Power storage element and method for producing power storage element

Abstract

In one embodiment of the present invention, this power storage element comprises: an electrode body having a flat surface; and a stainless steel container that houses the electrode body. The container has, on an inner surface thereof, a protrusion provided at a position facing the flat surface of the electrode body. The electrode body has an outermost layer containing inorganic particles as a main component.

Description

Electricity storage element and method for manufacturing the same

[0001] The present invention relates to an energy storage element and a method for manufacturing an energy storage element.

[0002] Chargeable and dischargeable energy storage elements (secondary batteries, capacitors, etc.) are used in various devices, such as electric vehicles and other vehicles, and home appliances. Known energy storage elements include electrode bodies, such as wound or stacked types, that have a positive electrode and a negative electrode. Such electrode bodies are housed in a container together with, for example, an electrolyte, to form an energy storage element.

[0003] Patent document 1 describes an energy storage element that includes a wound electrode body and a container that houses the electrode body, and the container has a convex portion on its inner surface that directly or indirectly contacts the electrode body.

[0004] Japanese Patent Application Publication No. 2013-239376

[0005] In the energy storage device described in Patent Document 1, which includes a container having a convex portion on its inner surface, the convex portion is said to have the effect of suppressing movement of the electrode body due to vibration. However, when the convex portion is provided on the inner surface of the container, when inserting the electrode body into the container during the manufacturing process of the energy storage device, the electrode body may get caught on the convex portion on the inner surface of the container, making insertion difficult. Furthermore, the electrode body getting caught on the convex portion may cause problems with the electrode body (e.g., falling off of active material, occurrence of wrinkles, etc.). In particular, when the container is made of stainless steel, the container is hard and does not easily deform, so the above-mentioned inconvenience caused by the electrode body getting caught on the convex portion becomes more pronounced.

[0006] The present invention has been made based on the above circumstances, and its object is to provide an energy storage element having a stainless steel container with a convex portion on the inner surface, which has excellent ease of insertion of the electrode body during the manufacturing process, and a method for manufacturing such an energy storage element.

[0007] An energy storage element according to one embodiment of the present invention comprises an electrode body having a flat surface and a stainless steel container for housing the electrode body, the container having a convex portion on its inner surface located opposite the flat surface of the electrode body, and the electrode body having an outermost layer primarily composed of inorganic particles.

[0008] A method for manufacturing a storage element according to another aspect of the present invention includes preparing an electrode body having a flat surface, preparing a stainless steel container having a convex portion on its inner surface, and inserting the electrode body into the container so that the flat surface of the electrode body faces the convex portion on the inner surface of the container, wherein the electrode body has an outermost layer primarily composed of inorganic particles.

[0009] According to any one embodiment of the present invention, it is possible to provide an energy storage element having a stainless steel container with a convex portion on the inner surface, which has excellent insertability of the electrode body during the manufacturing process, and a manufacturing method for such an energy storage element.

[0010] FIG. 1 is a schematic perspective view showing an energy storage element according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the energy storage element of FIG. 1 as viewed along arrows II. FIG. 3 is a schematic partial cross-sectional view of the container of FIG. 1 as viewed along arrows II. FIG. 4 is a schematic perspective view showing the outline of the configuration of an electrode body of the energy storage element of FIG. 1. FIG. 5 is a schematic partial cross-sectional view showing the outline of the configuration of an electrode body of the energy storage element of FIG. 1. FIG. 6 is a schematic cross-sectional view showing an energy storage element according to another embodiment different from the energy storage element of FIG. 1. FIG. 7 is a schematic cross-sectional view showing an energy storage element according to yet another embodiment. FIG. 8 is a schematic plan view showing an energy storage device formed by assembling a plurality of the energy storage elements of FIG. 1.

[0011] First, an overview of the energy storage element and the method for manufacturing the energy storage element disclosed in this specification will be described.

[0012] (1) An energy storage element according to one aspect of the present invention comprises an electrode body having a flat surface and a stainless steel container that houses the electrode body, the container having a convex portion on its inner surface that faces the flat surface of the electrode body, and the electrode body having an outermost layer primarily composed of inorganic particles.

[0013] The energy storage element described in (1) above is an energy storage element including a stainless steel container having a convex portion on the inner surface, and exhibits excellent electrode assembly insertion properties during the manufacturing process. The reason for this effect is unclear, but the following reasons are presumed. If the outermost layer of the electrode assembly is formed of a material that has a high frictional force against the inner surface of the container, such as a resin layer, the electrode assembly is likely to get caught on the convex portion on the inner surface of the container when inserted into the container. In contrast, if the outermost layer of the electrode assembly is a layer primarily composed of inorganic particles, the frictional force between the surface of the electrode assembly and the inner surface of the container is small. In such cases, the electrode assembly is more likely to slide against the inner surface of the container when inserted into the container, making it less likely to get caught on the convex portion on the inner surface of the container. Even if another member is interposed between the electrode assembly and the container, the electrode assembly is more likely to slide against the other member, making it less likely to get caught on the convex portion on the inner surface of the container. For these reasons, it is presumed that the energy storage element described in (1) above exhibits excellent electrode assembly insertion properties during the manufacturing process. Furthermore, in the energy storage element described in (1) above, the electrode body has excellent insertability during the manufacturing process, making it difficult for defects to occur in the electrode body during insertion, and suppressing the occurrence of defects during the manufacturing process.

