Power storage element

Abstract

This power storage element comprises an electrode body, wherein the electrode body includes a wound electrode plate, the electrode plate includes a formation part in which an active material layer is formed, and a non-formation part in which the active material layer is not formed. The non-formation part is arranged on one side in the winding axis direction of the electrode plate of the formation part. The formation part has a plurality of recessed parts recessed in the thickness direction of the electrode plate. The formation part comprises a first region including one end in the winding axis direction and a second region including the other end in the winding axis direction. A first opening ratio, which is the opening ratio of the recessed parts in the first region, is larger than a second opening ratio, which is the opening ratio of the recessed parts in the second region.

Description

Energy storage element

[0001] The present invention relates to an energy storage element.

[0002] Patent Literature 1 discloses a secondary battery including a wound electrode assembly in which a positive electrode and a negative electrode are wound around a winding axis with a separator interposed therebetween. This wound electrode assembly has an inorganic layer on the inner peripheral surface of the separator wound at the innermost periphery. With this secondary battery, when electrodes and the like are wound around the rotational center axis of a winding core of a winding device as the winding axis and the winding core is removed to form the wound electrode assembly, the inorganic layer reduces the frictional force between the wound electrode assembly and the winding core, preventing misalignment of the wound electrode assembly.

[0003] Japanese Patent Application Laid-Open No. 2017-27681

[0004] In the conventional secondary battery described above, when the winding core is removed to form the wound electrode body, the inorganic layer reduces the frictional force between the wound electrode body and the winding core, thereby preventing misalignment of the wound electrode body.

[0005] However, when manufacturing a wound electrode assembly, the electrode plate may be distorted in a manner that causes it to curve in the short direction of the electrode plate (hereinafter, simply referred to as "electrode plate distortion") due to, for example, thermal expansion of the active material layer provided in the electrode plate. When distortion occurs in the electrode plate, the electrode plate is likely to slip when being wound. Such misalignment of the electrode plate due to electrode plate distortion cannot be suppressed even with the structure of the conventional secondary battery described above.

[0006] The present invention was made by the inventors of the present application by focusing on the above-mentioned problems, and has an object to provide an energy storage element with improved reliability.

[0007] A storage element according to one aspect of the present invention is an energy storage element comprising an electrode body, wherein the electrode body comprises a wound electrode plate, the electrode plate comprising a formed portion on which an active material layer is formed and a non-formed portion on which the active material layer is not formed, the non-formed portion being arranged on one side of the formed portion in the direction of the winding axis of the electrode plate, the formed portion having a plurality of recesses recessed in the thickness direction of the electrode plate, the formed portion comprising a first region including an end portion on one side in the direction of the winding axis and a second region including an end portion on the other side in the direction of the winding axis, and a first opening ratio which is the opening ratio of the recesses in the first region being greater than a second opening ratio which is the opening ratio of the recesses in the second region.

[0008] According to the present invention, it is possible to provide an energy storage element with improved reliability.

[0009] FIG. 1 is a perspective view showing the appearance of an energy storage element according to an embodiment. FIG. 2 is a perspective view showing components arranged inside a container of the energy storage element according to the embodiment. FIG. 3 is a perspective view showing a schematic configuration of an electrode body according to the embodiment. FIG. 4 is a view showing a state in which an electrode plate according to the embodiment is vacuum dried. FIG. 5 is a view showing an electrode plate in a state in which distortion has occurred. FIG. 6 is a view showing an example of an arrangement layout of multiple recesses in an electrode plate according to the embodiment. FIG. 7 is a cross-sectional view showing an example shape of the recesses according to the embodiment. FIG. 8 is a view showing a state in which an electrode plate according to the embodiment is wound by a winding device. FIG. 9 is a view showing an electrode plate in a state in which distortion has been corrected. FIG. 10 is a plan view showing a schematic configuration of an electrode plate according to a first modification of the embodiment. FIG. 11 is a plan view showing a schematic configuration of an electrode plate according to a second modification of the embodiment. FIG. 12 is a partial cross-sectional view showing a schematic configuration of an electrode plate according to a third modification of the embodiment. FIG. 13 is a plan view schematically showing a configuration of an energy storage device including an energy storage element according to the embodiment. FIG. 14 is a view showing a first example in which multiple recesses are arranged in a staggered pattern. FIG. 15 is a view showing a second example in which multiple recesses are arranged in a staggered pattern.

[0010] (1) One aspect of the present invention provides an energy storage element comprising an electrode body, the electrode body comprising a wound electrode plate, the electrode plate comprising a formed portion on which an active material layer is formed and a non-formed portion on which the active material layer is not formed, the non-formed portion being disposed on one side of the formed portion in the direction of the winding axis of the electrode plate, the formed portion having a plurality of recesses recessed in the thickness direction of the electrode plate, the formed portion comprising a first region including an end portion on one side in the direction of the winding axis and a second region including an end portion on the other side in the direction of the winding axis, and a first aperture ratio which is the aperture ratio of the recesses in the first region being greater than a second aperture ratio which is the aperture ratio of the recesses in the second region.

[0011] According to an energy storage device according to one aspect of the present invention, multiple recesses are formed in the formation portion of the electrode plate, where the active material layer is formed. Furthermore, the aperture ratio (first aperture ratio) of the recesses in the first region closest to the non-formation portion where no active material layer is formed is greater than the aperture ratio (second aperture ratio) of the recesses in the second region farthest from the non-formation portion. That is, the first aperture ratio of the first region, where the amount of elongation in the winding direction of the electrode plate (in other words, the longitudinal direction of the electrode plate; the same applies hereinafter) is relatively small due to differences in the density of the active material layer, is greater than the aperture ratio of the second region, where the amount of elongation is relatively large. Therefore, the difference in the amount of elongation in the winding direction of the formation portion due to thermal expansion of the active material layer during the manufacture of the electrode assembly, which is caused by differences in the position of the winding axis, is reduced. As a result, distortion of the electrode plate due to the difference in elongation is suppressed or corrected, thereby suppressing misalignment of the electrode plate in the winding axis direction (winding misalignment) in a wound electrode assembly. Thus, an energy storage device according to one aspect of the present invention is an energy storage device with improved reliability.

[0012] (2) In the energy storage element described in (1) above, the formation portion may have a convex portion formed on a rear side of the concave portion.

[0013] According to the energy storage element described in (2) above, the relatively deep recesses are formed, so that the effect of the recesses making the electrode plates more likely to stretch can be more reliably obtained. That is, the difference between the first aperture ratio and the second aperture ratio more efficiently suppresses or corrects distortion of the electrode plates.

[0014] (3) In the energy storage element described in (1) or (2) above, the electrode plate may include a current collector foil, and in the forming portion, the active material layer may be formed on one side of the current collector foil in the thickness direction, and each of the plurality of recesses may be formed by the current collector foil and the active material layer being recessed on the other side in the thickness direction.

