Electrodes and non-aqueous electrolyte secondary batteries

Abstract

To provide a novel electrode that can suppress the increase in reaction resistance. [Solution] An electrode comprising a current collector and an active material layer, wherein the active material layer includes a first active material layer formed on the current collector and a second active material layer formed on the current collector so as to cover the first active material layer and the current collector surrounding the first active material layer, wherein the reaction resistance of the second active material layer is lower than the reaction resistance of the first active material layer and the diffusion resistance of the first active material layer is lower than the diffusion resistance of the second active material layer.

Description

[Technical Field]

[0001] This disclosure relates to electrodes and non-aqueous electrolyte secondary batteries. [Background technology]

[0002] Patent Document 1 (Japanese Patent Publication No. 2013-149403) discloses a negative electrode for a lithium-ion secondary battery that includes a first negative electrode layer formed on a negative electrode current collector and a second negative electrode layer formed on the first negative electrode layer, wherein the average particle size of the negative electrode active material contained in the second negative electrode layer is smaller than the average particle size of the negative electrode active material contained in the first negative electrode layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-149403 [Overview of the project] [Problems that the invention aims to solve]

[0004] To ensure good input / output characteristics over the long term, it is necessary to reduce reaction resistance and efficiently move lithium ions from the electrode surface towards the current collector. To overcome these problems, Patent Document 1 discloses a negative electrode having the above-mentioned characteristics. However, there is room for improvement in suppressing the increase in reaction resistance.

[0005] The object of this disclosure is to provide a novel electrode that can suppress the increase in reaction resistance. [Means for solving the problem]

[0006] [1] An electrode having a current collector and an active material layer, The active material layer includes a first active material layer formed on the current collector and a second active material layer formed on the first active material layer and the current collector surrounding it so as to cover the first active material layer. The reaction resistance of the second active material layer is lower than that of the first active material layer. An electrode in which the diffusion resistance of the first active material layer is lower than the diffusion resistance of the second active material layer.

[0007] Since the second active material layer is formed to cover the first active material layer, the second active material layer is used in the battery reaction at the start of the reaction. The reaction resistance of the second active material layer is lower than that of the first active material layer. Therefore, it is expected that the increase in reaction resistance will be suppressed.

[0008] Furthermore, after the start of the battery reaction, the first active material layer can be used for the battery reaction. The diffusion resistance of the first active material layer is lower than that of the second active material layer. Therefore, it is expected that the increase in diffusion resistance will be suppressed.

[0009] [2] The first active material layer comprises the first active material, The earlier second active material layer contains the second active material, The electrode according to [1], wherein the average particle diameter of the second active material is smaller than the average particle diameter of the first active material.

[0010] [3] The first active material layer comprises a first binder, The aforementioned second active material layer comprises a second binder, The electrode according to [1] or [2], wherein the content of the second binder in the second active material layer is lower than the content of the first binder in the first active material layer.

[0011] [4] The electrode according to any one of [1] to [3], wherein the basis weight per unit area of ​​the second active material layer is smaller than the basis weight per unit area of ​​the first active material layer.

[0012] [5] The electrode according to any one of [1] to [4], wherein the active material layer is formed intermittently.

[0013] [6] A non-aqueous electrolyte secondary battery comprising an electrode as described in any of [1] to [5]. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery in the present embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing an example of an electrode in the present embodiment. [Figure 3] Figure 3 is a schematic cross-sectional view showing another example of an electrode in the present embodiment. [Figure 4] Figure 4 is a schematic cross-sectional view showing the structure of the negative electrode in the example. [Figure 5] Figure 5 is a table showing the structure of the negative electrode and the experimental results in the example.

Mode for Carrying Out the Invention

[0015] Hereinafter, one embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment"), and one example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure. The present embodiment and the present example are illustrative in all respects. The present embodiment and the present example are non-restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, any configuration is extracted from the present embodiment, and it is also initially planned that they can be arbitrarily combined.

