Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery comprises an electrode body in which a strip-shaped positive electrode (11) and a strip-shaped negative electrode are wound along the length direction with a separator disposed therebetween. The non-aqueous electrolyte secondary battery is characterized in that: the positive electrode (11) includes a positive electrode core body (30), a positive electrode mixture layer (31) that is formed over the positive electrode core body (30) and that contains a positive electrode active material as a main component, a protective layer (32) that is formed over the positive electrode core body (30) and that contains an insulating material as a main component, and a mixed layer (33) which is formed over the positive electrode core body (30) and in which the positive electrode mixture layer (31) and the protective layer (32) are mixed; and the protective layer (32), the mixed layer (33), and the positive electrode mixture layer (31) are arranged in the stated order going from the winding-start end (11A) of the positive electrode (11) toward the winding-finish side.

Description

Non-aqueous electrolyte secondary battery

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

[0002] Conventionally, non-aqueous electrolyte secondary batteries are known that have an electrode body in which a positive electrode and a negative electrode are wound with a separator in between. Generally, the positive electrode has a positive electrode core and a positive electrode mixture layer formed on the positive electrode core. Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which a region is provided at the widthwise end of the positive electrode where the positive electrode mixture layer is not formed and the positive electrode core is exposed, and a part of this region is covered with an insulating layer. Furthermore, in the non-aqueous electrolyte secondary battery of Patent Document 1, a layer in which the positive electrode mixture layer and the insulating layer are mixed is formed at the boundary between the positive electrode mixture layer and the insulating layer.

[0003] Japanese Patent Publication No. 2023-85907

[0004] With the recent increase in the capacity of non-aqueous electrolyte secondary batteries, the volume change of the negative electrode during charging and discharging has become larger. When the volume change of the negative electrode during charging and discharging becomes large, stress tends to concentrate on the negative electrode opposite the starting end of the positive electrode winding when charging and discharging is repeated, which may cause deformation of the negative electrode. As a result of our investigation, it has become clear that deformation of the negative electrode at the starting end of the positive electrode winding can be suppressed by not forming a positive electrode mixture layer at the starting end of the positive electrode winding and by reducing the thickness of the positive electrode. On the other hand, when the above configuration is adopted, peeling of the positive electrode mixture layer may occur at the starting end of the positive electrode mixture layer winding.

[0005] Furthermore, the positive electrode core has lower resistance compared to the positive electrode mixture layer. Therefore, if the region where the positive electrode core is exposed due to the absence of a positive electrode mixture layer comes into contact with the negative electrode, an internal short circuit may occur. Thus, as disclosed in Patent Document 1, it is conceivable to cover the region where the positive electrode core is exposed due to the absence of a positive electrode mixture layer with an insulating layer made of an insulating material. On the other hand, as a result of the inventors' investigations, it became clear that when the technology disclosed in Patent Document 1 is adopted, there is a tendency for the battery capacity to decrease.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound along the length direction via a separator, wherein the positive electrode comprises a positive electrode core, a positive electrode mixture layer formed on the positive electrode core and mainly containing a positive electrode active material, a protective layer formed on the positive electrode core and mainly containing an insulating material, and a mixed layer formed on the positive electrode core in which the components of the positive electrode mixture layer and the components of the protective layer are mixed, and the protective layer, mixed layer and positive electrode mixture layer are arranged in order from the beginning end of the winding of the positive electrode toward the end end of the winding.

[0007] According to a non-aqueous electrolyte secondary battery, one aspect of this disclosure, deformation of the negative electrode at the starting end of the positive electrode winding can be suppressed while simultaneously suppressing peeling of the positive electrode mixture layer and improving battery capacity.

[0008] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is one example of an embodiment. This is a plan view of the winding start side of the outer surface of the winding in an unfolded state of the positive electrode, which is one example of an embodiment. This is a cross-sectional view along line AA in Figure 2. This is a diagram corresponding to Figure 3, showing another example of a positive electrode in an embodiment.

[0009] Hereinafter, an example of an embodiment of the non-aqueous electrolyte secondary battery according to this disclosure will be described in detail with reference to the drawings. However, the non-aqueous electrolyte secondary battery according to this disclosure is not limited to the embodiments described below.

