Non-aqueous electrolyte secondary battery

Abstract

This invention provides a non-aqueous electrolyte secondary battery with improved charge-discharge cycle performance. As one embodiment of this invention, the non-aqueous electrolyte secondary battery comprises: an electrode body wound with a strip-shaped positive electrode and a strip-shaped negative electrode separated by a spacer; an electrolyte; and an outer packaging body containing the electrode body and the electrolyte. The negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector and comprising a negative electrode active material and a solid electrolyte. For the negative electrode mixture layer, the content of the solid electrolyte at the inner end of the winding is higher than the content of the solid electrolyte at the outer end of the winding, and there is a region where the content of the solid electrolyte continuously decreases from the inner end side to the outer end side.

Description

Technical Field

[0001] This invention relates to a non-aqueous electrolyte secondary battery. Background Technology

[0002] The positive and negative electrodes of a non-aqueous electrolyte secondary battery each have a current collector and an agent layer formed on the surface of the current collector. The agent layer contains an active material capable of reversibly adsorbing and releasing Li ions. Patent documents 1-3 disclose a technique in which an inorganic solid electrolyte with Li ion conductivity is contained in the agent layer to improve battery safety and maintain performance.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-527603

[0006] Patent Document 2: Japanese Patent Application Publication No. 2008-117542

[0007] Patent Document 3: Japanese Patent Application Publication No. 2011-44252 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in non-aqueous electrolyte secondary batteries with wound electrode bodies, the uneven distribution of electrolyte within the electrode body occurs due to the expansion and contraction of the electrode body during charging and discharging. This leads to a decrease in battery capacity when repeatedly charged and discharged. The technology disclosed in Patent Document 1 does not address the distribution of electrolyte within the electrode body, leaving room for improvement in its charge-discharge cycle characteristics.

[0010] The purpose of this invention is to provide a non-aqueous electrolyte secondary battery with improved charge-discharge cycle characteristics.

[0011] Methods for solving problems

[0012] A non-aqueous electrolyte secondary battery, as an embodiment of the present invention, is characterized by comprising: an electrode body wound with a strip-shaped positive electrode and a strip-shaped negative electrode separated by a spacer; an electrolyte; and an outer packaging body containing the electrode body and the electrolyte. The negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector and containing a negative electrode active material and a solid electrolyte. For the negative electrode mixture layer, the content of the solid electrolyte at the inner end of the winding is higher than the content of the solid electrolyte at the outer end of the winding, and there is a region in which the content of the solid electrolyte continuously decreases from the inner end side to the outer end side.

[0013] Invention Effects

[0014] According to the secondary battery as one aspect of the present invention, the charge-discharge cycle characteristics can be improved. Attached Figure Description

[0015] Figure 1 This is an axial cross-sectional view of a cylindrical secondary battery as an example of an implementation method.

[0016] Figure 2 yes Figure 1 The diagram shows a three-dimensional view of the wound-type electrode body of the secondary battery.

[0017] Figure 3 This is a front view showing the positive and negative electrodes of an electrode body constituting an example of an implementation in an unfolded state.

[0018] Figure 4 (a)~(d) represent Figure 3 The graph shows the change in the content of solid electrolyte in the negative electrode mixture layer along its length. Detailed Implementation

[0019] Hereinafter, an example of an embodiment of the cylindrical secondary battery of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, values, orientations, etc., are examples used to facilitate understanding of the present invention and can be appropriately varied depending on the specifications of the cylindrical secondary battery. Furthermore, in the following description, where multiple embodiments and modifications are included, it is initially conceived that their characteristic parts are appropriately combined.