[0016] In this specification, when a compound is expressed by a stoichiometric composition formula such as "LiCoO2", the stoichiometric composition formula is only a representative example. For example, when lithium cobaltate is expressed as "LiCoO2", unless otherwise specified, lithium cobaltate is not limited to the composition ratio of "Li / Co / O = 1 / 1 / 2", and may contain Li, Co, and O in any composition ratio. The composition ratio may be non-stoichiometric.

[0017] "Reaction resistance" indicates the resistance that is dominant during the 0 to 1 second after the start of the battery reaction among the resistances. "Diffusion resistance" indicates the resistance that is dominant after 1 second after the start of the battery reaction among the resistances.

[0018] "Average particle size (D50)" refers to the particle size at which the cumulative distribution of the volume-based particle size distribution (cumulative distribution) reaches 50%. The particle size distribution can be measured by laser diffraction.

[0019] "Electrodes" may be positive electrodes, negative electrodes, or bipolar electrodes. "Non-aqueous electrolyte secondary battery" may also be abbreviated as "battery." "Battery" may be a monopolar battery or a bipolar battery.

[0020] <Nonaqueous electrolyte secondary battery> Figure 1 is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery in this embodiment. The battery 100 includes a power generation element 50. The battery 100 may include an outer casing. The outer casing may house the power generation element 50. The outer casing may be, for example, a metal case or a pouch made of aluminum laminate film. The outer casing may be provided with a positive electrode terminal and a negative electrode terminal. The power generation element 50 includes a negative electrode 10, a separator 30, and a positive electrode 20. The power generation element 50 may be connected to the positive electrode terminal and the negative electrode terminal.

[0021] The negative electrode 10 includes a negative electrode current collector 11 and a negative electrode active material layer 12. The negative electrode current collector 11 may include, for example, copper (Cu) foil. The negative electrode active material layer 12 includes a negative electrode active material and a binder. The negative electrode active material layer 12 may further include, for example, a conductive material. The conductive material may include, for example, carbon nanotubes (CNTs). The amount of conductive material may be, for example, 0.1 to 10% by mass fraction.

[0022] The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22. The positive electrode current collector 21 may include, for example, Al foil. The positive electrode active material layer 22 includes a positive electrode active material and a binder. The positive electrode active material layer 22 may further include, for example, a conductive material. The conductive material may include, for example, acetylene black (AB). The amount of conductive material may be, for example, 0.1 to 10% by mass fraction.

[0023] The separator 30 is porous. The separator 30 is permeable to the electrolyte. The separator 30 separates the negative electrode 10 and the positive electrode 20. The separator 30 is electrically insulating. The separator 30 may contain, for example, a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 30 may have, for example, a single-layer structure or a multi-layer structure. The separator 30 may consist substantially of a PE layer, or it may be formed by laminating a PP layer, a PE layer, and a PP layer in that order.

[0024] The electrolyte contains a solvent and a lithium salt. The solvent is aprotic. The solvent may contain any components. For example, the solvent may contain at least one selected from the group consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0025] The lithium salt is a supporting electrolyte. The lithium salt is dissolved in the solvent. The lithium salt may contain, for example, at least one selected from the group consisting of LiPF6, LiTFSI, and LiBF4. The lithium salt may have a molar concentration of, for example, 0.5 mol / L or more and 2.0 mol / L or less.

[0026] The electrolyte may further contain any additives. For example, the electrolyte may contain additives in an amount of 0.01% to 5% by mass. The additive may include at least one selected from the group consisting of vinylene carbonate (VC) and vinylethylene carbonate (VEC), etc. A gel electrolyte or solid electrolyte may be used instead of the electrolyte.

[0027] <Electrode> Figure 2 is a schematic cross-sectional view showing an example of an electrode in this embodiment. Figure 2 illustrates the case where the electrode is a negative electrode. The negative electrode 10 includes a negative electrode current collector 11 and a negative electrode active material layer 12. The negative electrode active material layer 12 includes a first negative electrode active material layer 13 and a second negative electrode active material layer 14. The first negative electrode active material layer 13 is formed on the negative electrode current collector 11. The second negative electrode active material layer 14 is formed on the first negative electrode active material layer 13 and the surrounding negative electrode current collector 11 so as to cover the first negative electrode active material layer 13. The second negative electrode active material layer 14 covers the entire first negative electrode active material layer 13 so that the first negative electrode active material layer 13 is not exposed.

