Power storage device

Abstract

This power storage device includes an electrode body (14) and a current collector plate (18) that is fixed to an axial-direction end of the electrode body (14). A first electrode (11) of the electrode body has an uncoated portion (34), which is provided to an end positioned closer to the current collector plate (18) side than a laminated portion (35) is, and in which an electrode active material layer has not been laminated. The uncoated portion (34) is connected to the current collector plate (18) in a state where the uncoated portion (34) is bent toward the inner peripheral side of the electrode body. The uncoated portion (34) is provided with a first cut and a second cut. The uncoated portion (34) has: a no-cut portion (50) having a first end that is a winding-end end and a second end that is the first cut, there being no cut between the first end and the second end; and a with-cut portion (51) provided with a second cut between a third end that is the first cut and a fourth end that is a winding-start end. The winding-direction length of the no-cut portion (50) is at least one turn from the winding-end end of the uncoated portion (34).

Description

Power storage device

[0001] The present disclosure relates to an electricity storage device.

[0002] As described in Patent Document 1, a conventional energy storage device includes a cylindrical case with a bottom, an electrode assembly disposed within the case, and a cap assembly (sealing body) that closes the opening of the case. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and the positive and negative electrodes are wound with the separator interposed therebetween. A current collector plate is disposed above the electrode assembly within the case, and the current collector plate is fixed to and electrically connected to the axial end of the positive electrode of the electrode assembly. The current collector plate is electrically connected to the cap assembly. An uncoated portion free of active material is provided at the axial end of the positive electrode, and the uncoated portion has multiple independent regions separated in the winding direction by slits. The independent regions are fixed to the current collector plate in a pressurized and deformed state.

[0003] Japanese Patent Application Laid-Open No. 2006-12827

[0004] The configuration described in Patent Document 1 can suppress the occurrence of wrinkles when the axial end of the positive electrode is bent, compared to a configuration with a plain area without an independent area, thereby increasing the number of welding points between the current collector plate and the positive electrode and potentially reducing the electrical resistance at the connection between the positive electrode and the current collector plate. However, because the plain area has a narrow independent area at the outermost periphery, there is a possibility that the outermost independent area of ​​the plain area will deform outward after the tip end portion of the plain area is bent inward. In this case, the outermost periphery of the plain area may come into contact with the inner surface of the case, causing a short circuit.

[0005] Therefore, an object of the present disclosure is to provide a highly reliable electricity storage device that can suppress connection failures of electrode bodies connected to current collector plates.

[0006] The electricity storage device according to the present disclosure comprises a cylindrical case with a bottom, an electrode body in which the first electrode and the second electrode are wound together with the separator interposed therebetween, the electrode body having a first electrode, a second electrode having a polarity different from that of the first electrode, and a separator interposed between the first electrode and the second electrode, and a current collector plate fixed to and electrically connected to an end of the electrode body in the axial direction, the first electrode having a laminated portion in which an electrode active material layer is laminated, and an uncoated portion provided at the end on the current collector plate side and in which no electrode active material layer is laminated, the uncoated portion being bent toward the inner circumferential side of the electrode body. the uncoated portion is connected to the current collector plate in a state in which the uncoated portion has a first slit and at least one second slit located on the winding start side of the first slit so as to extend from the end on the current collector plate side, the uncoated portion includes an unslit portion in the region from the winding end to the first slit, where there is no slit at a middle position in the winding direction, and an slit portion in the region from the first slit to the winding start end, where the second slit is located at a middle position in the winding direction, and the length of the unslit portion in the winding direction is a length equivalent to one revolution or more from the winding end of the uncoated portion.

[0007] According to the present disclosure, a first electrode is connected to a current collector plate, and an uncoated portion of the first electrode is provided with a slit portion. This prevents wrinkles from forming in the uncoated portion when the uncoated portion is bent toward the inner periphery. The uncoated portion also has an unslit portion between a first end, which is the outermost winding end, and a second end, which is the first slit. The unslit portion has a length in the winding direction that is equal to or longer than one full turn from the winding end of the uncoated portion. This prevents a small, independent region separated in the winding direction by a slit at the outermost periphery of the uncoated portion. This prevents a portion of the outermost winding portion of the uncoated portion from being bent toward the outer periphery and coming into contact with the case, thereby preventing a short circuit. This prevents poor connection of the electrode body connected to the current collector plate and improves the reliability of the energy storage device.

[0008] FIG. 2 is an axial cross-sectional view of an electricity storage device according to an embodiment of the present disclosure. FIG. 3 is an enlarged view of part A of FIG. 1 , showing a schematic view. FIG. 4 is a perspective view showing upper and lower current collector plates and electrode bodies constituting the electricity storage device of FIG. 1 , with a portion of the upper end cut away. FIG. 5 is a cross-sectional view taken along the line B-B of FIG. 1 . FIG. 6 is a schematic view showing a developed state of a positive electrode in an embodiment. FIG. 7 is a perspective view showing upper and lower current collector plates and electrode bodies constituting an electricity storage device according to another example of the embodiment, with a portion of the upper end cut away. FIG. 8 is a schematic view showing a developed state of a positive electrode constituting an electricity storage device according to another example of the embodiment. FIG. 9 is a diagram corresponding to FIG. 4 in an electricity storage device according to another example of the embodiment. FIG. 10 is a schematic view showing a developed state of a positive electrode constituting an electricity storage device according to another example of the embodiment. FIG. 11 is a schematic view showing a developed state of a positive electrode constituting an electricity storage device according to another example of the embodiment.

