Power storage device

Abstract

To provide a technology that can suppress deformation of a case during charging.SOLUTION: A power storage device 1 includes: an electrode assembly 10 in which electrode plates are stacked in a plurality of layers; a case 20 that houses the electrode assembly 10; and a cushioning material 30 that is a plate-shaped member made of elastic resin and housed in the case 20 so as to intersect with a stacking direction of the electrode plates. In the power storage device 1, a bending elastic modulus BE of the cushioning material 30 is 30 MPa to 100 MPa. With this configuration, the cushioning material 30 can adequately absorb the expansion of the electrode assembly 10, so that deformation of the case 20 during charging can be suppressed.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a power storage device.

Background Art

[0002] In recent years, power storage devices such as lithium-ion secondary batteries have been suitably used for portable power sources such as personal computers and mobile terminals, and power sources for driving vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). This type of power storage device includes an electrode body that is a power storage element and a case that houses the electrode body.

[0003] In the secondary battery described in Japanese Patent Application Laid-Open No. 2022-74288, a heat sink is housed in the battery case. This heat sink has protrusions that contact the side surface of the electrode body (or the inner surface of the battery case). And this heat sink is composed of an elastic body. As a result, when the electrode body expands, the protrusions are crushed, and the contact area between the side surface of the electrode body (or the inner surface of the battery case) and the heat sink increases. Thereby, heat dissipation of the electrode body can be promoted.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in recent power storage devices, the electrode body has been made to have a higher capacity. Since the amount of expansion during charging of this high-capacity electrode body is extremely larger than that of the conventional one, there is a risk that the metal case may plastically deform. The technology disclosed herein has been made in view of such problems, and provides a technology capable of suppressing case deformation during charging.

Means for Solving the Problems

[0006] In view of the above problems, a power storage device having the following configuration is provided.

[0007] The power storage device disclosed herein includes an electrode body in which a plurality of electrode plates are laminated, a case that houses the electrode body, and a buffer material that is a plate-shaped member made of an elastic resin and is housed in the case so as to intersect the lamination direction of the electrode plates. And the flexural modulus B E is 30 MPa to 100 MPa.

[0008] In the power storage device having the above configuration, a buffer material having a flexural modulus of 100 MPa or less is provided. Such a buffer material elastically deforms flexibly with respect to an external force, and thus can preferably absorb the expansion of the electrode body. As a result, even when the electrode body expands greatly during charging, case deformation can be suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the drawings. Matters other than those specifically mentioned in this specification, which are necessary for the implementation of the technology disclosed herein (for example, the detailed composition of the electrolytic solution, etc.), can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common general knowledge in the relevant field. Note that the notation "A~B" indicating a range in this specification includes the meaning of "greater than A" and "less than B" in addition to the meaning of "A or more and B or less".

[0011] Note that the "power storage device" in this specification is a concept that includes a device in which a charge carrier moves between a pair of electrodes (a positive electrode and a negative electrode) to cause a charge and discharge reaction. That is, the power storage device in the technology disclosed herein includes, in addition to secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors.

[0012] <First Embodiment> 1. Configuration of the Power Storage Device Hereinafter, with reference to FIGS. 1 to 3, a first embodiment of the power storage device disclosed herein will be described. FIG. 1 is a perspective view schematically showing the power storage device according to the first embodiment. FIG. 2 is a cross-sectional view schematically showing the internal structure of the power storage device according to the first embodiment. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 as viewed in the direction of the arrow. In the drawings, the reference signs L, R, F, Rr, U, and D represent left, right, front, rear, top, and bottom, respectively. Also, the reference signs X, Y, and Z in the drawings represent the width direction, depth direction, and height direction of the power storage device, respectively. However, these are merely directions determined in advance for convenience of explanation and do not limit the technology disclosed herein.

[0013] The power storage device 1 according to the first embodiment is a lithium-ion secondary battery. As shown in FIGS. 1 to 3, this power storage device 1 includes an electrode body 10, a case 20, and a buffer material 30. Further, this power storage device 1 includes an insulating holder 40. Hereinafter, each component will be described.

