Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery is characterized by having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the positive electrode mixture layer includes a positive electrode active material and a dielectric, and the ratio (D50 of the dielectric / D50 of the positive electrode active material) of a volume-based median diameter (D50) of the dielectric to a volume-based median diameter (D50) of the positive electrode active material is 0.15-0.6.

Description

[Technical Field]

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

[0002] In recent years, non-aqueous electrolyte secondary batteries, which consist of a positive electrode, a negative electrode, and a non-aqueous electrolyte, and perform charging and discharging by moving lithium ions and other elements between the positive and negative electrodes, have been widely used as high-power, high-energy-density secondary batteries.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery equipped with a positive electrode material in which barium titanate, a dielectric, is present on the surface of the positive electrode active material. Furthermore, it is stated that the non-aqueous electrolyte secondary battery disclosed in Patent Document 1 has reduced interfacial resistance due to the presence of barium titanate on the surface of the positive electrode active material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-116129 [Overview of the Initiative]

[0005] Incidentally, when mixing dielectric and positive electrode active material during the manufacturing of a positive electrode, the dielectric may aggregate and not disperse uniformly. Furthermore, since the dielectric itself has insulating properties, a battery with a positive electrode where the dielectric is unevenly distributed may have high charge transfer resistance.

[0006] Therefore, the present disclosure aims to provide a non-aqueous electrolyte secondary battery with low charge transfer resistance.

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode composite layer provided on the positive electrode current collector, the positive electrode composite layer comprises a positive electrode active material and a dielectric, and the ratio of the volume-based median diameter (D50) of the dielectric to the volume-based median diameter (D50) of the positive electrode active material (D50 of the dielectric / D50 of the positive electrode active material) is 0.15 or more and 0.6 or less.

[0008] According to one aspect of this disclosure, a non-aqueous electrolyte secondary battery with low charge transfer resistance can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. [Figure 2] This figure shows the relative charge transfer resistances of the batteries in each embodiment and other comparative examples, with the charge transfer resistance of the battery in Comparative Example 1 set to 1. [Modes for carrying out the invention]

[0010] An example of an embodiment will be described in detail below. The drawings referenced in the description of the embodiment are schematic representations, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual objects.

[0011] Figure 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. The non-aqueous electrolyte secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, a non-aqueous electrolyte, insulating plates 18 and 19 arranged above and below the electrode body 14, respectively, and a battery case having a case body 16 and a sealing body 17 for housing the above components. In addition, other forms of electrode bodies may be used instead of the wound electrode body 14, such as a laminated electrode body in which the positive electrode and negative electrode are alternately stacked with a separator. Examples of battery cases include metal cases such as cylindrical, rectangular, coin-shaped, and button-shaped cases, and resin cases formed by laminating resin sheets (so-called laminated type).

[0012] The case body 16 is, for example, a metal container in the shape of a bottomed cylinder. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22 that supports the sealing body 17, which is a part of the side surface that protrudes inward. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and its upper surface supports the sealing body 17.

[0013] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the non-aqueous electrolyte secondary battery 10 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0014] In the non-aqueous electrolyte secondary battery 10 shown in FIG. 1, the positive electrode lead 20 attached to the positive electrode 11 extends toward the sealing body 17 through the through hole of the insulating plate 18, and the negative electrode lead 21 attached to the negative electrode 12 extends toward the bottom side of the case body 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the filter 23 which is the bottom plate of the sealing body 17 by welding or the like, and the cap 27 which is the top plate of the sealing body 17 electrically connected to the filter 23 serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the case body 16 by welding or the like, and the case body 16 serves as the negative electrode terminal.

[0015] [Positive Electrode] The positive electrode 11 includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. It is desirable that the positive electrode mixture layer be disposed on both sides of the positive electrode current collector.

[0016] For the positive electrode current collector, a foil of a metal stable within the potential range of the positive electrode such as aluminum or an aluminum alloy, a film having the metal disposed on the surface layer, etc. can be used. The positive electrode current collector has a thickness of, for example, about 10 μm to 100 μm.

