JP7779055B2 - Energy storage element and manufacturing method thereof - Google Patents

Description

The present invention relates to an energy storage element and a method for manufacturing the same.

Chargeable and dischargeable energy storage elements (secondary batteries, capacitors, etc.) are used in a variety of devices, including electric vehicles and other vehicles, and home appliances. A well-known energy storage element is one that includes 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 between them. This electrode assembly is housed in a container together with an electrolyte to form an energy storage element.

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."

JP 2014-239049 A

As shown in Figure 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 to bridge the inner surface of the cylindrical portion 408. A strip-shaped positive electrode and a strip-shaped negative electrode are wound around the winding core 406 in a stacked state with a strip-shaped separator interposed therebetween, 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 Figures 11 and 12). However, when the wound electrode body 402, which is arranged in the center, is pressed in the thickness direction by the winding core 406, the distance between the inner surfaces of the cylindrical portions 408 becomes smaller, as shown in Figure 12, causing wrinkles to form in the inner circumferential excess portion 409 of the winding core 406, and the load applied from the winding core 406 to the wound electrode body 402 becomes uneven. If the load applied to the wound electrode body 402 is uneven, gaps will form between the electrodes in areas where the load is light, which may cause a decrease in charge/discharge performance.

The present invention was made based on the above circumstances, and its purpose 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.

An energy storage element according to one aspect of the present invention comprises a flat wound electrode body and a winding core arranged in the center of the wound electrode body. The winding core has a flat shape with two fold-back positions and is formed by winding a strip-shaped sheet material. The winding core has a cylindrical portion and an inner circumferential excess portion arranged inside the cylindrical portion, with only one end fixed to the cylindrical portion. The length of the inner circumferential excess portion is 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.

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 disposed at the center, and pressing the wound electrode body together with the winding core in the thickness direction. The winding core has a flat shape with two fold-back positions formed by winding a strip-shaped sheet material, and the winding core has a cylindrical portion and an inner circumferential excess portion disposed inside the cylindrical portion, only one end of which is fixed to the cylindrical portion. 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 the fixed position with the cylindrical portion to the fold-back position farther from the fixed position.

One aspect of the present invention provides an energy storage element in which the occurrence of gaps between electrodes is suppressed, and a method for manufacturing such an energy storage element.

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

First, we will provide an overview of the energy storage element and its manufacturing method disclosed in this specification.

An energy storage element according to one aspect of the present invention comprises a flat wound electrode body and a winding core arranged in the center of the wound electrode body. The winding core has a flat shape with two fold-back positions and is formed by winding a strip-shaped sheet material. The winding core has a cylindrical portion and an inner circumferential excess portion arranged inside the cylindrical portion, with only one end fixed to the cylindrical portion. The length of the inner circumferential excess portion is 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.

In this energy storage element, the occurrence of gaps between electrodes is suppressed. The reason for this effect is unclear, but the following reason is presumed. In this energy storage element, the length of the inner surplus 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 surplus portion. For this reason, the load applied from the winding core to the wound electrode body is highly uniform, and it is presumed that the occurrence of gaps between the electrodes is suppressed.

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, FIG. 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.

It is preferable that the winding core has two inner circumferential excess portions, and that the total length of the two inner circumferential excess portions is shorter than the distance between their respective fixed positions with the cylindrical portion. In such a 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 for wrinkles to occur and further suppressing the occurrence of gaps between the electrodes.

It is preferable that the length of the inner circumferential excess portion is at least 10 times the average thickness of the sheet member. If the inner circumferential excess portion has such a sufficient length, when the winding core and wound electrode body are manufactured by winding, the inner circumferential excess portion is sufficiently sandwiched between the opposing cylindrical portion of the winding core and the winding shaft, thereby preventing the winding core from shifting.

The average thickness of the sheet-like member is the average value of thicknesses measured at any five locations.

It is preferable that the length of the inner circumferential excess portion is 3 mm or more. Even in such cases, 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 assembly by winding.

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 disposed at the center, and pressing the wound electrode body together with the winding core in the thickness direction. The winding core has a flat shape with two fold-back positions formed by winding a strip-shaped sheet material, and the winding core has a cylindrical portion and an inner circumferential excess portion disposed inside the cylindrical portion, only one end of which is fixed to the cylindrical portion. 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 the fixed position with the cylindrical portion to the fold-back position farther from the fixed position.