[0014] (1) Electrode body The electrode body 10 is a power generation element in the power storage device 1. This electrode body 10 is configured by laminating a plurality of electrode plates in multiple layers. Specifically, the electrode body 10 includes a positive electrode plate (positive electrode plate 12) on the positive electrode side and a negative electrode plate (negative electrode plate 14) on the negative electrode side. As shown in FIG. 3, the positive electrode plate 12 is a sheet-like member facing the first side wall 22c of the case 20 described later. On the other hand, the negative electrode plate 14 is also a sheet-like member facing the first side wall 22c of the case 20. And, as shown in FIG. 2, the positive electrode plate 12 includes a positive electrode core 12a and a positive electrode active material layer 12b applied to the surface of the positive electrode core 12a. Further, the negative electrode plate 14 includes a negative electrode core 14a and a negative electrode active material layer 14b applied to the surface of the negative electrode core 14a. And the electrode body 10 in the present embodiment is a laminated electrode body in which a plurality of positive electrode plates 12 and negative electrode plates 14 are alternately laminated in the depth direction Y. Note that, as shown in FIG. 3, a separator 16, which is a sheet-like insulating member, is interposed between the positive electrode plate 12 and the negative electrode plate 14.

[0015] As shown in FIG. 2, at one end (the right side R in FIG. 2) of the electrode body 10 in the width direction X, a positive electrode connection portion 10A is formed by laminating a positive electrode core 12a to which the positive electrode active material layer 12b is not applied. On the other hand, at the other end (the left side L in FIG. 2) of the electrode body 10, a negative electrode connection portion 10B is formed by laminating a negative electrode core 14a to which the negative electrode active material layer 14b is not applied. And at the central portion of the electrode body 10 in the width direction X, a core portion 10C is formed in which the positive electrode active material layer 12b and the negative electrode active material layer 14b face each other with the separator 16 interposed therebetween.

[0016] Note that, as the materials of the respective members (such as the positive electrode, negative electrode, and separator) constituting the electrode body 10, materials that can be used in general power storage devices can be used without particular limitation. For example, a metal foil mainly composed of aluminum or the like is used for the positive electrode core 12a. Further, the positive electrode active material layer 12b contains a positive electrode active material as a main component. This positive electrode active material reversibly occludes / releases charge carriers (such as lithium ions). Examples of the positive electrode active material include lithium transition metal composite oxides and the like. For example, lithium cobalt oxide, lithium manganate, lithium nickel oxide, lithium nickel composite oxide, lithium nickel cobalt manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium iron nickel manganese composite oxide, and the like can be mentioned. Among these, from the viewpoint of battery performance, lithium nickel cobalt manganese composite oxide can be preferably used.

[0017] On the other hand, a metal foil mainly composed of copper or the like is used for the negative electrode core 14a. Further, the negative electrode active material layer 14b contains a negative electrode active material that reversibly occludes / releases charge carriers in relation to the positive electrode active material. As this negative electrode active material, carbon materials such as artificial graphite, natural graphite, and amorphous carbon can be used. Further, as other examples of the negative electrode active material, silicon materials such as Si, SiO, and SiC can be mentioned. In particular, the technology disclosed herein is preferably applied to a power storage device using a silicon material as the negative electrode active material. While the silicon material exhibits a higher capacity compared to the carbon material, the amount of expansion of the electrode body during charging tends to be extremely large. Although it will be described in detail later, even when such a silicon material is used, according to the technology disclosed herein, deformation of the case due to the expansion of the electrode body can be sufficiently suppressed.

[0018] (2) Case The case 20 is a container for housing the electrode body 10. As shown in FIG. 1, the case 20 in this embodiment is a flat box-shaped container. The case 20 is preferably a metal member having a certain strength or more. As an example of the material of the case 20, metal materials such as aluminum and aluminum alloys can be mentioned. In addition, inside the case 20, in addition to the electrode body 10, an electrolytic solution (not shown) is also housed. Since the electrolytic solution that can be used in a general power storage device can be used without particular limitation, a detailed description thereof will be omitted.

