Positive electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery

Abstract

This positive electrode active material which is contained in a nonaqueous electrolyte secondary battery has a layered rock salt structure and is represented by a composition formula LixNayWzNiaMnbM11-a-bM2cM3dOe, where M1 is at least one element that is selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al, M2 is at least one element that is selected from the group consisting of alkali metals other than Li and Na, alkaline earth metals, and La, M3 is at least one element that is selected from the group consisting of Ta, Nb, Mo, Zr, and Sb, 0.8 ≤ x ≤ 1.15, 0 < y ≤ 0.2, 0 < z ≤ 0.2, 0.8 < x + y ≤ 1.35, 0 < a ≤ 1, 0 ≤ b < 1, 0 ≤ 1 – a - b < 1, 0 < c ≤ 1, 0 ≤ d ≤ 1, and e is a value that satisfies electrical neutrality.

Description

Positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery, and in particular to a positive electrode active material for a non-aqueous electrolyte secondary battery containing Li and Na, and a non-aqueous electrolyte secondary battery using this positive electrode active material for a non-aqueous electrolyte secondary battery.

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been widely used for various applications such as vehicle applications and power storage applications, and many studies have been conducted on non-aqueous electrolyte secondary batteries. Patent Document 1 discloses a positive electrode active material in which sodium cobalt oxide is subjected to ion exchange to contain Li and Na in the positive electrode active material in order to improve the battery capacity and cycle characteristics of lithium cobalt oxide as a positive electrode active material.

[0003] Japanese Patent Application Laid-Open No. 2023-143694

[0004] In recent years, the application fields of non-aqueous electrolyte secondary batteries have been expanding, and improvements in battery capacity and cycle characteristics are increasingly being demanded of non-aqueous electrolyte secondary batteries. The existing technologies disclosed in Patent Document 1 and the like do not fully meet the demands for higher capacity and improved cycle characteristics, and there is still room for improvement.

[0005] An object of the present disclosure is to provide a positive electrode active material that contributes to higher capacity and improved cycle characteristics.

[0006] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure has a layered rock salt structure and has the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅIn the formula, M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value that satisfies electrical neutrality.

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by including a positive electrode containing the above-described positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

[0008] According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, it is possible to achieve improvements in the battery capacity and cycle characteristics of the non-aqueous electrolyte secondary battery.

[0009] 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention;

[0010] In recent years, non-aqueous electrolyte secondary batteries have been required to have higher capacities and improved cycle characteristics. The present inventors have conducted extensive research into positive electrode active materials having a layered rock salt structure. As a result, the present inventors have discovered a positive electrode active material having the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ(wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality), it has been found that improvements in the battery capacity and cycle characteristics of nonaqueous electrolyte secondary batteries can be achieved. Although the detailed mechanism is unclear, it is believed that the adoption of the above composition for the positive electrode active material having a layered rock salt structure facilitates the insertion and release of Li. More specifically, it is believed that the layered rock salt structure is stabilized by incorporating W, an element M2 selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La, and an element M3 selected from the group consisting of Ta, Nb, Mo, Zr, and Sb into the positive electrode active material, and the thickness of the Li layer in the layered rock salt structure is adjusted to a predetermined size by allowing a predetermined proportion of Na to coexist with Li.

[0011] Hereinafter, with reference to the drawings, an example of an embodiment of a positive electrode active material according to the present disclosure and a nonaqueous electrolyte secondary battery using the positive electrode active material will be described in detail. Note that configurations obtained by selectively combining the respective components of the multiple embodiments and modifications described below are included within the scope of the present disclosure.

[0012] In the following, a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical, bottomed exterior body 16 is exemplified as a nonaqueous electrolyte secondary battery; however, the exterior body of the battery is not limited to a cylindrical exterior body. The nonaqueous electrolyte secondary battery according to the present disclosure may be, for example, a prismatic battery with a prismatic exterior body, a coin-type battery with a coin-type exterior body, or a pouch-type battery with an exterior body composed of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode assembly is not limited to a wound type, but may also be a stacked type electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween. Furthermore, the design of the nonaqueous electrolyte secondary battery according to the present disclosure is not limited to the design of the exemplified nonaqueous electrolyte secondary battery, and known nonaqueous electrolyte secondary battery designs may also be applied.

[0013] FIG. 1 is an axial cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte, and an exterior body 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The exterior body 16 is a cylindrical metal container with a bottom that is open on one axial side, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the battery will be referred to as the top, and the bottom side of the exterior body 16 will be referred to as the bottom.

[0014] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and stacked alternately in the radial direction of the electrode assembly 14. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. Two separators 13 are arranged, for example, to sandwich the positive electrode 11. The electrode assembly 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the lateral direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the lateral end faces of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode assembly 14.

[0015] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom side of the exterior body 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the exterior body 16 by welding or the like, and the exterior body 16 serves as the negative electrode terminal.

[0016] A gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior body 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior body 16 by the grooved portion 22 and the open end of the exterior body 16 that is crimped to the sealing body 17.

