Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

Abstract

A positive electrode for nonaqueous electrolyte secondary batteries according to the present invention is provided with a positive electrode core body and a positive electrode mixture layer that is formed on the surface of the positive electrode core body. The positive electrode mixture layer has a void fraction of from 23% by volume to 50% by volume; the positive electrode mixture layer contains at least a positive electrode active material, carbon nanotubes serving as a conductive assistant, and a polyvinylidene fluoride serving as a binder; the carbon nanotubes have a particle diameter of from 5 nm to 40 nm and an aspect ratio of from 100 to 1,000; the content of the carbon nanotubes in the positive electrode mixture layer is from 0.2% by mass to 5% by mass; and the number of polyvinylidene fluoride molecules contained per unit mass of the positive electrode mixture layer is from 0.005 to 0.030.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

Background Art

[0002] In recent years, there has been an increasing demand for higher capacity in secondary batteries. Patent Document 1 discloses a high-capacity secondary battery in which the volume ratio of the positive electrode active material in the positive electrode composite material is 97.1% to 99.6%, and the volume ratio of the voids in the positive electrode composite material layer is 16% to 22%, thereby increasing the density of the positive electrode active material in the positive electrode composite material layer to 3.7 g / cc or more.

[0003] Also, in the positive electrode composite material layer, a high-capacity secondary battery can be obtained by reducing the content of the binder and increasing the content of the positive electrode active material. Patent Document 2 discloses that a positive electrode composite material slurry having suitable properties for producing a high-capacity positive electrode composite material layer can be obtained by using polyvinylidene fluoride having a molecular weight of 600,000 to 1,000,000 as a binder and controlling the preparation temperature to 30°C to 60°C.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] When the positive electrode composite material layer is densified as disclosed in Patent Document 1, it may become difficult for lithium ions to move between the particles of the positive electrode active material, resulting in high resistance. Also, even when polyvinylidene fluoride having a molecular weight of 600,000 to 1,000,000 is used as disclosed in Patent Document 2, if the content of polyvinylidene fluoride is low, the stability of the positive electrode composite material slurry may deteriorate, resulting in high resistance. The techniques disclosed in Patent Documents 1 and 2 do not consider battery resistance and there is still room for improvement.

[0006] The positive electrode for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode core and a positive electrode composite layer formed on the surface of the positive electrode core. The porosity of the positive electrode composite layer is 23% to 50% by volume. The positive electrode composite layer contains at least a positive electrode active material, carbon nanotubes as a conductive auxiliary material, and polyvinylidene fluoride as a binder. The carbon nanotubes have a particle diameter of 5 nm to 40 nm, an aspect ratio of 100 to 1000, and a content in the positive electrode composite layer of 0.2% to 5% by mass. The number of molecules of polyvinylidene fluoride contained per unit mass of the positive electrode composite layer is 0.005 to 0.030.

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes the above positive electrode for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

[0008] According to the present disclosure, a secondary battery with high capacity and low resistance can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] There is a demand for high-capacity and high-output secondary batteries. By reducing the porosity and increasing the density of the positive electrode composite layer, it is possible to increase the capacity of the secondary battery. However, the lithium ions may have difficulty moving between the particles of the positive electrode active material, and the secondary battery may have high resistance. As a result of intensive studies by the present inventors, while adjusting the porosity of the positive electrode composite layer to an appropriate range, adding a predetermined amount of carbon nanotubes with a high aspect ratio, and setting the number of molecules of polyvinylidene fluoride contained per unit mass of the positive electrode composite layer to a predetermined range, it has been found that a secondary battery with both high capacity and low resistance can be obtained. Due to the synergistic effect of polyvinylidene fluoride and carbon nanotubes, the dispersibility of the positive electrode active material, polyvinylidene fluoride, and carbon nanotubes in the positive electrode composite slurry is improved, enabling uniform coating. In addition, polyvinylidene fluoride and carbon nanotubes act in a composite manner to improve the adhesion strength between the positive electrode active materials and improve the electron conductivity. Due to these synergistic effects, the positive electrode and the battery can be made to have low resistance. This effect can be obtained by setting the number of molecules of polyvinylidene fluoride contained per unit mass of the positive electrode composite layer to a predetermined range even when the amount of polyvinylidene fluoride is small.