[0019] The case 20 includes a case body 22 and a sealing plate 24. The case body 22 is a box-shaped body having an upper surface opening 22a. Specifically, the case body 22 includes a bottom portion 22b that is a long rectangular plate-shaped member, a pair of first side walls 22c that extend upward U from the long sides (sides along the width direction X) of the bottom portion 22b, and a pair of second side walls 22d that extend upward U from the short sides (sides along the depth direction Y) of the bottom portion 22b. And on the upper surface of the case body 22, a planar rectangular upper surface opening 22a surrounded by the first side walls 22c and the second side walls 22d is formed. On the other hand, the sealing plate 24 is a plate-shaped member that closes the upper surface opening 22a of the case body 22. Specifically, as shown in FIGS. 2 and 3, the sealing plate 24 is fitted into the upper surface opening 22a of the case body 22. And the boundary between the case body 22 and the sealing plate 24 is joined by laser welding or the like.

[0020] In addition, a positive electrode terminal 26 and a negative electrode terminal 28 are attached to the case 20. The positive electrode terminal 26 is provided at one end (left side L in the figure) in the width direction X of the sealing plate 24. The positive electrode terminal 26 is a long conductive member extending in the height direction Z. The upper end portion U of the positive electrode terminal 26 is exposed outside the case 20. On the other hand, the lower end portion D of the positive electrode terminal 26 is connected to the positive electrode connection portion 10A inside the case 20. Also, the negative electrode terminal 28 is provided at the other end (right side R in the figure) in the width direction X of the sealing plate 24. The negative electrode terminal 28 is a long conductive member extending in the height direction Z in the same manner as the positive electrode terminal 26. The upper end portion U of the negative electrode terminal 28 is exposed outside the case 20. The lower end portion D of the negative electrode terminal 28 is connected to the negative electrode connection portion 10B inside the case 20.

[0021] (3) Insulating Holder Moreover, the power storage device 1 according to the present embodiment includes an insulating holder 40 that insulates the electrode body 10 and the case 20. The insulating holder 40 is a box-shaped member formed by bending an insulating film (sheet). The electrode body 10 is accommodated inside the box-shaped insulating holder 40. As a result, since the insulating holder 40 is interposed between the electrode body 10 and the case 20, conduction between the electrode body 10 and the case 20 can be prevented. Note that as the material of the insulating holder 40, conventionally known insulating materials can be used without particular limitation. However, considering material costs and ease of molding, etc., the insulating holder 40 is preferably composed of a resin material such as polypropylene (PP) or polyethylene (PE). Also, the thickness of the insulating holder 40 is preferably 75 μm to 200 μm, and more preferably 90 μm to 160 μm. Thereby, high levels of insulation and moldability can be achieved simultaneously.

[0022] (4) Buffer Material The buffer material 30 is a plate-shaped member made of an elastic resin. As shown in FIG. 3, the buffer material 30 is accommodated in the case 20 so as to intersect the stacking direction (the depth direction Y in FIG. 3) of the electrode plates (the positive electrode plate 12 and the negative electrode plate 14). Specifically, the buffer material 30 is a plate-shaped member extending in the height direction Z and the width direction (the direction perpendicular to the plane of FIG. 3). And the buffer material 30 is interposed between the electrode body 10 and the case 20. More specifically, the buffer material 30 is disposed outside the insulating holder 40 so as to face the second side wall 22d of the case 20. The buffer material 30 thus disposed can absorb the expansion of the electrode body 10 along the stacking direction (depth direction Y).

[0023] Here, in the power storage device 1 according to the present embodiment, the flexural modulus B of the buffer material 30 E is 30 MPa to 100 MPa. As the flexural modulus B E becomes smaller, it can be said that it is more easily elastically deformed with respect to external stress (that is, it has high cushioning properties). Therefore, the flexural modulus B EThe buffer material 30 having a bending elastic modulus B of 100 MPa or less is flexible and elastically deforms in response to an external force, and can therefore suitably absorb the expansion of the electrode assembly 10. This makes it possible to suppress deformation of the case 20 even if the electrode assembly 10 expands significantly. From the viewpoint of more suitably suppressing deformation of the case 20, the bending elastic modulus B of the buffer material 30 is set to 100 MPa or less. E The upper limit of the flexural modulus B is preferably 95 MPa or less, more preferably 85 MPa or less, further preferably 75 MPa or less, and particularly preferably 65 MPa or less. E The buffer material 30 having an extremely low bending elastic modulus B is easily deformed during the manufacture of the electricity storage device 1, and is therefore difficult to insert between the electrode assembly 10 and the case 20. For this reason, from the viewpoint of manufacturing efficiency, it is preferable to use a buffer material 30 having a bending elastic modulus B E The lower limit of the bending elastic modulus B may be set to 30 MPa or more (preferably 35 MPa or more, more preferably 40 MPa or more, even more preferably 45 MPa or more, and particularly preferably 50 MPa or more). E Examples of resin materials that satisfy this requirement include PFA resin, ABS resin, PC resin, POM resin, PET resin, PA6 resin, PP resin, and PPE resin.

