Power storage element

Abstract

A power storage element according to one aspect of the present invention has a laminate structure provided with a positive electrode base material, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode base material in the stated order, and comprises a negative electrode tab connected to the negative electrode base material. The negative electrode active material layer contains at least one negative electrode active material selected from the group consisting of metallic lithium and substances alloyed with elemental lithium. An electrically insulating inorganic member is arranged on a side surface at a portion where the positive electrode active material layer faces the negative electrode active material layer with the solid electrolyte layer interposed therebetween, among the side surfaces of the positive electrode active material layer. The positive electrode active material layer and the electrically insulating inorganic member are both laminated on the same surface of the positive electrode base material. A portion where the electrically insulating inorganic member and the negative electrode tab overlap is present when viewed in the lamination direction. The overlapping portion is provided with a fixing member that covers at least part of the negative electrode tab, thereby fixing the negative electrode tab.

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. Non-aqueous electrolyte secondary batteries generally have a pair of electrically isolated electrodes and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as energy storage elements other than non-aqueous electrolyte secondary batteries.

[0003] In recent years, energy storage elements have been proposed that use solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and polymer solid electrolytes as the nonaqueous electrolyte, instead of nonaqueous electrolyte solutions in which an electrolyte salt is dissolved in a liquid such as an organic solvent. Patent Document 1 describes an all-solid-state battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, in which the negative electrode layer contains a silicon material as the negative electrode active material. Patent Document 2 describes an all-solid-state battery having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, in which the negative electrode layer contains metallic lithium as the negative electrode active material.

[0004] JP 2021-082514 A JP 2020-184407 A

[0005] Silicon materials and metallic lithium are known as negative electrode active materials that undergo large volume changes during charge and discharge. In energy storage devices in which a solid electrolyte layer is interposed between a positive electrode active material layer and a negative electrode active material layer and a negative electrode active material that undergoes large volume changes during charge and discharge is used, short circuits during charge and discharge and a decrease in discharge capacity with charge and discharge cycles are particularly likely to occur.

[0006] In response to these inconveniences, the inventors have discovered that in an energy storage element having a solid electrolyte layer interposed between a positive electrode active material layer and a negative electrode active material layer, by disposing an electrical insulating member on at least the side surface of the positive electrode active material layer at a portion where the positive electrode active material layer faces the negative electrode active material layer via the solid electrolyte layer, and by using a structure in which the positive electrode active material layer and the electrical insulating member are both stacked on the same surface of the positive electrode substrate, it is possible to suppress the occurrence of short circuits during charge and discharge and to increase the capacity retention rate after charge and discharge cycles.

[0007] However, in an energy storage element having the above structure, when a negative electrode tab connected to the negative electrode substrate is provided, a new problem has been found in that the negative electrode tab is prone to breakage near the connection to the negative electrode substrate. Specifically, the inventors have found that when the electrical insulating member disposed on the side surface of the positive electrode active material layer is an inorganic member and there is a portion where the electrical insulating member and the negative electrode tab overlap when viewed in the stacking direction, breakage of the negative electrode tab is likely to occur.

[0008] An object of the present invention is to provide an energy storage element in which a solid electrolyte layer is interposed between a positive electrode active material layer and a negative electrode active material layer, and which uses a negative electrode active material that undergoes a large volume change during charge and discharge, wherein the occurrence of short circuits during charge and discharge is suppressed, the capacity retention rate after charge and discharge cycles is high, and furthermore, breakage of the negative electrode tab is unlikely to occur.

[0009] An energy storage element according to one aspect of the present invention has a laminated structure including, in this order, a positive electrode substrate, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode substrate; the energy storage element includes a negative electrode tab connected to the negative electrode substrate; the negative electrode active material layer contains at least one negative electrode active material selected from the group consisting of metallic lithium and materials that are alloyed with lithium; an electrically insulating inorganic member is disposed on at least a side surface of the positive electrode active material layer, the side surface being a portion where the positive electrode active material layer faces the negative electrode active material layer with the solid electrolyte layer interposed therebetween; the positive electrode active material layer and the electrically insulating inorganic member are both laminated on the same surface of the positive electrode substrate; there is a portion where the electrically insulating inorganic member and the negative electrode tab overlap as viewed in the stacking direction; and the energy storage element includes a fixing member that fixes the negative electrode tab by covering at least a portion of the overlapping portion.

[0010] An energy storage element according to one aspect of the present invention is an energy storage element in which a solid electrolyte layer is interposed between a positive electrode active material layer and a negative electrode active material layer, and which uses a negative electrode active material that undergoes a large volume change upon charge and discharge. The energy storage element is less susceptible to short circuits during charge and discharge, has a high capacity retention rate after charge and discharge cycles, and is less susceptible to breakage of the negative electrode tab.

[0011] FIG. 1 is a schematic plan view of an energy storage element according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the energy storage element of FIG. 1 taken along the line A-A. FIG. 3 is a schematic cross-sectional view of an energy storage element according to a second embodiment of the present invention. FIG. 4 is a schematic plan view of an energy storage element according to a third embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of the energy storage element of FIG. 4 taken along the line B-B. FIG. 6 is a schematic cross-sectional view of an energy storage element according to a fourth embodiment of the present invention. FIG. 7 is a schematic perspective view showing each component of an energy storage element according to a fifth embodiment of the present invention. FIG. 8 is a schematic diagram showing an energy storage device formed by assembling a plurality of energy storage elements according to the first embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of energy storage elements according to Production Examples 1 and 2 and Reference Production Example 1. FIG. 10 is a schematic cross-sectional view of energy storage elements according to Comparative Production Example 1 and Reference Production Example 2. FIG. 11 is a schematic cross-sectional view of an energy storage element according to Comparative Production Example 2. FIG. 12 is a schematic cross-sectional view of energy storage elements according to Production Examples 3 and 4. FIG. 13 is a schematic cross-sectional view of the energy storage elements of Production Examples 5 to 7.

[0012] First, an overview of the energy storage element disclosed in this specification will be described.

[0013] (1) An energy storage element according to one aspect of the present invention has a laminated structure including, in this order, a positive electrode substrate, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode substrate; the energy storage element includes a negative electrode tab connected to the negative electrode substrate; the negative electrode active material layer contains at least one negative electrode active material selected from the group consisting of metallic lithium and materials that are alloyed with lithium; an electrically insulating inorganic member is disposed on at least a side surface of the positive electrode active material layer, the side surface being a portion where the positive electrode active material layer faces the negative electrode active material layer with the solid electrolyte layer interposed therebetween; the positive electrode active material layer and the electrically insulating inorganic member are both laminated on the same surface of the positive electrode substrate; there is a portion where the electrically insulating inorganic member and the negative electrode tab overlap as viewed in the stacking direction; and the energy storage element includes a fixing member that fixes the negative electrode tab by covering at least a portion of the overlapping portion.

[0014] The energy storage element described in (1) above has a solid electrolyte layer interposed between a positive electrode active material layer and a negative electrode active material layer, and uses a negative electrode active material that undergoes a large volume change during charge and discharge. This energy storage element suppresses the occurrence of short circuits during charge and discharge, has a high capacity retention rate after charge and discharge cycles, and is less susceptible to breakage of the negative electrode tab. While the reason for this is unclear, the following is presumed. Metallic lithium and substances that form an alloy with lithium are negative electrode active materials that undergo a large volume change during charge and discharge. In conventional energy storage elements that have a solid electrolyte layer interposed between a positive electrode active material layer and a negative electrode active material layer and use a negative electrode active material that undergoes a large volume change during charge and discharge, the positive electrode active material layer and the solid electrolyte layer are prone to deformation due to the large volume change of the negative electrode active material layer. In such cases, the positive electrode active material layer and the solid electrolyte layer deform with repeated charge and discharge, causing cracks and other problems, which can easily lead to short circuits and a decrease in discharge capacity. In contrast, in the energy storage device described in (1) above, an electrically insulating inorganic member is disposed on at least a side surface of the positive electrode active material layer where the positive electrode active material layer faces the negative electrode active material layer via the solid electrolyte layer, and the positive electrode active material layer and the electrically insulating inorganic member are both stacked on the same surface of the positive electrode substrate. In this structure, at least the region of the positive electrode active material layer that contributes to charge and discharge is surrounded by the positive electrode substrate, the solid electrolyte layer, and the electrically insulating inorganic member. Furthermore, the electrically insulating inorganic member is fixed together with the positive electrode active material layer by the positive electrode substrate, making deformation of the positive electrode active material layer less likely. Therefore, in the energy storage device described in (1) above with this structure, cracks are less likely to occur in the positive electrode active material layer even after repeated charge and discharge, and further, cracks in the solid electrolyte layer due to cracks in the positive electrode active material layer are also suppressed. Therefore, it is presumed that the energy storage device described in (1) above has reduced short-circuiting and a high capacity retention rate after charge and discharge cycles. Furthermore, in the energy storage element described in (1) above, cracks are unlikely to occur in the positive electrode active material layer and the solid electrolyte layer even after repeated charge and discharge, and therefore the coulomb efficiency after charge and discharge cycles is also high.On the other hand, as described above, when an electrically insulating inorganic member (an inorganic electrically insulating member) is disposed on the side surface of the positive electrode active material layer and there is a portion where the electrically insulating inorganic member and the negative electrode tab overlap when viewed in the stacking direction, the negative electrode tab is likely to break. This is thought to be because, in such a structure, as shown in FIG. 2 (described in detail later), the negative electrode tab 17 is likely to be pressed against the corner portion 40 of the rigid electrically insulating inorganic member 16, either directly or via another member (insulating tape 19 in FIG. 2 ), resulting in stress concentration in a portion of the negative electrode tab 17 (the portion that contacts the corner portion 40 of the electrically insulating inorganic member 16 directly or via another member). In contrast, the energy storage element described in (1) above is provided with a fixing member (fixing member 20 in FIG. 2 ) that fixes the negative electrode tab by covering at least a portion of the negative electrode tab in the portion where the electrically insulating inorganic member and the negative electrode tab overlap when viewed in the stacking direction. In the energy storage element described in (1) above, it is presumed that the portion of the negative electrode tab that is prone to breakage due to contact with the electrically insulating inorganic member is covered and fixed by the fixing member, making the negative electrode tab less likely to break.

