Energy storage element and manufacturing method thereof

Abstract

To provide a power storage element in which generation of a gap between electrodes is suppressed.SOLUTION: A power storage element comprises a wound electrode body 2 having a flat shape and a winding core 6 disposed in a central part of the wound electrode body. The winding core has a flat shape formed by winding a belt-like sheet member and including two folding positions 7A and 7B. The winding core 6 includes a cylindrical part 8 and inner peripheral margin parts 9A and 9B which are disposed inside of the cylindrical part and in which only one end is fixed to the cylindrical part. A length of the inner peripheral margin parts is shorter than a distance from fixing positions 10A and 10B with the cylindrical part 8 to the folding position at a farther side with respect to the fixing positions.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Chargeable and dischargeable energy storage elements (secondary batteries, capacitors, etc.) are used in various devices, such as electric vehicles and other vehicles, and home appliances. Known energy storage elements include a wound electrode assembly in which a positive electrode and a negative electrode are wound around a cylindrical core in a stacked state with a separator interposed therebetween. Such an electrode assembly is housed in a container together with an electrolyte to form an energy storage element.

[0003] As a winding core used in a wound-type electrode body, Patent Document 1 describes "a winding core constructed using a sheet, characterized in that the inner surface of one end of the sheet is joined to the inner surface of a predetermined location on the sheet, while the outer surface of the other end of the sheet is joined to the outer surface of another predetermined location on the sheet, and the sheet between the two joined locations is arranged so as to span the inside of the annular portion of the sheet." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-239049 Summary of the Invention [Problem to be solved by the invention]

[0005] As shown in Fig. 11, the winding core 406 described in Patent Document 1 is formed by winding a strip-shaped sheet material around two winding shafts 62A and 62B, and has a structure including a cylindrical portion 408 and an inner peripheral excess portion 409 that is provided so as to bridge the inner surface of the cylindrical portion 408. A strip-shaped positive electrode and a strip-shaped negative electrode are superimposed on each other with a strip-shaped separator interposed therebetween and wound around this winding core 406, thereby producing a flat wound electrode body 402. The wound electrode body 402 thus produced, with the winding core 406 disposed at the center, is removed from the winding shafts 62A and 62B and stored in a container while being pressed in the thickness direction (the vertical direction in Figs. 11 and 12). However, when the wound electrode body 402, in which the winding core 406 is arranged at the center, is pressed in the thickness direction, the distance between the inner surfaces of the cylindrical portions 408 becomes small, causing wrinkles to form in the inner circumferential excess portion 409 of the winding core 406, as shown in Figure 12, and causing the load applied from the winding core 406 to the wound electrode body 402 to become uneven. When the load applied to the wound electrode body 402 is uneven, gaps occur between the electrodes in areas where the load is small, which can cause a decrease in charge / discharge performance.

[0006] The present invention has been made based on the above circumstances, and its object is to provide an energy storage element in which the occurrence of gaps between electrodes is suppressed, and a method for manufacturing such an energy storage element. [Means for solving the problem]

[0007] An energy storage element according to one aspect of the present invention comprises a wound electrode body having a flat shape and a winding core arranged in the center of the wound electrode body, the winding core having a flat shape with two fold-back positions formed by winding a strip-shaped sheet material, the winding core having a cylindrical portion and an inner surplus portion arranged inside the cylindrical portion and having only one end fixed to the cylindrical portion, the length of the inner surplus portion being shorter than the distance from the fixed position with the cylindrical portion to the fold-back position on the side farther from the fixed position.