[0017] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0018] The positive electrode 11, the negative electrode 12, the separator 13, and the nonaqueous electrolyte that constitute the nonaqueous electrolyte secondary battery 10 will be described in detail below, with the positive electrode 11 being particularly described below.

[0019] The positive electrode 11 includes a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode core can be a foil of a metal such as aluminum, an aluminum alloy, stainless steel, or titanium that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on its surface.

[0020] The positive electrode mixture layer preferably contains a positive electrode active material, a conductive agent, and a binder, and is provided on both sides of the positive electrode core. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, the conductive agent, and the binder onto the positive electrode core, drying the coating, and then compressing it to form positive electrode mixture layers on both sides of the positive electrode core.

[0021] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. One type of conductive agent may be used alone, or multiple types may be used in combination. The content of the conductive agent is not particularly limited, but is, for example, 0.1 mass% or more and 5 mass% or less with respect to the mass of the positive electrode mixture layer.

[0022] Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer; and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. One type of binder may be used alone, or multiple types may be used in combination. The content of the binder is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less, relative to the mass of the positive electrode mixture layer.

[0023] The positive electrode active material has a layered rock salt structure and has the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mnｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ In this composition formula, M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al, M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La, M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb, and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality. The composite oxide constituting the positive electrode active material contains Li, Na, W, Ni, and M2 as essential elements. The composite oxide preferably further contains Mn. The composite oxide preferably further contains M3. The contents of Li, Na, W, Ni, Mn, M1, M2, and M3 contained in the positive electrode active material can be measured using an ICP optical emission spectrometer (for example, CIROS-120 manufactured by SPECTRO).

[0024] The positive electrode active material preferably has an O3-type layered rock salt structure. A positive electrode active material having an O3-type layered rock salt structure has a higher discharge voltage and is superior in energy density to those having other structures such as an O2-type layered rock salt structure.

[0025] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅIn the formula, the molar ratio of Na (y) may be more than 0 and not more than 0.2 (0<y≦0.2), but is preferably 0.01 or more, and more preferably 0.04 or more. When the molar ratio of Na (y) is 0.01≦y≦0.2 or 0.04≦y≦0.2, the magnitude of the lattice constant c tends to satisfy the predetermined condition, making it easier to achieve a high capacity.

[0026] Also, the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ In the formula, the molar ratio (y) of Na is preferably 0.16 or less, more preferably 0.13 or less. When the molar ratio (y) of Na is 0<y≦0.16 or 0<y≦0.13, the layered structure of the composite oxide is thought to be stable, and the improvement in discharge capacity and capacity retention rate is more pronounced. Note that when the molar ratio (y) of Na exceeds 0.2, Na ions may be extracted by the positive electrode during charge and the extracted Na ions may be occluded by the negative electrode. This may result in a reaction with the non-aqueous electrolyte during charge and discharge, generating by-products that may reduce the charge and discharge capacity and charge and discharge efficiency of the battery. Therefore, an example of a suitable range for the molar ratio (y) of Na is 0.01≦y≦0.16 or 0.04≦y≦0.13.

[0027] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅIn the formula, the molar ratio (x) of Li may be 0.80 or more and 1.15 or less (0.80≦x≦1.15), preferably 0.82 or more, more preferably 0.84 or more. The upper limit of the molar ratio (x) of Li is preferably 1.00, more preferably 0.95. Examples of suitable ranges of the molar ratio (x) of Li are 0.80≦x≦1.00, 0.80≦x≦0.95, 0.82≦x≦1.15, 0.82≦x≦1.00, 0.82≦x≦0.95, 0.84≦x≦1.15, 0.84≦x≦1.00, or 0.84≦x≦0.95. When the molar ratio (x) of Li is within this range, the effect of improving the discharge capacity and capacity retention rate becomes more significant.

[0028] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ In the formula, the total molar ratio of Li and Na (x + y) may be greater than 0.80 and less than or equal to 1.35 (0.8 < x + y ≦ 1.35), but is preferably 0.85 or greater, more preferably 0.90 or greater, and even more preferably 0.95 or greater. The upper limit of the total molar ratio of Li and Na (x + y) is preferably 1.15, more preferably 1.05. An example of a suitable range for the total molar ratio of Li and Na (x + y) is 0.80 < x + y ≦ 1.10, 0.80 < x + y ≦ 1.05, 0.85 ≦ x + y ≦ 1.10, 0.85 ≦ x + y ≦ 1.05, 0.90 ≦ x + y ≦ 1.10, 0.90 ≦ x + y ≦ 1.05, 0.95 ≦ x + y ≦ 1.10, or 0.95 ≦ x + y ≦ 1.05. If the total molar ratio (x+y) of Li and Na is within this range, the effects of improving the discharge capacity and capacity retention rate become more significant.