[0015] (2) In the energy storage element described in (1) above, the positive electrode active material layer, the solid electrolyte layer, the negative electrode active material layer, and the negative electrode substrate may be provided in this order on both sides of the positive electrode substrate, and the negative electrode tab may be connected to each of the two negative electrode substrates.

[0016] The energy storage element described in (2) above has a structure in which each layer is laminated on both sides of a single positive electrode substrate, and thus has advantages such as high energy density. On the other hand, in the case of an energy storage element having such a laminated structure, the negative electrode substrate and the negative electrode tab connected thereto are located in the outermost layer, and therefore, when these are sealed in a container, stress is particularly concentrated on a portion of the negative electrode tab. For this reason, if a fixing member is not present in an energy storage element having such a structure, breakage of the negative electrode tab is likely to occur. Therefore, the energy storage element described in (2) above particularly fully obtains the advantage of suppressing breakage of the negative electrode tab by the fixing member.

[0017] (3) In the energy storage element described in (1) or (2) above, the negative electrode substrate and the negative electrode tab may be connected by welding.

[0018] When the negative electrode substrate and the negative electrode tab are connected by welding, the connection tends to break easily if a fixing member is not provided. Therefore, the energy storage element described in (3) above has a particularly sufficient advantage in that the fixing member prevents the negative electrode tab from breaking.

[0019] (4) In the energy storage device according to any one of (1) to (3) above, the electrically insulating inorganic member may contain a solid electrolyte.

[0020] According to the energy storage element described in (4) above, since the electrically insulating inorganic member contains a solid electrolyte, the initial Coulomb efficiency and discharge capacity can be increased. Furthermore, when the electrically insulating inorganic member contains a solid electrolyte, the solid electrolyte layer and the electrically insulating inorganic member can be integrally formed, which makes it possible to efficiently manufacture the energy storage element described in (4) above.

[0021] (5) In the energy storage element according to any one of (1) to (4) above, the solid electrolyte layer and the electrically insulating inorganic member may be coating layers formed from the same material.

[0022] In the energy storage element described in (5) above, the solid electrolyte layer and the electrically insulating inorganic member can be provided by coating using the same material, and therefore the energy storage element described in (5) above can be efficiently manufactured.

[0023] (6) In the energy storage device according to any one of (1) to (5) above, the fixing member may be a resin member.

[0024] According to the energy storage element described in (6) above, the negative electrode tab is fixed using a resin member, making it more difficult for the negative electrode tab to break.

[0025] (7) The energy storage element according to any one of (1) to (6) above may be an all-solid-state energy storage element.

[0026] The energy storage element described in (7) above is an energy storage element in which a solid electrolyte layer is interposed between a positive electrode active material layer and a negative electrode active material layer, and is particularly useful as an all-solid-state energy storage element because it is suppressed from short-circuiting during charge and discharge, has a high capacity retention rate after charge and discharge cycles, and is less susceptible to breakage of the negative electrode tab.

[0027] An energy storage element, a method for manufacturing an energy storage element, an energy storage device, and other embodiments according to one 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.

[0028] <Electricity storage element 10> As one embodiment of the energy storage element of the present invention, an all-solid-state secondary battery, which is an all-solid-state energy storage element, will be described below as a specific example. The energy storage element 10 shown in Figures 1 and 2 has a layered structure including a positive electrode substrate 11, a positive electrode active material layer 12, a solid electrolyte layer 13, an anode active material layer 14, and an anode substrate 15, in this order (see particularly Figure 2).

[0029] The energy storage element 10 further includes an electrically insulating inorganic member 16. The electrically insulating inorganic member 16 is disposed on at least a portion of the side surface 21 of the positive electrode active material layer 12 where the positive electrode active material layer 12 faces the negative electrode active material layer 14 with the solid electrolyte layer 13 interposed therebetween. In the positive electrode active material layer 12 of the energy storage element 10 shown in FIGS. 1 and 2 , there is no portion that does not face the negative electrode active material layer 14 with the solid electrolyte layer 13 interposed therebetween. In other words, the entire side surface 21 of the positive electrode active material layer 12 corresponds to the portion of the side surface where the positive electrode active material layer 12 faces the negative electrode active material layer 14 with the solid electrolyte layer 13 interposed therebetween. Therefore, in the energy storage element 10, the electrically insulating inorganic member 16 is disposed on the entire side surface 21 of the positive electrode active material layer 12. The positive electrode active material layer 12 and the electrically insulating inorganic member 16 are both laminated on the same surface (the upper surface in FIG. 2 ) of the positive electrode substrate 11. That is, in this embodiment, the positive electrode active material layer 12 is surrounded by the positive electrode substrate 11 , the solid electrolyte layer 13 and the electrically insulating inorganic member 16 .

[0030] Because of this structure, the energy storage element 10 is less likely to develop cracks in the positive electrode active material layer 12 even after repeated charge and discharge, and furthermore, cracks in the solid electrolyte layer 13 due to cracks in the positive electrode active material layer 12 are also suppressed. Therefore, the energy storage element 10 is suppressed from developing short circuits during charge and discharge, and has a high capacity retention rate and coulombic efficiency after charge and discharge cycles. Note that the energy storage element 10 and the like shown in each figure are not intended to limit the orientation when used, etc.

[0031] 1 and 2 , the electrically insulating inorganic member 16 disposed on the side surface 21 of the positive electrode active material layer 12 contains a solid electrolyte. In this embodiment, the electrically insulating inorganic member 16 disposed on the side surface 21 of the positive electrode active material layer 12 may be integrated with the solid electrolyte layer 13. The solid electrolyte layer 13 and the electrically insulating inorganic member 16 may be coating layers formed from the same material. When the electrically insulating inorganic member 16 and the solid electrolyte layer 13 are integrated, the portion laminated directly on the positive electrode substrate 11 may be distinguished as the electrically insulating inorganic member 16, and the portion laminated on the positive electrode active material layer 12 may be distinguished as the solid electrolyte layer 13.

[0032] The energy storage element 10 in which the electrically insulating inorganic member 16 contains a solid electrolyte has the advantages of suppressing the occurrence of short circuits during charge and discharge, having a high capacity retention rate after charge and discharge cycles, having a large initial Coulomb efficiency and discharge capacity, and being able to be efficiently manufactured. The reason why the initial Coulomb efficiency and discharge capacity are large in the energy storage element 10 is presumed to be because the electrically insulating inorganic member 16 arranged on the side surface 21 of the positive electrode active material layer 12 contains a solid electrolyte and has ion conductivity, so that the portion of the negative electrode active material layer 14 that does not face the positive electrode active material layer 12 can also contribute to charge and discharge.

[0033] In the energy storage element 10 of FIGS. 1 and 2 , when viewed in the stacking direction (when viewed in the Z direction), the outer edge of the solid electrolyte layer 13 surrounds the outer edge of the anode active material layer 14, and the area of ​​the solid electrolyte layer 13 is larger than the area of ​​the anode active material layer 14. Here, when the electrically insulating inorganic member 16 contains a solid electrolyte (typically, the electrically insulating inorganic member 16 and the solid electrolyte layer 13 are integrated), the outer edge of the solid electrolyte layer 13 refers to the outer edge of the electrically insulating inorganic member 16. In other words, the portion of the electrically insulating inorganic member 16 containing the solid electrolyte is also considered to be part of the solid electrolyte layer 13, and the outer edge of the solid electrolyte layer 13 is specified. In another embodiment of the energy storage element, when viewed in the stacking direction (when viewed in the Z direction), the outer edge of the solid electrolyte layer 13 may overlap the outer edge of the anode active material layer 14, and the areas of the solid electrolyte layer 13 and the anode active material layer 14 may be equal.

[0034] When viewed in the stacking direction (when viewed in the Z direction), the outer edge of the solid electrolyte layer 13 overlaps with or surrounds the outer edge of the negative electrode active material layer 14, thereby further increasing the Coulomb efficiency during charge and discharge of the energy storage element 10. In the case of an energy storage element having a structure in which the outer edge of the negative electrode active material layer 14 surrounds the outer edge of the solid electrolyte layer 13 when viewed in the stacking direction (when viewed in the Z direction), metallic lithium that is precipitated or alloyed in a portion of the negative electrode active material layer 14 that does not face the solid electrolyte layer 13 due to charging is unlikely to be dissolved or dealloyed during subsequent discharge. However, when viewed in the stacking direction (viewed in the Z direction), if the outer edge of the solid electrolyte layer 13 overlaps with or surrounds the outer edge of the anode active material layer 14, there is no portion of the anode active material layer 14 that does not face the solid electrolyte layer 13, and therefore metallic lithium deposited or alloyed in the anode active material layer 14 upon charging is sufficiently dissolved or dealloyed upon subsequent discharge. Furthermore, since there is no portion of the anode active material layer 14 that does not face the solid electrolyte layer 13, there is no difference in expansion and contraction rate during charge and discharge cycles between the portion of the anode active material layer 14 that faces the solid electrolyte layer 13 and the portion that does not face the solid electrolyte layer 13. This prevents cracks from occurring in the portion of the anode active material layer 14 that does not face the solid electrolyte layer 13, and further suppresses the occurrence of short circuits.

