Power storage element

Abstract

A power storage element according to one aspect of the present invention includes: a plurality of electrode body units that each have an electrode body in which a positive electrode and a negative electrode are stacked, and a separation layer which is superposed on the outermost surface of the electrode body; and a container that houses the plurality of electrode body units and has a safety valve. The plurality of electrode body units adjacent to each other are in contact with each other at the separation layer. The separation layer has a resin layer and an inorganic material layer. With respect to the plurality of electrode body units adjacent to each other, the total thickness of the separation layers that separate the electrode bodies from each other is 50 µm to 110 µm inclusive.

Description

Energy storage element

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

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. The non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. Other energy storage elements besides non-aqueous electrolyte secondary batteries include capacitors such as lithium ion capacitors and electric double layer capacitors, as well as energy storage elements using electrolytes other than non-aqueous electrolytes.

[0003] In an unexpected use of an energy storage element, the energy storage element may become hot, which may cause gas to be generated inside the energy storage element. In order to reduce the increase in internal pressure of the energy storage element due to gas generation, a safety valve may be provided in the container of the energy storage element. Patent Document 1 describes a battery in which a plurality of electrode groups are housed in an exterior member (container) and a safety valve is provided in the lid of the exterior member.

[0004] Japanese Patent Application Publication No. 2016-085910

[0005] When the safety valve is activated by gas generated inside the energy storage element, the electrode body in the container of the energy storage element may be attracted to the safety valve along with the gas. In this case, the electrode body may obstruct the flow path of the gas being discharged from the safety valve, which may prevent the gas from being quickly discharged outside the container. When multiple electrode bodies are housed in the container of the energy storage element, the amount of gas generated is likely to be large, making it particularly important that the gas be quickly discharged outside the container when the safety valve is activated. Furthermore, when the energy storage element has multiple electrode bodies, it is desirable to insulate the electrodes from each other to prevent short circuits between the electrodes.

[0006] The present invention has been made based on the above circumstances, and aims to provide an energy storage element having a plurality of electrode bodies and provided with a safety valve for discharging gas, which can effectively discharge gas when the safety valve is activated while ensuring insulation between the plurality of electrode bodies.

[0007] An energy storage element according to one aspect of the present invention comprises a plurality of electrode body units each having an electrode body in which positive and negative electrodes are stacked, and an isolation layer stacked on the outermost surface of the electrode body, and a container that houses the plurality of electrode body units and has a safety valve, wherein adjacent electrode body units are in contact with each other at the isolation layer, the isolation layer has a resin layer and an inorganic layer, and the total thickness of the isolation layer separating the electrode bodies in adjacent electrode body units is 50 μm or more and 110 μm or less.

[0008] An energy storage element according to one aspect of the present invention is an energy storage element having a plurality of electrode bodies and provided with a safety valve for discharging gas, and can effectively discharge gas when the safety valve is activated while ensuring insulation between the plurality of electrode bodies.

[0009] FIG. 1 is a see-through perspective view showing one embodiment of an energy storage element. FIG. 2 is a perspective view showing each component of the energy storage element of FIG. 1. FIG. 3 is a perspective view showing an outline of the configuration of an electrode unit of the energy storage element of FIG. 1. FIG. 4 is a schematic cross-sectional view of the energy storage element of FIG. 1 taken along line IV-IV. FIG. 5 is a schematic enlarged view of FIG. 4. FIG. 6 is a schematic cross-sectional view showing a state in which two welded electrode units are attracted to a safety valve. FIG. 7 is a schematic cross-sectional view showing a state in which two unwelded electrode units are attracted to a safety valve. FIG. 8 is a schematic view showing one embodiment of an energy storage device formed by assembling a plurality of energy storage elements.

[0010] First, an overview of the energy storage element disclosed in this specification will be described.

[0011] (1) An energy storage element according to one aspect of the present invention comprises a plurality of electrode body units each having an electrode body in which a positive electrode and a negative electrode are stacked, and an isolation layer stacked on the outermost surface of the electrode body; and a container that houses the plurality of electrode body units and has a safety valve, wherein adjacent electrode body units are in contact with each other at the isolation layer, the isolation layer has a resin layer and an inorganic layer, and the total thickness of the isolation layer separating the electrode bodies in adjacent electrode body units is 50 μm or more and 110 μm or less.

[0012] The energy storage element described in (1) above is an energy storage element having a plurality of electrode assemblies and is provided with a safety valve for discharging gas. The gas can be effectively discharged when the safety valve is activated while ensuring insulation between the plurality of electrode assemblies. The reason for this is presumed to be as follows: In an unexpected usage pattern, the energy storage element may become hot, generating gas inside the energy storage element. When the safety valve is activated by the gas, the electrode assemblies in the container of the energy storage element may be drawn toward the safety valve along with the gas. In this case, the electrode assemblies of the energy storage element may block the flow path of the gas discharged from the safety valve, preventing the gas from being promptly discharged outside the container. Meanwhile, in the energy storage element described in (1) above, the total thickness of the isolating layers separating the electrode assemblies in the plurality of electrode units is equal to or less than the upper limit. Therefore, heat is uniformly conducted to the isolating layers at high temperatures that would activate the safety valve of the energy storage element. Therefore, when the temperature exceeds the melting point of the resin contained in the resin layer, the resin layer in the isolating layers melts uniformly, facilitating welding of the plurality of electrode units together. Therefore, the positions of the plurality of electrode units are less likely to shift relative to one another, and it is possible to prevent one of the plurality of electrode units from being attracted to the safety valve and blocking the gas flow path. Furthermore, by welding the plurality of electrode units together, the plurality of electrode units are less likely to be attracted to the safety valve. That is, the energy storage element described in (1) above can effectively discharge gas when the safety valve is activated. Furthermore, since the isolation layer has the inorganic layer and the total thickness of the isolation layer is equal to or greater than the lower limit, insulation between the electrode bodies can be ensured.