[0009] Hereinafter, an embodiment of the power storage device according to the present disclosure will be described in detail with reference to the drawings. The power storage device according to the present disclosure may be a battery using an aqueous electrolyte or a battery using a nonaqueous electrolyte. Hereinafter, a cylindrical nonaqueous electrolyte secondary battery will be described as the power storage device according to the embodiment. However, the power storage device according to the present disclosure may have various configurations, such as a rectangular cylindrical shape, as long as it is a power storage device including a cylindrical case with a bottom, a wound electrode assembly disposed in the case, and a current collector plate fixed to and electrically connected to the axial end of the electrode assembly.

[0010] It is anticipated from the beginning that new embodiments may be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant description will be omitted. Furthermore, the drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component do not necessarily match between different drawings. In this specification, the axial opening side of the case 15 of the cylindrical secondary battery 10 is referred to as the "top" and the axial bottom side as the "bottom." That is, the bottom of the case 15 will be described as the bottom end. The energy storage device disclosed herein does not necessarily only cover devices in which the bottom of the case is positioned vertically below the opening when in use. For example, the bottom of the case may be configured vertically above the opening when in use. Furthermore, the present disclosure is not limited to the following embodiments and variations thereof, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0011] Fig. 1 is an axial cross-sectional view of a secondary battery 10, which is an electricity storage device according to an embodiment. Fig. 2 is an enlarged view of part A in Fig. 1, showing a schematic view of a portion thereof. Fig. 3 is a perspective view showing upper and lower current collector plates 18, 17 and an electrode body 14 constituting the secondary battery 10, with a portion of the upper end broken away. Fig. 4 is a cross-sectional view taken along the line B-B in Fig. 1.

[0012] 1 to 4 , a secondary battery 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a case 15 which is a metal can, and a sealing body 16. The wound electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all in the form of a long, substantially rectangular strip. The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0013] In the electrode assembly 14 , the positive electrode 11 protrudes upward beyond the negative electrode 12 and the separator 13 , and the negative electrode 12 protrudes downward beyond the positive electrode 11 and the separator 13 .

[0014] As shown in FIG. 2 , the positive electrode 11 has a positive electrode uncoated portion 34 where the positive electrode active material layer 32 is not provided and the positive electrode core 30 is exposed. The positive electrode uncoated portion 34 is located at the upper end, which is one end of the winding axis direction (hereinafter sometimes referred to as the axial direction) of the positive electrode 11 from the winding start end to the winding end end in the electrode plate longitudinal direction. The electrode plate longitudinal direction corresponds to the winding direction of the positive electrode 11 or the negative electrode 12 in a wound state. It is the longitudinal direction of the elongated rectangle when the positive electrode 11 or the negative electrode 12 is viewed in the thickness direction when the positive electrode 11 or the negative electrode 12 is unfolded along a plane. Note that a positive electrode protective layer (not shown) may be provided between the positive electrode active material layer 32 and the positive electrode uncoated portion 34 at the upper end of the positive electrode 11 to prevent short-circuiting of the positive electrode core 30. The positive electrode active material layer 32 corresponds to an electrode active material layer.

[0015] The negative electrode 12 has a negative electrode uncoated portion 44 where the negative electrode active material layer 42 ( FIG. 2 ) is not provided and the negative electrode core 40 ( FIG. 2 ) is exposed. The negative electrode uncoated portion 44 is located at the lower end, which is the other end in the axial direction, from the winding start end to the winding end end in the electrode plate longitudinal direction of the negative electrode 12. Therefore, the upper axial end of the electrode body 14 is composed of the positive electrode uncoated portion 34, and the lower axial end of the electrode body 14 is composed of the negative electrode uncoated portion 44.

[0016] In this embodiment, the positive electrode 11 corresponds to the first electrode, and the negative electrode 12 corresponds to the second electrode having a polarity different from that of the first electrode. Note that the first electrode may be the negative electrode 12, and the second electrode may be the positive electrode 11.

[0017] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolytic solution), and may be a solid electrolyte using a gel polymer or the like. The secondary battery 10 is preferably a lithium ion battery. The electrolyte salt may be, for example, LiBF ４ , LiPF ６Examples of the non-aqueous solvent include esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted product in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine.

[0018] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP). From the viewpoint of suppressing a decrease in the charge-discharge cycle characteristics of a nonaqueous electrolyte secondary battery or improving input characteristics, the nonaqueous electrolyte preferably contains 5% by mass or more of FEC, and more preferably 5% by mass to 15% by mass of FEC, relative to the mass of the nonaqueous electrolyte.

[0019] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0020] The positive electrode 11 includes a positive electrode core 30 and positive electrode active material layers 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The thickness of the positive electrode core 30 is, for example, 10 μm to 30 μm. The positive electrode active material layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be fabricated, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode active material layers 32 on both sides of the positive electrode core 30. The positive electrode active material layer 32 may be formed on only one side of the positive electrode core 30. The thickness of the positive electrode active material layer 32 on one side of the positive electrode substrate 30 is, for example, 10 μm or more and 150 μm or less.

[0021] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0022] Examples of the conductive agent contained in the positive electrode active material layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode active material layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, or polyethylene oxide (PEO).