[0010] Figure 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment. As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 comprises an electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, and a bottomed cylindrical outer casing 16 that houses the electrode body 14. The non-aqueous electrolyte secondary battery 10 also comprises a non-aqueous electrolyte housed in the outer casing 16 and a sealing body 17 that closes the opening of the outer casing 16. For the sake of explanation, the side with the sealing body 17 of the non-aqueous electrolyte secondary battery 10 will be referred to as "upper," and the bottom side of the outer casing 16 will be referred to as "lower."

[0011] Non-aqueous electrolytes are lithium ion conductive. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0012] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include 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 also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms of the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0013] 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, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, 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 a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0014] The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound in a spiral shape via a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in both the length and width directions than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0015] As will be described in more detail later, the positive electrode 11 has a long positive electrode core 30 and a positive electrode mixture layer 31 formed on the positive electrode core 30. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF). Preferably, the positive electrode mixture layer 31 is formed on both sides of the positive electrode core 30.

[0016] The negative electrode 12 comprises a long negative electrode core 40 and a negative electrode mixture layer 41 formed on the negative electrode core 40. The negative electrode core 40 can be made of a metal foil that is stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR). Preferably, the negative electrode mixture layer 41 is formed on both sides of the negative electrode core 40.

[0017] Generally, carbon materials that reversibly intercept and release lithium ions are used as the negative electrode active material. Suitable examples of carbon materials include natural graphite such as flake graphite, lump graphite, and earthy graphite, as well as artificial graphite such as lump graphite (MAG) and graphitized mesophase carbon microbeads (MCMB).

[0018] Furthermore, silicon-containing materials may be used as the negative electrode active material. Any silicon-containing material is acceptable, and examples include silicon alloys, silicon compounds, and silicon-containing composite materials. Among silicon-containing materials, silicon-containing composite materials are preferred. A preferred example of a silicon-containing composite material is SiO2. ２ Examples include materials in which Si fine particles are dispersed in a phase, a silicate phase such as lithium silicate, or an amorphous carbon phase. A conductive layer, such as a carbon film, may be formed on the particle surface of the composite material.

[0019] The thickness of the negative electrode 12 is, for example, 105 μm or more and 255 μm or less. In this embodiment, the thickness of the negative electrode 12 is substantially constant except for the outer peripheral exposed portion 42 and the region to which the negative electrode lead 21 is connected, which will be described later. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 15 μm or less. The thickness of the negative electrode mixture layer 41 is, for example, 50 μm or more and 120 μm or less on one side of the negative electrode core 40. The negative electrode 12 can be manufactured in the same way as the positive electrode 11 by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0020] The electrode body 14 has a positive electrode lead 20 connected to a positive electrode 11 and a negative electrode lead 21 connected to a negative electrode 12. In this embodiment, the positive electrode lead 20 is connected to the longitudinal center of the positive electrode 11, and the negative electrode lead 21 is connected to one longitudinal end of the negative electrode 12, which is located on the winding start side of the electrode body 14.

[0021] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends through a through-hole in the insulating plate 19 towards the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative electrode terminal.

[0022] In this embodiment, a negative electrode 12 is arranged on the outermost surface of the electrode body 14, and an outer peripheral exposed portion 42 is provided where the surface of the negative electrode core body 40 is exposed. At least a portion of the outer peripheral exposed portion 42 is in contact with the inner peripheral surface of the outer casing 16. By the outer peripheral exposed portion 42 contacting the inner peripheral surface of the outer casing 16, both ends in the longitudinal direction of the negative electrode 12 and the outer casing 16 are electrically connected, ensuring good current collection. The outer peripheral exposed portion 42 may be provided on a part of the outermost surface of the electrode body 14, but preferably it is provided over the entire outermost surface of the electrode body 14. A separator 13 may be arranged on the outermost surface of the electrode body 14.

[0023] The outer casing 16 is a bottomed cylindrical metal container. A gasket 28 is provided between the outer casing 16 and the sealing body 17, sealing the inside of the battery. The outer casing 16 has, for example, a grooved portion 22 formed by pressing the side surface from the outside. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The upper end of the outer casing 16 is bent inward and crimped to the periphery of the sealing body 17.

[0024] The sealing body 17 has a structure in which 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 in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except 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 radial centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27. This interrupts the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0025] The configuration of the winding start side of the positive electrode 11 will be described in detail below with reference to Figures 2 and 3. Figure 2 is a plan view of the winding start side of the outer surface of the winding of the positive electrode 11 in an unfolded state, and Figure 3 is a cross-sectional view taken along line AA in Figure 2.