[0024] The technology disclosed herein is particularly suitable for use in an electricity storage device using an electrode assembly with a large expansion ratio T2 / T1 during charging. Here, the "expansion ratio T2 / T1" is the ratio between the thickness T1 of the electrode assembly 10 at the beginning of charging (SOC=0%) and the thickness T2 of the electrode assembly 10 at the end of charging (SOC=100%). As described above, the electricity storage device 1 according to this embodiment has a flexural modulus B EThe buffer material 30 is flexibly deformed with a pressure of 100 MPa or less. Therefore, even if an electrode body 10 that expands significantly with an expansion ratio T2 / T1 of 1.017 or more (particularly 1.025 or more) is used, the deformation of the case 20 can be suppressed. In addition, according to this embodiment, even if an electrode body 10 that expands significantly with an expansion ratio T2 / T1 of 1.05 or more is used, the deformation of the case 20 can be sufficiently suppressed. However, from the viewpoint of more reliably suppressing the deformation of the case 20, it is preferable to design the expansion ratio T2 / T1 of the electrode body 10 to be 1.075 or less (more preferably 1.070 or less, even more preferably 1.065 or less, and particularly preferably 1.060 or less). The expansion ratio T2 / T1 of the electrode body 10 can be controlled by adjusting various materials (e.g., negative electrode active material) in the electrode plate.

[0025] As described above, in the electricity storage device 1 according to this embodiment, the bending elastic modulus B E In addition, in this embodiment, the thickness T E (see FIG. 3) is preferably adjusted to a predetermined range. This makes it possible to more suitably suppress deformation of the case 20 even when an electrode assembly 10 with a large expansion ratio T2 / T1 is used. For example, the thickness T E is preferably 5 mm or more, more preferably 7.5 mm or more, and particularly preferably 10 mm or more. This allows the buffer material 30 to sufficiently absorb the expansion of the electrode body 10. From the viewpoint of suppressing deformation of the case 20, the thickness T E The upper limit of the thickness T of the buffer material 30 is not particularly limited, and may be 30 mm or less, 28 mm or less, or 26 mm or less. E It is preferable to make the thickness of the buffer material 30 thin and to ensure a sufficient thickness of the electrode body 10. E is preferably 24 mm or less, more preferably 22 mm or less, and particularly preferably 20 mm or less.

[0026] Also, the cushioning material 30 preferably contains heat-diffusing particles. As described above, in the present embodiment, in order to suppress deformation of the case 20, a resin material with a low flexural modulus B E is used for the cushioning material 30. However, generally, a resin material with a low flexural modulus B E tends to have low heat diffusivity. In this case, since the cushioning material 30 functions as a heat insulating material, it may be difficult to cool the heated electrode body 10. On the other hand, by dispersing heat-diffusing particles in the cushioning material 30, excellent heat dissipation can be obtained while maintaining the flexural modulus B E at a low level. The content of the heat-diffusing particles with respect to the total mass of the cushioning material 30 is preferably 1 wt% or more, more preferably 5 wt% or more, further preferably 7.5 wt% or more, and particularly preferably 10 wt% or more. Thereby, a cushioning material 30 with more excellent heat dissipation can be obtained. On the other hand, the upper limit of the content of the heat-diffusing particles is preferably 20 wt% or less, more preferably 18 wt% or less, further preferably 16 wt% or less, and particularly preferably 15 wt% or less. Thereby, the cushioning property of the cushioning material 30 can be sufficiently maintained.