[0029] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅIn the formula, the molar ratio (z) of W may be 0.2 or less (0<z≦0.2), preferably 0.1 or less, more preferably 0.01 or less, and even more preferably 0.005 or less. The molar ratio (z) of W is preferably 0.001 or more, and more preferably 0.003 or more. Therefore, examples of suitable ranges for the molar ratio (z) of W are 0.001≦z≦0.2, 0.001≦z≦0.1, 0.001≦z≦0.01, 0.001≦z≦0.005, 0.003≦z≦0.2, 0.003≦z≦0.1, 0.003≦z≦0.01, or 0.003≦z≦0.005. When the molar ratio (z) of W is within the range, the effects of improving the discharge capacity and capacity retention rate become more pronounced.

[0030] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ In the formula, the molar ratio (a) of Ni may be 1 or less (0<a≦1), preferably 0.9 or less, more preferably 0.8 or less, and even more preferably 0.6 or less. The molar ratio (a) of Ni is preferably 0.3 or more, and more preferably 0.4 or more. Therefore, an example of a suitable range for the molar ratio (a) of Ni is 0.3≦a≦1, 0.3≦a≦0.9, 0.3≦a≦0.8, 0.3≦a≦0.6, 0.4≦a≦1, 0.4≦a≦0.9, 0.4≦a≦0.8, or 0.4≦a≦0.6. When the molar ratio (a) of Ni is within this range, the effects of improving the discharge capacity and capacity retention rate become more pronounced.

[0031] As described above, the positive electrode active material preferably contains Mn. ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅIn the formula, the molar ratio (b) of Mn is preferably 0.7 or less, more preferably 0.6 or less. The molar ratio (b) of Mn is preferably 0.1 or more, more preferably 0.3 or more. An example of a suitable range for the molar ratio (b) of Mn is 0.1≦b≦0.7 or 0.3≦a≦0.6. When the molar ratio (b) of Mn is within this range, the effects of improving the discharge capacity and capacity retention rate become more significant.

[0032] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ In the formula (I), M1 is at least one element selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al. The molar ratio (1-a-b) of M1 may be 0 or more and less than 1 (0≦1-a-b<1), but is preferably 0.10 or less (0≦1-a-b≦0.10), more preferably 0.08 or less (0≦1-a-b≦0.08), and even more preferably 0.05 or less (0≦1-a-b≦0.05).

[0033] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ In the formula (I), M1 preferably contains at least one element selected from Al and Co. For example, when Al is contained in the positive electrode active material, an example of a suitable range for the molar ratio (1-a-b) of Al is 0.005≦1-a-b≦0.025. When Co is contained in the positive electrode active material, an example of a suitable range for the molar ratio (1-a-b) of Co is 0.005≦1-a-b≦0.1.

[0034] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2ｃ M3 ｄ O ｅ In the formula, M2 is at least one element selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La. Preferably, M2 contains at least one element selected from Ca and Sr. The molar ratio (c) of M2 may be 1 or less (0<c≦1), but is preferably 0.1 or less, more preferably 0.01 or less, and even more preferably 0.0075 or less. The molar ratio (c) of M2 is preferably 0.001 or more, and more preferably 0.0033 or more. Therefore, an example of a suitable range for the molar ratio (c) of M2 is 0.001≦c≦1, 0.001≦c≦0.1, 0.001≦c≦0.01, 0.001≦c≦0.0075, 0.0033≦c≦1, 0.0033≦c≦0.1, 0.0033≦c≦0.01, or 0.0033≦c≦0.0075. When the molar ratio (c) of M2 is within this range, the effect of improving the discharge capacity and the capacity retention rate becomes more significant.

[0035] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅIn the formula, M3 is at least one element selected from the group consisting of Ta, Nb, Mo, Zr, and Sb. Preferably, M3 contains at least one element selected from Nb and Sb. As described above, the positive electrode active material preferably contains M3. The molar ratio (d) of M3 may be 1 or less (0≦d≦1), but is preferably 0.1 or less, more preferably 0.01 or less, and even more preferably 0.003 or less. The molar ratio (c) of M2 is preferably 0.001 or more, and more preferably 0.0025 or more. Therefore, an example of a suitable range for the molar ratio (c) of M2 is 0.001≦c≦1, 0.001≦c≦0.1, 0.001≦c≦0.01, 0.001≦c≦0.003, 0.0025≦c≦1, 0.0025≦c≦0.1, 0.0253≦c≦0.01, or 0.0025≦c≦0.003. When the molar ratio (c) of M2 is within this range, the effect of improving the discharge capacity and the capacity retention rate becomes more significant.

[0036] Composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅIn the formula, the molar ratio (e) of O is a value that satisfies electrical neutrality. In other words, the molar ratio (e) of O is a value that satisfies the valence of O in the positive electrode active material. The molar ratio (e) of O is not particularly limited as long as it satisfies the valence of O in the positive electrode active material, and may be, for example, e = x + y + 1, or e < x + y + 1, or e > x + y + 1. In particular, in the positive electrode active material immediately after production, when e < x + y + 1, the layered rock salt structure has a deficiency of oxygen. Furthermore, in the positive electrode active material immediately after production, when e > x + y + 1, the layered rock salt structure has an excess of oxygen. In a structure with oxygen deficiency, the oxygen deficiency improves the electronic conductivity of the positive electrode active material, but if the oxygen deficiency increases, the O3 structure cannot be maintained, which is thought to cause a decrease in charge / discharge capacity and cycle characteristics. In addition, in the structure where oxygen is in excess, the presence of oxygen between lattices improves the electronic conductivity of the positive electrode active material, but if the amount of oxygen in excess increases, the valence of Ni and Mn in the positive electrode active material increases, and it is thought that the charge capacity will be greatly reduced.Therefore, for example, when the total molar ratio of Ni, Mn and M1 is 1, the molar ratio (c) of O is preferably 1.8 or more and 2.3 or less, more preferably 1.85 or more and 2.25 or less.The oxygen content of the positive electrode active material can be measured using an oxygen / nitrogen analyzer (for example, EMGA-920 manufactured by Horiba, Ltd.).