[0028] The reaction resistance of the second negative electrode active material layer 14 is lower than that of the first negative electrode active material layer 13. The diffusion resistance of the first negative electrode active material layer 13 is lower than that of the second negative electrode active material layer.

[0029] A negative electrode active material layer 12 that satisfies these conditions can be obtained, for example, by satisfying at least one of the following (1) and (2). (1) The first negative electrode active material layer 13 contains the first negative electrode active material, and the second negative electrode active material layer 14 contains the second negative electrode active material, wherein the D50 of the second negative electrode active material is smaller than the D50 of the first negative electrode active material. (2) The first negative electrode active material layer 13 contains a first binder, and the second negative electrode active material layer 14 contains a second binder, with the content of the second binder in the second negative electrode active material layer 14 being lower than the content of the first binder in the first negative electrode active material layer 13.

[0030] (Regarding (1)) Generally, active materials with a large D50 can be used to ensure diffusion resistance and cycle characteristics, while active materials with a small D50 can be used to ensure reaction resistance. In addition, current tends to concentrate at the ends of the electrode (negative electrode) (both ends in the X direction in Figure 2) during the battery reaction. Therefore, by forming a second negative electrode active material layer 14 containing a second negative electrode active material with a small D50 so as to cover the first negative electrode active material layer 13, it is expected that the increase in reaction resistance will be suppressed.

[0031] Furthermore, since the D50 of the first negative electrode active material is larger than that of the second negative electrode active material, the first negative electrode active material layer 13 is thought to have more voids than the second negative electrode active material layer 14, allowing the electrolyte to diffuse more easily. Moreover, in the second negative electrode active material layer 14, the electrolyte is less likely to diffuse outside the negative electrode than in the first negative electrode active material layer 13, which has more voids. Therefore, as the battery reaction progresses, the first negative electrode active material layer 13 is more easily used in the battery reaction. This is expected to suppress the increase in diffusion resistance.

[0032] The D50 of the second negative electrode active material is not particularly limited, as long as it is smaller than the D50 of the first negative electrode active material. For example, the D50 of the first negative electrode active material may be 0.5 μm or more, 1 μm or more, or 2.5 μm or more. For example, the D50 of the first negative electrode active material may be less than 10 μm, 8 μm or less, or 6 μm or less. For example, the D50 of the second negative electrode active material may be 10 μm or more, 15 μm or more, or 20 μm or more. For example, the D50 of the second negative electrode active material may be 30 μm or less, 25 μm or less, or 20 μm or less.

[0033] The first negative electrode active material and the second negative electrode active material may be the same active material or different active materials. It is preferable that the first negative electrode active material and the second negative electrode active material are the same active material. The negative electrode active material may include, for example, at least one selected from the group consisting of graphite, soft carbon, and hard carbon. The same negative electrode active material may be used in (2) as well.

[0034] The content of each negative electrode active material in the first negative electrode active material layer 13 and the second negative electrode active material layer 14 may be, for example, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 97% or more by mass fraction. The content of each negative electrode active material in each negative electrode active material layer may be the same or different. The same content may apply in (2).

[0035] The first negative electrode active material layer 13 may contain a first binder, and the second negative electrode active material layer 14 may contain a second binder. The first binder and the second binder may be the same binder or different binders. Examples of such binders include carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR). The same binders can be used in (2) as well. The amount of each binder may be, for example, 0.1 to 10% by mass fraction.

[0036] (Regarding (2)) Generally, when the binder content is low, the binder coverage on the active material surface is low. Therefore, by forming the second negative electrode active material layer 14, which has a low binder content, to cover the first negative electrode active material layer 13, it is expected that the increase in reaction resistance will be suppressed.

[0037] Furthermore, since the content of the first binder in the first negative electrode active material layer 13 is higher than the content of the second binder in the second negative electrode active material layer 14, the first negative electrode active material layer 13 is thought to have more voids than the second negative electrode active material layer 14, and the electrolyte diffuses more easily. Therefore, for the same reasons as in (1) above, it is expected that the increase in diffusion resistance will be suppressed.