[0027] As described above, in order to suppress deformation of the case 20, the cushioning material 30 may have to use a resin material with low heat diffusivity. At this time, in order to ensure sufficient heat diffusivity of the entire cushioning material 30, it may be required to use heat-diffusing particles having a particularly high thermal conductivity. From such a viewpoint, the thermal conductivity of the heat-diffusing particles is preferably 50 W / m·K or more, more preferably 60 W / m·K or more, further preferably 70 W / m·K or more, and particularly preferably 80 W / m·K or more. On the other hand, the upper limit value of the thermal conductivity of the heat-diffusing particles is not particularly limited and may be 1500 W / m·K or less, 1000 W / m·K or less, 750 W / m·K or less, 500 W / m·K or less, or 200 W / m·K or less. Examples of materials having such a thermal conductivity include carbon materials such as carbon nanofibers, carbon nanotubes, acetylene black, and graphite, metal materials such as aluminum, nitride ceramics such as boron nitride and aluminum nitride, and carbide ceramics such as silicon carbide.

[0028] Among the above-described heat-diffusing particles, some have conductivity. Therefore, when the buffer material 30 constitutes a part of the insulating holder 40, it is preferable to adjust the addition amount of the heat-diffusing particles so that the buffer material 30 has sufficient insulation. For example, when a carbon material is used as the heat-diffusing particle, the content of the carbon material is preferably 15 wt% or less, and particularly preferably 12 wt% or less. Thereby, the insulation of the buffer material 30 can be sufficiently ensured. On the other hand, the content of the carbon material is preferably 3 wt% or more, more preferably 5 wt% or more, and particularly preferably 8 wt% or more. Thereby, a buffer material 30 having excellent heat dissipation can be obtained.

[0029] The first embodiment of the power storage device disclosed herein has been described above. However, the technology disclosed herein is not limited to the above-described embodiment. Hereinafter, other embodiments of the technology disclosed herein will be described.

[0030] <Second Embodiment> In the first embodiment, the plate-shaped buffer material 30 is disposed outside the insulating holder 40. However, the position of the buffer material 30 is not limited to the first embodiment. For example, in the second embodiment shown in FIG. 4, the insulating holder 40 and the buffer material 30 are integrated. Specifically, in the power storage device 1 according to the second embodiment, among the surfaces constituting the box-shaped insulating holder 40, the surface interposed between the electrode body 10 and the case 20 is the buffer material 30 (that is, the bending elastic modulus B E is a plate-shaped member made of an elastic resin having a value of 30 MPa to 100 MPa). Even when such a configuration is adopted, deformation of the case 20 due to expansion of the electrode body 10 can be suppressed.

[0031] <Third Embodiment> In the first and second embodiments, a buffer material 30 is interposed between the electrode body 10 and the case 20. However, the buffer material 30 only needs to be accommodated in the case 20 so as to intersect with the stacking direction of the electrode plates, and is not limited to the first and second embodiments. For example, as shown in FIG. 5, the buffer material 30 in the third embodiment is disposed inside the electrode body 10 (between the layers of the positive electrode plate 12 and the negative electrode plate 14). Specifically, in order to maintain the shape of the electrode body 10, a core material may be disposed inside the electrode body 10. The buffer material 30 (that is, the bending elastic modulus B E is a plate-like member made of an elastic resin having a value of 30 MPa to 100 MPa) can be used as the core material of the electrode body 10. Even in this case, deformation of the case 20 due to expansion of the electrode body 10 can be suppressed.

[0032] <Other Embodiments> In addition, the power storage device disclosed herein also includes forms not illustrated in FIGS. 1 to 5. For example, in the first to third embodiments, the number of buffer materials 30 accommodated in the case 20 is one. However, the number of buffer materials is not particularly limited and can be appropriately increased or decreased. For example, a pair of buffer materials may be prepared, and the electrode body may be interposed between the pair of buffer materials. The buffer material having such a configuration can also sufficiently absorb the expansion of the electrode body and suppress the deformation of the case. In the mode of using a plurality of buffer materials, the thickness T E of the buffer material means the total thickness of the plurality of buffer materials.

