Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery with enhanced discharging performance. A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is provided with an electrode having: a current collector; and a mixture layer that is formed on a surface of the current collector and that contains an active material, a conducting agent, and a binding agent. The mixture layer contains a first mixture layer facing the current collector and a second mixture layer laminated on a surface of the first mixture layer. A short-circuit resistance R1 of the first mixture layer and a short-circuit resistance R2 of the second mixture layer satisfy the relationship R1 < R2.

Description

[Technical Field]

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

[0002] Secondary batteries sometimes use electrodes in which a composite layer is formed on the surface of a current collector made of metal foil. Patent Document 1 discloses a positive electrode having a second layer made of a metal oxide such as Al2O3 and carbon between the current collector and the composite layer in order to suppress the increase in DC resistance (DCR) due to repeated charging and discharging. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2018-60604 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In recent years, increasing the thickness of the composite layer has been considered from the perspective of increasing capacity. As a result of diligent research by the present inventors, it has been found that increasing the thickness of the composite layer hinders the movement of lithium ions within the composite layer, which tends to reduce the discharge characteristics at high rates. The technology disclosed in Patent Document 1 raises concerns about a decrease in battery capacity due to the second layer which does not contain active material, and it does not take into account the decrease in discharge characteristics due to the thickening of the composite layer, so there is still room for improvement.

[0005] The purpose of this disclosure is to provide a non-aqueous electrolyte secondary battery with improved discharge characteristics. [Means for solving the problem]

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes an electrode having a current collector and a mixture layer formed on the surface of the current collector and containing an active material, a conductive agent, and a binder. The mixture layer includes a first mixture layer facing the current collector and a second mixture layer laminated on the surface of the first mixture layer, and the short-circuit resistance R1 of the first mixture layer and the short-circuit resistance R2 of the second mixture layer satisfy the relationship R1 < R2.

Advantages of the Invention

[0007] According to the non-aqueous electrolyte secondary battery which is one aspect of the present disclosure, the discharge characteristics can be improved.

Brief Description of the Drawings

[0008] [Figure 1] It is an axial cross-sectional view of a cylindrical secondary battery which is an example of an embodiment. [Figure 2] It is a view enlarging a part of the cross-section of an electrode in an example of an embodiment. [Figure 3] It is a Nyquist plot of the AC impedance measurement results of the positive electrode mixture layer. [Figure 4] It is a view showing discharge curves in Examples and Comparative Examples.

Modes for Carrying Out the Invention

[0009] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical outer package will be exemplified, but the electrode body is not limited to a wound type, and may be a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one through a separator. Further, the outer package is not limited to a cylindrical shape, and may be, for example, a rectangular shape, a coin shape, or the like. It may also be a pouch type composed of a laminate sheet including a metal layer and a resin layer.

[0010] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10, which is an example of an embodiment. In the secondary battery 10 shown in Figure 1, an electrode body 14 and a non-aqueous electrolyte (not shown) are housed in an outer casing 15. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13. For the sake of explanation, the side with the sealing body 16 will be referred to as "upper" and the bottom side of the outer casing 15 will be referred to as "lower".

[0011] The inside of the secondary battery 10 is sealed by closing the open end of the outer casing 15 with the sealing body 16. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the lower surface of the filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, becomes the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 to the bottom side of the outer casing 15 and is welded to the bottom inner surface of the outer casing 15. In the secondary battery 10, the outer casing 15 becomes the negative electrode terminal. If the negative electrode lead 20 is installed at the end, the negative electrode lead 20 extends outside the insulating plate 18 to the bottom side of the outer casing 15 and is welded to the bottom inner surface of the outer casing 15.

[0012] The outer casing 15 is, for example, a bottomed cylindrical metal outer casing. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the secondary battery 10. The outer casing 15 has grooves 21 that support the sealing body 16, which are formed, for example, by pressing the side surface from the outside. The grooves 21 are preferably formed in an annular shape along the circumferential direction of the outer casing 15, and their upper surface supports the sealing body 16 via the gasket 27.

