Electrode for secondary batteries, and secondary battery

Abstract

The present invention is characterized in that: a positive electrode (11) is provided with a long positive electrode core body (30), and a positive electrode mixture layer (32) and a coating layer (46) which are disposed on the positive electrode core body (30); the positive electrode core body (30) comprises, at an edge in the short-side direction of the positive electrode core body (30), a positive electrode core body exposed part (34) which extends in the longitudinal direction of the positive electrode core body (30) and in which the positive electrode core body (30) is exposed, a positive electrode mixture layer disposition part (33) in which the positive electrode mixture layer (32) is disposed, and a coating layer disposition part (35) in which the coating layer (46) is disposed between the positive electrode core body exposed part (34) and the positive electrode mixture layer disposition part (33); the coating layer (46) has a protective layer (48) that comprises an inorganic filler and a first binder, and an adhesive layer (50) that comprises a second binder; the adhesive layer (50) is disposed on the positive electrode core body (32) in the coating layer disposition part (35); and the protective layer (48) is disposed on the adhesive layer (50).

Description

Secondary battery electrode and secondary battery

[0001] The present disclosure relates to a technique for an electrode for a secondary battery and a secondary battery.

[0002] The secondary battery includes, for example, a wound electrode body in which a separator is disposed between a positive electrode having a positive electrode mixture layer disposed on a positive electrode core and a negative electrode having a negative electrode mixture layer disposed on a negative electrode core, and the positive electrode and negative electrode are wound together while being insulated by the separator.

[0003] For example, Patent Document 1 discloses that in a positive electrode constituting a wound electrode body, an insulating layer is disposed on the positive electrode core between the exposed portion of the positive electrode core and the portion where the positive electrode mixture layer is disposed, thereby suppressing the occurrence of short circuits between electrodes.

[0004] Japanese Patent Application Laid-Open No. 2020-72007

[0005] However, in the past, when the number of charge / discharge cycles increased, the protective layer sometimes fell off from the core body.

[0006] Therefore, an object of the present disclosure is to provide an electrode for a secondary battery in which the protective layer is prevented from falling off from the core body, and a secondary battery including the electrode.

[0007] An electrode for a secondary battery according to one aspect of the present disclosure comprises a long core body, a composite layer and a coating layer arranged on the core body, the core body having, at one end in the short direction of the core body, an exposed portion extending in the longitudinal direction of the core body and exposing the core body, a composite layer arrangement portion in which the composite layer is arranged, and a coating layer arrangement portion between the exposed portion and the composite layer arrangement portion in which the coating layer is arranged, the coating layer having a protective layer having an inorganic filler and a first binder, and an adhesive layer having a second binder, the adhesive layer being arranged on the core body in the coating layer arrangement portion, and the protective layer being arranged on the adhesive layer.

[0008] Furthermore, a secondary battery according to one aspect of the present disclosure includes an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and at least one of the positive electrode and the negative electrode is an electrode for the secondary battery.

[0009] According to one aspect of the present disclosure, it is possible to provide an electrode for a secondary battery in which the protective layer is prevented from falling off from the core body, and a secondary battery including the electrode.

[0010] FIG. 6 is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment. FIG. 7 is a partially enlarged cross-sectional view showing the configuration of the vicinity of the upper end of a wound electrode body in the winding axis direction. FIG. 8 is a schematic plan view showing a positive electrode before winding. FIG. 9 is a schematic cross-sectional view of the positive electrode taken along line A-A in FIG. 3. FIG. 10 is a partially enlarged cross-sectional view showing the configuration of the vicinity of the lower end of a wound electrode body in the winding axis direction. FIG. 11 is a schematic plan view showing a negative electrode before winding. FIG. 12 is a schematic cross-sectional view of the negative electrode taken along line A-A in FIG.

[0011] The drawings referred to in the following description of the embodiments are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual components.

