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 even if a steep short circuit occurs.SOLUTION: A positive electrode for a nonaqueous electrolyte secondary battery includes a positive electrode collector, and a positive electrode mixture layer that is formed on a surface of the positive electrode collector. The positive electrode mixture layer includes: a first positive electrode active material, which is a layered compound represented by a following formula (1); a second positive electrode active material which is represented by a following formula (2) and in which a film comprising a carbon material is formed on a surface of a phosphoric acid compound that has an olivine structure; and a conductive material. A value of a ratio of a specific surface area of the first positive electrode active material to a specific surface area of the second positive electrode active material is 0.005 or more and 0.025 or less. LiaNixCoyM11-x-yO2 (0<a≤1.2, 0<x≤0.9, 0<y≤0.5, 0<x+y<1)...(1) LiMnzM2bFe1-z-bPO4 (0<z≤0.9, 0≤b≤0.1, 0<z+b<1)...(2)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 in which a portion of the LiFePO4 is substituted with Mn; LiCoO2, LiNiO2, LiMnO2, LiCoNiO2, LiCoMO2, and LiNiMO2, 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 in which a portion of the LiFePO4 is substituted with Mn. Olivine compounds in which a portion of LiFePO4 is 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, in order to obtain thermal stability, an olivine compound having a particle size of about 0.1 to 3 μm and occupying a volume fraction of 5 to 100% in a positive electrode active material is mixed with a layered compound such as a lithium metal oxide. Also, in Patent Document 2, a layered compound is mixed with an olivine compound having an average particle size smaller than that of the layered compound in a positive electrode active material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6813487 [Patent Document 2] Patent No. 5574239 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the inventors of the present application have conducted research and found that these prior art technologies are insufficient in terms of the safety against sudden short circuits that is required of recent nonaqueous electrolyte secondary batteries. In particular, when multiple nonaqueous electrolyte secondary batteries are connected in parallel to form a battery pack, the resistance of the entire battery pack is reduced. Therefore, even if the same short circuit occurs, a short-circuit current tends to flow more rapidly than when a single nonaqueous electrolyte secondary battery is used. Therefore, a solution has been sought. Specifically, if the temperature of a nonaqueous electrolyte secondary battery becomes high enough to ensure separator meltdown, further short circuits will occur within the nonaqueous electrolyte secondary battery, leading to a chain reaction of heat generation. Therefore, there is a need for a nonaqueous electrolyte secondary battery that can suppress heat generation even when a sudden short circuit occurs.

[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 suppresses heat generation even when a sudden short circuit occurs. [Means for solving the problem]

[0008] In order to solve the above 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), and a second positive electrode active material that is represented by the general formula shown in the following formula (2) and has a coating made of a carbon material formed on the surface of a phosphate compound having an olivine structure, and a conductive material, and a value of a ratio of the specific surface area of the first positive electrode active material to the specific surface area of the second positive electrode active material is 0.005 or more and 0.025 or less. Li a Ni x Co y M1 1-x-y O2···(1) LiMn z M2 b Fe 1-z-b PO4···(2) 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, 0 < z + b < 1.

[0009] 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 second positive electrode active material has a tap density of 0.7 g / cc or more and 1.00 g / cc or less.

[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 a median diameter of the second positive electrode active material is 1 / 100 or more and 1 / 5 or less of a median diameter of the first positive electrode active material.

[0011] In the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, the second positive electrode active material may have a median diameter of 0.1 μm or more and 1.0 μm or less.

[0012] In addition, in the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, in the above invention, the ratio of the weight of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material may be 10% or more and 30% or less.

[0013] A 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 solution containing a lithium salt and a non-aqueous solvent. [Effects 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 even when a sudden short circuit occurs. [Brief explanation of the drawings]

[0015] [Figure 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. [Figure 2] FIG. 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. DETAILED DESCRIPTION OF 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 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 (1) below. The layered compound is a lithium (Li), nickel (Ni), and cobalt (Co)-containing composite metal oxide composed of layers of sheet-like particles. 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, and 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-based 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.

