, and the direction from the first curved wall portion 151g to the second curved wall portion 151g is a direction penetrating from the inner surface to the outer surface of the container 100g.

[0097] Although not shown, the electrode body of the energy storage device 10g according to Variation 6 has two tab portions protruding from each end face of the main body in the X-axis direction. The electrode body may have two positive electrode tab portions provided on the end face (one end face) of the main body in the positive X-axis direction and two negative electrode tab portions provided on the end face (other end face) of the main body in the negative X-axis direction. The electrode body may have one positive electrode tab portion and one negative electrode tab portion provided on the end face (one end face) of the main body 710 in the positive X-axis direction and one positive electrode tab portion and one negative electrode tab portion provided on the end face (other end face) of the main body in the negative X-axis direction. The arrangement of the positive electrode tab portion and the negative electrode tab portion on the end face (one end face) in the positive X-axis direction does not have to be the same as the arrangement of the positive electrode tab portion and the negative electrode tab portion on the end face (other end face) in the negative X-axis direction. The remaining configuration of the energy storage device 10g is the same as that of the energy storage device 10 according to the embodiment. The energy storage element 10h relating to variant 7 and the energy storage element 10i relating to variant 8, which will be described later, also have two tab portions protruding from each end face of the main body in the X-axis direction, but this description will be omitted.

[0098] Because a pair of terminals 300g (a pair of first terminals 301g and a pair of second terminals 302g) protrude from the outer surfaces of each curved wall portion (first curved wall portion 141g, second curved wall portion 151g) of the container 100g, the volumetric energy density of the energy storage element 10g can be increased compared to when the pair of terminals 300g protrude from each end of the container 100g in the winding axis direction (X-axis direction). Furthermore, the pair of first terminals 301g are located at the end of the energy storage element 10g in the direction from the second curved wall portion 151g toward the first curved wall portion 141g, and the pair of second terminals 302g are located at the end of the energy storage element 10g in the direction from the first curved wall portion 141g toward the second curved wall portion 151g. This makes it easy to approach the terminals 300g from the outside after unitizing multiple energy storage elements 10g. This facilitates electrical connection (e.g., welding) between the terminals 300g and a bus bar or the like. Furthermore, since the energy storage element 10g includes two pairs of terminals 300g (a pair of first terminals 301g and a pair of second terminals 302g), current can be efficiently extracted from the energy storage element 10g. In other words, by providing the energy storage element 10g with a four-terminal structure, resistance can be reduced, resulting in an energy storage element with excellent output performance.

[0099] (Variation 7) An energy storage element 10h according to Variation 7 will be described. FIG. 13 is a perspective view showing the appearance of the energy storage element 10h according to Variation 7. The long cylindrical region that serves as the reference for the outer shape of the container 100h of the energy storage element 10h is illustrated by a two-dot chain line L1. The energy storage element 10h differs from the energy storage element 10d according to Variation 3 (see FIG. 10) in that second terminals 302h and external gaskets 400h are arranged on a surface (first lower surface 114h or second lower surface 124h) parallel to the XY plane in each second recess 102h. In other words, one energy storage element 10h includes four terminals 300h and four external gaskets 400h. Here, a pair of first terminals 301h are arranged within a pair of first notches, and the terminal main body portion 330h is located within the space S1 created by the notches and does not protrude outward beyond the space S1. Similarly, a pair of second terminals 302h are arranged in a pair of second notches, and the terminal body portion 330h is located inside the space S2 created by the notches and does not protrude outward from the space S2.

[0100] The terminal installation surfaces of the energy storage element 10h are the surfaces facing the positive direction of the Z axis that form each first recess 101h and the surfaces facing the negative direction of the Z axis that form each second recess 101h. More specifically, the terminal installation surfaces located on the outer surface of the lid 170h in the positive direction of the X axis are the first upper surface 112h and the first lower surface 114h, and the terminal installation surfaces located on the outer surface of the lid 170h in the negative direction of the X axis are the second upper surface 122h and the second lower surface 124h. Here, the first upper surface 112h and the second upper surface 122h on which the pair of first terminals 301h are arranged can be said to be the outer surfaces of two wall portions that constitute the container 100h, and the direction approaching the first curved wall portion 141h from the second curved wall portion 151h penetrates from the inner surface to the outer surface of the container 100h. The first lower surface 114h and the second lower surface 124h of the lid 170h, on which the pair of second terminals 302h are arranged, can be considered to be the outer surfaces of two wall portions constituting the container 100h, in which the direction from the first curved wall portion 141h to the second curved wall portion 151h penetrates from the inner surface to the outer surface of the container 100h. The gas release valve 800h is arranged on a surface parallel to the YZ plane forming the second recess 102h, but may also be arranged on a surface parallel to the YZ plane forming the first recess 101f. The other configuration of the energy storage device 10h is the same as that of the energy storage device 10d according to Modification 3. In this way, in the energy storage device 10h according to Modification 7, two terminals 300h are arranged on each surface of the lid 170h facing the positive X-axis direction and the lid 170h facing the negative X-axis direction, and a pair of first terminals 301h and a pair of second terminals 302h are arranged on the wall portions of the container 100h.