[0012] Fig. 1 is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment. The secondary battery 10 shown in Fig. 1 includes an electrode assembly 14, an electrolyte, an outer can 15 that houses the electrode assembly 14, the electrolyte, etc., and a sealing body 16 that closes the opening of the outer can 15. The electrode assembly 14 is a wound electrode assembly in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. In the following description, for convenience of explanation, the sealing body 16 side will be referred to as "top" and the bottom side of the outer can 15 will be referred to as "bottom."

[0013] The electrolyte has, for example, ion conductivity (for example, lithium ion conductivity). The electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0014] The liquid electrolyte (electrolytic solution) contains, for example, 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

[0015] Furthermore, examples of the solid electrolyte that can be used include solid or gel-like polymer electrolytes, inorganic solid electrolytes, and the like. 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. For example, a polymer material that absorbs a non-aqueous solvent and gels is used as the matrix polymer. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. For example, the inorganic solid electrolyte can be a material known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, and the like). While the above-exemplified electrolytes are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may be an aqueous electrolyte.

[0016] The outer can 15 is, for example, a cylindrical metal container with a bottom. A gasket 27 is provided between the outer can 15 and the sealing body 16 to ensure airtightness inside the battery. The outer can 15 has, for example, a grooved portion 21 that protrudes inward from a portion of the side surface and supports the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and supports the sealing body 16 on its upper surface.

[0017] The sealing body 16 shown in FIG. 1 has a structure in which, in order from the electrode body 14 side, a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked. Each component constituting the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. If the internal pressure of the secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 23 may deform and rupture, 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 further increases, the upper valve body 25 may rupture, and gas may be discharged through the through-hole 26a of the cap 26.

[0018] The secondary battery 10 shown in FIG. 1 also includes a positive electrode current collector 18 disposed above the electrode assembly 14 in the winding axis direction, an annular insulating plate 19 disposed on the positive electrode current collector 18, and a connection lead 20. The positive electrode current collector 18 is a metal plate made of, for example, aluminum or an aluminum alloy. The connection lead 20 is a metal member made of, for example, aluminum or an aluminum alloy. The configuration of the positive electrode 11 will be described in detail later. A positive electrode core exposed portion 34, which is a part of a positive electrode core constituting the positive electrode 11, is joined to the positive electrode current collector 18 by welding or the like. The lower end of the connection lead 20 is joined to the upper surface of the positive electrode current collector 18 by welding or the like. The connection lead 20 extends through a through hole in the insulating plate 19 toward the sealing body 16, and the upper end of the connection lead 20 is joined to the lower surface of the filter 22 of the sealing body 16 by welding or the like. The positive electrode substrate exposed portion 34 is electrically connected to the filter 22 via the positive electrode current collector plate 18 and the connection lead 20. In other words, the cap 26 electrically connected to the filter 22 serves as the positive electrode terminal.

[0019] The secondary battery 10 shown in FIG. 1 also has a negative electrode current collector 17 arranged below the electrode assembly 14 in the winding axis direction. The negative electrode current collector 17 is a metal plate made of, for example, nickel or a nickel alloy. The configuration of the negative electrode 12 will be described in detail later; a negative electrode core exposed portion 44, which is a part of the negative electrode core constituting the negative electrode 12, is joined to the negative electrode current collector 17 by welding or the like. The negative electrode current collector 17 is then joined to the inner surface of the bottom plate of the outer can 15 by welding or the like. In other words, the negative electrode core exposed portion 44 is electrically connected to the outer can 15 via the negative electrode current collector 17, and the outer can 15 serves as a negative electrode terminal.

[0020] 1 employs an end-face current collecting structure in which exposed portions of the cores are joined to current collecting plates and current is collected directly from the cores in both the positive electrode 11 and the negative electrode 12. However, in the secondary battery of this embodiment, one of the positive and negative electrodes may have an end-face current collecting structure, and the other electrode may have a structure in which, instead of the end-face current collecting structure, an electrode lead is connected to the other electrode and current is collected via the electrode lead.

[0021] The configurations of the positive electrode 11, the negative electrode 12, and the separator 13 will be described in detail below.