[0017] The positive electrode mixture layer contains a positive electrode active material and a dielectric. It is preferable that the positive electrode mixture layer contain a binder in terms of binding the positive electrode active materials together to ensure the mechanical strength of the positive electrode mixture layer. Also, it is preferable that the positive electrode mixture layer contain a conductive material in terms of improving the conductivity of the layer.

[0018] The positive electrode 11 is produced, for example, as follows. First, a positive electrode active material, a dielectric, a binder, a conductive material, etc. are mixed, and this mixture is dispersed in a solvent to prepare a positive electrode mixture slurry. Then, this positive electrode mixture slurry is applied onto the positive electrode current collector, the coating film is dried, and then this coating film is rolled to produce the positive electrode 11.

[0019] The ratio of the median diameter (D50) of the dielectric to the median diameter (D50) of the positive electrode active material (D50 of dielectric / D50 of positive electrode active material) is 0.15 or more and 0.6 or less, preferably 0.26 or more and 0.45 or less. As mentioned above, when mixing the dielectric and positive electrode active material to manufacture the positive electrode, the dielectric may be unevenly distributed. Since the dielectric itself has insulating properties, uneven distribution of the dielectric in the positive electrode composite layer may increase the charge transfer resistance of the battery. However, by setting the D50 of dielectric / D50 of positive electrode active material within the above range, it is presumed that the uneven distribution of the dielectric is suppressed compared to cases outside the above range, and the dielectric is dispersed to a certain extent evenly in the positive electrode composite layer. As a result, for example, it is thought that lithium ions in the non-aqueous electrolyte are attracted to the vicinity of the positive electrode active material by the dielectric polarization of the dielectric, and the intercalation and release of lithium ions in the positive electrode active material are promoted, thereby reducing the charge transfer resistance of the battery.

[0020] In this disclosure, the volume-based median diameter (D50) refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% of the volume-based particle size distribution, and is also called the median diameter. The particle size and particle size distribution of the positive electrode active material and dielectric can be measured using a laser diffraction particle size distribution analyzer (for example, the MT3000II manufactured by Microtrac-Bell Corporation).

[0021] The volume-based median diameter (D50) of the positive electrode active material is preferably 5 μm to 20 μm, and more preferably 8 μm to 18 μm, in order to further reduce the charge transfer resistance of the battery.

[0022] The positive electrode active material is not particularly limited as long as it is a lithium composite oxide that can reversibly insert and remove lithium, but it is preferable to include a lithium composite oxide represented by the following general formula (1) in terms of increasing the battery capacity and having excellent charge-discharge cycle characteristics. Li a Ni b Co (1-b-c) Al c W d O e (1) In the formula, 0.9 < a ≤ 1.2, 0.88 ≤ b ≤ 0.96, 0.04 ≤ c ≤ 0.12, 1.9 ≤ e ≤ 2.1, and when W / (Ni + Co + Al + W) = d, it is preferable that 0.0003 ≤ d ≤ 0.002. The composition of the lithium composite oxide can be measured by inductively coupled plasma (ICP) emission spectroscopy.