[0101] The pair of first terminals 301h are provided within the pair of first recesses 101h so as to protrude from the second curved wall portions 151h in a direction approaching the first curved wall portions 141h, thereby reducing the amount of protrusion of the pair of first terminals 301h outward from the container 100h in the direction approaching the first curved wall portions 141h from the second curved wall portions 151h. Similarly, the pair of second terminals 302h are provided within the pair of second recesses 102h so as to protrude from the first curved wall portions 141h in a direction approaching the second curved wall portions 151h, thereby reducing the amount of protrusion of the pair of second terminals 302h outward from the container 100h in the direction approaching the second curved wall portions 151h from the first curved wall portions 141h. As described above, the energy storage element 10h includes two pairs of terminals 300h (a pair of first terminals and a pair of second terminals), allowing current to be extracted efficiently from the energy storage element 10f. Furthermore, by placing the terminals 300h within the notches (a pair of first notches and a pair of second notches), the volume of the storage element 10h is reduced, and the volumetric energy density of the storage element 10h is increased compared to when the terminals 300h are placed in the curved wall portions 141h and 151h.

[0102] (Modification 8) A description will be given of an energy storage device 10i according to Modification 8. Fig. 14 is a plan view showing the appearance of an energy storage device 10i according to Modification 8 when viewed from the positive direction of the X axis.

[0103] The energy storage element 10i differs from the energy storage element 10f of Modification 5 in that a pair of external gaskets 400i and a pair of second terminals 302i are arranged therein, but otherwise has the same configuration as the energy storage element 10f of Modification 5. With this configuration, a gap is generated in the Y-axis direction between the end of the energy storage element 10i in the X-axis direction and adjacent members (the energy storage element 10i and the case 2, etc.), and this gap can be used for heat dissipation from the energy storage element 10i, wiring, etc.

[0104] [Description of Energy Storage Device] A schematic configuration of the energy storage device 1 according to the present embodiment will be described. Fig. 15 is a perspective view showing the appearance of the energy storage device 1 according to the embodiment. Fig. 16 is an exploded perspective view showing each component of the energy storage device 1 according to the embodiment when disassembled.

[0105] The power storage device 1 is a device capable of charging with electricity from an external source or discharging electricity to an external source, and in this embodiment, has a substantially rectangular parallelepiped shape. The rectangular parallelepiped here refers to a hexahedron with all faces formed of rectangles or squares. The power storage device 1 is a power storage element module (battery assembly) used for power storage, power supply, or other purposes. Specifically, the power storage device 1 is used as a battery for driving or starting the engine of a moving object such as an automobile, motorcycle, personal watercraft, ship, snowmobile, agricultural machinery, construction machinery, automatic guided vehicle (AGV), or electric railway vehicle. Examples of the automobile include an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and a fossil fuel (gasoline, diesel, liquefied natural gas, etc.) vehicle. Examples of the electric railway vehicle include a train, a monorail, a linear motor car, and a hybrid train equipped with both a diesel engine and an electric motor. The power storage device 1 can also be used as a stationary battery for home or business use.

[0106] 15 and 16 , the energy storage device 1 includes a case 2. The case 2 accommodates a plurality of energy storage elements 10, a holding unit 20, a pair of exhaust members 50, a plurality of bus bars (not shown), and the like. The energy storage device 1 also includes external terminals (positive electrode external terminals and negative electrode external terminals) for electrically connecting to an external device, but these are not shown or described here. In addition to the above components, the energy storage device 1 may also include restraining members (end plates, side plates, etc.) that restrain the plurality of energy storage elements 10, bus bar holders that hold the bus bars, bus bar covers, circuit boards that monitor or control the charge and discharge states of the energy storage elements 10, and electrical components such as relays, fuses, shunt resistors, and connectors.