[0038] The content of the second binder in the second anode active material layer 14 is not particularly limited, as long as it is lower than the content of the first binder in the first anode active material layer 13. For example, the content of the first binder in the first anode active material layer 13 may be 1% or more, 2% or more, 3% or more, or 5% or more by mass fraction. For example, the content of the first binder in the first anode active material layer 13 may be 10% or less, 8% or less, 6% or less, or 5% or less by mass fraction. For example, the content of the second binder in the second anode active material layer 14 may be 0.1% or more, 0.5% or more, 1% or more, or 2% or more by mass fraction. For example, the content of the second binder in the second anode active material layer 14 may be 5% or less, 4% or less, 3% or less, or 2% or less by mass fraction.

[0039] The first binder and the second binder may be the same binder or different binders. It is preferable that the first binder and the second binder are the same binder.

[0040] The first negative electrode active material layer 13 may contain the first negative electrode active material, and the second negative electrode active material layer 14 may contain the second negative electrode active material. The D50 of each negative electrode active material may be, for example, 0.5 to 30 μm.

[0041] (Balance) The basis weight per unit area of ​​the second negative electrode active material layer 14 (second basis weight) may be smaller than the basis weight per unit area of ​​the first negative electrode active material layer 13 (first basis weight). This is expected to suppress the increase in reaction resistance. The ratio of the first basis weight to the second basis weight may be 50:50 to 95:5, or 55:45 to 85:15. Alternatively, the ratio may be 60:40 to 95:5, or 65:35 to 95:5. This is expected to suppress the increase in not only reaction resistance but also diffusion resistance.

[0042] The basis weight per unit area of ​​the negative electrode active material layer 12, i.e., the sum of the first basis weight and the second basis weight, is, for example, 10 mg / cm³. 2 More than 15mg / cm 2 Above, or 20 mg / cm³ 2 This may also be acceptable. From the perspective of increasing battery capacity, 20 mg / cm³ is recommended. 2 It is preferable that the above conditions are met.

[0043] As shown in Figure 2, if D is the thickness (outer dimensions in the Y direction) of the first negative electrode active material layer 13, and d1 is the difference between the thickness of the first negative electrode active material layer 13 and the thickness of the second negative electrode active material layer 14, then d1 may be smaller than D. Also, if d2 is the distance between the side surface of the second negative electrode active material layer 14 and the side surface of the first negative electrode active material layer 13 in the width direction (outer dimensions in the X direction) of the second negative electrode active material layer 14, then d2 may be smaller than D. Furthermore, d1 and d2 may be approximately the same. Current tends to concentrate at the ends of the electrode (negative electrode) (both ends in the X direction in Figure 2) during the battery reaction. Also, as the battery reaction progresses, the first negative electrode active material layer 13 becomes more easily used in the battery reaction. This is expected to suppress the increase in diffusion resistance. Note that at both ends in the width direction, each distance is d2.

[0044] The outline of the first negative electrode active material layer 13 may be rectangular or circular.

[0045] As shown in Figure 3, the negative electrode active material layer 12 may be formed intermittently (divided) in the width direction. This is expected to increase the area in contact with the electrolyte of the second negative electrode active material layer 14, thereby suppressing the increase in reaction resistance and diffusion resistance. In Figure 3, the negative electrode active material layer 12 is divided into three parts, but it may be divided into more than one part, for example, two parts.

[0046] The above explanation used the case where the electrode is a negative electrode as an example, but the electrode may also be a positive electrode. Even when the electrode is a positive electrode, it is expected that the increase in reaction resistance will be suppressed by satisfying the above conditions.

[0047] In the case of a positive electrode, the positive electrode active material may include at least one selected from the group consisting of, for example, LiCoO2, LiNiO2, LiMnO2, Li(NiCoMn)O2, and Li(NiCoAl)O2. For example, in "Li(NiCoMn)O2", "(NiCoMn)" indicates that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amounts of individual components are arbitrary. The binder may include, for example, polyvinylidene fluoride (PVdF).

