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

Abstract

To provide a positive electrode for a nonaqueous electrolyte secondary battery, capable of suppressing heat generation in a case where a short circuit occurs.SOLUTION: A positive electrode mixture layer includes a first positive electrode active material, which is a layered compound represented by a general formula (1), a second positive electrode active material which is represented by a general formula (2) and in which a film of a carbon material is formed on a surface of a phosphoric acid compound that has an olivine structure, and a conductive material, and satisfies a following formula (3). (1) LiaNixCoyM11-x-yO2 (0<a≤1.2, 0<x≤0.9, 0<y≤0.5, 0<x+y<1) (2) LiMnzM2bFe1-z-bPO4 (0<z≤0.9, 0≤b≤0.1, 0<z+b<1) (3 ) 0.760≤(W1×R1+W2×R2) / D≤0.960 [W1 (W2): tap density of the first (second) positive electrode active material, R1 (R2): weight ratio of the first (second) positive electrode active material when the total weight of the two positive electrode active materials is 1, D: density of the positive electrode mixture layer calculated on the basis of, a thickness of a positive electrode when a charging rate of a secondary battery after initial activation treatment is 0%]SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In non-aqueous electrolyte secondary batteries, ions in the electrolyte are responsible for electrical conduction. Lithium secondary batteries, one type of non-aqueous electrolyte secondary battery, are installed as power sources in small electronic devices such as digital cameras and laptop computers, as well as in vehicles. Lithium secondary batteries are composed of a positive electrode, a negative electrode, and a separator. Of these, the positive electrode includes a positive electrode current collector and a positive electrode mixture layer coated on the surface of the positive electrode current collector and containing a positive electrode active material, a conductive material, and a binder.

[0003] Positive electrode active materials for non-aqueous electrolyte secondary batteries include LiFePO4 or olivine compounds with a portion of LiFePO4 substituted with Mn, LiCoO2, LiNiO2, LiMnO2, LiCoNiO2, LiCoMO2, LiNiMO2, compounds in which some of the elements in these positive electrode active materials are substituted with other elements, and ternary layered compounds containing Co, Ni, or Mn. Layered compounds, in particular, offer high capacity and high voltage, making them suitable for applications where energy density is important. However, layered compounds have poor thermal stability in the charged state, making it difficult to suppress heat generation during short-circuiting when used in non-aqueous electrolyte secondary batteries. Therefore, to ensure the safety of non-aqueous electrolyte secondary batteries, techniques have been developed to blend layered compounds with LiFePO4 or olivine compounds with a portion of LiFePO4 substituted with Mn. Olivine compounds with a portion of LiFePO4 substituted with Mn have operating potentials not significantly different from those of layered compounds, making blending them easier to ensure safety without significantly reducing energy density.

[0004] For example, in Patent Document 1, LiNi 5 / 10 Co 2 / 10 Mn 3 / 10Using O2 and an olivine compound as the positive electrode active material, the conditions for suppressing an increase in the battery surface temperature during a short circuit are set based on the tap density and volume of the positive electrode active material, the porosity of the positive electrode active material layer, and the positive electrode active material occupancy rate of the positive electrode active material layer calculated from these values. According to the disclosure of Patent Document 1, the lower the positive electrode active material occupancy rate, i.e., the higher the effective porosity of the positive electrode active material layer, the easier it is to suppress an increase in the battery surface temperature during a short circuit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6202191 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Document 1, LiNi is used as the positive electrode active material. 5 / 10 Co 2 / 10 Mn 3 / 10 However, there has been insufficient research into the use of a layered compound and an olivine compound in which a portion of LiFePO4 is substituted with Mn. The layered compound and the olivine compound in which a portion of LiFePO4 is substituted with Mn have similar reaction potentials, and their reactivity with the electrolyte is different from that in Patent Document 1. For this reason, the inventors of the present application conducted extensive research and found that the value of the positive electrode active material occupancy specified in Patent Document 1 does not provide the effect of suppressing temperature rise during a short circuit. In other words, simply using the technology of Patent Document 1 may not be enough to suppress heat generation during a short circuit.

[0007] The present invention has been made in view of the above, and an object of the present invention is to provide a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that suppress heat generation during a short circuit. [Means for solving the problem]

[0008] When the inventors of the present application used a layered compound and an olivine compound in which part of LiFePO4 was substituted with Mn as the positive electrode active material, they discovered that when the degree of voids in the substantial positive electrode mixture layer calculated from a predetermined relational expression was rather small, heat generation during short circuit could be suppressed.

[0009] In order to solve the above-described problems and achieve the object, a positive electrode for a non-aqueous electrolyte secondary battery according to the present invention is a positive electrode for a non-aqueous electrolyte secondary battery including a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector, wherein the positive electrode mixture layer includes a first positive electrode active material that is a layered compound represented by the general formula shown in the following formula (1), a second positive electrode active material represented by the general formula shown in the following formula (2) and having a carbon material film formed on the surface of a phosphoric acid compound having an olivine structure, and a conductive material, and when the tap density (g / cc) of the first positive electrode active material is W1, the tap density (g / cc) of the second positive electrode active material is W2, the weight ratio of the first positive electrode active material when the total weight of the first and second positive electrode active materials is 1 is R1, the weight ratio of the second positive electrode active material when the total weight of the first and second positive electrode active materials is 1 is R2, and the density (g / cc) of the positive electrode mixture layer calculated based on the thickness of the positive electrode for a non-aqueous electrolyte secondary battery when the charging rate of the non-aqueous electrolyte secondary battery after the initial activation treatment is 0% is D, it is characterized by satisfying the following formula (3). Li a Ni x Co y M1 1-x-y O2···(1) LiMn z M2 b Fe 1-z-b PO4···(2) 0.760 ≦ (W1 × R1 + W2 × R2) / D ≦ 0.960 ···(3) However, in the above formula (1), M1 is at least one selected from Ti, Zr, Nb, W, P, Al, Mg, V, Mn, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, Cu, Ag, Ce, Pr, Ge, Bi, Ba, Er, La, Sm, Yb, Sb, Bi, S, and Zn, and satisfies 0 < a ≦ 1.2, 0 < x ≦ 0.9, 0 < y ≦ 0.5, 0 < x + y < 1. In the above formula (2), M2 is at least one selected from Ni, Co, Ti, Cu, Zn, Mg, Zr, Ca, Y, Mo, Ba, Pb, Bi, La, Ce, Nd, Gd, Al, Ga, and Sr, and satisfies 0 < z ≦ 0.9, 0 ≦ b ≦ 0.1, and 0 < z + b < 1.