[0023] A positive electrode protective layer may be provided between the positive electrode active material layer 32 and the positive electrode uncoated portion 34 on both sides of the upper end of the positive electrode core 30. The positive electrode protective layer may be an inorganic filler protective layer containing, for example, an inorganic material additive such as alumina, a resin such as a water-insoluble polymer such as polyvinylidene fluoride (PVdF), and a conductive additive such as acetylene black (AB) or carbon black (CB) in a predetermined ratio. For example, the positive electrode protective layer may be configured to contain an inorganic material such as alumina, a resin such as polyvinylidene fluoride (PVdF), and a conductive additive in a mass ratio of 100:16.7:0.5. The conductive additive may be omitted from the positive electrode protective layer.

[0024] The negative electrode 12 includes a negative electrode core 40 and a negative electrode active material layer 42 formed on both sides of the negative electrode core 40. The negative electrode core 40 may be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The thickness of the negative electrode core 40 is, for example, 5 μm to 30 μm. The negative electrode active material layer 42 includes a negative electrode active material and a binder. The negative electrode 12 can be fabricated, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode active material layer 42 on both sides of the negative electrode core 40. The negative electrode active material layer 42 may be formed on only one side of the negative electrode core 40. The thickness of the negative electrode active material layer 42 on one side of the negative electrode substrate 40 is, for example, 10 μm or more and 150 μm or less.

[0025] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. The negative electrode active material layer 42 may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0026] As in the case of the positive electrode 11, the binder contained in the negative electrode active material layer 42 may be a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like, but is preferably styrene-butadiene rubber (SBR) or a modified product thereof. In addition to SBR or the like, the negative electrode active material layer 42 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0027] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0028] 1 , the secondary battery 10 has a metal negative electrode current collector 17 made of nickel, nickel alloy, or the like, on the axially lower side of the electrode body 14. An uncoated negative electrode portion 44 protruding from the electrode body 14 is joined to the negative electrode current collector 17, which is joined to the inner surface of the bottom plate of the case 15. The case 15, to which the uncoated negative electrode portion 44 is electrically connected via the negative electrode current collector 17, serves as the negative electrode terminal.

[0029] The secondary battery 10 has a positive current collector 18 disposed within the case 15. The positive current collector 18 is a metal, disk-shaped plate made of aluminum, aluminum alloy, or the like, disposed axially above the electrode body 14. A positive electrode uncoated portion 34 protruding from the electrode body 14 is joined to the positive current collector 18. As a result, the positive current collector 18 is fixed to and electrically connected to the axial upper end of the electrode body 14. The secondary battery 10 has a circular insulating plate 19 axially above the positive current collector 18.

[0030] One end of a positive electrode connection lead 20 is joined to the upper surface of the positive electrode current collector 18 by welding or the like, the positive electrode connection lead 20 passes through a through-hole in the insulating plate 19 and extends toward the sealing body 16, and the other end of the positive electrode connection lead 20 is connected to the underside of a filter 22 of the sealing body 16 by welding or the like. A cap 26 that forms the top plate of the sealing body 16 is electrically connected to the filter 22. This electrically connects the positive electrode current collector 18 to the cap 26, and the cap 26 serves as a positive electrode terminal. The positive electrode connection lead 20 is a conductive member made of a metal primarily composed of aluminum or the like.

[0031] The secondary battery 10 further includes a resin gasket 27 disposed between the case 15 and the sealing body 16. The gasket 27 is sandwiched between the case 15 and the sealing body 16 to insulate the sealing body 16 from the case 15. The gasket 27 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the case 15 from the sealing body 16. The case 15 has an annular groove 21 in part of its axial direction.

[0032] The grooved portion 21 can be formed, for example, by spinning a portion of the side surface radially inward to create a recess radially inward. The case 15 has a bottomed tubular portion including the grooved portion 21 and an annular shoulder portion. The bottomed tubular portion houses the electrode assembly 14 and the nonaqueous electrolyte, and the shoulder portion is bent radially inward from the end of the open side of the bottomed tubular portion and extends inward. The shoulder portion is formed when the upper end of the case 15 is bent inward and crimped onto the peripheral edge of the sealing body 16. The sealing body 16 is crimped and fixed to the case 15 with a gasket 27 interposed between the shoulder portion and the grooved portion 21. In this manner, the internal space of the secondary battery 10 is sealed.

[0033] The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The filter 22 has at least one through-hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, with the insulating member 24 interposed between their respective peripheral edges.

[0034] When the secondary battery 10 generates abnormal heat and the internal pressure of the secondary battery 10 rises, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures and gas is discharged from the through-hole 26a of the cap 26. This gas discharge prevents the secondary battery 10 from deforming or exploding due to an excessive increase in internal pressure, thereby improving the safety of the secondary battery 10. It also reduces the impact of deformation or rupture of the secondary battery 10 on adjacent components (not shown).

[0035] 1 to 5, the peripheral configuration of the joint between the electrode body 14 and the positive electrode current collector plate 18 in the upper part of the secondary battery 10, and the configuration of the positive electrode 11 will be described. Fig. 5 is a schematic diagram showing the expanded state of the positive electrode 11.