[0048] <Method of manufacturing electrodes> The electrode manufacturing method in this embodiment includes, for example, a step of preparing a slurry containing an active material, a binder, and a solvent (preparation step), a step of forming a coating film by coating a current collector with the slurry (coating step), a step of drying the coating film (drying step), and a step of forming an active material layer by compressing the coating film (compression step). Below, an example of a manufacturing method for a negative electrode in this embodiment is shown, but the invention is not limited to this.

[0049] (Preparation process) In this step, a slurry containing a negative electrode active material, a binder, and a solvent is prepared. Conductive materials may be further added in this step. For example, the slurry is prepared by mixing the negative electrode active material, binder, conductive material, and solvent.

[0050] As slurries, a first negative electrode slurry is prepared to form the first negative electrode active material layer, and a second negative electrode slurry is prepared to form the second negative electrode active material layer. The first and second negative electrode slurries may be prepared by adjusting the D50 of each negative electrode active material and the amount of each binder to obtain the desired negative electrode active material layer. Any agitator, mixer, or disperser may be used to prepare each negative electrode slurry.

[0051] Examples of solvents include aqueous solvents and organic solvents. Examples of aqueous solvents include water. Examples of organic solvents include N-methyl-2-pyrrolidone (NMP).

[0052] (Coating process) In this process, a coating is formed by applying each negative electrode slurry to the negative electrode current collector. Any coating machine can be used for coating.

[0053] A negative electrode current collector is prepared. The first negative electrode slurry is coated onto the surface of the negative electrode current collector. The first negative electrode slurry is applied so that the first negative electrode active material layer has a desired first basis weight and width. After the application of the first negative electrode slurry, the second negative electrode slurry is coated onto the surface of the first negative electrode slurry. The second negative electrode slurry is applied so that the second negative electrode active material layer has a desired second basis weight and width. The width of the discharge section of the coating machine during the application of the second negative electrode slurry is set to be longer than the width of the discharge section of the coating machine during the application of the first negative electrode slurry.

[0054] <Drying process> In this process, the solvent within the coating film is evaporated by drying the film. Any drying apparatus can be used for drying.

[0055] <Compression process> In this process, each negative electrode active material layer is formed by compressing the coating film. Any compression device can be used for compression. The pressure can be adjusted so that the thickness of each negative electrode active material layer reaches the desired thickness.

[0056] A negative electrode is manufactured as described above. The negative electrode manufactured by the above method may be formed to include a first negative electrode active material layer formed on a negative electrode current collector, and a second negative electrode active material layer formed on the first negative electrode active material layer and the negative electrode current collector surrounding it so as to cover the first negative electrode active material layer. [Examples]

[0057] <Test Example 1> (Negative electrode) [No.1] A copper foil was prepared as the negative electrode current collector, graphite (D50: 15 μm) as the first negative electrode active material, carbon nanotubes (CNTs) as the conductive material, steel cellulose (SBR) as the binder, and water as the dispersion medium. The first negative electrode slurry was prepared by mixing the first negative electrode active material, conductive material, binder, and dispersion medium. The mixing ratio of the first negative electrode active material, conductive material, and binder was 97:1:2 by mass fraction. The negative electrode slurry was applied to the surface of the negative electrode current collector by a die coater and dried to form a negative electrode active material layer (basis weight: 20 mg / cm³).2 ) was formed. By compressing the negative electrode active material layer, negative electrode No. 1 was manufactured.

[0058] [No.2] A second negative electrode slurry was prepared by replacing the first negative electrode active material in the first negative electrode slurry with the second negative electrode active material, graphite (D50: 5 μm). The No. 2 negative electrode was manufactured in the same manner as No. 1, except that the second negative electrode slurry was used.