[0014] The term "major component" refers to the component with the highest content by mass. The "flat surface" may be a substantially flat surface, and may partially have wrinkles, depressions, steps, etc., for example. The "flat surface" is typically the outer surface of the electrode assembly where the positive electrode and negative electrode are stacked substantially parallel with a separator interposed therebetween. Regarding the "stainless steel container," for example, when the container is composed of a container body and a lid, the container body may be made of stainless steel. In this case, it is preferable that the entire container (both the container body and the lid) be made of stainless steel.

[0015] (2) In the energy storage element described in (1) above, the container may have recesses on its outer surface that conform to the shapes of the protrusions on the inner surface.

[0016] A container having recesses on its outer surface that conform to the shape of the protrusions on its inner surface is relatively easy to manufacture, for example, by processing a stainless steel plate of substantially uniform thickness. Therefore, the energy storage element described in (2) above has further advantages such as high productivity.

[0017] (3) In the energy storage element described in (1) or (2) above, when no external force is applied to the container, at least a portion of the flat surface of the electrode body may be in contact with a convex portion on the inner surface of the container directly or via another member.

[0018] Generally, in the case of an energy storage element configured such that, when no external force is applied to the container, at least a portion of the flat surface of the electrode body is in contact with a convex portion on the inner surface of the container, either directly or via another member, the convex portion on the inner surface of the container is likely to come into contact with the electrode body or another member when the electrode body is inserted, making it easy for the electrode body to get caught. Therefore, in the case of the energy storage element described above in (3), there is great technical significance in improving insertability by providing the electrode body with an outermost layer mainly composed of inorganic particles.

[0019] In addition, in the "state where no external force is applied to the container," atmospheric pressure may be applied to the container as the "external force." The energy storage element in the "state where no external force is applied to the container" may be an energy storage element under 1 atmosphere. In addition, "other members" refers to solid members such as insulating members described below, but does not include liquid members such as electrolyte.

[0020] (4) The energy storage device according to any one of (1) to (3) above may further include an insulating member interposed between the electrode body and the container.

[0021] The energy storage element described in (4) above has high electrical insulation between the electrode body and the container. Also, in the energy storage element described in (4) above provided with such an insulating member, the outermost layer of the electrode body and the insulating member are easily slippery, which results in excellent insertability of the electrode body during the manufacturing process.

[0022] (5) In the energy storage element described in any one of (1) to (4) above, the electrode body is a wound electrode body in which a positive electrode and a negative electrode are wound in a stacked state with a separator interposed therebetween, and the outermost layer of the electrode body may be a part of the separator.

[0023] In the case of the energy storage element described in (5) above, the positive electrode and the negative electrode are wound in a stacked state with a separator interposed therebetween, whereby an electrode body having a layer mainly composed of inorganic particles provided in the separator as the outermost layer can be easily produced, resulting in high productivity.

[0024] (6) In the energy storage element described in any one of (1) to (5) above, the electrode body may be a wound electrode body in which a positive electrode and a negative electrode are wound in a state in which they are stacked together with a separator interposed therebetween, the container may have a container body having an opening and a lid body that closes the opening, and the winding axis of the electrode body may be parallel to the lid body.

[0025] In the case of the energy storage element described in (6) above, when the wound electrode body is inserted into a container, the electrode body is inserted from the curved surface. Therefore, the energy storage element described in (6) above is particularly excellent in insertability, and defects in the electrode body during insertion are further suppressed.

[0026] (7) In the energy storage element described in any one of (1) to (5) above, the electrode body may be a wound electrode body in which a positive electrode and a negative electrode are wound in a state where they are stacked together with a separator interposed therebetween, the container may have a container body having an opening and a lid body that closes the opening, and the winding axis of the electrode body may be perpendicular to the lid body.

[0027] In the case of the energy storage element described in (7) above, when the wound electrode body is inserted into the container, it is inserted from the end face of the electrode body (the face where the end faces of the positive electrode and negative electrode are exposed). Usually, in such a case, the electrode body is likely to get caught when inserted, and if it gets caught, the electrode body is likely to become defective. Therefore, in the case of the energy storage element described in (7) above, there is great technical significance in improving the insertability by providing the electrode body with an outermost layer mainly composed of inorganic particles.

[0028] (8) Another aspect of the present invention relates to a method for manufacturing a storage element, comprising: preparing an electrode body having a flat surface; preparing a stainless steel container having a convex portion on its inner surface; and inserting the electrode body into the container so that the flat surface of the electrode body faces the convex portion on the inner surface of the container, wherein the electrode body has an outermost layer primarily composed of inorganic particles.