[0013] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are laminated in order from the side of the electrode body 14. Each member constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each member except the insulating member 24 is electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at the central portions of each, and the insulating member 24 is interposed between the peripheral portions of each. When the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 breaks, whereby the upper valve body 25 bulges toward the cap 26 side and separates from the lower valve body 23, thereby cutting off the electrical connection between the two. When the internal pressure further rises, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cap 26.

[0014] Hereinafter, the electrodes 30 (the positive electrode 11 and the negative electrode 12), the separator 13, and the non-aqueous electrolyte constituting the electrode body 14 will be described in detail.

[0015] [Electrode] First, the electrode 30 will be described while referring to FIG. 2. FIG. 2 is an enlarged view of a part of the cross section of the electrode in an example of the embodiment. The electrode 30 has a current collector 32 and a mixture layer 34 formed on the surface of the current collector 32. The mixture layer 34 may be formed only on one surface of the current collector 32, but is preferably formed on both surfaces of the current collector 32.

[0016] The electrode 30 may be either the positive electrode 11 or the negative electrode 12. That is, only the positive electrode 11 may have the configuration of the electrode 30, only the negative electrode 12 may have the configuration of the electrode 30, or both the positive electrode 11 and the negative electrode 12 may have the configuration of the electrode 30.

[0017] The current collector 32 can be made of metal foil or a film with a metal layer formed on its surface. The thickness of the current collector 32 is, for example, 5 to 20 μm. In the case of the positive electrode 11, the current collector 32 can be made of metal foil mainly composed of aluminum. In the case of the negative electrode 12, the current collector 32 can be made of metal foil mainly composed of copper. In this specification, "main component" means the component with the highest mass ratio. The current collector 32 may be aluminum foil that is substantially 100% aluminum, or copper foil that is substantially 100% copper.

[0018] The composite layer 34 contains an active material, a conductive agent, and a binder. Generally, lithium transition metal composite oxides are used as the active material for the positive electrode. Examples of metal elements contained in lithium transition metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, it is preferable to contain at least one of Ni, Co, and Mn. Carbon-based active materials such as natural graphite such as flake graphite, lump graphite, and clay graphite, lump artificial graphite (MAG), and graphitized mesophase carbon microbeads (MCMB) are used as the active material for the negative electrode. In addition, Si-based active materials that alloy with lithium may be used as the negative electrode active material. The active material is the main component of the compound layer 34, and the content of the active material in the compound layer 34 is preferably 85% to 99% by mass, and more preferably 90% to 99% by mass.

[0019] The positive electrode active material is, for example, a secondary particle formed by the aggregation of multiple primary particles. The particle size of the primary particles constituting the secondary particle is, for example, 0.05 μm to 1 μm. The particle size of the primary particle is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM). The secondary particles of the positive electrode active material are particles with a volume-based median diameter (D50) of, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, and particularly preferably 7 μm to 15 μm. D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of the positive electrode active material can be measured using a laser diffraction particle size distribution analyzer (for example, Microtrac-Bell MT3000II) with water as the dispersion medium.

[0020] Examples of conductive agents included in the composite layer 34 include carbon materials such as carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), and graphite. These may be used individually or in combination of two or more types. The conductive agent is preferably acetylene black.

[0021] Examples of binders included in the composite layer 34 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These may be used individually or in combination of two or more types. These resins may also be used in combination with cellulose derivatives such as carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc. Polytetrafluoroethylene is preferred as the binder.

[0022] As shown in FIG. 2, the composite agent layer 34 includes a first composite agent layer 36 facing the current collector 32 and a second composite agent layer 38 laminated on the surface of the first composite agent layer 36. Both the first composite agent layer 36 and the second composite agent layer 38 contain the above-mentioned active material, conductive agent, and binder. The active material, conductive agent, and binder contained in the first composite agent layer 36 and the second composite agent layer 38 may be the same or different from each other. The thickness of the first composite agent layer 36 is, for example, 5 μm to 200 μm, and the thickness of the second composite agent layer 38 is, for example, 100 μm to 200 μm.