[0013] In the present invention, the term "resin layer" refers to a layer whose main component is a resin as defined in JIS-K-6900 (1994). Here, "resin" refers to a polymer, and "main component" refers to the component with the largest mass content. The term "inorganic layer" refers to a layer whose main component is an inorganic compound. The resin content in the resin layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. The inorganic compound content in the inorganic layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. In addition, in the present invention, the term "thickness" refers to the average value of thicknesses measured at any five locations.

[0014] (2) In the energy storage element described in (1) above, the electrode body may be a wound electrode body having a shape with two curved surface portions and a pair of wide surface portions located between the two curved surface portions, and adjacent electrode body units may be in contact with each other at the isolation layer stacked on the wide surface portions.

[0015] In the energy storage element described in (2) above, the electrode units are in contact with each other at the separating layers stacked on the broad surface portion, which makes it easier to secure an area for welding the electrode units together at high temperatures at which the safety valve of the energy storage element would activate, making it less likely that the positions of the electrode units will shift at high temperatures at which the safety valve of the energy storage element would activate, and allowing gas to be more effectively discharged when the safety valve activates.

[0016] (3) In the energy storage element described in (2) above, at least one of the two curved portions may face an inner surface of the container on which the safety valve is disposed.

[0017] In the energy storage element described in (3) above, at least one of the two curved portions faces the inner surface of the container on which the safety valve is disposed, so that the curved portions of the electrode units formed by stacking the isolation layers are adjacent to each other in the curved portion and face the safety valve. Since the curved portions of the electrode units are adjacent in this manner, a space is easily formed along the curved shape between the safety valve and the curved portion, making it easy to ensure a space between the safety valve and the electrode unit. This allows gas to be more effectively discharged when the safety valve is activated.

[0018] (4) In the energy storage element described in (3) above, the safety valve may be located on an extension of contact surfaces of the adjacent electrode units.

[0019] The energy storage element described in (4) above can more effectively discharge gas when the safety valve is activated. The reason for this is presumed to be as follows: The extension surfaces of the contact surfaces of the adjacent electrode units are located midway between the curved portions of the adjacent electrode units. A relatively large space can be easily secured between the safety valve and the electrode unit midway between the curved portions. This allows gas to be more effectively discharged when the safety valve is activated.

[0020] (5) In the energy storage element according to any one of (1) to (4), the inorganic layer may have a thickness of 10% to 40% of the thickness of the isolation layer.

[0021] In the energy storage element described in (5) above, by having the thickness of the inorganic layer within the above range, insulation between the electrodes of the multiple electrode units is more ensured, and when the temperature exceeds the melting point of the resin contained in the resin layer when the safety valve is activated, the multiple electrode units can be more reliably welded together.

[0022] The above-mentioned "thickness of the inorganic layer" means the total thickness of the inorganic layers when a plurality of inorganic layers are present. The same applies to the "thickness of the isolation layer."

[0023] Hereinafter, an energy storage element, an energy storage device, a method for manufacturing an energy storage element according to one embodiment of the present invention, and other embodiments will be described in detail. Note that the names of the components (components) used in each embodiment may differ from the names of the components (components) used in the background art. In addition, although up, down, left, right, etc. are sometimes indicated in the following description, these directions are shown as examples and do not limit the directions in the usage form.

[0024] [Energy Storage Element] As shown in FIGS. 1 and 2, the energy storage element 1 includes two adjacent electrode body units 10a, 10b and a container 20. As shown in FIG. 4, each of the two electrode body units 10a, 10b includes an electrode body 30a (30b) and an isolation layer 60a (60b) laminated on the outermost surface of the electrode body 30a (30b). The two adjacent electrode body units 10a, 10b contact each other at the isolation layers 60a, 60b. The container 20 houses the two electrode body units 10a, 10b and has a safety valve 23. As shown in FIG. 3, the electrode body 30a has a positive electrode terminal 31 and a negative electrode terminal 32. As shown in FIG. 2, the positive electrode terminal 31 is electrically connected to a positive electrode external terminal 52 provided outside the container 20 via a positive electrode side connecting member (positive electrode lead) 51. The negative electrode terminal 32 is electrically connected to a negative electrode external terminal 54 provided outside the container 20 via a negative electrode side connecting member (negative electrode lead) 53. Furthermore, the energy storage element 1 includes an electrolyte (not shown) contained in the container 20. A portion of the electrolyte is present in a state of impregnating the positive electrode, negative electrode, and separator that constitute the electrode bodies 30a, 30b.