[0022] Fig. 2 is a partially enlarged cross-sectional view showing the configuration of the vicinity of the upper end in the winding axis direction of a wound electrode body. Fig. 3 is a schematic plan view showing the positive electrode before winding. Fig. 4 is a schematic cross-sectional view of the positive electrode taken along line A-A in Fig. 3. As shown in Figs. 2 to 4, the positive electrode 11 has a long positive electrode core 30, and a positive electrode mixture layer 32 and a coating layer 46 disposed on the positive electrode core 30. In the positive electrode 11, the positive electrode mixture layer 32 and the coating layer 46 are disposed on both sides of the positive electrode core 30, but may be disposed on only one side of the positive electrode core 30.

[0023] 3 and 4 , the positive electrode core 30 has a positive electrode mixture layer arrangement portion 33 in which the positive electrode mixture layer 32 is arranged, a positive electrode core exposed portion 34 that extends in the longitudinal direction of the positive electrode core 30 at the upper end in the shorter direction of the positive electrode core 30 and exposes the positive electrode core 30, and a coating layer arrangement portion 35 in which a coating layer 46 is arranged between the positive electrode mixture layer arrangement portion 33 and the positive electrode core exposed portion 34. In the positive electrode core 30, the coating layer arrangement portion 35 may be a portion between the positive electrode core exposed portion 34 located at the upper end in the shorter direction of the positive electrode core 30 and the positive electrode mixture layer arrangement portion 33, or the coating layer arrangement portion 35 may be the entire portion between the positive electrode core exposed portion 34 located at the upper end in the shorter direction of the positive electrode core 30 and the positive electrode mixture layer arrangement portion 33. As shown in FIGS. 1 and 2 , the positive electrode substrate exposed portion 34 is, for example, bent toward the center of the electrode body 14 and joined to the positive electrode current collector plate 18 .

[0024] The positive electrode substrate 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 having such a metal disposed on the surface thereof.

[0025] The positive electrode mixture layer 32 is disposed on the positive electrode core 30 in the positive electrode mixture layer disposing portion 33, and contains, for example, a positive electrode active material, a binder, a conductive material, and the like.

[0026] Examples of the positive electrode active material include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z , Li x Ni 1-y M y O z , Li x Mn2O4, Li x Mn 2-y M yO4, LiMPO4, Li2MPO4F (M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3). These may be used alone or in combination of two or more. In terms of increasing the capacity of the secondary battery 10, the positive electrode active material is preferably Li x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z It is preferable that the lithium-nickel composite oxide contains a lithium-nickel composite oxide such as (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B; 0<x≦1.2, 0<y≦0.9, 2.0≦z≦2.3).

[0027] Examples of the conductive material include carbon particles such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. These may be used alone or in combination of two or more.

[0028] Examples of binders include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, carboxymethyl cellulose (CMC) or salts thereof (CMC-Na, CMC-K, CMC-NH4, etc., or partially neutralized salts), polyethylene oxide (PEO), etc. These may be used alone or in combination of two or more.

[0029] As shown in FIG. 4 , the coating layer 46 includes a protective layer 48 having an inorganic filler and a first binder, and an adhesive layer 50 having a second binder. The adhesive layer 50 is disposed on the positive electrode core 30 in the coating layer disposition portion 35, and the protective layer 48 is disposed on the adhesive layer 50. As shown in FIG. 4 , the adhesive layer 50 may be disposed over the entire coating layer disposition portion 35 or may be disposed over a portion of the coating layer disposition portion 35. When the adhesive layer 50 is disposed over a portion of the coating layer disposition portion 35, the protective layer 48 is disposed so as to cover the entire adhesive layer 50, and the protective layer 48 is disposed in the coating layer disposition portion 35 where the adhesive layer 50 is not disposed. The protective layer 48 may be disposed over the entire adhesive layer 50 or may be disposed over a portion of the adhesive layer 50. Note that a portion of the coating layer 46 may be wedged between the positive electrode mixture layer 32 and the positive electrode core 30, or may cover a portion of the positive electrode mixture layer 32.

