Non-aqueous electrolyte secondary battery

Abstract

The present invention is characterized in that: a first electrode (11) has a first electrode core body (30) and a coating layer (31) that includes a first electrode mixture layer (32); the surface of the first electrode (11) is provided with a first electrode core body exposed part (34) where the coating layer (31) is not disposed and where the first electrode core body (30) is exposed; the coating layer (31) has a first region lined up with the first electrode core body exposed part (34) in the longitudinal direction of the first electrode (11), and a second region adjacent to the first electrode core body exposed part (34) and the first region (35) in the width direction of the first electrode (11); and, within the second region, at least part of a region overlapping a first electrode tab (20) in the width direction of the first electrode (11) is provided with a thick part (37) of greater thickness than other portions of the second region.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been known that include an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which a core exposed portion, where the positive electrode core is exposed, is provided in the longitudinal middle portion of the positive electrode. The core exposed portion is not formed across the entire width of the positive electrode, but is in contact with only one of both widthwise ends of the positive electrode. An electrode tab is also joined to the core exposed portion. To prevent the occurrence of internal short circuits, the core exposed portion and the electrode tab are covered with insulating protective tape or the like.

[0003] International Publication No. 2017 / 085917

[0004] Generally, for reasons such as reducing electrical resistance, the thickness of the electrode tab joined to the exposed portion of the core is greater than the thickness of one side of the mixture layer disposed on the surface of the core. In other words, the electrode tab protrudes in the thickness direction of the electrode. Therefore, when the electrode body is wound, misalignment may occur in the area where the thicknesses of the electrode tab and the mixture layer differ.

[0005] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including an electrode assembly in which a strip-shaped first electrode and a second electrode having different polarities are wound longitudinally with a separator interposed therebetween, the first electrode having a first electrode core and a coating layer disposed on the surface of the first electrode core and including a first electrode mixture layer, the surface of the first electrode having no coating layer disposed thereon and a first electrode core exposed portion where the first electrode core is exposed, the first electrode core exposed portion being disposed at both ends in the width direction of the first electrode the first electrode tab is connected to the first electrode core exposed portion and is led out from the one end, the coating layer has a first region aligned with the first electrode core exposed portion in the longitudinal direction of the first electrode, and a second region adjacent to the first electrode core exposed portion and the first region in the width direction of the first electrode, and at least a part of the second region overlapping with the first electrode tab in the width direction of the first electrode has a thick portion that is thicker than the rest of the second region.

[0006] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, it is possible to suppress the occurrence of misalignment when winding the electrode assembly.

[0007] 2 is an axial cross-sectional view of the nonaqueous electrolyte secondary battery of the first embodiment; FIG. 3 is a front view showing a developed state of a positive electrode included in the nonaqueous electrolyte secondary battery of the first embodiment; FIG. 4 is a cross-sectional view taken along line A-A in FIG. 2; and FIG. 5 is a view corresponding to FIG. 3 of a positive electrode included in the nonaqueous electrolyte secondary battery of the second embodiment.

[0008] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the nonaqueous electrolyte secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is initially assumed that the characteristic portions thereof will be used in appropriate combination.

[0009] [First Embodiment] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to a first embodiment. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), and an outer can 16 that houses the electrode assembly 14 and the nonaqueous electrolyte. The outer can 16 is a cylindrical metal container that is open on one axial side and has a bottom, and the opening of the outer can 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the nonaqueous electrolyte secondary battery 10 will be referred to as the "top" and the bottom side of the outer can 16 will be referred to as the "bottom."

[0010] The electrode assembly 14 has a structure in which a first electrode and a second electrode, which are strip-shaped and have different polarities, are wound in the longitudinal direction via a separator 13. In the following, a case in which the first electrode is a positive electrode 11 and the second electrode is a negative electrode 12 will be described.

[0011] The positive electrode 11, negative electrode 12, and separator 13 are spirally wound and stacked alternately in the radial direction of the electrode assembly 14. In the electrode assembly 14, the longitudinal direction of the positive electrode 11 and negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and negative electrode 12 is the axial direction. The nonaqueous electrolyte secondary battery 10 further includes a positive electrode tab 20 connected to the positive electrode 11 by welding or the like and extending from the upper end of the electrode assembly 14, and a negative electrode tab 21 connected to the negative electrode 12 by welding or the like and extending from the lower end of the electrode assembly 14.