[0011] Hereinafter, an example of an embodiment of the present disclosure will be described in detail. In this embodiment, a secondary battery 100 including a rectangular metal exterior body 1 is exemplified. However, the exterior body is not limited to a rectangle and may be, for example, a cylindrical shape or the like. Further, a wound electrode body 3 in which a positive electrode and a negative electrode are wound with a separator interposed therebetween is exemplified. However, it may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one with a separator interposed therebetween. The electrode body 3 is preferably of a wound type. Further, in both the positive electrode and the negative electrode, a case where each composite layer is formed on both surfaces of each core body is exemplified. However, each composite layer is not limited to being formed on both surfaces of each core body and may be formed on at least one surface.

[0012] As illustrated in FIG. 1, the secondary battery 100 includes a wound electrode body 3 that is formed in a flat shape having a flat portion and a pair of curved portions, with a positive electrode and a negative electrode wound via a separator, an electrolyte, and an exterior body 1 that houses the electrode body 3 and the electrolyte. Both the exterior body 1 and the sealing plate 2 are made of metal, preferably made of aluminum or an aluminum alloy.

[0013] The exterior body 1 has a bottom portion that is substantially rectangular in plan view and side wall portions erected on the periphery of the bottom portion. The side wall portions are formed perpendicular to the bottom portion. The dimensions of the exterior body 1 are not particularly limited. As an example, the length in the lateral direction is 60 to 160 mm, the height is 60 to 100 mm, and the thickness is 10 to 40 mm.

[0014] The positive electrode is a long body having a metal positive electrode core body and positive electrode composite layers formed on both surfaces of the core body, and a strip-shaped positive electrode core body exposed portion 4 in which the positive electrode core body is exposed along the longitudinal direction is formed at one end in the short side direction. Similarly, the negative electrode is a long body having a metal negative electrode core body and negative electrode composite layers formed on both surfaces of the core body, and a strip-shaped negative electrode core body exposed portion 5 in which the negative electrode core body is exposed along the longitudinal direction is formed at one end in the short side direction. The electrode body 3 has a structure in which the positive electrode and the negative electrode are wound via a separator with the positive electrode core body exposed portion 4 of the positive electrode disposed at one end side in the axial direction and the negative electrode core body exposed portion 5 of the negative electrode disposed at the other end side in the axial direction.

[0015] A positive current collector 6 is connected to the laminated portion of the exposed portion 4 of the positive electrode core of the positive electrode, and a negative current collector 8 is connected to the laminated portion of the exposed portion 5 of the negative electrode core of the negative electrode, respectively. A preferred positive current collector 6 is made of aluminum or an aluminum alloy. A preferred negative current collector 8 is made of copper or a copper alloy. The positive electrode terminal 7 has a positive electrode external conductive portion 13 disposed on the battery external side of the sealing plate 2, a positive electrode bolt portion 14 connected to the positive electrode external conductive portion 13, and a positive electrode insertion portion 15 inserted into a through hole provided in the sealing plate 2, and is electrically connected to the positive current collector 6. Further, the negative electrode terminal 9 has a negative electrode external conductive portion 16 disposed on the battery external side of the sealing plate 2, a negative electrode bolt portion 17 connected to the negative electrode external conductive portion 16, and a negative electrode insertion portion 18 inserted into a through hole provided in the sealing plate 2, and is electrically connected to the negative current collector 8.

[0016] The positive electrode terminal 7 and the positive current collector 6 are fixed to the sealing plate 2 via an inner side insulating member and an outer side insulating member, respectively. The inner side insulating member is disposed between the sealing plate 2 and the positive current collector 6, and the outer side insulating member is disposed between the sealing plate 2 and the positive electrode terminal 7. Similarly, the negative electrode terminal 9 and the negative current collector 8 are fixed to the sealing plate 2 via an inner side insulating member and an outer side insulating member, respectively. The inner side insulating member is disposed between the sealing plate 2 and the negative current collector 8, and the outer side insulating member is disposed between the sealing plate 2 and the negative electrode terminal 9.

[0017] The electrode body 3 is housed in the exterior body 1. The sealing plate 2 is connected to the opening edge portion of the exterior body 1 by laser welding or the like. The sealing plate 2 has an electrolyte injection hole 10, and after injecting the electrolyte into the exterior body 1, the electrolyte injection hole 10 is sealed with a sealing plug. A gas discharge valve 11 for discharging gas is formed in the sealing plate 2 when the pressure inside the battery becomes a predetermined value or more.

[0018] Hereinafter, the positive electrode, negative electrode, separator, and non-aqueous electrolyte constituting the electrode body 3 will be described in detail, particularly the positive electrode composite layer constituting the positive electrode.