[0037] The Li—Na composite oxide is, for example, a secondary particle formed by aggregation of a plurality of primary particles. The volume-based median diameter (D50) of the Li—Na composite oxide is, for example, 1 μm or more and 30 μm or less, or 3 μm or more and 20 μm or less. The D50 of the composite oxide is the particle size at which the volume cumulative value is 50% in the particle size distribution measured by a laser diffraction scattering method.

[0038] The BET specific surface area of ​​the Li-Na composite oxide is, for example, 0.1 m ２ / g or more 10m ２ / g or less, or 0.5m ２ / g or more 5m ２ The BET specific surface area of ​​the Li-Na composite oxide is 2 m ２ / g or more, which makes it possible to more significantly improve the discharge capacity. The BET specific surface area of ​​the composite oxide is measured according to the BET method (nitrogen adsorption method) described in JIS R1626.

[0039] The positive electrode active material contains the Li—Na composite oxide as a main component. Here, the term "main component" refers to the component that has the highest mass ratio among the components constituting the positive electrode active material. The mixture layer of the positive electrode 11 may contain a composite oxide other than the Li—Na composite oxide as the positive electrode active material, but the content of the Li—Na composite oxide is preferably 50 mass% or more, and may be substantially 100 mass%.

[0040] The positive electrode active material, which is one example of the embodiment, can be produced by the following method: Note that the production method described here is only an example, and the method for producing the positive electrode active material is not limited to this method.

[0041] The Li-Na composite oxide is produced through the steps of (1) mixing and firing a sodium raw material and a nickel raw material to synthesize a Na composite oxide, and (2) reacting the Na composite oxide with a lithium compound to exchange a portion of the Na in the Na composite oxide for Li.

[0042] In step (1), a tungsten raw material and a raw material containing element M2 are further added. The tungsten raw material and the raw material containing element M2 may be mixed and fired together with the sodium raw material and the nickel raw material, or may be added to a fired product obtained by mixing and firing the sodium raw material and the nickel raw material. An example of a method for adding them to the fired product is a method in which they are dissolved in an aqueous solution or the like and added. Furthermore, in step (1), it is preferable to add a manganese raw material, and a raw material containing element M1 and a raw material containing element M3 may also be added. In step (1), a manganese raw material is added, and a raw material containing element M1 and a raw material containing element M3 may also be added. In step (1), a tungsten raw material and a raw material containing element M2 may be added, which have the composition formula Na ｆ W ｇ Ni ｈ Mn ｉ M1 １－ｈ－ｉ M2 ｊ M3 ｋ O ｌIn the formula, M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and f≦1.15, 0<g≦1, 0<h≦1, 0≦i<1, 0≦1−h−i<1, 0<j≦1, 0≦k≦1, and 1 is a value that satisfies electrical neutrality.

[0043] As the sodium source, at least one selected from the group consisting of metallic sodium and sodium compounds is used. The sodium compound is not particularly limited as long as it contains Na, and examples thereof include CH ３ COONa, CH ３ COONa 3H ２ Acetates such as O, NaNO ３ Nitrates, Na etc. ２ SO ４ Sulfates such as Na ２ CO ３ Carbonates such as NaHCO ３ Hydrogen carbonates such as NaOH, hydroxides such as Na ２ O, Na ２ O ２ Among them, Na ２ CO ３ , NaHCO ３ , NaOH, NaNO ３ is preferred.

[0044] The nickel raw material is at least one selected from the group consisting of metallic nickel and nickel compounds. The nickel compound is not particularly limited as long as it contains Ni, and examples thereof include oxides such as NiO, Ni(OH), and the like. ２ , hydroxides such as NiOOH, NiNO ３ Nitrates such as NiCO ３ , Ni ４ CO ３ (OH) ６ (H ２ O) ４Carbonates such as NiSO ４ Among them, Ni(OH) ２ is preferred.

[0045] As a tungsten raw material, tungsten oxide (WO ３ ), lithium tungstate (Li ２ WO ４ , Li ４ WO ５ , Li ６ W ２ O ９ ) and the like. As the tungsten raw material, a solution containing W may be used. As the solution containing W, for example, WO ３ in an aqueous NaOH solution.