This manufacturing method makes it possible to produce an energy storage element in which the occurrence of gaps between electrodes is suppressed.

The following describes in detail 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. 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.

<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.

Figure 1 shows a storage element 1 as an example of a non-aqueous electrolyte secondary battery. This figure is a see-through view of the interior of the container. A flat wound electrode assembly 2 with a centrally located winding core (not shown in Figure 1) is housed in a rectangular container 3. The wound electrode assembly 2, together with the winding core, is housed in the container 3 while being pressed in the thickness direction. The wound electrode assembly 2 has a positive electrode and a negative electrode wound with a separator sandwiched between them. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51. The container 3 also contains a non-aqueous electrolyte (not shown) along with the wound electrode assembly 2. A portion of the non-aqueous electrolyte is impregnated into the interior of the wound electrode assembly 2.

(Wound electrode body and winding core)
The structures of the wound electrode body 2 and winding core 6 provided in the energy storage element 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.

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, stacked in this order. The center of the wound electrode body 2 has an area where the winding core 6 is located. The wound electrode body 2 can have the same configuration as conventionally known wound electrode bodies. The first separator and second separator may be made of 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.

The winding core 6 is located 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, all stacked in this order, around the winding core 6.

The winding core 6 is formed by winding a strip-shaped sheet material. For example, the winding core 6 is formed by winding two sheets of sheet material. 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.

Examples of materials for the sheet member that makes up 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 that makes up the wound electrode body 2 may be used as the sheet member that makes up the winding core 6. The average thickness of the sheet member that makes up 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.

The winding core 6 has a cylindrical portion 8 and two inner circumferential excess portions 9A, 9B. Furthermore, the overlapping sheet materials are fixed at two fixing positions 10A, 10B on the winding core 6 to prevent misalignment of the wound sheet materials. The sheet materials are fixed at these fixing positions 10A, 10B by welding, adhesive, or the like.

The cylindrical portion 8 is the main body of the winding core 6 and is formed by winding 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 multiple layer of sheet material, the difference in the number of stacked sheets between areas with and without inner circumferential excess portions 9A, 9B, i.e., the difference in thickness between different parts 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, allowing for a larger number of windings of the positive and negative electrodes in the wound electrode body 2, thereby increasing the energy density per volume of the energy storage element 1.

The inner circumferential excess portions 9A, 9B are positioned inside the cylindrical portion 8, with only one end 11A, 11B fixed to the cylindrical portion 8 at fixing positions 10A, 10B. The inner circumferential excess portions 9A, 9B are excess portions on the inner circumferential side of the sheet material that do not constitute the cylindrical portion 8.

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

As such, the lengths LA and LB of the inner surplus portions 9A and 9B of the winding core 6 are shorter than the distances DA and DB from the fixed positions 10A and 10B with the cylindrical portion 8 to the fold-back positions 7B and 7A on the far side of the fixed positions. Therefore, wrinkles are less likely to form in the inner surplus portions 9A and 9B even when the wound electrode body is pressed in the thickness direction, reducing the distance between the inner surfaces of the cylindrical portions. This ensures that the load applied from the winding core 6 to the wound electrode body 2 is highly uniform, suppressing the occurrence of gaps between the electrodes.

In the configuration shown in Figure 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. As a result, the two inner circumferential excess portions 9A, 9B do not overlap with each other on the winding core 6, making wrinkles less likely to occur and further suppressing the occurrence of gaps between the electrodes of the wound electrode body 2.

The lengths LA and LB of the inner circumferential excess portions 9A and 9B are preferably at least 10 times the average thickness of the sheet member, and more preferably at least 20 or 30 times. Furthermore, the lengths LA and LB of the inner circumferential excess portions 9A and 9B are preferably at least 3 mm, and more preferably at least 1 cm or 1.5 cm. When the inner circumferential excess portions 9A and 9B are of 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 preferred because it can significantly misalign the winding core during manufacturing, etc.