[0107] The case 2 is a substantially rectangular parallelepiped (box-shaped) container (module case) that constitutes the exterior body (housing, outer shell) of the energy storage device 1. The case 2 is an example of an external member. The case 2 is arranged outside the plurality of energy storage elements 10 and the holding unit 20, etc., and fixes the plurality of energy storage elements 10 and the holding unit 20, etc. in predetermined positions to protect them from impacts, etc. The case 2 is a metal case made of a metal member such as aluminum, aluminum alloy, stainless steel, iron, or plated steel sheet. The case 2 may be made of an insulating material such as a resin material. When the case 2 is made of a conductive material, the inner surface of the case 2 may be coated with an insulating material to ensure insulation from the energy storage elements 10.

[0108] 16 , the case 2 includes a case main body 30 that constitutes the main body of the case 2, and a case lid 40 that constitutes the lid of the case 2. The case main body 30 is a rectangular cylindrical housing (chassis) with a bottom and an opening 31 formed in the positive direction of the Z axis, and houses a plurality of energy storage elements 10, holding units 20, etc.

[0109] Specifically, the case body 30 includes a bottom wall 32 and a side wall 33. The bottom wall 32 is a flat, rectangular portion disposed at the end of the case body 30 in the negative Z-axis direction.

[0110] The side wall 33 is a rectangular annular wall extending in the positive Z-axis direction from the outer periphery of the bottom wall 32, and is provided continuously around the entire circumference of the bottom wall 32. The opening 31 is located inside the side wall 33. The side wall 33 is provided with a pair of exhaust ports 37, which are arranged in the negative Z-axis direction within the side wall 33 in this embodiment. Each exhaust port 37 connects the inside and outside of the case 2, and exhausts gas discharged from each energy storage element 10 to the outside of the case 2.

[0111] The case lid 40 is a flat, rectangular member that closes the rectangular opening 31 of the case body 30. The case body 30 and the case lid 40 are joined by welding, adhesive bonding, screwing, or the like, and the interior of the case 2 is sealed (airtight). The case body 30 and the case lid 40 may be made of the same material or different materials.

[0112] By including the above-described energy storage element 10 in the energy storage device 1, the length of the energy storage device 1 in the winding axis direction (X-axis direction) can be shortened, resulting in an energy storage device 1 with an increased volumetric energy density.

[0113] [Holding Unit] Fig. 17 is an explanatory diagram showing the holding unit 20, the case 2, and the energy storage device 10 according to the embodiment. In Fig. 17, only the case 2 is shown in cross section. As shown in Fig. 17, the holding unit 20 includes a plurality of holding members 21 arranged in the Y-axis direction.

[0114] The holding members 21 are arranged alternately with the energy storage elements 10 in the Y-axis direction and are members that hold the energy storage elements 10, and are responsible for insulating and / or heat-insulating the energy storage elements 10 from one another and from other components. In this embodiment, the holding members 21 are arranged so as to directly face the flat wall portion 131 of the container 100 and at least a portion of the curved wall portions 141 and 151 of the container 100, and to overlap the region of the electrode assembly 700 where the active material layer is formed (see FIGS. 6 and 16 ). The holding members 21 are insulating plate-like members that are arranged adjacent to the energy storage elements 10 in the positive or negative Y-axis direction of the energy storage elements 10 and that insulate the energy storage elements 10 from one another or from the case 2. The holding members 21 may be formed of an insulating material such as PC, PP, PE, PS, ABS resin, or a composite material thereof, or may be formed of a metal member whose surface is coated with an insulating material.

[0115] (Other Modifications) Although the energy storage element according to the embodiment of the present invention (including its modifications, the same applies hereinafter) has been described above, the present invention is not limited to the above-described embodiment. The embodiment disclosed herein is illustrative in all respects, and the scope of the present invention includes all modifications within the meaning and scope of the claims.