[0036] As shown in FIG. 2 , the positive electrode 11 has a laminated portion 35 in which positive electrode active material layers 32 are laminated on both sides of a positive electrode core 30, and a positive electrode uncoated portion 34 located above the laminated portion 35, closer to the positive electrode current collector plate 18. The positive electrode uncoated portion 34 has an axially extending portion 37 extending substantially parallel to the axial direction of the electrode body 14, and a current collector welded portion 38 bent in a bent or curved state from the upper end of the axially extending portion 37 toward the inner periphery and extending parallel to the lower surface of the positive electrode current collector plate 18. The current collector welded portion 38 is welded to the lower surface of the positive electrode current collector plate 18. A positive electrode protective layer may be provided on both sides of a portion of the axially extending portion 37 near the upper end of the laminated portion 35. 2 shows the current collector plate welded portion 38 and the underside of the positive current collector plate 18 as being spaced apart, but in reality, the upper surfaces of all current collector plate welded portions 38 in each winding portion of the positive electrode 11 are welded in contact with the underside of the positive current collector plate 18. As a result, the positive electrode uncoated portion 34 is provided at the upper end of the positive electrode 11 in the axial direction on the positive current collector plate 18 side, and no positive electrode active material layer is laminated thereon. In addition, the tip of the positive electrode uncoated portion 34 is connected to the positive current collector plate 18 in a state where it is bent toward the inner periphery of the electrode body 14.

[0037] 2, the current collector welds 38 of the positive electrode 11 partially overlap with each other at adjacent current collector welds 38. This reduces the electrical resistance between the positive electrode 11 and the positive current collector plate 18. Note that the current collector welds 38 in adjacent circumferential portions of the positive electrode 11 may not overlap.

[0038] Furthermore, in the embodiment, the positive electrode uncoated portion 34 has an uncut portion 50 provided at the outer peripheral end portion at the end on the positive electrode current collector plate 18 side, and a cut portion 51 provided in the remaining portion in the winding direction of the positive electrode 11. In Figure 2, of the positive electrode uncoated portion 34, the uncut portion 50 is indicated by a solid line, and the cut portion 51 is indicated by a dashed line.

[0039] As shown in the expanded state of the positive electrode 11 in FIG. 5 , the positive electrode uncoated portion 34 has a plurality of thin, straight slits 52, 53 formed along substantially the entire short side direction (the vertical direction in FIG. 5 ) of the positive electrode 11, extending from one end (the end (upper end) on the positive electrode current collector 18 side) to the other end (the boundary between the positive electrode uncoated portion 34 and the laminated portion 35). The plurality of slits 52, 53 do not have to be formed along substantially the entire short side direction of the positive electrode uncoated portion 34, but may be formed at a position including the end on the positive electrode current collector 18 side, for example, only at the tip end where bending toward the inner periphery is performed. The plurality of slits 52, 53 include a first slit 52 and a second slit 53. The second slits are a plurality of slits. The first slit 52 is located at the end of the slits, including the second slit 53, that is closest to the end of the winding in the winding direction. The second cut 53 is located closer to the start of winding than the first cut 52. In Fig. 5, the first cut 52 is shown as a cut that is wider in the winding direction than the second cut 53, but the first cut 52 and the second cut 53 may be thin cuts of the same width. Note that there may be only one second cut 53.

[0040] The uninterrupted portion 50 of the positive electrode uncoated portion 34 is a portion in which the first end is the outer peripheral winding end 54, the second end is the first slit 52, and there is no intermission between the first end and the second end. In other words, the uninterrupted portion 50 of the positive electrode uncoated portion 34 is a region without an intermission at the midpoint in the winding direction. The interrupted portion 51 of the positive electrode uncoated portion 34 is a portion in which the first slit 52 is the third end, the inner peripheral winding start end 55 is the fourth end, and a second slit 53 is provided between the third end and the fourth end. In other words, the interrupted portion 51 of the positive electrode uncoated portion 34 is a region in which the second slit 53 is provided at the midpoint in the winding direction. Furthermore, the winding direction length of the uninterrupted portion 50 (the left-right length in FIG. 5 ) is a length of at least one revolution from the winding end 54 of the positive electrode uncoated portion 34.

[0041] The positive electrode 11 is spirally wound together with the negative electrode 12 and the separator 13, and the tip of the positive electrode uncoated portion 34 is bent toward the inner periphery, thereby forming the electrode assembly 14 as shown in Figures 3 and 4. At this time, the tip of the negative electrode uncoated portion 44 shown in Figure 1 is also bent in a bent or curved state toward the inner periphery of the electrode assembly 14. In this state, when viewed from above as shown in Figure 4, the positive electrode uncoated portion 34 of the electrode assembly 14 has an uncut portion 50 arranged in at least the outermost circumferential portion, and a cut portion 51 having a plurality of second cuts 53 arranged inside the uncut portion 50.

[0042] According to the secondary battery 10 described above, the positive electrode uncoated portion 34 connected to the positive electrode current collector plate 18 has a slit portion 51 with a second slit 53. This prevents the positive electrode uncoated portion 34 from wrinkling when bent toward the inner periphery. The positive electrode uncoated portion 34 also has an unslit portion 50 between the first end, which is the outer peripheral winding end 54, and the second end, which is the first slit 52. The length of the unslit portion 50 in the winding direction is at least one full turn from the winding end 54 of the positive electrode uncoated portion 34. This prevents the outermost periphery of the positive electrode uncoated portion 34 from having a small, independent region separated by a slit in the winding direction. This means that only a portion of the unslit portion 50 is unlikely to bend in an unintended direction. This prevents a portion of the outermost periphery of the positive electrode uncoated portion 34 from bending toward the outer periphery and coming into contact with the case 15, thereby preventing a short circuit. Therefore, poor connection of the electrode body 14 connected to the positive current collector plate 18 can be suppressed, and the reliability of the secondary battery 10 can be improved.