(Method for 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 apparatus for manufacturing winding cores for energy storage elements will be described with reference to Figure 3. The winding core manufacturing apparatus includes a table 60 rotatable about a rotation axis 61, a pair of winding shafts 62A and 62B disposed on the table 60 with the rotation axis 61 sandwiched therebetween, and sheet insertion devices 64A and 64B that insert sheet members 63 onto the winding shafts 62A and 62B. The winding core manufacturing apparatus also includes chucks 65A and 65B that press and fix the sheet members 63 onto the winding shafts 62A and 62B, and that weld or adhere the sheet members 63.

First, as shown in Figure 3, sheet inserting devices 64A and 64B insert sheet material 63 between reel shafts 62A and 62B. At this time, one side of each of the two sheet materials 63 is pressed and fixed by chucks 65A and 65B so that it contacts the surface of reel shafts 62A and 62B. The length of the inserted sheet material 63 (the length beyond the portion of sheet material 63 pressed between reel shafts 62A and 62B and chucks 65A and 65B) is adjusted so that the inner surplus portions 9A and 9B (see Figure 4) formed have a predetermined length.

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. Note that 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 (fixed positions 10A and 10B) are welded or glued by the chucks 65A and 65B, and the sheet material 63 is cut behind the fixed positions 10A and 10B (toward the sheet insertion devices 64A and 64B). This results in a reel core 6 having a cylindrical portion 8 and two inner circumferential excess portions 9A and 9B positioned inside the cylindrical portion 8 and fixed at one end to the cylindrical portion 8 at the fixed positions 10A and 10B (see FIG. 5). In this embodiment, the table 60 rotates once, but it may rotate more times. Note that in Figure 5, part of the core manufacturing device (such as the table 60) is omitted from the illustration.

The manufacturing method shown in Figures 3 to 5, which uses two sheet members 63 to manufacture the winding core 6, requires fewer steps to cut the sheet members compared to the manufacturing method using a single sheet member, as described in the fourth embodiment, for example. Therefore, this manufacturing method can shorten the manufacturing time, among other things.

By winding the positive and negative electrodes with a separator interposed therebetween using a known method around the winding core 6 manufactured in this manner, the wound electrode body 2 can be manufactured as shown in Figure 5. Pulling the wound electrode body 2 together with the winding core 6 from the state shown in Figure 5 off the winding shafts 62A and 63B produces a flat wound electrode body 2 with the winding core 6 located 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 Figure 5, etc.), the wound electrode body 2 pressed in the thickness direction shown in Figure 2 is obtained.

The following describes in detail each component that makes up the energy storage element 1.

(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.

The positive electrode substrate is conductive. Whether or not a material is "conductive" is determined by a volume resistivity of 10 ⁷ Ω·cm measured in accordance with JIS-H-0505 (1975). Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of 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).

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

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 composition of the intermediate layer is not particularly limited, and may include, for example, a binder and a conductive agent.

The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may also contain optional components such as a conductive agent, binder, thickener, and filler, as needed.

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 typically used as the positive electrode active material for lithium ion secondary batteries. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO ₂ -type crystal structure, lithium transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having α-NaFeO type ₂ crystal structure include Li[Li _x Ni _(1-x) ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Co _(1-x-γ) ]O ₂ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li _x Co _(1-x) ]O ₂ (0≦x<0.5), Li[Li _x Ni _γ Mn _(1-x-γ) ]O ₂ (0≦x<0.5, 0<γ<1, 0<1-x-γ), Li[Li _x Ni _γ Mn _β Co _(1-x-γ-β) ]O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), Li[Li _x Ni _γ Co _β Al _(1-x-γ-β) ] O ₂ (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1, 0<1-x-γ-β), etc. Examples of lithium transition metal composite oxides having a spinel crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _(2-γ) O ₄ . 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.

The positive electrode active material is typically 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. Setting the average particle size of the positive electrode active material above the lower limit facilitates the production and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50%, based on the particle size distribution measured by laser diffraction/scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

To obtain powders of a specified particle size, mills and classifiers are used. Examples of milling methods include those using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, swirling air jet mill, or sieves. Wet milling, in which water or an organic solvent such as hexane is present, can also be used. Sieves and air classifiers are used as classification methods, both dry and wet, as needed.

The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less. By keeping 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.