[0019] [Positive Electrode] The positive electrode includes a positive electrode core body and a positive electrode composite layer formed on the surface of the positive electrode core body. For the positive electrode core body, a foil of a metal stable within the potential range of the positive electrode, such as aluminum or an aluminum alloy, or a film with such a metal disposed on the surface layer can be used.

[0020] The positive electrode composite layer contains at least a positive electrode active material, carbon nanotubes (hereinafter sometimes referred to as CNTs) as a conductive auxiliary material, and polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) as a binder. The positive electrode can be manufactured by applying a positive electrode composite slurry containing a positive electrode active material, a conductive auxiliary material, a binder, etc. on the positive electrode core body, drying the coating film, and then compressing it to form the positive electrode composite layer on both sides of the positive electrode core body. The thickness of the positive electrode composite layer is, for example, 10 μm to 150 μm on one side of the positive electrode core body.

[0021] The porosity of the positive electrode composite layer is 23% to 50% by volume. The porosity of the positive electrode composite layer is calculated according to the following formula from the bulk density of the positive electrode composite layer and the true density and content of each component such as the positive electrode active material, conductive auxiliary material, and binder contained in the positive electrode composite layer. By adjusting the compression ratio of the positive electrode composite layer, the bulk density of the positive electrode composite layer can be changed, so the porosity of the positive electrode composite layer can be changed.

[0022] Porosity of the positive electrode composite layer = 1 - (sum of (content / true density) for each component × bulk density of the positive electrode composite layer) Examples of the positive electrode active material contained in the positive electrode composite layer include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. 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 Mn2-y M y O4, LiMPO4, Li2MPO4F (where M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B; 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used alone or in combination of multiple kinds. In terms of achieving high capacity of the non-aqueous electrolyte secondary battery, the cathode active material is Li x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z (where M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B; 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3), etc., and preferably contains lithium nickel composite oxides.

[0023] The CNT contained in the cathode composite material layer may be either single-walled carbon nanotube (SWCNT) or multi-walled carbon nanotube (MWCNT). Also, as MWCNT, for example, CNTs with a tubular structure in which graphene sheets composed of six-membered carbon rings are wound parallel to the fiber axis, CNTs with a platelet structure in which graphene sheets composed of six-membered carbon rings are arranged perpendicular to the fiber axis, CNTs with a herringbone structure in which graphene sheets composed of six-membered carbon rings are wound at an oblique angle to the fiber axis, etc. can be used. In addition to CNT, the cathode composite material layer may contain carbon materials such as carbon black, acetylene black (AB), ketjen black, and graphite as conductive aids.

[0024] The CNTs have a particle size of 5 nm to 40 nm and an aspect ratio of 100 to 1000. By satisfying this range, an interaction with PVdF occurs, enabling the positive electrode and the battery to have a low resistance. Here, the particle size of the CNTs is calculated from the average value obtained by measuring the diameters of 10 CNTs using a scanning electron microscope (hereinafter sometimes referred to as SEM). Also, the length of the CNTs is calculated from the average value obtained by measuring the lengths of 10 CNTs using SEM. For example, the CNTs are observed using SEM at an acceleration voltage of 5 kV, and in an image at 50,000 times magnification (pixel number 1024×1280), the diameters and lengths of any 10 CNTs are measured, and the particle size and length can be determined from their average values. The aspect ratio is the value obtained by dividing the length by the particle size.

[0025] The content of CNTs in the positive electrode composite material layer is 0.2 mass% to 5 mass%, preferably 1.5 mass% to 3 mass%. Being within this range improves the dispersibility of CNTs in the positive electrode composite material slurry, resulting in a lower resistance positive electrode and battery.

[0026] The number of moles of PVdF contained per unit mass of the positive electrode composite material layer is 0.005 to 0.030, preferably 0.007 to 0.011. By satisfying this range, an interaction with CNTs occurs, enabling the positive electrode and the battery to have a low resistance. Here, the number of moles of PVdF contained per unit mass of the positive electrode composite material layer is the value obtained by dividing the content of PVdF (mass%) in the positive electrode composite material layer by the molecular weight of PVdF ( 10 g / mol). 4

[0027] The content of polyvinylidene fluoride in the positive electrode composite material layer may be 0.3 mass% to 2.5 mass%. Thereby, a lower resistance positive electrode and battery can be obtained.