[0029] According to the manufacturing method of an energy storage element described in (8) above, the insertion of the electrode body is excellent in the manufacturing process of an energy storage element including a stainless steel container having a convex portion on the inner surface, and therefore, according to the manufacturing method of an energy storage element described in (8) above, the electrode body is less likely to malfunction during insertion, and the occurrence of defects is suppressed.

[0030] Hereinafter, an energy storage element, a manufacturing method of an energy storage element, an energy storage device, and other embodiments according to an embodiment of the present invention will be described in detail. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0031] <Energy Storage Element 100> An energy storage element 100 according to one embodiment of the present invention, as shown in FIGS. 1 and 2, includes an electrode assembly 1, a non-aqueous electrolyte (not shown), and a container 2 for accommodating these. The energy storage element 100 is a non-aqueous electrolyte secondary battery, which is an example of an energy storage element. In this embodiment, the electrode assembly 1 is a flat, wound-type electrode assembly formed by winding a positive electrode and a negative electrode stacked together with a separator interposed therebetween, as described in detail below. The wound-type electrode assembly 1 has a pair of flat surfaces 3 facing each other across a winding axis W and a pair of curved surfaces 4 facing each other across the winding axis W (see FIGS. 2 and 4). The electrode assembly 1 also has a pair of end faces 42 perpendicular to the winding axis W (see FIG. 4). At least a portion of the non-aqueous electrolyte (not shown) is present in a state of permeating the positive electrode, negative electrode, and separator that constitute the electrode assembly 1. In another embodiment, a water-containing electrolyte solution or the like may be used instead of the non-aqueous electrolyte.

[0032] 1 includes, as other components, a positive electrode connection member 5, a positive electrode terminal 6, a negative electrode connection member 7, and a negative electrode terminal 8. The positive electrode of the electrode body 1 is electrically connected to the positive electrode terminal 6 via the positive electrode connection member 5. The negative electrode of the electrode body 1 is electrically connected to the negative electrode terminal 8 via the negative electrode connection member 7.

[0033] (Container) The container 2 is rectangular and has a roughly rectangular parallelepiped shape. The container 2 is composed of a container body 9 and a lid 10. The container body 9 is a roughly rectangular parallelepiped cylindrical member having four side walls 11, one bottom plate 18, and an opening. The lid 10 is a plate-like member that closes the opening of the container body 9. The container 2 has a structure in which the inside is sealed by welding the container body 9 and the lid 10 together after the electrode body 1 and other components are housed inside.

[0034] The container body 9 is made of stainless steel. Being made of stainless steel, the container body 9 has excellent strength. Examples of stainless steel used for the container body 9 include SUS304 and SUS430 as specified in the JIS standard. A material other than stainless steel (e.g., a metal other than stainless steel, a resin, etc.) may be used in part of the container body 9. For example, the surface of the container body 9 may be coated with another material. Preferably, 90% by mass or more of the material constituting the container body 9 is stainless steel, and more preferably, 99% by mass or more of the material constituting the container body 9 is stainless steel. Furthermore, the lid 10 is also preferably made of stainless steel; in other words, it is preferable that the entire container 2 is made of stainless steel. The material constituting the container 2 (container body 9 and lid 10) may be 90% by mass or more of the material constituting the container 2 is stainless steel, and may be 99% by mass or more of the material constituting the container 2 is stainless steel.

[0035] The electrode body 1 is housed in the container 2 such that the pair of flat surfaces 3 face a pair of opposing side walls 11 (usually a pair of side walls with larger areas among the four side walls 11) of the container 2 (container body 9). The container 2 has convex portions 12 on its inner surface, which are provided at positions facing the flat surfaces 3 of the electrode body 1. That is, each of the pair of opposing side walls 11 of the container 2 has a convex portion 12 on its inner surface. By providing such convex portions 12 on the inner surface of the container 2, movement of the electrode body 1 due to vibrations, etc., and expansion of the electrode body 1 due to repeated charging and discharging are suppressed, and as a result, deterioration of charge and discharge performance can be suppressed.

[0036] In this embodiment, when no external force is applied to the container 2, at least a portion (e.g., a central portion) of the flat surface 3 of the electrode body 1 is in direct contact with the convex portion 12 on the inner surface of the container 2. The convex portion 12 of the container 2 may simply be in contact with the flat surface 3 of the electrode body 1, or may be pressing against the flat surface 3 of the electrode body 1. When no external force is applied to the container 2, the ratio (t2 / t1) of the maximum thickness t2 of the electrode body 1 to the distance t1 between the pair of convex portions 12 may be 1.00 or more, or may be 1.01 or more. This ratio (t2 / t1) may be 1.2 or less, or may be 1.1 or less. The electrode body 1 may gradually expand due to repeated charge and discharge, resulting in the convex portion 12 of the container 2 pressing against the flat surface 3 of the electrode body 1. Note that the maximum thickness t2 of the electrode body 1 is the maximum thickness of the electrode body when discharged to the discharge cut-off voltage during normal use. Here, normal use refers to the case where the storage element is used under the charge and discharge conditions recommended or specified for the storage element.