[0026] As shown in Figures 2 and 3, the positive electrode 11 has a positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a film with such metal arranged on its surface. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less.

[0027] On the positive electrode core 30, a protective layer 32, a mixed layer 33 which is a mixture of the components of the positive electrode mixture layer 31 and the components of the protective layer 32, and the positive electrode mixture layer 31 are formed in order from the starting end 11A of the winding of the positive electrode 11 toward the winding end.

[0028] The positive electrode mixture layer 31 is a layer mainly containing positive electrode active material. Here, "main component" means that it accounts for 80% or more of the mass of the positive electrode mixture layer 31. The content of positive electrode active material is preferably 85% or more of the mass of the positive electrode mixture layer 31, and more preferably 90% or more of the mass. In addition to the positive electrode active material, the positive electrode mixture layer 31 contains a conductive agent such as acetylene black and a binder such as polyvinylidene fluoride (PVdF).

[0029] The positive electrode mixture layer 31 is not formed at the winding start end 11B of the positive electrode 11, but is formed from a position a predetermined length away from the winding start end 11A toward the winding end, and extends toward the winding end. This makes it possible to reduce the thickness of the winding start end 11B of the positive electrode 11. In this specification, the winding start end 11B of the positive electrode 11 refers to the region including the winding start end 11A and its vicinity.

[0030] As a result of the inventors' investigations, it was found that when the positive electrode mixture layer 31 is formed up to the winding start end 11A of the positive electrode 11, deformation of the negative electrode 12 occurs at the point facing the winding start end 11B of the positive electrode 11 when charging and discharging are repeated. When the positive electrode mixture layer 31 is formed up to the winding start end 11A of the positive electrode 11, the thickness of the winding start end 11B of the positive electrode 11 increases, and a large step is formed at the winding start end 11A of the positive electrode 11. As a result, it is presumed that stress tends to concentrate at the negative electrode 12 facing the winding start end 11B of the positive electrode 11, causing deformation of the negative electrode 12.

[0031] As in this embodiment, by not forming the positive electrode mixture layer 31 at the winding start end 11B of the positive electrode 11, the winding start end 31A of the positive electrode mixture layer 31 can be separated from the winding start end 11A of the positive electrode 11, thereby reducing the step formed at the winding start end 11A of the positive electrode 11. As a result, when charging and discharging are repeated, deformation of the negative electrode 12 that faces the winding start end 11B of the positive electrode 11 can be suppressed.

[0032] The thickness of the positive electrode mixture layer 31 is, for example, 50 μm or more and 120 μm or less on one side of the positive electrode core 30. In this embodiment, the positive electrode mixture layer 31 is formed on both sides of the positive electrode core 30.

[0033] The protective layer 32 is a layer mainly composed of an insulating material. Here, the main component means occupying 80% by mass or more of the mass of the protective layer 32. The content of the insulating material is preferably 85% by mass or more, more preferably 90% by mass or more of the mass of the protective layer 32. Further, the protective layer 32 may be an insulating layer substantially composed of only the insulating material.

[0034] The protective layer 32 is formed at the starting end portion 11B of the winding of the positive electrode 11 and covers a region on the surface of the positive electrode core 30 where the positive electrode active material layer 31 and the mixed layer 33 are not formed. The positive electrode core 30 has a lower resistance than the positive electrode active material layer 31. Therefore, when the exposed positive electrode core 30 comes into contact with the negative electrode 12 facing it, an internal short circuit may occur. Thus, by covering the positive electrode core 30 at the starting end portion 11B of the positive electrode 11 with the protective layer 32 mainly composed of an insulating material and not exposing the positive electrode core 30, it is possible to suppress the contact between the positive electrode core 30 and the negative electrode 12. As a result, an internal short circuit can be suppressed.

[0035] The thickness of the protective layer 32 is smaller than the thickness of the positive electrode active material layer 31. From the viewpoint of suppressing the occurrence of an internal short circuit and suppressing the deformation of the negative electrode 12 when charge and discharge are repeated, the thickness of the protective layer 32 is 3 μm or more and 40 μm or less, and may be 5 μm or more and 30 μm or less. Further, the thickness of the protective layer 32 is preferably 50% or less, more preferably 30% or less of the thickness of the positive electrode active material layer 31. The protective layer 32 has, for example, a substantially uniform thickness over the length direction of the positive electrode 11.