[0046] The manganese raw material is at least one selected from the group consisting of metallic manganese and manganese compounds. The manganese compound is not particularly limited as long as it contains Mn, and examples thereof include MnO, Mn ２ O ３ , Mn ３ O ４ , MnO ２ oxides such as Mn(OH) ２ , hydroxides such as MnOOH, MnCO ３ carbonates such as Mn(NO ３ ) ２ Nitrates such as MnSO ４ Among them, Mn(OH) ２ is preferred.

[0047] The raw material containing element M1 is at least one selected from the group consisting of element M1 and compounds of element M1. The compound containing element M1 is not particularly limited as long as it contains M1, and examples include oxides, hydroxides, carbonates, nitrates, and sulfates. Note that the raw material for the Na composite oxide may be a compound containing Ni and Mn, a compound containing Ni and M1, a compound containing Mn and M1, or a compound containing Ni, Mn, and M1.

[0048] The raw material containing element M2 is at least one selected from the group consisting of element M2 and compounds of element M2. The compound containing element M2 is not particularly limited as long as it contains M2, and examples thereof include oxides, hydroxides, carbonates, nitrates, and sulfates.

[0049] The raw material containing element M3 is at least one selected from the group consisting of element M3 and compounds of element M3. The compound containing element M3 is not particularly limited as long as it contains M3, and examples thereof include oxides, hydroxides, carbonates, nitrates, and sulfates.

[0050] The mixing ratio of the raw materials for the Na composite oxide may be set appropriately and is not particularly limited. For example, in the mixture of raw materials for the Na composite oxide, the molar ratio of Na is f, the molar ratio of W is g, the molar ratio of Ni is h, the molar ratio of Mn is i, the molar ratio of element M1 is 1-hi, the molar ratio of element M2 is j, and the molar ratio of element M3 is k. It is preferable to set the ratios so that 0.90≦f≦1.15, 0.001≦g≦0.2, 0.3≦h≦0.9, 0.1≦i≦0.7, 0≦1-hi≦0.1, 0.001≦j≦0.1, and 0.001≦k≦0.1. Furthermore, the method for mixing the raw materials is not particularly limited as long as it can uniformly mix the raw materials, and examples include mixing using a known mixer such as a mixer. W and element M3 may not be added during mixing, but may be added to the fired product as described below.

[0051] The mixture of raw materials is calcined in a calcination furnace in the atmosphere or in an oxygen stream. The calcination temperature is preferably 700°C or higher and 900°C or lower, more preferably 750°C or higher and 850°C or lower. The temperature rise rate is preferably slow, for example, 0.3°C / min or higher and 5.0°C / min or lower, or 0.5°C / min or higher and 3.0°C / min or lower. The calcination time is preferably 20 hours or longer when the calcination temperature is 750°C or higher and 850°C or lower. Here, the calcination time refers to the time from when the temperature of the calcination furnace reaches the calcination temperature to when the calcination ends and cooling begins. The calcined product is, for example, rapidly cooled in the atmosphere by being removed from the calcination furnace. The tungsten raw material and the raw material containing element M3 may be added to the calcined product in a dissolved state in an aqueous solution or the like. This allows W and M3 to be more uniformly dispersed in the Na composite oxide. The fired product to which the tungsten raw material and the raw material containing element M3 have been added may be dried by heat treatment or the like.

[0052] In step (2), a portion of the Na in the Na composite oxide is exchanged with Li. That is, the Li exchange must be performed so that a predetermined amount of Na remains. A suitable method for exchanging Na for Li includes adding a molten salt of a lithium compound (hereinafter referred to as "lithium molten salt") to the Na composite oxide and heating it. The lithium molten salt may be, for example, at least one selected from the group consisting of lithium hydroxide, lithium carbonate, lithium bicarbonate, lithium nitrate, lithium sulfate, lithium chloride, lithium iodide, and lithium bromide. Among these, it is preferable to use at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium bicarbonate, and it is more preferable to use lithium hydroxide. While lithium hydroxide may be anhydrous, it is preferably a hydrate. Using at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium bicarbonate as the lithium molten salt makes it easier to leave a predetermined amount of Na. When lithium hydroxide is used in the lithium molten salt, the molar ratio of lithium hydroxide to the total moles of the lithium molten salt is preferably 5 mol % or more, more preferably 25 mol % or more, even more preferably 50 mol % or more, and even more preferably 75 mol % or more. Furthermore, the lithium molten salt may essentially consist of only lithium hydroxide.

[0053] In step (2), the mixing ratio of the Na composite oxide and the lithium molten salt can be set appropriately. When only lithium hydroxide is used as the lithium molten salt, the mixing ratio of the Na composite oxide and the lithium molten salt is such that the molar ratio (Li / Na) of Li in the lithium molten salt to Na in the Na composite oxide is preferably 0.9 or more, more preferably 1.0 or more, and even more preferably 1.5 or more. Furthermore, (Li / Na) is preferably 15 or less, preferably 10 or less, and even more preferably 8 or less. Therefore, when only lithium hydroxide is used as the lithium molten salt, the mixing ratio of the Na composite oxide and the lithium molten salt is preferably 0.9 or more and 10 or less, more preferably 1.0 or more and 5 or less, and even more preferably 1.0 or more and 1.1 or less.