[0008] A method for manufacturing an energy storage element according to another aspect of the present invention includes obtaining a wound electrode body having a flat shape with a winding core arranged in the center, and pressing the wound electrode body together with the winding core in the thickness direction, wherein the winding core has a flat shape with two fold positions formed by winding a strip-shaped sheet material, the winding core has a tubular portion and an inner surplus portion arranged inside the tubular portion and only one end of which is fixed to the tubular portion, and when the wound electrode body is pressed together with the winding core, the length of the inner surplus portion is shorter than the distance from the fixed position with the tubular portion to the fold position farther from the fixed position. [Effects of the Invention]

[0009] According to one embodiment of the present invention, it is possible to provide an energy storage element in which the generation of gaps between electrodes is suppressed, and a method for manufacturing such an energy storage element. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing an energy storage device according to a first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a wound electrode body and a winding core provided in the energy storage element of FIG. [Figure 3] FIG. 3 is a first explanatory diagram showing the manufacturing process of the winding core etc. of FIG. [Figure 4] FIG. 4 is a second explanatory diagram showing the manufacturing process of the winding core etc. of FIG. [Figure 5] FIG. 5 is a third explanatory diagram showing the manufacturing process of the winding core etc. of FIG. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a winding core of the second embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing a winding core of the third embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view showing a winding core of the fourth embodiment. [Figure 9] FIG. 9 is an explanatory diagram showing the manufacturing process of the winding core of FIG. [Figure 10]FIG. 10 is a schematic diagram showing an embodiment of an electricity storage device configured by assembling a plurality of electricity storage elements. [Figure 11] FIG. 11 is an explanatory diagram showing a manufacturing process for a wound electrode body and a winding core provided in a conventional energy storage element. [Figure 12] FIG. 12 is a schematic cross-sectional view showing a wound electrode body and a winding core (in a pressed state) provided in a conventional energy storage element. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] An energy storage element according to one aspect of the present invention comprises a wound electrode body having a flat shape and a winding core arranged in the center of the wound electrode body, the winding core having a flat shape with two fold-back positions formed by winding a strip-shaped sheet material, the winding core having a cylindrical portion and an inner surplus portion arranged inside the cylindrical portion and having only one end fixed to the cylindrical portion, the length of the inner surplus portion being shorter than the distance from the fixed position with the cylindrical portion to the fold-back position on the side farther from the fixed position.

[0013] In this energy storage element, the occurrence of gaps between the electrodes is suppressed. The reason for this effect is not clear, but the following reason is presumed. In this energy storage element, the length of the inner circumferential excess portion of the winding core, which is fixed to the cylindrical portion at only one end, is shorter than the distance from the fixed position to the cylindrical portion to the folded-back position on the far side from the fixed position. Therefore, even when the wound electrode body is pressed in the thickness direction and the distance between the inner surfaces of the cylindrical portion is reduced, wrinkles are unlikely to occur in the inner circumferential excess portion. For this reason, it is presumed that the load applied from the winding core to the wound electrode body is highly uniform, suppressing the occurrence of gaps between the electrodes.

[0014] The length of the inner circumferential excess portion, the distance from the fixed position to the folded-back position, the distance between two fixed positions described later, etc. refer to the length, distance, etc. when viewed in the direction of the winding axis of the wound electrode body (see, for example, Figure 2.) If the length of the inner circumferential excess portion varies in the width direction, the length of the inner circumferential excess portion shall be the shortest length. In some cases, the fixing position of the inner circumferential excess portion relative to the tubular portion is located midway between two folding positions of the tubular portion, and the distances from the fixing position of the inner circumferential excess portion to each folding position are equal. In such cases, the length of the inner circumferential excess portion of the winding core needs to be shorter than the distance from the fixing position to the tubular portion to one of the folding positions.

[0015] It is preferable that the winding core has two inner circumferential excess portions, and the total length of the two inner circumferential excess portions is shorter than the distance between the positions where the two inner circumferential excess portions are fixed to the cylindrical portion. In this case, the two inner circumferential excess portions do not overlap even when the wound electrode body is pressed in the thickness direction, making it less likely that wrinkles will occur and further suppressing the occurrence of gaps between the electrodes.

[0016] The length of the inner circumferential excess portion is preferably 10 times or more the average thickness of the sheet member. When the inner circumferential excess portion has such a sufficient length, when the winding core and the wound-type electrode body are manufactured by winding, the inner circumferential excess portion is sufficiently sandwiched between the cylindrical portion of the winding core and the opposing winding shaft, thereby making it possible to prevent the winding core from shifting.