[0036] In the longitudinal direction of the positive electrode 11, the length of the protective layer 32 is preferably 0.5 mm or more, more preferably 1.0 mm or more. By setting the length of the protective layer 32 to 0.5 mm or more, deformation of the negative electrode 12 facing the start-end portion 11B of the winding of the positive electrode 11 can be further suppressed. Also, the length of the protective layer 32 is preferably 5.0 mm or less, more preferably 4.5 mm or less. By setting the length of the protective layer 32 to 5.0 mm or less, the area of the region where the positive electrode active material layer 31 is formed can be increased, and it becomes easier to achieve a high capacity of the battery. Therefore, in the longitudinal direction of the positive electrode 11, the length of the protective layer 32 is preferably 0.5 mm or more and 5.0 mm or less, more preferably 1.0 mm or more and 4.5 mm or less.

[0037] The insulating material constituting the protective layer 32 preferably contains at least a resin material. The resin material functions, for example, as a binder for bonding the positive electrode core 30 and the positive electrode active material layer 31. When the insulating material contains a resin material, peeling of the positive electrode active material layer 31 at the start-end 31A of the winding of the positive electrode active material layer 31 can be further suppressed.

[0038] The resin material contained in the insulating material constituting the protective layer 32 is preferably a polymer material. 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 its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0039] The insulating material may be composed of only resin materials, or may further contain inorganic materials. Examples of the inorganic materials include metal oxides, metal nitrides, metal fluorides, metal carbides, etc. Examples of the metal oxides include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, manganese oxide, etc. Examples of the metal nitrides include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, silicon nitride, etc. Examples of the metal fluorides include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, etc. Examples of the metal carbides include silicon carbide, boron carbide, titanium carbide, tungsten carbide, etc. Further, the inorganic material may be a porous aluminosilicate such as zeolite (M ２／ｎ O·Al ２ O ３ ·xSiO ２ ·yH ２ O, where M is a metal element, n is the valence of M, x≥2, y≥0), talc (Mg ３ Si ４ O １０ (OH) ２ ), barium titanate (BaTiO ３ ), strontium titanate (SrTiO ３ ), etc., or other minerals. These may be used alone or in combination of two or more.

[0040] The inorganic material is, for example, composed of particulate inorganic particles. The average particle diameter of the inorganic particles is, for example, 0.05 μm or more and 2 μm or less. Note that the average particle diameter of the inorganic particles means the particle diameter at which the cumulative frequency becomes 50% from the smaller particle diameter in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of the inorganic particles can be measured using a laser diffraction type particle size distribution measuring device (for example, manufactured by Microtrac Bell, MT3000II) with water as the dispersion medium.

[0041] When the insulating material contains the above-mentioned inorganic material, the content of the inorganic material relative to the total mass of the protective layer 32 is preferably, for example, 60% by mass or more and 99% by mass or less, and 70% by mass or more and 95% by mass or less. When the insulating material contains the above-mentioned inorganic material, it becomes easier to form the protective layer 32 on the surface of the positive electrode core 30.

[0042] The protective layer 32 may further contain a conductive agent in addition to the insulating material. In other words, the protective layer 32 may be a high-resistance layer with greater electrical resistance than the positive electrode core 30. Examples of conductive agents included in the protective layer 32 include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and carbon materials such as graphene. These may be used individually or in combination of two or more.

[0043] The mixed layer 33 is a layer formed by mixing the components of the positive electrode mixture layer 31 and the components of the protective layer 32. In other words, the mixed layer 33 is a layer containing the positive electrode active material contained in the positive electrode mixture layer 31 and the insulating material contained in the protective layer 32. In the mixed layer 33, for example, the positive electrode active material is dispersed throughout the mixed layer 33, and the insulating material is present throughout the mixed layer 33 to fill the gaps between the positive electrode active material. It is preferable that the mixed layer 33 is formed over the entire thickness direction of the positive electrode 11, as shown in Figure 3. It is preferable that the positive electrode active material and the insulating material are uniformly dispersed throughout the mixed layer, but they may be unevenly dispersed in the mixed layer 33.

[0044] The content of insulating material in the mixed layer 33 is less than the content of insulating material in the protective layer 32. The content of insulating material in the mixed layer 33 is, for example, 20% by mass or more and 80% or less of the mass of the mixed layer 33, and may be 30% or more and 70% or less. Furthermore, if the positive electrode mixture layer 31 contains insulating material such as a binder, the content of insulating material in the mixed layer 33 is greater than the content of insulating material in the positive electrode mixture layer 31.