[0020] Figure 1 This is an axial cross-sectional view of a cylindrical secondary battery 10 as an example of an implementation. Figure 1The secondary battery 10 shown contains an electrode body 14 and an electrolyte (not shown) within an outer casing 15. The electrode body 14 has a wound structure consisting of a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12, separated by a spacer 13. Non-aqueous solvents (organic solvents) such as carbonates, lactones, ethers, ketones, and esters can be used as the electrolyte, and two or more of these solvents can be mixed. When using two or more solvents, a mixed solvent containing cyclic carbonates and chain carbonates is preferred. For example, ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC) can be used as cyclic carbonates, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used as chain carbonates. LiPF6, LiBF4, LiCF3SO3, and mixtures thereof can be used as the electrolyte salt of the electrolyte. The solubility of the electrolyte salt relative to the non-aqueous solvent can be set, for example, to be 0.5–2.0 mol / L. It should be noted that, for ease of explanation, the sealing body 16 side will be designated as "upper" and the bottom side of the outer packaging body 15 as "lower" in the following description.

[0021] The opening of the outer packaging 15 is sealed by the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are respectively provided above and below the electrode body 14. The positive electrode lead 19 extends upward through the through hole in the insulating plate 17 and is welded to the lower surface of the filter 22, which serves as the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is electrically connected to the filter 22 and serves as the top plate of the sealing body 16, becomes the positive terminal. On the other hand, the negative electrode lead 20 extends towards the bottom side of the outer packaging 15 through the through hole in the insulating plate 18 and is welded to the inner bottom surface of the outer packaging 15. In the secondary battery 10, the outer packaging 15 becomes the negative terminal. It should be noted that when the negative electrode lead 20 is located at the outer end of the roll, the negative electrode lead 20 passes through the outside of the insulating plate 18, extends towards the bottom side of the outer packaging 15, and is welded to the inner bottom surface of the outer packaging 15.

[0022] The outer packaging 15 is, for example, a bottomed cylindrical metal can. A gasket 27 is provided between the outer packaging 15 and the sealing body 16 to ensure the airtightness of the interior of the secondary battery 10. The outer packaging 15 has a slotted portion 21 formed, for example, by stamping a side portion from the outside, that supports the sealing body 16. The slotted portion 21 is preferably formed in a ring shape along the circumferential direction of the outer packaging 15, and its upper surface supports the sealing body 16.

[0023] The sealing body 16 comprises, in sequence from the electrode body 14, a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. Each component constituting the sealing body 16 is, for example, circular or annular, and all components except the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, with the insulating member 24 sandwiched between their respective peripheral portions. When the internal pressure of the battery increases due to abnormal heat dissipation, for example, the lower valve body 23 breaks, causing the upper valve body 25 to bulge towards the cap 26 and detach from the lower valve body 23, thereby blocking the electrical connection between the two. When the internal pressure further increases, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cap 26.

[0024] Below, in reference Figure 2 Meanwhile, the electrode body 14 will be explained. Figure 2 This is a perspective view of the electrode body 14. As described above, the electrode body 14 has a spiral structure formed by winding a positive electrode 11 and a negative electrode 12 in a spiral shape with a spacer 13 between them. The positive electrode 11, the negative electrode 12, and the spacer 13 are all formed in a strip shape and are spirally wound around a core arranged along the winding axis 28, thereby forming an alternating layered state along the radial direction of the electrode body 14. In the radial direction, the side on the winding axis 28 is called the inner circumferential side, and the side opposite to it is called the outer circumferential side. In the electrode body 14, the length direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and the negative electrode 12 is the axial direction. The positive electrode lead 19 extends axially from approximately the center in the radial direction between the center and the outermost circumference at the upper end of the electrode body 14. In addition, the negative electrode lead 20 extends axially from near the winding axis 28 at the lower end of the electrode body 14.

[0025] The spacer 13 can be a porous sheet with ion permeability and insulation. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the spacer 13 is preferably an olefin resin such as polyethylene or polypropylene. The thickness of the spacer 13 is, for example, 10 μm to 50 μm. With the increasing capacity and high output power of batteries, the spacer 13 is trending towards thinner films. The spacer 13, for example, has a melting point of about 130°C to 180°C.