[0015] According to the energy storage element described in (3) above, after forming an active material layer on one side of the current collector foil in the thickness direction, a recess is formed by pressing or the like. Therefore, the recess can be formed more easily than when the recess is formed by controlling the thickness of the active material layer when forming the active material layer. Therefore, an energy storage element with improved reliability can be produced more efficiently.

[0016] (4) In the energy storage element described in any one of (1) to (3) above, in each of the first region and the second region, a plurality of the recesses may be arranged along the winding direction of the electrode plate, and the number of the recesses per unit length in the winding direction in the first region may be greater than the number of the recesses per unit length in the winding direction in the second region.

[0017] According to the energy storage element described in (4) above, the aperture ratio of each region can be controlled by controlling the number of recesses per unit length in the winding direction of the electrode plate. This makes it possible to easily manufacture electrode plates with different aperture ratios of recesses in each region. Therefore, energy storage elements with improved reliability can be manufactured more efficiently.

[0018] (5) In the energy storage element described in any one of (1) to (4) above, the formation portion may further include a third region located between the first region and the second region in the winding axis direction, and a third aperture ratio, which is the aperture ratio of the recess in the third region, may be smaller than the first aperture ratio and larger than the second aperture ratio.

[0019] In the energy storage element described in (5) above, the second aperture ratio, the third aperture ratio, and the first aperture ratio increase in this order. That is, the aperture ratios of the recesses in each of the three regions in the formation portion increase in the order of decreasing amounts of elongation in the winding direction due to differences in the densities of the active material layers, etc. Therefore, distortion of the electrode plate can be more effectively suppressed or corrected.

[0020] (6) In the energy storage element described in any one of (1) to (5) above, the opening ratio of the recess in the formation portion may increase from the other side to the one side in the direction of the winding axis.

[0021] According to the energy storage element described in (6) above, the opening ratio of the recesses in the formed portion increases toward the non-formed portion. That is, the smaller the amount of elongation in the winding direction caused by differences in the density of the active material layer, the larger the opening ratio of the recesses. Therefore, distortion of the electrode plate can be more effectively suppressed or corrected.

[0022] Hereinafter, with reference to the drawings, an energy storage element according to an embodiment of the present invention will be described. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component arrangement and connection configuration, manufacturing process, and manufacturing process sequence shown in the following embodiments are examples only and are not intended to limit the present invention. Furthermore, in each drawing, dimensions and the like are not strictly illustrated. Furthermore, in each drawing, the same or similar components are assigned the same reference numerals. The drawings are schematic diagrams in which emphasis, omission, and adjustment of proportions are appropriately made to illustrate the present invention, and may differ from the actual shapes, positional relationships, and proportions.

[0023] In the following description and drawings, the longitudinal direction of an unwound electrode plate is defined as the X-axis direction, the short-side direction of the electrode plate or the winding axis direction of the electrode body is defined as the Y-axis direction, and the thickness direction of the electrode plate is defined as the Z-axis direction. These X-axis, Y-axis, and Z-axis directions intersect each other (orthogonal in this embodiment). Depending on the orientation of the electrode plate during manufacturing of the electrode body, the Z-axis direction may not be the up-down direction. However, for convenience of explanation, the following description will be made assuming that the Z-axis direction is the up-down direction.

[0024] In the following description, for example, the positive X-axis direction refers to the direction of the arrow on the X-axis, and the negative X-axis direction refers to the direction opposite to the positive X-axis direction. The same applies to the Y-axis and Z-axis directions. When simply referring to the "X-axis direction," it means either one or both directions parallel to the X-axis. The same applies to terms related to the Y-axis and Z-axis.

[0025] Furthermore, expressions indicating relative directions or attitudes, such as parallel and perpendicular, also include cases where the directions or attitudes are not strictly the same. For example, "two directions are perpendicular" does not only mean that the two directions are completely perpendicular, but also means that the two directions are substantially perpendicular, i.e., that there is a difference of, for example, about several percent. In the following description, when the term "insulation" is used, it means "electrical insulation." The volume resistivity of an insulating material is 1×10 ６ Ωm or more is preferable, and 1×10 ７ Ωm or more is more preferable, and 1×10 １０ More preferably, it is Ωm or more.

[0026] (Embodiment) [1. General Description of Energy Storage Device 10] An energy storage device 10 according to this embodiment will be generally described with reference to Figures 1 to 3. Figure 1 is a perspective view showing the appearance of the energy storage device 10 according to the embodiment. Figure 2 is a perspective view showing components arranged inside a container 100 of the energy storage device 10 according to the embodiment.

[0027] Fig. 3 is a perspective view showing the general configuration of an electrode assembly 400 according to an embodiment. Elements such as a stacked and wound positive electrode plate 410 are partially expanded and illustrated in Fig. 3. Only some of the recesses 480 of the electrode plate 401 are shown in schematic form in Fig. 3.

[0028] 3 is a virtual axis that serves as the central axis when winding the positive electrode plate 410, etc. In this embodiment, the direction parallel to the winding axis W is also referred to as the winding axis direction Wd.

[0029] The energy storage element 10 is a secondary battery, more specifically, a nonaqueous electrolyte secondary battery such as a lithium-ion secondary battery. The energy storage element 10 is used as a battery for driving or starting the engine of a moving object such as an automobile, motorcycle, personal watercraft, ship, snowmobile, agricultural machinery, construction machinery, automatic guided vehicle (AGV), or electric railway vehicle. Examples of the automobile include an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and a fossil fuel (gasoline, diesel, liquefied natural gas, etc.) vehicle. Examples of the electric railway vehicle include a train, a monorail, a linear motor car, and a hybrid train equipped with both a diesel engine and an electric motor. The energy storage element 10 can also be used as a stationary battery for home or business use.

[0030] The energy storage element 10 is not limited to a non-aqueous electrolyte secondary battery, and may be a secondary battery other than a non-aqueous electrolyte secondary battery, or may be a capacitor. The energy storage element 10 may also be a primary battery.

[0031] As shown in Fig. 1, the energy storage element 10 includes a container 100 and a pair of (positive and negative) terminals 200. As shown in Fig. 2, the container 100 contains a pair of (positive and negative) current collectors 300 and an electrode assembly 400.

[0032] In addition to the above components, the energy storage element 10 may also include a spacer disposed on the side of the current collector 300, a gas release valve for releasing pressure when the pressure inside the container 100 increases, and an insulating film that encases the electrode assembly 400, etc. An electrolyte solution (non-aqueous electrolyte) is sealed inside the container 100, but is not shown in the figure. There are no particular restrictions on the type of electrolyte solution as long as it does not impair the performance of the energy storage element 10, and various types can be selected.

[0033] The container 100 includes a rectangular cylindrical container body 110 with a bottom, and a cover plate 120 that closes the opening of the container body 110. After the electrode assembly 400 and other components are housed inside the container 100, the cover plate 120 and the container body 110 are welded together, for example, to seal the interior of the container 100. There are no particular limitations on the materials for the container body 110 and the cover plate 120, but they are preferably weldable metals such as stainless steel, aluminum, aluminum alloy, iron, and plated steel sheet.