[0025] In the energy storage element 1, the two electrode units 10a, 10b can be easily welded together at the isolation layers 60a, 60b at high temperatures that would activate the safety valve 23. When the two electrode units 10a, 10b are welded together, the two electrode units 10a, 10b are less likely to be attracted to the safety valve 23, and blockage of the gas flow path can be suppressed. Furthermore, even when the two electrode units 10a, 10b are attracted to the safety valve 23, misalignment between the two electrode units 10a, 10b can be suppressed, and blockage of the gas flow path by one of the electrode units 10a (10b) can be suppressed. This point is explained schematically in Figures 6 and 7. If the electrode units 10a, 10b are welded together when the safety valve 23 is activated, the two electrode units 10a, 10b are attracted together toward the safety valve 23, as shown in Fig. 6, and the space between the two electrode units 10a, 10b (in Fig. 6, the space along the curved portions of the two electrode units 10a, 10b facing the safety valve 23) ensures a flow path for the gas discharged from the safety valve 23. On the other hand, if the electrode units 10a, 10b are not welded together or are not sufficiently welded together when the safety valve 23 is activated, as shown in Fig. 7, either one of the two electrode units 10a, 10b may be attracted independently toward the safety valve 23, which makes it easy for the flow path for the gas discharged from the safety valve 23 to become blocked.

[0026] 4, in this embodiment, the two electrode units 10a, 10b each have an electrode body 30a (30b) that is a flat, wound electrode body, and an isolation layer 60a (60b) that surrounds the electrode body 30a (30b) in the winding direction. The two isolation layers 60a, 60b insulate the two electrode bodies 30a, 30b of the two adjacent electrode units 10a, 10b from each other.

[0027] (Electrode Assembly) In this embodiment, the two electrode assemblies 30a, 30b included in the two electrode assembly units 10a, 10b have the same configuration. Therefore, the following description will focus on one electrode assembly 30a, and the description of the other electrode assembly 30b will be omitted. As shown in FIG. 3 , the electrode assembly 30a is formed by longitudinally winding a strip-shaped negative electrode 35, a strip-shaped first separator 34, a strip-shaped positive electrode 33, and a strip-shaped second separator 36, stacked in this order. Note that the dashed-dotted line labeled W1 in FIGS. 2 and 3 represents the winding axis of the electrode assembly 30a. The winding axis W1 is an imaginary axis. The electrode assembly 30a is disposed so that the winding axis W1 is parallel to the horizontal direction (the Y-axis direction in FIGS. 2 and 3 ). In the energy storage device 1, the winding axis W1 of the electrode assembly 30a is parallel to the bottom surface of the container 20 (see FIG. 2 ). 4, the electrode body 30a has two curved surface portions 44 and a pair of wide surface portions 45 located between the two curved surface portions 44. One of the two curved surface portions 44 faces the lid 22 of the container 20, which will be described later, and the other faces the bottom surface of the container 20. One of the pair of wide surface portions 45 faces the side surface of the container 20 (the side surface with the largest area), and the other faces the wide surface portion 45 of the electrode body 30b of the adjacent electrode body unit 10b.

[0028] The positive electrode 33 has a strip-shaped positive electrode substrate 38 and positive electrode active material layers 39 laminated on both sides of the positive electrode substrate 38. The negative electrode 35 has a strip-shaped negative electrode substrate 40 and negative electrode active material layers 41 laminated on both sides of the negative electrode substrate 40. The positive electrode substrate 38 and the negative electrode substrate 40 are conductive substrates such as metal foil. Details of each component of the positive electrode 33, negative electrode 35, etc. will be described later.

[0029] In the electrode body 30a, the positive electrode 33 and the negative electrode 35 are wound with separators 34, 36 interposed therebetween, offset from each other in the direction of the winding axis W1. The positive electrode 33 has a positive electrode active material layer non-laminated portion 42 where the positive electrode active material layer 39 is not laminated at one end (the lower end in FIG. 3 ) in the direction of the winding axis W1. The negative electrode 35 has a negative electrode active material layer non-laminated portion 43 where the negative electrode active material layer 41 is not laminated at the other end (the upper end in FIG. 3 ) in the direction of the winding axis W1. The positive electrode terminal 31 is formed by the exposed positive electrode substrate 38 (positive electrode active material layer non-laminated portion 42), and the negative electrode terminal 32 is formed by the exposed negative electrode substrate 40 (negative electrode active material layer non-laminated portion 43). In this way, the flat wound electrode body 30a has a positive electrode terminal 31 and a negative electrode terminal 32 located at both ends thereof (both ends in the direction of the winding axis W1 and the Y-axis direction).

[0030] (Isolation Layer) In this embodiment, the two isolation layers 60a, 60b of the two electrode body units 10a, 10b have the same configuration. Therefore, the following description will focus on one isolation layer 60a, and the description of the other isolation layer 60b will be omitted. In this embodiment, the isolation layer 60a is formed by winding a strip-shaped member around the electrode body 30a in the winding direction of the electrode body 30a. More specifically, the isolation layer 60a is formed by winding and stacking the separator extension 37 connected to the longitudinal end of the second separator 36 around the outer periphery of the electrode body 30a (see FIG. 3 ). More specifically, the second separator 36 and the separator extension 37 are integrated to form a single strip-shaped member. In this way, by integrating the second separator 36 and the separator extension 37 constituting the isolation layer 60a into a single strip-shaped member, the manufacturability of the energy storage device 1 can be improved. 3, the dashed two-dot line labeled B represents the boundary between the second separator 36 and the separator extension 37. The boundary B is an imaginary line, and in this embodiment, is a straight line parallel to the Y-axis. The second separator 36 is the portion of the belt-shaped member that is wound inward from the outermost periphery of the electrode (the outermost periphery of the positive electrode 33 or the negative electrode 35) when the belt-shaped member is wound, and the separator extension 37 is the portion of the belt-shaped member that is wound outward from the outermost periphery of the electrode when the belt-shaped member is wound.