[0116] The direction of approach from the second curved wall portion to the first curved wall portion is determined as follows: A point located at the center of the second curved wall portion in the length direction (X direction in FIG. 4 ) and the center of the second curved wall portion in the width direction (Y direction in FIG. 4 ) is defined as the second curved wall portion center point. A point located at the center of the first curved wall portion in the length direction (X direction in FIG. 4 ) and the center of the first curved wall portion in the width direction (Y direction in FIG. 4 ) is defined as the first curved wall portion center point. In the container of the energy storage device, the direction of approach from the second curved wall portion to the first curved wall portion is defined as the direction from the center point of the second curved wall portion toward the center point of the first curved wall portion. One or more wall portions in which the direction of approach from the second curved wall portion to the first curved wall portion penetrates from the inner surface to the outer surface of the container refers to wall portions in which, when penetrated linearly from the second curved wall portion in the direction of approaching the first curved wall portion, the majority of the area is in the direction from the inner surface to the outer surface of the container. The penetration does not need to penetrate perpendicular to the wall surface and may be inclined relative to the perpendicular. Examples of such one or more wall portions in which the direction from the second curved wall portion to the first curved wall portion is a direction penetrating from the inner surface to the outer surface of the container include the first curved wall portions 141 and 141d in FIGS. 4 and 12 and the wall portions in which the terminals (300c, 300d, 300h) are installed in the pair of first recesses (101c, 101d, 101h) in FIGS. 9, 10, and 13. It should be noted that which of the multiple curved wall portions present in the wall of the container is designated as the first curved wall portion and which is the second curved wall portion can be arbitrarily determined. When one curved wall portion is designated as the first curved wall portion and another curved wall portion is designated as the second curved wall portion, there may be a combination of a first curved wall portion and a second curved wall portion that satisfies the following condition: "The pair of terminals are arranged in one or more wall portions among the wall portions constituting the container in which the direction from the second curved wall portion to the first curved wall portion is a direction penetrating from the inner surface to the outer surface of the container, and the pair of terminals protrude from the second curved wall portion in a direction approaching the first curved wall portion." The pair of terminals protruding from the second curved wall portion in a direction approaching the first curved wall portion does not necessarily mean that the protruding direction of the pair of terminals is exactly the same as the direction approaching the first curved wall portion from the second curved wall portion. Even if the two directions are misaligned, it is sufficient that the amount of protrusion of the pair of terminals from the second curved wall portion in the direction approaching the first curved wall portion is expressed as a positive value.

[0117] In the above embodiment, the case where each terminal is arranged at both ends of the container in the direction of the winding axis (X-axis direction) has been exemplified, but each terminal may be arranged at a position other than the ends in the direction of the winding axis (X-axis direction).

[0118] In the above embodiment, the case where only one electrode body 700 is housed in the container has been exemplified, but two or more electrode bodies arranged in the X-axis direction may be housed in the container.

[0119] In the above embodiment, the flat portion 712 of the electrode assembly 700 has an overall flat shape, but at least a portion of the flat portion 712 of the electrode assembly 700 may have a recessed shape in the direction toward the center of the winding axis. In such a case, at least a portion of the flat wall portion of the container may have a bulged shape so as to fit along the outer surface of the flat portion 712 of the electrode assembly 700.

[0120] In the above embodiment, a case has been illustrated in which the curved portions 711 of the opposing electrode bodies 700 are in direct contact with the curved wall portion of the container, but an insulating sheet or the like may also be placed between the opposing curved portions 711 and the curved wall portion.

[0121] In the above embodiment, the gas release valve is disposed on the cover, but the gas release valve may be disposed on a flat wall portion or a curved wall portion of the energy storage element. The number of gas release valves may be one, two, or three or more.

[0122] In the above embodiment, the energy storage device 1 in which a plurality of energy storage elements 10 are housed in the case 2 is exemplified, but the energy storage device may also be one in which one or more energy storage elements are housed in the case.

[0123] In the above embodiment, a case in which a plurality of energy storage devices 10 are housed in the case 2, which is an external member, has been described as an example, but the external member may simply fix the energy storage devices without housing them. In this case, the external member may be a frame body or the like disposed outside the energy storage devices.

[0124] In the above embodiment, the case where the external member is a box-shaped case 2 is exemplified. The external member may be formed by aluminum die-casting. Furthermore, the external member may be a component constituting a moving body such as an automobile. Examples of the moving body itself include a skeletal structure of the moving body, a bogie, a chassis, etc.

[0125] In the above embodiment, the pack-type energy storage device 1 in which the energy storage elements 10 and the holding unit 20 are housed in the case 2 has been exemplified, but a module-type energy storage device may also be used.

[0126] Any combination of the components included in the above-described embodiments and their modifications is also included within the scope of the present invention.

[0127] The present invention can be applied to an electric storage element such as a lithium ion secondary battery and an electric storage device including the same.