[0010] Further, in the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, in the above invention, it is preferable that the median diameter of the first positive electrode active material is larger than the D90 of the second positive electrode active material.

[0011] Further, in the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, in the above invention, it is preferable that the tap density W2 of the second positive electrode active material is 0.7 g / cc or more and 1.00 g / cc or less.

[0012] Further, in the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, in the above invention, it is preferable that the weight ratio R2 of the second positive electrode active material is 0.1 or more and 0.3 or less.

[0013] Further, the non-aqueous electrolyte secondary battery according to the present invention includes the positive electrode for a non-aqueous electrolyte secondary battery according to the above invention, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt and a non-aqueous solvent.

Advantages of the Invention

[0014] According to the present invention, it is possible to obtain a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that suppress heat generation during short circuit.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a cross-sectional view for explaining the configuration of a non-aqueous electrolyte secondary battery including the positive electrode for a non-aqueous electrolyte secondary battery according to Embodiment 1 of the present invention. [Figure 2] FIG. 2 is an exploded perspective view for explaining the configuration of a non-aqueous electrolyte secondary battery including the positive electrode for a non-aqueous electrolyte secondary battery according to Embodiment 2 of the present invention.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following description. Furthermore, various modifications and improvements can be made to the present embodiments, and such modifications and improvements can also be included in the present invention.

[0017] Although details will be described later, FIG. 1 is a cross-sectional view of a laminate-type nonaqueous electrolyte secondary battery, and FIG. 2 is an exploded perspective view for explaining the configuration of a coin-type nonaqueous electrolyte secondary battery. 1 and 2 show configuration examples of a laminate-type nonaqueous electrolyte secondary battery and a coin-type nonaqueous electrolyte secondary battery as examples of embodiments, but the shape of the nonaqueous electrolyte secondary battery in the present invention is not particularly limited and may be flat, cylindrical, prismatic, coin-type, etc. Furthermore, the exterior body of the nonaqueous electrolyte secondary battery is not particularly limited either and known materials such as laminate film, aluminum, aluminum alloy, and stainless steel can be used.

[0018] (Embodiment 1) Fig. 1 is a cross-sectional view illustrating the configuration of a nonaqueous electrolyte secondary battery including a positive electrode for a nonaqueous electrolyte secondary battery according to embodiment 1 of the present invention. The nonaqueous electrolyte secondary battery 1 shown in Fig. 1 is a stacked-type nonaqueous electrolyte secondary battery formed by stacking a plurality of pairs of a positive electrode, a negative electrode, and a separator.

[0019] The non-aqueous electrolyte secondary battery 1 includes a bag-shaped exterior body 2 made of laminate film. An electrode group 3 having a laminated structure is housed within the exterior body 2. The laminate film has a structure in which, for example, multiple (e.g., two) plastic films are stacked together with a metal foil such as aluminum foil sandwiched between adjacent plastic films. One of the two plastic films is a heat-sealable resin film. The exterior body 2 is made by stacking two laminate films with the heat-sealable resin films facing each other, and houses the electrode group 3 and non-aqueous electrolyte between these laminate films. The two laminate film portions around the electrode group 3 are heat-sealed to each other to seal, thereby hermetically housing the electrode group 3 and non-aqueous electrolyte.

[0020] The electrode group 3 has a positive electrode 4, a negative electrode 5, a separator 6, a positive electrode lead 7, a positive electrode tab 8, a negative electrode lead 9, and a negative electrode tab 10. The separator 6 is interposed between the positive electrode 4 and the negative electrode 5. The electrode group 3 has a multi-layer structure in which the negative electrode 5 is located as the outermost layer and the separator 6 is located between the negative electrode 5 and the inner surface of the exterior body 2.

[0021] The positive electrode 4 is composed of a positive electrode current collector 41 and a positive electrode mixture layer 42 formed on one or both surfaces of the positive electrode current collector 41 .

[0022] The positive electrode current collector 41 is made of aluminum, nickel, stainless steel, titanium, other alloys, etc. Among these, it is preferable to use aluminum from the viewpoint of electronic conductivity and battery operating potential.

[0023] The positive electrode mixture layer 42 includes a first positive electrode active material, a second positive electrode active material, a conductive material, and a binder. The density of the positive electrode mixture layer 42 is adjusted by, for example, pressing. The first and second positive electrode active materials are each capable of absorbing and desorbing lithium.

[0024] The first positive electrode active material is a layered compound represented by the general formula shown in the following formula (1). The layered compound is a lithium (Li) - nickel (Ni) - cobalt (Co) - containing composite metal oxide in which sheet - like particles form layers. Li a Ni x Co y M1 1-x-y O2···(1) However, in the general formula (1), M1 is at least one selected from titanium (Ti), zirconium (Zr), niobium (Nb), tungsten (W), phosphorus (P), aluminum (Al), magnesium (Mg), vanadium (V), manganese (Mn), calcium (Ca), strontium (Sr), chromium (Cr), iron (Fe), boron (B), gallium (Ga), indium (In), silicon (Si), molybdenum (Mo), yttrium (Y), tin (Sn), copper (Cu), silver (Ag), cerium (Ce), praseodymium (Pr), germanium (Ge), bismuth (Bi), barium (Ba), erbium (Er), lanthanum (La), samarium (Sm), ytterbium (Yb), antimony (Sb), bismuth (Bi), sulfur (S), and zinc (Zn), and satisfies 0 < a ≦ 1.2, 0 < x ≦ 0.9, 0 < y ≦ 0.5, 0 < x + y < 1.