[0054] The heating temperature in the Li exchange step is preferably 200°C or higher and 400°C or lower, more preferably 250°C or higher and 350°C or lower. If the heating temperature exceeds 400°C, the reaction may proceed rapidly, resulting in a non-uniform reaction. On the other hand, if the heating temperature is lower than 200°C, the reaction may not proceed sufficiently, and excess Na may remain. The heat treatment time is set to, for example, 3 hours or higher and 10 hours or lower after the temperature is increased at a rate of 3.0°C / min or higher and 8.0°C / min or lower to reach the target heat treatment temperature. After the heat treatment, the mixture is cooled. The cooling method is not particularly limited, and may be, for example, natural cooling (cooling in a furnace).

[0055] After cooling, the resulting product is thoroughly washed with water, ethanol, methanol, or the like, and then dried to obtain a Li—Na composite oxide. The atmosphere for drying after washing is not particularly limited and may be air or vacuum. Furthermore, after washing, another heating treatment or another washing treatment may be performed.

[0056] [Negative Electrode] The negative electrode 12 may have, for example, a negative electrode core and a negative electrode mixture layer formed on the surface of the negative electrode core, or a metal Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode core, and lithium metal may be deposited on the surface of the negative electrode core upon charging. When the negative electrode 12 has a negative electrode mixture layer, the negative electrode mixture layer is preferably formed on both sides of the negative electrode core. The negative electrode core may be a foil of a metal stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with such a metal disposed on the surface. The thickness of the negative electrode core is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode core. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. to the surface of a negative electrode core, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0057] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, carbon materials such as graphite are used. Graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, metals that alloy with Li, such as Si and Sn, metal compounds containing Si, Sn, and lithium-titanium composite oxides may also be used as the negative electrode active material. Furthermore, those provided with a carbon coating may also be used. For example, SiO ｘ (0.5≦x≦1.6) or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2) may be used in combination with graphite.

[0058] Examples of binders contained in the negative electrode mixture layer include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0059] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0060] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0061] [Non-aqueous electrolyte] The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0062] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0063] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0064] Examples of the 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 ethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0065] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less, per 1 L of the non-aqueous solvent.

[0066] The non-aqueous electrolyte may contain an additive such as an unsaturated carbonate ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, a sulfate compound, a borate ester compound, a phosphate ester compound, or a phosphite ester compound.

[0067] Examples of unsaturated cyclic carbonates include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. Some of the hydrogen atoms in the unsaturated cyclic carbonate may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by intermolecular condensation of multiple carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0068] Examples of phenol compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0069] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanatomethylcyclohexane (BIMCH). Examples of sultone compounds include propane sultone and propene sultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethyl phosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethyl phosphite and tris(trimethylsilyl)phosphite.

[0070] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0071] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0072] Example 1 Preparation of Positive Electrode Active Material A hydroxide containing Ni and Mn in a molar ratio of 1:1 and tungsten oxide (WO ３ ) and niobium oxide (Nb ２ O ５ ) and calcium hydroxide (Ca(OH) ２) and sodium carbonate were mixed in a molar ratio of Ni:Mn:W:Nb:Ca:Na=0.5:0.5:0.005:0.0025:0.0075:1.05, and the resulting mixture was heated at a temperature increase rate of 1°C / min, calcined at 820°C for 20 hours in air, and then quenched in air to obtain a Na composite oxide. Next, lithium hydroxide hydrate (LiOH.H ２ O) and Na composite oxide were mixed in a molar ratio of Li:Na = 1.05:1, and the resulting mixture was heated at a temperature increase rate of 5°C / min and then heated in air at 280°C for 5 hours. Thereafter, the product was cooled at a temperature decrease rate of 2°C / min and washed with a sufficient amount of water. Thereafter, the solution was suction filtered to remove the filtrate, and the residue remaining on the filter paper was heat-treated in vacuum at 180°C for 4 hours to obtain a Li-Na composite oxide. The resulting Li-Na composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and the composite oxides satisfy the following conditions: 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value that satisfies electrical neutrality).

[0073] [Fabrication of Positive Electrode] The Li—Na composite oxide was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solids mass ratio of 92:5:3, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was applied to a positive electrode core made of aluminum foil, and after drying the coating, the coating was rolled with a rolling roller to obtain a positive electrode having a positive electrode mixture layer formed on the positive electrode core.

[0074] [Preparation of Non-Aqueous Electrolyte] A mixed solvent of fluoroethylene carbonate (FEC) and methyl propionate (FMP) in a volume ratio of 1:3 was dissolved in lithium hexafluorophosphate (LiPF ６ ) was dissolved in the solution to a concentration of 1 mol / liter to prepare a non-aqueous electrolyte.

[0075] [Preparation of Test Cell] A lithium metal foil was used as the negative electrode, and the positive and negative electrodes were arranged facing each other with a separator interposed therebetween to prepare an electrode assembly. This electrode assembly and the nonaqueous electrolyte solution were placed in a coin-shaped outer can, and the opening of the outer can was sealed with a gasket and a sealing member to prepare a test cell (nonaqueous electrolyte secondary battery).