[0035] In the energy storage element 10 of FIGS. 1 and 2 , when viewed in the stacking direction (Z direction, plan view), the outer edge of the negative electrode active material layer 14 surrounds the outer edge of the positive electrode active material layer 12, and the area of ​​the negative electrode active material layer 14 is larger than the area of ​​the positive electrode active material layer 12. In another embodiment, when viewed in the stacking direction (Z direction), the outer edge of the negative electrode active material layer 14 overlaps the outer edge of the positive electrode active material layer 12, and the areas of the negative electrode active material layer 14 and the positive electrode active material layer 12 may be equal. The ratio of the area of ​​the negative electrode active material layer 14 to the area of ​​the positive electrode active material layer 12 is preferably 1.0 to 2.0, more preferably 1.0 to 1.5, and even more preferably 1.0 to 1.1. Furthermore, in the energy storage element 10 of FIGS. 1 and 2 , when viewed in the stacking direction (Z direction), the outer edges of the positive electrode substrate 11 and the electrically insulating inorganic member 16 overlap each other. When viewed in the stacking direction (Z direction), the outer edges of the negative electrode active material layer 14 and the negative electrode substrate 15 overlap each other.

[0036] In the energy storage element 10 of Figures 1 and 2, the outer edge shape of each component (positive electrode substrate 11, positive electrode active material layer 12, solid electrolyte layer 13, negative electrode active material layer 14, negative electrode substrate 15, and electrically insulating inorganic member 16) when viewed in the stacking direction (when viewed in the Z direction) is rectangular or may be square. However, the shape of each component is not limited to such a rectangular shape when viewed from above. For example, each component may be circular when viewed from above.

[0037] The energy storage element 10 in FIGS. 1 and 2 includes a negative electrode tab 17 connected to a negative electrode substrate 15. The energy storage element 10 also includes a positive electrode tab 18 connected to a positive electrode substrate 11. The negative electrode tab 17 and the positive electrode tab 18 are conductive plate-like members that are electrically connected to the outside. The negative electrode substrate 15 and the negative electrode tab 17 may be connected at their end faces, or may be connected with their end faces overlapping each other. The same applies to the positive electrode substrate 11 and the positive electrode tab 18. The negative electrode substrate 15 and the negative electrode tab 17 are electrically connected by, for example, welding. The negative electrode substrate 15 and the negative electrode tab 17 may be integral and made of the same material. The same applies to the positive electrode substrate 11 and the positive electrode tab 18.

[0038] 1 and 2 , there is a portion 30 where the electrically insulating inorganic member 16 and the negative electrode tab 17 overlap when viewed in the stacking direction (Z direction). In the energy storage element 10 of FIGS. 1 and 2 , in order to insulate the positive electrode substrate 11 from the negative electrode tab 17, insulating tape 19 is provided in the stacked portion between the positive electrode substrate 11 and the electrically insulating inorganic member 16 so as to cover the end face of the positive electrode substrate 11 in the portion overlapping with the negative electrode tab 17 when viewed in the stacking direction (Z direction). Therefore, in the overlapping portion 30, the electrically insulating inorganic member 16 and the negative electrode tab 17 overlap directly or via the insulating tape 19. In another embodiment, the electrically insulating inorganic member and the negative electrode tab may overlap via a member such as a solid electrolyte layer.

[0039] The energy storage element 10 in FIGS. 1 and 2 includes a fixing member 20 that fixes the negative electrode tab 17 by covering at least a portion of the overlapping portion 30. The fixing member 20 is a sheet-like member. The fixing member 20 is provided so as to cover the portion of the negative electrode tab 17 that is located above the electrically insulating inorganic member 16 and to fix the portion of the negative electrode tab 17 that is located above the electrically insulating inorganic member 16 to the electrically insulating inorganic member 16. In other words, the fixing member 20 is provided so as to cover the portion 30 where the electrically insulating inorganic member 16 and the negative electrode tab 17 overlap (the portion of the negative electrode tab 17 that is located above the electrically insulating inorganic member 16) as viewed in the stacking direction (as viewed in the Z direction), and portions 31 where the electrically insulating inorganic members 16 adjacent to each other in the width direction of the negative electrode tab 17 are exposed in the overlapping portion 30. The fixing member 20 may be provided so as to cover the connection portion between the negative electrode tab 17 and the negative electrode substrate 15.

[0040] The electrically insulating inorganic member 16 in the energy storage device 10 has a corner 40 when viewed in the cross-sectional direction (see FIG. 2 ). This corner 40 includes a portion (corner 40A) formed along the shape of the positive electrode active material layer 12 and an edge portion (corner 40B) of the electrically insulating inorganic member 16. Furthermore, the electrically insulating inorganic member 16 has a step, as shown in FIG. 2 , which forms two corners 40A and 40B. In the energy storage device 10, the portion of the negative electrode tab 17, where stress is concentrated, that contacts the corner 40 of the electrically insulating inorganic member 16 directly or via another member (insulating tape 19) is covered and fixed by the fixing member 20. In other words, the fixing member 20 protects the portion of the negative electrode tab 17 that is prone to fracture. Because such a fixing member 20 is provided, fracture of the negative electrode tab 17 is less likely to occur in the energy storage device 10.

[0041] The energy storage element 10 also includes a container (not shown) that houses a laminate (electrode assembly) of the positive electrode substrate 11, the positive electrode active material layer 12, the solid electrolyte layer 13, the negative electrode active material layer 14, and the negative electrode substrate 15. The material, shape, etc. of the container are not particularly limited, and it may be a sheet-like member. When the electrode assembly is sealed with the sheet-like member, the negative electrode tab 17 is likely to be pressed against the electrically insulating inorganic member 16 directly or via another member (insulating tape 19), which may result in breakage. Therefore, such an energy storage element 10 particularly fully obtains the advantage of suppressing breakage of the negative electrode tab 17 with the fixing member 20.

[0042] The main components of the energy storage device 10 will be described in detail below.

[0043] (Positive Electrode Substrate) The positive electrode substrate 11 is a substrate that supports the positive electrode active material layer 12 and the electrically insulating inorganic member 16. The positive electrode substrate 11 may be a plate-shaped member. The positive electrode substrate 11 has electrical conductivity. Whether or not the positive electrode substrate 11 has "electrical conductivity" is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 －２The resistance is determined using Ω cm as a threshold value. The material of the positive electrode substrate 11 may be a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate 11 include foil, vapor deposition 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 11. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0044] The average thickness of the positive electrode substrate 11 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 11 within the above range, the strength of the positive electrode substrate 11 can be increased while also increasing the energy density per volume of the energy storage device 10. Furthermore, by setting the average thickness of the positive electrode substrate 11 to be equal to or greater than the above lower limit, the strength of the positive electrode substrate 11 is increased, and as a result, deformation of the positive electrode active material layer 12, the electrically insulating inorganic member 16, and the solid electrolyte layer 13 becomes less likely to occur. The average thickness is the average value of thicknesses measured at any five locations.

[0045] (Positive Electrode Active Material Layer) The positive electrode active material layer 12 contains a positive electrode active material. The positive electrode active material layer 12 can be formed from a so-called positive electrode mixture containing the positive electrode active material. The positive electrode active material layer 12 contains optional components such as a solid electrolyte, a conductive agent, a binder, a thickener, and a filler, as necessary.

[0046] 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. ２As 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 ４Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The 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, or they may form composites with other materials. As the positive electrode active material, lithium transition metal composite oxides are preferred, such as α-NaFeO ２ Lithium transition metal composite oxides having a crystalline structure of the above type are more preferred. In the positive electrode active material layer 12, one of these materials may be used alone, or two or more of them may be used in combination.

[0047] 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 12 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. The "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).

[0048] 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.

[0049] The content of the positive electrode active material in the positive electrode active material layer 12 is preferably 30% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and even more preferably 65% ​​by mass or more and 85% by mass or less. 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 12 can be achieved.

[0050] The solid electrolyte can be selected from any material that has lithium ion conductivity 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. From the viewpoint of high ion conductivity, sulfide solid electrolytes are preferred. In the positive electrode active material layer 12, one or more solid electrolytes can be used.

[0051] The sulfide solid electrolyte may be, for example, Li ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ -Li ２ O, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-P ２ S ５ -Li ３ N., Li. ２ S-SiS ２ , Li ２ S-SiS ２ - LiI, Li ２ S-SiS ２ - LiBr, Li ２ S-SiS ２ -LiCl, Li ２ S-SiS ２ -B ２ S３ - LiI, Li ２ S-SiS ２ -P ２ S ５ - LiI, Li ２ S-B ２ S ３ , Li ２ S-P ２ S ５ -Z ｍ S ２ｎ (where m and n are positive numbers, and Z is Ge, Zn, or Ga.), Li ２ S-GeS ２ , Li ２ S-SiS ２ -Li ３ P.O. ４ , Li ２ S-SiS ２ -Li ｘ MO ｙ (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In.), Li １０ GeP ２ S １２ etc.

[0052] When the positive electrode active material layer 12 contains a solid electrolyte, the content of the solid electrolyte is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 40% by mass, and even more preferably 15% by mass to 30% by mass. The solid electrolyte may be present in the positive electrode active material layer 12 in the form of a composite with the positive electrode active material or the like.

[0053] The conductive agent contained in the positive electrode active material layer 12 is not particularly limited as long as it is a material that is conductive. Examples of such conductive agents include carbon materials, metals, conductive ceramics, etc. Carbon materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Non-graphitic carbon includes carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Carbon black includes furnace black, acetylene black, ketjen black, etc. Graphene-based carbon includes graphene, carbon nanotubes (CNT), fullerene, etc. The conductive agent may be in the form of a powder, fiber, etc. 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, fibrous conductive agents are preferred in terms of electronic conductivity, etc. The conductive agent may be present in the positive electrode active material layer 12 in the form of a composite with a positive electrode active material, a solid electrolyte, etc.

