All-solid-state battery cell

Abstract

The purpose of the present invention is to provide an all-solid-state battery cell in which lithium does not leak to the outside even when the lithium melts. An all-solid-state battery cell according to the present invention is provided with: an electrode laminate; an exterior body that accommodates the electrode laminate; and a pair of insulating shape holders that hold the shape of the exterior body so as to secure a space between the exterior body and the electrode laminate even in a state in which the inner region of the exterior body is decompressed, the pair of shape holders each having a flat plate-shaped flat plate portion and a side surface portion joined to an end portion of the flat plate portion, and a flat plate portion located at the outermost portion in the stacking direction of the electrode stack, the flat plate portion having an outer shape larger than the outer shape of the electrode stack when viewed along the stacking direction, and the tip end surface of the side surface portion of one shape holder facing the tip end surface of the side surface portion of the other shape holder.

Description

Technical Field

[0001] The present invention relates to an all-solid-state battery cell. Background Art

[0002] It is known that there is an all-solid-state battery having a structure in which an electrode stack is housed in an outer casing. An invention related to a method for manufacturing such an all-solid-state battery is described in Patent Document 1 (JP2017-117696A). Patent Document 1 describes a method for manufacturing an all-solid-state battery as follows: the generation of wrinkles in the outer casing at the portion in contact with the stacking direction surface of the stack can be suppressed, while the volume energy density is improved. The document describes a manufacturing method having the following steps: a step of arranging the stack in the outer casing; a step of sealing the peripheral edge of the stack arranged in the outer casing in a reduced pressure atmosphere; a step of pressurizing the outer casing against the stacking direction surface of the stack while maintaining the reduced pressure atmosphere after the sealing step using a pressurizing member; and a release step of changing the atmosphere from a reduced pressure atmosphere to an atmospheric pressure atmosphere while maintaining the pressurization by the pressurizing member. Summary of the invention

[0003] In the all-solid-state battery described in Patent Document 1, the stacked body disposed in the outer casing is sealed in a reduced pressure atmosphere, so that the outer casing and the stacked body are in close contact with each other, that is, substantially no space is formed between the outer casing and the stacked body.

[0004] However, as an all-solid-state battery, it is known that there is a battery using metallic lithium as the negative electrode active material. In such an all-solid-state battery, for example, there is a situation where, in the event of a fault (short circuit, etc.), the metallic lithium is heated to a melting point. As a result, there is a possibility that the molten lithium flows out. As described in Patent Document 1, when there is no space between the outer casing and the laminate, there is a possibility that the molten lithium leaks out to the outside.

[0005] It is desirable that even if lithium melts, the melted lithium does not leak to the outside. Therefore, an object of the present invention is to provide an all-solid-state battery cell in which lithium does not leak to the outside even if lithium melts.

[0006] The all-solid-state battery of the present invention comprises an electrode stack, an outer casing, and a pair of shape retainers. The electrode stack includes a positive electrode, a solid electrolyte layer, and a negative electrode, and is constructed in a manner using metallic lithium as a negative electrode active material. The outer casing is flexible and accommodates the electrode stack. A pair of shape retainers are arranged in the outer casing in a manner of being located at both ends in the stacking direction of the electrode stack. The pair of shape retainers maintain the shape of the outer casing so that space is ensured between the outer casing and the electrode stack even when the internal area of ​​the outer casing is depressurized. The pair of shape retainers respectively have a flat plate portion and a side portion connected to the end of the flat plate portion. The flat plate portion is arranged at the end of the electrode stack in the stacking direction. When viewed along the stacking direction, the outer shape of the flat plate portion is larger than the outer shape of the electrode stack. The top end surface of the side surface portion of one shape retainer is opposite to the top end surface of the other shape retainer. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic cross-sectional view showing the all-solid-state battery module according to the first embodiment.

[0008] Figure 2 The diagram is a cross-sectional view and a plan view schematically showing the structure of a battery cell.