[0017] The average thickness of the sheet-like member is the average value of thicknesses measured at any five points.

[0018] The length of the inner circumferential excess portion is preferably 3 mm or more. Even in such a case, the inner circumferential excess portion has a sufficient length, which can prevent misalignment of the winding core when manufacturing the winding core and wound electrode body by winding.

[0019] A method for manufacturing an energy storage element according to another aspect of the present invention includes obtaining a wound electrode body having a flat shape with a winding core arranged in the center, and pressing the wound electrode body together with the winding core in the thickness direction, wherein the winding core has a flat shape with two fold positions formed by winding a strip-shaped sheet material, the winding core has a tubular portion and an inner surplus portion arranged inside the tubular portion and only one end of which is fixed to the tubular portion, and when the wound electrode body is pressed together with the winding core, the length of the inner surplus portion is shorter than the distance from the fixed position with the tubular portion to the fold position farther from the fixed position.

[0020] According to this manufacturing method, it is possible to manufacture an energy storage element in which the occurrence of gaps between electrodes is suppressed.

[0021] 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.

[0022] <Electricity Storage Element: First Embodiment> The present invention relates to an energy storage element having a flattened shape, a winding core disposed at the center of the winding electrode body, an electrolyte, and a container that accommodates the winding electrode body, the winding core, and the electrolyte. As an example of the energy storage element, a nonaqueous electrolyte secondary battery will be described.

[0023] FIG. 1 shows an energy storage element 1 as an example of a non-aqueous electrolyte secondary battery. Note that this figure is a see-through view of the inside of the container. A wound electrode body 2 having a flat shape with a winding core (not shown in FIG. 1) arranged in the center is housed in a square container 3. The wound electrode body 2 is housed in the container 3 together with the winding core while being pressed in the thickness direction. The wound electrode body 2 has a positive electrode and a negative electrode that are wound with a separator sandwiched between them. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51. A non-aqueous electrolyte (not shown) is housed in the container 3 together with the wound electrode body 2. A portion of the non-aqueous electrolyte is impregnated into the interior of the wound electrode body 2.

[0024] (Wound electrode body and winding core) The structures of the wound electrode body 2 and winding core 6 provided in the energy storage device 1 will be described in detail below with reference to Fig. 2 etc. Fig. 2 shows the state in which the winding core 6 and the wound electrode body 2 are pressed in the thickness direction (the vertical direction in Fig. 2) after production, in other words, the state in which they are housed in the container 3. Fig. 2 is a cross-sectional view of the wound electrode body 2 as viewed in the direction of the winding axis, in other words, a cross-sectional view taken along a cut surface perpendicular to the winding axis.

[0025] The wound electrode body 2 is a wound electrode body formed by, for example, winding a strip-shaped first separator, a strip-shaped negative electrode, a strip-shaped second separator, and a strip-shaped positive electrode in a stacked state in this order. The wound electrode body 2 has a central region where a winding core 6 is disposed. The wound electrode body 2 can have the same configuration as conventionally known wound electrode bodies. The first separator and the second separator may be the same material. The specific configurations of the components (positive electrode, negative electrode, and separator) that make up the wound electrode body 2 will be described later.

[0026] The winding core 6 is disposed at the center of the wound electrode body 2. In other words, for example, the wound electrode body 2 is formed by winding a strip-shaped first separator, a strip-shaped negative electrode, a strip-shaped second separator, and a strip-shaped positive electrode in a stacked state in this order around the winding core 6.

[0027] The winding core 6 is formed by winding a strip-shaped sheet member. The winding core 6 is formed, for example, by winding two sheets of the sheet member. The winding core 6 has a flat shape with two folding positions 7A and 7B. The winding core 6 may be completely folded at the two folding positions 7A and 7B, or may be smoothly curved into a roughly semicircular shape in cross section.