[0026] Below, in reference Figure 3 and Figure 4 At the same time, the positive and negative electrodes of this embodiment will be explained. Figure 3 This is a front view of the positive electrode 11 and negative electrode 12 that constitute the electrode body 14. Figure 3 In the diagram, the positive electrode 11 and the negative electrode 12 are represented in their unfolded state. For example... Figure 3As illustrated, in the electrode body 14, to prevent lithium deposition at the negative electrode 12, the negative electrode 12 is formed to be larger than the positive electrode 11. Specifically, the axial length of the negative electrode 12 is greater than the width length of the positive electrode 11. In addition, the length of the negative electrode 12 is greater than the length of the positive electrode 11. Thus, when the electrode body 14 is wound, at least the portion of the positive electrode 11 in which the positive electrode flux layer 32 is formed is positioned opposite the portion of the negative electrode 12 in which the negative electrode flux layer 42 is formed, separated by the spacer 13.

[0027] The positive electrode 11 has a strip-shaped positive current collector 30 and a positive electrode flux layer 32 formed on the surface of the positive current collector 30. The positive electrode flux layer 32 is formed on at least one of the inner and outer peripheral sides of the positive current collector 30, and is suitable for being formed on all areas of both sides of the positive current collector 30 except for the positive electrode exposed portion 34 described later. For example, a foil of metal such as aluminum or a film of such metal disposed on the surface can be used as the positive current collector 30. The thickness of the positive current collector 30 is, for example, 10 μm to 30 μm.

[0028] The positive electrode additive layer 32 preferably comprises a positive electrode active material, a conductive agent, and a binder. The positive electrode additive layer 32 can be manufactured, for example, by coating a positive electrode additive slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) onto both sides of the positive electrode current collector 30, drying it, and then calendering it.

[0029] The positive electrode 11 has a positive electrode exposure portion 34 that exposes the surface of the positive electrode current collector 30. The positive electrode exposure portion 34 is the portion connected to the positive electrode lead 19 and whose surface is not covered by the positive electrode binder layer 32. The positive electrode exposure portion 34 is made wider than the positive electrode lead 19 in the length direction. The positive electrode exposure portion 34 is suitable to be provided on both sides of the positive electrode 11 in a manner that coincides with the thickness direction of the positive electrode 11. For example, the positive electrode lead 19 is joined to the positive electrode exposure portion 34 by ultrasonic welding.

[0030] Figure 3 In the example shown, a positive electrode exposed portion 34 is provided along the entire width of the positive electrode 11 at its central length. The positive electrode exposed portion 34 can be formed at either the inner or outer end of the positive electrode 11 winding; however, from the viewpoint of current collection, it is preferable to provide it at a position approximately equidistant from both the inner and outer ends. By connecting the positive electrode lead 19 to the positive electrode exposed portion 34 located at this position, when the electrode is wound as an electrode body 14, the positive electrode lead 19 is configured to protrude upwards from its end face in the width direction approximately at the center of the electrode body 14 in the radial direction. For example, the positive electrode exposed portion 34 can be provided by intermittently coating a portion of the positive electrode current collector 30 without coating it with the positive electrode paste.

[0031] As the positive electrode active material contained in the positive electrode mixture layer 32, lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni can be exemplified. The lithium transition metal oxide is, for example, Li 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, Li2MPO4F, wherein M is at least one selected from the group consisting 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 may be used alone or in combination of two or more. From the viewpoint of achieving higher capacity of a non-aqueous electrolyte secondary battery, 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 lithium-nickel composite oxides such as (wherein M is at least one selected from the group consisting 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).

[0032] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, and graphite. They may be used alone or in combination of two or more thereof.