[0034] The terminals 200 are electrode terminals electrically connected to the electrode assembly 400 via the current collectors 300. That is, the positive electrode terminal 200 is electrically connected to the positive electrode plate of the electrode assembly 400 via the current collectors 300, and the negative electrode terminal 200 is electrically connected to the negative electrode plate of the electrode assembly 400 via the current collectors 300. The terminals 200 are attached to the cover plate 120 arranged above the electrode assembly 400 via an insulating gasket (not shown).

[0035] The electrode assembly 400 includes two electrode plates 401 and two separators 430 and is an electricity storage element (power generation element) capable of storing electricity. In this embodiment, the electrode assembly 400 is a wound electrode assembly formed by winding two electrode plates 401 and two separators 430. As shown in FIG. 3 , the electrode assembly 400 has a flattened shape in a direction perpendicular to the winding axis W. That is, when viewed from the direction of the winding axis W, the electrode assembly 400 has an overall oval shape, with the straight portions of the oval shape being flat and the curved portions of the oval shape being curved. Therefore, the electrode assembly 400 has a pair of opposing curved end portions (portions facing each other in the longitudinal direction of the oval shape across the winding axis W) and a pair of intermediate portions between the pair of curved end portions (portions facing each other in the lateral direction of the oval shape across the winding axis W).

[0036] In the present embodiment, the two electrode plates 401 included in the electrode assembly 400 include a positive electrode plate 410 that is the positive electrode plate 401 and a negative electrode plate 420 that is the negative electrode plate 401. The positive electrode plate 410 is an electrode plate in which a positive electrode active material layer 414 is formed on the surface of a current collector foil 411 that is a long strip of metal foil. The negative electrode plate 420 is an electrode plate in which a negative electrode active material layer 424 is formed on the surface of a current collector foil 421 that is a long strip of metal foil. More specifically, the positive electrode plate 410 includes a formed portion 415 in which the active material layer 414 is formed and a non-formed portion 416 in which the active material layer 414 is not formed. The non-formed portion 416 is a portion in which the positive electrode current collector foil 411 is exposed. The negative electrode plate 420 includes a formed portion 425 where the active material layer 424 is formed, and a non-formed portion 426 where the active material layer 424 is not formed. The non-formed portion 426 is a portion where the negative electrode current collector foil 421 is exposed.

[0037] The positive electrode current collector foil 411 is made of aluminum or an aluminum alloy, etc. The negative electrode current collector foil 421 is made of copper or a copper alloy, etc. The active material layer 414 includes a positive electrode active material, a binder, a conductive material, etc. The active material layer 424 includes a negative electrode active material, a binder, a thickener, etc. Any known material can be used as the positive electrode active material and the negative electrode active material as long as it is capable of absorbing and releasing charge transport ions.

[0038] As the positive electrode active material, LiM1PO ４ , LiMSiO ４ , LiM1BO ３ (M1 is one or more metal elements selected from Fe, Ni, Mn, Co, etc.), polyanion compounds such as lithium titanate, LiM2 ２ O ４ (M2 is one or more metal elements selected from Fe, Ni, Mn, Co, etc.), spinel-type lithium transition metal oxides such as LiMO ２ (M3 is one or more metal elements selected from Fe, Ni, Mn, Co, etc.) and the like can be used. Examples of the negative electrode active material include lithium metal, lithium alloys, alloys capable of absorbing and releasing lithium ions, carbon materials (e.g., graphite, non-graphitizable carbon, easily graphitizable carbon, amorphous carbon, etc.), silicon oxides, metal oxides, and lithium metal oxides (Li４ Ti ５ O １２ etc.), polyphosphate compounds, or Co, commonly called conversion anodes ３ O ４ and Fe ２ Examples of the metal include compounds of transition metals such as P and elements of Groups 14 to 16.

[0039] Separator 430 is a microporous sheet made of resin. Any known material can be used as the material for separator 430 as long as it does not impair the performance of energy storage device 10. For example, separator 430 can be made of a woven fabric or nonwoven fabric that is insoluble in organic solvents, or a synthetic resin microporous film made of a polyolefin resin such as polyethylene.

[0040] In the present embodiment, the electrode assembly 400 includes a positive electrode plate 410 and a negative electrode plate 420 wound with a separator 430 interposed therebetween, offset from each other in the winding axis direction Wd. The positive electrode plate 410 and the negative electrode plate 420 have, at their offset ends, portions (non-formed portions 416, 426) where no active material layer is formed and the current collecting foil is exposed. That is, the electrode assembly 400 includes a positive electrode connection portion 456 formed by winding and stacking the non-formed portion 416 at one end in the winding axis direction Wd. The electrode assembly 400 includes a negative electrode connection portion 466 formed by winding and stacking the non-formed portion 426 at the other end in the winding axis direction Wd. The positive electrode connection portion 456 is joined to the positive electrode current collector 300, and the negative electrode connection portion 466 is joined to the negative electrode current collector 300 (see FIG. 2 ). As a result, the positive electrode terminal 200 and the positive electrode connection part 456 of the electrode body 400 are electrically connected via the positive electrode current collector 300. The negative electrode terminal 200 and the negative electrode connection part 466 of the electrode body 400 are electrically connected via the negative electrode current collector 300.

[0041] [2. Regarding the Electrode Plate 401 and the Multiple Recesses 480] In the energy storage element 10 configured as described above, the electrode plate 401 included in the electrode body 400 includes multiple recesses 480 recessed in the thickness direction. Specifically, as shown in FIG. 3 , the positive electrode plate 401 (positive electrode plate 410) includes multiple recesses 480 in the forming portion 415. In this embodiment, the electrode plate 401 includes multiple recesses 480, thereby suppressing winding misalignment when the electrode plate 401 is wound. Below, focusing on the positive electrode plate 401 (positive electrode plate 410) of the two electrode plates 401, the effect of the multiple recesses 480 in suppressing winding misalignment of the electrode plate 401 will be described. The various structural features and effects of the positive electrode plate 401 (positive electrode plate 410) described below may also be applied to the negative electrode plate 401 (negative electrode plate 420) as appropriate.

[0042] FIG. 4 is a diagram showing a state in which the electrode plate 401 according to the embodiment is vacuum-dried. FIG. 5 is a diagram showing the electrode plate 401 in a state in which distortion has occurred. FIG. 6 is a diagram showing an example of the layout of a plurality of recesses 480 in the electrode plate 401 according to the embodiment. FIG. 7 is a cross-sectional view showing an example of the shape of the recesses 480 according to the embodiment. FIG. 7 is a cross-sectional view of a portion of the electrode plate 401, taken along line VII-VII in FIG. 6. FIG. 8 is a diagram showing a state in which the electrode plate 401 according to the embodiment is wound by a winding device 600. In FIG. 8, the negative electrode plate 401 (negative electrode plate 420) and separator 430 included in the electrode assembly 400 are not shown. FIG. 9 is a diagram showing the electrode plate 401 in a state in which distortion has been corrected.