[0045] Since the mixed layer 33 contains more insulating material such as resin material than the positive electrode mixture layer 31, it has high adhesion to the positive electrode core 30. Therefore, by providing the mixed layer 33, it is possible to suppress peeling of the positive electrode mixture layer 31 at the winding start end 31A of the positive electrode mixture layer 31.

[0046] Even if the winding start end of the positive electrode mixture layer 31 is formed on the protective layer 32, it is considered that peeling of the positive electrode mixture layer 31 at the winding start end 31A is suppressed. However, if the protective layer 32 is interposed between the winding start end of the positive electrode mixture layer 31 and the positive electrode core 30, the conductive path between the positive electrode core 30 and the winding start end of the positive electrode mixture layer 31 is obstructed, and the battery capacity decreases. On the other hand, since the mixed layer 33 contains positive electrode active material, it has lower resistance than the protective layer 32, so the positive electrode active material of the mixed layer 33 provided on the positive electrode core 30 can be charged and discharged. Therefore, by providing the mixed layer 33 on the positive electrode core 30, it is possible to improve the battery capacity while suppressing peeling of the positive electrode mixture layer 31. In this specification, the winding start end of the positive electrode mixture layer 31 refers to the region including the winding start end 31A of the positive electrode mixture layer 31 and its vicinity.

[0047] In this embodiment, the thickness of the mixed layer 33 is approximately the same as the thickness of the positive electrode mixture layer 31. The thickness of the mixed layer 33 is approximately uniform along the length of the positive electrode 11. However, the thickness of the mixed layer 33 may be less than the thickness of the positive electrode mixture layer 31.

[0048] In the longitudinal direction of the positive electrode 11, the length of the mixed layer 33 is preferably 0.5 mm or more, and more preferably 1.0 mm or more. By making the length of the mixed layer 33 0.5 mm or more, peeling of the positive electrode mixture layer 31 at the winding start end 31A of the positive electrode mixture layer 31 can be further suppressed. Furthermore, the length of the mixed layer 33 is preferably 5.0 mm or less, and more preferably 4.5 mm or less. By making the length of the mixed layer 33 5.0 mm or less, the area of ​​the region where the positive electrode mixture layer 31 is formed can be increased, making it easier to achieve a higher battery capacity. Therefore, in the longitudinal direction of the positive electrode 11, the length of the mixed layer 33 is preferably 0.5 mm or more, 5.0 mm or less, and more preferably 1.0 mm or more, 4.5 mm or less.

[0049] The positive electrode 11 of this embodiment can be manufactured, for example, by applying a positive electrode mixture slurry that forms the positive electrode mixture layer 31 and a protective layer slurry that forms the protective layer 32 to the surface of the positive electrode core 30 using a multilayer die coater. When using a multilayer die coater, the positive electrode mixture slurry and the protective layer slurry can be applied to the surface of the positive electrode core 30 simultaneously or separately. When applying at least one of the positive electrode mixture slurry and the protective layer slurry to the surface of the positive electrode core 30 using a multilayer die coater, the positive electrode core 30 moves relative to the multilayer die coater. Therefore, by changing the timing of application of the positive electrode mixture slurry and the protective layer slurry, the positions in which the positive electrode mixture layer 31, the protective layer 32, and the mixed layer 33 are formed can be controlled.

[0050] Specifically, at the winding start end 11A of the positive electrode 11, only the protective layer slurry is applied to the surface of the positive electrode core 30. This forms a protective layer 32 at the winding start end 11A of the positive electrode 11. Then, at a predetermined timing, the positive electrode mixture layer slurry is applied to the surface of the positive electrode core 30 together with the protective layer slurry. This forms a mixed layer 33 on the winding end side of the protective layer 32, which is a mixture of the protective layer slurry and the positive electrode mixture layer slurry. The method for adjusting the degree of dispersion of the components of the protective layer and the positive electrode mixture layer will be explained later. Then, at a predetermined timing, the application of the protective layer slurry is stopped, and only the positive electrode mixture layer slurry is applied to the surface of the positive electrode core 30. This forms a positive electrode mixture layer 31 on the winding end side of the mixed layer 33. After drying the prepared coating film, it is compressed to produce a positive electrode 11 having a positive electrode mixture layer 31, a protective layer 32, and a mixed layer 33.