[0009] Figure 3 This is a schematic cross-sectional view showing the structure of a battery cell when metallic lithium is melted.

[0010] Figure 4 It is a schematic cross-sectional view showing a battery unit according to the second embodiment.

[0011] Figure 5 It is a schematic cross-sectional view showing a battery unit according to a third embodiment.

[0012] Figure 6 It is a cross-sectional view and a plan view schematically showing a battery cell according to a fourth embodiment. DETAILED DESCRIPTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0014] (First embodiment)

[0015] Figure 1 1 is a schematic cross-sectional view showing an all-solid-state battery module 9 using an all-solid-state battery cell 1 (hereinafter, sometimes simply referred to as a battery cell 1) according to the present embodiment. Figure 1As shown, the all-solid-state battery module 9 has a plurality of battery cells 1 and a pair of end plates 8. The plurality of battery cells 1 are stacked. The pair of end plates 8 are configured to clamp the plurality of stacked battery cells 1 in the stacking direction. The pair of end plates 8 are pressurized in a compressive manner by a pressurizing mechanism not shown. As a result, a compressive load is applied to the plurality of battery cells 1.

[0016] However, in this embodiment, the structure of each battery cell 1 is studied. Hereinafter, the structure of the battery cell 1 will be described.

[0017] Figure 2 1 is a cross-sectional view (a) and a top view (b) schematically showing the structure of the battery cell 1. Figure 3 It is a schematic cross-sectional view showing the structure of the battery cell 1 when lithium is melted.

[0018] like Figure 2 As shown, the battery cell 1 has an electrode stack 2, an outer casing 3, a pair of shape retainers (4a and 4b), and collector ears (6-1 and 6-2). The electrode stack 2 is arranged in the outer casing 3. The electrode stack 2 is constructed in a manner using metallic lithium as a negative electrode active material. A pair of shape retainers (4a and 4b) are also arranged in the outer casing 3. A pair of shape retainers (4a and 4b) maintain the shape of the outer casing 3 so that even if the internal area of ​​the outer casing 3 is depressurized, the outer casing 3 is not in close contact with the electrode stack 2. That is, a space is ensured between the outer casing 3 and the electrode stack 2. Specifically, a space is ensured on both sides of the electrode stack 2 in the direction of connecting the collector ears 6-1 and the collector ears 6-2.

[0019] According to the above-mentioned structure, even if the metallic lithium contained in the electrode stack 2 is melted, the melted lithium is contained in the space between the outer casing 3 and the electrode stack 2 (see Figure 3 ). Therefore, the melted lithium is prevented from leaking to the outside of the outer casing 3.

[0020] Hereinafter, each part of the battery unit 1 will be described in detail.

[0021] The electrode stack 2 has a structure in which a plurality of monomers are stacked. Each monomer has a positive electrode, a solid electrolyte layer, and a negative electrode. The solid electrolyte layer is sandwiched between the positive electrode and the negative electrode. In addition, as already described, the electrode stack 2 is constructed in a manner using metallic lithium as a negative electrode active material. In such an electrode stack 2, as already described, when the temperature reaches an extremely high temperature, there is a possibility that lithium melts and leaks out of the electrode stack 2.

[0022] In addition, the "electrode stack" of the present invention also includes an electrode stack in which no negative electrode exists during discharge and a negative electrode is generated during charge. That is, the electrode stack 2 may be an electrode stack in which no lithium exists on the negative electrode side during discharge and lithium moves from the positive electrode side to the negative electrode side during charge to form a negative electrode.

[0023] In the electrode stack 2, a current collector (5-1 or 5-2) is sandwiched between adjacent monomers. One of the current collectors 5-1 and 5-2 is a positive electrode current collector, and the other is a negative electrode current collector. A plurality of current collectors (5-1 and 5-2) are provided. The current collectors (5-1 and 5-2) protrude from the side of the electrode stack 2, converge into one at the end thereof, and are connected to the collector ears (6-1 and 6-2).