[0043] When manufacturing the positive electrode plate 401 according to the embodiment, a composite material containing a positive electrode active material, which is the material for the active material layer 414, is applied to the center of the short side of a long, strip-shaped current collector foil A, which is the base material of the current collector foil 411. Then, the current collector foil A (base material of the current collector foil 411) to which the composite material has been applied is cut along the longitudinal direction of the current collector foil A at the center of the short side. This produces two electrode plates 401. As a result, a region where the composite material is not applied is provided at one end of the current collector foil 411 in the short side direction (the Y-axis direction in FIG. 5 ; the same applies hereinafter). In other words, a non-formation portion 416 where the active material layer 414 is not formed is provided at this end of the current collector foil 411. In this embodiment, the composite material is applied to both sides of the current collector foil 411 in the thickness direction (the Z-axis direction in FIG. 5 ; the same applies hereinafter).

[0044] More specifically, when applying the composite material to the current collecting foil A, the current collecting foil A is moved in the longitudinal direction of the current collecting foil A while the composite material flows out of a slit extending in the lateral direction of the current collecting foil A. This results in a current collecting foil A in which the composite material is applied to the center portion in the lateral direction and the both ends in the lateral direction are not coated with the composite material. When the composite material is applied in this manner, the composite material has fluidity, so the amount of composite material flowing out from the center portion of the slit in the lateral direction is greater than the amount of composite material flowing out from both ends in the lateral direction. As a result, in the electrode plate 401 obtained by cutting the current collecting foil A at the center position in the lateral direction, the thickness of the active material layer 414 formed by the applied composite material increases from one end of the current collecting foil 411 close to the non-forming portion 416 to the other end far from the non-forming portion 416 in the lateral direction. Therefore, the current collecting foil 411 with the active material layer 414 is compressed in the thickness direction by, for example, passing between a pair of rollers. This uniformizes the thickness of the active material layer 414. That is, the thickness of the active material layer 414 becomes approximately uniform in the short-side direction of the current collector foil 411. Thereafter, the current collector foil 411 (i.e., the electrode plate 401 in the middle of manufacture) including the active material layer 414 with a uniform thickness is wound around a reel 715 and vacuum-dried in a vacuum dryer 700, as shown in FIG. 4 . That is, the electrode plate 401 is heated under vacuum. At this time, the heated active material layer 414 thermally expands. When the active material layer 414 thermally expands, the active material layer 414 is compressed in the radial direction because the electrode plate 401 is wound. As a result, the thermal expansion of the active material layer 414 is likely to manifest as elongation in the circumferential direction (the X-axis direction in FIG. 5 ). Furthermore, as described above, the active material layer 414 is compressed to uniformize its thickness in the short-side direction of the current collector foil 411. Therefore, the density of active material layer 414 increases from one end to the other end in the widthwise direction of current collector foil 411. In other words, the other end in the widthwise direction of current collector foil 411 (the end farther from non-formed portion 416), where the density of active material layer 414 is high, experiences a greater amount of elongation due to thermal expansion of active material layer 414 than the one end in the widthwise direction of current collector foil 411 (the end adjacent to non-formed portion 416), where the density of active material layer 414 is low.As a result, as shown in Fig. 5, in a plan view (when viewed from the Z-axis direction), distortion occurs in the electrode plate 401 after vacuum drying, causing it to curve in the short direction of the electrode plate 401. When the electrode plate 401 is wound in this state to form the electrode body 400 (see Fig. 8), the distortion of the electrode plate 401 makes it easy for misalignment to occur in the winding.

[0045] Therefore, in this embodiment, the electrode plate 401 is processed before being wound to prevent the electrode plate 401 from being misaligned. Specifically, as shown in Figures 6 and 7, a plurality of recesses 480 are formed in the active material layer 414 of the electrode plate 401. There are no particular limitations on the method for forming the plurality of recesses 480 in the electrode plate 401. For example, the plurality of recesses 480 as shown in Figure 6 may be formed by pressing a roller having a cylindrical base and a plurality of protrusions arranged on the outer circumferential surface of the base against the electrode plate 401 and rotating it, or by winding the electrode plate 401 around the roller.

[0046] Furthermore, in the electrode plate 401 according to the present embodiment, the aperture ratio of the plurality of recesses 480 differs from region to region. The aperture ratio of the recesses 480 is the sum of the aperture areas of the recesses 480 in a plan view per unit area common to all regions. This unit area is preferably an area including two or more recesses 480 in each of one or more regions, excluding regions with one or zero recesses 480. If the aperture areas of the plurality of recesses 480 are the same, the aperture ratio of the recesses 480 is equivalent to the number of recesses 480 per unit area (i.e., the density of the recesses 480). In other words, if the aperture areas of the plurality of recesses 480 are the same, the comparison of the aperture ratios of the recesses 480 between regions may be performed by comparing the number of recesses 480 between regions.

[0047] 6, in the present embodiment, the aperture ratio (first aperture ratio) in a first region 461 adjacent to non-formation portion 416 in active material layer 414 is greater than the aperture ratio (second aperture ratio) in a second region 462 including an end portion of active material layer 414 far from non-formation portion 416. As a result, when electrode plate 401 is wound as shown in FIG. 8, distortion of electrode plate 401 (see FIG. 5) is corrected, and as a result, winding slippage of electrode plate 401 is suppressed.

[0048] More specifically, as shown in FIG. 7 , each of the plurality of recesses 480 includes a portion that is deformed to recess from one side to the other side in the thickness direction of the electrode plate 401 and / or a portion that is thinner than the other portions. Therefore, when the electrode plate 401 is pulled in the longitudinal direction of the electrode plate 401 (the X-axis direction in FIG. 7 ), each of the plurality of recesses 480 deforms to extend along the longitudinal direction, thereby functioning as a portion that stretches the electrode plate 401 in the longitudinal direction. Therefore, as shown in FIG. 8 , when the electrode plate 401 is subjected to tension T due to winding, the first region 461, which has a relatively large opening ratio of the recesses 480, is more likely to stretch in the longitudinal direction of the electrode plate 401 (i.e., the winding direction of the electrode plate 401) than the second region 462, which has a relatively small opening ratio. Therefore, the electrode plate 401, which was distorted as shown in FIG. 6 , is wound while the distortion is corrected by the tension T. As a result, winding misalignment of the electrode plate 401 is suppressed. For example, when the wound electrode plate 401 is unfolded, as shown in FIG. 9, the distortion of the electrode plate 401 is eliminated or almost eliminated, and each of the multiple recesses 480 remains to such an extent that its existence can be confirmed.

[0049] 8, the electrode plate 401 is wound to have a flat shape in a direction perpendicular to the winding axis W. However, when the electrode plate 401 and the separator 430 are wound by the winding device 600, they may be wound to have a circular roll shape. In this case, the electrode body 400, which has been once formed into a circular roll shape, may be compressed in a direction perpendicular to the winding axis W, thereby forming the electrode body 400 (see FIGS. 2 and 3) into an oval shape when viewed from the direction of the winding axis W.