The conductive agent is not particularly limited as long as it is a material that is conductive. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Non-graphitic carbon includes carbon nanofiber, pitch-based carbon fiber, and carbon black. Carbon black includes furnace black, acetylene black, and ketjen black. Graphene-based carbon includes graphene, carbon nanotubes (CNT), and fullerene. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNT may be used. Among these, carbon black is preferred from the standpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the content of the conductive agent within this range, the energy density of the energy storage element can be increased.

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.

The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within this range, the positive electrode active material can be stably maintained.

Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. If 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.

The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; carbonates such as calcium carbonate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; nitrides such as aluminum nitride and silicon nitride; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica; and synthetic versions of these.

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.

(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.

The negative electrode substrate is electrically conductive. Materials used for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys of these metals, and carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. 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.

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

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

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.

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 typically used as the negative electrode active material for lithium ion secondary batteries. Examples of negative electrode active materials include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; titanium-containing oxides such as Li ₄ Ti ₅ O ₁₂ , LiTiO _{2 , and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; 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 mixed and used.

"Graphite" refers to a carbon material in which the average lattice spacing (d ₀₀₂ ) of the (002) plane, as determined by X-ray diffraction before charge/discharge or in a discharged state, 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.

"Non-graphitic carbon" refers to a carbon material in which the average lattice spacing (d ₀₀₂ ) of the (002) plane, as determined by X-ray diffraction before charge/discharge or in a discharged state, is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitic carbon include 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.

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

The term "non-graphitizable carbon" refers to a carbon material having the above d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

The term "easily graphitizable carbon" refers to a carbon material having the above d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

The negative electrode active material is typically in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. 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 to 100 μm. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm to 1 μm. Setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit facilitates the production and handling of the negative electrode active material. Setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit improves the electronic conductivity of the negative electrode active material layer. A pulverizer, classifier, or the like is used to obtain powder with a specified particle size. The pulverization and classification methods can be selected from, for example, the methods exemplified for the positive electrode above. 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.

The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By keeping the content of the negative electrode active material within this range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

(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.

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 less than the specified value 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 aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, 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 may be mixed and used. Of these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate are preferred from the perspective of the safety of the energy storage element.

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

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

(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.

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 in these compounds have been substituted with halogens may also be used.

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, and 1,2-diphenylvinylene carbonate. Of these, EC is preferred.

Examples of chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Of these, EMC is preferred.

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 promotes dissociation of the electrolyte salt, improving the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate reduces 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.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

Examples of the lithium salt include inorganic lithium salts such _{as LiPF6} , _LiPO2F2 , _LiBF4 , _LiClO4 , and _LiN ( _SO2F ) ₂ ; lithium oxalate salts 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.

The content of the electrolyte salt in the non-aqueous electrolyte solution at 20°C and 1 atmosphere is preferably 0.1 mol/dm3 or ^more and ^2.5 mol/dm3 or less, more preferably ^0.3 mol/dm3 or ^more and 2.0 mol/dm3 or less, even more preferably 0.5 mol/dm3 or ^more and 1.7 mol/dm3 or ^less , and particularly preferably 0.7 mol/dm3 or ^more and 1.5 mol/ ^dm3 or less. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte solution can be increased.

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

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

<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.

In this manufacturing method, the method described above as the "method for manufacturing 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 located 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 for the winding core and wound electrode body provided in the energy storage element according to the embodiment of the present invention.

The manufacturing method may further include placing 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, and placing the electrolyte in the container. Preparing the electrolyte may also mean preparing the electrolyte. Placing the electrolyte in the container can be performed by any known method. For example, if a nonaqueous electrolyte solution is used as the electrolyte, the nonaqueous electrolyte solution can be injected through an injection port formed in the container, and the injection port can then be sealed.

<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.

The winding core 106 shown in Figure 6 differs from the winding core 6 shown in Figure 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 Figure 2. As shown in Figure 6, the length LA' of the inner circumferential excess portion 109A of the winding core 106 is shorter than the distance DA' from the fixed position 110A of the inner circumferential excess portion 109A to the tubular portion 108 to the turn-back position 107B on the far side of the fixed position 110A. Similarly, the length LB' of the inner circumferential excess portion 109B is shorter than the distance DB' from the fixed position 110B of the inner circumferential excess portion 109B to the tubular portion 108 to the turn-back position 107A on the far side of the fixed 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 portions 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.