[0024] The collector tab 6-1 and the collector tab 6-2 are provided to electrically connect the electrode stack 2 to the outside. One end of each collector tab (6-1 and 6-2) is arranged inside the outer casing 3, and the other end is arranged outside the outer casing 3.

[0025] The outer casing 3 is provided for the purpose of protecting the electrode stack 2. The outer casing 3 is flexible and accommodates the electrode stack 2. Specifically, the outer casing 3 is composed of a pair of sheets. The pair of sheets are arranged on the upper and lower sides of the electrode stack 2 and bonded at the sealing portion 7 on the side of the electrode stack 2. In addition, the outer casing 3 partially clamps the collector tab 6-1 and the collector tab 6-2. In the portion where the collector tab 6-1 and the collector tab 6-2 are provided, the outer casing 3 is sealed by the collector tab 6-1 and the collector tab 6-2.

[0026] The material of the outer casing 3 is not particularly limited, and for example, an aluminum film or the like can be used.

[0027] As described above, the pair of shape retainers (4a and 4b) is provided to ensure a space between the outer casing 3 and the electrode stack 2 even when the inner region of the outer casing 3 is depressurized. The pair of shape retainers (4a and 4b) is provided so as to be located at the two outermost portions (uppermost portion and lowermost portion) of the electrode stack 2 in the stacking direction.

[0028] Specifically, a pair of shape retaining members (4a and 4b) respectively have a flat plate portion (4a-1, 4b-1) and a side surface portion (4a-2, 4b-2).

[0029] Each flat plate portion (4a-1, 4b-1) is in the shape of a flat plate. The flat plate portions (4a-1 and 4b-1) are arranged on the upper surface and the lower surface of the electrode stack 2. When viewed along the stacking direction, the outer shape of each flat plate portion (4a-1, 4b-1) is larger than the outer shape of the electrode stack 2. In addition, the outer shape of the electrode stack 2 referred to here refers to the outer shape of the portion (active area) where the positive electrode, the solid electrolyte layer, and the negative electrode overlap.

[0030] Specifically, each flat plate portion (4a-1, 4b-1) is substantially rectangular in shape and is larger than the electrode stack 2 in its length direction (i.e., the direction connecting the collector tab 6-1 and the collector tab 6-2). In addition, in the width direction, the outer shape of each flat plate portion (4a-1, 4b-1) may be larger than the outer shape of the electrode stack 2 or may be the same as the outer shape of the electrode stack 2.

[0031] Each side portion (4a-2, 4b-2) is connected to the end of each flat plate portion (4a-1, 4b-1) and extends in a manner of standing up from each flat plate portion (4a-1, 4b-1). The side portion 4a-2 and the side portion 4b-2 are arranged in a manner that their top ends face each other. In other words, the top end of the side portion 4a-2 overlaps with the top end of the side portion 4b-2 in the stacking direction.

[0032] In addition, each shape retainer (4a and 4b) is formed of an insulating material. In addition, each shape retainer (4a and 4b) is formed of a material having such strength that it does not deform even when the internal area of ​​the outer body 3 is depressurized. Moreover, each shape retainer (4a and 4b) is formed of a material having such heat resistance that it is not damaged even when the metal lithium is melted at a high temperature. As such a material, for example, a heat-resistant resin or the like can be used.

[0033] As described above, in this embodiment, a pair of shape retainers (4a and 4b) are used to ensure a space on the side of the electrode stack 2. Therefore, even if the metal lithium melts, the melted lithium is contained in the space. Therefore, the melted lithium is unlikely to leak to the outside of the outer body 3.