[0025] The second positive electrode active material is a compound represented by the general formula shown in the following formula (2), and a film made of a carbon material is formed on the surface of a phosphate compound (olivine - type compound) having an olivine structure. LiMn z M2 b Fe 1-z-b PO4···(2) However, in the general formula (2), M2 is at least one selected from nickel (Ni), cobalt (Co), titanium (Ti), copper (Cu), zinc (Zn), magnesium (Mg), zirconium (Zr), calcium (Ca), yttrium (Y), molybdenum (Mo), barium (Ba), lead (Pb), bismuth (Bi), lanthanum (La), cerium (Ce), neodymium (Nd), gadolinium (Gd), aluminum (Al), gallium (Ga), and strontium (Sr), and satisfies 0 < z ≤ 0.9, 0 ≤ b ≤ 0.1, and 0 < z + b < 1. Since the positive electrode mixture layer 42 contains the second positive electrode active material, the second positive electrode active material with high thermal stability covers the periphery of the first positive electrode active material with low thermal stability, so that when a short circuit occurs, the heat generation reaction due to the direct contact between the first positive electrode active material and the non-aqueous electrolyte can be reduced.

[0026] The carbon material is a conductive carbon material. The second positive electrode active material is coated with a carbon material on at least a part of the surface of at least some of the primary particles by a film composed of the carbon material present on the surface of the second positive electrode active material. The purity of carbon and the thickness of the carbon film can be arbitrarily selected, but it is preferably controlled so that the ratio of the weight of the carbon material to the weight of the entire second positive electrode active material is 0.1% or more and 5% or less.

[0027] Also, when the tap density (g / cc) of the first positive electrode active material is W1, the tap density (g / cc) of the second positive electrode active material is W2, the weight ratio of the first positive electrode active material when the total weight of the first and second positive electrode active materials is 1 is R1, the weight ratio of the second positive electrode active material when the total weight of the first and second positive electrode active materials is 1 is R2, and the density (g / cc) of the positive electrode mixture layer 42 is D, the following formula (3) is satisfied. 0.760 ≤ (W1 × R1 + W2 × R2) / D ≤ 0.960 ···(3) Here, the density D of the positive electrode mixture layer 42 refers to a value calculated based on the thickness of the positive electrode when the state of charge (SOC) of the non-aqueous electrolyte secondary battery after the initial activation treatment is performed by charging and discharging for at least one cycle is 0%.

[0028] In the above formula (3), the value of (W1 × R1 + W2 × R2) / D is the ratio of the density of the positive electrode mixture layer to the weight average tap density of the positive electrode active material, and represents the substantial degree of porosity in the positive electrode mixture layer. If the value of the above formula is less than 0.760, the positive electrode mixture layer becomes too dense, which may cause distortion in the electrode during the pressing process during electrode fabrication and reduce the efficiency of battery fabrication. If the value of the above formula is greater than 0.960, the substantial degree of porosity in the positive electrode mixture layer increases, resulting in a large area of ​​direct contact between the first positive electrode active material and the nonaqueous electrolyte even when the positive electrode mixture layer 42 contains a second positive electrode active material. Therefore, when the nonaqueous electrolyte secondary battery is short-circuited, the first positive electrode active material, which has low thermal stability, is likely to react exothermically with the nonaqueous electrolyte, making it difficult to suppress heat generation in the nonaqueous electrolyte secondary battery. In other words, by ensuring that the value of the above formula is 0.760 or more and 0.960 or less, the degree of substantial voids in the positive electrode mixture layer can be reduced while maintaining the production efficiency in the pressing step during electrode production, and therefore the exothermic reaction between the first positive electrode active material and the nonaqueous electrolyte during a short circuit can be reduced to the greatest extent possible, and heat generation in the nonaqueous electrolyte secondary battery can be suppressed.

[0029] Furthermore, the weight ratio R2 of the second positive electrode active material is preferably 0.1 or more and 0.3 or less. If the weight ratio of the second positive electrode active material exceeds 0.3 (30%), the charge / discharge curve of the nonaqueous electrolyte secondary battery 1 tends to have more steps (the number of inflection points increases), making it difficult to estimate the depth of charge and state of degradation from the voltage and current values ​​during charge / discharge, reducing its practicality. If the weight ratio of the second positive electrode active material is below 0.1 (10%), the first positive electrode active material may not be sufficiently covered by the second positive electrode active material. If the first positive electrode active material is not sufficiently covered by the second positive electrode active material, electrolyte decomposition occurs on the surface of the first positive electrode active material, making thermal runaway more likely to occur during a short circuit.

[0030] The tap density of the second positive electrode active material is preferably 0.7 g / cc or more and 1.00 g / cc or less, and more preferably 0.8 g / cc or more. When the tap density is 1.00 g / cc or less, the primary particles of the second positive electrode active material do not form high-density granules or secondary particles but have a bulky shape, allowing them to more tightly surround the first positive electrode active material, thereby suppressing heat generation due to thermal runaway during short circuit. This not only reduces the temperature rise of the non-aqueous electrolyte secondary battery during short circuit, but also reduces swelling, cracking, and rupture due to electrolyte decomposition on the surface of the first positive electrode active material caused by temperature rise. On the other hand, when the tap density is greater than 1.00 g / cc, the second positive electrode active material is in a high-density granular state, making it difficult to tightly surround the first positive electrode active material, making it difficult to prevent temperature rise in the non-aqueous electrolyte secondary battery during short circuit, and making swelling, cracking, and rupture more likely to occur. Furthermore, if the tap density is less than 0.70 g / cc, the dispersibility of the second positive electrode active material decreases during the preparation of the slurry for the positive electrode mixture layer 42, making it more likely to aggregate and induce streaks during the preparation of the positive electrode, making it difficult to prepare a positive electrode of uniform quality. Furthermore, if the tap density is 0.80 g / cc or higher, the dispersibility of the second positive electrode active material during the preparation of the slurry is improved.