<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.

The winding core 206 shown in Figure 7 is formed by winding a single strip-shaped sheet material, and has a tubular portion 208 and one inner surplus portion 209. The overlapping sheet material is 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 the fixing position 210B of the inner surplus portion 209 with the tubular portion 208 to the fold-back position 207A on the far side from this fixing position 210B.

In this way, an energy storage element including a winding core 206 with only one inner circumferential 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 highly productive.

<Electricity Storage Element: Fourth Embodiment>
The energy storage element according to the 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 the energy storage element according to the fourth embodiment includes a winding core 306 instead of the winding core 6.

The winding core 306 shown in Figure 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 Figure 8 differs from the winding core 6 shown in Figure 2, etc., in that the cylindrical portion 308 is essentially composed 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 Figures 3 to 5, etc. For example, in the state shown in Figure 9, where the table 60 is rotated half a clockwise direction from the state shown in Figure 3, the overlapping portions of the sheet member 63 and the winding shafts 62A, 62B (fixed positions 310A, 310B) are welded or glued, and the rear of the fixed positions 310A, 310B in the sheet member 63 (towards the sheet insertion devices 64A, 64B) is cut, thereby obtaining the winding core 306 in the form shown in Figure 8.

When the cylindrical portion 308 is formed from a substantially single sheet material, as in this embodiment, the winding core 306 can be made thinner, allowing for a greater number of windings of the positive and negative electrodes 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 achieve an increased energy density per volume, among other things.

<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, it is sufficient that the technology of the present invention is applied to at least one energy storage element included in the energy storage unit.

Figure 10 shows an example of a storage device 30 that further aggregates storage units 20, each of which is an aggregation of two or more electrically connected storage elements 1. The storage device 30 may include a bus bar (not shown) that electrically connects two or more storage elements 1, a bus bar (not shown) that electrically connects two or more storage units 20, etc. The storage unit 20 or storage device 30 may also include a status monitoring device (not shown) that monitors the status of one or more storage elements.

<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.

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

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, with a non-conductive layer formed on the active material layer of the positive electrode or negative electrode. Furthermore, in the energy storage element of the present invention, the sheet member that constitutes the winding core may be continuous with the separator that constitutes the wound electrode body.

The winding core provided in the energy storage element of the present invention may be manufactured by a method different from that described in the above embodiment. For example, the winding core may be manufactured by obtaining a winding core 406 having an inner circumferential excess portion 409 extending across the inner surface of a cylindrical portion 408 as shown in FIG. 11, and then cutting the inner circumferential excess portion 409 into two pieces. With this manufacturing method, the winding core is manufactured from a single sheet material, making it relatively easy to manufacture the winding core.

The present invention can be applied to energy storage elements used as power sources for automobiles, other vehicles, electronic devices, etc.

1 Energy storage element 2, 402 Wound electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 6, 106, 206, 306, 406 Winding core 7A, 7B, 107A, 107B, 207A Fold-back position 8, 108, 208, 308, 408 Cylindrical portion 9A, 9B, 109A, 109B, 209, 309A, 309B, 409 Inner peripheral excess portion 10A, 10B, 110A, 110B, 210A, 210B, 310A, 310B Fixing position 11A, 11B One end 20 Energy storage unit 30 Energy storage device 60 Table 61 Rotating shaft 62A, 62B Winding shaft 63 Sheet member 64A, 64B Sheet insertion device 65A, 65B Chuck

Claims (6)

a wound electrode body having a flat shape;
a winding core disposed at the center of the wound electrode body,
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, only one end of which is fixed to the cylindrical portion;
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. 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 sum of the lengths of the two inner circumferential excess portions is shorter than the distance between the respective fixed positions with the cylindrical portion. The energy storage element described in claim 1 or claim 2, wherein the length of the inner circumferential excess portion is 10 times or more the average thickness of the sheet member. The energy storage element described in claim 1, claim 2, or claim 3, wherein the length of the inner circumferential excess portion is 3 mm or more. 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 winding core in a thickness direction. obtaining a wound electrode body having a flat shape with a winding core disposed at the center thereof; and pressing the wound electrode body together with the winding core in a thickness direction;
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, only one end of which is fixed to the cylindrical portion;
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.