[0023] A dielectric is a substance that is more dielectric than conductive and can be said to be an insulator against a DC voltage. Examples of dielectrics include composite oxides having a crystal structure of any of the XYO3 type, X2Y2O7 type, and XX’3Y4O 12 type. X is one or more elements selected from alkali metal elements (e.g., Group 1 elements such as Na, K, Rb, Cs, etc.), alkaline earth metal elements (e.g., Group 2 elements such as Ca, Sr, Ba, etc.), rare earth metal elements (e.g., La, Ce, Nd, Sm, Gd, Yb, etc.), Cu, Pb, and Bi. X’ is, for example, one or more elements selected from transition metal elements and is an element different from X. Y is one or more elements selected from transition metal elements and Sn. The transition metal elements are, for example, elements belonging to Groups 3 to 11 of the IUPAC classification. For example, Group 4 elements (e.g., Ti, Zr, Hf, etc.), Group 5 elements (e.g., V, Nb, Ta, etc.), Group 6 elements (Cr, Mo, W, etc.), Group 7 elements (Mn, Tc, etc.), Group 8 elements (Fe, Ru, Os, etc.), Group 9 elements (Co, Rh, Ir, etc.), Group 10 elements (Ni, Pd, Pt, etc.), Group 11 elements (Cu, Ag, Au, etc.), and rare earth metal elements (La, Ce, Sm, etc.) can be mentioned. Also, Y preferably contains an element different from X, and more preferably consists of an element different from X. Particularly preferred dielectrics include, for example, BaTiO3, etc. The crystal structure of the dielectric can be confirmed by XRD measurement using CuKα rays.

[0024] The relative permittivity of the dielectric is preferably 8 or more and 500 or less, and more preferably 50 or more and 500 or less. Also, the volume resistivity at 20°C is preferably 1 × 10 5 Ω·m or more, and preferably 1 × 10 6It is more preferable that it be Ω·m or greater, 1 × 10 10 It is more preferable that the value be Ω·m or greater.

[0025] The dielectric content is preferably 2% by mass or less, and more preferably 1% by mass or less, relative to the mass of the positive electrode active material. If the dielectric content exceeds 2% by mass relative to the mass of the positive electrode active material, it may lead to a decrease in battery capacity compared to when it is 2% by mass or less. The lower limit of the dielectric content is not particularly limited, but in terms of effectively reducing the charge transfer resistance of the battery, it may be, for example, 0.1% by mass or more relative to the mass of the positive electrode active material.

[0026] Examples of conductive materials included in the positive electrode composite layer include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. These may be used individually or in combination of two or more types. The content of the conductive material in the positive electrode composite layer is preferably 0.5% by mass or more and 4% by mass or less, and more preferably 0.5% by mass or more and 1.5% by mass or less.

[0027] Examples of binders included in the positive electrode composite layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), polyethylene oxide (PEO), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types. The binder content in the positive electrode composite layer is preferably, for example, 0.5% by mass or more and 4% by mass or less, and more preferably 0.5% by mass or more and 1.5% by mass or less.

[0028] [Negative electrode] The negative electrode 12 is composed of, for example, a negative electrode current collector and a negative electrode composite layer formed on the current collector. The negative electrode current collector can be made of a metal foil that is stable in the negative electrode potential range, such as copper, or a film on which the metal is arranged on the surface. The negative electrode composite layer includes, for example, a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, as follows: First, the negative electrode active material, binder, etc. are mixed, and this mixture is dispersed in a solvent to prepare a negative electrode composite slurry. This negative electrode composite slurry is applied to the negative electrode current collector, the coating is dried, and then the coating is rolled to manufacture the negative electrode 12.

[0029] The negative electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions. Examples include lithium alloys such as metallic lithium, lithium-aluminum alloys, lithium-lead alloys, lithium-silicon alloys, and lithium-tin alloys; carbon materials such as graphite, coke, and calcined organic materials; and metal oxides such as SnO2, SnO, and TiO2. These can be used individually or in combination of two or more.

[0030] The binders included in the negative electrode composite layer are the same as those in the positive electrode: fluororesins, PAN, polyimide resins, acrylic resins, polyolefin resins, SBR, CMC or their salts, PAA or its salts, PEO, PVA, etc. The negative electrode composite layer may also contain a conductive material, similar to the positive electrode.

[0031] [Separator] For example, a porous sheet having ion permeability and insulating properties can be used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The separator 13 is composed of, for example, polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may also be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as polyolefin. Furthermore, the separator 13 may be a multilayer separator containing a polyethylene layer and a polypropylene layer, and may have a surface layer composed of aramid resin or a surface layer containing an inorganic filler.