[0028] Examples of materials for the sheet member constituting the winding core 6 include polyolefins such as polyethylene and polypropylene, and resins such as polyphenylene sulfide and polyethylene terephthalate. This sheet member may be non-porous or porous. The same separator as that constituting the wound electrode body 2 may be used as the sheet member constituting the winding core 6. The average thickness of the sheet member constituting the winding core 6 is preferably 10 μm or more and 1 mm or less, and more preferably 40 μm or more and 300 μm or less.

[0029] The winding core 6 has a cylindrical portion 8 and two inner peripheral excess portions 9A, 9B. In addition, in the winding core 6, the overlapping sheet members are fixed at two fixing positions 10A, 10B to prevent misalignment of the wound sheet members. The sheet members are fixed at these fixing positions 10A, 10B by welding, adhesive, or the like.

[0030] The cylindrical portion 8 is the main body of the winding core 6 and is formed by winding a sheet material. In the embodiment shown in FIG. 2, the cylindrical portion 8 is formed from a double layer of sheet material. However, the cylindrical portion 8 may be formed from three or more layers of sheet material by winding more layers, or from a single layer of sheet material (fourth embodiment: see FIGS. 8 and 9). When the cylindrical portion 8 is formed from a double or more layer of sheet material, the difference in the number of stacked sheets of the sheet material between the portions with and without the inner circumferential excess portions 9A, 9B, i.e., the difference in thickness between the portions of the winding core 6, is relatively small. Therefore, when inserting the wound electrode body 2 into the container 3, the wound electrode body 2 is less likely to get caught on the inner surface of the container 3, and can be easily inserted into the container 3. On the other hand, when the cylindrical portion 8 is formed from a single layer of sheet material, the winding core 6 becomes thinner, and the number of windings of the positive and negative electrodes in the wound electrode body 2 can be increased, thereby increasing the energy density per volume of the energy storage element 1.

[0031] The inner surplus portions 9A, 9B are arranged inside the cylindrical portion 8, and only one end 11A, 11B is fixed to the cylindrical portion 8 at fixing positions 10A, 10B. The inner surplus portions 9A, 9B are surplus portions on the inner circumferential side of the sheet member that do not constitute the cylindrical portion 8.

[0032] The length LA of the inner surplus portion 9A is shorter than the distance DA from the fixing position 10A of the inner surplus portion 9A to the fold-back position 7B on the far side of the fixing position 10A to the tubular portion 8. Similarly, the length LB of the inner surplus portion 9B is shorter than the distance DB from the fixing position 10B of the inner surplus portion 9B to the fold-back position 7A on the far side of the fixing position 10B to the tubular portion 8. The fold-back positions 7A and 7B are the fold-back positions on the inner surface of the tubular portion 8.

[0033] In this way, the lengths LA, LB of the inner circumferential excess portions 9A, 9B of the winding core 6 are shorter than the distances DA, DB from the fixing positions 10A, 10B with the cylindrical portion 8 to the turn-back positions 7B, 7A on the far side of the fixing positions, so wrinkles are unlikely to form in the inner circumferential excess portions 9A, 9B even when the wound electrode body is pressed in the thickness direction and the distance between the inner surfaces of the cylindrical portions is reduced. This results in a high uniformity of the load applied from the winding core 6 to the wound electrode body 2, suppressing the occurrence of gaps between the electrodes.

[0034] 2, the total length (LA+LB) of the two inner circumferential excess portions 9A, 9B is shorter than the distance (DX) between the fixing positions 10A, 10B with the respective cylindrical portions 8. Therefore, in the winding core 6, the two inner circumferential excess portions 9A, 9B do not overlap with each other, making it less likely that wrinkles will occur and further suppressing the occurrence of gaps between the electrodes of the wound electrode body 2.

