Secondary battery

Abstract

Provided is a secondary battery capable of suppressing the occurrence of wrinkles and cracks in a protective layer. The lithium ion secondary battery is characterized in that the positive electrode comprises a positive electrode core material and a positive electrode mixture layer arranged on the positive electrode core material, one side end part of the positive electrode core material is provided with a positive electrode core material exposed part in which the positive electrode mixture layer is not arranged, and a protective layer containing a water-insoluble polymer and an inorganic filler is arranged on the positive electrode core material exposed part. The protective layer has: a first protective layer disposed in a region facing the negative electrode with a separator interposed therebetween in the exposed positive electrode core part; and a second protective layer disposed in a region of the exposed portion of the positive electrode core material that is farther from the positive electrode mixture layer than in a region in which the first protective layer is disposed, the mass ratio of the inorganic filler in the first protective layer being greater than the mass ratio of the inorganic filler in the second protective layer. The mass ratio of the water-insoluble polymer in the second protective layer is greater than the mass ratio of the water-insoluble polymer in the first protective layer.

Description

Technical Field

[0001] This application relates to a technology for a secondary battery. Background Technology

[0002] Secondary batteries may have, for example, wound electrode bodies or stacked electrode bodies. The wound electrode body is formed by winding the positive and negative electrodes while insulating them from each other with spacers. The positive electrode has a positive electrode core material with a positive electrode flux layer and the negative electrode has a negative electrode core material with a negative electrode flux layer. The stacked electrode body is formed by stacking the positive and negative electrodes while insulating them from each other with spacers.

[0003] However, in secondary batteries, such as lithium-ion batteries, the negative electrode flux layer is designed to be larger than the positive electrode flux layer in order to allow the negative electrode active material to smoothly absorb and store lithium ions released from the positive electrode active material during charging. That is, in secondary batteries, there are many structures where the exposed portion of the positive electrode core material without a positive electrode flux layer faces the negative electrode through a spacer.

[0004] In a structure where the exposed portion of the positive electrode core material without a positive electrode binder layer is sandwiched between a spacer and the negative electrode, if a part of the negative electrode facing the exposed portion of the positive electrode core material, or negative electrode active material peeled off from the negative electrode, punctures the spacer due to falling, vibration, or other reasons, causing the negative electrode to come into contact with the exposed portion of the positive electrode core material, a secondary battery will overheat due to an internal short circuit.

[0005] For example, Patent Documents 1 to 4 disclose a technique for suppressing internal short circuits in secondary batteries by providing a protective layer on the exposed portion of the positive electrode core material facing the negative electrode, which is sandwiched between a spacer.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2007-95656

[0009] Patent Document 2: Japanese Patent Application Publication No. 2007-103356

[0010] Patent Document 3: Japanese Patent Application Publication No. 2012-234822

[0011] Patent Document 4: Japanese Patent Application Publication No. 2021-184397 Summary of the Invention

[0012] However, due to their low flexibility and rigidity, traditional protective layers can develop wrinkles and cracks during battery manufacturing after the protective layer is formed, resulting in reduced insulation.

[0013] Therefore, the purpose of this application is to provide a secondary battery that can suppress the generation of wrinkles and cracks in the protective layer.

[0014] One aspect of the secondary battery of this application is characterized by having an electrode body having a positive electrode, a negative electrode, and a spacer disposed between the positive electrode and the negative electrode. The positive electrode includes a positive electrode core material and a positive electrode additive layer disposed on the positive electrode core material. At one end of the positive electrode core material, there is an exposed portion without the positive electrode additive layer. On the exposed portion, a protective layer comprising a non-water-soluble polymer and an inorganic filler is disposed. The protective layer has: a first protective layer disposed in the exposed portion in a region that separates the spacer from the negative electrode; and a second protective layer disposed in the exposed portion in a region that is further away from the positive electrode additive layer than the region where the first protective layer is disposed. The mass ratio of the inorganic filler in the first protective layer is greater than the mass ratio of the inorganic filler in the second protective layer, and the mass ratio of the non-water-soluble polymer in the second protective layer is greater than the mass ratio of the non-water-soluble polymer in the first protective layer.

[0015] According to one aspect of this application, a secondary battery capable of suppressing the formation of wrinkles and cracks in the protective layer can be provided. Attached Figure Description

[0016] Figure 1 This is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment.

[0017] Figure 2 This is a partially enlarged cross-sectional view of the electrode body constituting the secondary battery of this embodiment.