[0043] Furthermore, the cut portion 51 is provided with a plurality of second cuts 53. This allows the winding direction length of each independent region 56 divided in the winding direction by the second cuts 53 to be reduced in the cut portion 51, making it easier for the independent regions 56 to face in a direction that does not cause wrinkles when bent. This further reduces the occurrence of wrinkles in the positive electrode uncoated portion 34 when bent.

[0044] On the other hand, in a comparative secondary battery in which the uncoated positive electrode portion connected to the positive current collector plate of the positive electrode is provided with an uninterrupted portion along the entire length in the winding direction, the radius of curvature of the uncoated positive electrode portion during winding decreases from the outermost periphery toward the inner periphery, which makes the inner periphery of the uncoated positive electrode portion more susceptible to wrinkles when the tip is bent toward the inner periphery.

[0045] Furthermore, in the secondary battery 10 of this embodiment, the length of the uninterrupted portion 50 in the winding direction can be two or more and six or fewer revolutions from the winding end 54 of the positive electrode uncoated portion 34. The radius of curvature of the positive electrode uncoated portion 34 in the winding direction is larger the closer to the outermost periphery, so wrinkles are less likely to occur even when the tip is bent inward. In particular, when the uninterrupted portion 50 is formed in a portion of the positive electrode uncoated portion 34 six or fewer revolutions from the winding end 54, wrinkles are less likely to occur. Furthermore, when the length of the uninterrupted portion 50 in the winding direction is two or more revolutions from the winding end 54 of the positive electrode uncoated portion 34, the uninterrupted portion 50 is provided not only at the outermost periphery during winding but also at a portion of the revolution that is further inward than the outermost periphery. As a result, the independent region 56 formed by the second slit 53 is located further inward from the outermost periphery. This more reliably prevents a portion of the positive electrode uncoated portion 34 in the winding direction from being bent outward and coming into contact with the case 15, thereby more reliably preventing a short circuit. In the secondary battery 10 of this embodiment, the length of the uninterrupted portion 50 in the winding direction may be set to be equal to or greater than one circumference around the inner periphery of the case 15 and equal to or less than two circumferences around the inner periphery of the case 15.

[0046] Fig. 6 is a perspective view showing the upper and lower positive and negative current collector plates 18 and 17 and the electrode body 14a that constitute a secondary battery according to another embodiment, with a portion of the upper end cut away. Fig. 7 is a schematic view showing the expanded state of the positive electrode 11a that constitutes the secondary battery according to another embodiment.

[0047] In this configuration, as shown in FIG. 6 , the orientation of the second slits 53a is inclined relative to the winding direction at the tip portion of the positive electrode uncoated portion 34a bent inward. To achieve this configuration, as shown in FIG. 7 , in the expanded state of the positive electrode 11, the extension line L1 extending from each second slit 53a toward the tip of the positive electrode uncoated portion 34a intersects with the extension line L2 extending toward the tip of the edge of the winding start end 55 of the slit portion 51 along the winding axis (in the direction from the stacked portion 35 toward the positive electrode uncoated portion 34a). This makes it easier to bend the positive electrode uncoated portion 34a toward the inner periphery while smoothly overlapping adjacent independent regions 56a in the winding direction. This further reduces the occurrence of wrinkles when the positive electrode uncoated portion 34a is bent.

[0048] Furthermore, each second cut 53a extends from the boundary 57 between the positive electrode uncoated portion 34a and the laminated portion 35 toward the tip of the positive electrode uncoated portion 34a. The boundary 57-side end T1, which is the innermost end of the second cut 53a, is located closer to the end of the winding than the tip end T2 of the positive electrode uncoated portion 34a of the second cut 53a. This makes it easier for the highly rigid boundary 57-side end (e.g., part P in FIG. 7 ) of the independent region 56a at the start of winding to overlap the boundary 57-side end (e.g., part Q in FIG. 7 ) of the independent region 56a at the end of winding when the positive electrode uncoated portion 34a shown in FIG. 7 is bent inward. Repeating this process from the start of winding toward the end of winding of the cut portion 51 more effectively suppresses the rise of the independent region 56a at the end of winding. Furthermore, the positive electrode uncoated portion 34a can be easily bent or nearly bent toward the inner periphery and wound while preventing wrinkles from forming in the positive electrode uncoated portion 34a. This makes it easier to reduce the vertical height of the bent positive electrode uncoated portion 34a.

[0049] Alternatively, each second cut 53a may be inclined in the opposite direction to the configuration shown in FIG. 7 , i.e., the edge of the second cut 53a on the boundary 57 side may be inclined closer to the start of winding than the tip end of the positive electrode uncoated portion 34a of the second cut 53a. In this configuration, when the positive electrode uncoated portion 34a is bent inward, the acute-angled tip of the independent region with low rigidity at the start of winding (e.g., the portion corresponding to the R portion in FIG. 7 ) may overlap the obtuse-angled tip of the independent region with high rigidity at the end of winding (e.g., the portion corresponding to the S portion in FIG. 7 ). This reduces the effect of suppressing the rising of the independent region 56a at the end of winding of the cut portion 51 compared to the configuration shown in FIG. 7 .