[0026] The carbon material is an electrically conductive carbon material. The second positive electrode active material has a coating of the carbon material present on the surface of the second positive electrode active material, and at least a portion of the surface of at least some of the primary particles is coated with the carbon material. The purity of the carbon and the thickness of the carbon coating can be selected arbitrarily, but it is preferable to control the weight ratio of the carbon material to the total weight of the second positive electrode active material so that it is 0.1% or more and 5% or less.

[0027] In prior art such as those described in Patent Documents 1 and 2, attention has often been focused on the particle size of the first and second positive electrode active materials to suppress heat generation during a short circuit. However, through extensive research by the present inventors, it has become clear that the specific surface area, rather than the particle size, of each positive electrode active material is important. Generally, even positive electrode active materials with roughly the same particle size can have significantly different specific surface areas depending on their shape, and therefore, simply controlling the particle size alone does not produce the desired results. Here, when the specific surface area of ​​the first positive electrode active material is S1 and the specific surface area of ​​the second positive electrode active material is S2, the ratio of the specific surface area S1 to the specific surface area S2 (S1 / S2) is 0.005 or more and 0.025 or less. More preferably, it is 0.010 or more and 0.020 or less. When the ratio S1 / S2 is 0.025 or less, i.e., when the specific surface area of ​​the second positive electrode active material is significantly larger than that of the first positive electrode active material, the second positive electrode active material is likely to surround the first positive electrode active material in the positive electrode mixture layer 42. This minimizes the exothermic reaction between the first positive electrode active material and the nonaqueous electrolyte, even during a sudden short circuit, thereby suppressing heat generation in the nonaqueous electrolyte secondary battery. Note that the specific surface area is the surface area per unit area. When the ratio S1 / S2 is less than 0.005, i.e., when the specific surface area of ​​the second positive electrode active material is significantly larger than that of the first positive electrode active material, the second positive electrode active material is less dispersible and more likely to aggregate during the preparation of the slurry for the positive electrode mixture layer 42. It is believed that the aggregation deteriorates the mixed state of the first and second positive electrode active materials, making it impossible for the second positive electrode active material to surround the first positive electrode active material as tightly as in conventional cases, and therefore heat generation during short circuiting cannot be sufficiently suppressed.Furthermore, when the ratio S1 / S2 is greater than 0.025, it is believed that the second positive electrode active material cannot surround the first positive electrode active material as tightly as in conventional cases, making it impossible to sufficiently suppress heat generation during short circuiting.

[0028] 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. This is thought to enable them to surround the first positive electrode active material more tightly than conventional particles, 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 surround the first positive electrode active material. This makes it difficult to prevent temperature rise in the non-aqueous electrolyte secondary battery during short circuit, and makes 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.

[0029] The median diameter of the second positive electrode active material is preferably 1 / 100 to 1 / 5 of the median diameter of the first positive electrode active material. Furthermore, the median diameter of the second positive electrode active material is preferably 0.1 μm to 1.0 μm. When these requirements are met, the second positive electrode active material is believed to surround the first positive electrode active material more tightly than conventional materials, further suppressing heat generation due to thermal runaway during a short circuit. Therefore, not only is the temperature of the nonaqueous electrolyte secondary battery less likely to rise during a short circuit, but swelling, cracking, or rupture due to decomposition of the electrolyte on the surface of the first positive electrode active material due to temperature rise is also less likely to occur. If the median diameter of the second positive electrode active material is significantly smaller than that of the first positive electrode active material, the dispersibility of the second positive electrode active material decreases during the preparation of the slurry for the positive electrode mixture layer 42, leading to aggregation and the occurrence of streaks during the preparation of the positive electrode, making it difficult to produce a positive electrode of uniform quality. Furthermore, if the median diameter of the second positive electrode active material is less than 0.1 μm, the crystallinity of the second positive electrode active material itself tends to be extremely low, making material synthesis itself difficult. If the median diameter of the second positive electrode active material is 1 / 20 or more (1 / 5 or less) of the median diameter of the first positive electrode active material, or if the median diameter of the second positive electrode active material is 0.5 μm or more, the dispersibility of the second positive electrode active material during the preparation of the slurry is improved. Note that the median diameter is sometimes referred to as D50 in this specification.