[0076] [Evaluation of Discharge Capacity] The test cell was subjected to constant current charging at a constant current of 0.2 C at 25° C. until the battery voltage reached 4.5 V, and then constant voltage charging at a voltage of 4.5 V until the current value reached 0.02 C. After a 20-minute rest, constant current discharging was performed at a constant current of 0.2 C until the battery voltage reached 2.5 V. This charge / discharge cycle was counted as one cycle, and three cycles were performed, and the discharge capacity at the third cycle was measured.

[0077] [Evaluation of Capacity Retention Rate] The test cell for which the discharge capacity evaluation was performed was subjected to the above charge-discharge cycle 22 times, and the discharge capacity of the final cycle (the 25th cycle in total) was measured. The capacity retention rate of the test cell was calculated using the following formula to evaluate the charge-discharge cycle characteristics: Capacity retention rate (%) = (discharge capacity at the 25th cycle / discharge capacity at the 3rd cycle) × 100

[0078] Example 2 A test cell was prepared and evaluated in the same manner as in Example 1, except that the composition and preparation method of the Na composite oxide were changed in the preparation of the positive electrode active material. More specifically, in Example 2, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and calcium hydroxide (Ca(OH) ２ ) and sodium carbonate were mixed in a molar ratio of Ni:Mn:Ca:Na = 0.5:0.5:0.0075:1.05. Further, WO was added to the mixture after baking and quenching so that the molar ratio of W was 0.003 and the molar ratio of Nb was 0.003 relative to the molar ratio of Ni + Mn (1) in the positive electrode active material. ３ A solution obtained by dissolving the above in an aqueous NaOH solution and a solution obtained by dissolving ammonium niobate (V) oxalate hydrate in water were added. The resulting Li—Na composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and the composite oxides satisfy the following conditions: 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value that satisfies electrical neutrality).

[0079] Example 3 A test cell was produced and evaluated in the same manner as in Example 1, except that the composition and production method of the Na composite oxide were changed in the production of the positive electrode active material. More specifically, in Example 3, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and antimony oxide (Sb ２ O ３ ) and calcium hydroxide (Ca(OH) ２) and strontium hydroxide (Sr(OH) ２ ) and sodium carbonate were mixed in a molar ratio of Ni:Mn:Sb:Ca:Sr:Na=0.5:0.5:0.003:0.0025:0.0008:1.05. Further, WO was added to the mixture after baking and quenching so that the molar ratio of W was 0.003 relative to the molar ratio of Ni+Mn in the positive electrode active material (1). ３ The resulting Li-Na composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and the composite oxides satisfy the following conditions: 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value that satisfies electrical neutrality).

[0080] Comparative Example 1 A test cell was prepared and evaluated in the same manner as in Example 1, except that the composition of the Na composite oxide was changed in the preparation of the positive electrode active material. More specifically, in Comparative Example 1, a hydroxide containing Ni and Mn in a molar ratio of 1:1 was mixed with sodium carbonate in a molar ratio of Ni:Mn:Na=0.5:0.5:1.05. The obtained Li-Na composite oxide had a composition formula of Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ(wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality), the molar ratio of W (z) and the molar ratio of M2 (c) were outside their respective ranges.

[0081] Comparative Example 2 A test cell was produced and evaluated in the same manner as in Example 1, except that the composition of the Na composite oxide was changed in the preparation of the positive electrode active material. More specifically, in Comparative Example 2, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and tungsten oxide (WO ３ ) and sodium carbonate were mixed in a molar ratio of Ni:Mn:W:Na=0.5:0.5:0.005:1.05. The obtained Li—Na composite oxide had a composition formula of Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality) the molar ratio (c) of M2 was outside the range.

[0082] Comparative Example 3 A test cell was produced and evaluated in the same manner as in Example 1, except that the composition of the Na composite oxide was changed in the preparation of the positive electrode active material. More specifically, in Comparative Example 3, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and calcium hydroxide (Ca(OH) ２ ) and sodium carbonate were mixed in a molar ratio of Ni:Mn:Ca:Na=0.5:0.5:0.005:1.05. The obtained Li—Na composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality) the molar ratio (z) of W in

[0083] Comparative Example 4 A test cell was prepared and evaluated in the same manner as in Example 1, except that the composition of the Na composite oxide was changed in the preparation of the positive electrode active material. More specifically, in Comparative Example 4, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and antimony oxide (Sb ２ O ３ ) and sodium carbonate were mixed in a molar ratio of Ni:Mn:Sb:Na=0.5:0.5:0.0025:1.05. The obtained Li—Na composite oxide had a composition formula of Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ(wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality), the molar ratio of W (z) and the molar ratio of M2 (c) were outside their respective ranges.