[0050] Furthermore, each second slit 53a is inclined at an angle α of 30 degrees or more and 80 degrees or less with respect to the boundary 57 between the positive electrode uncoated portion 34a and the laminated portion 35. This makes it easier to bend or nearly bend the positive electrode uncoated portion 34a inward while suppressing wrinkles in the positive electrode uncoated portion 34a. On the other hand, if the angle α is greater than 80 degrees, it becomes difficult to smoothly overlap adjacent independent regions 56a, thereby reducing the effect of suppressing wrinkles during bending. If the angle α is less than 30 degrees, the length of the second slit 53a becomes excessively large compared to the width of the end of the independent region 56a on the laminated portion 35 side in the winding direction. This makes the independent region 56a elongated and reduced in rigidity, making it difficult to hold the adjacent independent region bent inward.

[0051] In order to prevent wrinkles from occurring in the positive electrode uncoated portion 34a while making it easier to hold the adjacent independent region in a bent inward state, it is more preferable that the angle α of each second cut 53a be greater than or equal to 30 degrees and less than or equal to 60 degrees.

[0052] The inventors conducted an experiment in which the angle α was changed to several different angles in the range of 40 degrees to 90 degrees, and the folded height (height in the vertical direction) was compared when the uncoated positive electrode portion was bent inward so as not to cause wrinkles in the uncoated positive electrode portion. The results of this experiment showed that the folded height could be significantly reduced when the angle α was 60 degrees or less. In this example, the other configurations and operations are the same as those of Figures 1 to 5.

[0053] Figure 8 is a schematic diagram showing the expanded state of a positive electrode 11b constituting a secondary battery according to another embodiment. In this example, the second slit 53b in the configurations shown in Figures 6 and 7 has a triangular concave shape including a first linear portion 58 inclined with respect to the winding direction and a second linear portion 59 aligned along the short side of the positive electrode 11b. The direction of the first linear portion 58 is the same as the direction of the second slit 53a in the configuration shown in Figure 7. Adjacent independent regions 56b are separated by the second slit 53b. The first slit 52b has the same shape as the second slit 53b.

[0054] The second cut and the first cut may have a V-shaped concave shape including a first linear portion 58 and a second linear portion that is inclined with respect to the winding direction in the opposite direction to the first linear portion 58. In this example, the other configurations and functions are the same as those in Figures 1 to 5 or Figures 6 and 7.

[0055] 9 is a view corresponding to FIG. 4 of a secondary battery 10a according to another example of the embodiment. In the configuration of this example, the seamless portion 50a in the uncoated positive electrode portion 34c of the positive electrode 11c includes a plurality of peaks 60 that protrude upward, that is, in a direction from the laminated portion 35 (see FIG. 2) toward the positive current collector 18 (see FIG. 2), and a valley 61 that is located between two of the peaks 60 and recessed downward, that is, in a direction from the positive current collector 18 toward the laminated portion 35. In the seamless portion 50a, the peaks 60 and the valleys 61 are alternately arranged in the winding direction.

[0056] The positive current collector plate 18 and the two peaks 60 are joined by welding. In FIG. 9 , the peaks of the peaks 60 are shown within the dashed-line frame U1, and the bottoms of the valleys 61 are shown within the dashed-line frame U2. By controlling the bending of the positive uncoated portion 34c toward the inner periphery so as to concentrate wrinkles in the valleys 61 of the seamless portion 50a, wrinkles generated in the peaks 60 due to bending can be reduced. This increases the flat area on the top surfaces of the peaks 60, thereby increasing the bonding strength with the positive current collector plate 18. Furthermore, to increase the bonding area between the peaks 60 and the positive current collector plate 18, the length of the peaks 60 in the winding direction is preferably greater than the length of the valleys 61 in the winding direction. In this example, the other configurations and functions are similar to those of FIGS. 1 to 5 .

[0057] 10 is a schematic diagram showing the expanded state of a positive electrode 11d constituting a secondary battery of another example of the embodiment. In the configuration of this example, in the expanded state of the positive electrode 11d in the configuration shown in FIGS. 1 to 5, the length d1 of the entire unslit portion 50b of the positive electrode uncoated portion 34d along the short side of the positive electrode 11d, including the winding end end 54a of the unslit portion 50b, is smaller than the length d2 of the slit portion 51 along the short side, including the winding end end 62 of the slit portion 51. A portion of the winding end end 62 forms a first slit 52c.

[0058] According to the configuration of this example, the vertical length of the uninterrupted portion 50b of the positive electrode 11d in the unfolded state can be reduced. This further reduces the occurrence of wrinkles in the outer periphery when the portion near the winding end 54a, which forms the outer periphery of the positive electrode uncoated portion 34d, is bent or curved toward the inner periphery during winding. This increases the bonding strength between the positive electrode 11d and the positive current collector plate. Other configurations and functions of this example are similar to those of the configurations of FIGS. 1 to 5.

[0059] FIG. 11 is a schematic diagram showing the expanded state of a positive electrode 11e constituting a secondary battery according to another embodiment. In this example, in the expanded state of the positive electrode 11e shown in FIGS. 1 to 5, the winding end 54b of the seamless portion 50c is located closer to the winding start side of the positive electrode 11e than the winding end 35a of the laminated portion 35. As a result, the positive electrode uncoated portion 34e is not extended from the upper end of the winding end side of the laminated portion 35, which is the end on the positive electrode current collector plate side, and a stepped uncoated portion cut portion 63 is formed. In this case, as in the configurations of the above examples, the winding direction length of the seamless portion 50c is at least one full turn from the winding end of the positive electrode uncoated portion 34e.