[0033] In addition, the power storage device 1 according to each of the above-described embodiments uses a stacked electrode body as the electrode body 10. However, the “stacking of electrode plates” in this specification includes not only a mode of stacking a large number of electrode plates but also a mode of winding and overlapping a long strip-shaped electrode plate. That is, the power storage device disclosed herein may use a wound electrode body as the electrode body. Further, as shown in FIGS. 3 to 5, in the power storage device 1 according to each of the above-described embodiments, one electrode body 10 is accommodated in the case 20. However, the number of electrode bodies in the technology disclosed herein is not particularly limited and may be plural.

[0034] Although the technologies disclosed herein have been described in detail above, these are merely examples and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes of the specific examples exemplified above. That is, the technologies disclosed herein include the forms described in Items 1 to 9 below.

[0035] [Item 1] An electrode body in which a plurality of electrode plates are laminated, A case for housing the electrode body, A buffer material which is a plate-like member made of an elastic resin and is housed in the case so as to intersect the lamination direction of the electrode plates and a power storage device in which the flexural modulus B E of the buffer material is 30 MPa to 100 MPa.

[0036] [Item 2] The expansion ratio T2 / T1 of the electrode body, which is the ratio of the thickness T2 of the electrode body in the late stage of charging to the thickness T1 of the electrode body in the initial stage of charging, is 1.017 to 1.075. The power storage device according to Item 1.

[0037] [Item 3] The electrode body contains a silicon material as a negative electrode active material. The power storage device according to Item 2.

[0038] [Item 4] The thickness T E of the buffer material is 5 mm or more. The power storage device according to any one of Items 1 to 3.

[0039] [Item 5] The buffer material further contains heat diffusion particles. The power storage device according to any one of Items 1 to 4.

[0040] [Item 6] The thermal conductivity of the heat diffusion particles is 50 W / m·K to 1500 W / m·K. The power storage device according to Item 5.

[0041] [Item 7] The power storage device according to item 5 or 6, wherein the content of the heat diffusion particles relative to the total mass of the buffer material is 1 wt% to 20 wt%.

[0042] [Item 8] The power storage device according to any one of items 1 to 7, wherein the buffer material is interposed between the electrode body and the case.

[0043] [Item 9] The power storage device according to any one of items 1 to 8, wherein the buffer material is interposed between layers of the plurality of electrode plates.

Explanation of reference numerals

[0044] 1 Power storage device 10 Electrode body 12 Positive electrode plate 12a Positive electrode core 12b Positive electrode active material layer 14 Negative electrode plate 14a Negative electrode core 14b Negative electrode active material layer 16 Separator 20 Case 22 Case body 24 Sealing plate 26 Positive electrode terminal 28 Negative electrode terminal 30 Buffer material 40 Insulating holder

Claims

1. An electrode body in which a plurality of electrode plates are stacked, a case that houses the electrode body, and a buffer material that is a plate-shaped member made of an elastic resin and is housed in the case so as to intersect the stacking direction of the electrode plates comprising The flexural modulus B of the buffer material Ｅ is 30 MPa to 100 MPa, the power storage device.

2. The thickness T of the electrode body at the initial stage of charging １ to the thickness T of the electrode body at the later stage of charging ２ The expansion ratio T of the electrode body, which is the ratio ２ / T １ is 1.017 to 1.

075. The power storage device according to claim 1

3. The power storage device according to claim 2, wherein the electrode body contains a silicon material as a negative electrode active material.

4. The thickness T of the buffer material Ｅ The power storage device according to claim 2, wherein the thickness is 5 mm or more.

5. The power storage device according to claim 1, wherein the buffer material further contains heat diffusion particles.

6. The power storage device according to claim 5, wherein the heat conductivity of the heat diffusion particles is 50 W / m·K to 1500 W / m·K.

7. The power storage device according to claim 6, wherein the content of the heat diffusion particles with respect to the total mass of the buffer material is 1 wt% to 20 wt%.

8. The power storage device according to any one of claims 1 to 7, wherein the buffer material is interposed between the electrode body and the case.

9. The power storage device according to any one of claims 1 to 7, wherein the buffer material is interposed between layers of the plurality of electrode plates.

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