[0031] In the positive electrode mixture layer 42, the median diameter of the first positive electrode active material is larger than the D90 of the second positive electrode active material. If the median diameter of the first positive electrode active material, measured by laser diffraction / scattering or the like, is smaller than the D90 of the second positive electrode active material, the proportion of the second positive electrode active material, which has a particle diameter larger than that of the first positive electrode active material, will be greater, and the second positive electrode active material will not be able to surround the first positive electrode active material without gaps. As a result, the contact area of ​​the first positive electrode active material with the electrolyte increases, making thermal runaway more likely to occur during a short circuit, and increasing the amount of heat generated by the cell. Note that the median diameter may also be referred to as D50 in this specification.

[0032] The above-mentioned median diameter, D90, and tap density refer to values ​​in the positive electrode mixture layer 42 after the nonaqueous electrolyte secondary battery has been fabricated. However, these values ​​are generally equivalent to the median diameter, D90, and tap density of the first positive electrode active material and the second positive electrode active material before the positive electrode is fabricated. Therefore, if the median diameter, D90, and tap density values ​​of the first positive electrode active material and the second positive electrode active material before fabrication satisfy the requirements of the present invention, the fabricated positive electrode can be considered to also satisfy the requirements of the present invention.

[0033] Whether the median diameter, D90, and tap density of the first and second positive electrode active materials in the fabricated positive electrode mixture layer satisfy the requirements of the present invention can be confirmed, for example, by the following method. The nonaqueous electrolyte secondary battery is disassembled in an argon-filled glove box to remove the positive electrode 4. The positive electrode 4 is washed with an appropriate solvent (e.g., dimethyl carbonate) and then vacuum-dried to remove the solvent. The positive electrode is then immersed in a solvent such as N-methyl-2-pyrrolidone and subjected to ultrasonic waves to separate the positive electrode mixture layer 42 from the positive electrode current collector 41. The solvent in which the separated positive electrode mixture layer 42 is dispersed is centrifuged to separate the various substances in the positive electrode mixture layer 42. The median diameter and D90 of the separated first and second positive electrode active materials can be measured, for example, by laser diffraction / scattering. The tap density can be measured, for example, by placing the materials in a container, tapping the container, and measuring the weight divided by the volume of the container to fill the gaps between the particles. The nonaqueous electrolyte secondary battery used above may have been subjected to initial activation or charge / discharge cycling in any step, and it is preferable to set the charge rate of the nonaqueous electrolyte secondary battery to 0% beforehand when removing the positive electrode 4.

[0034] The conductive material assists electron conduction in the positive electrode. The conductive material is not particularly limited, and known materials can be used. Examples of conductive materials include conductive carbon powders such as acetylene black and carbon black such as ketjen black, carbon nanotubes, carbon nanofibers, graphene, activated carbon, and graphite. The conductive material may be made of a single material or multiple materials (e.g., a first conductive material and a second conductive material).

[0035] The binder binds the positive electrode current collector, the positive electrode active material, and the conductive material. There are no particular limitations on the binder, and known or commercially available binders can be used. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and styrene-butadiene rubber (Styrene-Butadiene Examples of the rubber include SBR, butadiene rubber, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), butyl rubber, poly(meth)acrylate (PMMA), polyethylene oxide (PEO), polypropylene oxide (PO), polyepichlorohydrin, polyphosphazene, polyacrylonitrile, hexafluoropropylene (HFP), and copolymers thereof, or a mixture of two or more thereof.

[0036] The negative electrode 5 is composed of a negative electrode current collector 51 and a negative electrode mixture layer 52 containing a negative electrode active material formed on one or both surfaces of the negative electrode current collector 51 or metallic lithium (not shown).

[0037] Although there is no particular limitation on the negative electrode current collector 51, it is preferable to use a metal. Suitable metals include aluminum foil and copper, and depending on the application, a porous aluminum current collector may also be used. Among these, copper is preferable from the viewpoint of electronic conductivity and battery operating potential.

[0038] The negative electrode mixture layer 52 is made of, for example, lithium, a lithium alloy, a titanium-niobium alloy, or a material such as graphite, amorphous carbon, or a transition metal composite oxide (e.g., Li4Ti5O 12 The negative electrode mixture layer 52 contains at least one active material selected from the group consisting of titanium dioxide (TiNb2O7, TiNb2O7, etc.), an alloy capable of absorbing and releasing lithium, and silicon. Among these, graphite is preferred because it has an operating potential very close to that of metallic lithium, allows charging and discharging at a high operating voltage, and has excellent cycle characteristics. Graphite may also be used in combination with other negative electrode active materials. The negative electrode mixture layer 52 also contains a conductive material and a binder. The conductive material and binder may be the same materials as those used in the positive electrode 4.

[0039] The separator 6 is disposed between the positive electrode and the negative electrode and has a porosity that allows the components of the non-aqueous electrolyte to pass through. The separator 6 is formed, for example, using a porous sheet separator made of polymer or fiber, a nonwoven fabric separator, or the like. The separator 6 may be made of a material such as polyethylene, polypropylene, aramid, or polyimide, or may have multiple layers of different materials including these. However, from the viewpoint of providing a shutdown function in the event of heat generation, it is preferable that the separator 6 has a layer containing polyethylene. The pore size of the separator 6 is preferably 0.01 to 10 μm, and the thickness is preferably 5 to 30 μm. The separator 6 may also be formed by laminating a ceramic layer as a heat-resistant insulating layer on a porous substrate. When a solid electrolyte is used as the non-aqueous electrolyte, the separator 6 may not be present.

[0040] The positive electrode leads 7 extend downward from the positive electrode mixture layer 42, for example, as shown in FIG. 1. As an example, each positive electrode lead 7 is a portion of the positive electrode current collector 41 that is not coated with the positive electrode mixture layer 42. The positive electrode leads 7 are bundled and joined to each other at the end opposite to the positive electrode mixture layer 42 side within the exterior body 2.