[0054] The content of the conductive agent in the positive electrode active material layer 12 is preferably 0.3 mass % to 10 mass %, more preferably 1 mass % to 5 mass %, and even more preferably 3 mass % or less. By setting the content of the conductive agent within the above range, it is possible to increase the energy density of the energy storage element 10, etc.

[0055] 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.

[0056] The content of the binder in the positive electrode active material layer 12 is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 5% by mass, and even more preferably 3% by mass or less. By setting the binder content within the above range, the positive electrode active material can be stably maintained.

[0057] The filler is not particularly limited. Examples of the filler 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. In one embodiment of the present invention, the content of the filler in the positive electrode active material layer 12 may be 5% by mass or less, 1% by mass or less, or even 0% by mass.

[0058] The positive electrode active material layer 12 may contain, as a component other than the positive electrode active material, solid electrolyte, conductive agent, binder, and filler, a typical non-metallic element such as B, N, P, F, Cl, Br, or I; a typical metallic element such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, or Ba; or a transition metal element such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, or W.

[0059] The average thickness of the positive electrode active material layer 12 is preferably 20 μm or more and 1,000 μm or less, more preferably 40 μm or more and 500 μm or less, even more preferably 60 μm or more and 300 μm or less, and even more preferably 80 μm or more and 200 μm or less. By setting the average thickness of the positive electrode active material layer 12 to be equal to or greater than the above lower limit, it is possible to obtain an energy storage element 10 having a high energy density. By setting the average thickness of the positive electrode active material layer 12 to be equal to or less than the above upper limit, it is possible to reduce the size of the energy storage element 10.

[0060] The mass per unit area of ​​the positive electrode active material layer 12 is 5 mg / cm ２ 100mg / cm or more ２ Preferably, 10 mg / cm or less ２ More than 70mg / cm ２ More preferably, 20 mg / cm or less２ 50mg / cm or more ２ The following is even more preferable. By setting the mass per unit area of ​​the positive electrode active material layer 12 to be equal to or greater than the above lower limit, it is possible to obtain an energy storage element 10 having a high energy density. By setting the mass per unit area of ​​the positive electrode active material layer 12 to be equal to or less than the above upper limit, it is possible to reduce the size of the energy storage element 10, for example.

[0061] (Solid Electrolyte Layer) The solid electrolyte layer 13 contains a solid electrolyte. The solid electrolyte contained in the solid electrolyte layer 13 can be selected from the materials exemplified for the positive electrode active material layer 12, and a sulfide solid electrolyte is preferred from the viewpoint of high ionic conductivity, etc. In the solid electrolyte layer 13, one or more solid electrolytes can be used. The solid electrolyte used in the solid electrolyte layer 13 may be the same as or different from the solid electrolytes contained in the other layers.

[0062] The content of the solid electrolyte in the solid electrolyte layer 13 is preferably 70% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 99.9% by mass or less.

[0063] The solid electrolyte layer 13 contains Li ３ P.O. ４ The cathode active material layer 12 may contain optional components such as phosphate compounds, oxides, halogen compounds, binders, and fillers. The optional components such as binders and fillers can be selected from the materials exemplified for the cathode active material layer 12.

[0064] When the solid electrolyte layer 13 contains a binder, the content of the binder in the solid electrolyte layer 13 is preferably 1 mass % or more and 20 mass % or less, more preferably 5 mass % or more and 18 mass % or less, and even more preferably 8 mass % or more and 16 mass % or less.

[0065] The average thickness of the solid electrolyte layer 13 is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 40 μm or more and 150 μm or less. By setting the average thickness of the solid electrolyte layer 13 to be equal to or greater than the above-mentioned lower limit, it is possible to reliably insulate the positive electrode active material layer 12 and the negative electrode active material layer 14. By setting the average thickness of the solid electrolyte layer 13 to be equal to or less than the above-mentioned upper limit, it is possible to increase the energy density of the energy storage element 10.

[0066] (Negative Electrode Active Material Layer) The negative electrode active material layer 14 contains a negative electrode active material. In one embodiment of the present invention, the negative electrode active material layer 14 can be formed from a so-called negative electrode mixture containing the negative electrode active material. The negative electrode active material layer 14 may contain a mixture or composite containing the negative electrode active material and a solid electrolyte or the like. The negative electrode active material layer 14 contains optional components such as a solid electrolyte, a conductive agent, a binder, a filler, etc., as necessary. The types of these optional components in the negative electrode active material layer 14 are the same as the optional components of the positive electrode active material layer 12 described above.

[0067] The negative electrode active material layer 14 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, solid electrolyte, conductive agent, binder, and filler.

[0068] The negative electrode active material layer 14 contains, as the negative electrode active material, at least one selected from the group consisting of metallic lithium and a material that alloys with lithium. Such a negative electrode active material is a negative electrode active material that undergoes a large volume change during charge and discharge. By applying one embodiment of the present invention to an energy storage device that uses such a negative electrode active material, the occurrence of short circuits during charge and discharge is suppressed and the capacity retention rate after charge and discharge cycles is significantly improved. The negative electrode active material preferably contains a material that alloys with lithium, and more preferably is a material that alloys with lithium.

[0069] The metallic lithium serving as the negative electrode active material may be present in the negative electrode active material layer 14 as pure metallic lithium consisting essentially of lithium element alone, or as a lithium alloy containing other elements. Examples of the lithium alloy include a lithium-silver alloy, a lithium-zinc alloy, a lithium-calcium alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, and a lithium-indium alloy. The lithium alloy may contain multiple elements other than lithium element.

[0070] When metallic lithium is used as the negative electrode active material, the negative electrode active material layer 14 may be a pure metallic lithium foil or a lithium alloy foil. The negative electrode active material layer 14 may be a non-porous layer (a solid layer). Alternatively, the negative electrode active material layer 14 may be a porous layer containing particles containing metallic lithium.

[0071] Examples of substances that can be alloyed with lithium include silicon-based active materials (silicon element, silicon oxide, etc.), tin-based active materials (tin element, tin oxide, etc.), germanium-based active materials (germanium element, germanium oxide, etc.), aluminum-based active materials (aluminum element, aluminum oxide, etc.), magnesium-based active materials (magnesium element, magnesium oxide, etc.), and zinc-based active materials (zinc element, zinc oxide, etc.). Silicon-based active materials refer to substances that contain silicon element and can be alloyed with lithium element. The same applies to tin-based active materials, etc. Among these, silicon-based active materials are preferred as substances that can be alloyed with lithium element.

[0072] In one embodiment of the present invention, the negative electrode active material is particulate (powder). When the negative electrode active material is particulate, each negative electrode active material particle expands and contracts three-dimensionally during charging and discharging, causing the negative electrode active material layer to also expand and contract three-dimensionally. In such cases, deformation of the positive electrode active material layer and the solid electrolyte layer generally tends to occur in response to the expansion and contraction of the negative electrode active material layer. Therefore, when one embodiment of the present invention is applied to an energy storage device using a particulate negative electrode active material, the suppression of deformation of the positive electrode active material layer significantly suppresses the occurrence of short circuits and increases the capacity retention rate after charge-discharge cycling.

[0073] When the negative electrode active material is in a foil (plate) shape, metallic lithium is deposited and dissolved, or alloyed and dealloyed, on the surface of the negative electrode active material layer 14 during charge and discharge. That is, the direction of the deposition and dissolution or alloying and dealloying of metallic lithium during charge and discharge is two-dimensional. In contrast, when the negative electrode active material is in a particulate shape, the negative electrode active material particles and the solid electrolyte are present in a mixed state in the negative electrode active material layer 14. Therefore, the direction of the deposition and dissolution or alloying and dealloying of metallic lithium during charge and discharge is three-dimensional. In either case, metallic lithium is unlikely to be deposited and dissolved or alloyed and dealloyed in the negative electrode active material in the portion of the negative electrode active material layer 14 that does not face the solid electrolyte layer 13. However, if the negative electrode active material is particulate and the direction of deposition and dissolution or alloying and dealloying of metallic lithium during charge and discharge is three-dimensional, during charging, the negative electrode active material particles expand, improving the contact state between the negative electrode active material particles and thereby reducing the charge transfer resistance of the negative electrode active material layer 14. Furthermore, due to a driving force that balances the potential difference generated between the portion of the negative electrode active material layer 14 facing the solid electrolyte layer 13 and the other portion, metallic lithium also diffuses into the solid phase of the negative electrode active material particles in the portion of the negative electrode active material layer 14 that does not face the solid electrolyte layer 13. During subsequent discharge, on the other hand, the negative electrode active material particles shrink, reducing the contact state between the negative electrode active material particles and thereby increasing the charge transfer resistance of the negative electrode active material layer 14, resulting in a problem in that the metallic lithium that has diffused into the solid phase of the negative electrode active material particles in the portion of the negative electrode active material layer 14 that does not face the solid electrolyte layer 13 is difficult to dissolve or dealloy. In such a case, when combined with the feature of the energy storage element according to one embodiment of the present invention in which the outer edge of the solid electrolyte layer 13 overlaps with the outer edge of the negative electrode active material layer 14 or the outer edge of the solid electrolyte layer 13 surrounds the outer edge of the negative electrode active material layer 14 as viewed in the stacking direction (as viewed in the Z direction), metallic lithium precipitated or alloyed in the negative electrode active material particles of the negative electrode active material layer 14 upon charging is efficiently dissolved or dealloyed during subsequent discharging, thereby more significantly achieving the effect of increasing the Coulomb efficiency during charging and discharging.

[0074] The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm, or 10 nm to 20 μm, or 100 nm to 3 μm. Setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit facilitates the production or handling of the negative electrode active material. Setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit improves the electronic conductivity of the negative electrode active material layer 14. 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 active material layer 12. In another embodiment, the negative electrode active material may be in the form of a foil, etc.