[0030] The volume resistivity of the protective layer 48 is set to, for example, 10 ７ It is preferable that the resistance is Ω·cm or more, and 10 ９ The resistivity is more preferably Ω·cm or more. The protective layer 48 is preferably located opposite the negative electrode 12 via the separator 13, in that this can further suppress the occurrence of short circuits between the electrodes.

[0031] Examples of inorganic fillers contained in the protective layer 48 include oxides such as alumina, silica, zirconia, titania, magnesia, ceria, yttria, zinc oxide, iron oxide, barium titanium oxide, and alumina-silica composite oxide; nitrides such as silicon nitride, titanium nitride, boron nitride, and aluminum nitride; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; covalently bonded crystals such as silicon and diamond; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, boehmite, apatite, mullite, spinel, and olivine; and compounds containing at least one of these. Examples of inorganic fillers include SnO ２ The particles may be made electrically insulating by treating the surfaces of conductive particles such as oxides such as tin-indium oxide (ITO), carbonaceous materials such as carbon black and graphite with an electrically insulating material (for example, the material of the inorganic filler).

[0032] Examples of the first binder contained in the protective layer 48 and the second binder contained in the adhesive layer 50 include fluorine-containing polymers such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and copolymers of vinylidene fluoride and hexafluoropropylene, polyacrylonitrile (PAN), acrylic resin, polyolefin resin, styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyethylene oxide (PEO), copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, and polyamideimide.

[0033] The first binder and the second binder preferably contain polyvinylidene fluoride (PVDF) in terms of electrochemical stability, adhesiveness, etc., and in particular, the first binder preferably contains homo-type polyvinylidene fluoride in terms of adhesive strength with the adhesive layer 50, and the second binder preferably contains modified polyvinylidene fluoride in terms of adhesive strength with the core and protective layer 48. As the modified polyvinylidene fluoride, acid-modified polyvinylidene fluoride is preferred in terms of improving adhesiveness, and carboxylic acid-modified polyvinylidene fluoride is particularly preferred. Homo-type polyvinylidene fluoride is a vinylidene fluoride homopolymer into which no modifying groups such as carboxylic acid groups have been introduced.

[0034] The content of the inorganic filler and the first binder contained in the protective layer 48 is preferably in a range of 70:30 to 95:5 in mass ratio (inorganic filler:first binder), and more preferably in a range of 80:20 to 90:10. By setting the content of the inorganic filler and the first binder within the above ranges, the insulating properties of the protective layer 48 are further improved, and it becomes possible to further suppress the occurrence of short circuits between electrodes.

[0035] The content of the second binder in the adhesive layer 50 is preferably 95% by mass or more, and more preferably 100% by mass, in order to improve adhesion between the protective layer 48 and the core and further suppress detachment of the protective layer 48. The adhesive layer 50 may also contain a filler such as an inorganic filler, but the content is preferably 5% by mass or less, and more preferably 0% by mass, in order to reduce adhesion, etc.

[0036] The thickness of the adhesive layer 50 is preferably 0.03 μm or more, and more preferably 0.1 μm or more, in order to improve adhesion to the core body and the protective layer 48 and to further prevent the protective layer 48 from falling off. The upper limit of the thickness of the adhesive layer 50 may be, for example, 2.0 μm or less.

[0037] The porosity of the protective layer 48 is, for example, preferably 10% or more and 60% or less, more preferably 35% or more and 56% or less, and even more preferably 40% or more and 56% or less. When the porosity of the protective layer 48 satisfies the above range, for example, a decrease in the strength of the protective layer 48 is suppressed, and damage such as the occurrence of cracks in the protective layer 48 is suppressed even with a large number of charge / discharge cycles. Furthermore, when the porosity of the protective layer 48 satisfies the above range, for example, the insulating properties of the protective layer 48 are further improved, making it possible to further suppress the occurrence of short circuits between electrodes.