[0060] According to the configuration of this example, the positive electrode uncoated portion 34e can be easily provided on the inner side of the outermost periphery of the positive electrode 11e, which includes the winding end 35a of the laminated portion 35. This allows the positive electrode uncoated portion 34e to be significantly separated from the inner periphery of the case 15 (see FIG. 1), thereby more reliably preventing a short circuit. Also, referring to FIG. 1, even if the outer diameters of the positive electrode current collector 18 and the insulating plate 19 are reduced, it is possible to more reliably prevent the outermost periphery of the positive electrode uncoated portion 34e from passing between the outer surfaces of the positive electrode current collector 18 and the insulating plate 19 and the inner periphery of the case 15 and coming into contact with the underside of the grooved portion 21, thereby preventing a short circuit.

[0061] On the other hand, it is possible to eliminate the seamless portion 50c and further increase the length of the uncoated cut portion 63 in the winding direction. However, in that case, the current path connecting the positive electrode and the positive current collector plate 18 would be significantly reduced. This would cause the electrical resistance at the connection between the positive electrode and the positive current collector plate 18 to become excessively high. The configuration of this example can prevent such inconvenience, and further, since the seamless portion 50c is provided for at least one turn in the winding direction from the winding end 54b of the positive electrode uncoated portion 34e, short circuits can be more reliably prevented. In this example, the other configurations and functions are the same as those of the configurations of FIGS. 1 to 5.

[0062] The present disclosure will be further described by the following embodiments. Configuration 1: A cylindrical case (15) with a bottom, and a first electrode (11, 11a, 11b, 11c, 11d, 11e, 12) disposed in the case (15), and a second electrode (12, 11, 11a, 11b, 11c, 11d, 11e) having a polarity different from that of the first electrode (11, 11a, 11b, 11c, 11d, 11e, 12), and the first electrode (11, 11a, 11b, 11c, 11d, 11e, 12). and the second electrodes (12, 11, 11a, 11b, 11c, 11d, 11e), and a separator (13) arranged between the first electrodes (11, 11a, 11b, 11c, 11d, 11e), wherein the first electrodes (11, 11a, 11b, 11c, 11d, 11e, 12) and the second electrodes (12, 11, 11a, 11b, 11c, 11d, 11e) are wound with the separator (13) interposed therebetween; a current collector plate (18) fixed to and electrically connected to an end portion in the axial direction of the electrode body (14, 14a), wherein the first electrode (11, 11a, 11b, 11c, 11d, 11e, 12) has a laminated portion (35) on which electrode active material layers (32, 42) are laminated, and an uncoated portion (34, 34a, 34b, 34c, 34d, 34e) provided at the end portion located closer to the current collector plate (18) than the laminated portion (35) and on which the electrode active material layer (32, 42) is not laminated, and the uncoated portion (34, 34a, 34b, 34c, 34d, 34e) is connected to the current collector plate (18) in a state where it is bent toward an inner periphery of the electrode body (14, 14a), The uncoated portion (34, 34a, 34b, 34c, 34d, 34e) has a first slit (52, 52a, 52b) and a second slit (53, 53a, 53b) located on the winding start side of the first slit (52, 52a, 52b) so as to extend from one end on the current collector plate (18) side to the other end, and the uncoated portion (34, 34a, 34b, 34c, 34d, 34e) has a first end which is the winding end end (54, 54a, 54b), a second end which is the first slit (52, 52a, 52b), and an unslit portion (50, 50a, 50b, 50c) with no slit between the first end and the second end, and a third end which is the first slit (52, 52a,a cut portion (51) having a fourth end (52b) and a fourth end (55) that is a winding start end, and the second cut (53, 53a, 53b) is provided between the third end and the fourth end, and the length of the uncut portion (50, 50a, 50b, 50c) in the winding direction is a length equivalent to one revolution or more from the winding end end (54, 54a, 54b) of the uncoated portion (34, 34a, 34b, 34c, 34d, 34e). Configuration 2: The power storage device (10, 10a) according to Configuration 1, wherein the at least one second cut (53, 53a, 53b) is a plurality of second cuts (53, 53a, 53b) provided in the cut portion (51). Configuration 3: The energy storage device (10, 10a) according to Configuration 1 or 2, wherein the length in the winding direction of the unslit portion (50, 50a, 50b, 50c) is a length of two or more and six or less revolutions from the winding end (54, 54a, 54b) of the uncoated portion (34, 34a, 34b, 34c, 34d, 34e).Configuration 4: The energy storage device (10) according to any one of Configurations 1 to 3, wherein, in a deployed state of the first electrode (11a, 11b, 12), an extension line (L1) of the second slit (53a, 53b) extending toward the tip of the uncoated portion (34a, 34b) intersects with an extension line (L2) extending toward the tip of the winding start end (55) of the slit portion (51). Configuration 5: The energy storage device (10) according to Configuration 4, wherein the second cuts (53a, 53b) extend from a boundary (57) between the uncoated portions (34a, 34b) and the laminated portion (35) toward the tip ends of the uncoated portions (34a, 34b), and an end (T1) of the second cuts (53a, 53b) on the boundary (57) side is located closer to the end of the winding than an end (T2) of the second cuts (57) on the tip side of the uncoated portions (34a, 34b).The electricity storage device (10) according to configuration 5, wherein the seamless portion (50a) is inclined at an angle of 30 degrees or more and 80 degrees or less with respect to a boundary (57) between the laminated portion (35) and the current collector plate (18).Configuration 7: The electricity storage device (10a) according to any one of configurations 1 to 6, wherein the seamless portion (50a) includes two peaks (60) protruding from the laminated portion (35) in a direction toward the current collector plate (18), and a valley (61) located between the two peaks (60) and recessed in a direction from the current collector plate (18) toward the laminated portion (35), and the current collector plate (18) and the two peaks (60) are joined. Configuration 8: The electricity storage device (10) according to any one of Configurations 1 to 3, and 7, wherein, in a deployed state of the first electrode (11d), a length (d1) of the winding end end (54a) of the seamless portion (50b) along the short side direction of the first electrode (11d) is smaller than a length (d2) of the winding end end (62) of the slit portion (51) along the short side direction.Configuration 9: The electricity storage device (10) according to any one of Configurations 1 to 8, wherein, in a deployed state of the first electrode (11e), the winding end end (54b) of the seamless portion (50c) is located closer to the winding start side of the first electrode (11e) than the winding end end (35a) of the laminated portion (35).