[0033] Examples of binders contained in the positive electrode binder layer 32 include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. One type can be used alone, or two or more can be used in combination. When preparing the positive electrode binder slurry with an aqueous solvent, styrene-butadiene rubber (SBR), nitrile rubber (NBR), CMC or its salts, polyacrylic acid or its salts, and polyvinyl alcohol can be used.

[0034] The negative electrode 12 has a strip-shaped negative electrode current collector 40 and a negative electrode flux layer 42 formed on the surface of the negative electrode current collector 40. The negative electrode flux layer 42 is formed on at least one of the inner and outer peripheral sides of the negative electrode current collector 40, and is suitable for being formed on all areas of both sides of the negative electrode current collector 40 except for the negative electrode exposed portion 44 described later. As the negative electrode current collector 40, for example, a foil of metal such as copper, or a film of such metal disposed on the surface can be used. The thickness of the negative electrode current collector 40 is, for example, 5 μm to 30 μm.

[0035] The negative electrode mixture layer 42 comprises a negative electrode active material and a solid electrolyte. The negative electrode mixture layer 42 may also include a binder. The negative electrode mixture layer 42 can be manufactured, for example, by coating a negative electrode mixture slurry containing a negative electrode active material, a solid electrolyte, a binder, and a solvent such as water onto both sides of the negative electrode current collector 40, drying it, and then calendering it.

[0036] Figure 3 In the example shown, at the inner end of the negative electrode 12 along its length, a negative electrode exposed portion 44 is provided along the entire width of the current collector. The negative electrode exposed portion 44 is the portion connecting the negative electrode lead 20 and is the portion of the surface of the negative electrode current collector 40 not covered by the negative electrode binder layer 42. The negative electrode exposed portion 44 is made wider in the length direction than the width of the negative electrode lead 20. The negative electrode exposed portion 44 is adapted to be provided on both sides of the negative electrode 12 in a manner that overlaps in the thickness direction of the negative electrode 12.

[0037] Figure 3 In this configuration, the inner end 42a of the negative electrode mixture layer 42 is adjacent to the exposed negative electrode portion 44. On the other hand, the outer end 42b of the negative electrode mixture layer 42 is the same as the outer end of the negative electrode 12. The negative electrode mixture layer 42 is continuously present from the inner end 42a to the outer end 42b.

[0038] In this embodiment, for example, ultrasonic welding is used to join the negative electrode lead 20 to the inner peripheral surface of the negative electrode current collector 40. One end of the negative electrode lead 20 is disposed in the negative electrode exposed portion 44, and the other end extends downward from the lower end of the negative electrode exposed portion 44.

[0039] The placement of the negative lead 20 is not limited to Figure 3 In the example shown, the negative electrode lead 20 can also be provided only at the outer end of the negative electrode 12. Alternatively, the negative electrode lead 20 can be provided at both the inner and outer ends of the negative electrode 12. In this case, the current-collecting capacity is improved. This can also be achieved by connecting the exposed negative electrode portion 44 at the outer end of the negative electrode 12 to the outer packaging body 15 (see reference). Figure 1 The inner circumferential surface of the negative electrode 12 is in contact with the negative electrode, and the outer end of the negative electrode 12 is electrically connected to the outer packaging body 15 without using the negative electrode lead 20. For example, the negative electrode exposed portion 44 is provided by intermittent coating of a portion of the negative electrode current collector 40 without coating the negative electrode mixture slurry.

[0040] As the negative electrode active material contained in the negative electrode compound layer 42, there are no particular limitations as long as it is a material that can reversibly absorb and release lithium ions. For example, carbon-based materials such as natural graphite and artificial graphite, metals such as Si and Sn that are alloyed with lithium, or alloys or oxides containing them can be used.