[0035] The lengths LA and LB of the inner circumferential excess portions 9A and 9B are preferably 10 times or more, more preferably 20 times or more, or 30 times or more, the average thickness of the sheet member. Furthermore, the lengths LA and LB of the inner circumferential excess portions 9A and 9B are preferably 3 mm or more, more preferably 1 cm or more, or 1.5 cm or more. When the inner circumferential excess portions 9A and 9B have sufficient length, as shown in FIG. 4 (described later), when the winding core 6 and the wound electrode body 2 are manufactured by winding, the inner circumferential excess portions 9A and 9B are sufficiently sandwiched between the cylindrical portion 8 of the winding core 6 and the opposing winding shafts 62A and 62B, thereby preventing misalignment of the winding core 6. Note that a winding core without an inner circumferential excess portion is not preferable because it can significantly misalign the winding core during manufacturing.

[0036] (Method of manufacturing the winding core and wound electrode body) Next, a method for manufacturing a winding core and a wound electrode body in which this winding core is disposed at the center will be described with reference to Figures 3 to 5. First, a winding core manufacturing device for manufacturing winding cores for energy storage elements will be described with reference to Figure 3. The winding core manufacturing device includes a table 60 rotatable about a rotation axis 61, a pair of winding shafts 62A and 62B disposed on table 60 with the rotation axis 61 sandwiched between them, and sheet insertion devices 64A and 64B that insert sheet members 63 onto winding shafts 62A and 62B. The winding core manufacturing device also includes chucks 65A and 65B that press and fix sheet member 63 onto winding shafts 62A and 62B, and that weld or adhere sheet member 63.

[0037] First, as shown in Fig. 3, sheet insertion devices 64A, 64B insert sheet members 63 between both reel shafts 62A, 62B. At this time, one surface of each of the two sheet members 63 is pressed and fixed by chucks 65A, 65B so that it comes into contact with the surface of reel shafts 62A, 62B. Furthermore, the length of the inserted sheet member 63 (the length beyond the portion of sheet member 63 pressed between reel shafts 62A, 62B and chucks 65A, 65B) is adjusted so that the formed inner peripheral excess portions 9A, 9B (see Fig. 4) have a predetermined length.

[0038] When the table 60 is rotated clockwise from the state shown in FIG. 3, the sheet material 63 is wound around the circumferential surfaces of the reel shafts 62A and 62B as shown in FIG. 4. The chucks 65A and 65B are configured to be movable (retractable) so that the sheet material 63 does not get caught in the chucks 65A and 65B when the table 60 rotates half a turn from the state shown in FIG. 3. In the state shown in FIG. 4, the overlapping portions of the sheet material 63 and the reel shafts 62A and 62B (fixing positions 10A and 10B) are welded or bonded by the chucks 65A and 65B, and the sheet material 63 is cut behind the fixing positions 10A and 10B (toward the sheet insertion devices 64A and 64B). This results in a winding core 6 having a cylindrical portion 8 and two inner circumferential excess portions 9A and 9B disposed inside the cylindrical portion 8 and fixed at one end to the cylindrical portion 8 at the fixing positions 10A and 10B (see FIG. 5). In this embodiment, the table 60 is rotated once, but it may be rotated more times. In Fig. 5, part of the core manufacturing device (such as the table 60) is omitted from the illustration.

[0039] 3 to 5, a method of manufacturing the winding core 6 using two sheet members 63 has fewer steps of cutting the sheet member than, for example, the manufacturing method using one sheet member described in the fourth embodiment. Therefore, such a manufacturing method can reduce the manufacturing time.

[0040] The wound electrode body 2 shown in Fig. 5 can be manufactured by winding the positive and negative electrodes with a separator interposed therebetween by a known method around the winding core 6 manufactured in this way. From the state shown in Fig. 5, the wound electrode body 2 is pulled out from the winding shafts 62A and 63B together with the winding core 6, thereby obtaining a flat wound electrode body 2 with the winding core 6 disposed in the center. Then, by pressing this wound electrode body 2 together with the winding core 6 in the thickness direction (the vertical direction in Fig. 5 etc.), the wound electrode body 2 in the state pressed in the thickness direction shown in Fig. 2 is obtained.

[0041] Each of the members constituting the energy storage device 1 will be specifically described below.

[0042] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0043] The positive electrode substrate is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0044] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the energy storage element.