[0041] One end of the positive electrode tab 8 is joined to the positive electrode lead 7, and the other end passes through the sealing portion of the exterior body 2 and extends to the outside.

[0042] The negative electrode leads 9 each extend upward from the negative electrode mixture layer 52, for example, as shown in FIG. 1. They may extend in the same direction as the positive electrode lead 7, provided that they do not come into contact with the positive electrode lead 7. As an example, each negative electrode lead 9 is a portion of the negative electrode current collector 51 that is not coated with the negative electrode mixture layer 52. The negative electrode leads 9 are bundled and joined to each other at the end opposite to the negative electrode mixture layer 52 side within the exterior body 2.

[0043] One end of the negative electrode tab 10 is joined to the negative electrode lead 9, and the other end passes through the sealing portion of the exterior body 2 and extends to the outside.

[0044] The nonaqueous electrolyte may be a nonaqueous electrolytic solution or a solid electrolyte. The following describes the nonaqueous electrolytic solution in particular. The nonaqueous electrolytic solution is enclosed within the exterior body 2. The nonaqueous electrolytic solution injection portion of the exterior body 2 is sealed after the nonaqueous electrolytic solution is injected. The nonaqueous electrolytic solution contains an electrolyte and a nonaqueous solvent.

[0045] The electrolyte is not particularly limited, and any lithium salt commonly used in non-aqueous electrolyte secondary batteries can be used. For example, LiPF, LiAsF, LiBF, LiCF, SO, LiN(C m F 2m+1 SO2)(C n F 2n+1 SO2) (m and n are integers of 1 or more), LiC(C p F 2p+1 SO2)(C q F 2q+1 SO2)(C r F 2r+1Examples of electrolytes that can be used include lithium difluoro(oxalato)borate (SO2) (p, q, and r are integers of 1 or greater), lithium difluoro(oxalato)borate, and lithium bis(oxalato)borate. These electrolytes may be used alone or in combination of two or more. From the viewpoints of lithium ion conductivity, the viscosity of the electrolyte, and the temperature characteristics of conductivity, the electrolyte should preferably have a concentration of 0.1 to 3 mol / L, and preferably 0.5 to 1.5 mol / L.

[0046] The non-aqueous solvent contains a cyclic carbonate and / or a chain carbonate as a main component. The cyclic carbonate is preferably at least one selected from ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). The chain carbonate is preferably at least one selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The cyclic carbonate is related to the degree of dissociation of the electrolyte components, and the chain carbonate is related to the viscosity of the electrolyte solution.

[0047] In addition, additives other than the lithium salts may be included for the purpose of forming a high-quality coating on the surface of the negative electrode active material through reductive decomposition during charge and discharge. The additives are not particularly limited, but examples include vinylene carbonate, fluoroethylene carbonate, 1,3,2-dioxathiolane 2,2-dioxide (MMDS), 1,5,2,4-dioxadithiane 2,2,4,4-tetraoxide, tris(trimethylsilyl) phosphite, 1-propene 1,3-sultone, and Li2PO2F2. These additives may be used alone or in combination. They may also be used in combination with other additives. Furthermore, other additives may also be used alone.

[0048] In the present embodiment 1, in the positive electrode 4 of the nonaqueous electrolyte secondary battery 1, the positive electrode mixture layer 42 is configured so that (W1×R1+W2×R2) / D satisfies 0.760 or more and 0.960 or less, where W1 is the tap density of the first positive electrode active material, W2 is the tap density of the second positive electrode active material, R1 is the weight ratio of the first positive electrode active material when the total weight of the first and second positive electrode active materials is 1, R2 is the weight ratio of the second positive electrode active material when the total weight of the first and second positive electrode active materials is 1, and D is the density of the positive electrode mixture layer 42. Here, as described above, LiNi 5 / 10 Co 2 / 10 Mn 3 / 10 O2 and LiMn 0.7 Fe 0.3 When PO4 is mixed, the reactivity with the electrolyte can be increased by reducing the reaction area. Therefore, in the present embodiment 1, the density of the electrode 4 is increased relative to the density of the entire active material obtained from the weight average of the tap densities of the active materials. In other words, by reducing the substantial voids in the electrode 4, the contact area with the electrolyte is reduced, and rapid heat generation due to thermal decomposition of the positive electrode 4 is suppressed. According to the present embodiment 1, it is possible to obtain a positive electrode 4 and a nonaqueous electrolyte secondary battery 1 that suppress heat generation during a short circuit.

[0049] (Embodiment 2) 2 is an exploded perspective view illustrating the configuration of a nonaqueous electrolyte secondary battery including a positive electrode for a nonaqueous electrolyte secondary battery according to Embodiment 2 of the present invention. Nonaqueous electrolyte secondary battery 1A includes case 110, leaf spring 111, positive electrode current collector 112, positive electrode mixture layer 113, separator 114, negative electrode 115, gasket 116, and cap 117. Positive electrode current collector 112 and positive electrode mixture layer 113 form positive electrode 118.

[0050] In the nonaqueous electrolyte secondary battery 1A, the case 110 and the cap 117 are fixed together by crimping or the like, and the battery is filled with a nonaqueous electrolyte. The nonaqueous electrolyte secondary battery 1A is liquid-tightly sealed by the case 110, the gasket 116, and the cap 117. The positive electrode current collector 112, the positive electrode mixture layer 113, the separator 114, and the negative electrode 115 are biased toward the cap 117 by the leaf spring 111. This keeps the components in close contact with each other.

[0051] The positive electrode current collector 112 is made of the same material as the positive electrode current collector 41 . The positive electrode mixture layer 113 has the same configuration as the positive electrode mixture layer 42 .

[0052] Separator 114 is a porous disk-shaped material and is provided between positive electrode 115 and negative electrode 115. Separator 114 has the same structure as separator 6.

[0053] The nonaqueous electrolyte may be the same as that of the first embodiment.

[0054] The negative electrode 115 has the same configuration as the negative electrode 5 .