[0075] The content of the anode active material in the anode active material layer 14 is preferably 30% by mass or more and 100% by mass or less. When the anode active material is metallic lithium, the content of the anode active material in the anode active material layer 14 may be 90% by mass or more, 99% by mass or more, or even 100% by mass. When the anode active material is a substance that alloys with lithium element, the content of the anode active material in the anode active material layer 14 is preferably 40% by mass or more and 90% by mass or less, and more preferably 50% by mass or more and 70% by mass or less. By setting the content of the anode active material within the above range, both high energy density and manufacturability of the anode active material layer 14 can be achieved.

[0076] The solid electrolyte contained in the negative electrode active material layer 14 is preferably a sulfide solid electrolyte from the viewpoint of high ionic conductivity. In the negative electrode active material layer 14, one or more solid electrolytes can be used. The solid electrolyte used in the negative electrode active material layer 14 may be the same as or different from the solid electrolytes contained in other layers. The solid electrolyte may be present in the negative electrode active material layer 14 in the form of a composite with the negative electrode active material or the like. When the negative electrode active material layer 14 contains a solid electrolyte, the content of the solid electrolyte is preferably 10% by mass or more and 70% by mass or less, more preferably 20% by mass or more and 60% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less.

[0077] The conductive agent contained in the negative electrode active material layer 14 can be selected and used in the same manner as the conductive agent contained in the positive electrode active material layer 12 .

[0078] The content of the binder in the negative electrode active material layer 14 is preferably 0.5% by mass to 10% by mass, and more preferably 1% by mass to 5% by mass.

[0079] In one embodiment of the present invention, the negative electrode active material layer 14 is porous. When the negative electrode active material layer is porous, the negative electrode active material layer expands and contracts three-dimensionally during charge and discharge. In such a case, deformation of the positive electrode active material layer and the solid electrolyte layer generally tends to occur in accordance with the expansion and contraction of the negative electrode active material layer. Therefore, when one embodiment of the present invention is applied to an energy storage device having a porous negative electrode active material layer, the suppression of deformation of the positive electrode active material layer significantly suppresses the occurrence of short circuits and increases the capacity retention rate after charge and discharge cycles.

[0080] The porosity of the negative electrode active material layer 14 is, for example, 5% to 70%, and may be 20% to 60%. The porosity of the negative electrode active material layer 14 refers to a value calculated from the true density of the negative electrode active material layer 14 calculated from the true density of each component constituting the negative electrode active material layer 14 and the apparent density of the negative electrode active material layer 14 using the following formula: Porosity (%) = 100 - (apparent density / true density) x 100

[0081] The apparent density of the negative electrode active material layer 14 refers to the value obtained by dividing the mass of the negative electrode active material layer 14 by the apparent volume of the negative electrode active material layer 14. The apparent volume refers to the volume including voids, and can be calculated as the product of the average thickness and area of ​​the negative electrode active material layer 14.

[0082] The average thickness of the negative electrode active material layer 14 is preferably 5 μm or more and 1,000 μm or less, and more preferably 60 μm or more and 500 μm or less. By setting the average thickness of the negative electrode active material layer 14 to be equal to or greater than the above lower limit, it is possible to obtain an energy storage element 10 having a high energy density. By setting the average thickness of the negative electrode active material layer 14 to be equal to or less than the above upper limit, it is possible to reduce the size of the energy storage element 10.

[0083] The mass per unit area of ​​the negative electrode active material layer 14 is 0.5 mg / cm ２ 20mg / cm or more ２ Preferably, less than 1 mg / cm ２ 10mg / cm or more ２More preferably, 2 mg / cm or less ２ 5mg / cm or more ２ The following is even more preferable. By setting the mass per unit area of ​​the negative electrode active material layer 14 to be equal to or greater than the above lower limit, it is possible to obtain an energy storage element 10 having a high energy density. By setting the mass per unit area of ​​the negative electrode active material layer 14 to be equal to or less than the above upper limit, it is possible to reduce the size of the energy storage element 10, for example.

[0084] (Negative electrode substrate) The negative electrode substrate 15 is a substrate that supports the negative electrode active material layer 14. The negative electrode substrate 15 may be a plate-shaped member. The negative electrode substrate 15 is conductive. As the material of the negative electrode substrate 15, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, carbonaceous materials, etc. are used. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate 15 include foil, vapor-deposited film, mesh, and porous material, and foil is preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate 15. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0085] The average thickness of the negative electrode substrate 15 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 15 within the above range, the strength of the negative electrode substrate 15 can be increased while increasing the energy density per volume of the energy storage element 10.

[0086] (Electrically insulating inorganic member) When viewed in the stacking direction (when viewed in the Z direction), the electrically insulating inorganic member 16 is arranged like a frame surrounding the positive electrode active material layer 12. It is preferable that the side surface 21 of the positive electrode active material layer 12 is in contact with the electrically insulating inorganic member 16. In this case, the positive electrode active material layer 12 is strongly constrained by the electrically insulating inorganic member 16, which further suppresses deformation of the positive electrode active material layer 12, further suppresses the occurrence of short circuits during charge and discharge, and further increases the capacity retention rate and coulombic efficiency after charge and discharge cycles.

[0087] The electrically insulating inorganic member 16 is an electrically insulating member primarily composed of an inorganic material. "Electrically insulating" means that the member is not electrically conductive. "Mainly composed of an inorganic material" means that the inorganic material content is greater than 50% by mass. In the electrically insulating inorganic member 16, the inorganic material content is preferably 80% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 100% by mass or less. In the energy storage element 10 of the embodiment shown in Figures 1 and 2, the electrically insulating inorganic member 16 contains a solid electrolyte. The solid electrolyte contained in the electrically insulating inorganic member 16 is preferably an inorganic substance. Furthermore, the electrically insulating inorganic member 16 may be formed integrally with the solid electrolyte layer 13 using the same material. Therefore, the specific and preferred aspects of the components and their contents constituting the electrically insulating inorganic member 16 in this embodiment are the same as the specific and preferred aspects of the components and their contents constituting the solid electrolyte layer 13 described above.

[0088] In other embodiments, the electrically insulating inorganic member 16 may be a member that does not contain a solid electrolyte, or may be a member made of a material different from that of the solid electrolyte layer.

[0089] (Positive Electrode Tab and Negative Electrode Tab) The positive electrode tab 18 and the negative electrode tab 17 are each a conductive plate-like member. The positive electrode tab 18 and the negative electrode tab 17 may each be a metal plate or a metal foil. Specific and preferred embodiments of the material of the positive electrode tab 18 are the same as those of the positive electrode substrate 11 described above. Specific and preferred embodiments of the material of the negative electrode tab 17 are the same as those of the negative electrode substrate 15 described above.

[0090] The average thickness of the positive electrode tab 18 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 tab 18 within the above range, it is possible to increase the strength of the positive electrode tab 18 while reducing the weight of the energy storage element 10.

[0091] The average thickness of the negative electrode tab 17 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 tab 17 within the above range, it is possible to increase the strength of the negative electrode tab 17 while reducing the weight of the energy storage element 10.

[0092] (Fixing Member) The material of the fixing member 20 is not particularly limited as long as it can cover and fix at least a portion of the negative electrode tab 17. The fixing member 20 is preferably an electrically insulating member, and is also preferably a resin member. For example, a resin tape, an adhesive resin, or the like can be used as the fixing member 20.

[0093] The average thickness of the fixing member 20 may be 1 μm or more and 500 μm or less, or 3 μm or more and 100 μm or less. By setting the average thickness of the fixing member 20 within the above range, it is possible to, for example, reduce the size of the energy storage element 10 while sufficiently suppressing breakage of the negative electrode tab 17.

[0094] The method for manufacturing the energy storage element 10 is not particularly limited, but the following method can be used, for example.

[0095] The positive electrode active material layer 12 is disposed on the positive electrode substrate 11. The positive electrode active material layer 12 can be disposed, for example, by coating a paste-like positive electrode mixture. When coating the paste-like positive electrode mixture, for example, the coating is performed in a masked state on the positive electrode substrate 11, and the mask is removed after coating, thereby providing the positive electrode active material layer 12 in a predetermined shape. The positive electrode active material layer 12 can also be disposed by transferring a positive electrode active material layer 12 that has been previously formed into a predetermined shape.

[0096] Next, a layer containing a solid electrolyte is disposed so as to cover the positive electrode active material layer 12 disposed on the positive electrode substrate 11, thereby obtaining a first laminate. The layer containing a solid electrolyte is a layer in which the solid electrolyte layer 13 and the electrically insulating inorganic member 16 are integrated, and may be a coated layer. The layer containing a solid electrolyte (a layer in which the solid electrolyte layer 13 and the electrically insulating inorganic member 16 are integrated) can be disposed by, for example, coating a solid electrolyte material containing a solid electrolyte, a binder, and a dispersion medium.

[0097] Furthermore, the negative electrode active material layer 14 is laminated on the negative electrode substrate 15 to obtain a second laminate. This lamination can be performed by a conventionally known method (transfer, coating, etc.).

[0098] The obtained first laminate and second laminate are superimposed on each other so that the positive electrode active material layer 12 and the negative electrode active material layer 14 face each other via the solid electrolyte layer 13, and then hot-pressed to obtain an electrode body (a laminate of the first laminate and the second laminate).

[0099] Thereafter, the positive electrode tab 18 is connected to the positive electrode substrate 11, and the negative electrode tab 17 is connected to the negative electrode substrate 15. These connections can be made by welding or the like. Then, a fixing member 20 is provided to fix the negative electrode tab 17. Note that the positive electrode substrate 11 and the positive electrode tab 18 can be formed as an integrated member, and the negative electrode substrate 15 and the negative electrode tab 17 can be formed as an integrated member. In such cases, the step of connecting the positive electrode tab 18 and the negative electrode tab 17 is omitted. The insulating tape 19 can be provided at an appropriate timing.