[0012] The positive electrode 11 has a positive electrode core 30 and a coating layer 31 disposed on the surface of the positive electrode core 30. The positive electrode core 30 can be made of a foil of a metal, 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 its surface. The coating layer 31 is disposed on the surface of the positive electrode core 30 excluding a positive electrode core exposed portion 34 (see FIG. 2 ), which will be described later, and includes a positive electrode mixture layer 32. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer 32 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., onto the positive electrode core 30, drying the coating, and then compressing it.

[0013] The positive electrode mixture layer 32 is a layer containing particulate lithium-containing composite oxide as a positive electrode active material. The lithium-containing composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium-containing composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, Al, and Mn. Examples of suitable composite oxides include lithium-containing composite oxides containing Ni, Co, and Mn, and lithium-containing composite oxides containing Ni, Co, and Al.

[0014] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0015] The negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 41 disposed on the surface of the negative electrode core 40. The negative electrode core 40 can be made of a foil of a metal 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 negative electrode mixture layer 41 contains a negative electrode active material, a binder, and, if necessary, a conductive agent. The negative electrode mixture layer 41 can be produced by applying a negative electrode mixture slurry containing the negative electrode active material and the binder to the surface of the negative electrode core 40, drying the coating, and then compressing it.

[0016] The negative electrode mixture layer 41 generally contains, as the negative electrode active material, a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite, such as flake graphite, massive graphite, and amorphous graphite, and artificial graphite, such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Furthermore, the negative electrode active material may include a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element.

[0017] As with the positive electrode mixture layer 32, the binder contained in the negative electrode mixture layer 41 can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene butadiene rubber (SBR) is preferably used. The negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer 41 may also contain a conductive agent such as CNT.

[0018] 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. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0019] The non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0020] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0021] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. 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. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0022] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode tab 20 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode tab 21 passes through a through-hole in the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode tab 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode tab 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0023] As described above, the outer can 16 is a cylindrical metal container with a bottom and an opening at one axial end, and the opening of the outer can 16 is closed by a sealing body 17 .

[0024] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0025] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When abnormal heat generation causes an increase in the internal pressure of the battery, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged through a vent hole in the cap 27.

[0026] Next, the positive electrode 11 will be described in detail with reference to Figures 2 and 3. Figure 2 is a front view showing the positive electrode 11 in a developed state, and Figure 3 is a cross-sectional view taken along line AA in Figure 2.

[0027] 2 and 3 , the positive electrode 11 has a positive electrode core 30 and a coating layer 31 disposed on the surface of the positive electrode core 30 and including a positive electrode mixture layer 32. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The coating layer 31 is disposed on each of the first surface 11A and the second surface 11B of the positive electrode 11.

[0028] 2 , a positive electrode core exposed portion 34 where the coating layer 31 is not disposed and the positive electrode core 30 is exposed is provided in the longitudinal middle portion of the positive electrode 11. The positive electrode core exposed portions 34 are provided, for example, on the first surface 11A and the second surface 11B of the positive electrode 11, respectively, and are arranged at positions where they overlap each other in the thickness direction of the positive electrode 11. The length of the positive electrode core exposed portion 34 along the longitudinal direction of the positive electrode 11 is, for example, 5 mm or more and 50 mm or less. The positive electrode core exposed portion 34 can be produced by intermittent application in which the positive electrode mixture slurry is not applied to a portion of the positive electrode core 30.

[0029] The positive electrode substrate exposed portion 34 contacts only the upper end 11X of the positive electrode 11 in the width direction, but not the lower end 11Y of the positive electrode 11 in the width direction. A coating layer 31 is disposed on the surface of the positive electrode substrate 30 in a region that overlaps the positive electrode substrate exposed portion 34 in the width direction of the positive electrode 11. That is, the coating layer 31 can be divided into a first region 35 aligned with the positive electrode substrate exposed portion 34 in the longitudinal direction of the positive electrode 11 and a second region 36 adjacent to the positive electrode substrate exposed portion 34 and the first region 35 in the width direction of the positive electrode 11. Configuring the positive electrode substrate exposed portion 34 as described above increases the area of ​​the coating layer 31, including the positive electrode mixture layer 32, and facilitates increasing the capacity of the nonaqueous electrolyte secondary battery 10. The thickness of the coating layer 31 in the first region 35 is substantially the same as the thickness of the coating layer 31 in the second region 36, except for the region where the thick portion 37 (described later) is formed. The thickness of the coating layer 31 in the first region 35 and the thickness of the coating layer 31 in the second region 36 may be different from each other.