[0018] Figure 3 This is a schematic top view showing the positive electrode before winding.

[0019] Figure 4 yes Figure 3 A schematic cross-sectional view of the positive electrode at line AA. Detailed Implementation

[0020] The accompanying drawings referred to in the following description of the embodiments are schematic drawings, and the size ratios of the constituent elements depicted in the drawings may sometimes differ from the actual objects.

[0021] Figure 1 This is a cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment. Figure 1The secondary battery 10 shown includes an electrode body 14 having a positive electrode 11, a negative electrode 12, and a spacer 13 disposed between the positive electrode 11 and the negative electrode 12. This electrode body 14 is a wound type electrode body formed by winding the positive electrode 11 and the negative electrode 12 with the spacer 13 in between. It should be noted that in this embodiment, the electrode body is not limited to a wound type; it can also be a stacked type electrode body formed by distributing the spacer between the positive and negative electrodes and stacking them together.

[0022] The positive electrode 11 includes a positive electrode core material 15 and positive electrode binder layers 16 formed on both sides of the positive electrode core material 15. Additionally, at one end 26 of the positive electrode core material 15 in the winding axis direction of the electrode body 14, a positive electrode core material exposed portion 27 is formed, without or without the positive electrode binder layer 16. A protective layer (described later) is disposed on the positive electrode core material exposed portion 27. Figure 1 (Not shown in the image).

[0023] The negative electrode 12 includes a negative electrode core material 17 and negative electrode binder layers 18 formed on both sides of the negative electrode core material 17. At one end of the negative electrode core material 17 on the other end 29 side in the winding axis direction of the electrode body 14, a negative electrode core material exposed portion 30 is formed without the negative electrode binder layer 18.

[0024] Additionally, the secondary battery 10 includes a battery casing 19, a negative electrode current collector 22, a sealing plate 24, an insulating gasket 25, and a positive electrode current collector 28. The electrode body 14 is housed within the battery casing 19 along with an electrolyte (not shown). The battery casing 19 is a generally cylindrical component, closed at one end by a bottom 20 and open at the other end. The bottom 20 has a through hole 21 in its central portion. The through hole 21 is closed by a protrusion 23 of the negative electrode current collector 22, and the edge of the through hole 21 and the surface of the protrusion 23 are joined together by welding or the like. The protrusion 23 of the negative electrode current collector 22 also serves as the negative terminal. Furthermore, the other end of the battery casing 19 is closed by the sealing plate 24 and an insulating gasket 25 installed around the periphery of the sealing plate 24.

[0025] The exposed portion 27 of the positive electrode core is electrically connected to a positive current collector 28, which is disposed within the battery casing 19 at one end 26 in the direction of the winding axis of the electrode body 14, and to a sealing plate 24, which also serves as a positive terminal. On the other hand, the exposed portion 30 of the negative electrode core is electrically connected to a negative current collector 22, which is disposed within the battery casing 19 at the other end 29 in the direction of the winding axis of the electrode body 14.

[0026] The exposed portion 27 of the positive electrode core material is bent toward the center side of the electrode body 14, and the front end portion 31 of the bent exposed portion 27 of the positive electrode core material is joined to the positive electrode current collector plate 28. It should be noted that when the exposed portion 27 of the positive electrode core material is bent toward the center side of the electrode body 14, a part of the front end portion 31 of the exposed portion 27 of the positive electrode core material on the outer peripheral surface side of the positive electrode core material 15 on the winding outer peripheral side becomes the joint portion with the positive electrode current collector plate 28. On the other hand, the front end portion 31 of the exposed portion 27 of the positive electrode core material on the inner peripheral surface side of the positive electrode core material 15 on the winding inner peripheral side faces the one end portion 26 of the electrode body 14 in the winding axis direction. Similarly, the exposed portion 30 of the negative electrode core material is bent toward the center side of the electrode body 14, and the front end portion 32 of the bent exposed portion 30 of the negative electrode core material is joined to the negative electrode current collector plate 22. In this way, Figure 1 The secondary battery 10 shown has a so-called tabless structure (Japanese: タブレス構造) in which current is directly collected from the positive electrode core material 15 and the negative electrode core material 17. However, the secondary battery 10 of the present embodiment is not limited to the tabless structure. For example, it may also be a structure in which leads are joined to the positive electrode core material 15 and the negative electrode core material 17 and current is collected via the leads. It should be noted that in the tabless structure, the front end of the exposed portion 27 of the positive electrode core material and the front end of the exposed portion 30 of the negative electrode core material may be joined to the positive electrode current collector plate 28 and the negative electrode current collector plate 22 without bending the exposed portion 27 of the positive electrode core material and the exposed portion 30 of the negative electrode core material.