[0038] The porosity of the protective layer 48 is measured as follows. A backscattered electron image of the cross section of the protective layer is taken using a scanning electron microscope (SEM). The obtained cross-sectional image of the protective layer is imported into a computer and binarized using image analysis software (e.g., ImageJ, manufactured by the National Institutes of Health, USA). A binarized image is obtained in which particle cross sections in the cross-sectional image are colored black and voids between particles are colored white. The area of ​​the white region in this binarized image is determined, and the ratio of the area of ​​the white region to the area of ​​the cross-sectional image of the protective layer is calculated, thereby determining the porosity of the protective layer.

[0039] An example of a method for manufacturing the positive electrode 11 will be described. First, a slurry for the positive electrode mixture layer containing a positive electrode active material, a binder, and a conductive material is prepared. A slurry for the protective layer containing a first binder and an inorganic filler, and a slurry for the adhesive layer containing a second binder are also prepared. Then, the slurry for the positive electrode mixture layer is applied to the positive electrode core 30 in the positive electrode mixture layer placement portion 33, excluding an exposed portion at one end in the short direction of the positive electrode core 30. At the same time, a slurry for the adhesive layer is applied to the positive electrode core 30 in the coating layer placement portion 35, and then a slurry for the protective layer is applied thereon, thus performing a two-layer coating process. Next, the coating film of the positive electrode mixture layer 32 and the coating layer 46 (the adhesive layer 50 and the protective layer 48) applied to the positive electrode core 30 are dried and then rolled using a rolling roller or the like. This allows the positive electrode 11 of this embodiment to be obtained.

[0040] Fig. 5 is a partially enlarged cross-sectional view showing the configuration of the vicinity of the lower end of the winding axis direction of a wound electrode body. Fig. 6 is a schematic plan view showing the negative electrode before winding. Fig. 7 is a schematic cross-sectional view of the negative electrode taken along line A-A in Fig. 6. As shown in Figs. 5 to 7, the negative electrode 12 has an elongated negative electrode core 40, and a negative electrode mixture layer 42 and a coating layer 46 disposed on the negative electrode core 40. In the negative electrode 12, the negative electrode mixture layer 42 and the coating layer 46 are disposed on both sides of the negative electrode core 40, but may be disposed on only one side of the negative electrode core 40.

[0041] 6 and 7 , the negative electrode core 40 has a negative electrode mixture layer arrangement portion 43 in which the negative electrode mixture layer 42 is arranged, a negative electrode core exposed portion 44 that extends in the longitudinal direction of the negative electrode core 40 at the lower end in the shorter direction of the negative electrode core 40 and exposes the negative electrode core 40, and a coating layer arrangement portion 35 in which a coating layer 46 is arranged between the negative electrode mixture layer arrangement portion 43 and the negative electrode core exposed portion 44. In the negative electrode core 40, the coating layer arrangement portion 35 may be a portion between the negative electrode core exposed portion 44 located at the lower end in the shorter direction of the negative electrode core 40 and the negative electrode mixture layer arrangement portion 43, or the coating layer arrangement portion 35 may be the entire portion between the negative electrode core exposed portion 44 located at the lower end in the shorter direction of the negative electrode core 40 and the negative electrode mixture layer arrangement portion 43. As shown in FIGS. 1 and 5 , the negative electrode substrate exposed portion 44 is, for example, bent toward the center of the electrode body 14 and joined to the negative electrode current collector plate 17 .

[0042] The negative electrode substrate 40 can be made of a foil of a metal such as copper that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface thereof.

[0043] The negative electrode mixture layer 42 is disposed on the negative electrode substrate 40 in the negative electrode mixture layer disposing portion 43, and contains, for example, a negative electrode active material, a binder, and the like.

[0044] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Examples of 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. In addition to carbon materials, examples of negative electrode active materials include metals that alloy with lithium, such as Si and Sn, alloys containing such metals, and compounds containing such metals. Examples of binders include the same materials as those used in the positive electrode 11. The negative electrode mixture layer 42 may also contain a conductive agent.