[0030] Furthermore, the weight ratio of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material is preferably 10% or more and 30% or less. If the weight ratio of the second positive electrode active material exceeds 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 practicality. If the weight ratio of the second positive electrode active material is below 10%, it becomes difficult for the second positive electrode active material to sufficiently surround the first positive electrode active material.

[0031] The above-mentioned median diameter, tap density, and specific surface area refer to values ​​within 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, tap density, and specific surface area 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, tap density, and specific surface area 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.

[0032] Whether the median diameter 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 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 by, for example, placing the materials in a container, tapping the container, and measuring the weight divided by the volume of 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.

[0033] 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).

[0034] 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.

[0035] 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).

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] In the present embodiment 1, in the positive electrode 4 of the nonaqueous electrolyte secondary battery 1, the positive electrode mixture layer 42 has a first positive electrode active material represented by general formula (1) and a second positive electrode active material containing a compound represented by general formula (2), and has a specific surface area S1, and the ratio S1 / S2 of the specific surface area S1 of the first positive electrode active material to the specific surface area S2 of the second positive electrode active material is set to 0.005 or more and 0.025 or less. By satisfying the above conditions in the positive electrode mixture layer 42, the second positive electrode active material coats the first positive electrode active material, and decomposition of the electrolyte on the surface of the first positive electrode active material is suppressed, making thermal runaway less likely to occur during a short circuit. According to the present embodiment 1, a positive electrode 4 and a nonaqueous electrolyte secondary battery 1 can be obtained that suppress heat generation even when a sudden short circuit occurs.

[0048] (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.

[0049] 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.

[0050] 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 .

[0051] 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.

[0052] The nonaqueous electrolyte may be the same as that of the first embodiment.

[0053] The negative electrode 115 has the same configuration as the negative electrode 5 .

[0054] In the present second embodiment, in the positive electrode 118 of the nonaqueous electrolyte secondary battery 1A, the positive electrode mixture layer 113 has a first positive electrode active material represented by general formula (1) and a second positive electrode active material containing a compound represented by general formula (2), and has a specific surface area S1, and a ratio S1 / S2 of the specific surface area S1 of the first positive electrode active material to the specific surface area S2 of the second positive electrode active material is set to 0.005 or more and 0.025 or less. According to the present second embodiment, similar to the first embodiment, it is possible to obtain the positive electrode 118 and the nonaqueous electrolyte secondary battery 1A that suppress heat generation even when a sudden short circuit occurs. [Example]

[0055] 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.

[0056] <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.

[0057] 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 to set the density of the positive electrode mixture layer to 2.7 g / cm. 3 Thereafter, the positive electrode mixture layer was applied to the rectangular portion of the positive electrode sheet, and the uncoated portion was cut so as to protrude in a rectangular shape as a positive electrode lead from one side of the rectangular portion coated with the positive electrode mixture layer. The protruding portion was not formed with the positive electrode mixture layer and functioned as a positive electrode lead.

[0058] <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.

[0059] 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 3 Thereafter, 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.

[0060] <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.

[0061] <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, and the negative electrode terminal was connected to the bundled negative lead by ultrasonic welding. The fabricated 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.

[0062] <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).

[0063] <Calculation of specific surface area> The specific surface area of ​​each positive electrode active material was calculated by applying the BET equation to the values ​​measured by the nitrogen adsorption method. The specific surface area of ​​NCM was designated S1, and the specific surface area of ​​LMFP was designated S2.

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

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

[0066] <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.

[0067] 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 ratio of the specific surface areas of NCM and LMFP (hereinafter simply referred to as the "ratio") (S1 / S2) was 0.018. After a nail penetration test, the cell did not split, and the surface temperature was 78°C. [Table 1]

[0068] 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. 2 / g, and the D50 of the NCM was 14.0 μm. The ratio (S1 / S2) was 0.012. After the nail penetration test, the cells were not ruptured and the surface temperature was 69°C.

[0069] 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. 2 The same as in Example 1 except that the LMFP had a tap density of 0.78 g / cc and a D50 of 0.80 μm. The ratio (S1 / S2) was 0.015. After the nail penetration test, the cells were not ruptured and the surface temperature was 81°C.