[0030] A positive electrode tab 20 is joined to the positive electrode substrate exposed portion 34 on the first surface 11A of the positive electrode 11. The positive electrode tab 20 extends from the upper end 11X of the positive electrode 11. The first surface 11A of the positive electrode 11 to which the positive electrode tab 20 is joined may be located on either the inner winding surface side or the outer winding surface side in the radial direction of the electrode body 14.

[0031] The positive electrode tab 20 is made of, for example, a metal containing aluminum as a main component. The thickness of the positive electrode tab 20 is greater than the thickness of one side of the positive electrode mixture layer 32 included in the coating layer 31 for reasons such as reducing electrical resistance. The thickness of the positive electrode tab 20 is, for example, 100 μm or more and 200 μm or less.

[0032] An insulating protective tape 50 is provided on the surface of the positive electrode 11, covering the positive electrode core exposed portion 34. The protective tape 50 covers the entire surface of the positive electrode core exposed portion 34, a portion of the positive electrode tab 20, and the coating layer 31 around the positive electrode core exposed portion 34. By providing the protective tape 50, short-circuiting between the positive electrode core exposed portion 34 and the positive electrode tab 20 and the negative electrode 12 can be suppressed.

[0033] The protective tape 50 is, for example, an adhesive tape having a base layer and an adhesive layer formed on one surface of the base layer. A heat-resistant layer containing inorganic particles such as metal oxide may be provided between the base layer and the adhesive layer. The base layer may be made of any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate). The thickness of the base layer is, for example, 5 μm or more and 50 μm or less, and preferably 10 μm or more and 30 μm or less.

[0034] The adhesive layer is a portion for adhering the protective tape 50 to the surface of the positive electrode 11. The thickness of the adhesive layer is, for example, 1 μm or more and 30 μm or less, and preferably 5 μm or more and 25 μm or less. The adhesive layer may contain at least one of a rubber-based polymer and an acrylic-based polymer. The rubber-based polymer and the acrylic-based polymer have adhesive properties, and therefore can adhere the protective tape 50 to the surface of the positive electrode 11. The adhesive layer may further contain, for example, a silicone-based polymer.

[0035] As shown in Figures 2 and 3, in at least a part of the second region 36 of the coating layer 31, an area that overlaps the positive electrode tab 20 and the positive electrode 11 in the width direction, has a thick portion 37 that is thicker than the other parts of the second region 36.

[0036] In this embodiment, the thick portion 37 includes the positive electrode mixture layer 32 and a resin layer 33 formed on the surface of the positive electrode mixture layer 32. That is, the thick portion 37 has a laminated structure made up of the positive electrode mixture layer 32 and the resin layer 33, and the coating layer 31 in the region other than the thick portion 37 has a single-layer structure made up of only the positive electrode mixture layer 32. The thickness of the positive electrode mixture layer 32 is approximately constant throughout the entire second region 36, and is, for example, 50 μm or more and 100 μm or less on one side of the positive electrode core 30. Therefore, the thick portion 37 is configured to be thicker than the region other than the thick portion 37 by the thickness of the resin layer 33.

[0037] If the coating layer 31 does not have the thick portion 37 and is composed only of the positive electrode mixture layer 32 having a substantially constant thickness, misalignment of the winding is likely to occur around the positive electrode tab 20 when the electrode body 14 is wound. This is because the thickness of the positive electrode tab 20 is greater than the thickness of the positive electrode mixture layer 32, resulting in a configuration in which the positive electrode tab 20 protrudes in the thickness direction of the positive electrode 11.

[0038] As a result of investigations by the present inventors, it has become clear that the thickness of the region of the second region 36 of the coating layer 31 that overlaps with the positive electrode tab 20 and the positive electrode 11 in the width direction has a significant effect on winding misalignment during winding of the electrode assembly 14. Specifically, as in the present embodiment, by providing a thick portion 37 in the region of the second region 36 of the coating layer 31 that overlaps with the positive electrode tab 20 and the positive electrode 11 in the width direction and reducing the thickness difference between the coating layer 31 and the positive electrode tab 20, it is possible to suppress the occurrence of winding misalignment during winding of the electrode assembly 14. Note that if the thickness of the entire coating layer 31 is increased, the outer diameter of the electrode assembly 14 will increase excessively, making it difficult to insert the electrode assembly 14 into the outer can 16.