[0045] The coating layer 46 is the same as that on the positive electrode side, and therefore its description will be omitted.

[0046] An example of a method for manufacturing the negative electrode 12 will be described. First, a negative electrode mixture layer slurry containing a negative electrode active material and a binder is prepared. A protective layer slurry containing a first binder and an inorganic filler, and an adhesive layer slurry containing a second binder are also prepared. The negative electrode mixture layer slurry is then applied to the negative electrode core 40 in the negative electrode mixture layer placement portion 43, excluding an exposed portion at one end in the short direction of the negative electrode core 40. The adhesive layer slurry is then applied to the negative electrode core 40 in the coating layer placement portion 35, and the protective layer slurry is then applied thereon, thus performing a two-layer coating process. Next, the coating film of the negative electrode mixture layer 42 and the coating layer 46 (the adhesive layer 50 and the protective layer 48) applied to the negative electrode core 40 are dried and then rolled using a rolling roller or the like. This allows the negative electrode 12 of this embodiment to be obtained.

[0047] In this embodiment, the coating layer 46 is applied to both the positive electrode 11 side and the negative electrode 12 side, but the coating layer 46 may be applied to either one of the positive electrode 11 or the negative electrode 12. Generally, to ensure efficient charging and discharging, the negative electrode mixture layer 42 is designed to be larger than the positive electrode mixture layer 32. This may cause the positive electrode core 30, on which the positive electrode mixture layer 32 is not disposed, to come into contact with the opposing negative electrode, resulting in a short circuit. Therefore, in order to prevent a short circuit between the two electrodes, it is preferable to apply the coating layer 46 to at least the positive electrode 11 side.

[0048] [Separator] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include olefin-based resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, the separator 13 may be a multilayer separator including a polyethylene layer and a polypropylene layer, and the surface of the separator 13 may be coated with a material such as an aramid-based resin or ceramic.

[0049] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0050] Example 1 [Preparation of Positive Electrode] A rock salt-type lithium-containing transition metal oxide (NCA) having a layered structure containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0) was mixed with acetylene black (AB) and polyvinylidene fluoride (PVDF) in a mass ratio of NCA:AB:PVDF = 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry was applied to the positive electrode mixture layer placement portion on both sides of a long aluminum foil, dried, and the coating was compressed using a roller to form a positive electrode mixture layer. Next, an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to homogeneous polyvinylidene fluoride and stirred to prepare a slurry for the adhesive layer. The obtained adhesive layer slurry was applied to the coating layer placement area (3 mm wide) on both sides of a long aluminum foil and then dried to form a 0.1 μm thick adhesive layer. Furthermore, a temperature above the melting point of PVDF was applied. Next, alumina and homo-type polyvinylidene fluoride were mixed in a mass ratio of alumina:polyvinylidene fluoride = 82:18, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a protective layer slurry. The obtained protective layer slurry was applied to the coating layer and then dried to form a protective layer with a thickness of 25 μm and a porosity of 45.0%. One end of the aluminum foil in the short direction was an exposed portion where the aluminum foil was exposed. In this way, a positive electrode was fabricated. The thickness of the adhesive layer and the porosity of the protective layer were evaluated using a SEM.

[0051] [Preparation of Negative Electrode] Lumped artificial graphite (C), silicon oxide (Si), sodium carboxymethylcellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of C:SiO:CMC-Na:SBR = 95:2:2:1, and an appropriate amount of water was added and stirred to prepare a negative electrode slurry. The resulting negative electrode slurry was applied to the negative electrode mixture layer-forming portion on both sides of a long electrolytic copper foil, dried, and the coating was compressed using a roller to form a negative electrode mixture layer. One end of the electrolytic copper foil in the short direction was an exposed portion where the electrolytic copper foil was exposed. In this way, a negative electrode was prepared.