[0050] As described above, the energy storage device 10 according to this embodiment is an energy storage device 10 including an electrode assembly 400, and the electrode assembly 400 includes a wound electrode plate 401. The electrode plate 401 includes a formed portion 415 where an active material layer 414 is formed and a non-formed portion 416 where the active material layer 414 is not formed. The non-formed portion 416 is located on one side of the formed portion 415 in the winding axis direction Wd of the electrode plate 401 (the positive Y-axis direction in FIG. 6 ; the same applies below). The formed portion 415 has a plurality of recesses 480 formed therein that are recessed in the thickness direction of the electrode plate 401. The formed portion 415 includes a first region 461 that includes an end portion on one side of the winding axis direction Wd and a second region 462 that includes an end portion on the other side of the winding axis direction Wd (the negative Y-axis direction in FIG. 6 ; the same applies below). A first aperture ratio, which is the aperture ratio of the recesses 480 in the first region 461 , is greater than a second aperture ratio, which is the aperture ratio of the recesses 480 in the second region 462 .

[0051] According to this configuration, a plurality of recesses 480 are formed in the formation portion 415 where the active material layer 414 is formed. Furthermore, the first aperture ratio of the recesses 480 in the first region 461 closest to the non-formation portion 416 where the active material layer 414 is not formed is greater than the second aperture ratio of the recesses 480 in the second region 462 farthest from the non-formation portion 416. That is, the first aperture ratio of the first region 461, in which the amount of elongation in the winding direction of the electrode plate 401 is relatively small due to differences in the density of the active material layer 414, is greater than the aperture ratio of the second region 462, in which the amount of elongation is relatively large. In other words, the first region 461, in which the amount of elongation due to thermal expansion of the active material layer 414 is small, elongates by a larger amount due to tension T (see FIG. 8 ) than the second region 462, in which the amount of elongation due to thermal expansion of the active material layer 414 is large. Therefore, the difference in the amount of elongation in the winding direction of the forming portion 415 due to thermal expansion of the active material layer 414 or the like during the manufacture of the electrode body 400, which is caused by different positions in the direction of the winding axis Wd, is reduced. As a result, distortion of the electrode plate 401 caused by the difference in the amount of elongation is suppressed or corrected, thereby suppressing misalignment (winding misalignment) of the electrode plate 401 in the direction of the winding axis Wd in the wound electrode body 400. In this way, the energy storage element 10 according to this embodiment is an energy storage element 10 with improved reliability.

[0052] In the present embodiment, each of the plurality of recesses 480 provided in the forming portion 415 of the electrode plate 401 has a depth Db (see FIG. 7 ) of about 50 μm and a substantially circular opening diameter Da (see FIG. 7 ) of about 2000 μm. The size of the recesses 480 is not limited to this, and the depth Db may be such that only the active material layer 414 formed on one surface of the current collecting foil 411 is recessed. The opening diameter Da of the recesses 480 may be any value between 500 μm and 5000 μm.

[0053] If the depth Db of the recess 480 is too large, or if the recess 480 is formed using a mold that creates corners on the protrusion 485 behind the recess 480, cracks may occur in the active material layer 414 at the protrusion 480. This is presumably because the active material layer 414 forming the surface of the protrusion 485 is unable to follow the deformation of the electrode plate 401 when forming the recess 480. Therefore, when viewed from the positive Z-axis direction, the shape of the recess 480 is preferably not rectangular, but is preferably elliptical, and more preferably circular. Furthermore, when the shape of the recess 480 when viewed from the positive Z-axis direction is polygonal, such as triangular or rectangular, if the corners are rounded, cracks in the active material layer 414 at the protrusion 485 are suppressed. The cross-sectional shape of the recess 480 (the shape of a cross section parallel to the Z-axis direction) is preferably a dome shape, such as a shape that does not locally cause a sharp bend in the electrode plate 401 (see FIG. 7 ).

[0054] In energy storage device 10 according to this embodiment, as shown in FIG. 7, convex portion 485 is formed on the rear side of concave portion 480 in forming portion 415 .

[0055] In this manner, in the present embodiment, the relatively deep recesses 480 are formed, and therefore the effect of the recesses 480 making the electrode plate 401 more likely to stretch can be more reliably obtained. In other words, the difference between the first aperture ratio and the second aperture ratio more efficiently suppresses or corrects distortion of the electrode plate 401.

[0056] More specifically, in this embodiment, electrode plate 401 includes current collector foil 411. In forming portion 415, active material layer 414 is formed on one side in the thickness direction of current collector foil 411. Each of the multiple recesses 480 is formed by current collector foil 411 and active material layer 414 being recessed toward the other side in the thickness direction. That is, in this embodiment, as shown in FIG. 7 , active material layers 414 are provided on both sides of current collector foil 411 in the thickness direction (Z-axis direction), and active material layer 414 including recess 480 is one of these two active material layers 414 (active material layer 414 in the positive Z-axis direction in FIG. 7 ). That is, recess 480 is a portion recessed in the negative Z-axis direction in active material layer 414 in the positive Z-axis direction of current collector foil 411.

[0057] According to this configuration, after the active material layer 414 is formed on one side in the thickness direction of the current collector foil 411, the recess 480 is formed by pressing or the like. Therefore, the recess 480 can be formed more easily than when the recess 480 is formed by controlling the thickness of the active material layer 414 when forming the active material layer 414. Therefore, the energy storage device 10 with improved reliability can be manufactured more efficiently.

[0058] In the forming portion 415 of the electrode plate 401 according to the present embodiment, a plurality of recesses 480 are arranged in each of the first region 461 and the second region 462 along the winding direction (the X-axis direction in FIG. 6 ) of the electrode plate 401. The number of recesses 480 per unit length in the winding direction in the first region 461 is greater than the number of recesses 480 per unit length in the winding direction in the second region 462.

[0059] According to this configuration, the magnitude relationship between the first aperture ratio and the second aperture ratio can be determined by the magnitude of the number of recesses 480 per unit length in the winding direction. Therefore, the aperture ratio for each region can be controlled by controlling the number of recesses 480 per unit length in the winding direction of the electrode plate 401. This makes it possible to easily manufacture electrode plates 401 having different aperture ratios for the recesses 480 in each region. Therefore, it is possible to more efficiently manufacture energy storage devices 10 with improved reliability. More specifically, in this embodiment, the aperture areas of the multiple recesses 480 are approximately the same. Therefore, the aperture ratio for each region can be more accurately controlled by controlling the number of recesses 480 per unit length in the winding direction of the electrode plate 401.

[0060] The magnitude relationship between the first aperture ratio and the second aperture ratio may be determined based on the number of recesses 480 lined up in the short-side direction of the electrode plate 401. For example, consider a case where, in the first region 461 and the second region 462, a plurality of recesses 480 are lined up in the short-side direction but not in the winding direction, or a case where a plurality of recesses 480 are arranged at equal intervals in the winding direction and a plurality of recesses 480 are lined up in the short-side direction. In this case, the magnitude relationship between the first aperture ratio and the second aperture ratio may be determined based on the number of recesses 480 per unit length in the short-side direction of the electrode plate 401.