[0027] Figure 2 is a partial enlarged cross-sectional view of the electrode body constituting the secondary battery of the present embodiment. As Figure 2 shown, the exposed portion 27 of the positive electrode core material disposed on one side end portion of the positive electrode core material 15 has an exposed portion 27a of the positive electrode core material 15 on one surface side and an exposed portion 27b of the positive electrode core material 15 on the other surface side. Hereinafter, one surface of the positive electrode core material 15 is set as the inner peripheral surface of the positive electrode core material 15 on the winding inner peripheral side, and the exposed portion 27a of the positive electrode core material 15 on one surface side is referred to as the exposed portion 27a of the inner peripheral surface side. In addition, the other surface of the positive electrode core material 15 is set as the outer peripheral surface of the positive electrode core material 15 on the winding outer peripheral side, and the exposed portion 27b of the positive electrode core material 15 on the other surface side is referred to as the exposed portion 27b of the outer peripheral surface side. It should be noted that the inner peripheral surface of the positive electrode core material 15 is the surface of the positive electrode core material 15 located on the inner side in the radial direction of the wound positive electrode 11 when the positive electrode 11 is wound, and the outer peripheral surface of the positive electrode core material 15 is the surface of the positive electrode core material 15 located on the outer side in the radial direction of the wound positive electrode 11.

[0028] As Figure 2As shown, protective layers 40 are respectively disposed on the exposed positive electrode core material 27a on the inner peripheral side and the exposed positive electrode core material 27b on the outer peripheral side. The protective layers 40 comprise non-water-soluble polymers and inorganic fillers, and have a first protective layer 42 and a second protective layer 44. Regarding the volume resistivity of the protective layers 40 (the volume resistivity of each of the first protective layer 42 and the second protective layer 44), considering the suppression of internal short circuits in the battery, a volume resistivity of, for example, 10 is preferred. 7 Ω·cm or higher, more preferably 10 9 Ω·cm or higher.

[0029] The first protective layer 42 is disposed in the region of the exposed positive electrode core material (27a, 27b) that is separated from the negative electrode 12 by the spacer 13. The second protective layer 44 is disposed side-by-side with the first protective layer 42 in the region of the exposed positive electrode core material (27a, 27b) that is further away from the positive electrode binder layer 16 than the region where the first protective layer 42 is disposed. The first protective layer 42 and the second protective layer 44 are preferably adjacent, but they can also be disposed with a gap between them. Furthermore, the mass ratio of inorganic filler in the first protective layer 42 is greater than the mass ratio of inorganic filler in the second protective layer 44, and the mass ratio of non-water-soluble polymers in the second protective layer 44 is greater than the mass ratio of non-water-soluble polymers in the first protective layer 42.

[0030] Conventionally, to ensure high insulation, the protective layer is a rigid, single-layer structure containing a large amount of inorganic filler. In the manufacturing process of secondary batteries, the positive electrode compound layer and the protective layer are calendered using calendering rollers, etc. However, this calendering process can cause wrinkles in the rigid, single-layer protective layer, leading to a decrease in its insulation performance. However, in this embodiment, a second protective layer 44 is provided on the outside of the first protective layer 42, which has increased flexibility compared to the first protective layer 42 by reducing the ratio of inorganic filler and increasing the ratio of non-water-soluble polymers. Therefore, the stress applied to the first protective layer 42 during calendering can be alleviated by the second protective layer 44. As a result, wrinkles in the protective layer 40 during calendering can be suppressed. Furthermore, to connect the exposed positive electrode core 27 to the positive electrode current collector 28, the exposed positive electrode core 27 is sometimes bent. However, if the bending point is on the protective layer 40, cracks can occur in the protective layer, leading to a decrease in its insulation performance. On the other hand, in this embodiment, for example, if the bending position is located at the highly flexible second protective layer 44, the generation of cracks in the protective layer 40 can be suppressed. It should be noted that by placing the bending position at the second protective layer 44, the second protective layer 44 remains at the front end 31 of the exposed positive electrode core 27 after bending. Therefore, the second protective layer 44 can be used to prevent contact between the end 26 of the electrode body 14 in the winding axis direction and the facing surface of the front end 31. For example, due to the charging and discharging of the secondary battery 10, the negative electrode 12 may protrude from the end 26 of the electrode body 14 and contact the front end 31. However, by placing the bending position at the second protective layer 44 as described above, the second protective layer 44 can be used to prevent contact between the negative electrode 12 and the front end 31.