[0100] Next, the electrode assembly provided with the positive electrode tab 18, the negative electrode tab 17, etc., is sealed while sandwiched between a pair of sheet-like members or the like. Examples of the sheet-like member used for sealing include a laminated film of a metal foil and a resin film. At this time, the tip portions of the positive electrode tab 18 and the negative electrode tab 17 are arranged so as to be exposed outside the sealing member (container) formed from the pair of sheet-like members or the like. During sealing, the negative electrode tab 17 may be deformed into a shape that conforms to the surface shape of the electrically insulating inorganic member 16, etc., as shown in FIG. 2 . The same applies to the positive electrode tab 18. Through this process, the energy storage element 10 having the structure shown in FIGS. 1 and 2 can be obtained. Note that a rectangular container or the like may also be used as the container.

[0101] 3 has a structure in which a positive electrode active material layer 12, a solid electrolyte layer 13, a negative electrode active material layer 14, and a negative electrode substrate 15 are provided in this order on both sides of a positive electrode substrate 11. That is, the energy storage element 110 has a layer structure in which a first negative electrode substrate 15, a first negative electrode active material layer 14, a first solid electrolyte layer 13, a first positive electrode active material layer 12, a positive electrode substrate 11, a second positive electrode active material layer 12, a second solid electrolyte layer 13, a second negative electrode active material layer 14, and a second negative electrode substrate 15 are laminated in this order.

[0102] Furthermore, an electrically insulating inorganic member 16 is disposed on each side surface of the two positive electrode active material layers 12, and an anode tab 17 is connected to each of the two negative electrode substrates 15. A positive electrode tab (not shown) is connected to the positive electrode substrate 11. Furthermore, insulating tape 19 is provided in the laminated portion between the positive electrode substrate 11 and the electrically insulating inorganic member 16 so as to cover the end face of the positive electrode substrate 11 in the portion overlapping with each negative electrode tab 17 when viewed in the stacking direction. When viewed in the stacking direction, there are portions where each electrically insulating inorganic member 16 and each negative electrode tab 17 overlap, and fixing members 20 are provided in the overlapping portions to fix each negative electrode tab 17 by covering at least a portion of each.

[0103] 1 and 2, except that the energy storage element 110 shown in Fig. 3 has a positive electrode active material layer 12, a solid electrolyte layer 13, a negative electrode active material layer 14, and a negative electrode substrate 15 provided on both sides of a positive electrode substrate 11. Since the components of the energy storage element 110 are the same as those of the energy storage element 10, the same reference numerals are used and descriptions thereof will be omitted.

[0104] The energy storage element 110 has a structure in which layers are laminated on both sides of a single positive electrode substrate 11, and thus has advantages such as high energy density. On the other hand, in the case of an energy storage element 110 having such a laminated structure, the negative electrode substrates 15 and the negative electrode tabs 17 connected thereto are located in the outermost layers, and therefore, when sealing these, stress tends to concentrate particularly on a portion of each negative electrode tab 17 (a portion that contacts the corner portion 40 of the electrically insulating inorganic member 16 directly or via the insulating tape 19). For this reason, the energy storage element 110 particularly fully obtains the advantage that the fixing member 20 prevents the negative electrode tabs 17 from breaking.

[0105] The energy storage element 110 shown in FIG. 3 includes two negative electrode tabs 17, with one negative electrode tab 17 connected to each of the two negative electrode substrates 15. However, the number of negative electrode tabs, etc., is not limited to this configuration. The number of negative electrode substrates and the number of negative electrode tabs may be the same or different. The same applies to the number of positive electrode substrates and the number of positive electrode tabs. For example, one negative electrode tab may be bent and connected to two negative electrode substrates. Furthermore, the energy storage element may be provided with three or more negative electrode tabs.

[0106] <Energy storage element 210> The energy storage element 210 shown in Figures 4 and 5 is similar to the energy storage element 10 shown in Figures 1 and 2, except that the fixing member 220 has a frame-like (picture frame-like) shape. The fixing member 220 is provided so as to cover the entire outer edge of the electrically insulating inorganic member 16, and covers and fixes the portion of the negative electrode tab 17 that overlaps with the electrically insulating inorganic member 16. The energy storage element 210 provided with such a fixing member 220 also suppresses the occurrence of short circuits during charge and discharge, has a high capacity retention rate after charge and discharge cycles, and is less likely to break the negative electrode tab 17, as with the energy storage element 10, etc. The components of the energy storage element 210 other than the fixing member 220 are similar to the components of the energy storage element 10, and therefore will be denoted by the same numbers and will not be described again.

[0107] <Energy Storage Element 310> The energy storage element 310 shown in FIG. 6 has a laminated structure including a positive electrode substrate 11, a positive electrode active material layer 12, a solid electrolyte layer 13, a negative electrode active material layer 14, and a negative electrode substrate 15, in this order. The energy storage element 310 further includes an electrically insulating inorganic member 316. The electrically insulating inorganic member 316 is disposed on the entire side surface 21 of the positive electrode active material layer 12. The positive electrode active material layer 12 and the electrically insulating inorganic member 316 are both laminated on the same surface of the positive electrode substrate 11. That is, in this embodiment, the positive electrode active material layer 12 is surrounded by the positive electrode substrate 11, the solid electrolyte layer 13, and the electrically insulating inorganic member 316. The energy storage element 310 shown in FIG. 6 also includes a positive electrode tab (not shown), a negative electrode tab 17, and a fixing member 20, similar to the energy storage elements 10 shown in FIGS. 1 and 2.

[0108] 6 differs from the energy storage element 10 shown in Figures 1 and 2 in that the electrically insulating inorganic member 316 is made of a material different from that of the solid electrolyte layer 13, but is otherwise similar to the energy storage element 10. Therefore, the components of the energy storage element 310 other than the electrically insulating inorganic member 316 are denoted by the same reference numerals as those of the energy storage element 10, and descriptions thereof will be omitted.

[0109] In the energy storage element 310 in which the solid electrolyte layer 13 and the electrically insulating inorganic member 316 are made of different materials, similar to the energy storage element 10, the occurrence of short circuits during charging and discharging is suppressed, the capacity retention rate after charge and discharge cycles is high, and furthermore, breakage of the negative electrode tab 17 is unlikely to occur.

[0110] The electrically insulating inorganic member 316 may be configured to contain, for example, electrically insulating inorganic particles, or may be configured to contain electrically insulating inorganic particles and a binder.

[0111] The electrically insulating inorganic particles can be selected from, for example, the materials exemplified as the filler in the positive electrode active material layer 12. As the electrically insulating inorganic particles, inorganic oxide particles are preferred, and alumina is more preferred. One or more types of electrically insulating inorganic particles can be used.

[0112] The content of the electrically insulating inorganic particles in the electrically insulating inorganic member 316 is preferably 70% by mass to 99% by mass, more preferably 80% by mass to 98% by mass, and even more preferably 90% by mass to 97% by mass.

[0113] The binder contained in the electrically insulating inorganic member 316 can be selected from the materials exemplified as the binder in the positive electrode active material layer 12 .

[0114] The binder content in the electrically insulating inorganic member 316 is preferably 1% by mass to 15% by mass, more preferably 2% by mass to 10% by mass, and even more preferably 3% by mass to 8% by mass.

[0115] The electrically insulating inorganic member 316 may contain a solid electrolyte. The electrically insulating inorganic member 316 may contain electrically insulating inorganic particles, a solid electrolyte, and a binder, and may further contain other components.

[0116] The method for manufacturing the energy storage element 310 is not particularly limited, but the following method can be used, for example.

[0117] The electrically insulating inorganic member 316 is arranged in a frame shape on the positive electrode substrate 11. The electrically insulating inorganic member 316 can be arranged by transferring the electrically insulating inorganic member 316, which has been formed in advance into a predetermined shape, onto the positive electrode substrate 11.

[0118] Next, the positive electrode active material layer 12 is disposed within the electrically insulating inorganic member 316 disposed in a frame shape on the positive electrode substrate 11 to obtain a first laminate. The positive electrode active material layer 12 can be disposed by transferring the positive electrode active material layer 12 that has been formed into a predetermined shape in advance. The positive electrode active material layer 12 may also be disposed by coating a paste-like positive electrode mixture, or the like.

[0119] Furthermore, a second laminate is obtained by sequentially laminating the negative electrode active material layer 14 and the solid electrolyte layer 13 on the negative electrode substrate 15. The lamination can be performed by a conventionally known method (transfer, coating, etc.).

[0120] The obtained first laminate and second laminate are superposed on each other so that the positive electrode active material layer 12 and the negative electrode active material layer 14 face each other via the solid electrolyte layer 13, and then hot-pressed. Thereafter, similar to the manufacturing method of the energy storage element 10 described above, a positive electrode tab, a negative electrode tab 17, a fixing member 20, etc. are provided, and the resulting structure is sealed with a pair of films or the like, thereby obtaining the energy storage element 310 having the structure shown in FIG. 6. The solid electrolyte layer 13 may be laminated on the first laminate, or may be laminated on both the first laminate and the second laminate.

[0121] 7 has a layered structure including, in this order, a positive electrode substrate 11, a positive electrode active material layer 412, a solid electrolyte layer 13, a negative electrode active material layer 414, and a negative electrode substrate 15. The energy storage element 410 is also provided with a positive electrode tab 18 connected to the positive electrode substrate 11, a negative electrode tab 17 connected to the negative electrode substrate 15, and a fixing member 20 that fixes the negative electrode tab 17 by covering at least a portion of the negative electrode tab 17. The positive electrode substrate 11, the solid electrolyte layer 13, the negative electrode substrate 15, the positive electrode tab 18, the negative electrode tab 17, and the fixing member 20 included in the energy storage element 410 are similar to those included in the energy storage element 10 described as other embodiments, and therefore the same reference numerals are used and description thereof will be omitted.