[0031] As shown in FIG. 5 , the separator extension 37 includes a resin layer 371 and an inorganic layer 372 laminated on the resin layer 371. That is, the isolation layer 60a formed by the separator extension 37 includes the resin layer 371 and the inorganic layer 372. FIG. 5 shows, as an example, an isolation layer 60a formed by winding the separator extension 37 twice. That is, in this example, the isolation layer 60a includes two separator extensions 37, and includes two resin layers 371 and two inorganic layers 372. The resin layer 371 is located on the outermost surface of the isolation layer 60a. By having the resin layer 371 located on the outermost surface of the isolation layer 60a, the electrode unit 10a including the isolation layer 60a can be easily welded to the adjacent electrode unit 10b when the temperature of the energy storage device 1 becomes high enough to activate the safety valve 23.

[0032] As shown in Fig. 4, two adjacent electrode body units 10a, 10b are in contact with each other at the isolation layers 60a, 60b (in this embodiment, the portions of the isolation layers 60a, 60b that are in contact with the wide surface portions 45) that are laminated on the wide surface portions 45 of the two electrode bodies 30a, 30b. Furthermore, as shown in Fig. 5, two adjacent electrode body units 10a, 10b are in contact with each other at the resin layers 371 that are located on the outermost surfaces of the isolation layers 60a, 60b. At high temperatures that would activate the safety valve 23 of the energy storage device 1, the resin layers 371 that are not located on the outermost surfaces of the isolation layers 60a, 60b may also melt and seep onto the surfaces of the electrode body units 10a, 10b, thereby contributing to the welding of the two electrode body units 10a, 10b.

[0033] Examples of the shape of the resin layer 371 of the separator extension 37 include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength. The resin layer 371 contains a resin. To ensure insulation between the electrode bodies 30a and 30b of adjacent electrode body units 10a and 10b, the resin constituting the resin layer 371 is preferably, for example, a polyolefin such as polyethylene or polypropylene, polyimide, or aramid, with polyolefin being more preferred. Furthermore, by using the above-described materials as the resin constituting the resin layer 371, the adjacent electrode body units 10a and 10b can be easily welded together at high temperatures that would activate the safety valve 23 of the energy storage device 1. A composite material of these resins may also be used as the resin constituting the resin layer 371.

[0034] The lower limit of the melting point of the resin constituting the resin layer 371 is preferably 120°C, more preferably 150°C, even more preferably 180°C, even more preferably 200°C, and particularly preferably 220°C. On the other hand, the upper limit of the melting point of the resin constituting the resin layer 371 is preferably 250°C, more preferably 240°C, and even more preferably 230°C. By setting the melting point of the resin constituting the resin layer 371 to be equal to or higher than the above lower limit, it is easy to ensure insulation between the electrode bodies 30a, 30b of adjacent electrode body units 10a, 10b in the normal usage of the energy storage element 1. Furthermore, by setting the melting point of the resin constituting the resin layer 371 to be equal to or lower than the above upper limit, adjacent electrode body units 10a, 10b can be easily welded together at high temperatures that would activate the safety valve 23 of the energy storage element 1.

[0035] The inorganic layer 372 of the separator extension 37 contains an inorganic compound. The inorganic compound of the inorganic layer 372 may be in particulate form. The inorganic layer 372 contains, for example, particles of the inorganic compound and a binder. The inorganic layer 372 is formed, for example, by applying a mixture of the inorganic compound particles and the binder to the resin layer 371 and then heat treating it. The inorganic compound contained in the inorganic layer preferably loses 5% or less in mass when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere, and more preferably loses 5% or less in mass when heated from room temperature to 800°C. Examples of such inorganic compounds 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-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 is preferred, with aluminum oxide being more preferred, from the viewpoint of ensuring insulation between the electrode bodies 30a and 30b of adjacent electrode body units 10a and 10b.

[0036] The porosity of the second separator 36 and the separator extension 37 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.

[0037] The lower limit of the ratio of the total thickness of the inorganic layers 372 to the total thickness of the isolation layers 60a, 60b (the ratio of the thickness of the inorganic layer 372 to the thickness of one isolation layer 60a (60b)) is preferably 10%, more preferably 15%, and even more preferably 20%. On the other hand, the upper limit of the ratio of the total thickness of the inorganic layers 372 to the total thickness of the isolation layers 60a, 60b is preferably 40%, more preferably 35%, and even more preferably 30%. When the ratio is equal to or greater than the lower limit, insulation between the electrode bodies 30a, 30b of adjacent electrode units 10a, 10b can be easily ensured. Furthermore, when the ratio is equal to or less than the upper limit, the total thickness of the inorganic layers 372 can be kept within an appropriate range relative to the total thickness of the resin layer 371, and adjacent electrode units 10a, 10b can be easily welded together at high temperatures that would activate the safety valve 23 of the energy storage element 1. The ratio of the total thickness of the inorganic layer 372 to the total thickness of the isolation layers 60a, 60b may be equal to or greater than any of the lower limits described above and equal to or less than any of the upper limits described above.