[0034] Next, an example of a method for manufacturing the battery cell 1 of the present embodiment is described. When manufacturing the above-mentioned battery cell 1, first, an electrode stack 2 is prepared, and the current collectors (5-1 and 5-2) are connected to the current collector ears (6-1 and 6-2). Next, a pair of shape retainers (4a and 4b) are arranged above and below the electrode stack 2. Moreover, a pair of sheets for forming the outer body 3 are arranged in a manner covering the pair of shape retainers (4a and 4b). Next, the area inside the pair of sheets is depressurized, and at the same time, the pair of sheets is pressurized, and the pair of sheets are sealed at the sealing portion 7. Thus, the battery cell 1 can be obtained. Among them, when the pressure is reduced, the sheet for forming the outer body 3 is sucked inward. Therefore, it is possible to eliminate excess space and reduce the size of the battery cell 1. On the other hand, since a pair of shape retainers (4a and 4b) are provided, space is ensured on the side of the electrode stack 2.

[0035] In addition, in this embodiment, a space is formed on the side of the electrode stack 2. Preferably, a space is formed on the side of the electrode stack 2 where the collector tab 6-1 and the collector tab 6-2 are provided. The volume energy density of the battery cell 1 is reduced by an amount corresponding to the space. However, if Figure 1 As shown, the all-solid-state battery is usually provided as an all-solid-state battery module 9 formed by stacking a plurality of battery cells 1. In the all-solid-state battery module 9, a collector ear or the like is usually arranged in the area on the side of each battery cell 1, which becomes a dead angle. Therefore, even if a space is formed on the side of the battery cell 1 (especially, on the collector ear side), the volume energy density of the all-solid-state battery module 9 is substantially unchanged. That is, there is no disadvantage caused by forming a surplus space.

[0036] However, in order to make the battery reaction efficient in the all-solid-state battery, it is necessary to apply a load to the electrode stack 2. Therefore, it is preferable to study the length of the side portions (4a-2 and 4b-2) in a manner that applies pressure (load) to the electrode stack 2. Specifically, the length of the side portions (4a-2 and 4b-2) along the stacking direction (in Figure 2 The sum of the lengths (a1+a2) of the side portions (4a-2 and 4b-2) is set to be less than the thickness of the electrode stack 2 when the SOC (State Of Charge) is 0%. "SOC" is a parameter indicating the state of charge of the electrode stack 2. The state in which the SOC is 0% refers to a fully discharged state. The electrode stack 2 using metallic lithium as the negative electrode active material expands during charging and contracts during discharge. In other words, the thickness of the electrode stack 2 is minimum in the fully discharged state. By setting the sum of the lengths (a1+a2) of the side portions (4a-2 and 4b-2) to be less than the thickness of the electrode stack 2 when the SOC is 0%, a gap is formed between one side portion 4a-2 and the other side portion 4b-2 except when fully discharged (see Figure 2 ). Thus, one shape retainer 4a does not interfere with another shape retainer 4b. The pressure applied to the battery cell 1 is applied to the electrode stack 2 via each shape retainer (4a and 4b). The application of pressure is not hindered by each shape retainer (4a and 4b), and therefore, the battery reaction is not hindered.

[0037] It is more preferable to set the total length (a1+a2) of the side portions (4a-2 and 4b-2) to be the same as the thickness of the electrode stack 2 when the SOC is 0%. In addition, the so-called "same" here also includes the concept of being approximately the same. By adopting such a structure, it is possible to more reliably prevent the molten lithium from leaking to the outside of the outer casing 3. That is, if the lithium melts and leaks from the electrode stack 2, the thickness of the electrode stack 2 becomes smaller. If the total length (a1+a2) of the side portions (4a-2 and 4b-2) is equal to the thickness of the electrode stack 2 when the SOC is 0%, then when the thickness of the electrode stack 2 becomes smaller due to the melting of lithium, the gap between the side portions (4a-2) and the side portions (4b-2) is closed (refer to Figure 3 As a result, it is difficult for the molten lithium to reach the sealing portion 7 which is prone to leakage, and the leakage of lithium can be prevented more reliably.