[0031] Inorganic fillers contained in the protective layer 40 may include, for example, oxides such as alumina, silicon dioxide, zirconium oxide, titanium dioxide, magnesium oxide, cerium dioxide, yttrium oxide, zinc oxide, iron oxide, barium titanium oxide, and alumina-silicon dioxide 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, kaolinite clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, boehmite, apatite, mullite, spinel, olivine, etc., or compounds containing at least one of them. Alternatively, inorganic fillers can also be particles that are electrically insulating by surface treatment of conductive particles such as SnO2, tin-indium oxide (ITO) and other oxides, carbon black, graphite and other carbonaceous materials with electrically insulating materials (such as the materials of the aforementioned inorganic fillers).

[0032] The non-water-soluble polymer contained in the protective layer 40 is preferably a non-water-soluble polymer that dissolves in less than 1 part by mass of water per 100 parts by mass at 20°C. Examples include fluorinated polymers such as polyvinylidene fluoride (PVDF), copolymers of PVDF and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamide-imide, cross-linked polymers of cellulose and chitosan pyrrolidone carboxylate, and derivatives of chitin or chitosan. Examples of chitosan derivatives include polymers obtained by glycerolizing chitosan and cross-linked chitosan. Among these, considering electrochemical stability, the non-water-soluble polymer preferably includes a fluorinated polymer, and particularly preferably includes polyvinylidene fluoride (PVDF).

[0033] The mass ratio of the non-water-soluble polymer in the first protective layer 42 is preferably 2% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 25% by mass or less. Furthermore, the mass ratio of the non-water-soluble polymer in the second protective layer 44 is preferably 50% by mass or more and 100% by mass or less, more preferably 75% by mass or more and 100% by mass or less. By satisfying the above-mentioned ranges for the mass ratio of the non-water-soluble polymer, the insulation of the first protective layer 42 or the flexibility of the second protective layer 44 is further improved. As a result, internal short circuits caused by contact between the negative electrode 12 and the exposed portion 27 of the positive electrode core material are less likely to occur, or the formation of wrinkles and cracks in the protective layer 40 caused by the battery manufacturing process is further suppressed. It should be noted that the first protective layer 42 and the second protective layer 44 may contain components other than the non-water-soluble polymer and inorganic filler.

[0034] Figure 3 This is a schematic top view showing the positive electrode before winding. Figure 4 yes Figure 3 A schematic cross-sectional view of the positive electrode at the AA line. Regarding the thickness of the first protective layer 42 and the second protective layer 44, considering insulation and flexibility, it is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 40 μm or less. Furthermore, regarding the width (W1) of the first protective layer 42 and the width (W2) of the second protective layer 44, considering reducing the likelihood of internal short circuits caused by contact between the negative electrode 12 and the exposed portions 27 (27a, 27b) of the positive electrode core material, it is preferably 2 mm or more, more preferably 2 mm or more and 5 mm or less. It should be noted that the width (W1) of the first protective layer 42 and the width (W2) of the second protective layer 44 are the lengths of each layer in the direction in which the first protective layer 42 and the second protective layer 44 are arranged.

[0035] When bending the exposed positive electrode core 27 to join it to the positive current collector 28, it is preferable to bend it between the first protective layer 42 and the second protective layer 44 and join the bent front end 31 to the positive current collector 28. When the first protective layer 42 and the second protective layer 44 are adjacent, it is preferable to bend it at the boundary between the first protective layer 42 and the second protective layer 44. By setting the bending position between (or at the boundary) the first protective layer 42 and the second protective layer 44, bending the exposed positive electrode core 27 is easy, and the generation of cracks in the protective layer 40 can be further suppressed. In addition, since the second protective layer 44 remains at the front end 31 of the exposed positive electrode core 27, even if the negative electrode 12 protrudes from one end 26 of the electrode body 14 due to the charging and discharging of the secondary battery 10, the second protective layer 44 can be used to prevent the negative electrode 12 from contacting the front end 31.