[0038] The lower limit of the ratio of the total thickness of the resin layer 371 to the total thickness of the isolation layers 60a, 60b (the ratio of the thickness of the resin layer 371 to the thickness of one isolation layer 60a (60b)) is preferably 60%, more preferably 65%, and even more preferably 70%. On the other hand, the upper limit of the ratio of the total thickness of the resin layer 371 to the total thickness of the isolation layers 60a, 60b is preferably 90%, more preferably 85%, and even more preferably 80%. When the ratio is equal to or greater than the lower limit, adjacent electrode body units 10a, 10b can be easily welded together at high temperatures that would activate the safety valve 23 of the energy storage element 1. When the ratio is equal to or less than the upper limit, the total thickness of the resin layer 371 can be kept within an appropriate range relative to the total thickness of the inorganic layer 372, and insulation between the electrode bodies 30a, 30b of adjacent electrode body units 10a, 10b can be easily ensured. The ratio of the total thickness of the resin layer 371 to the total thickness of the isolation layers 60a, 60b may be equal to or greater than any of the lower limits described above and equal to or less than any of the upper limits described above.

[0039] The lower limit of the ratio of the total thickness of the resin layers 371 to the total thickness of the inorganic layers 372 (the ratio of the thickness of the resin layers 371 to the thickness of the inorganic layers 372 in one isolation layer 60a (60b)) is preferably 1.5, more preferably 2.0, and even more preferably 2.2. On the other hand, the upper limit of the ratio of the total thickness of the resin layers 371 to the total thickness of the inorganic layers 372 is preferably 9.0, more preferably 6.0, and even more preferably 3.0. When the ratio is equal to or greater than the lower limit, adjacent electrode units 10a, 10b can be easily welded together at high temperatures that would activate the safety valve 23 of the energy storage device 1. When the ratio is equal to or less than the upper limit, insulation between the electrode bodies 30a, 30b of adjacent electrode units 10a, 10b can be easily ensured. The ratio of the total thickness of the resin layers 371 to the total thickness of the inorganic layers 372 may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits.

[0040] As shown in Fig. 4, in two adjacent electrode units 10a, 10b, the two electrode assemblies 30a, 30b are separated by two isolation layers 60a, 60b. As shown in Fig. 5, in this embodiment, the total thickness d of the isolation layers 60a, 60b separating the electrode assemblies 30a, 30b is the sum of the thickness d1 of the isolation layer 60a of the electrode unit 10a and the thickness d2 of the isolation layer 60b of the electrode unit 10b. The lower limit of the total thickness d of the isolation layers 60a, 60b separating the electrode assemblies 30a, 30b is 50 µm, more preferably 55 µm, and even more preferably 60 µm. On the other hand, the upper limit of the total thickness d of the isolation layers 60a, 60b separating the electrode assemblies 30a, 30b is 110 µm, more preferably 105 µm, and even more preferably 100 µm. When the total thickness d of the isolating layers 60a, 60b is equal to or greater than the above-mentioned lower limit, insulation between the electrode bodies 30a, 30b of adjacent electrode body units 10a, 10b can be more easily ensured. Furthermore, when the total thickness d of the isolating layers 60a, 60b is equal to or less than the above-mentioned upper limit, heat is more easily conducted uniformly to the isolating layers 60a, 60b at high temperatures such that the safety valve 23 of the energy storage device 1 operates, and adjacent electrode body units 10a, 10b can be easily welded to each other. The total thickness d of the isolating layers 60a, 60b separating the electrode bodies 30a, 30b may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits. In this embodiment, the thickness of the isolating layers 60a, 60b can be adjusted by, for example, changing the number of turns of the separator extension 37 wound around the electrode bodies 30a, 30b. The thickness of the second separator 36 and the single layer of separator extension 37 may be 10 μm or more and 40 μm or less, or may be 15 μm or more and 30 μm or less.

[0041] <Container> The container 20 contains the two electrode units 10a, 10b and an electrolyte. The container 20 has a rectangular parallelepiped shape and, as shown in FIG. 2 , is composed of a container body 21 that is open at the top (upper side in FIG. 2 ) and a lid 22 that is a plate-like member that closes the opening of the container body 21. A positive electrode external terminal 52 and a negative electrode external terminal 54 are attached to the outer surface of the lid 22 via an insulating gasket or the like (not shown). A safety valve 23 is provided in the center of the lid 22. The safety valve 23 may be provided so as to be located between the positive electrode external terminal 52 and the negative electrode external terminal 54. The lid 22 may further be provided with a liquid injection port or the like.

[0042] The container 20 is made of metal. For example, the container 20 may be made of aluminum or stainless steel, with aluminum being preferred. Using an aluminum container has the advantage of being lightweight. Note that aluminum includes not only pure aluminum but also aluminum alloys. The outer surface of the metal container 20 may be coated with a material other than metal, such as by painting.

[0043] After the two electrode units 10a, 10b are housed inside the container 20, the container body 21 and the lid 22 are welded or the like. Thereafter, the container 20 is sealed by pouring an electrolyte solution into the inside of the container 20 through a filling port or the like. In this manner, the container 20 has a structure that seals the inside. In a normally unforeseen usage pattern of the energy storage element 1, the energy storage element 1 may become hot, causing gas to be generated inside the energy storage element 1. Because the container 20 has a structure that seals the inside, the internal pressure of the energy storage element 1, more specifically, the pressure inside the container 20, may increase when the above-mentioned gas is generated.