[0028] The molecular weight of polyvinylidene fluoride may be from 1.1 million to 1.4 million. Thereby, a cathode and a battery with lower resistance can be obtained. Further, in addition to PVdF, the cathode composite layer may contain, as a binder, a fluororesin such as polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide, an acrylic resin, a polyolefin, etc., and these resins may be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc.

[0029] [Negative electrode] The negative electrode has a negative electrode core and a negative electrode composite layer formed on the surface of the negative electrode core. For the negative electrode core, a foil of a metal stable within the potential range of the negative electrode such as copper or a copper alloy, a film having the metal disposed on the surface layer, etc. can be used. The negative electrode composite layer contains a negative electrode active material and a binder. The thickness of the negative electrode composite layer is, for example, 10 μm to 150 μm on one side of the current collector. The negative electrode can be manufactured by applying a negative electrode composite slurry containing a negative electrode active material, a binder, etc. on the negative electrode core, drying the coating film, and then rolling to form the negative electrode composite layer on both sides of the negative electrode core.

[0030] The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, artificial massive graphite, and artificial graphite such as graphitized mesophase carbon microbeads. Further, as the negative electrode active material, a metal that alloys with Li such as Si or Sn, a metal compound containing Si or Sn, a lithium titanium composite oxide, etc. may be used. For example, a Si-containing compound represented by SiO x (0.5 ≦ x ≦ 1.6), or Li 2y SiO (2+y) A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0 < y < 2) etc. may be used in combination with graphite.

[0031] As the binder contained in the negative electrode composite layer, similar to the case of the positive electrode, fluorine-containing resins such as PTFE and PVdF, PAN, polyimide, acrylic resin, polyolefin, etc. may be used, but preferably styrene-butadiene rubber (SBR) is used. Further, the negative electrode composite layer may contain CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. The negative electrode composite layer contains, for example, SBR and CMC or its salt.

[0032] [Separator] For the separator, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, etc. As the material of the separator, polyolefins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator may have a single-layer structure or may have a laminated structure. Further, on the surface of the separator, a resin layer with high heat resistance such as an aramid resin, a filler layer containing a filler of an inorganic compound may be provided.

[0033] [Non-aqueous electrolyte] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. Examples of the halogen-substituted product include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP), etc.

[0034] Examples of the above esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc., chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, etc., cyclic carboxylic acid esters such as γ-butyrolactone (GBL), γ-valerolactone (GVL), etc., and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, etc.

[0035] 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.

[0036] 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), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 0 or more}, etc. are mentioned. The lithium salt may be used alone or in combination of multiple kinds. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is, for example, 0.8 mol to 1.8 mol per 1 L of the non-aqueous solvent.

[0037] <Example> Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0038] <Example 1> [Fabrication of positive electrode] As the positive electrode active material, a lithium transition metal oxide represented by LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 was used. As the conductive auxiliary material, CNT having a particle diameter of 10 nm and an aspect ratio of 100 to 1000 (hereinafter, CNT-A) was used. As PVdF, one having a molecular weight of 1.1 million was used. The positive electrode active material, CNT, and PVdF were mixed at a mass ratio of 97.3:0.2:2.5, and kneaded while adding N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite slurry. Next, leaving the portion to which the positive electrode core lead made of aluminum foil is connected, the positive electrode composite slurry was applied to both sides, and the coating film was dried. Then, after rolling the coating film using a roller so that the porosity of the positive electrode composite layer becomes 50% by volume, it was cut into a predetermined electrode size to fabricate a positive electrode having a positive electrode composite layer formed on both sides of the positive electrode core.

[0039] [Fabrication of negative electrode] Graphite as the negative electrode active material, sodium salt of CMC, and dispersion of SBR were mixed at a solid content mass ratio of 99 / 0.6 / 0.4, and an appropriate amount of water was added to prepare a negative electrode composite slurry. Next, leaving the portions where leads are connected on both sides of the negative electrode core made of copper foil, the negative electrode composite slurry was applied and the coating film was dried. Then, after rolling the coating film using a roller, it was cut into a predetermined electrode size to produce a negative electrode with negative electrode composite layers formed on both sides of the negative electrode core. The packing density of the negative electrode composite layer was 1.17 g / cm 3 It was.

[0040] [Preparation of Non-aqueous Electrolyte] 1 part by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 25:35:40, and LiPF6 was dissolved at a ratio of 1.15 mol / L to prepare a non-aqueous electrolyte.