[0061] In this embodiment, a plurality of recesses 480 are formed so that the opening ratio of each region in forming portion 415 changes gradually in the direction of the winding axis Wd (the Y-axis direction in FIG. 6 ). Specifically, this is explained as follows.

[0062] In electrode plate 401 according to the present embodiment, forming portion 415 further includes a third region 463 located between first region 461 and second region 462 in winding axis direction Wd (see FIG. 6 ). A third aperture ratio, which is the aperture ratio of recesses 480 in third region 463, is smaller than the first aperture ratio and larger than the second aperture ratio.

[0063] As described above, in the present embodiment, the second aperture ratio, the third aperture ratio, and the first aperture ratio increase in this order. That is, when comparing the aperture ratios of recesses 480 in the three regions of formed portion 415, the aperture ratio of the region closer to non-formed portion 416 is greater than the aperture ratio of the region farther from non-formed portion 416. In other words, the aperture ratios of recesses 480 in the three regions of formed portion 415 increase in order of decreasing amount of elongation in the winding direction caused by differences in density of active material layer 414, etc. Therefore, distortion of electrode plate 401 can be more effectively suppressed or corrected.

[0064] More specifically, in forming portion 415 according to the present embodiment, the opening ratio of recess 480 changes in more stages in the winding axis direction Wd. That is, in forming portion 415, the opening ratio of recess 480 increases from the other side to one side in the winding axis direction Wd.

[0065] As described above, in the present embodiment, the opening ratio of recesses 480 in formed portion 415 increases as they approach non-formed portion 416. In other words, the opening ratio of recesses 480 increases as the amount of elongation in the winding direction caused by differences in density of active material layer 414 decreases. Therefore, distortion of electrode plate 401 can be more effectively suppressed or corrected.

[0066] FIG. 6 illustrates a state in which one row of recesses 480 is formed by multiple recesses 480 lined up in the X-axis direction, and six rows of recesses 480 are lined up at equal intervals in the winding axis direction Wd (Y-axis direction). The number of recesses 480 included in each of these six rows of recesses 480 increases toward the non-forming portion 416. In other words, in FIG. 6, the opening ratio of the recesses 480 increases in six stages as the recesses 480 move from the other side to one side in the winding axis direction Wd (from the negative Y-axis direction to the positive Y-axis direction). In other words, the opening ratio of the recesses 480 may vary in the winding axis direction Wd within each of the first region 461, the second region 462, and the third region 463. For example, consider a case in which each of these six rows of recesses 480 is divided into six mutually different regions. In this case, the first region 461 includes a first region A and a first region B in descending order of proximity from the non-forming portion 416, and the second region 462 includes a second region A and a second region B in descending order of proximity from the non-forming portion 416. The third region 463 includes a third region A and a third region B in descending order of proximity from the non-forming portion 416. Furthermore, if the aperture ratios of the recesses 480 in each of these regions are first aperture ratio A, first aperture ratio B, second aperture ratio A, second aperture ratio B, third aperture ratio A, and third aperture ratio B, then the order is first aperture ratio A > first aperture ratio B > third aperture ratio A > third aperture ratio B > second aperture ratio A > second aperture ratio B. In other words, the aperture ratios of the six regions decrease with increasing distance from the non-forming portion 416. In this way, the aperture ratios of the recesses 480 vary in multiple stages, which can more efficiently suppress or correct distortion of the electrode plate 401 (see FIG. 5 ), in which the amount of elongation in the winding direction due to thermal expansion of the active material layer 414 gradually changes in the winding axis direction Wd.

[0067] In the above description, each of the first region 461, the second region 462, and the third region 463 includes two regions (comparison regions) used for comparing the aperture ratios of the recesses 480. However, each of the first region 461, the second region 462, and the third region 463 may include three or more comparison regions.

[0068] In the present embodiment, multiple recesses 480 are formed in electrode plate 401 that has been distorted by vacuum drying (see FIG. 6 ). However, multiple recesses 480 may be formed in formation portion 415 before vacuum drying electrode plate 401. For example, multiple recesses 480 may be formed in formation portion 415 of electrode plate 401 in the layout shown in FIG. 6 after electrode plate 401 is compressed to make the thickness of active material layer 414 uniform, but before vacuum drying.

[0069] The above has described the energy storage element 10 according to the embodiment, focusing on the configuration of the electrode assembly 400. However, the configuration of the electrode assembly 400 included in the energy storage element 10 may differ from the configuration described using Figures 2 to 9. Therefore, the following will describe the configuration of the electrode assembly 400, focusing on the differences from the above embodiment. Each of the electrode plates 401a, 401b, and 401c shown in the following modifications is an electrode plate that can be included in the electrode assembly 400 of the energy storage element 10 in place of the electrode plate 401 according to the embodiment.

[0070] 10 is a plan view showing the general configuration of an electrode plate 401a according to a first modification of the embodiment. As shown in FIG. 10, the electrode plate 401a according to this modification has a plurality of recesses 480, and a first aperture ratio, which is the aperture ratio of the recesses 480 in a first region 461, is larger than a second aperture ratio, which is the aperture ratio of the recesses 480 in a second region 462. These configurations are common to the electrode plate 401 according to the embodiment.

[0071] In this modified example, the opening areas of the multiple recesses 480 are different from one another, resulting in a first opening ratio greater than the second opening ratio. In this respect, the electrode plate 401 according to the embodiment differs. Specifically, FIG. 10 illustrates a state in which one row of recesses 480 is formed by multiple recesses 480 aligned in the X-axis direction, and six rows of recesses 480 are aligned at equal intervals in the winding axis direction Wd (Y-axis direction). Each of these six rows of recesses 480 includes the same number of recesses 480. However, the opening areas of the recesses 480 included in each row of recesses 480 increase from the other side to one side in the winding axis direction Wd. In other words, the opening areas of the recesses 480 closer to the non-forming portion 416 are greater than the opening areas of the recesses 480 farther from the non-forming portion 416. Therefore, as shown in FIG. 10, the number of recesses 480 included in each of the second region 462, the third region 463, and the first region 461 is the same at "4", but the second aperture ratio, the third aperture ratio, and the first aperture ratio are larger in that order.

[0072] Even in this case, the same effect as in the above embodiment is achieved. That is, the difference in the amount of elongation in the winding direction of the forming portion 415 due to thermal expansion of the active material layer 414 included in the electrode plate 401a, which is caused by the difference in the position of the winding axis Wd, is reduced. As a result, distortion of the electrode plate 401a caused by the difference in the amount of elongation is suppressed or corrected, thereby suppressing winding misalignment of the electrode plate 401a.

[0073] 10 , the six rows of recesses 480 each include the same number of recesses 480, but the six rows of recesses 480 may include different numbers of recesses 480. For example, the number of recesses 480 included in each of the six rows of recesses 480 may increase as the row approaches the non-forming portion 416. In other words, the opening ratio of the recesses 480 in each region may be controlled by changing both the number and opening area of ​​the recesses 480 in each region.