[0039] In this embodiment, the thick portion 37 is provided so as to substantially coincide with a region of the second region 36 of the coating layer 31 that overlaps with the positive electrode tab 20 and the positive electrode 11 in the width direction. The thick portion 37 is provided across the entire width of the positive electrode 11 in the second region 36. Note that the thick portion 37 may be provided in only a portion of the second region 36 in the width direction of the positive electrode 11.

[0040] The thick portion 37 may be provided in a region of the second region 36 of the coating layer 31 that at least partially overlaps with the positive electrode tab 20 and the positive electrode 11 in the width direction. In other words, a portion of the thick portion 37 may be provided in a region of the second region 36 of the coating layer 31 that does not overlap with the positive electrode tab 20 and the positive electrode 11 in the width direction. On the other hand, if the area in which the thick portion 37 is provided increases excessively, the outer diameter of the electrode body 14 may become too large. Therefore, the thick portion 37 is preferably provided in a region of the second region 36 of the coating layer 31 that overlaps with the positive electrode substrate exposed portion 34 and the positive electrode 11 in the width direction.

[0041] As described above, the positive electrode tab 20 is joined to the first surface 11A of the positive electrode 11. Therefore, the thick portion 37 is preferably provided on the first surface 11A of the positive electrode 11. The thick portion 37 may also be provided on the second surface 11B of the positive electrode 11 to which the positive electrode tab 20 is not joined.

[0042] As described above, the thick portion 37 is configured to be thicker than the region other than the thick portion 37 by the thickness of the resin layer 33. The thickness of the thick portion 37 is preferably equal to or greater than the thickness of the positive electrode tab 20. The thickness of the thick portion 37 is, for example, 1.0 to 1.5 times, or may be 1.0 to 1.25 times, the thickness of the positive electrode tab 20. If the thickness of the thick portion 37 is more than 1.5 times the thickness of the positive electrode tab 20, the difference in thickness between the positive electrode tab 20 and the coating layer 31 becomes large, which may actually make winding slippage more likely to occur. The thickness of the thick portion 37 may be, for example, 100 μm to 300 μm, or 100 μm to 250 μm.

[0043] The resin layer 33 is a layer containing at least a resin material. The resin layer 33 may be, for example, a layer containing a resin material and inorganic particles. Examples of the inorganic particles contained in the resin layer 33 include metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles. Examples of the metal oxide particles include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide. Examples of the metal nitride particles include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of the metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Examples of the metal carbide particles include silicon carbide, boron carbide, titanium carbide, and tungsten carbide. Furthermore, the inorganic particles include zeolite (M ２／ｎ O.Al ２ O ３ xSiO ２ ・yH ２ O, M is a metal element, n is the valence of M, x≧2, y≧0), porous aluminosilicates such as talc (Mg ３ Si ４O １０ (OH) ２ ), layered silicates such as barium titanate (BaTiO ３ ), strontium titanate (SrTiO ３ These may be used alone or in combination of two or more.

[0044] The content of inorganic particles in the resin layer 33 is, for example, 50% by mass or more and 95% by mass or less, preferably 60% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 90% by mass or less, relative to the total mass of the resin layer 33.

[0045] The resin material contained in the resin layer 33 functions as a binder that bonds the individual inorganic particles together and between the inorganic particles and the positive electrode mixture layer 32. The resin material is preferably a polymer material, and examples thereof include fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide-based resins, polyamide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0046] The resin layer 33 preferably has a thickness such that the sum of the thickness of the positive electrode mixture layer 32 and the thickness of the resin layer 33 is equal to or greater than the thickness of the positive electrode tab 20. The thickness of the resin layer 33 is, for example, 50 μm or more and 200 μm or less. The thickness of the resin layer 33 may be approximately constant across the entire width of the positive electrode 11, or may vary in the width of the positive electrode 11.

[0047] The resin layer 33 can be prepared by applying a coating liquid containing dispersed inorganic particles to the surface of the positive electrode mixture layer 32. The coating liquid is prepared by mixing the inorganic particles and a resin material and then adding an appropriate amount of water or the like. The solid content concentration of the coating liquid is, for example, 3% by mass or more and 50% by mass or less. Examples of methods for applying the coating liquid to the surface of the positive electrode mixture layer 32 include gravure coating, spraying, die coating, roll coating, reverse roll coating, screen printing, and inkjet printing. The prepared coating may also be subjected to a drying process to remove the solvent. The drying method is not particularly limited, and may be, for example, natural drying, ventilation drying using hot air or the like, heat drying, reduced pressure / vacuum drying, or a combination thereof.