[0070] 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. 2 The same as in Example 1 except that the LMFP had a tensile strength of 1.04 g / cc, a tap density of 1.04 g / cc, and a D50 of 1.00 μm. The ratio (S1 / S2) was 0.019. After the nail penetration test, the cell ruptured and the surface temperature was 124°C.

[0071] 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. 2 The same as in Example 1 except that the tensile strength of the LMFP was 0.90 g / cc, the tap density of the LMFP was 0.90 g / cc, and the D50 of the NCM was 4.9 μm. The ratio (S1 / S2) was 0.020. After the nail penetration test, there was no cell rupture, and the surface temperature was 86°C.

[0072] 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.2 / g, specific surface area S2 is 20.6m 2 / g, and the D50 of the NCM was 4.3 μm. The ratio (S1 / S2) was 0.020. After the nail penetration test, the cell ruptured and the surface temperature was 119°C.

[0073] 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. 2 The same as in Example 1, except that the density of the NCM was 0.91 g / cc, the tap density of the LMFP was 0.91 g / cc, the D50 of the NCM was 21.3 μm, and the D50 of the LMFP was 1.50 μm. The ratio (S1 / S2) was 0.016. After the nail penetration test, the cell ruptured and the surface temperature was 135°C.

[0074] Example 8 A non-aqueous electrolyte secondary battery was fabricated using a positive electrode having the physical properties shown in Table 1 as the positive electrode mixture layer. 2 The same as in Example 1 except that the tensile strength of the NCM was 8.1 μm and the D50 of the NCM was 8.1 μm. The ratio of the specific surface areas of the NCM and the LMFP (S1 / S2) was 0.025. After the nail penetration test, the cells did not rupture and the surface temperature was 106°C.

[0075] 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. 2 / g, specific surface area S2 is 23.8m 2 The same as in Example 1, except that the tap density of the LMFP was 0.78 g / cc, the D50 of the NCM was 18.3 μm, and the D50 of the LMFP was 0.80 μm. The ratio of the specific surface areas of the NCM and LMFP (S1 / S2) was 0.005. After the nail penetration test, the cells did not rupture, and the surface temperature was 103°C.

[0076] 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. 2The same as in Example 1, except that the NCM had a tensile strength of 0.79 g / cc, the tap density of the LMFP was 0.79 g / cc, and the D50 of the LMFP was 0.50 μm. The ratio of the specific surface areas (S1 / S2) of the NCM and the LMFP was 0.014. After the nail penetration test, the cells did not rupture, and the surface temperature was 86°C.

[0077] 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 procedure was the same as in Example 1, except that the proportion of LMFP was 5%. The ratio of the specific surface areas of NCM and LMFP (S1 / S2) was 0.018. After a nail penetration test, the cell did not split, and the surface temperature was 136°C.

[0078] 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 procedure was the same as in Example 1, except that the proportion of LMFP was 10%. The ratio of the specific surface areas of NCM and LMFP (S1 / S2) was 0.018. After a nail penetration test, the cell did not split, and the surface temperature was 107°C.

[0079] 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 procedure was the same as in Example 1, except that the proportion of LMFP was 30%. The ratio of the specific surface areas of NCM and LMFP (S1 / S2) was 0.018. After a nail penetration test, the cell did not split, and the surface temperature was 69°C.

[0080] 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. 2 / g, specific surface area S2 is 24.5m 2 The same as in Example 1, except that the tap density of the LMFP was 1.02 g / cc, the D50 of the NCM was 14.0 μm, and the D50 of the LMFP was 5.20 μm. The ratio of the specific surface areas of the NCM and LMFP (S1 / S2) was 0.009. After the nail penetration test, the cell ruptured and the surface temperature was 151°C.

[0081] Example 15 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. 2 / g, specific surface area S2 is 22.7m 2 The same as in Example 1, except that the tap density of the LMFP was 1.05 g / cc, the D50 of the NCM was 14.0 μm, and the D50 of the LMFP was 4.80 μm. The ratio of the specific surface areas of the NCM and LMFP (S1 / S2) was 0.010. After the nail penetration test, the cell ruptured and the surface temperature was 146°C.