[0036] In the case of the wound electrode body 14, it is preferable that the ratio of width (B) to width (A) (B / A) is 0.3 or more and 0.6 or less. The width (A) is the combined width of the first protective layer 42 and the second protective layer 44 disposed on the exposed positive electrode core material 27a on the inner peripheral side, and the width (B) is the combined width of the first protective layer 42 and the second protective layer 44 disposed on the exposed positive electrode core material 27b on the outer peripheral side. By setting B / A to the above range, it is possible to ensure that the space in the exposed positive electrode core material 27b on the outer peripheral side is not as large as the space where the protective layer 40 is disposed. Therefore, the bonding of this space with the positive electrode current collector 28 becomes easier, and the bonding strength and electronic conductivity between the positive electrode 11 and the positive electrode current collector 28 can be improved. It should be noted that, when B / A meets the above-mentioned range, when bending the exposed portion 27 of the positive electrode core material towards the center of the electrode body 14, it is preferable to bend between (or at the boundary) the first protective layer 42 and the second protective layer 44 of the exposed portion 27a of the positive electrode core material disposed on the inner peripheral surface. This can suppress the generation of cracks in the protective layer 40 of the exposed portion 27a of the positive electrode core material disposed on the inner peripheral surface, thus further suppressing the occurrence of internal short circuits caused by contact with the negative electrode 12. On the other hand, although any part of the second protective layer 44 may be a bending position on the exposed portion 27b of the positive electrode core material on the outer peripheral surface, since the second protective layer 44 is flexible as described above, the generation of cracks in the protective layer 40 caused by bending can be minimized.

[0037] The following describes the materials used in the positive electrode 11, negative electrode 12, spacer 13, and electrolyte.

[0038] [positive electrode]

[0039] The positive electrode core material 15 can be a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum or aluminum alloy, or a film of the metal disposed on its surface. The positive electrode binder layer 16 may contain, for example, a positive electrode active material, a binder, and a conductive material. Since the protective layer 40 has been described above, its description is omitted.

[0040] Examples of lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni can be cited as positive electrode active materials. For example, Li0.05 is a lithium transition metal oxide. 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 y O4, LiMPO4, and 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). They can be used individually or in combination. From the perspective of achieving high capacity in the secondary battery 10, the positive electrode active material preferably contains Li. x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z (M: at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3) and other lithium nickel composite oxides.

[0041] Conductive materials include, for example, carbon black (CB), acetylene black (AB), Ketjen black, and carbon-based particles such as graphite. They can be used alone or in combination of two or more.

[0042] Examples of bonding materials include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH4, etc., and also partially neutralized salts), and polyethylene oxide (PEO). They can be used alone or in combination of two or more.

[0043] An example of the manufacturing method of the positive electrode 11 will be described. First, a slurry for a positive electrode additive layer comprising a positive electrode active material, a binder material, and a conductive material is prepared. Additionally, a first protective layer slurry and a second protective layer slurry comprising a water-insoluble polymer and an inorganic filler are prepared. Here, the mass ratio of the inorganic filler in the first protective layer slurry is greater than the mass ratio of the inorganic filler in the second protective layer slurry, and the mass ratio of the water-insoluble polymer in the second protective layer slurry is greater than the mass ratio of the water-insoluble polymer in the first protective layer slurry. Furthermore, the positive electrode additive layer slurry is applied to one or both sides of the positive electrode core 15, excluding the exposed portion 27 at one side end of the positive electrode core 15, while the first protective layer slurry and the second protective layer slurry are applied side-by-side to the uncoated exposed portion 27 of the positive electrode core 15. The order in which these slurries are applied is not particularly limited. For example, these slurries can be applied simultaneously, or the slurry for the first protective layer and the slurry for the second protective layer can be applied after the slurry for the positive electrode additive layer. After the coatings of the positive electrode additive layer 16 and the protective layer 40 applied to the positive electrode core material 15 are dried, they are calendered using calendering rolls or the like. Thus, the positive electrode 11 of this embodiment can be obtained. As mentioned above, in this embodiment, since a second protective layer 44 is provided on the outside of the first protective layer 42, which improves the flexibility compared to the first protective layer 42 by reducing the ratio of inorganic fillers and increasing the ratio of non-water-soluble polymers, the second protective layer 44 can be used to relieve the stress applied to the first protective layer 42 during calendering and suppress the formation of wrinkles in the protective layer 40 during calendering. Furthermore, conventionally, when a slurry containing a large amount of inorganic filler is coated onto the positive electrode core material 15, dripping occurs at the ends of the coating, resulting in a thinner thickness at the ends of the formed protective layer 40. Therefore, it is sometimes impossible to adequately ensure the insulation properties of the ends of the protective layer 40. However, the second protective layer slurry has a high proportion of non-water-soluble polymers and high viscosity. Therefore, by coating the second protective layer slurry onto the outside of the coating formed from the first protective layer slurry, as in this embodiment, a coating film of the second protective layer slurry can be formed, suppressing dripping at the ends of the coating formed from the first protective layer 42. In addition, the coating film formed from the highly viscous second protective layer slurry is less prone to dripping at its ends. Therefore, the thickness of the ends of the resulting protective layer 40 (the ends of the first protective layer 42 and the ends of the second protective layer 44) is less likely to become thin, thus adequate insulation properties can be ensured.