[0037] In addition, when no external force is applied to the container 2, whether or not at least a part of the flat surface 3 of the electrode body 1 is in contact with the protrusions 12 on the inner surface of the container 2 directly or via another member is confirmed by an X-ray cross-sectional image. In addition, the distance t1 between the pair of protrusions 12 and the maximum thickness t2 of the electrode body 1 are also measured based on the X-ray cross-sectional image.

[0038] In this embodiment, the container 2 (container body 9) has recesses 13 on its outer surface that conform to the shapes of the protrusions 12 on its inner surface. That is, the pair of side walls 11 of the container 2 (container body 9) are plates of substantially uniform thickness, and their central portions are recessed from the outside to the inside. The protrusions 12 and recesses 13 preferably have a substantially rectangular shape when viewed from the front (as viewed in the Y direction). The ratio of the area of ​​one protrusion 12 to the area of ​​one flat surface 3 of the electrode body 1 may be, for example, 0.1 to 0.9, or 0.3 to 0.8 (e.g., 0.5 to 0.8).

[0039] 3 , the convex portion 12 on the inner surface of the container 2 in this embodiment is composed of a flat surface 14 and a slope 15 that is continuous with the flat surface 14. The slope 15 is also continuous with a surface 16 on the inner surface of the container 2 other than the convex portion 12. Only the flat surface 14 of the convex portion 12 may be in contact with the flat surface 3 of the electrode body 1, or the slope 15 may be in contact with the flat surface 3 of the electrode body 1 together with the flat surface 14. The surface 16 on the inner surface of the container 2 other than the convex portion 12 may be in contact with the flat surface 3 of the electrode body 1, etc.

[0040] The height H of the protrusions 12 on the inner surface of the container 2 is set appropriately depending on the size of the container 2, etc., but is preferably 1 mm or more and 10 mm or less, and more preferably 1.5 mm or more and 4 mm or less. The angle θ formed between the surface 16 other than the protrusions 12 on the inner surface of the container 2 and the slope 15 is preferably 160° or more and 178° or less, and more preferably 170° or more and 176° or less. When the height H of the protrusions 12 and the angle θ formed between the surface 16 other than the protrusions 12 and the slope 15 are within the above ranges, the above-mentioned effects of the protrusions 12 can be fully exhibited. However, since conventional electrode bodies tend to get caught on the protrusions when inserting an electrode body, providing the electrode body with an outermost layer mainly composed of inorganic particles has a particularly great technical significance in terms of improving insertability.

[0041] It is preferable that the corner 17 formed by the flat surface 14 and the inclined surface 15 is chamfered. The radius of curvature at the corner 17 is preferably 5 mm or more and 100 mm or less, and more preferably 10 mm or more and 50 mm or less. By chamfering the corner 17, the insertability of the electrode body 1 can be further improved.

[0042] (Electrode Assembly) The electrode assembly 1 is a flat, wound-type electrode assembly. As shown in FIG. 4 , the electrode assembly 1 is formed by stacking a strip-shaped positive electrode 21, a strip-shaped first separator 22a, a strip-shaped negative electrode 23, and a strip-shaped second separator 22b in this order, and then winding the stacked components longitudinally with the second separator 22b facing outward. As described above, this flat, wound-type electrode assembly 1 has a pair of flat surfaces 3 facing each other across the winding axis W, a pair of curved surfaces 4 facing each other across the winding axis W, and a pair of end surfaces 42 perpendicular to the winding axis W. The electrode assembly 1 is housed in the container 2 such that the winding axis W is parallel to the lid 10 of the container 2 (the X direction). That is, the pair of curved surfaces 4 of the electrode assembly 1 face the bottom plate 18 of the container body 9 or the lid 10.

[0043] As shown in FIGS. 4 and 5 , the positive electrode 21 includes a strip-shaped positive electrode substrate 25 and positive electrode active material layers 26 laminated on both sides of the positive electrode substrate 25. The negative electrode 23 includes a strip-shaped negative electrode substrate 27 and negative electrode active material layers 28 laminated on both sides of the negative electrode substrate 27. The separators 22 (22a, 22b) each include a strip-shaped substrate layer 29 and a layer 30 containing inorganic particles as a main component laminated on one side of the substrate layer 29 (hereinafter, the "layer containing inorganic particles as a main component" may also be referred to as the "inorganic layer"). The separators 22 (22a, 22b) are stacked such that the inorganic layer 30 faces the positive electrode 21. Note that the separators 22 (22a, 22b) may include a substrate layer 29 with the inorganic layer 30 laminated on both sides of the substrate layer 29. Details of each component will be described later.