[0052] [Preparation of Non-Aqueous Electrolyte] Lithium hexafluorophosphate (LiPF ) was added to a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of EC:DMC=30:70. ６ ) at 1 mol / L, LiBF ２ (C ２ O ４ ) were dissolved in a concentration of 0.1 mol / L to prepare a non-aqueous electrolyte solution.

[0053] [Secondary Battery Fabrication] A wound electrode assembly was prepared by spirally winding a positive electrode and a negative electrode with a polyethylene microporous membrane separator interposed therebetween. A positive electrode current collector and a negative electrode current collector were placed on the top and bottom of the electrode assembly, respectively. At the top end of the electrode assembly, the exposed portion of the aluminum foil serving as the positive electrode core was folded toward the center of the electrode assembly and then welded to the positive electrode current collector. At the bottom end of the electrode assembly, the exposed portion of the electrolytic copper foil serving as the negative electrode core was folded toward the center of the electrode assembly and then welded to the negative electrode current collector. The electrode assembly was then housed in a bottomed cylindrical outer can, and the negative electrode current collector was welded to the bottom of the bottomed cylindrical outer can. The positive electrode current collector and the sealing plate were connected with a connecting tab. After a nonaqueous electrolyte was poured into the outer can, the opening of the outer can was sealed with a sealing plate via a gasket, completing the fabrication of a cylindrical secondary battery.

[0054] Example 2 A secondary battery was fabricated in the same manner as in Example 1, except that the thickness of the adhesive layer was set to 0.03 μm.

[0055] Example 3 A secondary battery was fabricated in the same manner as in Example 1, except that the thickness of the adhesive layer was set to 1.0 μm.

[0056] Example 4 A secondary battery was fabricated in the same manner as in Example 1, except that in preparing the slurry for the adhesive layer, the homo-type polyvinylidene fluoride was replaced with carboxylic acid-modified polyvinylidene fluoride into which a carboxylic acid group had been introduced.

[0057] Example 5 A secondary battery was fabricated in the same manner as in Example 1, except that in preparing the slurry for the protective layer, alumina and homotype polyvinylidene fluoride were mixed in a mass ratio of alumina:polyvinylidene fluoride = 61:39 to form a protective layer with a porosity of 10.0%.

[0058] Example 6 A secondary battery was fabricated in the same manner as in Example 1, except that in preparing the slurry for the protective layer, alumina and homotype polyvinylidene fluoride were mixed in a mass ratio of alumina:polyvinylidene fluoride = 60:40 to form a protective layer with a porosity of 8.0%.

[0059] Example 7 A secondary battery was fabricated in the same manner as in Example 1, except that in preparing the slurry for the protective layer, alumina and homotype polyvinylidene fluoride were mixed in a mass ratio of alumina:polyvinylidene fluoride = 95:5 to form a protective layer with a porosity of 60.0%.

[0060] Example 8 A secondary battery was fabricated in the same manner as in Example 1, except that in preparing the slurry for the protective layer, alumina and homotype polyvinylidene fluoride were mixed in a mass ratio of alumina:polyvinylidene fluoride = 98:2 to form a protective layer with a porosity of 62.0%.

[0061] Comparative Example A test cell was prepared in the same manner as in Example 1, except that no adhesive layer was formed.

[0062] [Details of Reliability Test] A charge / discharge test was conducted on each of the obtained secondary batteries. In the charge / discharge test, the batteries were charged in a thermostatic chamber at 45°C under the following conditions, then rested for 20 minutes, and discharged under the following conditions. (Charge) Constant current charging was performed at a current of 0.5 C until the battery voltage reached 4.2 V. Thereafter, constant voltage charging was performed at a voltage of 4.2 V until the current value reached 50 mA. (Discharge) Constant current discharging was performed at a current of 0.5 C until the battery voltage reached 2.5 V.