[0122] The positive electrode active material layer 412 and the negative electrode active material layer 414 each have a rectangular shape when viewed in the stacking direction (when viewed in the Z direction, in a plan view).

[0123] The specific and preferred forms of the positive electrode active material layer 412 are the same as those of the positive electrode active material layer 12 included in the energy storage element 10 shown in Figures 1 and 2. The specific and preferred forms of the negative electrode active material layer 414 are the same as those of the negative electrode active material layer 14 included in the energy storage element 10 shown in Figures 1 and 2.

[0124] A first electrically insulating inorganic member 416 is disposed on each of a pair of opposing first side surfaces 418 of the positive electrode active material layer 412. When viewed in the stacking direction (viewed in the Z direction), the pair of first electrically insulating inorganic members 416 are provided in the form of strips along the X direction, sandwiching the positive electrode active material layer 412. The average thickness of the positive electrode active material layer 412 and the average thickness (average thickness in the Z direction) of the first electrically insulating inorganic members 416 are preferably the same.

[0125] A second electrically insulating inorganic member 417 is disposed on each of a pair of opposing second side surfaces 419 of the negative electrode active material layer 414. When viewed in the stacking direction (viewed in the Z direction), the pair of second electrically insulating inorganic members 417 are provided in strip shapes along the Y direction, sandwiching the negative electrode active material layer 414. The average thickness of the negative electrode active material layer 414 and the average thickness (average thickness in the Z direction) of the second electrically insulating inorganic members 417 are preferably the same.

[0126] Examples of materials constituting the first electrically insulating inorganic member 416 and the second electrically insulating inorganic member 417 include the same materials as those constituting the electrically insulating inorganic members in the other embodiments described above.

[0127] In the energy storage element 410, an electrically insulating inorganic member (first electrically insulating inorganic member 416) is disposed only on a first side surface 418 of the side surface of the positive electrode active material layer 412, the first side surface 418 including the side surface of a portion of the positive electrode active material layer 412 facing the negative electrode active material layer 414 with the solid electrolyte layer 13 interposed therebetween. The portion of the positive electrode active material layer 412 facing the negative electrode active material layer 414 with the solid electrolyte layer 13 interposed therebetween is a portion that contributes to charging and discharging. The side surface of the portion of the positive electrode active material layer 412 that contributes to charging and discharging is surrounded by the first electrically insulating inorganic member 416 and a portion of the positive electrode active material layer 412 that does not contribute to charging and discharging. In addition, the positive electrode active material layer 412 and the first electrically insulating inorganic member 416 are fixed or supported by the positive electrode substrate 11. Therefore, the portion of the positive electrode active material layer 412 facing the negative electrode active material layer 414 with the solid electrolyte layer 13 interposed therebetween (the portion that contributes to charging and discharging) is less likely to deform. Therefore, in the energy storage element 410, cracks are unlikely to occur in the positive electrode active material layer 412 (particularly the portion of the positive electrode active material layer 412 facing the negative electrode active material layer 414 via the solid electrolyte layer 13) even after repeated charge and discharge, the occurrence of short circuits is suppressed, and the capacity retention rate and coulombic efficiency after charge and discharge cycles are high. Furthermore, in the energy storage element 410, the portion of the negative electrode tab 17 that is prone to breakage due to contact with the electrically insulating inorganic member (first electrically insulating inorganic member 416) is covered and fixed by the fixing member 20, so that breakage of the negative electrode tab 17 is unlikely to occur.

[0128] <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.

[0129] 8 shows an example of an energy storage device 70 in which energy storage units 60, each of which is an assembly of two or more electrically connected energy storage elements 10, are further assembled. The energy storage device 70 may include a bus bar (not shown) that electrically connects two or more energy storage elements 10, a bus bar (not shown) that electrically connects two or more energy storage units 60, etc. The energy storage unit 60 or the energy storage device 70 may include a status monitoring device (not shown) that monitors the status of one or more energy storage elements 10.

[0130] <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.

[0131] The energy storage device according to the present invention may include other layers than those described above. For example, an intermediate layer may be disposed between the positive electrode active material layer and the positive electrode substrate, or an intermediate layer may be disposed between the negative electrode active material layer and the negative electrode substrate. The configuration of the intermediate layer is not particularly limited, and may include, for example, a binder and a conductive agent.

[0132] In the above embodiment, the case where the energy storage element is used as a chargeable and dischargeable all-solid-state secondary battery has been described, but the type, shape, size, capacity, etc. of the energy storage element are arbitrary. The present invention is also applicable to various secondary batteries and capacitors such as electric double layer capacitors and lithium ion capacitors. The present invention can also be applied to an energy storage element having bipolar electrodes. The energy storage element according to the present invention may contain a liquid. Examples of such an energy storage element include an energy storage element in which voids in the positive electrode active material layer, solid electrolyte layer, negative electrode active material layer, etc. are filled with a nonaqueous electrolyte solution containing an ionic liquid, etc.

[0133] EXAMPLES The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0134] [Manufacturing Example 1] A frame-shaped electrically insulating inorganic member having inner dimensions of 2.0 cm x 2.0 cm, outer dimensions of 3.0 cm x 3.0 cm, and an average thickness of 100 μm was laminated by transfer onto the surface of a 3.0 cm x 3.0 cm roughened aluminum foil as a positive electrode substrate. The electrically insulating inorganic member was a molded mixture of 95 parts by mass of alumina, which is an electrically insulating inorganic particle, and 5 parts by mass of PVDF, which is a binder. Next, a positive electrode active material layer laminated on a polyimide film was arranged by transfer within the frame of the electrically insulating inorganic member laminated on the positive electrode substrate, to obtain a first laminate. The positive electrode active material layer contained a positive electrode active material (LiNi １／２ Co １／５ Mn ３／１０ O ２ The positive electrode active material layer was formed from a positive electrode mixture containing 76 parts by mass of a sulfide solid electrolyte, 20 parts by mass of a conductive agent (fibrous carbon), and 2 parts by mass of a binder containing a styrene structure and a butadiene structure. The mass per unit area of ​​the positive electrode active material layer was 30 mg / cm. ２The average thickness was 100 μm. A 2.5 cm × 2.5 cm square anode active material layer was disposed on the surface of a 2.5 cm × 2.5 cm copper foil as the anode substrate. The anode active material layer was formed from a cathode mixture consisting of 55 parts by mass of anode active material (silicon element: average particle size 0.8 μm), 39 parts by mass of a sulfide solid electrolyte, 3 parts by mass of a conductive agent (fibrous carbon), and 3 parts by mass of the binder. The mass per unit area of ​​the anode active material layer was 2.5 mg / cm ２ Next, an argyrodite-type sulfide solid electrolyte layer was laminated by transfer onto the surface of the negative electrode active material layer to obtain a second laminate. The first laminate and the second laminate were overlapped so that the positive electrode active material layer and the negative electrode active material layer faced each other via the solid electrolyte layer, and hot-pressed to obtain the energy storage element of Production Example 1 having the structure shown in FIG. 9. In producing the energy storage element, the first laminate was produced in a dry air atmosphere, and the other steps were carried out in an argon atmosphere with a dew point of −50° C. or lower. The same applies to Comparative Production Examples 1 and 2, Reference Production Examples 1 and 2, and Production Examples 2 to 4.

[0135] Comparative Production Example 1 An energy storage element of Comparative Production Example 1 having the structure shown in FIG. 10 was obtained in the same manner as in Production Example 1, except that no frame-shaped electrically insulating inorganic member was provided when the first laminate was produced.

[0136] [Comparative Manufacturing Example 2] A positive electrode active material layer was disposed on the surface of a roughened aluminum foil as a positive electrode substrate. The positive electrode active material layer had the same composition as in Manufacturing Example 1. The positive electrode substrate on which the positive electrode active material layer was disposed was cut to 2.0 cm x 2.0 cm and placed in a frame-shaped electrically insulating inorganic member with inner dimensions of 2.0 cm x 2.0 cm, outer dimensions of 3.0 cm x 3.0 cm, and an average thickness of 110 μm to obtain a first laminate. The frame-shaped electrically insulating inorganic member was prepared by laminating a mixture of 95 parts by mass of alumina and 5 parts by mass of PVDF on a polyimide film and cutting it into a predetermined shape. A second laminate was obtained in the same procedure as Manufacturing Example 1. The first laminate and the second laminate were superimposed so that the positive electrode active material layer and the negative electrode active material layer faced each other via the solid electrolyte layer, and then hot-pressed to obtain a storage element of Comparative Manufacturing Example 2 having the structure of FIG. 11.

[0137] Reference Production Example 1 An energy storage element of Reference Production Example 1 having the structure shown in FIG. 9 was obtained in the same manner as in Production Example 1, except that the negative electrode active material layer was formed from a negative electrode mixture comprising 58 parts by mass of a negative electrode active material (graphite), 39 parts by mass of a sulfide solid electrolyte, and 3 parts by mass of a binder.

[0138] Reference Production Example 2 An energy storage element of Reference Production Example 2 having the structure shown in FIG. 10 was obtained in the same manner as in Comparative Production Example 1, except that the negative electrode active material layer was formed from a negative electrode mixture comprising 58 parts by mass of a negative electrode active material (graphite), 39 parts by mass of a sulfide solid electrolyte, and 3 parts by mass of a binder.

[0139] [Production Example 2] An electricity storage element of Production Example 2 having the structure shown in Figure 9 was obtained in the same manner as in Production Example 1, except that the negative electrode active material layer was formed from a negative electrode mixture including 44 parts by mass of a negative electrode active material (silicon element: average particle size 0.8 µm), 50 parts by mass of a sulfide solid electrolyte, 3 parts by mass of a conductive agent (fibrous carbon), and 3 parts by mass of a binder.