[0044] In the wound electrode body 1 configured as shown in Figures 4 and 5, the outermost layer is the inorganic layer 30 of the second separator 22b. In this way, the electrode body 1 has an outermost layer mainly composed of inorganic particles. This outermost layer is part of the separator 22, and specifically, the inorganic layer 30 of the second separator 22b. In the production of the wound electrode body 1 of Figure 4, it is also possible to wind only the second separator 22b multiple times in the final stage of winding, resulting in a structure in which only the separator 22 is layered.

[0045] In another embodiment, an electrode assembly can be used in which the separator is wound in a superimposed state so that the inorganic layer faces the negative electrode. In this case, too, the electrode assembly can be obtained by winding the electrode assembly so that the inorganic layer of the separator forms the outermost layer. In yet another embodiment, the outermost layer of the electrode assembly can be formed of a member other than the inorganic layer of the separator. For example, an electrode assembly can be used in which an electrode assembly main body composed of a positive electrode, a negative electrode, and a separator consisting only of a resin substrate layer is coated with an insulating film having an inorganic layer. In this case, by coating the electrode assembly main body with an insulating film so that the inorganic layer is located on the outer surface, an electrode assembly having an outermost layer mainly composed of inorganic particles can be obtained.

[0046] In the energy storage element 100, the outermost layer of the electrode body 1 is the inorganic layer 30 as described above, and therefore the electrode body 1 has excellent insertability during the manufacturing process, even though the energy storage element includes a stainless steel container 2 having protrusions 12 on its inner surface. Furthermore, in the energy storage element 100 of this embodiment, the winding axis W of the electrode body 1 is parallel to the lid 10 of the container 2. In this case, when the electrode body 1 is inserted into the container 2, the curved surface 4 of the electrode body 1 is inserted into the container body 9 first, and the curved surface 4 comes into contact with the protrusions 12 first, resulting in even better insertability.

[0047] <Energy Storage Element 101> An energy storage element 101 according to another embodiment shown in Fig. 6 includes two electrode bodies 1, a non-aqueous electrolyte (not shown), and a container 2 that accommodates these. The energy storage element 101 further includes an insulating member 40 interposed between the two electrode bodies 1 and the container 2. The energy storage element 101 is substantially the same as the energy storage element 100 described above, except that it accommodates two electrode bodies 1 and further includes an insulating member 40. In the energy storage element 101, too, when no external force is applied to the container 2, it is preferable that at least a portion (e.g., a central portion) of the flat surface 3 of the electrode body 1 contacts the protrusion 12 on the inner surface of the container 2 via the insulating member 40, which is another member.

[0048] The insulating member 40 may be formed in a bag shape (insulating bag) to encase the two electrode bodies 1. The insulating member 40 is made of an electrically insulating material. The insulating member 40 may be formed, for example, of a resin film. Examples of materials for the insulating member 40 include polyolefins such as polyethylene and polypropylene, polyimide, and aramid, with polyolefin being preferred. In the energy storage element 101, the insulating member 40 is provided between the electrode body 1 and the container 2, thereby providing high electrical insulation between the electrode body 1 and the container 2 and further suppressing movement of the electrode body 1 due to vibrations and the like. Even in the energy storage element 101 provided with such an insulating member 40, the effect of excellent electrode body insertion ease during the manufacturing process can be achieved.

[0049] The energy storage element 101 has multiple electrode bodies 1 housed in a container 2. In general, in the case of an energy storage element in which multiple electrode bodies are housed in a container, some of the multiple electrode bodies may get caught on a protrusion on the inner surface of the container during insertion, causing misalignment between the multiple electrode bodies. Therefore, by applying the present invention, which improves the insertability of the electrode bodies, to an energy storage element in which multiple electrode bodies are housed in a container, the effect of suppressing misalignment between the multiple electrode bodies is also achieved.

[0050] <Energy Storage Element 102> An energy storage element 102 according to another embodiment shown in FIG. 7 includes an electrode assembly 41, a non-aqueous electrolyte (not shown), and a container 2 that accommodates these. The container 2 in this embodiment has a structure similar to that of the container 2 in FIG. 1 and other figures. That is, the container 2 includes a container body 9 having an opening and a lid 10 that closes the opening. Similarly to the electrode assembly 1 in FIG. 1 and other figures, the electrode assembly 41 is a flat, wound electrode assembly in which a positive electrode and a negative electrode are stacked and wound with a separator interposed therebetween. The electrode assembly 41 also has a pair of flat surfaces 3 that face each other across the winding axis W, a pair of curved surfaces (not shown in FIG. 7) that face each other across the winding axis W, and a pair of end surfaces 42 that are perpendicular to the winding axis W. However, in this embodiment, the electrode assembly 41 is housed in the container 2 such that the winding axis W of the electrode assembly 41 is perpendicular (in the Z direction) to the lid 10 of the container 2. That is, a pair of end faces 42 of the electrode body 41 face the bottom plate 18 or the lid 10 of the container body 9. The end faces 42 of the electrode body 41 are faces perpendicular to the winding axis W of the electrode body 41, and are faces at which the end faces of the positive and negative electrodes are exposed. The energy storage element 102 of this embodiment is substantially similar to the above-described energy storage element 100, except that the orientation of the electrode body 41 is different from that of the electrode body 1.