[0023] The short-circuit resistance R1 of the first composite agent layer 36 and the short-circuit resistance R2 of the second composite agent layer 38 satisfy the relationship R1 < R2. Thereby, the resistance of the electrode 30 can be reduced and the discharge characteristics of the battery can be improved. In addition, since the first composite agent layer 36 contains an active material, it has ion conductivity and contributes to increasing the capacity of the battery. The short-circuit resistances R1 and R2 can be measured using an alternating current impedance measuring device. More specifically, it can be calculated by measuring the alternating current impedance of 7 MHz to 0.1 Hz and performing a Nyquist plot on the measurement data.

[0024] The measurement result of the alternating current impedance of the first composite agent layer 36 preferably does not draw an arc on the low-frequency side in the Nyquist plot. By having conductivity such that the first composite agent layer 36 does not draw an arc on the low-frequency side, the resistance of the electrode 30 can be sufficiently reduced and the discharge characteristics of the battery can be improved. In addition, the measurement result of the alternating current impedance of the second composite agent layer 38 preferably does not draw an arc in the Nyquist plot in the same manner as the first composite agent layer 36, but may draw an arc as the capacity of the battery increases (for example, increasing the resistance by reducing the conductive agent).

[0025] It is preferable that the content C1 of the conductive agent in the first composite layer 36 and the content C2 of the conductive agent in the second composite layer 38 satisfy the relationship C1 > C2. This makes the conductivity of the first composite layer 36 higher than that of the second composite layer 38, thereby improving the discharge characteristics of the battery. C1 is preferably 3% to 20% by mass, more preferably 5% to 15% by mass, and particularly preferably 5% to 10% by mass, based on the total mass of the first composite layer 36. C2 is preferably 0% to 3% by mass, more preferably 0.1% to 2% by mass, and particularly preferably 0.5% to 1.5% by mass, based on the total mass of the second composite layer 38.

[0026] It is preferable that the relationship A1 > A2 is satisfied between the electronic conductivity A1 of the active material contained in the first composite layer 36 and the electronic conductivity A2 of the active material contained in the second composite layer 38. For example, the positive electrode active material contained in the first composite layer 36 may be an NCA-based lithium transition metal composite oxide containing Ni, Co, and Al, and the positive electrode active material contained in the second composite layer 38 may be a NiMn-based lithium transition metal composite oxide containing Ni and Mn. The electronic conductivity of the active material can be measured, for example, by the electronic resistance of a pellet obtained by compressing the powder. From the viewpoint of improving electronic conductivity, it is preferable that the first composite layer 36 contains CNTs.

[0027] The electrode 30 can be fabricated, for example, as follows. (1) The raw materials containing the active material are dry-mixed and rolled to produce a sheet-like first mixture layer 36. (2) The raw materials containing the active material are dry-mixed and rolled to produce a sheet-like second mixture layer 38. (3) The electrode 30 is fabricated by bonding the first composite layer 36 and the second composite layer 38 to the surface of the current collector 32, starting from the current collector 32 side.

[0028] The raw materials preferably include a fibrous binder such as fibrillated polytetrafluoroethylene (PTFE). The fibrous binder is a dry powder and not a powder dispersed in a dispersion such as water. This allows the composite layer 34 to be prepared by a dry process including dry mixing. Here, a dry process is a process in which the active material, binder, conductive agent, etc. are mixed without using a solvent, that is, the active material, binder, conductive agent, etc. are mixed in a state where the solid content concentration is substantially 100%. In addition to the fibrous binder, the composite layer 34 may also contain a binder such as non-fibrillated polyvinylidene fluoride (PVdF).