[0032] [Non-aqueous electrolytes] Non-aqueous electrolytes comprise a non-aqueous solvent and an electrolyte salt. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may also contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine.

[0033] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone; and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.

[0034] Examples of the above ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methylphenyl ether. Examples include chain ethers such as ethylphenyl ether, butylphenyl ether, pentylphenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0035] Examples of the above nitriles include acetonitrile, propionitrile, butyronitrile, valeronitrile, n-heptanitrile, succinonitrile, glutalonitrile, adibonitrile, pimeronitrile, 1,2,3-propanetricarbonitride, and 1,3,5-pentanetricarbonitride.

[0036] Examples of the halogen-substituted compounds mentioned above include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0037] Examples of electrolyte salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C nF 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), LiN(SO2CF3)2, LiN(C l F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 1 or more}, and imide salts such as these may be mentioned. The electrolyte salt may be used alone of these, or may be used in mixture of multiple kinds. The concentration of the electrolyte salt is, for example, 0.8 to 1.8 mol per 1 L of non-aqueous solvent.

Example

[0038] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0039] <Example 1> [Production of positive electrode active material] LiNi 0.91 Co 0.04 Al 0.05 Particles of lithium composite oxide A having a layered structure represented by O2, and tungsten oxide (WO3) were mixed at a predetermined ratio and then heat-treated to obtain lithium composite oxide B containing a tungsten compound. This lithium composite oxide B was used as the positive electrode active material. The median diameter (D50) on a volume basis of this positive electrode active material was 12.0 μm. In addition, the addition amount of the tungsten compound was 0.08 atomic% in terms of tungsten element with respect to the total molar amount of the metal elements excluding lithium in lithium composite oxide A.

[0040] [Production of positive electrode] A positive electrode slurry was prepared by mixing 100 parts by mass of positive electrode active material, 1 part by mass of acetylene black as a conductive material, 1 part by mass of polyvinylidene fluoride as a binder, and 0.3 parts by mass of barium titanate (BaTiO3) with a volume-based median diameter (D50) of 3.8 μm, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP). This slurry was applied to both sides of a positive electrode current collector made of aluminum foil, and after the coating film was dried, the electrode was rolled with a rolling roller to obtain a positive electrode in which positive electrode slurry layers were formed on both sides of the positive electrode current collector.

[0041] [Fabrication of the negative electrode] A negative electrode slurry was prepared by mixing 95 parts by mass of a negative electrode active material consisting of graphite powder and silicon oxide, 3 parts by mass of carboxymethylcellulose (CMC), 2 parts by mass of styrene-butadiene rubber (SBR), and an appropriate amount of water. This slurry was applied to both sides of a negative electrode current collector made of copper foil, and after the coating film was dried, the material was rolled with a rolling roller to obtain a negative electrode in which a negative electrode slurry layer was formed on both sides of the negative electrode current collector.

[0042] [Preparation of non-aqueous electrolytes] A non-aqueous electrolyte was obtained by dissolving LiPF6 at a concentration of 1.0 mol / L in a mixed non-aqueous solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC).

[0043] [Fabrication of non-aqueous electrolyte secondary batteries] A positive electrode lead was attached to the positive electrode prepared above, and a negative electrode lead was attached to the negative electrode prepared above. A polyethylene microporous membrane was placed between these two electrodes as a separator, and a wound electrode body was fabricated by winding it in a spiral shape. After placing the electrode body and the non-aqueous electrolyte inside an aluminum laminate casing, the peripheral edge of the casing was heated and welded to obtain a non-aqueous electrolyte secondary battery.

[0044] <Example 2> A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that 0.5 parts by mass of barium titanate (BaTiO3) was used.

[0045] <Example 3> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that barium titanate (BaTiO3) with a volume-based median diameter (D50) of 5.4 μm was used.

[0046] <Example 4> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that barium titanate (BaTiO3) with a volume-based median diameter (D50) of 3.1 μm was used.