[0055] In the present second embodiment, in the positive electrode 118 of the nonaqueous electrolyte secondary battery 1A, the positive electrode mixture layer 113 is configured so that (W1×R1+W2×R2) / D satisfies 0.760 or more and 0.960 or less, where W1 is the tap density of the first positive electrode active material, W2 is the tap density of the second positive electrode active material, R1 is the weight ratio of the first positive electrode active material when the total weight of the first and second positive electrode active materials is 1, R2 is the weight ratio of the second positive electrode active material when the total weight of the first and second positive electrode active materials is 1, and D is the density of the positive electrode mixture layer 42. According to the present second embodiment, it is possible to obtain a positive electrode 118 and a nonaqueous electrolyte secondary battery 1A that suppress heat generation during a short circuit. [Example]

[0056] The present invention will be described in more detail below by way of examples, but the present invention is not limited to the following examples in any way.

[0057] <How to make the positive electrode> LiNi as the first positive electrode active material 0.5 Co 0.2 Mn 0.3 O2(NCM) 75.2 wt% and LiMn as the second positive electrode active material. 0.7 Fe 0.3 A positive electrode active material slurry was prepared by mixing 18.8 wt% of PO4 (LMFP), 2 wt% of graphite as a first conductive material, 3 wt% of acetylene black as a second conductive material, 1 wt% of polyvinylidene fluoride (PVDF) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a viscosity adjusting solvent.

[0058] The obtained positive electrode active material slurry was applied to both sides of a 20 μm thick aluminum foil serving as a positive electrode current collector, and then dried to form a positive electrode mixture layer. The amount of the positive electrode mixture layer applied per side was 99 g / m. 2 Next, the positive electrode was subjected to press working. After that, it was cut so that the uncoated portion protruded rectangularly from one side of the rectangular portion coated with the positive electrode mixture layer as a positive electrode lead. The protruding portion did not have a positive electrode mixture layer formed thereon, and functioned as a positive electrode lead.

[0059] <Method for producing the negative electrode> A negative electrode active material slurry was prepared by mixing 96.7 wt % graphite as the negative electrode active material, 0.3 wt % acetylene black as the conductive material, 1.5 wt % styrene butadiene rubber as the binder, 1.5 wt % carboxymethyl cellulose as the thickener, and an appropriate amount of ion-exchanged water as the viscosity adjusting solvent.

[0060] The prepared negative electrode active material slurry was applied to both sides of a 10 μm thick copper foil as a negative electrode current collector and dried to form a negative electrode mixture layer, thereby producing a negative electrode. The coating amount of the negative electrode mixture layer per side was 58 g / m. 2 Next, the negative electrode was subjected to press working to set the density of the negative electrode mixture layer to 1.2 g / cm 3Thereafter, the negative electrode mixture layer was formed on the rectangular portion, and the uncoated portion was cut so as to protrude in a rectangular shape from one side of the rectangular portion on which the negative electrode mixture layer was formed. The protruding portion was not formed with the negative electrode mixture layer and functioned as a negative electrode lead.

[0061] <Preparation of non-aqueous electrolyte> A non-aqueous electrolyte solution was prepared by dissolving 1.3 mol / L of LiPF6 as a lithium salt and 3 wt% of vinylene carbonate as an additive in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 2:5:3.

[0062] <Fabrication of electrode element> Next, an electrode element was fabricated by alternately stacking positive electrodes with positive collector leads and negative electrodes with negative collector leads on a zigzag-like separator. The separator consisted of a polyethylene substrate layer with polypropylene surface layers on both sides (PE / PP / PE). The separator was 20 μm thick. The positive and negative electrode leads were then bundled together, and the positive electrode terminal was connected to the bundled positive lead by ultrasonic welding. The negative electrode terminal was also connected to the bundled negative lead by ultrasonic welding. The resulting electrode element had a thickness of 3.0 mm and a rated capacity of 4.8 Ah. The "rated capacity" here refers to the discharge capacity measured when a constant-current-constant-voltage charge (cutoff current: 0.05 C) was performed at an upper voltage of 4.2 V and a current value of 0.5 C, followed by a constant-current discharge at a lower voltage of 2.7 V and a current value of 0.2 C.

[0063] <Fabrication of Non-Aqueous Electrolyte Secondary Battery> Two laminate films were prepared as exterior bodies, each having a structure in which a heat-sealable resin layer made of polyolefin, a metal layer made of aluminum foil, and a protective layer made of nylon resin and polyester resin were laminated in this order. The heat-sealable resin layers of the two laminate films were arranged facing each other, and the laminate films were overlapped with their adhesive surfaces facing each other so that electrode groups could be accommodated in the two accommodating recesses. The electrode groups were arranged so that the portions where the heat-sealable resin parts of each terminal were formed passed between the edges of the two laminate films, leaving a portion of each terminal exposed to the outside. In this state, the heat-sealable resin layers of the laminate films were heat-sealed along the three edges, including the two edges from which the tabs of the laminate films extended. Next, the electrolyte solution prepared above was injected into the one edge of the exterior body that was not heat-sealed. Next, the remaining edge of the exterior body was heat-sealed under reduced pressure to produce a nonaqueous electrolyte secondary battery (cell).

[0064] <Tap density> As specified in JIS standard Z2504:2020, powdered NCM and LMFP were placed in separate containers. The containers were then tapped 100 times to measure the weight divided by the volume of the particles to fill the gaps between them. This was used as the tap density. A shaking specific gravity meter was used for the measurements.

[0065] <Particle size measurement> The median diameter of NCM was the particle diameter (D50) at which the relative particle amount was 50% as measured by the laser diffraction / scattering method described in JIS standard Z8825:2013. Similarly, the D90 of LMFP was the particle diameter (D90) at which the relative particle amount was 90%. Measurements were performed using a laser diffraction particle size distribution analyzer SALD-2300 (Shimadzu Corporation).