[0051] In the case of the energy storage element 102 of this embodiment, when the electrode body 41 is inserted into the container 2, the electrode body 41 is inserted into the container body 9 from the end face 42, and the end face 42 first comes into contact with the protrusion 12. Normally, in such a case, when the electrode body 41 is inserted, the electrode body 41 is likely to get caught on the protrusion 12, and if caught, problems are likely to occur with the electrode body 41. Therefore, there is great technical significance in providing the electrode body 41 with an outermost layer mainly composed of inorganic particles, thereby improving insertability.

[0052] The main components of the energy storage device according to one embodiment of the present invention will be described in detail below.

[0053] (Positive Electrode) As described above, the positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an optional intermediate layer.

[0054] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２ The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0055] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate and also increase the energy density per volume of the energy storage element.

[0056] The intermediate layer is an optional layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0057] The positive electrode active material layer contains a positive electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0058] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of absorbing and releasing lithium ions is usually used. Examples of the positive electrode active material include α-NaFeO ２Examples of suitable lithium transition metal composite oxides include those having a α-type crystal structure, those having a spinel type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. ２ As the lithium transition metal composite oxide having a crystalline structure, for example, Li[Li ｘ Ni （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Co （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Co （１－ｘ） ]O ２ (0≦x<0.5), Li[Li ｘ Ni γ Mn （１－ｘ－γ） ]O ２ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li ｘ Ni γ Mn β Co （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), Li[Li ｘ Ni γ Co β Al （１－ｘ－γ－β） ]O ２ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1−x−γ−β), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li ｘ Mn ２ O ４ , Li ｘ Ni γ Mn （２－γ） O ４ Examples of polyanion compounds include LiFePO ４ , LiMnPO ４ , LiNiPO ４ , LiCoPO ４ , Li ３ V ２ (P.O. ４ ) ３ , Li ２ MnSiO ４ , Li ２CoPO ４ Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination.

[0059] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above-mentioned lower limit or more, the positive electrode active material is easily manufactured or handled. By setting the average particle size of the positive electrode active material to the above-mentioned upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0060] To obtain powders with a predetermined particle size, grinders, classifiers, etc. are used. Grinding methods include, for example, methods using a mortar, ball mill, sand mill, vibration ball mill, planetary ball mill, jet mill, counter jet mill, swirling airflow jet mill, or sieves. Wet grinding in the presence of water or an organic solvent such as hexane can also be used during grinding. As classification methods, sieves, air classifiers, etc. are used as needed for both dry and wet methods.

[0061] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0062] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNT may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0063] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent in this range, the energy density of the energy storage element can be increased.

[0064] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0065] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass, by which the positive electrode active material can be stably maintained.

[0066] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. When a thickener is used, the content of the thickener in the positive electrode active material layer is preferably 5% by mass or less, and more preferably 1% by mass or less. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0067] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. When a filler is used, the content of the filler in the positive electrode active material layer is preferably 5% by mass or less, and even 1% by mass or less. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0068] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0069] As described above, the negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an optional intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode.

[0070] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, carbonaceous materials, and the like are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0071] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate and also increase the energy density per volume of the energy storage element.

[0072] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0073] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0074] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li ４ Ti ５ O １２ , LiTiO ２、 TiNb ２ O ７Examples of the material include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0075] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0076] "Non-graphitic carbon" refers to a carbon having an average lattice spacing (d ００２ ) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitizable carbon include non-graphitizable carbon and graphitizable carbon. Examples of non-graphitizable carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0077] Here, the "discharged state" refers to a state in which the battery is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released from the carbon material serving as the negative electrode active material. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode is 0.7 V or higher.

[0078] "Non-graphitizable carbon" refers to the above-mentioned d ００２ The carbon material has a particle size of 0.36 nm or more and 0.42 nm or less.

[0079] "Graphitizable carbon" refers to the above-mentioned d ００２ The term "carbon material" refers to a carbon material having a particle size of 0.34 nm or more and less than 0.36 nm.

[0080] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the negative electrode active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material layer may be in the form of a foil.

[0081] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0082] (Separator) The separator can be appropriately selected from known separators. For example, a separator consisting of only a substrate layer, or a separator having an inorganic layer formed on one or both surfaces of the substrate layer, can be used. As described above, when a separator having an inorganic layer formed on at least one surface of the substrate layer is used, an electrode assembly having an outermost layer mainly composed of inorganic particles can be efficiently produced by winding the positive electrode and the negative electrode stacked with the separator interposed therebetween, resulting in high productivity.