[0041] Negative electrode active materials can include carbon-based and silicon-based materials. Examples of silicon-based materials include Si, Si-containing alloys, and SiO₂. x Silicon oxides, etc. (x is 0.8 to 1.6). Silicon-based materials are negative electrode active materials that can improve battery capacity more than carbon-based materials. From the viewpoint of improving battery capacity and suppressing the decline in charge-discharge cycle characteristics, the content of silicon-based materials in the negative electrode active material is preferably 3% by mass or more relative to the mass of the negative electrode active material. The upper limit of the silicon-based material content is, for example, 20% by mass. The average particle diameter (D50, median particle size in volumetric reference) of carbon-based materials is, for example, 5 μm to 40 μm, and the D50 of silicon-based materials is, for example, 1 μm to 15 μm. D50 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution reaches 50% from the smallest particle size, also known as the median diameter. The particle size distribution of carbon-based and silicon-based materials can be measured using a laser diffraction particle size distribution measuring device (e.g., Microtrac Bel Co., Ltd., MT3000II) with water as the dispersion medium.

[0042] The solid electrolyte contained in the negative electrode layer 42 is not particularly limited as long as it has Li ion conductivity; it can be an inorganic solid electrolyte or a polymeric solid electrolyte. Examples of inorganic solid electrolytes include Li7La3Zr2O. 12 (LLZ), Li 1.5 Al 0.5 Ge 1.5 P3O 12 (LAGP), Li5La3Ta2O 12(LLTO), etc. Examples of polymeric solid electrolytes include polymeric electrolytes that contain electrolyte salts such as LiPF6 in polyethylene oxide (PEO).

[0043] From the perspective of stability, inorganic solid electrolytes are preferred. The average particle diameter (D50, median particle size on a volume basis) of inorganic solid electrolytes is, for example, 0.01 μm to 10 μm.

[0044] The content of solid electrolyte in the negative electrode mixture layer 42 is, for example, 1% to 10% by mass. Here, the content of solid electrolyte is the percentage of the mass of solid electrolyte relative to the mass of the negative electrode active material. As will be described later, the content of solid electrolyte varies along the length of the negative electrode mixture layer 42.

[0045] Examples of binders contained in the negative electrode binder layer 42 include styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and also partially neutralized salts), polyvinyl alcohol (PVA), etc. Additionally, binders may include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. They may be used individually or in combination of two or more.

[0046] Below, in reference Figure 4 At the same time as (a) to (d), Figure 3 The variation in the content of solid electrolyte in the negative electrode mixture layer 42 along the length direction is explained. Figure 4 In (a), the content of solid electrolyte in the inner end 42a is higher than that in the outer end 42b, and the content of solid electrolyte decreases proportionally from the inner end 42a to the outer end 42b. When the electrode body 14 expands and contracts due to the charging and discharging of the battery, the inner end 42a is subjected to greater stress than the outer end 42b, thus making it more difficult for electrolyte to penetrate compared to the outer end 42b. Since the content of solid electrolyte in the inner end 42a is higher than that in the outer end 42b, the unevenness of the reaction caused by the charging and discharging of the battery in the inner end 42a and the outer end 42b can be suppressed, thereby improving the charge-discharge cycle characteristics of the battery. In high-rate charging and discharging, unevenness of electrolyte is easily generated in the inner end 42a and the outer end 42b, thus the effect of the present invention is significant.

[0047] The content of solid electrolyte at the inner end 42a is preferably 1% to 15% by mass relative to the mass of the negative electrode active material. This allows for the improvement of the battery's charge-discharge cycle characteristics while maintaining battery capacity.

[0048] In addition, such as Figure 4 As shown in (b), the slope of the rate of decrease in the content of solid electrolyte from the inner end 42a to the outer end 42b of the roll may not be constant and may change along the way. Figure 4 In (c), the content of solid electrolyte decreases from the inner end 42a to the outer end 42b, and the content of solid electrolyte remains constant between the inner end 42a and the outer end 42b. Figure 4 In (d), the content of solid electrolyte decreases from the inner end 42a to the outer end 42b, and remains constant near the outer end 42b. Similarly, as long as the content of solid electrolyte decreases from the inner end 42a to the outer end 42b, the content of solid electrolyte can also remain constant near the inner end 42a. Figure 4 As shown in (c) and (d), it is sufficient to provide a region in at least a portion of the negative electrode mixture layer 42 where the content of solid electrolyte continuously decreases from the inner end 42a side to the outer end 42b side. In this region, it is preferable that the content of solid electrolyte decreases linearly; however, it may also decrease non-linearly. This allows the content of solid electrolyte at the inner end 42a of the negative electrode mixture layer 42 to be higher than the content of solid electrolyte at the outer end 42b.