[0063] The above charge and discharge constitutes one cycle, and 500 charge and discharge cycles were performed. After 500 cycles, the secondary battery was disassembled, and the state of the protective layer was visually observed. If the protective layer was peeled off from the aluminum foil, it was evaluated as having fallen off the protective layer. If the protective layer was attached to the aluminum foil but cracks had occurred in the protective layer, it was evaluated as having damaged the protective layer. The results are shown in Table 1.

[0064]

[0065] As shown in Table 1, in Examples 1 to 8, no protective layer peeling occurred even after repeated charge-discharge cycles (0 out of 10 tests). On the other hand, in the Comparative Example, peeling of the protective layer was observed after repeated charge-discharge cycles (3 out of 10 tests). From these results, it can be said that by using an electrode in which an adhesive layer is disposed on the coating layer-disposing portion of the positive electrode core and a protective layer is disposed on the adhesive layer, peeling of the protective layer is suppressed even with many charge-discharge cycles. Among Examples 1 to 8, Examples 1 to 5 and 7, which used protective layers with porosities of 10% or more and 60% or less, did not experience any damage to the protective layer (0 out of 10 tests).

[0066] The present disclosure is further described by the following embodiments. Configuration 1: A secondary battery electrode comprising a long core body, a mixture layer, and a coating layer disposed on the core body, the core body having, at one end in the shorter direction of the core body, an exposed portion extending in the longitudinal direction of the core body and exposing the core body, a mixture layer-disposed portion in which the mixture layer is disposed, and a coating layer-disposed portion between the exposed portion and the mixture layer-disposed portion in which the coating layer is disposed, the coating layer having a protective layer including an inorganic filler and a first binder, and an adhesive layer including a second binder, the adhesive layer being disposed on the core body in the coating layer-disposed portion, and the protective layer being disposed on the adhesive layer. Configuration 2: A secondary battery electrode according to Configuration 1, wherein the adhesive layer has a thickness of 0.03 μm or more. Configuration 3: The secondary battery electrode according to Configuration 1 or 2, wherein the first binder comprises a homotype polyvinylidene fluoride polymer and the second binder comprises a modified polyvinylidene fluoride. Configuration 4: The secondary battery electrode according to any one of Configurations 1 to 3, wherein the porosity of the protective layer is 10% or more and 60% or less. Configuration 5: A secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and at least one of the positive electrode and the negative electrode is the secondary battery electrode according to any one of Configurations 1 to 4.

[0067] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17 negative electrode current collector plate, 18 positive electrode current collector plate, 19 insulating plate, 20 connection lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a through hole, 27 gasket, 30 positive electrode core, 32 positive electrode mixture layer, 33 positive electrode mixture layer arrangement portion, 34 positive electrode core exposed portion, 35 coating layer arrangement portion, 40 negative electrode core, 42 negative electrode mixture layer, 43 negative electrode mixture layer arrangement portion, 44 negative electrode core exposed portion, 46 coating layer, 48 protective layer, 50 adhesive layer.

Claims

1. An electrode for a secondary battery comprising a long core body, a composite layer and a coating layer disposed on the core body, the core body having, at one end in the short direction of the core body, an exposed portion extending in the longitudinal direction of the core body and exposing the core body, a composite layer disposition portion in which the composite layer is disposed, and a coating layer disposition portion between the exposed portion and the composite layer disposition portion in which the coating layer is disposed, the coating layer having a protective layer having an inorganic filler and a first binder, and an adhesive layer having a second binder, the adhesive layer being disposed on the core body in the coating layer disposition portion, and the protective layer being disposed on the adhesive layer.

2. The secondary battery electrode according to claim 1, wherein the adhesive layer has a thickness of 0.03 μm or more.

3. The electrode for a secondary battery according to claim 1 or 2, wherein the first binder contains a homotype polyvinylidene fluoride polymer, and the second binder contains a modified polyvinylidene fluoride.

4. The secondary battery electrode according to claim 1 or 2, wherein the porosity of the protective layer is 10% or more and 60% or less.

5. A secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, wherein at least one of the positive electrode and the negative electrode is the secondary battery electrode according to claim 1 or 2.

Images