[0044] [negative electrode]

[0045] The negative electrode core material 17 can be a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, or a film of the metal disposed on its surface. The negative electrode binder layer 18 may contain, for example, a negative electrode active material and a binder material.

[0046] Examples of negative electrode active materials include lithium metal, lithium-aluminum alloys, lithium-lead alloys, lithium-silicon alloys, lithium-tin alloys, and other lithium alloys; carbon materials such as graphite, coke, and sintered organic matter; and metal oxides such as SnO2, SnO, and TiO2. One type can be used alone, or two or more can be used in combination.

[0047] Similar to the case of cathode 11, examples of binders include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH4, etc., and also partially neutralized salts), and polyethylene oxide (PEO). These can be used individually or in combination of two or more.

[0048] An example of a method for manufacturing the negative electrode 12 will be described. First, a negative electrode binder layer containing a negative electrode active material, a binder material, etc., is coated with a slurry onto the negative electrode core material 17, excluding the exposed portion at one side end (one or both sides). After coating with the negative electrode binder layer slurry, the coating film of the negative electrode binder layer 18 is dried and calendered using calendering rollers or the like. This yields the negative electrode 12.

[0049] [Spacer]

[0050] The spacer 13 may be made of a porous sheet material, for example, that has ion permeability and insulation properties. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Suitable materials for the spacer 13 include olefin resins such as polyethylene and polypropylene, and cellulose. The spacer 13 may also be a laminate containing a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Alternatively, it may be a multilayer spacer containing a polyethylene layer and a polypropylene layer, or a spacer with an aromatic polyamide resin, ceramic, or other material coated on its surface.

[0051] [Electrolytes]

[0052] Electrolytes, for example, possess ionic conductivity (e.g., lithium-ion conductivity). Electrolytes can be liquid electrolytes (electrolytes) or solid electrolytes.

[0053] Liquid electrolytes (electrolytes) may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents may include, for example, esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may contain halogen-substituted derivatives (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are replaced by halogen atoms such as fluorine. Electrolyte salts may include, for example, lithium salts such as LiPF6.

[0054] In addition, as a solid electrolyte, examples include solid or gel-like polymer electrolytes and inorganic solid electrolytes. Polymer electrolytes, for example, contain lithium salts and a matrix polymer, or contain a non-aqueous solvent, lithium salts, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels after absorbing a non-aqueous solvent is used. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. It should be noted that although the electrolytes exemplified above are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and can also be an aqueous electrolyte.

[0055] This application is further illustrated by the following embodiments.

[0056] Component 1:

[0057] A secondary battery includes an electrode body having a positive electrode, a negative electrode, and a spacer disposed between the positive electrode and the negative electrode.

[0058] The aforementioned positive electrode includes a positive electrode core material and a positive electrode additive layer disposed on the aforementioned positive electrode core material.

[0059] At one end of the aforementioned positive electrode core material, there is an exposed portion where the aforementioned positive electrode binder layer is not disposed.

[0060] A protective layer comprising non-water-soluble polymers and inorganic fillers is disposed on the aforementioned exposed portion.

[0061] The aforementioned protective layer comprises: a first protective layer disposed in the exposed portion in a region that separates the spacer from the negative electrode; and a second protective layer disposed in the exposed portion in a region that is further away from the positive electrode binder layer than the region in which the first protective layer is disposed.

[0062] The mass ratio of the inorganic filler in the first protective layer is greater than the mass ratio of the inorganic filler in the second protective layer, and the mass ratio of the non-water-soluble polymer in the second protective layer is greater than the mass ratio of the non-water-soluble polymer in the first protective layer.