[0082] Example 16 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. 2 / g, specific surface area S2 is 16.2m 2 The same as in Example 1, except that the tap density of the LMFP was 1.06 g / cc, the D50 of the NCM was 14.0 μm, and the D50 of the LMFP was 3.70 μm. The ratio of the specific surface areas of the NCM and LMFP (S1 / S2) was 0.014. After the nail penetration test, the cell ruptured and the surface temperature was 139°C.

[0083] Example 17 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. 2 / g, specific surface area S2 is 12.4m 2 The same as in Example 1, except that the tap density of the LMFP was 1.09 g / cc, the D50 of the NCM was 14.0 μm, and the D50 of the LMFP was 3.20 μm. The ratio of the specific surface areas of the NCM and LMFP (S1 / S2) was 0.019. After the nail penetration test, the cell ruptured and the surface temperature was 143°C.

[0084] Example 18 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. 2 / g, specific surface area S2 is 11.2m 2The same as in Example 1, except that the tap density of the LMFP was 1.11 g / cc, the D50 of the NCM was 14.0 μm, and the D50 of the LMFP was 2.90 μm. The ratio of the specific surface areas of the NCM and LMFP (S1 / S2) was 0.021. After the nail penetration test, the cell ruptured and the surface temperature was 152°C.

[0085] Example 19 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. 2 The results are the same as in Example 1, except that the NCM had a 0.69 g / cc tap density and a 0.80 μm D50 of the LMFP. The ratio of the specific surface areas of the NCM and the LMFP (S1 / S2) was 0.014. After the nail penetration test, the cell did not split open, and the surface temperature was 87°C. However, the positive electrode had numerous streaks, making it unsuitable for continuous production and industrially undesirable.

[0086] Example 20 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. 2 / g, specific surface area S2 is 25.6m 2 The results are the same as in Example 1, except that the tap density of the LMFP was 0.79 g / cc, the D50 of the NCM was 51.4 μm, and the D50 of the LMFP was 0.50 μm. The ratio of the specific surface areas of the NCM and LMFP (S1 / S2) was 0.008. After a nail penetration test, the cell did not split open, and the surface temperature was 75°C. However, the positive electrode had numerous streaks, making it unsuitable for continuous production and industrially undesirable.

[0087] (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. 2 / g, and the D50 of the NCM was 6.2 μm. The ratio (S1 / S2) was 0.029. After the nail penetration test, the cell ruptured and the surface temperature was 522°C.

[0088] (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. 2 The same as in Example 1 except that the LMFP had a tensile strength of 1.08 g / cc, a tap density of 1.08 g / cc, and a D50 of 1.10 μm. The ratio (S1 / S2) was 0.027. After the nail penetration test, the cell ruptured and the surface temperature was 451°C.

[0089] (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. 2 / g, specific surface area S2 is 30.1m 2 The same as in Example 1, except that the tap density of the LMFP was 1.04 g / cc, the D50 of the NCM was 18.3 μm, the tap density of the LMFP was 1.04 g / cc, and the D50 of the LMFP was 2.40 μm. The ratio (S1 / S2) was 0.004. After the nail penetration test, the cell ruptured and the surface temperature was 498°C.

[0090] As shown in Table 1, in Examples 1 to 20, the surface temperature after nail penetration was 152°C or lower. On the other hand, in Comparative Examples 1 to 3, the cells split and the surface temperature was as high as 451°C or higher. It is believed that in Comparative Examples 1 to 3, 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 20 suppressed heat generation even when a sudden short circuit occurred and have thermal stability. Among them, Examples 1 to 3, 5, 8 to 10, 12, and 13 did not pose any industrial problems and no cell splitting was observed, so it can be said that they have particularly excellent thermal stability. [Explanation of symbols]

[0091] 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, a ratio of the specific surface area of ​​the first positive electrode active material to the specific surface area of ​​the second positive electrode active material is 0.005 or more and 0.025 or less; 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 second positive electrode active material has a tap density of 0.7 g / cc or more and 1.00 g / cc or less.

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

3. the median diameter of the second positive electrode active material is 1 / 100 or more and 1 / 5 or less of the median diameter of the first positive electrode active material; 3. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 or 2.

4. The median diameter of the second positive electrode active material is 0.1 μm or more and 1.0 μm or less.

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

5. a ratio of the weight of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material is 10% or more and 30% or less; 5. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1.

6. The positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, 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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