[0045] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0046] The positive electrode active material layer contains a positive electrode active material and, if necessary, optional components such as a conductive agent, a binder, a thickener, and a filler.

[0047] The positive electrode active material can be appropriately selected from known positive electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the positive electrode active material for a lithium ion secondary battery. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(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) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β). Lithium transition metal composite oxides with spinel-type crystal structures include Li x Mn2O4, Li x Ni γ Mn (2-γ)Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0048] 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 lower limit or more, the positive electrode active material becomes easier to manufacture and handle. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. 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).

[0049] 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.

[0050] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the positive electrode active material within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0051] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0052] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the content of the conductive agent within this range, the energy density of the energy storage element can be increased.

[0053] 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.

[0054] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the positive electrode active material can be stably maintained.

[0055] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0056] The filler is not particularly limited, and 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, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0057] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0058] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0059] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, alloys thereof, and carbonaceous materials are used as the material for the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foils, vapor-deposited films, meshes, and porous materials, with foils being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0060] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the energy storage element.

[0061] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as needed. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0062] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0063] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、Examples of the material include titanium-containing oxides such as TiNbO; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Among these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0064] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0065] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0066] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode is 0.7 V or higher.

[0067] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0068] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0069] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphate compound, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above-mentioned lower limit, the negative electrode active material can be easily produced or handled. By setting the average particle size of the negative electrode active material to be equal to or less than the above-mentioned upper limit, the electronic conductivity of the negative electrode active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the powder classification method can be selected from, for example, the methods exemplified for the positive electrode. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material layer may be in the form of a foil.

[0070] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0071] (separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin films are preferred from the viewpoint of strength, and nonwoven fabrics are preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0072] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the energy storage device.

[0073] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0074] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0075] (non-aqueous electrolyte) The nonaqueous electrolyte can be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolytic solution. The nonaqueous electrolytic solution contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0076] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used.

[0077] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0078] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0079] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0080] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0081] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, lithium oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0082] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0083] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0084] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0085] <Method of manufacturing an energy storage element> A manufacturing method of an energy storage element according to one embodiment of the present invention includes obtaining a wound electrode body having a flat shape with a winding core arranged in the center, and pressing the wound electrode body together with the winding core in the thickness direction, wherein the winding core has a flat shape with two fold positions formed by winding a strip-shaped sheet material, the winding core has a tubular portion and an inner surplus portion arranged inside the tubular portion and only one end of which is fixed to the tubular portion, and when the wound electrode body is pressed together with the winding core, the length of the inner surplus portion is shorter than the distance from the fixed position with the tubular portion to the fold position farther from the fixed position.

[0086] In this manufacturing method, the method described above as a "manufacturing method for a winding core and a wound electrode body" can be specifically adopted to obtain a wound electrode body having a flat shape with a winding core arranged in the center and to press the wound electrode body together with the winding core in the thickness direction. The specific form of the winding core and wound electrode body obtained by this manufacturing method is the same as that described as the winding core and wound electrode body provided in the energy storage element according to the embodiment of the present invention.

[0087] The manufacturing method may further include housing the wound electrode body, in which the core is disposed at the center and pressed in the thickness direction, in a container, preparing an electrolyte, housing the electrolyte in the container, etc. Preparing the electrolyte may be preparing the electrolyte. Housing the electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the electrolyte, the non-aqueous electrolyte solution may be injected through an injection port formed in the container, and then the injection port may be sealed.

[0088] <Electricity Storage Element: Second Embodiment> The energy storage element according to the second embodiment of the present invention includes a winding core 106 shown in Fig. 6. The energy storage element according to the second embodiment is similar to the energy storage element according to the first embodiment, except that the energy storage element according to the second embodiment includes a winding core 106 instead of the winding core 6.