[0038] Preferably, the size of the remaining space formed inside the outer casing 3 is larger than the volume of the melted metal lithium in the fully charged state. By adopting such a structure, even if the metal lithium is completely melted, the melted lithium is completely contained in the space inside the outer casing 3. In addition, the volume V of the melted metal lithium is Li (cm 3 ) can be calculated using the following formula.

[0039] [Formula 1]

[0040]

[0041] In the above formula, Q is the cell capacity (Ah). r is the A / C ratio. F is the Faraday constant, which is 9.65×10 4 [C / mol]. M is the molar mass of lithium, which is 6.94 [g / mol]. d1 is the density of molten lithium, which is 0.512 [g / cm 3 ]

[0042] The first embodiment has been described above. Hereinafter, the configuration and effects of the present embodiment will be summarized with reference to representative configurations and effects.

[0043] The battery cell 1 of this embodiment has an electrode stack 2, an outer casing 3, and a pair of insulating shape retainers (4a and 4b). The electrode stack includes a positive electrode, a solid electrolyte layer, and a negative electrode, and is constructed in a manner using metallic lithium as a negative electrode active material. The outer casing 3 is flexible and accommodates the electrode stack 2. A pair of shape retainers (4a and 4b) are arranged in the outer casing 3 in a manner of being located at the two outermost parts in the stacking direction of the electrode stack 2. In addition, the pair of shape retainers (4a and 4b) maintain the shape of the outer casing 3 so that a space is ensured between the outer casing 3 and the electrode stack 2 even when the internal area of ​​the outer casing 3 is depressurized. The pair of shape retainers (4a and 4b) respectively have a flat plate portion (4a-1, 4b-1) and a side portion (4a-2, 4b-2) connected to the end of the flat plate portion (4a-1, 4b-1). The flat plate portion (4a-1, 4b-1) is located at the outermost portion in the stacking direction of the electrode stack 2. Furthermore, when viewed along the stacking direction, the outer shape of the flat plate portion (4a-1, 4b-1) is larger than the outer shape of the electrode stack 2. The top end surface of the side surface portion (4a-2) of one shape retainer 4a is opposite to the top end surface of the other shape retainer 4b. According to such a structure, a space is formed between the outer casing 3 and the electrode stack 2, so that even if the metal lithium is melted, the lithium is contained in the space and does not leak to the outside of the outer casing 3.

[0044] In a preferred embodiment, the total length of the side portions (4a-2, 4b-2) of the pair of shape retainers (4a and 4b) along the stacking direction is less than the thickness of the electrode stack 2 when the SOC is 0%. By adopting such a structure, the pair of shape retainers (4a and 4b) do not interfere with each other. The pressure for pressurizing the battery cell 1 is not hindered by the pair of shape retainers (4a and 4b) and is also applied to the electrode stack 2. Therefore, the battery reaction is not hindered.

[0045] In a preferred embodiment, the total length of the side portions (4a-2, 4b-2) of the pair of shape retainers (4a and 4b) along the stacking direction is equal to the thickness of the electrode stack 2 when the SOC is 0%. By adopting such a structure, when the molten metal lithium leaks out of the electrode stack 2, the gap between the side portions (4a-2 and 4b-2) is closed. Therefore, the molten metal lithium is more difficult to leak to the outside of the outer body 3.

[0046] In a preferred embodiment, a surplus space having a larger volume than that of a case where the metallic lithium present in a fully charged state is melted is formed inside the outer casing 3. By adopting such a structure, even if all the metallic lithium contained in the electrode stack 2 is melted, all the melted lithium can be accommodated in the surplus space. Therefore, the melted metallic lithium can be more reliably prevented from leaking to the outside of the outer casing 3.

[0047] (Second embodiment)

[0048] Next, the second embodiment will be described. In the following description, since the same configuration as that of the first embodiment can be adopted, detailed description will be omitted.