[0059] [No.3] A first negative electrode slurry and a second negative electrode slurry were prepared. The first negative electrode slurry was coated onto the surface of the negative electrode current collector using a die coater. The basis weight of the first negative electrode slurry after drying was 15 mg / cm². 2 The coating was applied in this manner. The second negative electrode slurry was applied on top of the first negative electrode slurry using a die coater. At this time, the width of the discharge nozzle of the die coater when applying the first negative electrode slurry was the same as the width of the discharge nozzle when applying the second negative electrode slurry. The basis weight of the second negative electrode slurry after drying was 5 mg / cm². 2 The coating was applied in such a manner. As the coating film dries, the negative electrode active material layer (total basis weight: 20 mg / cm³) 2 A negative electrode was formed. By compressing the negative electrode active material layer, negative electrode No. 3 was manufactured.

[0060] [No.4] The No. 4 negative electrode was manufactured in the same manner as No. 3, except that the width of the discharge section of the die coater during coating of the second negative electrode slurry was set to be longer than the width of the discharge section of the die coater during coating of the first negative electrode slurry.

[0061] [No.5] The No. 5 negative electrode was manufactured in the same manner as No. 4, except that the second negative electrode slurry and the first negative electrode slurry were applied in that order. Furthermore, the width of the die coater's discharge section during the application of the first negative electrode slurry was set to be longer than the width of the die coater's discharge section during the application of the second negative electrode slurry.

[0062] Note that FIG. 4 is a schematic cross-sectional view showing the configuration of the negative electrode in the embodiment. Which configuration of the negative electrodes of each No. is shown in (a) to (e) of FIG. 4 shall be shown in FIG. 5.

[0063] (Non-aqueous electrolyte secondary battery) As the positive electrode current collector, Al foil, as the positive electrode active material, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, as the conductive material, CNT, as the binder, PVdF, and as the dispersion medium, NMP were each prepared. By mixing the above positive electrode active material, conductive material, binder, and dispersion medium, a positive electrode slurry was prepared. The mixing ratio (mass ratio) of the positive electrode active material, conductive material, and binder was 98:1:1. The positive electrode slurry was coated on the surface of the positive electrode current collector and dried, whereby a positive electrode active material layer (coating weight: 40 mg / cm 2 ) was formed. By compressing the positive electrode active material layer, a positive electrode was manufactured.

[0064] As the separator, a resin film was prepared. The resin film had a three-layer structure (PP layer / PE layer / PP layer).

[0065] By mixing EC, DMC, and EMC, a mixed solvent was prepared. The mixing ratio (volume ratio) of EC, DMC, and EMC was 3:3:4. By dissolving LiPF6 and (1.1 mol / L) in the solvent, an electrolytic solution was prepared. <00上記正極活物質と、導電材と、バインダと、分散媒とが混合されることにより、正極スラリーが準備された。正極活物質と導電材とバインダとの混合比(質量比)は、98:1:1であった。正極スラリーが正極集電体の表面に塗工され、乾燥されることにより、正極活物質層(目付量:40mg / cm

[0066] The positive electrode, separator, and negative electrodes of each No. were laminated in this order to form a power generation element. An external terminal was attached to the power generation element. As the case, a laminate film pouch was prepared. The power generation element was housed in the case. The power generation element and the terminal were electrically connected. The electrolytic solution was injected into the case. After injecting the electrolytic solution, the case was sealed. Thus, non-aqueous electrolyte secondary batteries (test batteries) of No. 1 to 5 were manufactured.

[0067] (Evaluation) At an ambient temperature of 25°C, the resistance was evaluated by setting the SOC to 50% and discharging at 3C for 20 seconds. The resistance value R1 was calculated from the voltage drop from 0 to 1 second, and the resistance value R2 was calculated from the voltage drop from 1 to 20 seconds. The results are shown in Table 1 of Figure 5. In this example, R1 is the reaction resistance and R2 is the diffusion resistance. The capacity of each test battery was 6000mAh.

[0068] (result) From Table 1 in Figure 5, R1 for No. 4 was lower than that of No. 1 and 3, and equivalent to that of No. 2. Similarly, R2 for No. 4 was equivalent to that of No. 1 and 3, and lower than that of No. 2. On the other hand, both R1 and R2 for No. 5 showed high values.