[0089] The winding core 106 shown in Fig. 6 differs from the winding core 6 shown in Fig. 2 in that the length of the inner circumferential excess portions 109A, 109B is longer than the inner circumferential excess portions 9A, 9B of the winding core 6 shown in Fig. 2. As shown in Fig. 6, the length LA' of the inner circumferential excess portion 109A of the winding core 106 is shorter than the distance DA' from the position 110A at which the inner circumferential excess portion 109A is fixed to the tubular portion 108 to the turn-back position 107B on the far side from the fixation position 110A. Similarly, the length LB' of the inner circumferential excess portion 109B is shorter than the distance DB' from the position 110B at which the inner circumferential excess portion 109B is fixed to the tubular portion 108 to the turn-back position 107A on the far side from the fixation position 110B. On the other hand, the total length (LA'+LB') of the two inner circumferential excess portions 109A, 109B is longer than the distance (DX') between the fixing positions 110A, 110B with the respective tubular portion 108. In such a case, as shown in Fig. 6, the overlapping of the two inner circumferential excess portions 109A, 109B suppresses the occurrence of wrinkles, thereby suppressing the occurrence of gaps between the electrodes of the wound electrode body 2. In particular, the overlapping portion of the two inner circumferential excess portions 109A, 109B is pressed more strongly due to the greater number of stacked sheet members than in other portions, making it more difficult for wrinkles to occur in the inner circumferential excess portions 109A, 109B.

[0090] <Electricity Storage Element: Third Embodiment> The energy storage element according to the third embodiment of the present invention includes a winding core 206 shown in Fig. 7. The energy storage element according to the third embodiment is similar to the energy storage element according to the first embodiment, except that the energy storage element according to the third embodiment includes a winding core 206 instead of the winding core 6.

[0091] 7 is formed by winding a single strip-shaped sheet member, and has a tubular portion 208 and one inner surplus portion 209. The overlapping sheet members are fixed at two fixing positions 210A and 210B. The length L of the inner surplus portion 209 of the winding core 206 is shorter than the distance D from fixing position 210B where the inner surplus portion 209 is fixed to the tubular portion 208 to the turn-back position 207A on the far side from fixing position 210B.

[0092] In this way, an energy storage element including a winding core 206 having only one inner peripheral excess portion 209 is also included in the embodiments of the present invention, and can achieve the effect of suppressing the occurrence of gaps between electrodes. Furthermore, the winding core 206 in this embodiment can be formed from a single sheet member, which is excellent in productivity.

[0093] <Electricity Storage Element: Fourth Embodiment> An energy storage element according to a fourth embodiment of the present invention includes a winding core 306 shown in Fig. 8. The energy storage element according to the fourth embodiment is similar to the energy storage element according to the first embodiment except that it includes winding core 306 instead of winding core 6.

[0094] The winding core 306 shown in Fig. 8 has a cylindrical portion 308 and two inner circumferential excess portions 309A, 309B. The winding core 306 is formed by winding two sheet members, and the overlapping sheet members are fixed at two fixing positions 310A, 310B. The winding core 306 shown in Fig. 8 differs from the winding core 6 shown in Fig. 2 and other figures in that the cylindrical portion 308 is essentially made of a single sheet member. Such a winding core 306 can be manufactured in accordance with the manufacturing method of the winding core 6 shown in Figs. 3 to 5 and other figures. For example, in the state shown in FIG. 9, where table 60 is rotated a half turn clockwise from the state shown in FIG. 3, the overlapping portions of sheet member 63 and winding shafts 62A and 62B (fixed positions 310A and 310B) are welded or glued, and the rear of fixed positions 310A and 310B in sheet member 63 (toward sheet insertion devices 64A and 64B) is cut, thereby obtaining winding core 306 in the form shown in FIG. 8.

[0095] When the cylindrical portion 308 is formed from a substantially single sheet member as in the present embodiment, the core 306 can be made thinner, and it is possible to increase the number of windings of the positive electrode and negative electrode in the wound electrode body 2. Therefore, the energy storage element according to the fourth embodiment, which includes such a wound electrode body 2, can increase the energy density per volume, etc.

[0096] <Electricity storage device> The energy storage element of this embodiment can be mounted as an energy storage unit (battery module) configured by assembling a plurality of energy storage elements 1 in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one energy storage element included in the energy storage unit.