[0049] The following describes a method for forming a negative electrode mixture layer 42 in which the content of solid electrolyte varies from one side (inner end 42a) to the other (outer end 42b). To form this negative electrode mixture layer 42, a multilayer die coater is preferably used. Using the multilayer die coater, multiple negative electrode mixture slurries with different solid electrolyte contents can be simultaneously coated onto the negative electrode current collector 40 while adjusting their mixing ratio. When coating the negative electrode mixture slurry onto the negative electrode current collector 40, the negative electrode current collector 40 moves relative to the multilayer die coater. Therefore, by coating multiple negative electrode mixture slurries with different solid electrolyte contents onto the negative electrode current collector 40 while changing their mixing ratio at a given time, a region in the negative electrode mixture layer 42 where the solid electrolyte content varies from the inner end 42a to the outer end 42b can be formed at any location. For example, a first negative electrode slurry containing a solid electrolyte and a second negative electrode slurry with a lower solid electrolyte content than the first negative electrode slurry are prepared. Then, using a multilayer die coater, the first and second negative electrode slurries are coated from the inner end 42a to the outer end 42b of the negative electrode current collector 40 while increasing the mixing ratio of the second negative electrode slurry to the first negative electrode slurry, thereby obtaining a negative electrode slurry with… Figure 4 (a) shows the negative electrode compound layer 42 in the distribution diagram.

[0050] It should be noted that, like Figure 3 As shown in the positive electrode 11, when the negative electrode compound layer 42 of the negative electrode 12 is divided into two or more parts by the exposed portion, it is only necessary to make the content of solid electrolyte in the inner end 42a of the roll higher than the content of solid electrolyte in the outer end 42b of the roll. Preferably, at least a portion of the negative electrode compound layer 42 that is continuous from the inner end 42a of the roll forms a region in which the content of solid electrolyte decreases from the inner end 42a side to the outer end 42b side.

[0051] Example

[0052] The present invention will be further described below with reference to embodiments; however, the present invention is not limited to these embodiments.

[0053] [The production of the positive electrode]

[0054] 95 parts by weight of LiNi 0.8 Co 0.15 Al 0.05 O2, 2.5 parts by mass of acetylene black (AB), and 2.5 parts by mass of polyvinylidene fluoride (PVdF) with an average molecular weight of 1.1 million are mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added to prepare a positive electrode slurry with a solid content of 70% by mass. This positive electrode slurry is then coated onto both sides of a strip-shaped positive electrode current collector made of aluminum foil and dried. After drying, it is calendered and cut to a given electrode size to create a positive electrode with a positive electrode slurry layer formed on both sides of the current collector. Approximately at the center of the positive electrode along its length, a positive electrode exposure portion is formed, where no slurry layer is present on the surface of the current collector. An aluminum positive electrode lead is soldered to the positive electrode exposure portion.