[0044] The safety valve 23 is a valve that opens to release gas when gas is generated in the container 20 and the pressure inside the container 20 increases. The safety valve 23 may be referred to as a gas exhaust valve, a pressure release valve, or the like. The safety valve 23 includes a weakened portion 23a formed by thinning a portion of the lid 22 and a groove portion 23b formed by cutting into the weakened portion 23a. As shown in FIG. 1 , in this embodiment, the weakened portion 23a has an elliptical planar shape. The groove portion 23b has a shape in which two grooves of different orientations are connected to each end of one groove, i.e., a planar shape in which two Y-shapes are connected. This makes the weakened portion 23a more likely to break at the groove connection. Therefore, when a predetermined pressure acts on the safety valve 23 from inside the container 20, the weakened portion 23a breaks at the groove 23b, and the material of the weakened portion 23a around the groove 23b opens toward the outside of the container 20 to form an opening as a pressure relief hole. The pressure at which the safety valve 23 opens can be controlled by the shape of the weakened portion 23a in the weakened portion 23a, the thickness of the material around the groove 23b of the weakened portion 23a, the shape of the groove 23b, the depth of the groove 23b, etc. The structure of the safety valve 23 is not limited to the above structure, and any known structure can be used that opens when the pressure inside the container 20 increases and causes the pressure inside the container 20 to decrease.

[0045] As described above, one of the two curved portions 44 of the electrode body 30a (30b) faces the lid 22 of the container 20. That is, the curved portion 44 faces the inner surface of the container 20 on which the safety valve 23 is disposed (see FIG. 4). Because the curved portion 44 faces the inner surface of the container 20 on which the safety valve 23 is disposed, the curved portion of the electrode body unit 10a (10b) is likely to be attracted to the safety valve 23 when the safety valve 23 is activated. As shown in FIG. 4, in this embodiment, the two curved portions of the two electrode body units 10a, 10b are adjacent to each other and face the safety valve 23. Therefore, a space following the curved shape is formed between the safety valve 23 and the two adjacent curved portions of the two electrode body units 10a, 10b. This makes it possible to easily secure space for gas discharge between the two electrode units 10a, 10b and the safety valve 23, as shown in Figure 6, even if the electrode units 10a, 10b are attracted to the safety valve 23 when the safety valve 23 is activated.

[0046] During normal operation of the energy storage device 1, the safety valve 23 is located between an imaginary plane S1 that passes through the winding axis W1 of one electrode body 30a and is parallel to the wide surface portion 45 of the electrode body 30a, and an imaginary plane S2 that passes through the winding axis W2 of the other electrode body 30b and is parallel to the wide surface portion 45 of the electrode body 30b (see FIG. 4 ). That is, the weakened portion 23a and the groove 23b of the safety valve 23 are located between the two imaginary planes S1 and S2. The weakened portion 23a and the groove 23b of the safety valve 23 are not located on the two imaginary planes S1 and S2. By having the safety valve 23 located between the two imaginary planes S1 and S2 in this way, even if the electrode body units 10a and 10b are attracted to the safety valve 23 when the safety valve 23 is activated, a space for gas release can be more easily secured between the two electrode body units 10a and 10b and the safety valve 23, as shown in FIG. 6 .

[0047] During normal operation of the energy storage device 1, the safety valve 23 is located on an extension S3 of the contact surfaces of the two adjacent electrode units 10a, 10b (see FIG. 4 ). More specifically, the weakened portion 23a and groove portion 23b of the safety valve 23 are located on the extension S3 of the contact surfaces of the two adjacent electrode units 10a, 10b. By positioning the safety valve 23 on the extension S3 in this way, even if the electrode units 10a, 10b are attracted to the safety valve 23 when the safety valve 23 is activated, it is possible to more easily ensure space for gas release between the two electrode units 10a, 10b and the safety valve 23, as shown in FIG. 6 .

[0048] The positive electrode, negative electrode, separator, and electrolyte solution in the energy storage element according to one embodiment of the present invention will be described in detail below.

[0049] (Positive electrode) As described above, the positive electrode has a positive electrode substrate and positive electrode active material layers laminated on both sides of the positive electrode substrate. The positive electrode may further have an intermediate layer provided between the positive electrode substrate and the positive electrode active material layer. Alternatively, a positive electrode in which the positive electrode active material layer is laminated on only one side of the positive electrode substrate may be used.

[0050] 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).

[0051] 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.

[0052] The intermediate layer is a 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.

[0053] 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.

[0054] 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 ２ Examples 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 ２ CoPO 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.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0063] 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 can be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein can be preferably implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0064] 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.

[0065] (Negative electrode) As described above, the negative electrode has a negative electrode substrate and negative electrode active material layers laminated on both sides of the negative electrode substrate. The negative electrode may further have an intermediate layer provided between the negative electrode substrate and the negative electrode active material layer. Also, a negative electrode in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate can be used. The configuration of the intermediate layer that may be provided on the negative electrode is not particularly limited, and can be selected from the configurations exemplified for the positive electrode, for example.

[0066] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials 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 foils, vapor-deposited films, meshes, and porous materials, with foils 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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 ７ Examples 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.

[0071] "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.

[0072] "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.

[0073] Here, the "discharged state" of the carbon material refers to a state in which the carbon material, which is the negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, this refers to a state in which the open circuit voltage is 0.7 V or higher in 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.

[0074] "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.

[0075] "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.

[0076] 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.

[0077] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved. When the negative electrode active material is metallic Li, the content of the negative electrode active material in the negative electrode active material layer may be 99% by mass or more, or may be 100% by mass.

[0078] (Separator) The separator may have the same structure as the separator extension 37 described above, and therefore a description thereof will be omitted.