[0097] 10 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more energy storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more energy storage elements.

[0098] <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.

[0099] In the above embodiment, the case where the energy storage element is used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (e.g., a lithium ion secondary battery) has been described, but the type, shape, size, capacity, etc. of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries and capacitors such as electric double layer capacitors and lithium ion capacitors. The present invention can also be applied to energy storage elements whose electrolyte is an electrolyte other than a non-aqueous electrolyte.

[0100] In the above embodiment, a wound electrode body has been described in which a positive electrode and a negative electrode are wound in a stacked state with a separator interposed therebetween. However, the wound electrode body does not need to include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state in which a non-conductive layer is formed on the active material layer of the positive electrode or the negative electrode. Furthermore, in the energy storage element of the present invention, the sheet member constituting the winding core may be continuous with the separator constituting the wound electrode body.

[0101] The winding core provided in the energy storage element of the present invention may be manufactured by a method different from the method described in the above embodiment. For example, the winding core may be manufactured by obtaining winding core 406 having inner circumferential excess portion 409 extending across the inner surface of cylindrical portion 408 as shown in Fig. 11, and then cutting inner circumferential excess portion 409 into two pieces. In such a manufacturing method, the winding core is manufactured from a single sheet member, making it relatively easy to manufacture the winding core. [Industrial Applicability]

[0102] The present invention can be applied to an electric storage element used as a power source for automobiles, other vehicles, electronic devices, and the like. [Explanation of symbols]

[0103] 1. Energy storage element 2, 402 Wound electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 6, 106, 206, 306, 406 core 7A, 7B, 107A, 107B, 207A Folding position 8, 108, 208, 308, 408 Cylindrical part 9A, 9B, 109A, 109B, 209, 309A, 309B, 409 Excess inner circumference 10A, 10B, 110A, 110B, 210A, 210B, 310A, 310B Fixed position 11A, 11B One end 20 Energy storage unit 30 Electricity storage device 60 tables 61 Rotation axis 62A, 62B winding shaft 63 Sheet material 64A, 64B Sheet Insertion Device 65A, 65B chuck

Claims

1. a wound electrode body having a flat shape; a winding core disposed at the center of the wound electrode body; Equipped with the winding core has a flat shape with two folding positions, and is formed by winding a strip-shaped sheet member; The above winding core is A cylindrical portion; an inner peripheral excess portion disposed inside the cylindrical portion and having only one end fixed to the cylindrical portion; and The length of the inner circumferential excess portion is shorter than the distance from the fixed position with the cylindrical portion to the folded-back position on the side farther from the fixed position.

2. the winding core has two of the inner peripheral excess portions, 2. The energy storage element according to claim 1, wherein when the wound electrode body is pressed in the thickness direction together with the winding core, the total length of the two inner circumferential excess portions is shorter than the distance between the respective fixed positions with the cylindrical portion.

3. 3. The energy storage element according to claim 1, wherein the length of the inner peripheral excess portion is at least 10 times the average thickness of the sheet member.

4. 4. The energy storage element according to claim 1, wherein the inner circumferential excess portion has a length of 3 mm or more.

5. a container for accommodating the wound electrode body with the winding core disposed at the center thereof; 5. The energy storage element according to claim 1, wherein the wound electrode body is housed in the container while being pressed together with the core in a thickness direction.

6. To obtain a wound electrode body having a flat shape with a winding core disposed at the center, and Pressing the wound electrode body together with the winding core in the thickness direction. Equipped with the winding core has a flat shape with two folding positions, and is formed by winding a strip-shaped sheet member; The above winding core is A cylindrical portion; an inner peripheral excess portion disposed inside the cylindrical portion and having only one end fixed to the cylindrical portion; and a method for manufacturing an energy storage element, wherein, when the wound electrode body is pressed together with the winding core, the length of the inner circumferential excess portion is shorter than the distance from a fixed position with the cylindrical portion to the folded-back position on the side farther from the fixed position.

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