[0074] 11 is a plan view showing the outline of the configuration of an electrode plate 401b according to Modification 2 of the embodiment. As shown in Fig. 11, the electrode plate 401b according to this modification has a plurality of recesses 480, and a first aperture ratio, which is the aperture ratio of the recesses 480 in a first region 461, is larger than a second aperture ratio, which is the aperture ratio of the recesses 480 in a second region 462. These configurations are common to the electrode plate 401 according to the embodiment.

[0075] In this modification, a first region 461 including an end on one side in the direction of winding axis Wd (the positive Y-axis direction in FIG. 11 ) has a plurality of recesses 480, and a second region 462 including an end on the other side in the direction of winding axis Wd (the negative Y-axis direction in FIG. 11 ) has no recesses 480. That is, in this modification, the second aperture ratio is "0", and therefore the first aperture ratio is larger than the second aperture ratio, and in this respect, it differs from electrode plate 401 according to the embodiment.

[0076] Even in this case, the same effect as in the above embodiment is achieved. That is, the difference in the amount of elongation in the winding direction of the forming portion 415 due to thermal expansion of the active material layer 414 of the electrode plate 401b, which is caused by the difference in the position of the winding axis Wd, is reduced. As a result, distortion of the electrode plate 401b caused by the difference in the amount of elongation is suppressed or corrected, thereby suppressing winding misalignment of the electrode plate 401b.

[0077] 11 , it is assumed that the density of active material layer 414 is substantially constant in the winding axis direction Wd, and therefore it is not necessary to adjust the amount of elongation in the winding direction (X-axis direction in FIG. 11 ) by one or more recesses 480 within second region 462. In this case, second region 462 does not need to include recesses 480.

[0078] 12 is a partial cross-sectional view showing the outline of the configuration of an electrode plate 401c according to a third modification of the embodiment. The electrode plate 401c according to this modification includes a plurality of recesses 480c arranged in the layout shown in FIG. 6, similar to the electrode plate 401 according to the embodiment. In the electrode plate 401c, a first aperture ratio, which is the aperture ratio of the recesses 480 in the first region 461, is larger than a second aperture ratio, which is the aperture ratio of the recesses 480 in the second region 462. These configurations are common to the electrode plate 401 according to the embodiment.

[0079] In this modification, active material layers 414 are provided on both sides of current collector foil 411 in the thickness direction (Z-axis direction), and recesses 480 provided in one of these two active material layers 414 (the active material layer 414 in the positive Z-axis direction in FIG. 12 ) are formed by recessing only active material layer 414. In other words, the portion of current collector foil 411 adjacent to recesses 480 in the Z-axis direction is not substantially curved or compressed.

[0080] Even in this case, the electrode plate 401c has a recess 480c, which is a portion that is deformed so as to recess from one side to the other in the thickness direction of the electrode plate 401c and is thinner than the other portions. Therefore, the recess 480c can function as a portion that makes the electrode plate 401c easier to stretch. As a result, the difference in the amount of elongation in the winding direction of the forming portion 415 due to thermal expansion of the active material layer 414 of the electrode plate 401c, which is caused by the difference in the position of the winding axis Wd, is reduced. As a result, distortion of the electrode plate 401c caused by the difference in the amount of elongation is suppressed or corrected, thereby suppressing winding misalignment of the electrode plate 401c.

[0081] 13 is a plan view schematically illustrating the configuration of an energy storage device 900 including the energy storage device 10 according to the embodiment. As shown in FIG. 13 , the energy storage device 10 according to the embodiment may be used in the energy storage device 900. In this case, the technology of the present invention may be applied to at least one energy storage element 10 included in the energy storage device 900.

[0082] The energy storage device 900 shown in FIG. 13 includes a plurality of energy storage units 800 arranged therein. The energy storage unit 800 is composed of a plurality of electrically connected energy storage elements 10. The energy storage device 900 may include a bus bar (not shown) that electrically connects the plurality of energy storage elements 10, and a bus bar (not shown) that electrically connects the plurality of energy storage units 800. The energy storage unit 800 or the energy storage device 900 may include a state monitoring device (not shown) that monitors the state of one or more energy storage elements 10. The energy storage device 900 may include only one energy storage unit 800. In this case, the energy storage unit 800 may be referred to as a "energy storage device."

[0083] In this application, the energy storage device 900 includes one or more energy storage elements 10 according to the above-described embodiment, but the energy storage device 900 may include energy storage elements 10 according to each of variants 1 to 3 instead of or in addition to one or more energy storage elements 10.

[0084] While the configurations of the energy storage device 10 according to the embodiments of the present invention and their modifications have been described above, the present invention is not limited to the above-described embodiments and modifications. The embodiments and modifications disclosed herein are illustrative in all respects, and the scope of the present invention includes all modifications within the meaning and scope of the claims.

[0085] In the above embodiment and variants 1 to 3, various features have been described for the positive electrode plate 410, which is the positive electrode plate 401 of the two electrode plates 401 included in the electrode assembly 400. However, as described above, these various features may also be applied to the negative electrode plate 420, which is the negative electrode plate 401. That is, the following description may also be made for the negative electrode plate 420. In the electrode plate 401, which is the negative electrode plate 420, the non-formed portion 426 is located on one side of the formed portion 425 in the winding axis direction Wd of the electrode plate 401 (see FIG. 3 ). The formed portion 425 has multiple recesses 480 formed in the thickness direction of the electrode plate 401. The formed portion 425 includes a first region that includes an end on one side in the winding axis direction Wd and a second region that includes an end on the other side in the winding axis direction Wd. The first aperture ratio, which is the aperture ratio of the recesses 480 in the first region, is greater than the second aperture ratio, which is the aperture ratio of the recesses 480 in the second region. In this case, it is explained that in electrode plate 401 which is positive electrode plate 410, non-formed portion 416 is arranged on the other side of formed portion 415 in the winding axis direction Wd of electrode plate 401.

[0086] In this way, by providing the negative electrode plate 420, which is the negative electrode plate 401, with the plurality of recesses 480, the same effect as when the positive electrode plate 410 is provided with the plurality of recesses 480 is achieved. That is, the difference in the amount of elongation in the winding direction of the forming portion 425 due to thermal expansion of the active material layer 424 or the like, which is caused by the difference in the position in the winding axis direction Wd, is reduced. As a result, distortion of the electrode plate 401 caused by the difference in the amount of elongation is suppressed or corrected, and thereby, misalignment (winding misalignment) of the electrode plate 401 in the winding axis direction Wd in the wound electrode body 400 is suppressed.

[0087] The electrode plate 401 included in the electrode body 400 may have the active material layer 414 on only one side of the current collecting foil 411. Even in this case, by providing the electrode plate 401 with a plurality of recesses 480, distortion of the electrode plate 401 caused by thermal expansion of the active material layer 414 or the like is suppressed or corrected, thereby suppressing winding slippage of the electrode plate 401.