[0051] The degree of dispersion of the insulating material in the mixed layer 33 can be adjusted by the solid content concentration of the positive electrode mixture layer slurry or the protective layer slurry and the drying conditions of the coating film. By reducing the solid content concentration of the positive electrode mixture layer slurry or the protective layer slurry, the dispersibility of the insulating material in the mixed layer 33 is improved. The solid content concentration of the positive electrode mixture layer slurry and the protective layer slurry is, for example, 3% by mass or more and 30% by mass or less. In addition, by increasing the drying temperature of the coating film, the dispersibility of the insulating material in the mixed layer 33 is improved. The drying temperature of the coating film is, for example, 100°C or more and 150°C or less.

[0052] As described above, in this embodiment, the positive electrode 11 has a protective layer 32, a mixed layer 33 which is a mixture of the components of the positive electrode mixture layer 31 and the components of the protective layer 32, and the positive electrode mixture layer 31 formed on the positive electrode core 30 in order from the winding start end 11A toward the winding end. By not forming the positive electrode mixture layer 31 over the winding start end 11A of the positive electrode 11, the step formed at the winding start end 11A of the positive electrode 11 can be reduced. As a result, deformation of the negative electrode 12 opposite the winding start end 11A of the positive electrode 11 can be suppressed when charging and discharging are repeated. Furthermore, by forming the mixed layer 33 with a large content of insulating material on the winding start side of the positive electrode mixture layer 31, peeling of the positive electrode mixture layer 31 at the winding start end 31A can be suppressed. Furthermore, by forming a mixed layer 33 containing the positive electrode active material on the positive electrode core 30, a conductive path is ensured, and the battery capacity can be improved. In other words, the non-aqueous electrolyte secondary battery 10 equipped with the positive electrode 11 of this embodiment can suppress deformation of the negative electrode 12 near the winding start end 11A of the positive electrode 11, while also suppressing peeling of the positive electrode mixture layer 31 and improving the battery capacity. Note that at least one of the protective layer 32 and the mixed layer 33 may be formed on the winding end side as well as the winding start side of the positive electrode 11.

[0053] Next, a modified example of the positive electrode 11 will be described with reference to Figure 4. Figure 4 is a diagram of the modified positive electrode 11, corresponding to Figure 3.

[0054] As shown in Figure 4, the mixed layer 33 of this embodiment has an inclined portion 34 in which the thickness of the mixed layer 33 decreases as it approaches the winding start end 11A of the positive electrode 11. By providing the inclined portion 34, the step formed on the winding start end side of the positive electrode 11 can be reduced. As a result, even when charging and discharging are repeated, stress concentration on the negative electrode 12 is further reduced, and deformation of the negative electrode 12 can be further suppressed.

[0055] In the longitudinal direction of the positive electrode 11, the length of the inclined portion 34 may be, for example, 0.5 mm or more and 5 mm or less, or 1 mm or more and 3 mm or less. In this case, while suppressing peeling of the positive electrode mixture layer 31, deformation of the negative electrode 12 at the winding start side of the positive electrode 11 can be further suppressed.

[0056] The inclined portion 34 can be created, for example, by reducing the amount of the positive electrode mixture slurry and the protective layer slurry applied as it approaches the starting end 11A of the positive electrode 11.

[0057] In the example shown in Figure 4, the inclined portion 34 is formed on the winding start side of the mixed layer 33, and the region on the winding end side of the mixed layer 33 has a substantially constant thickness. However, the inclined portion 34 may be formed over the entire length of the mixed layer 33. In addition to the mixed layer 33, a region may be provided on the winding start side of the positive electrode mixture layer 31 in which the thickness of the positive electrode mixture layer 31 decreases as it approaches the winding start end 11A of the positive electrode 11.

[0058] Furthermore, in the example shown in Figure 4, the thickness of the mixed layer 33 decreases linearly as it approaches the winding start end 11A of the positive electrode 11, but it may also decrease non-linearly as it approaches the winding start end 11A of the positive electrode 11. In addition, the inclined portion 34 may be provided not only on the winding start side of the positive electrode 11 but also on the winding end side of the positive electrode 11.

[0059] The present disclosure will be further illustrated below with reference to examples, but the present disclosure is not limited to these examples.