[0029] In the step of (1) for producing the first mixture layer 36 and the step of (2) for producing the second mixture layer 38, the active material and the fibrous binder may be mixed to produce mixture particles with a solid content of substantially 100%, and then the mixture particles may be rolled to form a sheet to produce the mixture layer 34. In the step of (3) for bonding the first mixture layer 36 and the second mixture layer 38 to the current collector 32, the order in which the current collector 32, the first mixture layer 36, and the second mixture layer 38 are bonded to each other is not particularly limited, and the current collector 32, the first mixture layer 36, and the second mixture layer 38 may be bonded to each other simultaneously, or the first mixture layer 36 and the second mixture layer 38 may be bonded to form the mixture layer 34, and then the current collector 32 and the mixture layer 34 may be bonded together. To bond the current collector 32, the first mixture layer 36, and the second mixture layer 38 together, for example, they may be passed between two rolls and linear pressure applied.

[0030] [Separator] The separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a laminated structure. Furthermore, the surface of the separator 13 may be provided with a heat-resistant resin layer such as aramid resin, or a filler layer containing an inorganic compound filler.

[0031] [Non-aqueous electrolytes] A non-aqueous electrolyte (electrolyte) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted solvents in which at least some of the hydrogen atoms of the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted solvents include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0032] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.

[0033] Examples of the above ethers include cyclic ethers such as 1,3 - dioxolane, 4 - methyl - 1,3 - dioxolane, tetrahydrofuran, 2 - methyltetrahydrofuran, propylene oxide, 1,2 - butylene oxide, 1,3 - dioxane, 1,4 - dioxane, 1,3,5 - trioxane, furan, 2 - methylfuran, 1,8 - cineole, crown ether, etc.; and chain ethers such as 1,2 - dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o - dimethoxybenzene, 1,2 - diethoxyethane, 1,2 - dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1 - dimethoxymethane, 1,1 - diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0034] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), etc.; LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1Examples include imide salts such as SO2){l,m are integers greater than or equal to 0}. Lithium salts may be used individually or in mixtures of multiple types. Of these, LiPF6 is preferred from the viewpoint of ionic conductivity and electrochemical stability. The concentration of the lithium salt is preferably, for example, 0.8 moles to 1.8 moles per liter of non-aqueous solvent. [Examples]

[0035] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0036] <Example 1> [Preparation of the positive electrode mixture layer] LiRing 0.5 Co 0.2 Mn 0.3 A first cathode active material particle consisting of O2, acetylene black (AB), and polytetrafluoroethylene (PTFE) were placed in a mixer in a mass ratio of 94:3:3 and mixed to produce a first cathode mixture particle. Then, the first cathode mixture particle was passed between two rolls and rolled to produce a first cathode mixture layer with a thickness of 130 μm. LiNi 0.5 Co 0.2 Mn 0.3 A second cathode active material particle consisting of O2, acetylene black (AB), and polytetrafluoroethylene (PTFE) were placed in a mixer in a mass ratio of 98:1:1 and mixed to produce a second cathode mixture particle. Subsequently, the second cathode mixture particle was passed between two rolls and rolled to produce a second cathode mixture layer with a thickness of 110 μm.

[0037] [Fabrication of the positive electrode] With the first positive electrode compound layer and the second positive electrode compound layer laminated in order from the positive electrode current collector side onto one surface of an Al foil serving as the positive electrode current collector, the positive electrode current collector, the first positive electrode compound layer, and the second positive electrode compound layer were pressed together using two rolls to integrate them, and then cut to a predetermined electrode size to obtain the positive electrode.

[0038] [Fabrication of the negative electrode] The lithium foil was cut to a predetermined electrode size to obtain the negative electrode.

[0039] [Electrolyte] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 20:75:5. Lithium hexafluoride phosphate (LiPF6) was dissolved in this mixed solvent at a concentration of 1.3 mol / liter to obtain an electrolyte.

[0040] [Test cell] A test cell was fabricated by placing the positive electrode and the negative electrode, as described above, facing each other via a polypropylene separator, along with the electrolyte, in a cup-shaped battery case, and sealing the battery case with a sealing plate via a gasket placed at the opening of the battery case.