[0083] Examples of the shape of the separator substrate layer include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous electrolyte retention. As the material for the separator substrate layer, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the separator substrate layer.

[0084] The inorganic layer typically contains inorganic particles as a main component and a binder. The inorganic particles contained in the inorganic layer preferably undergo a mass loss of 5% or less when heated from room temperature to 500°C in the atmosphere, and more preferably undergo a mass loss of 5% or less when heated from room temperature to 800°C in the atmosphere. The inorganic particles are typically non-conductive. Examples of inorganic compounds that form inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of the safety of the energy storage element. Furthermore, from the viewpoint of improving the insertability of the electrode assembly when the inorganic layer of the separator is the outermost layer of the electrode assembly, barium sulfate, silicon oxide, aluminum oxide, or aluminosilicate is preferred.

[0085] The content of inorganic particles in the inorganic layer is preferably 50% by mass or more and 99% by mass or less, and more preferably 70% by mass or more and 97% by mass or less. When the content of inorganic particles in the inorganic layer is within the above range, not only the heat resistance but also the insertability of the electrode assembly can be improved when the inorganic layer of the separator is the outermost layer of the electrode assembly.

[0086] The binder in the inorganic layer may be any of those exemplified as the binder for the positive electrode active material layer, etc. The content of the binder in the inorganic layer is, for example, preferably 1% by mass or more and 50% by mass or less, and more preferably 3% by mass or more and 30% by mass or less.

[0087] When the outermost layer of the electrode assembly is a member other than the inorganic layer of the separator, the member may be porous or non-porous, but is preferably porous from the viewpoint of ensuring the flow of the electrolyte solution, etc. When the outermost layer of the electrode assembly is a member other than the inorganic layer of the separator, the specific and preferred forms of the outermost layer of the electrode assembly are the same as the specific and preferred forms of the inorganic layer of the separator described above.

[0088] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0089] (Non-aqueous electrolyte) The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. The non-aqueous electrolyte may be a non-aqueous electrolyte solution. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0090] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0091] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Of these, EC is preferred.

[0092] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0093] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0094] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0095] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ , LiN(SO ２ F) ２inorganic lithium salts such as lithium oxalate salts, lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); ３ CF ３ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ), LiC(SO ２ CF ３ ) ３ , LiC(SO ２ C ２ F ５ ) ３ Among these, inorganic lithium salts are preferred, and LiPF ６ is more preferred.

[0096] The content of the electrolyte salt in the non-aqueous electrolyte solution is 0.1 mol / dm at 20°C and 1 atmosphere. ３ 2.5mol / dm or more ３ It is preferably 0.3 mol / dm or less. ３ 2.0mol / dm or more ３ It is more preferable that it is 0.5 mol / dm or less. ３ More than 1.7mol / dm ３ It is more preferable that it is 0.7 mol / dm or less. ３ 1.5mol / dm or more ３ By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0097] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, and sulfur dioxide. Examples of the additive include dimethyl ether, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, and lithium difluorophosphate. These additives may be used alone or in combination of two or more.

[0098] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass, based on the total mass of the non-aqueous electrolyte. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0099] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0100] The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0101] As the sulfide solid electrolyte, in the case of a lithium ion secondary battery, for example, Li ２ S-P ２ S ５ , LiI-Li ２ S-P ２ S ５ , Li １０ Ge-P ２ S １２ etc.

[0102] The shape of the energy storage element according to the embodiment of the present invention is not particularly limited. The energy storage element may be, for example, a prismatic battery as shown in FIG. 1 or the like, or a flat battery, a coin battery, a button battery, or the like.

[0103] <Method for manufacturing energy storage element> The method for manufacturing the energy storage element of this embodiment can be appropriately selected from known methods, but the following method is preferred. That is, a method for manufacturing an energy storage element according to one embodiment of the present invention includes preparing an electrode body having a flat surface, preparing a stainless steel container having convex portions on its inner surface, and inserting the electrode body into the container so that the flat surface of the electrode body faces the convex portions on the inner surface of the container, wherein the electrode body has an outermost layer mainly composed of inorganic particles. The manufacturing method may further include preparing a non-aqueous electrolyte and housing the non-aqueous electrolyte in the container.

[0104] Preparing an electrode assembly having a flat surface includes, for example, preparing a positive electrode, a negative electrode, and a separator, and forming an electrode assembly by stacking or winding the positive electrode and the negative electrode with the separator interposed therebetween. For example, as described above, by using a separator having an inorganic layer as the separator and winding the separator so that the inorganic layer is the outermost layer, an electrode assembly having an outermost layer mainly composed of inorganic particles can be efficiently produced.

[0105] When inserting the electrode body into the container, the electrode body is usually inserted through the opening of the container body. At this time, the electrode body may be inserted with the winding axis of the electrode body parallel to the opening, or may be inserted with the winding axis of the electrode body perpendicular to the opening. In the former case, the electrode body is disposed in the container as in the energy storage element 100 shown in FIG. 1 etc. In the latter case, the electrode body is disposed in the container as in the energy storage element 102 shown in FIG. 7.