[0047] <Example 5> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that barium titanate (BaTiO3) with a volume-based median diameter (D50) of 2.2 μm was used.

[0048] <Comparative Example 1> A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that barium titanate (BaTiO3) was not added.

[0049] <Comparative Example 2> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that barium titanate (BaTiO3) with a volume-based median diameter (D50) of 10.0 μm was used.

[0050] <Comparative Example 3> A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that barium titanate (BaTiO3) with a volume-based median diameter (D50) of 1.2 μm was used.

[0051] [Measurement of charge transfer resistance] The non-aqueous electrolyte secondary batteries of each example and comparative example were charged with a constant current of 0.2C at a temperature of 25°C until the battery voltage reached 4.2V. AC impedance measurements were performed on these non-aqueous electrolyte secondary batteries in the range of 0.1Hz to 1kHz, and Cole-Cole plots were created. The charge transfer resistance of the batteries was determined from the diameter of the approximately semicircles appearing in the obtained Cole-Cole plots. The charge transfer resistance of the battery in Comparative Example 1 was set to 1, and the charge transfer resistances of the batteries in each example and the other comparative examples were calculated as relative values ​​(INDEX). The results are shown in Table 1 and Figure 2.

[0052] [Table 1]

[0053] As shown in Examples 1 to 5, when the ratio of the volume-based median diameter (D50) of the dielectric to the volume-based median diameter (D50) of the positive electrode active material (D50 of the dielectric / D50 of the positive electrode active material) was within the range of 0.15 to 0.6, the charge transfer resistance of the battery could be kept lower than that of Comparative Example 1. On the other hand, as shown in Comparative Examples 2 to 3, when the ratio of the volume-based median diameter (D50) of the dielectric to the volume-based median diameter (D50) of the positive electrode active material (D50 of the dielectric / D50 of the positive electrode active material) was outside the range of 0.15 to 0.6, the charge transfer resistance of the battery was higher than that of Comparative Example 1. [Explanation of Symbols]

[0054] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Case body, 17 Sealing body, 18,19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding part, 23 Filter, 24 Lower valve body, 25 Insulating material, 26 Upper valve body, 27 Cap, 28 Gasket.

Claims

1. A non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte, The positive electrode comprises a positive electrode current collector and a positive electrode composite material layer provided on the positive electrode current collector. The positive electrode composite layer comprises a positive electrode active material and a dielectric. A non-aqueous electrolyte secondary battery in which the ratio of the volume-based median diameter (D50) of the dielectric to the volume-based median diameter (D50) of the positive electrode active material (D50 of the dielectric / D50 of the positive electrode active material) is 0.15 or more and 0.6 or less.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the dielectric is 2% by mass or less relative to the mass of the positive electrode active material.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the ratio of the volume-based median diameter (D50) of the dielectric to the volume-based median diameter (D50 of the positive electrode active material) (D50 of the dielectric / D50 of the positive electrode active material) is 0.26 or more and 0.45 or less.

4. The non-aqueous electrolyte secondary battery according to claim 2, wherein the content of the dielectric is 1% by mass or less relative to the mass of the positive electrode active material.

5. The dielectric is BaTiO ３ A non-aqueous electrolyte secondary battery according to claim 1 or 2, comprising:

6. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the volume-based median diameter (D50) of the positive electrode active material is 5 μm or more and 20 μm or less.

7. The positive electrode active material is of the general formula Li ａ Ni ｂ Co （１－ｂ－ｃ） Al ｃ W ｄ O ｅ A non-aqueous electrolyte secondary battery according to claim 1 or 2, comprising a lithium composite oxide represented by the formula (wherein 0.9 < a ​​≤ 1.2, 0.88 ≤ b ≤ 0.96, 0.04 ≤ c ≤ 0.12, 1.9 ≤ e ≤ 2.1, and when W / (Ni + Co + Al + W) = d, 0.0003 ≤ d ≤ 0.002).

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