[0063] 10, 10a Secondary battery, 11, 11a, 11b, 11c, 11d, 11e Positive electrode, 12 Negative electrode, 13 Separator, 14, 14a Electrode body, 15 Case, 16 Sealing body, 17 Negative electrode current collector plate, 18 Positive electrode current collector plate, 19 Insulating plate, 20 Positive electrode connection lead, 21 Grooved portion, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Insulating member, 25 Upper valve body, 26 Cap, 27 Gasket, 30 Positive electrode core, 32 Positive electrode active material layer, 34, 34a, 34b, 34c, 34d, 34e Positive electrode uncoated portion, 35 Laminated portion, 37 Axial extension portion, 38 Current collector plate welding portion, 40 Negative electrode core, 42 Negative electrode active material layer, 44 Negative electrode uncoated portion, 50, 50a, 50b, 50c: uncut portion, 51: cut portion, 52, 52a, 52b: first cut, 53, 53a, 53b: second cut, 54, 54a, 54b: winding end end, 55: winding start end, 56, 56a, 56b: independent region, 57: boundary, 58: first straight portion, 59: second straight portion, 60: peak portion, 61: valley portion, 62: winding end end.

Claims

1. An electrode assembly comprising: a cylindrical case with a bottom; an electrode assembly arranged within the case, the electrode assembly having a first electrode, a second electrode having a polarity different from that of the first electrode, and a separator arranged between the first electrode and the second electrode, the first electrode and the second electrode being wound with the separator interposed therebetween; and a current collector plate fixed to and electrically connected to an end of the electrode assembly in the axial direction, wherein the first electrode has: a laminated portion where an electrode active material layer is laminated; and an uncoated portion which is provided at the end located closer to the current collector plate than the laminated portion and where the electrode active material layer is not laminated, the uncoated portion being connected to the current collector plate in a state where it is bent towards the inner periphery of the electrode assembly, and the uncoated portion has a first slit and a second slit located closer to the start of winding than the first slit so as to extend from one end on the current collector plate side to the other end, and the uncoated portion has: an uncut portion having a first end which is the end of winding, a second end which is the first cut, and no cut between the first end and the second end; and an cut portion having a third end which is the first cut, a fourth end which is the start of winding, and the second cut between the third end and the fourth end, wherein the length of the uncut portion in the winding direction is at least one revolution from the end of winding of the uncoated portion.

2. The energy storage device according to claim 1, wherein the second cut is a plurality of cuts provided in the cut portion.

3. The energy storage device according to claim 1 or 2, wherein the length of the uninterrupted portion in the winding direction is at least two turns and at most six turns from the winding end of the uncoated portion.

4. The energy storage device according to claim 1 or 2, wherein, in the unfolded state of the first electrode, an extension line of the second slit extending toward the tip of the uncoated portion intersects with an extension line of the slit portion extending toward the tip of the winding start end.

5. The energy storage device according to claim 4, wherein the second cut extends from the boundary between the uncoated portion and the laminated portion toward the tip of the uncoated portion, and the boundary side end of the second cut is located closer to the end of the winding than the tip side end of the second cut of the uncoated portion.

6. The energy storage device according to claim 5, wherein the second cut is provided at an angle of 30 degrees or more and 80 degrees or less with respect to the boundary between the uncoated portion and the laminated portion.

7. The energy storage device according to claim 1 or 2, wherein the seamless portion includes two peaks protruding from the laminated portion in a direction toward the current collector plate, and a valley portion located between the two peaks and recessed in a direction from the current collector plate toward the laminated portion, and the current collector plate and the two peaks are joined together.

8. The energy storage device according to claim 1 or 2, wherein, in the unfolded state of the first electrode, the length along the short side of the first electrode at the end of the winding of the unslit portion is smaller than the length along the short side of the winding of the end of the winding of the slit portion.

9. The energy storage device according to claim 1 or 2, wherein, in a deployed state of the first electrode, the winding end of the seamless portion is located closer to the winding start side of the first electrode than the winding end of the laminated portion.

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