[0055] [Making the negative electrode]

[0056] Graphite with an average particle diameter (D50) of 20 μm and SiO with a D50 of 5 μm were used as the negative electrode active materials. Additionally, Li7La3Zr2O with a D50 of 1 μm was used. 12(LLZ) was used as the solid electrolyte. A first negative electrode slurry was prepared by mixing 95 parts by mass of graphite, 5 parts by mass of SiO, 10 parts by mass of LLZ, 1 part by mass of carboxymethyl cellulose (CMC), and 1 part by mass of styrene-butadiene rubber (SBR) with an appropriate amount of water. A second negative electrode slurry was prepared by mixing 95 parts by mass of graphite, 5 parts by mass of SiO, 1 part by mass of CMC, and 1 part by mass of SBR with an appropriate amount of water. The first and second negative electrode slurries were then placed in a multilayer die-coating machine and coated on both sides of a strip-shaped negative electrode current collector made of copper foil, from the inner end to the outer end of the roll, while continuously varying the mixing ratio of the first and second negative electrode slurries from 1:0 to 0:1. The coating was then allowed to dry. After the dried coating is rolled using rollers, it is cut to a given electrode size to produce a negative electrode with a negative electrode flux layer formed on both sides of the negative electrode current collector. A negative electrode exposure portion without flux layer is provided at the inner end of the roll, exposing the surface of the current collector, and a nickel negative electrode lead is soldered to the negative electrode exposure portion.

[0057] [Preparation of Electrolytes]

[0058] Five parts by mass of vinylene carbonate (VC) were added to 100 parts by mass of a mixed solvent containing ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC = 1:3 by volume). LiPF6 was dissolved in this mixed solvent to a concentration of 1 mol / L to prepare an electrolyte.

[0059] [Making a Second-hand Battery]

[0060] An electrode body is fabricated by winding the aforementioned positive and negative electrodes together with a polyethylene spacer in between. Insulating plates are placed above and below the electrode body, and the electrode body is housed within a cylindrical outer casing. Then, the negative electrode lead is soldered to the bottom of the outer casing, and the positive electrode lead is soldered to the sealing body. Afterward, electrolyte is injected into the outer casing using a depressurized method, and the outer casing is sealed by riveting the open end to the sealing body with a gasket in between, thus fabricating a secondary battery. The fabricated secondary battery has a capacity of 2500mAh.

[0061] <Example 2>

[0062] Except that the amount of LLZ contained in the first negative electrode slurry was set to 6 parts by mass during the preparation of the negative electrode, a secondary battery was prepared in the same manner as in Example 1.

[0063] <Example 3>

[0064] Except that the amount of LLZ contained in the first negative electrode slurry was set to 14 parts by mass during the preparation of the negative electrode, a secondary battery was prepared in the same manner as in Example 1.

[0065] <Example 4>

[0066] Except that the amount of LLZ contained in the first negative electrode slurry was set to 18 parts by mass during the preparation of the negative electrode, a secondary battery was prepared in the same manner as in Example 1.

[0067] <Comparative Example 1>

[0068] Except that the first negative electrode slurry and the second negative electrode slurry were not mixed in the fabrication of the negative electrode, and the second negative electrode slurry was only coated on both sides of the negative electrode current collector, the secondary battery was fabricated in the same manner as in Example 1.

[0069] <Comparative Example 2>

[0070] In the fabrication of the negative electrode, 95 parts by mass of graphite, 5 parts by mass of SiO, 5 parts by mass of LLZ, 1 part by mass of CMC and 1 part by mass of SBR were mixed and an appropriate amount of water was added to prepare a third negative electrode slurry. The third negative electrode slurry was coated on both sides of the negative electrode current collector. Otherwise, a secondary battery was fabricated in the same manner as in Example 1.

[0071] <Comparative Example 3>

[0072] Except that, in the fabrication of the negative electrode, the mixing ratio of the first negative electrode slurry to the second negative electrode slurry is continuously changed from 0:1 to 1:0 while coating from the inner end of the negative electrode current collector to the outer end of the roll, the secondary battery is fabricated in the same manner as in Example 1.

[0073] <Comparative Example 4>

[0074] Except that the amount of LLZ contained in the third negative electrode slurry was set to 3 parts by mass during the preparation of the negative electrode, a secondary battery was prepared in the same manner as Comparative Example 2.