[0049] Figure 4 2 is a schematic cross-sectional view showing a battery unit 1 according to a second embodiment. In this embodiment, the outer casing 3 is bonded to each flat plate portion (4a-1 and 4b-1). Figure 4 In the figure, the bonding portion is indicated as bonding portion (10a-1 and 10b-1). According to such a structure, even when the battery cell 1 is pressurized, the outer casing 3 and the flat plate portion (4a-1 and 4b-1) do not slide. Therefore, wrinkles are less likely to occur in the outer casing 3.

[0050] In addition, each flat plate portion (4a-1 and 4b-1) may be bonded to the exterior body 3 over the entire surface or may be bonded to the exterior body 3 only partially.

[0051] In a preferred embodiment, the outer casing 3 is bonded to each flat plate portion (4a-1 and 4b-1), but not bonded to each side portion (4a-2 and 4b-2). According to such a structure, when the electrode stack 2 shrinks, the outer casing 3 can bend to the outside of the lateral direction of the electrode stack 2. Therefore, the outer casing 3 can easily follow the expansion and contraction of the electrode stack 2.

[0052] (Third embodiment)

[0053] Next, a third embodiment will be described. In addition, since the same configuration as that of the above-described embodiment can be adopted, detailed description will be omitted.

[0054] Figure 5 : is a schematic cross-sectional view showing a battery cell 1 according to the third embodiment. In this embodiment, a gap is provided between the side portion 4a-2 and the side portion 4b-2 (the gap may be closed when fully discharged). That is, the total length of the side portions (4a-2 and 4b-2) along the stacking direction is less than or equal to the thickness of the electrode stack 2 when the SOC is 0%.

[0055] Furthermore, the outer casing 3 is bonded to the top end surfaces of the side surfaces (4a-2 and 4b-2). Figure 5 In the figure, the bonding portion is indicated as bonding portion 12.

[0056] As a result of the outer body 3 being bonded to the top end surfaces of the side portions (4a-2, 4b-2), the outer body 3 has a shape that is recessed inward between the side portions (4a-2, 4b-2) and the sealing portion 7. In other words, the outer body 3 is bonded to the pair of shape retaining members (4a and 4b) in a manner that rolls up the side portions (4a-2, 4b-2).

[0057] According to this embodiment, the outer casing 3 can bend between the side portion 4a-2 and the side portion 4b-2. Therefore, the outer casing 3 is easy to follow the expansion and contraction of the electrode stack 2. Among them, when the electrode stack 2 shrinks, the outer casing 3 does not bend outward, but bends inward. Therefore, when shrinking, the area of ​​the battery cell 1 when viewed along the stacking direction does not increase. Therefore, it is preferred for the purpose of space saving.

[0058] In addition, in this embodiment, the outer casing 3 may be bonded to each flat plate portion (4a-1 and 4b-1) or may not be bonded to each flat plate portion (4a-1 and 4b-1). In a preferred embodiment, the outer casing 3 is bonded to each flat plate portion (4a-1 and 4b-1).

[0059] In addition, the outer casing 3 may be bonded to the outer surface of each side surface portion (4a-2 and 4b-2) or not bonded. In a preferred embodiment, the outer casing 3 is not bonded to the outer surface of each side surface portion (4a-2 and 4b-2).

[0060] (Fourth embodiment)

[0061] Next, a fourth embodiment will be described. In addition, since the same configuration as that of the above-described embodiment can be adopted, detailed description will be omitted.

[0062] Figure 6 1 and 2 are a cross-sectional view (a) of a battery cell 1 according to a fourth embodiment and a plan view (b) showing the shape of a flat plate portion 4a-1. In this embodiment, an opening 11 is provided in each of the flat plate portions (4a-1 and 4b-1).