[0066] <Initial battery activation> The fabricated cell was transferred to a thermostatic chamber set at 25°C and subjected to five cycles of initial activation. The first cycle consisted of a constant-current / constant-voltage charge with a current of 0.1C, an upper voltage of 4.2V, and a cutoff current of 0.05C, followed by a constant-current discharge with a current of 0.5C and a lower voltage of 2.7V. The second to fifth cycles consisted of a constant-current / constant-voltage charge with a current of 0.2C, a voltage of 4.2V, and a cutoff current of 0.05C, followed by a constant-current discharge with a current of 0.2C and a cutoff voltage of 2.7V. A 15-minute rest period was set after each charge and discharge. After the fifth cycle, the cell was charged at 0.2C for one hour, and the SOC was adjusted to 20%.

[0067] <Measurement of density after initial activation> A separate cell was prepared for the nail penetration test described below, and was initially activated under the same conditions. The cell was then adjusted to 0% SOC by constant-current discharge at a current of 0.5 C and a lower limit voltage of 2.7 V. The cell was then disassembled in an argon-filled glove box and the positive electrode was removed. The density (D) after initial activation was calculated from the thickness of the positive electrode.

[0068] <Nail penetration test> The fabricated nonaqueous electrolyte secondary battery (cell) was previously subjected to constant-current / constant-voltage charging (cutoff current: 0.05C) with a maximum voltage of 4.2V and a current value of 0.5C. A stainless steel nail (3mm diameter) was driven into the center of the cell at a nail penetration rate of 0.1mm / s and a nail penetration depth of 3.0mm, just before penetration. The maximum cell surface temperature (hereafter referred to as "surface temperature") after nail penetration was measured. The cell's appearance was also inspected one hour after nail penetration to confirm the presence of cracks other than the nail penetration area. This test was based on the international standard IEC TR 62660-4, but the nail penetration depth was increased to facilitate heat generation, resulting in a simultaneous short circuit of more positive and negative electrodes. This test simulated a very severe short circuit condition.

[0069] Example 1 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The value of (W1 × R1 + W2 × R2) / D was 0.900. The density of the positive electrode mixture layer immediately after pressing was 2.70 g / cm 3 After the nail penetration test, the cell did not split and the surface temperature was 78°C. [Table 1]

[0070] Example 2 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W2 was 0.800 g / cc and the LMFP D90 was 12.4 μm. The value of (W1 × R1 + W2 × R2) / D was 0.887. After a nail penetration test, the cell split open, and the surface temperature was 122°C.

[0071] Example 3 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W2 was 1.05 g / cc and the LMFP D90 was 9.50 μm. The value of (W1 × R1 + W2 × R2) / D was 0.907. After a nail penetration test, the cell split open, and the surface temperature was 136°C.

[0072] Example 4 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W2 was 0.790 g / cc and the LMFP D90 was 9.70 μm. The value of (W1 × R1 + W2 × R2) / D was 0.886. After a nail penetration test, the cell did not split, and the surface temperature was 94°C.

[0073] Example 5 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W1 was 2.80 g / cc, the density D was 2.55 g / cc, and the D50 of the NCM was 14.0. The value of (W1 × R1 + W2 × R2) / D was 0.954. After a nail penetration test, the cell did not split, and the surface temperature was 98°C.

[0074] Example 6 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The density of the positive electrode mixture layer immediately after pressing was 2.60 g / cc, and the density D after initial activation was 2.48 g / cc. The battery was the same as in Example 1. The value of (W1 × R1 + W2 × R2) / D was 0.932. After a nail penetration test, the cell did not split, and the surface temperature was 104°C.

[0075] Example 7 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The positive electrode mixture layer had the same density as Example 1, with the exception that the density immediately after pressing was 3.00 g / cc and the density D after initial activation was 2.86 g / cc. The value of (W1 × R1 + W2 × R2) / D was 0.808. After a nail penetration test, the cell did not split, and the surface temperature was 74°C.

[0076] Example 8 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the ratio R1 was 0.700, the ratio R2 was 0.300, the density of the positive electrode mixture layer immediately after pressing was 2.5 g / cc, and the density D after initial activation was 2.40 g / cc. The value of (W1 × R1 + W2 × R2) / D was 0.893. After a nail penetration test, the cell did not split, and the surface temperature was 72°C.

[0077] Example 9 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the ratio R1 was 0.900, the ratio R2 was 0.100, the density of the positive electrode mixture layer immediately after pressing was 2.9 g / cc, and the density D after initial activation was 2.76 g / cc. The value of (W1 × R1 + W2 × R2) / D was 0.899. After a nail penetration test, the cell did not split, and the surface temperature was 129°C.

[0078] Example 10 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The tap density W1 was 2.51 g / cc, the density of the positive electrode mixture layer immediately after pressing was 3.00 g / cc, the density D after initial activation was 2.86 g / cc, and the D50 of the NCM was 9.80 μm. The battery was the same as in Example 1. The value of (W1 × R1 + W2 × R2) / D was 0.769. After a nail penetration test, the cell did not split, and the surface temperature was 88°C.

[0079] Example 11 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the ratio R1 was 0.950, the ratio R2 was 0.0500, the density of the positive electrode mixture layer immediately after pressing was 2.90 g / cc, and the density D after initial activation was 2.76 g / cc. The value of (W1 × R1 + W2 × R2) / D was 0.930. After a nail penetration test, the cell split open, and the surface temperature was 142°C.

[0080] Example 12 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W2 was 1.06 g / cc and the LMFP D90 was 14.6 μm. The value of (W1 × R1 + W2 × R2) / D was 0.907. After a nail penetration test, the cell split open, and the surface temperature was 143°C.

[0081] Example 13 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W1 was 2.80 g / cc, the tap density W2 was 1.06 g / cc, the D50 of the NCM was 14.0 μm, and the D90 of the LMFP was 14.6 μm. The value of (W1 × R1 + W2 × R2) / D was 0.954. After a nail penetration test, the cell split open, and the surface temperature was 149°C.