[0060] <Example 1> [Preparation of positive electrode mixture layer slurry] As the positive electrode active material, lithium nickelate (LiNi) containing cobalt and aluminum was used. ０．８８ Co ０．０９ Al ０．０３ O ２ A positive electrode active material was used. 100 parts by mass of this positive electrode active material was mixed with 1 part by mass of acetylene black (AB) as a conductive agent and 1 part by mass of polyvinylidene fluoride (PVDF) as a binder. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was then added to prepare a positive electrode mixture layer slurry.

[0061] [Preparation of protective layer slurry] Titanium oxide (TiO) as an inorganic material with an average uniform particle size of 0.7 μm ２ The particles and polyvinylidene fluoride (PVDF) as a resin material were mixed in a solid content mass ratio of 90:10, and then an appropriate amount of NMP was added to make a protective layer slurry so that the solid content concentration was 30% by mass.

[0062] [Fabrication of the positive electrode] A protective layer slurry and a positive electrode mixture layer slurry were applied using a die coater to a positive electrode core made of aluminum foil with a thickness of 15 μm and a width of 62.6 mm, starting from one end on both sides, so that a protective layer, a mixed layer, and a positive electrode mixture layer were formed in that order. The prepared coating film was then dried in an oven at 120°C, cut to the predetermined electrode size, and rolled using a roller to produce the positive electrode. In the longitudinal direction of the positive electrode, the length of the protective layer was 3.0 mm and the length of the mixed layer was 2.5 mm. The thickness of the protective layer was 10 μm, and the thickness of the mixed layer and positive electrode mixture layer was 80 μm.

[0063] Furthermore, a portion of the positive electrode core was provided in the longitudinal center of the positive electrode, where the positive electrode compound layer was not formed on both sides of the positive electrode core. A 120 μm thick aluminum positive electrode lead was then fixed to this exposed portion of the positive electrode core by ultrasonic welding.

[0064] [Fabrication of the negative electrode] A mixture of graphite and silicon-containing material in a mass ratio of 95:5 was used as the negative electrode active material. 100 parts by mass of this negative electrode active material was mixed with 1 part by mass of styrene-butadiene rubber (SBR) as a binder and 1 part by mass of carboxymethylcellulose (CMC) as a thickener, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, dried, cut to a predetermined electrode size, and rolled using a roller to obtain a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core. Furthermore, a negative electrode core exposed portion was formed at one end in the longitudinal direction of the negative electrode, in which no negative electrode mixture layer was formed on both sides of the negative electrode core, and a nickel negative electrode lead was fixed to this negative electrode core exposed portion by ultrasonic welding.

[0065] [Preparation of Non-Aqueous Electrolyte] 100 parts by mass of a mixed solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7, to which 5 parts by mass of vinylene carbonate (VC) is added, and lithium hexafluoride phosphate (LiPF) is added. ６ A non-aqueous electrolyte was prepared by dissolving ) at a concentration of 1.5 mol / liter.

[0066] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] A wound electrode body was fabricated by spirally winding the positive and negative electrodes with a separator in between. During this process, the areas with protective and mixed layers were positioned on the starting side of the positive electrode. Insulating plates were placed above and below the electrode body, and the electrode body was housed in an outer casing. The negative electrode lead was welded to the bottom of the bottomed cylindrical outer casing, and the positive electrode lead was welded to the sealing body. After injecting the above-mentioned non-aqueous electrolyte into the outer casing, the opening of the outer casing was sealed with the sealing body via a gasket to fabricate a non-aqueous electrolyte secondary battery.

[0067] <Comparative Example 1> A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that in the preparation of the positive electrode, only the positive electrode mixture layer slurry was applied and no protective layer slurry was applied. In other words, the positive electrode of Comparative Example 1 does not have a protective layer or a mixing layer.

[0068] <Comparative Example 2> In the preparation of the positive electrode, a protective layer slurry was applied to one end of both sides of the positive electrode core, dried, and then the positive electrode mixture layer slurry was applied to both sides of the positive electrode core so as to overlap a portion of the protective layer. In other words, the positive electrode of Comparative Example 2 does not have a mixed layer, and the starting end of the winding of the positive electrode mixture layer is positioned on the protective layer.