[0140] [Production Example 3] An energy storage element of Production Example 3 having the structure shown in Fig. 12 was obtained in the same manner as in Production Example 2, except that, when producing the first laminate, a positive electrode active material layer was placed within the frame of the electrically insulating inorganic member, and then a solid electrolyte layer was further laminated by transfer onto the surfaces of the electrically insulating inorganic member and the positive electrode active material layer. That is, in Production Example 3 and Production Example 4 described later, solid electrolyte layers were laminated on both the surface of the positive electrode active material layer and the surface of the negative electrode active material layer, and the solid electrolyte layers were overlapped to obtain an energy storage element.

[0141] [Manufacturing Example 4] An energy storage element of Manufacturing Example 4 was obtained in the same manner as in Manufacturing Example 3, except that a 2.0 cm × 2.0 cm square anode active material layer in a planar view was disposed as the anode active material layer on the surface of a 2.0 cm × 2.0 cm copper foil as the anode substrate. That is, in Manufacturing Example 4, when viewed in the stacking direction, the outer edge of the anode active material layer overlaps the outer edge of the cathode active material layer, and the area of ​​the anode active material layer and the area of ​​the cathode active material layer are equal.

[0142] [Manufacturing Example 5] A 2.0 cm x 2.0 cm square cathode active material layer was disposed on the surface of a 2.5 cm x 2.5 cm aluminum foil as a cathode substrate. The cathode active material layer was formed by coating with the same composition as in Manufacturing Example 2. Next, a solid electrolyte layer and an electrically insulating inorganic member were integrally formed using the same material to cover the cathode active material layer on the cathode substrate, thereby obtaining a first laminate. The solid electrolyte layer and the electrically insulating inorganic member were formed by coating with the same material as the solid electrolyte layer in Manufacturing Example 2. A 2.1 cm x 2.1 cm square anode active material layer was disposed on the surface of a 2.1 cm x 2.1 cm copper foil as a cathode substrate, thereby obtaining a second laminate. The anode active material layer was formed with the same composition as in Manufacturing Example 2. The first laminate and the second laminate were superposed on each other so that the positive electrode active material layer and the negative electrode active material layer faced each other via the solid electrolyte layer, and hot-pressed to obtain the energy storage element of Production Example 5 having the structure shown in Fig. 13. Note that the production of each of the energy storage elements of Production Examples 5 to 7 was all carried out in an argon atmosphere with a dew point of -50°C or lower.

[0143] [Production Example 6] A storage element of Production Example 6 was obtained in the same manner as in Production Example 5, except that a negative electrode active material layer having a square shape in plan view of 2.5 cm x 2.5 cm was placed on the surface of a copper foil of 2.5 cm x 2.5 cm as a negative electrode substrate.

[0144] [Production Example 7] A storage element of Production Example 7 was obtained in the same manner as in Production Example 5, except that a negative electrode active material layer having a square shape in plan view of 2.0 cm x 2.0 cm was placed on the surface of a copper foil of 2.0 cm x 2.0 cm as a negative electrode substrate.

[0145] (Charge / Discharge Test) A charge / discharge cycle test was conducted for each of the energy storage elements of Production Example 1, Comparative Production Examples 1 and 2, and Reference Production Examples 1 and 2 at a temperature of 50°C as follows. Constant-current, constant-voltage charging was performed with a charging current of 0.1 C and a charge cut-off voltage of 4.25 V. The charge was terminated until the charging current reached 0.025 C. Subsequently, constant-current discharging was performed with a discharging current of 0.1 C and a discharge cut-off voltage of 2.5 V (3.0 V for Reference Production Examples 1 and 2). A 10-minute rest period was provided after each charge and discharge. This charge / discharge cycle was repeated for three cycles. Table 1 shows the Coulombic efficiency (Coulombic efficiency after charge / discharge cycles) at the third cycle for each energy storage element, and the percentage of the discharge capacity at the third cycle relative to the discharge capacity at the first cycle (capacity retention rate after charge / discharge cycles). Note that a short circuit occurred during the charge / discharge cycle test for the energy storage element of Comparative Production Example 1. In Table 1, "-" indicates that no measurement was performed. Furthermore, for each of the energy storage elements of Production Examples 2 to 7, a one-cycle charge-discharge test was performed in the same manner as above at a temperature of 50° C. The coulombic efficiency (initial coulombic efficiency) and discharge capacity (initial discharge capacity) of each energy storage element are shown in Table 2.

[0146]

[0147]

[0148] As shown in Table 1, the energy storage device of Comparative Production Example 1, in which an electrically insulating inorganic member was not disposed on the side surface of the positive electrode active material layer, experienced a short circuit during a charge-discharge test. Furthermore, the energy storage device of Comparative Production Example 2, in which the positive electrode active material layer and the electrically insulating inorganic member were not laminated on the same surface of the positive electrode substrate, experienced no short circuit, but exhibited a low capacity retention rate after charge-discharge cycling and a slightly low Coulombic efficiency. In contrast, the energy storage device of Production Example 1, in which an electrically insulating inorganic member was disposed on the side surface of the positive electrode active material layer and the positive electrode active material layer and the electrically insulating inorganic member were laminated on the same surface of the positive electrode substrate, experienced no short circuit and exhibited high capacity retention rate and Coulombic efficiency after charge-discharge cycling. As can be seen from the comparison between Reference Production Example 1 and Reference Production Example 2, when graphite, which exhibits minimal volume change during charge-discharge, was used as the negative electrode active material, there was little difference between the structures in terms of the occurrence of short circuits and the capacity retention rate after charge-discharge cycling. It was confirmed that the occurrence of short circuits during charge and discharge and the decrease in discharge capacity with charge and discharge cycles are problems that occur particularly in energy storage devices in which a solid electrolyte layer is interposed between a positive electrode active material layer and a negative electrode active material layer and a negative electrode active material that experiences a large volume change with charge and discharge. Furthermore, as shown in Table 2, it was confirmed that the initial Coulomb efficiency and discharge capacity were high in each of the energy storage devices of Production Examples 5 to 7 in which the electrically insulating inorganic member disposed on the side surface of the positive electrode active material layer contained a solid electrolyte.

[0149] [Comparative Example 1] A positive electrode tab was connected to the positive electrode substrate of the energy storage element obtained in Production Example 5, and a negative electrode tab was connected to the negative electrode substrate. Aluminum foil was used for the positive electrode tab, and copper foil was used for the negative electrode tab. The tabs were connected by ultrasonic welding. The energy storage element of Production Example 5 with the attached tabs was then sandwiched and sealed between a pair of sheet-like metal-resin composite films to obtain the energy storage element of Comparative Example 1. In the energy storage element of Comparative Example 1, fracture occurred near the base of the negative electrode tab (the portion overlapping the electrically insulating inorganic member when viewed in the stacking direction).

[0150] [Example 1] A positive electrode tab was connected to the positive electrode substrate of the energy storage element obtained in Production Example 5, and a negative electrode tab was connected to the negative electrode substrate. Aluminum foil was used for the positive electrode tab, and copper foil was used for the negative electrode tab. The tabs were connected by ultrasonic welding. When viewed in the stacking direction, the negative electrode tab was fixed by covering it with a resin tape as a fixing member at the portion where the electrically insulating inorganic member and the negative electrode tab overlapped. The energy storage element of Production Example 5 with the tab and fixing member attached was then sandwiched and sealed between a pair of sheet-like metal-resin composite films, thereby obtaining the energy storage element of Example 1. In the energy storage element of Example 1, no breakage of the negative electrode tab occurred.

[0151] 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.

[0152] REFERENCE SIGNS LIST 10, 110, 210, 310, 410 Energy storage element 11 Positive electrode substrate 12, 412 Positive electrode active material layer 13 Solid electrolyte layer 14, 414 Negative electrode active material layer 15 Negative electrode substrate 16, 316 Electrically insulating inorganic member 17 Negative electrode tab 18 Positive electrode tab 19 Insulating tape 20, 220 Fixing member 21 Side surface 30 Portion where electrically insulating inorganic member and negative electrode tab overlap 31 Portion where electrically insulating inorganic member is exposed 40 Corner portion 416 First electrically insulating inorganic member 417 Second electrically insulating inorganic member 418 First side surface 419 Second side surface 60 Energy storage unit 70 Energy storage device

Claims

1. An energy storage element having a laminated structure including a positive electrode substrate, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode substrate in this order, comprising a negative electrode tab connected to the negative electrode substrate, the negative electrode active material layer containing at least one negative electrode active material selected from the group consisting of metallic lithium and materials that are alloyed with lithium, an electrically insulating inorganic member being disposed on at least a portion of a side surface of the positive electrode active material layer where the positive electrode active material layer faces the negative electrode active material layer with the solid electrolyte layer interposed therebetween, the positive electrode active material layer and the electrically insulating inorganic member being laminated together on the same surface of the positive electrode substrate, there being a portion where the electrically insulating inorganic member and the negative electrode tab overlap when viewed in the stacking direction, and comprising a fixing member that fixes the negative electrode tab by covering at least a portion of the overlapping portion.

2. The energy storage element according to claim 1, wherein the positive electrode active material layer, the solid electrolyte layer, the negative electrode active material layer, and the negative electrode substrate are provided in this order on both sides of the positive electrode substrate, and the negative electrode tab is connected to each of the two negative electrode substrates.

3. The energy storage element according to claim 1 or 2, wherein the negative electrode substrate and the negative electrode tab are connected by welding.

4. The energy storage element according to claim 1 or 2, wherein the electrically insulating inorganic member contains a solid electrolyte.

5. The energy storage element according to claim 1 or 2, wherein the solid electrolyte layer and the electrically insulating inorganic member are coated layers made of the same material.

6. The energy storage device according to claim 1 or 2, wherein the fixing member is a resin member.

7. The energy storage element according to claim 1 or 2, which is an all-solid-state energy storage element.

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