[0075] <Comparative Example 5>

[0076] Except that the amount of LLZ contained in the third negative electrode slurry was set to 7 parts by mass during the preparation of the negative electrode, a secondary battery was prepared in the same manner as Comparative Example 2.

[0077] <Comparative Example 6>

[0078] Except that the amount of LLZ contained in the third negative electrode slurry was set to 9 parts by mass during the preparation of the negative electrode, a secondary battery was prepared in the same manner as Comparative Example 2.

[0079] [Evaluation of Capacity Retention Rate]

[0080] The non-aqueous electrolyte secondary batteries of the examples and comparative examples were charged to 4.2V at a constant current of 1C at an ambient temperature of 25°C, and then charged to a current of 0.05C at a constant voltage of 4.2V. After being left to stand for 20 minutes, they were discharged to 2.5V at a constant current of 0.5C. This charge-discharge cycle was defined as one cycle, and 300 cycles were performed. The capacity retention rate of the non-aqueous electrolyte secondary batteries of each example and comparative example during the charge-discharge cycle was calculated using the following formula.

[0081] Capacity retention rate = (Discharge capacity in the 300th cycle / Discharge capacity in the 1st cycle) × 100

[0082] Table 1 summarizes the evaluation results of the capacity retention of the non-aqueous electrolyte secondary batteries of the examples and comparative examples. In addition, Table 1 also shows the content of solid electrolyte in the inner and outer ends of the winding and the content of solid electrolyte in the negative electrode compound layer (the average content of the entire negative electrode compound layer).

[0083] [Table 1]

[0084]

[0085] The battery of the embodiment exhibits improved capacity retention compared to the battery of Comparative Example 1, which does not contain a solid electrolyte. Furthermore, the battery of the embodiment exhibits improved capacity retention compared to the batteries of Comparative Examples 2 and 4-6, which uniformly contain a solid electrolyte throughout the entire negative electrode binder layer. Additionally, the battery of the embodiment exhibits improved capacity retention compared to the battery of Comparative Example 3, which has a high content of solid electrolyte at the outer end of the negative electrode binder layer. As can be seen from the results shown in Table 1, a significant improvement in capacity retention can be achieved using a specific configuration method for the solid electrolyte.

[0086] Explanation of reference numerals in the attached figures

[0087] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Spacer, 14 Electrode body, 15 Outer packaging body, 16 Sealing body, 17, 18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Slotted part, 22 Filter, 23 Lower valve body, 24 Insulating component, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket, 28 Winding shaft, 30 Positive electrode current collector, 32 Positive electrode binder layer, 34 Positive electrode exposed part, 40 Negative electrode current collector, 42 Negative electrode binder layer, 42a Inner end of the roll, 42b Outer end of the roll, 44 Negative electrode exposed part.

Claims

1. A non-aqueous electrolyte secondary battery, comprising: an electrode body wound with a strip-shaped positive electrode and a strip-shaped negative electrode separated by a spacer; an electrolyte; and an outer packaging body containing the electrode body and the electrolyte. The negative electrode has a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector, which includes negative electrode active material and solid electrolyte. For the negative electrode mixture layer, the content of the solid electrolyte at the inner end of the roll is higher than that at the outer end of the roll, and there is a region where the content of the solid electrolyte continuously decreases from the inner end side to the outer end side of the roll.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The content of the solid electrolyte in the negative electrode mixture layer is more than 1% by mass and less than 10% by mass.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The solid electrolyte is an inorganic solid electrolyte.

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The negative electrode active material comprises carbon-based materials and silicon-based materials. The content of the silicon-based material in the negative electrode active material is more than 3% by mass relative to the mass of the negative electrode active material.

5. The non-aqueous electrolyte secondary battery according to claim 3, wherein, The negative electrode active material comprises carbon-based materials and silicon-based materials. The content of the silicon-based material in the negative electrode active material is more than 3% by mass relative to the mass of the negative electrode active material.

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