[0063] Composition 2:

[0064] According to the secondary battery described in configuration 1, the mass ratio of the non-water-soluble polymer in the first protective layer is 2% by mass or more and 30% by mass or less, and the mass ratio of the non-water-soluble polymer in the second protective layer is 50% by mass or more and 100% by mass or less.

[0065] Composition 3:

[0066] According to the secondary battery described in configuration 1 or 2, the thicknesses of the first protective layer and the second protective layer are respectively 5 μm or more and 50 μm or less.

[0067] Composition 4:

[0068] According to any one of the configurations 1 to 3, the width of the first protective layer and the width of the second protective layer are both 2 mm or more.

[0069] Component 5:

[0070] According to any one of the configurations 1 to 4, the exposed portion is bent between the first protective layer and the second protective layer, and the bent front end is connected to the positive electrode current collector.

[0071] Composition 6:

[0072] According to any one of the following configurations of the secondary battery, the electrode body is a wound electrode body formed by winding the positive electrode and the negative electrode with the spacer in between.

[0073] The ratio (A / B) of width (B) to width (A) is 0.3 or more and 0.6 or less. The width (A) is the combined width of the first protective layer and the second protective layer disposed on the exposed portion on the inner peripheral surface side of the positive electrode core material that becomes the inner peripheral side of the winding. The width (B) is the combined width of the first protective layer and the second protective layer disposed on the exposed portion on the outer peripheral surface side of the positive electrode core material that becomes the outer peripheral side of the winding.

[0074] Explanation of reference numerals in the attached figures

[0075] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Spacer, 14 Electrode body, 15 Positive electrode core material, 16 Positive electrode binder layer, 17 Negative electrode core material, 18 Negative electrode binder layer, 19 Battery casing, 20 Bottom, 21 Through hole, 22 Negative electrode current collector, 23 Protrusion, 24 Sealing plate, 25 Insulating gasket, 26 One end, 27, 27a, 27b Positive electrode core material exposed portion, 28 Positive electrode current collector, 29 The other end, 30 Negative electrode core material exposed portion, 31 Front end, 32 Front end, 40 Protective layer, 42 First protective layer, 44 Second protective layer.

Claims

1. A secondary battery comprising an electrode body having a positive electrode, a negative electrode, and a spacer disposed between the positive electrode and the negative electrode. The positive electrode comprises a positive electrode core material and a positive electrode additive layer disposed on the positive electrode core material. At one end of the positive electrode core material, there is an exposed portion where the positive electrode binder layer is not disposed. A protective layer comprising a water-insoluble polymer and inorganic fillers is disposed on the exposed portion. The protective layer comprises: a first protective layer disposed in the exposed portion, in a region that sandwiches the spacer and faces the negative electrode; and a second protective layer disposed in the exposed portion, in a region that is further away from the positive electrode compound layer than the region in which the first protective layer is disposed. The mass ratio of the inorganic filler in the first protective layer is greater than that in the second protective layer, and the mass ratio of the non-water-soluble polymer in the second protective layer is greater than that in the first protective layer.

2. The secondary battery according to claim 1, wherein, The mass ratio of the non-water-soluble polymer in the first protective layer is more than 2% by mass and less than 30% by mass, and the mass ratio of the non-water-soluble polymer in the second protective layer is more than 50% by mass and less than 100% by mass.

3. The secondary battery according to claim 1 or 2, wherein, The thicknesses of the first protective layer and the second protective layer are respectively 5 μm or more and 50 μm or less.

4. The secondary battery according to claim 1 or 2, wherein, The widths of the first protective layer and the second protective layer are both 2 mm or more.

5. The secondary battery according to claim 1 or 2, wherein, The exposed portion is bent between the first protective layer and the second protective layer, and the bent front end is connected to the positive current collector.

6. The secondary battery according to claim 1 or 2, wherein, The electrode body is a wound type electrode body formed by winding the positive electrode and the negative electrode with the spacer sandwiched between them. The ratio of width B to width A, i.e., A / B, is 0.3 or more and 0.6 or less. Width A is the combined width of the first protective layer and the second protective layer disposed on the exposed portion on the inner peripheral surface side of the positive electrode core material that becomes the inner peripheral side of the winding. Width B is the combined width of the first protective layer and the second protective layer disposed on the exposed portion on the outer peripheral surface side of the positive electrode core material that becomes the outer peripheral side of the winding.

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