[0088] The electrode plate 401 may have recesses 480 on both sides in the thickness direction. For example, the electrode plate 401 shown in Fig. 7 may have recesses 480 recessed in the negative Z-axis direction on the surface of the forming portion 415 in the positive Z-axis direction, as well as recesses 480 recessed in the positive Z-axis direction on the surface in the negative Z-axis direction. In this case, the opening ratio in a predetermined region may be calculated using the total opening area of ​​the multiple recesses 480 included in the predetermined region in a plan view and provided on both sides of the forming portion 415 in the Z-axis direction.

[0089] The plurality of recesses 480 are preferably arranged in a staggered pattern, as shown in Figures 14 and 15. Figure 14 is a diagram showing a first example of a case where the plurality of recesses 480 are arranged in a staggered pattern, and Figure 15 is a diagram showing a second example of a case where the plurality of recesses 480 are arranged in a staggered pattern.

[0090] As shown in FIGS. 14 and 15 , when the recesses 480 are arranged in a staggered pattern, another recess 480 is present in the longitudinal direction (X-axis direction) of the electrode plate 410 in the region between two recesses 480 aligned in the lateral direction (Y-axis direction) of the electrode plate 410. That is, when viewed from the longitudinal direction (X-axis direction), another recess 480 is disposed in the gap between adjacent recesses 480 in the lateral direction (the same direction as the Y-axis direction and the winding axis Wd). Therefore, in the region including the staggered recesses 480, the effect of suppressing or correcting distortion of the electrode plate 410 by the recesses 480 is obtained evenly in the lateral direction of the electrode plate 410. When the recesses 480 are arranged in a staggered pattern as shown in FIGS. 14 or 15 , the aperture ratio of the recesses 480 can be changed in the lateral direction (Y-axis direction) by thinning out one or more recesses 480 from among the recesses 480 aligned in the longitudinal direction (X-axis direction).

[0091] More specifically, in the layout of the plurality of recesses 480 shown in FIG. 14 (hereinafter referred to as layout A), where P is the pitch, which is the distance between two recesses 480 in the longitudinal direction (X-axis direction), and D is the diameter of a circular recess 480 when viewed from the positive Z-axis direction, P≦2×D is satisfied. As a result, when viewed from the longitudinal direction (X-axis direction), the plurality of recesses are arranged without gaps in the lateral direction (Y-axis direction). On the other hand, in the layout of the plurality of recesses 480 shown in FIG. 15 (hereinafter referred to as layout B), P>2×D. Therefore, when viewed from the longitudinal direction (X-axis direction), a gap G exists between two recesses 480. Therefore, from the viewpoint of obtaining the effect of the recesses 480 of suppressing or correcting distortion of the electrode plate 410 evenly in the lateral direction of the electrode plate 410, layout A shown in FIG. 14 is preferable to layout B shown in FIG. 15.

[0092] The shape of recess 480 when viewed from the positive direction of the Z axis is not limited to a circular shape, and may be an elliptical shape, an oval shape, etc. When recess 480 is not a circular shape when viewed from the positive direction of the Z axis, the length of recess 480 in the short side direction (Y axis direction) of electrode plate 410 is used as value D indicating the size of recess 480.

[0093] Layout A and layout B may be mixed in one electrode plate 410. For example, layout A may be adopted as the layout for arranging the plurality of recesses 480 in the first region 461, and layout B may be adopted as the layout for arranging the plurality of recesses 480 in at least one of the second region 462 and the third region 462.

[0094] It is not necessary to impart any regularity to the layout of the plurality of recesses 480. The plurality of recesses 480 may be arranged randomly in the forming portion 415 of the electrode plate 401. Even in this case, if the opening areas of the plurality of recesses 480 are the same, for example, a state can be created in which the first opening ratio is greater than the second opening ratio as long as the density of the recesses 480 (the number of recesses 480 per unit area) increases from one side to the other side of the winding axis direction Wd (from the negative Y-axis direction to the positive Y-axis direction in FIG. 6 ).

[0095] The wound electrode assembly 400 included in the energy storage device 10 is housed in the container 100 in an orientation in which the winding axis W (see FIG. 3 ) is parallel to the opposing direction of the short side surfaces of the container body 110 (see FIG. 2 ). However, the orientation of the electrode assembly 400 is not limited to this. For example, the electrode assembly 400 may be housed in the container 100 in an orientation in which the winding axis W is parallel to the arrangement direction of the cover plate 120 and the container body 110.

[0096] The various supplementary points regarding the positive electrode plate 401 described above may be appropriately applied to the negative electrode plate 401. Configurations constructed by arbitrarily combining the components included in the above-described embodiments and their modifications are also included within the scope of the present invention.

[0097] The present invention can be applied to an electric storage element such as a lithium ion secondary battery.

[0098] REFERENCE SIGNS LIST 10 Energy storage element 400 Electrode body 401, 401a, 401b, 401c Electrode plate 410 Positive electrode plate 411, 421 Current collecting foil 414, 424 Active material layer 415, 425 Formed portion 416, 426 Non-formed portion 420 Negative electrode plate 430 Separator 456 Positive electrode connecting portion 461 First region 462 Second region 463 Third region 466 Negative electrode connecting portion 480, 480c Concave portion 485 Convex portion 800 Energy storage unit 900 Energy storage device

Claims

1. An energy storage element comprising an electrode body, wherein the electrode body comprises a wound electrode plate, the electrode plate comprising a formed portion where an active material layer is formed and a non-formed portion where the active material layer is not formed, the non-formed portion being arranged on one side of the formed portion in the direction of the winding axis of the electrode plate, the formed portion having a plurality of recesses formed therein that are recessed in the thickness direction of the electrode plate, the formed portion comprising a first region that includes an end portion on one side in the direction of the winding axis and a second region that includes an end portion on the other side in the direction of the winding axis, and a first aperture ratio that is the aperture ratio of the recesses in the first region is greater than a second aperture ratio that is the aperture ratio of the recesses in the second region.

2. The energy storage element according to claim 1, wherein a convex portion is formed on the rear side of the concave portion in the forming portion.

3. The energy storage element according to claim 1 or 2, wherein the electrode plate comprises a current collecting foil, and in the forming portion, the active material layer is formed on one side of the current collecting foil in the thickness direction, and each of the plurality of recesses is formed by the current collecting foil and the active material layer being recessed on the other side in the thickness direction.

4. A storage element as described in claim 1 or 2, wherein in each of the first region and the second region, a plurality of the recesses are arranged along the winding direction of the electrode plate, and the number of the recesses per unit length in the winding direction in the first region is greater than the number of the recesses per unit length in the winding direction in the second region.

5. The energy storage element according to claim 1 or 2, wherein the formation portion further comprises a third region located between the first region and the second region in the direction of the winding axis, and a third aperture ratio, which is the aperture ratio of the recess in the third region, is smaller than the first aperture ratio and larger than the second aperture ratio.

6. The energy storage element according to claim 1 or 2, wherein the opening ratio of the recess in the formation portion increases from the other side to the one side in the direction of the winding axis.

Images