[0079] (Electrolyte) The electrolyte can be appropriately selected from known electrolytes. A non-aqueous electrolyte can be suitably used as the electrolyte. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ , LiN(SO ２ F) ２ inorganic 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.

[0086] 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.

[0087] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, and silyl. Aromatic compounds such as cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above 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, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, 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, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0088] 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.

[0089] [Energy 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 storage power source. In this case, the technology of the present invention may be applied to at least one energy storage element included in the energy storage unit. FIG. 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 1, 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 1, a bus bar (not shown) that electrically connects the two or more energy storage units 200, or the like. 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.

[0090] [Method for Manufacturing Energy Storage Element] The method for manufacturing the energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing a plurality of electrode assemblies, preparing a plurality of electrode assembly units by laminating an isolation layer on the outermost surfaces of each of the plurality of electrode assemblies, preparing an electrolyte solution, and housing the plurality of electrode assembly units and the electrolyte solution in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween. Preparing the plurality of electrode assembly units by laminating an isolation layer on the outermost surfaces of each of the plurality of electrode assemblies may include forming the plurality of electrode assembly units by winding a separator extension connected to or integrated with the separator that forms the plurality of electrode assemblies around each of the electrode assemblies.

[0091] The method for placing the electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte is used as the electrolyte, the non-aqueous electrolyte may be poured into the container through an inlet formed in the container, and the inlet may then be sealed.

[0092] [Other Embodiments] The energy storage device of the present invention is 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.

[0093] In the above embodiment, the case where the energy storage element is used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (for example, 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, capacitors such as electric double layer capacitors and lithium ion capacitors, or energy storage elements using electrolytes other than non-aqueous electrolytes.

[0094] In the above embodiment, the electrode assembly in which the positive electrode and the negative electrode are stacked with a separator interposed therebetween has been described, but the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode.

[0095] In the above embodiment, the case where the electrode body is a wound electrode body has been described, but the electrode body may also be a laminated electrode body in which a positive electrode and a negative electrode are laminated.

[0096] In the above embodiment, the two electrode units have the same configuration, but the configuration of the electrode units, such as the thickness of the isolation layer, may be different from each other.

[0097] In the above embodiment, the isolating layer is formed by a separator extension connected to the longitudinal end of a separator constituting the electrode assembly, but the present invention is not limited to this configuration. The isolating layer may be formed, for example, by sandwiching an insulating resin plate between the electrode assemblies. Furthermore, in the above embodiment, the isolating layer is formed by a separator extension of one separator constituting the electrode assembly, but the isolating layer may be formed by separator extensions of multiple separators.

[0098] In the above embodiment, the separator and separator extension constituting the electrode assembly have the same configuration. However, the separator and separator extension constituting the electrode assembly may have different configurations. That is, any known separator may be selected as the separator constituting the electrode assembly. In the example shown in FIG. 5 , the separator extension is wound twice to form an isolating layer (i.e., one isolating layer has two resin layers and two inorganic layers). However, the present invention is not limited to this configuration. For example, the separator extension may be wound three or more times (e.g., three to five times). One isolating layer may have three or more resin layers and three or more inorganic layers (e.g., three to five). By having one isolating layer have three or more resin layers and three or more inorganic layers, an electrode unit having the isolating layer can be stably welded to an adjacent electrode unit when the temperature of the energy storage device becomes high enough to activate the safety valve.

[0099] In the above embodiment, the case where the energy storage element has two adjacent electrode body units has been described, but the energy storage element may have three or more adjacent electrode body units. However, as in the above embodiment, a case where the energy storage element has two electrode body units is preferable from the viewpoint of more reliably welding all of the electrode body units together at high temperatures (and thus preventing one of the electrode body units from being attracted to the safety valve and blocking the gas flow path).

[0100] In the above embodiment, the case where one safety valve is provided in the container has been described, but the container may be provided with a plurality of safety valves.

[0101] In the above embodiment, the separator extension portion forming the isolation layer of the electrode unit has been described as having a resin layer and an inorganic layer, but the isolation layer or separator extension portion may have any layer or configuration other than a resin layer and an inorganic layer.

[0102] In the above embodiment, the case where the resin layer is located on the outermost surface of the isolation layer has been described, but the inorganic layer may be located on the outermost surface of the isolation layer.

[0103] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0104] Example 1 (Preparation of Positive Electrode) α-NaFeO ２ It has a LiNi type crystal structure ０．６ Co ０．２ Mn ０．２ O ２ A lithium transition metal composite oxide represented by the formula (I) was used. A positive electrode mixture paste containing the above positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio (solid content equivalent) of 93:4:3, and containing N-methylpyrrolidone (NMP) as a dispersion medium, was prepared. The above positive electrode mixture paste was applied to aluminum foil as a positive electrode substrate, dried, and pressed to produce a positive electrode in which a positive electrode active material layer was laminated on the positive electrode substrate.

[0105] (Fabrication of Negative Electrode) A negative electrode mixture paste containing graphite as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a mass ratio (solid content equivalent) of 98:1:1, and containing water as a dispersion medium, was prepared. The negative electrode mixture paste was applied to copper foil as a negative electrode substrate, dried, and pressed to fabricate a negative electrode in which a negative electrode active material layer was laminated on the negative electrode substrate.

[0106] (Preparation of non-aqueous electrolyte) LiPF was dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35. ６ to 1.0 mol / dm ３ (20° C., 1 atmosphere) to prepare a non-aqueous electrolyte solution.