[0063] According to the present embodiment, each shape retaining member (4a and 4b) can be made lighter by providing the opening 11. Thus, the weight energy density of the battery cell 1 can be improved.

[0064] The position of the opening 11 is not particularly limited. However, it is preferred that the opening 11 has an outer shape larger than the outer shape of the electrode stack 2 when viewed along the stacking direction. In other words, the outer shape of the opening 11 is located outside the outer shape of the electrode stack 2 when viewed along the stacking direction.

[0065] As described above, since the outer shape of the opening 11 is larger than the outer shape of the electrode stack 2, each shape retainer (4a and 4b) does not interfere with the electrode stack 2. The upper surface and the lower surface of the electrode stack 2 are in direct contact with the outer body 3. The position of the outer surface of each shape retainer (4a and 4b) in the thickness direction is consistent with the position of the upper surface and the lower surface of the electrode stack 2. Therefore, although a pair of shape retainers (4a and 4b) are provided, the thickness of the battery cell 1 in the stacking direction does not increase. Thus, the volume energy density is not impaired.

[0066] Furthermore, when the outer shape of the opening 11 is larger than the outer shape of the electrode stack 2, the pair of shape retainers (4a and 4b) cannot be supported by the electrode stack 2. However, by bonding the flat plate portions (4a-1 and 4b-1) to the outer casing 3, the pair of shape retainers (4a and 4b) can be supported by the outer casing 3.

[0067] As mentioned above, although the embodiment of the present invention has been described, the above embodiment merely shows a part of application examples of the present invention, and the protection scope of the present invention is not intended to be limited to the specific structure of the above embodiment.

[0068] This application claims priority based on Japanese Patent Application No. 2022-100726 filed with the Japan Patent Office on June 22, 2022, the entire contents of which are incorporated herein by reference.

Claims

1. An all-solid-state battery cell, comprising: An electrode stack comprising a positive electrode, a solid electrolyte layer, and a negative electrode, wherein metallic lithium is used as a negative electrode active material; an outer casing having flexibility and housing the electrode stack; and a pair of insulating shape retaining members, which are provided in the outer casing so as to be located at the two outermost parts in the stacking direction of the electrode stack, and maintain the shape of the outer casing so as to ensure a space between the outer casing and the electrode stack even when the internal area of ​​the outer casing is depressurized, The pair of shape retaining members respectively have: a flat plate portion; and a side portion joined to an end of the flat plate portion, The flat plate portion is located at the outermost portion in the stacking direction of the electrode stack. When viewed along the stacking direction, the outer shape of the flat plate portion is larger than the outer shape of the electrode stack. The top end surface of the side surface portion of one of the shape retaining members faces the top end surface of the other shape retaining member.

2. The all-solid-state battery cell according to claim 1, wherein: The flat plate portion is provided with an opening.

3. The all-solid-state battery cell according to claim 2, wherein: When viewed along the stacking direction, the outer shape of the opening is located outside the outer shape of the electrode stack.

4. The all-solid-state battery cell according to claim 1 or 2, wherein: The outer casing is bonded to the flat plate portion.

5. The all-solid-state battery cell according to claim 4, wherein: The exterior body is not bonded to the side surface portion.

6. The all-solid-state battery cell according to claim 1 or 2, wherein: The exterior body is bonded to the top end surface of the side surface portion.

7. The all-solid-state battery cell according to claim 1 or 2, wherein: The total length of the side surface portions of the pair of shape retaining members along the stacking direction is equal to or less than the thickness of the electrode stack when the SOC is 0%.

8. The all-solid-state battery cell according to claim 1 or 2, wherein: The total length of the side surface portions of the pair of shape retaining members along the stacking direction is equal to the thickness of the electrode stack when the SOC is 0%.

9. The all-solid-state battery cell according to claim 1 or 2, wherein: A surplus space having a larger volume than that in the case where the metallic lithium present in the fully charged state is melted is formed inside the outer casing.

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