[0106] The method for placing the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be poured into the container through an inlet formed in the container, and then the inlet may be sealed.

[0107] <Electricity Storage Device> The energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) configured by assembling a plurality of energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, it is sufficient that the technology of the present invention is applied to at least one energy storage element included in the energy storage unit.

[0108] 8 shows an example of an energy storage device 300 in which energy storage units 200, each of which is an assembly of two or more electrically connected energy storage elements 100, are further assembled. The energy storage device 300 may include a bus bar (not shown) that electrically connects the two or more energy storage elements 100, a bus bar (not shown) that electrically connects the two or more energy storage units 200, etc. The energy storage unit 200 or the energy storage device 300 may include a status monitoring device (not shown) that monitors the status of one or more energy storage elements.

[0109] <Other Embodiments> The energy storage element and the method for manufacturing an energy storage element of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0110] In the above embodiment, the case where the energy storage element is used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (e.g., a lithium ion secondary battery) has been described, but the energy storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0111] In the above embodiment, the description has focused on the case where the electrode body is a wound type electrode body, but the configuration of the electrode body is not limited as long as it has a flat surface and an outermost layer mainly composed of inorganic particles. The electrode body may be a laminated type electrode body in which multiple positive electrodes, multiple negative electrodes, and multiple separators are laminated, an electrode body in which at least one of the positive electrodes and the negative electrodes is laminated in a zigzag pattern, etc.

[0112] In the above embodiment, the container has on its outer surface recesses that conform to the shape of the convex portions on its inner surface, but the container does not have to have on its outer surface recesses that conform to the shape of the convex portions on its inner surface. For example, by thickening a portion of the side wall of the container so that a convex portion is formed on the inner surface, it is possible to create a container that has convex portions on its inner surface but no concave portions on its outer surface.

[0113] The present invention can be applied to an electric storage element used as a power source for automobiles, other vehicles, electronic devices, and the like.

[0114] DESCRIPTION OF SYMBOLS 100, 101, 102 Energy storage element 1, 41 Electrode body 2 Container 3 Flat surface 4 Curved surface 5 Positive electrode connecting member 6 Positive electrode terminal 7 Negative electrode connecting member 8 Negative electrode terminal 9 Container body 10 Lid 11 Side wall 12 Convex portion 13 Concave portion 14 Flat surface 15 Sloped surface 16 Inner surface other than the convex portion 17 Corner portion formed by the flat surface and the slope 18 Bottom plate 21 Positive electrode 22 (22a, 22b) Separator 23 Negative electrode 25 Positive electrode substrate 26 Positive electrode active material layer 27 Negative electrode substrate 28 Negative electrode active material layer 29 Substrate layer 30 Inorganic layer 40 Insulating member 42 End surface 200 Energy storage unit 300 Energy storage device t1 Distance between a pair of convex portions t2 Maximum thickness of electrode body W: Winding axis H: Height of convex part θ: Angle between the inner surface other than the convex part and the slope

Claims

1. An energy storage element comprising: an electrode body having a flat surface; and a stainless steel container for housing the electrode body, wherein the container has a convex portion on its inner surface that faces the flat surface of the electrode body; and the electrode body has an outermost layer primarily composed of inorganic particles.

2. The energy storage element according to claim 1, wherein the container has a recess on its outer surface that conforms to the shape of the protrusion on the inner surface.

3. A storage element as described in claim 1 or claim 2, wherein when no external force is applied to the container, at least a portion of the flat surface of the electrode body is in contact with a convex portion on the inner surface of the container directly or via another member.

4. The energy storage element according to claim 1 or 2, further comprising an insulating member interposed between the electrode body and the container.

5. The energy storage element according to claim 1 or 2, wherein the electrode body is a wound type electrode body in which a positive electrode and a negative electrode are wound in a stacked state with a separator interposed therebetween, and the outermost layer of the electrode body is a part of the separator.

6. The energy storage element according to claim 1 or 2, wherein the electrode body is a wound type electrode body in which a positive electrode and a negative electrode are wound in a stacked state with a separator interposed therebetween, the container has a container body having an opening and a lid body that covers the opening, and the winding axis of the electrode body is parallel to the lid body.

7. The energy storage element according to claim 1 or 2, wherein the electrode body is a wound type electrode body in which a positive electrode and a negative electrode are wound in a stacked state with a separator interposed therebetween, the container has a container body having an opening and a lid body that covers the opening, and the winding axis of the electrode body is perpendicular to the lid body.

8. A method for manufacturing an energy storage element, comprising: preparing an electrode body having a flat surface; preparing a stainless steel container having a convex portion on its inner surface; and inserting the electrode body into the container so that the flat surface of the electrode body faces the convex portion on the inner surface of the container, wherein the electrode body has an outermost layer mainly composed of inorganic particles.

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