[0048] As described above, by providing the thick portion 37 in at least a part of the region of the second region 36 of the coating layer 31 that overlaps the positive electrode tab 20 and the positive electrode 11 in the width direction, it is possible to reduce the difference in thickness between the coating layer 31 and the positive electrode tab 20 in the width direction of the positive electrode 11. As a result, it is possible to suppress the occurrence of misalignment when the electrode body 14 is wound.

[0049] Furthermore, in the above embodiment, the positive electrode 11 has one positive electrode substrate exposed portion 34 , but may have two or more positive electrode substrate exposed portions 34 .

[0050] In addition, in the above embodiment, the first electrode is a positive electrode 11 and the second electrode is a negative electrode 12, but the first electrode may be a negative electrode 12 and the second electrode may be a positive electrode 11.

[0051] Second Embodiment Next, a positive electrode 11 constituting a nonaqueous electrolyte secondary battery 10 according to a second embodiment will be described in detail with reference to Fig. 4. Fig. 4 is a view of the positive electrode 11 according to the second embodiment, corresponding to Fig. 3. Below, the same reference numerals are used for components common to the first embodiment, and redundant explanations are omitted, and differences from the first embodiment will be mainly described.

[0052] As shown in Fig. 4, the positive electrode 11 of the second embodiment is similar to the positive electrode 11 of the first embodiment in that a thick portion 37 having a larger thickness than the remaining portion of the second region 36 is provided in a region of the second region 36 of the coating layer 31 that overlaps the positive electrode tab 20 and the positive electrode 11 in the width direction. On the other hand, the thick portion 37 of the second embodiment differs from the thick portion 37 of the first embodiment in that it is composed only of the positive electrode mixture layer 32 and does not include the resin layer 33. In other words, the coating layer 31 of the positive electrode 11 of the second embodiment is composed only of the positive electrode mixture layer 32.

[0053] An example of a method for forming the thick portion 37 having a locally large thickness is to locally reduce the linear pressure, which is the compression load relative to the roll width, when applying a positive electrode mixture slurry to the positive electrode core 30 and compressing it with a roll press or the like. According to this method, the packing density of the positive electrode mixture layer 32 arranged in the thick portion 37 becomes smaller than the packing density of the positive electrode mixture layer 32 arranged in regions other than the thick portion 37.

[0054] Another method for forming the thick portion 37 is, for example, to locally increase the amount of positive electrode mixture slurry applied when applying the positive electrode mixture slurry onto the positive electrode core 30. According to this method, the basis weight, which is the mass of the positive electrode mixture layer 32 per unit area, of the positive electrode mixture layer 32 arranged in the thick portion 37 becomes larger than the basis weight of the positive electrode mixture layer 32 arranged in the region other than the thick portion 37.

[0055] On the other hand, if the basis weight of the positive electrode mixture layer 32 arranged in the thick portion 37 is larger than the basis weight of the positive electrode mixture layer 32 arranged in a region other than the thick portion 37, the capacity of the positive electrode 11 in the thick portion 37 may become too large relative to the capacity of the negative electrode 12 facing the thick portion 37. In this case, there is a risk of Li deposition occurring in the negative electrode 12. Therefore, it is preferable that the capacity per unit mass of the positive electrode mixture layer 32 arranged in the thick portion 37 is smaller than the capacity per unit mass of the positive electrode mixture layer 32 arranged in a region of the second region 36 other than the thick portion 37. This makes it possible to maintain a balance between the capacity of the positive electrode 11 in the thick portion 37 and the capacity of the negative electrode 12 facing the thick portion 37. As a result, Li deposition does not occur in the negative electrode 12, and the occurrence of shear during winding of the electrode assembly 14 can be suppressed.

[0056] The capacity per unit mass of the positive electrode mixture layer 32 can be adjusted by changing the content of the positive electrode active material contained in the positive electrode mixture layer 32. That is, the content of the positive electrode active material in the first positive electrode mixture slurry applied to the region where the thick portion 37 is to be formed is made smaller than the content of the positive electrode active material in the second positive electrode mixture slurry applied to regions other than the region where the thick portion 37 is to be formed. This makes it possible to make the capacity per unit mass of the positive electrode mixture layer 32 arranged in the thick portion 37 smaller than the capacity per unit mass of the positive electrode mixture layer 32 arranged in regions of the second region 36 other than the thick portion 37. The content of the positive electrode active material in the first positive electrode mixture slurry is, for example, 50% by mass or more and 95% by mass or less, and the content of the positive electrode active material in the second positive electrode mixture slurry is, for example, 70% by mass or more and 99% by mass or less.