[0128] DESCRIPTION OF SYMBOLS 1 Energy storage device 2 Case (external member) 10, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i Energy storage element 20 Holding unit 21 Holding member 30 Case body 31 Opening 32 Bottom wall 33 Side wall 37 Exhaust port 40 Case lid 100, 100b, 100c, 100d, 100e, 100f, 100g, 100h Container 101c, 101d, 101h First recess (first notch) 102d, 102h Second recess (second notch) 110, 110c, 110d First side surface portion 112a Through hole 120, 120c, 120d Second side surface portion 122a Through hole 130 Long side surface 131, 131c, 131d, 131f, Flat wall portion 140 Top surface 141, 141b, 141c, 141d, 141g, 141h Curved wall portion (first curved wall portion) 151, 151c, 151d, 151g, 151h Curved wall portion (second curved wall portion) 150 Bottom surface 160, 160c, 160f Container body 170, 170c, 170d, 170f, 170h Lid body 300, 300c, 300d, 300e, 300f, 300g, 300h Terminal 301g, 301h First terminal 302g, 302g, 302i Second terminal 330, 330c, 330e, 330h Terminal body portion 340 Shaft portion 400 External gasket 500 Internal gasket 600 Current collector 630 First joint portion 640 Second joint portion 700 Electrode body 710 Main body portion 711 Curved portion 712 Flat portion 720 Tab portion 721 Positive electrode tab portion 722 Negative electrode tab portion 740 Positive electrode plate 741 Positive electrode current collector foil 742 Positive electrode active material layer 743, 753 Projecting piece 750 Negative electrode plate 751 Negative electrode current collector foil 752 Negative electrode active material layer 761, 762 Separator 800, 800c, 800d, 800h Gas release valve L Winding axis L1 Range serving as reference for the outer shape of the container (shown by a two-dot chain line) S1, S2 Space

Claims

1. An energy storage element comprising: an electrode body having wound electrodes; a container that houses the electrode body; and a pair of terminals that are arranged in the container, wherein the electrode body has a flat shape with a pair of opposing curved portions and a flat portion connecting the pair of curved portions, and the container comprises: a pair of curved wall portions that respectively face the pair of curved portions of the electrode body, and flat wall portions that respectively face both sides of the flat portion of the electrode body, wherein the pair of curved wall portions are a first curved wall portion and a second curved wall portion, and an inner surface of the first curved wall portion and an inner surface of the second curved wall portion have curved shapes that follow the curved portions of the electrode body, and an inner surface of the flat wall portion has a flat shape that follows the flat portion of the electrode body, wherein the pair of terminals are arranged in one or more wall portions that form the container, the direction approaching the first curved wall portion from the second curved wall portion being a direction that penetrates from the inner surface to the outer surface of the container, and the pair of terminals protrude from the second curved wall portion in a direction approaching the first curved wall portion.

2. The energy storage element according to claim 1, wherein the pair of terminals protrude from an outer surface of the first curved wall portion in a direction from the second curved wall portion toward the first curved wall portion.

3. The energy storage element described in claim 1, wherein the container has a pair of notches that are mutually positioned in the winding axis direction of the electrode body, the pair of notches are arranged at a position that sandwiches the first curved wall portion of the container in the winding axis direction, and the pair of terminals are arranged within the pair of notches and on a surface that extends from the second curved wall portion toward the first curved wall portion in a direction that penetrates from the inner surface of the container to the outer surface of the container, and protrude from the second curved wall portion in a direction that approaches the first curved wall portion.

4. An energy storage element as described in claim 1, comprising a pair of first terminals and a pair of second terminals arranged in the container, wherein the pair of first terminals protrude from an outer surface of the first curved wall portion in a direction from the second curved wall portion toward the first curved wall portion, and the pair of second terminals protrude from the outer surface of the second curved wall portion in a direction from the first curved wall portion toward the second curved wall portion.

5. An energy storage element as described in claim 1, comprising a pair of first terminals and a pair of second terminals disposed in the container, wherein the pair of first terminals are the pair of terminals, wherein the container has a pair of first notches and a pair of second notches, wherein the pair of first notches are disposed at positions sandwiching the first curved wall portion of the container in the winding axial direction of the electrode body, wherein the pair of second notches are disposed at positions sandwiching the second curved wall portion of the container in the winding axial direction, wherein the pair of first terminals are disposed within the pair of first notches and on a surface on which a direction from the second curved wall portion to the first curved wall portion passes through a direction from the inner surface of the container to the outer surface of the container, and protrude from the second curved wall portion in a direction approaching the first curved wall portion, and wherein the pair of second terminals are disposed within the pair of second notches and on a surface on which a direction from the first curved wall portion to the second curved wall portion passes through a direction from the inner surface of the container to the outer surface of the container, and protrude from the first curved wall portion in a direction approaching the second curved wall portion.

6. The electrode plate includes a positive electrode active material, and the positive electrode active material is α-NaFeO ２ 6. The energy storage element according to claim 1, comprising a lithium transition metal composite oxide having a Nb-type crystal structure, wherein a content of nickel element relative to the transition metal element contained in the lithium transition metal composite oxide is 50 mol % or more.

7. An electricity storage device comprising the electricity storage element according to any one of claims 1 to 5.

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