[0107] (Preparation of Energy Storage Element) A separator was used, which consisted of a polyolefin microporous membrane (resin layer) with an inorganic layer primarily composed of aluminum oxide laminated on one side. The average thickness of the polyolefin microporous membrane was 7 μm, and the average thickness of the inorganic layer was 3 μm. The positive electrode and negative electrode were laminated via this separator to prepare a wound electrode assembly. A separator extension, which was integrated with the separator and had a similar configuration to the separator, was further wound around the electrode assembly to prepare an electrode assembly unit having an isolation layer composed of the separator extension. The number of times the separator extension was wound was adjusted so that the isolation layer had a thickness of 30 μm. Two of the electrode assembly units were prepared and stored in an aluminum container equipped with a safety valve. The electrode assembly units were arranged so that the broad surfaces of the electrode assembly units were in contact with each other, and the total thickness of the isolation layer separating the electrodes of the two electrode assembly units was 60 μm. Thereafter, the nonaqueous electrolyte solution was poured into the container, and the container was sealed to obtain the electricity storage element of Example 1.

[0108] <Examples 2 and 3 and Comparative Examples 1 and 2> The energy storage elements of Examples 2 and 3 and Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the total thickness of the isolation layers separating the electrodes of the two electrode units was as shown in Table 1.

[0109] <Comparative Examples 3 and 4> The energy storage elements of Comparative Examples 3 and 4 were obtained in the same manner as in Example 1, except that a separator consisting only of a polyolefin microporous membrane (resin layer) was used and the total thickness of the isolation layers separating the electrodes of the two electrode units was set as shown in Table 1.

[0110] <Evaluation> Each of the obtained energy storage elements was heated using a heater placed outside the container to activate the safety valve. Then, each energy storage element was disassembled, and the positional deviation between the two electrode units was measured. The measurement results are shown in Table 1.

[0111] The insulation between the electrodes of the two electrode units was evaluated by measuring AC resistance using an AC current of 100 kHz. An AC resistance of 1.0 kΩ or more between the two electrodes was considered to have high insulation, and an AC resistance of less than 1.0 kΩ was considered to have low insulation. The evaluation results are shown in Table 1.

[0112]

[0113] As shown in Table 1, in Comparative Example 1, the insulating properties between the electrode assemblies were low because the isolating layer was too thin. Furthermore, the misalignment upon activation of the safety valve exceeded 1 mm, making it impossible to weld the electrode assembly units together. In Comparative Examples 3 and 4, the insulating properties between the electrode assemblies were low because the isolating layer did not include an inorganic layer. In Comparative Example 2, although the isolating layer included an inorganic layer, the isolating layer was too thick, making it impossible to weld the electrode assembly units together. In contrast, in Examples 1 to 3, the isolating layer included an inorganic layer, and the total thickness of the isolating layers was within an appropriate range, making it impossible to weld the electrode assembly units together, making it impossible to weld the electrode assembly units together. Furthermore, the insulating properties between the electrode assemblies were also high. These results demonstrate that when the isolating layers separating the electrode assemblies include a resin layer and an inorganic layer, and the total thickness of the isolating layers is within an appropriate range, it is possible to ensure insulation between the electrode assemblies while effectively discharging gas upon activation of the safety valve.

[0114] The present invention can be applied to electric storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0115] REFERENCE SIGNS LIST 1 Energy storage element 10a, 10b Electrode body unit 20 Container 21 Container body 22 Lid 23 Safety valve 23a Weakened portion 23b Groove portion 30a, 30b Electrode body 31 Positive electrode terminal 32 Negative electrode terminal 33 Positive electrode 34 First separator 35 Negative electrode 36 Second separator 37 Separator extension portion 371 Resin layer 372 Inorganic layer 38 Positive electrode substrate 39 Positive electrode active material layer 40 Negative electrode substrate 41 Negative electrode active material layer 42 Positive electrode active material layer non-laminated portion 43 Negative electrode active material layer non-laminated portion 44 Curved surface portion 45 Wide surface portion 51 Positive electrode side connecting member 52 Positive electrode external terminal 53 Negative electrode side connecting member 54 Negative electrode external terminal 60a, 60b Isolation layer 200 Energy storage unit 300 Energy storage device B Boundary d1, d2 Thickness d Total thickness S1, S2 Virtual plane S3 Extension plane W1, W2 Winding axis

Claims

1. An energy storage element comprising: a plurality of electrode units having an electrode body in which positive and negative electrodes are stacked, and an isolation layer stacked on the outermost surface of the electrode body; and a container that houses the plurality of electrode units and has a safety valve, wherein adjacent electrode units are in contact with each other at the isolation layer, the isolation layer having a resin layer and an inorganic layer, and the total thickness of the isolation layer separating the electrode bodies in adjacent electrode units is 50 μm or more and 110 μm or less.

2. The energy storage element described in claim 1, wherein the electrode body is a wound electrode body having a shape with two curved surface portions and a pair of wide surface portions located between the two curved surface portions, and adjacent electrode body units are in contact with each other at the isolation layer stacked on the wide surface portions.

3. The energy storage element according to claim 2, wherein at least one of the two curved surfaces faces the inner surface of the container on which the safety valve is disposed.

4. The energy storage element according to claim 3, wherein the safety valve is located on an extension of the contact surfaces of the adjacent electrode units.

5. The energy storage element according to any one of claims 1 to 4, wherein the thickness of the inorganic layer is 10% or more and 40% or less of the thickness of the isolation layer.

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