[0041] [Fabrication of Test Cell] Leads were respectively attached to the negative electrode and the positive electrode, and a laminated electrode body was fabricated by alternately laminating one sheet of each electrode via a separator. As the separator, a single-layer polypropylene separator was used. The fabricated electrode body and the non-aqueous electrolyte were housed in a rectangular battery case to fabricate a test cell.

[0042] [Measurement of Composite Layer Resistance and Interface Resistance] In the positive electrode before being incorporated into the test cell, the composite layer resistance (Ω·cm), which is the resistance of the entire composite layer, and the interface resistance (Ω·cm 2 ) between the positive electrode core and the positive electrode composite layer were measured. The increase amount of the composite layer resistance and the increase amount of the interface resistance were calculated by subtracting the measurement results of the positive electrode fabricated as described above from the measurement results of the positive electrode taken out after immersing the positive electrode in dimethyl carbonate (DMC) at 80°C for 18 hours. For the measurement of the composite layer resistance and the interface resistance, an electrode resistance measuring instrument (device name: XF057) manufactured by Hioki E.E. Corporation was used.

[0043] [Evaluation of DC Resistance] For the above test cell, under an environment of 25°C, constant current charging was performed at a constant current of 0.3C until the state of charge (SOC) reached 50%. After reaching SOC 50%, constant voltage charging was performed until the current value reached 0.02C. Thereafter, constant current discharging was performed at a constant current of 50C for 10 seconds. The DC resistance was calculated by dividing the difference between the open circuit voltage (OCV) and the closed circuit voltage (CCV) 10 seconds after discharging by the discharge current 10 seconds after discharging, as shown in the following formula.

[0044] DC resistance = [OCV - CCV (10 seconds after discharging)] / discharge current (10 seconds after discharging) <Examples 2 to 14, Comparative Examples 1 to 21> As shown in Table 1 and Table 2, except for changing the content of the positive electrode active material, the type and content of the conductive assistant, the content and molecular weight of PVdF, and the porosity of the positive electrode composite material layer, the positive electrode and the test cell were produced and evaluated in the same manner as in Example 1. Note that CNT-B of the conductive assistant has a particle size of 150 nm and is a CNT with an aspect ratio of 10 to 70.

[0045] Table 1 and Table 2 summarize the results of the increase in the resistance of the composite material layer, the increase in the interfacial resistance, and the DC resistance for the examples and comparative examples. Table 1 and Table 2 also describe the composition of the positive electrode composite material layer composed of the positive electrode active material, the conductive assistant, and PVdF, and the porosity of the positive electrode composite material layer.

[0046]

Table 1

[0047]

Table 2

[0048] As can be seen from Table 1 and Table 2, in all of Examples 1 to 14, the resistance of the positive electrode and the battery was smaller than that of Comparative Examples 1 to 21. Also, in Examples 1 to 14, the content of the positive electrode active material in the positive electrode composite material layer was 90% by mass or more, and high-capacity positive electrodes and batteries could be produced.

Explanation of Signs

[0049] 1 Outer casing 2 Sealing plate 3 Electrode body 4 Positive electrode core exposed part 5 Negative electrode core exposed part 6 Positive electrode current collector 7 Positive electrode terminal 8 Negative electrode current collector 9 Negative electrode terminal 10 Electrolyte injection hole 11 Gas discharge valve 13 Positive electrode external conductive part 14 Positive electrode bolt part 15 Positive electrode insertion part 16 Negative electrode external conductive part 17 Negative electrode bolt part 18 Negative electrode insertion part 100 Secondary battery

Claims

1. A positive electrode core body and a positive electrode composite material layer formed on the surface of the positive electrode core body, The porosity of the positive electrode composite material layer is 23% to 50% by volume, The positive electrode composite material layer contains at least a positive electrode active material, carbon nanotubes as a conductive auxiliary material, and polyvinylidene fluoride as a binder, The carbon nanotubes have a particle diameter of 5 nm to 40 nm, an aspect ratio of 100 to 1000, and a content in the positive electrode composite material layer of 0.2% to 5% by mass, The molecular weight of the polyvinylidene fluoride is 1.1 million to 1.4 million, The number of molecules of polyvinylidene fluoride contained per unit mass of the positive electrode composite material layer is 0.006 to 0.011, A positive electrode for a non-aqueous electrolyte secondary battery, wherein the content of polyvinylidene fluoride in the positive electrode composite material layer is 0.3% to 2.5% by mass.

2. A non-aqueous electrolyte secondary battery comprising the positive electrode for a non-aqueous electrolyte secondary battery according to Claim 1, a negative electrode, and a non-aqueous electrolyte.

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