[0057] Furthermore, the positive electrode mixture layer 32 disposed in the thick portion 37 may be composed of a plurality of layers having different capacities per unit mass of the positive electrode mixture layer 32. For example, the positive electrode mixture layer 32 disposed in the thick portion 37 may have a laminated structure including a first layer in which the capacity per unit mass of the positive electrode mixture layer 32 is substantially the same as the capacity per unit mass of the positive electrode mixture layer 32 disposed in an area other than the thick portion 37, and a second layer in which the capacity per unit mass of the positive electrode mixture layer 32 is smaller than that of the first layer.

[0058] The present disclosure is further illustrated by the following embodiments: Configuration 1: a first electrode core exposed portion in contact with only one of both ends in a width direction of the first electrode, a first electrode tab connected to the first electrode core exposed portion and extending from the one end, the coating layer having a first region aligned with the first electrode core exposed portion in the longitudinal direction of the first electrode, and a second region adjacent to the first electrode core exposed portion and the first region in the width direction of the first electrode, and a thick portion having a thickness greater than that of the remaining part of the second region is provided in at least a portion of the second region that overlaps with the first electrode tab in the width direction of the first electrode. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the thickness of the thick portion is equal to or greater than the thickness of the first electrode tab.Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the thick portion has a laminated structure including the first electrode mixture layer and a resin layer disposed on the surface of the first electrode mixture layer.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the basis weight of the first electrode mixture layer disposed in the thick portion is greater than the basis weight of the first electrode mixture layer disposed in a region of the second region other than the thick portion.Configuration 5: The nonaqueous electrolyte secondary battery according to Configuration 4, wherein the capacity per unit mass of the first electrode mixture layer disposed in the thick portion is smaller than the capacity per unit mass of the first electrode mixture layer disposed in a region of the second region other than the thick portion.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the thick portion is provided across the entire width of the first electrode in the second region. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of configurations 1 to 6, wherein the first electrode is a positive electrode.

[0059] REFERENCE SIGNS LIST 10 nonaqueous electrolyte secondary battery, 11 positive electrode (first electrode), 11A first surface, 11B second surface, 11X upper end, 11Y lower end, 12 negative electrode (second electrode), 13 separator, 14 electrode body, 16 outer can, 17 sealing body, 18 insulating plate, 19 insulating plate, 20 positive electrode tab, 21 negative electrode tab, 22 grooved portion, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cap, 28 gasket, 30 positive electrode core, 31 coating layer, 32 positive electrode mixture layer, 33 resin layer, 34 positive electrode core exposed portion, 35 first region, 36 second region, 37 thick portion, 40 negative electrode core, 41 negative electrode mixture layer, 50 protective tape.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which strip-shaped first and second electrodes of opposite polarity are wound longitudinally with a separator interposed therebetween, wherein the first electrode comprises a first electrode core and a coating layer disposed on the surface of the first electrode core and including a first electrode mixture layer, the surface of the first electrode is free of the coating layer and has a first electrode core exposed portion where the first electrode core is exposed, the first electrode core exposed portion contacts only one of both widthwise ends of the first electrode, a first electrode tab is connected to the first electrode core exposed portion and is led out from the one end, and the coating layer comprises: a first region aligned with the first electrode core exposed portion in the longitudinal direction of the first electrode; and a second region adjacent to the first electrode core exposed portion and the first region in the widthwise direction of the first electrode, a thick portion having a thickness greater than that of other portions of the second region is provided in at least a portion of a region of the second region that overlaps with the first electrode tab in a width direction of the second region.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thickness of said thick portion is equal to or greater than the thickness of said first electrode tab.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thick portion has a laminated structure including the first electrode mixture layer and a resin layer disposed on the surface of the first electrode mixture layer.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the basis weight of the first electrode mixture layer disposed in the thick portion is greater than the basis weight of the first electrode mixture layer disposed in an area of ​​the second region other than the thick portion.

5. The nonaqueous electrolyte secondary battery according to claim 4, wherein the capacity per unit mass of the first electrode mixture layer disposed in the thick portion is smaller than the capacity per unit mass of the first electrode mixture layer disposed in an area of ​​the second region other than the thick portion.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thick portion is provided across the entire width of the first electrode in the second region.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode is a positive electrode.

Images