[0041] <Example 2> In the preparation of the first cathode mixture layer, a test cell was prepared in the same manner as in Example 1, except that the mixing ratio of cathode active material particles, AB, and PTFE was changed to 90:5:5 by mass ratio.

[0042] <Example 3> In the preparation of the first cathode mixture layer, a test cell was prepared in the same manner as in Example 1, except that the mixing ratio of cathode active material particles, AB, and PTFE was changed to 85:10:5 by mass ratio.

[0043] <Comparative Example 1> In the preparation of the positive electrode, a test cell was manufactured in the same manner as in Example 1, except that the second positive electrode mixture layer was laminated only on one surface of the Al foil and then pressed to integrate the positive electrode current collector and the first positive electrode mixture layer.

[0044] <Comparative Example 2> In the preparation of the first positive electrode mixture layer, a test cell was prepared in the same manner as in Example 1, except that the mixing ratio of positive electrode active material particles, AB, and PTFE was changed to 98:0:2 by mass ratio.

[0045] [Measurement of AC impedance of the positive electrode mixture layer] LiRing 0.5 Co 0.2 Mn 0.3 Positive electrode mixture layers were fabricated by varying the mixing ratio of positive electrode active material particles consisting of O2, AB, and PTFE, and the AC impedance of each positive electrode mixture layer was measured. Specifically, positive electrode mixture particles were fabricated by mixing positive electrode active material particles, AB, and PTFE in predetermined mixing ratios using a mixer. Then, the positive electrode mixture particles were rolled between two rolls to produce a positive electrode mixture layer with a thickness of 130 μm. Six positive electrode mixture layers were fabricated with mixing ratios of positive electrode active material particles / AB / PTFE by mass ratio: 98 / 0 / 2, 98 / 1 / 1, 96 / 2 / 2, 94 / 3 / 3, 90 / 5 / 5, and 85 / 10 / 5. Figure 3 shows the AC impedance measured for each mixture layer from 7 MHz to 0.01 Hz using an AC impedance meter, and the measurement data is plotted as a Nyquist plot.

[0046] [Evaluation of discharge characteristics] Each test cell in the examples and comparative examples was charged at a constant current of 0.05C at a temperature of 25°C until the battery voltage reached 4.5V. Then, it was discharged at a constant current of 0.7C until the battery voltage reached 2.5V.

[0047] Figure 4 shows the evaluation results of the discharge characteristics for the test cells of the examples and comparative examples.

[0048] As can be seen from Figure 4, in all three examples, the discharge capacity was improved and the voltage value was higher compared to comparative examples 1 and 2, confirming that the discharge characteristics were improved by the presence of the first positive electrode mixture layer, which has a lower short-circuit resistance than the second positive electrode mixture layer. [Explanation of Symbols]

[0049] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17,18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket, 30 Electrode, 32 Current collector, 34 Compound layer, 36 First compound layer, 38 Second compound layer

Claims

1. Current collector and, The electrode comprises a composite layer formed on the surface of the current collector, containing an active material, a conductive agent, and a binder. The aforementioned mixture layer consists of a first mixture layer facing the current collector and a second mixture layer laminated on the surface of the first mixture layer. The short-circuit resistance R1 of the first mixture layer and the short-circuit resistance R2 of the second mixture layer satisfy the relationship R1 < R2. The AC impedance measurement results of the first mixture layer do not form an arc on the low-frequency side in the Nyquist plot. The electronic conductivity A1 of the active material contained in the first combination layer and the electronic conductivity A2 of the active material contained in the second combination layer satisfy the relationship A1 > A2. The first composite layer contains carbon nanotubes, and the battery is a non-aqueous electrolyte secondary battery.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content C1 of the conductive agent in the first composite layer and the content C2 of the conductive agent in the second composite layer satisfy the relationship C1 > C2.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive agent is acetylene black.

4. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the binder is fibrillated polytetrafluoroethylene.

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