[0082] Example 14 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W1 was 2.69 g / cc, the tap density W2 was 0.690 g / cc, and the LMFP D90 was 7.80 μm. The value of (W1 × R1 + W2 × R2) / D was 0.891. After a nail penetration test, the cell did not split, and the surface temperature was 88°C. However, the positive electrode had numerous streaks, making it unsuitable for continuous production and industrially undesirable.

[0083] (Comparative Example 1) A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The positive electrode mixture layer had the same density as in Example 1, with the exception that the density D immediately after pressing was 2.50 g / cc and the density D after initial activation was 2.40 g / cc. The value of (W1 × R1 + W2 × R2) / D was 0.963. After a nail penetration test, the cell split open, and the surface temperature was 511°C.

[0084] (Comparative Example 2) A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1 except that the tap density W1 was 2.85 g / cc and the D50 of the NCM was 17.3 μm. The value of (W1 × R1 + W2 × R2) / D was 0.962. After a nail penetration test, the cell split open, and the surface temperature was 485°C.

[0085] (Comparative Example 3) A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the ratio R1 was 0.900 and the ratio R2 was 0.100. The value of (W1 × R1 + W2 × R2) / D was 0.965. After a nail penetration test, the cell split open, and the surface temperature was 539°C.

[0086] Comparative Example 4 A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The tap density W1 was 2.85 g / cc, the ratio R1 was 0.700, the ratio R2 was 0.300, the density of the positive electrode mixture layer immediately after pressing was 2.50 g / cc, the density D after initial activation was 2.36 g / cc, and the D50 of the NCM was 17.3 μm. The battery was the same as in Example 1. The value of (W1 × R1 + W2 × R2) / D was 0.967. After a nail penetration test, the cell split open, and the surface temperature was 601°C.

[0087] (Comparative Example 5) A nonaqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. The battery was the same as in Example 1, except that the tap density W1 was 2.80 g / cc, the tap density W2 was 1.21 g / cc, the density D was 2.57 g / cc, and the NCM D50 was 14.0 μm. The value of (W1 × R1 + W2 × R2) / D was 0.966. After a nail penetration test, the cell split open, and the surface temperature was 574°C.

[0088] If the value of (W1×R1+W2×R2) / D is less than 0.760, the positive electrode mixture layer will be too dense, which may cause distortion in the electrode during the pressing process when producing the electrode, reducing the production efficiency during battery production. Therefore, this was not implemented.

[0089] As shown in Table 1, in Examples 1 to 14, the surface temperature after nail penetration was 149°C or lower. On the other hand, in Comparative Examples 1 to 5, the cells split and the surface temperature was as high as 485°C or higher. It is believed that in Comparative Examples 1 to 5, separator meltdown occurred, causing a short circuit inside the cell and resulting in a chain reaction of heat generation. From these results, it can be said that Examples 1 to 14 suppressed heat generation during a short circuit and had thermal stability. Among them, Examples 1 and 4 to 10 did not pose any industrial problems and no cell splitting was observed, so it can be said that they had particularly excellent thermal stability. [Explanation of symbols]

[0090] 1, 1A non-aqueous electrolyte secondary battery 2. Exterior body 3 electrode groups 4, 118 positive electrode 5, 115 negative electrode 6, 114 Separator 7 Positive lead 8 Positive tab 9 Negative lead 10 Negative electrode tab 41, 112 Positive electrode current collector 42, 113 Positive electrode mixture layer 51 Negative electrode current collector 52 negative electrode mixture layer 110 cases 111 Leaf spring 116 Gasket 117 Cap

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery, comprising: a positive electrode current collector; and a positive electrode mixture layer formed on a surface of the positive electrode current collector, The positive electrode mixture layer is a first positive electrode active material that is a layered compound represented by the following general formula (1); Li ａ Ni ｘ Co ｙ M1 １－ｘ－ｙ O ２ (where 0<a≦1.2, 0<x≦0.9, 0<y≦0.5, 0<x+y<1) ... (1) a second positive electrode active material in which a coating film made of a carbon material is formed on a surface of a phosphate compound having an olivine structure, the second positive electrode active material being represented by the following general formula (2): LiMn ｚ M2 ｂ Fe １－z－ｂ P.O. ４ (where 0<z≦0.9, 0≦b≦0.1, 0<z+b<1) ... (2) A conductive material; Including, When the tap density (g / cc) of the first positive electrode active material is W1, the tap density (g / cc) of the second positive electrode active material is W2, the weight ratio of the first positive electrode active material when the total weight of the first and second positive electrode active materials is 1 is R1, the weight ratio of the second positive electrode active material when the total weight of the first and second positive electrode active materials is 1 is R2, and the density (g / cc) of the positive electrode mixture layer calculated based on the thickness of the positive electrode for a nonaqueous electrolyte secondary battery when the charge rate of the nonaqueous electrolyte secondary battery after initial activation treatment is 0%, the following formula (3) is satisfied: 0.760≦(W1×R1+W2×R2) / D≦0.960 (3) A positive electrode for a non-aqueous electrolyte secondary battery. In the above formula (1), M1 is at least one selected from Ti, Zr, Nb, W, P, Al, Mg, V, Mn, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, Cu, Ag, Ce, Pr, Ge, Bi, Ba, Er, La, Sm, Yb, Sb, Bi, S, and Zn; In the above formula (2), M2 is at least one selected from Ni, Co, Ti, Cu, Zn, Mg, Zr, Ca, Y, Mo, Ba, Pb, Bi, La, Ce, Nd, Gd, Al, Ga, and Sr.

2. The median diameter of the first positive electrode active material is larger than D90 of the second positive electrode active material.

2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1.

3. The second positive electrode active material has a tap density W2 of 0.7 g / cc or more and 1.00 g / cc or less.

3. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2.

4. The weight ratio R2 is 0.1 or more and 0.3 or less.

4. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1.

5. The positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, a negative electrode; A separator; a non-aqueous electrolyte solution containing a lithium salt and a non-aqueous solvent; A non-aqueous electrolyte secondary battery comprising:

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