[0069] To evaluate the adhesion of the positive electrodes prepared in Example 1 and Comparative Examples 1 and 2, each prepared positive electrode was bent 180° along the outer surface of a 3 mm diameter round rod. The surface of the positive electrode was then visually inspected to evaluate whether or not there was any peeling at the starting end of the positive electrode mixture layer. When bending the positive electrode along the outer surface of the round rod, the starting end of the positive electrode mixture layer was made in contact with the outer surface of the round rod. As a result, no peeling of the positive electrode mixture layer occurred at the starting end of the positive electrode mixture layer in the positive electrodes of Example 1 and Comparative Example 2. On the other hand, peeling of the positive electrode mixture layer occurred at the starting end of the positive electrode mixture layer in the positive electrode of Comparative Example 1.

[0070] [Evaluation of Discharge Capacity] The non-aqueous electrolyte secondary batteries of Example 1 and Comparative Examples 1 and 2 were charged to 4.2V with a constant current of 0.2C at a temperature of 25°C, and then charged to 0.02C with a constant voltage of 4.2V. After that, they were discharged to 2.5V with a constant current of 0.2C, and the discharge capacity was measured.

[0071] Table 1 shows the discharge capacities of the non-aqueous electrolyte secondary batteries of Example 1 and Comparative Examples 1 and 2. The discharge capacities in Table 1 are expressed as relative values, with the discharge capacity of Comparative Example 1 set to 100; a higher value indicates a higher capacity. Table 1 also shows whether or not a protective layer and a mixing layer were present.

[0072]

[0073] As shown in Table 1, the non-aqueous electrolyte secondary battery of Example 1 has a higher capacity than the non-aqueous electrolyte secondary battery of Comparative Example 2, and achieves the same capacity as the non-aqueous electrolyte secondary battery of Comparative Example 1. Therefore, the non-aqueous electrolyte secondary battery equipped with the positive electrode of this embodiment can achieve both suppression of peeling of the positive electrode mixture layer and improvement of battery capacity.

[0074] This disclosure is further illustrated by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound along the length direction via a separator, wherein the positive electrode comprises a positive electrode core, a positive electrode mixture layer formed on the positive electrode core and mainly comprising a positive electrode active material, a protective layer formed on the positive electrode core and mainly comprising an insulating material, and a mixed layer formed on the positive electrode core and being a mixture of the components of the positive electrode mixture layer and the components of the protective layer, wherein the protective layer, the mixed layer, and the positive electrode mixture layer are arranged in order from the beginning end of the winding of the positive electrode toward the end end of the winding. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the insulating material comprises a resin material. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the insulating material comprises an inorganic material. Configuration 4: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the mixed layer has a sloped portion in which the thickness of the mixed layer decreases as it approaches the starting end of the winding of the positive electrode. Configuration 5: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the length of the mixed layer in the longitudinal direction of the positive electrode is 0.5 mm or more and 5.0 mm or less. Configuration 6: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the length of the protective layer in the longitudinal direction of the positive electrode is 0.5 mm or more and 5.0 mm or less. Configuration 8: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the thickness of the protective layer is 50% or less of the maximum thickness of the positive electrode mixture layer. Configuration 9: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 8, wherein the thickness of the protective layer is 5 μm or more and 25 μm or less.

[0075] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 11A Starting end of winding, 11B Starting end of winding, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18 Insulating plate, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core body, 31 Positive electrode mixture layer, 31A Starting end of winding, 32 Protective layer, 33 Mixing layer, 34 Inclined section, 40 Negative electrode core body, 41 Negative electrode mixture layer, 42 Outer peripheral exposed section.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound along the length direction via a separator, wherein the positive electrode comprises: a positive electrode core; a positive electrode mixture layer formed on the positive electrode core and mainly containing a positive electrode active material; a protective layer formed on the positive electrode core and mainly containing an insulating material; and a mixed layer formed on the positive electrode core and in which the components of the positive electrode mixture layer and the components of the protective layer are mixed, wherein the protective layer, the mixed layer, and the positive electrode mixture layer are arranged in order from the starting end of the winding of the positive electrode toward the ending end of the winding.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating material includes a resin material.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating material includes an inorganic material.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the mixed layer has a sloped portion in which the thickness of the mixed layer decreases as it approaches the starting end of the winding of the positive electrode.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the length of the mixed layer in the longitudinal direction of the positive electrode is 0.5 mm or more and 5.0 mm or less.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the length of the protective layer in the longitudinal direction of the positive electrode is 0.5 mm or more and 5.0 mm or less.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the protective layer is 50% or less of the maximum thickness of the positive electrode mixture layer.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the protective layer is 5 μm or more and 25 μm or less.

Images