[0069] <Test Example 2> (Negative electrode) [No.6] A second negative electrode slurry and a third negative electrode slurry were prepared, in which the mixing ratio (mass ratio) of the negative electrode active material, conductive material, and binder in the second negative electrode slurry was changed to 98:1:1. The No. 6 negative electrode was manufactured in the same manner as No. 3, except that the third negative electrode slurry was coated on top of the second negative electrode slurry.

[0070] [No.7] The No. 7 negative electrode was manufactured in the same manner as No. 4, except that the second negative electrode slurry and the third negative electrode slurry were applied in that order. Furthermore, the width of the die coater's discharge section during the application of the third negative electrode slurry was set to be longer than the width of the die coater's discharge section during the application of the second negative electrode slurry.

[0071] (evaluation) Test batteries No. 6 and 7 were manufactured using the same method as in Test Example 1. The resistance of each test battery was measured using the same method as in Test Example 1. The results are shown in Table 2 of Figure 5. Table 2 also includes the evaluation results for No. 2, which used only the second negative electrode slurry.

[0072] From Table 2 in Figure 5, R1 for No. 7 was lower than that of No. 2 and 6, while R2 for No. 7 was equivalent to that of No. 2 and 6.

[0073] <Test Example 3> (Negative electrode) [No.8~11] The negative electrodes No. 8 to 11 were manufactured in the same manner as No. 4, except that the first and second weights were changed to the values ​​shown in Table 3 of Figure 5.

[0074] (evaluation) Test batteries No. 8-11 were manufactured using the same method as in Test Example 1. The resistance of each test battery was measured using the same method as in Test Example 1. The results are shown in Table 3 of Figure 5. Table 3 also includes the evaluation results for No. 4, which has the same composition.

[0075] From Table 3 in Figure 5, R1 values ​​for Nos. 8-11 were all equivalent to those for No. 4. Furthermore, R2 values ​​for Nos. 9-11 were all equivalent to those for No. 4.

[0076] <Test Example 4> (Negative electrode) [No. 12, 13] The negative electrodes No. 12 and 13 were manufactured in the same manner as No. 4, except that the negative electrode active material layer was changed to a two-part and a three-part division.

[0077] (evaluation) Test batteries No. 12 and 13 were manufactured using the same method as in Test Example 1. The resistance of each test battery was measured using the same method as in Test Example 1. The results are shown in Table 4 in Figure 5. Table 4 also includes the evaluation results for No. 4, which has the same composition but was not divided.

[0078] (result) From Table 4 in Figure 5, R1 and R2 for No. 12 were lower than those for No. 4. Furthermore, R1 and R2 for No. 13 were lower than those for both No. 4 and No. 12. [Explanation of Symbols]

[0079] 10 Negative electrode, 11 Negative electrode current collector, 12 Negative electrode active material layer, 13 First negative electrode active material layer, 14 Second negative electrode active material layer, 20 Positive electrode, 21 Positive electrode current collector, 22 Positive electrode active material layer, 30 Separator, 50 Power generation element, 100 Non-aqueous electrolyte secondary battery.

Claims

1. An electrode having a current collector and an active material layer, The active material layer includes a first active material layer formed on the current collector and a second active material layer formed on the first active material layer and the current collector surrounding it so as to cover the first active material layer. The reaction resistance of the second active material layer is lower than that of the first active material layer. An electrode in which the diffusion resistance of the first active material layer is lower than the diffusion resistance of the second active material layer.

2. The first active material layer contains the first active material, The aforementioned second active material layer contains the second active material, The electrode according to claim 1, wherein the average particle diameter of the second active material is smaller than the average particle diameter of the first active material.

3. The first active material layer comprises a first binder, The aforementioned second active material layer includes a second binder, The electrode according to claim 1, wherein the content of the second binder in the second active material layer is lower than the content of the first binder in the first active material layer.

4. The electrode according to claim 1, wherein the basis weight per unit area of ​​the second active material layer is smaller than the basis weight per unit area of ​​the first active material layer.

5. The electrode according to claim 1, wherein the active material layer is formed intermittently.

6. A non-aqueous electrolyte secondary battery comprising the electrode described in any one of claims 1 to 5.

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