[0084] Comparative Example 5 A test cell was produced and evaluated in the same manner as in Example 1, except that the composition of the Na composite oxide was changed in the preparation of the positive electrode active material. More specifically, in Comparative Example 5, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and calcium hydroxide (Ca(OH) ２ ) and strontium hydroxide (Sr(OH) ２ ) and sodium carbonate were mixed in a molar ratio of Ni:Mn:Ca:Sr:Na=0.5:0.5:0.0025:0.0008:1.05. The obtained Li—Na composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality) the molar ratio (z) of W in

[0085] Comparative Example 6 In the preparation of a positive electrode active material, a hydroxide containing Ni and Mn in a molar ratio of 1:1 was mixed with lithium hydroxide in a molar ratio of Ni:Mn:Li=0.5:0.5:1.07, and the resulting mixture was heated at a temperature increase rate of 5°C / min, baked at 900°C for 10 hours in air, and then cooled at a temperature decrease rate of 10°C / min to obtain a Na-free Li composite oxide. The obtained Li composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality), the molar ratio of Na (y), the molar ratio of W (z), and the molar ratio of M2 (c) were outside their respective ranges. A test cell was prepared and evaluated in the same manner as in Example 1, except that this composite oxide was used as the positive electrode active material.

[0086] Comparative Example 7 In the preparation of a positive electrode active material, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and tungsten oxide (WO ３ ) and lithium hydroxide were mixed in a molar ratio of Ni:Mn:W:Li = 0.5:0.5:0.006:1.07, and the resulting mixture was heated at a temperature increase rate of 5°C / min, calcined at 900°C for 10 hours in air, and then cooled at a temperature decrease rate of 10°C / min to obtain a Na-free Li composite oxide. The resulting Li composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mnｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality), the molar ratio of Na (y) and the molar ratio of M2 (c) were outside their respective ranges. A test cell was prepared and evaluated in the same manner as in Example 1, except that this composite oxide was used as the positive electrode active material.

[0087] Comparative Example 8 In the preparation of a positive electrode active material, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and calcium hydroxide (Ca(OH) ２ ) and lithium hydroxide were mixed in a molar ratio of Ni:Mn:Ca:Li = 0.5:0.5:0.006:1.07, and the resulting mixture was heated at a temperature increase rate of 5°C / min, calcined at 900°C for 10 hours in air, and then cooled at a temperature decrease rate of 10°C / min to obtain a Na-free Li composite oxide. The resulting Li composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ(wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality), the molar ratio of Na (y) and the molar ratio of W (z) were outside the ranges. A test cell was prepared and evaluated in the same manner as in Example 1 except that this composite oxide was used as the positive electrode active material.

[0088] Comparative Example 9 In the preparation of a positive electrode active material, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and niobium oxide (Nb ２ O ５ ) and lithium hydroxide were mixed in a molar ratio of Ni:Mn:Nb:Li = 0.5:0.5:0.003:1.07, and the resulting mixture was heated at a temperature increase rate of 5°C / min, calcined at 900°C for 10 hours in air, and then cooled at a temperature decrease rate of 10°C / min to obtain a Na-free Li composite oxide. The resulting Li composite oxide had the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ(wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality), the molar ratio of Na (y), the molar ratio of W (z), and the molar ratio of M2 (c) were outside their respective ranges. A test cell was prepared and evaluated in the same manner as in Example 1, except that this composite oxide was used as the positive electrode active material.

[0089] The evaluation results (discharge capacity and capacity retention rate) for the test cells of the examples and comparative examples are shown in Table 1. Table 1 also shows the results of the tests in which the positive electrode active material was a material having the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value that satisfies electrical neutrality).

[0090]

[0091] As shown in Table 1, the test cells of the Examples have improved discharge capacities and capacity retention rates compared to the test cells of the Comparative Examples. More specifically, the batteries of Examples 1 to 3, which use a positive electrode active material containing predetermined amounts of Li, Na, W, and M2, are able to achieve both high discharge capacities and high capacity retention rates. On the other hand, the batteries of Comparative Examples 1 to 5, which use a positive electrode active material containing Li and Na but not W or M2, have lower capacity retention rates than the batteries of the Examples. Furthermore, the batteries of Comparative Examples 6 to 9, which use a positive electrode active material containing no Li or Na, have lower discharge capacities than the batteries of the Examples. Therefore, it is believed that the batteries have a layered rock salt structure and have the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ (wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value that satisfies electrical neutrality), it can be seen that both battery capacity and cycle characteristics are improved by using a positive electrode active material represented by the formula:

[0092] The present disclosure will be further described by the following embodiments. Configuration 1: A positive electrode active material for a non-aqueous electrolyte secondary battery having a layered rock salt structure, comprising: ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅwherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al, M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La, and M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb, and wherein 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality. Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein M1 contains at least one element selected from Al and Co. Configuration 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein a satisfies 0.3≦a≦1. Configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein a satisfies 0.4≦a≦0.9. Configuration 6: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein y satisfies 0.05≦y≦0.2. Configuration 7: The BET specific surface area is 2 m ２ / g or more. Configuration 8: A nonaqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, a negative electrode, and a nonaqueous electrolyte.

[0093] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery having a layered rock salt structure, the positive electrode active material having the composition formula Li ｘ Na ｙ W ｚ Ni ａ Mn ｂ M1 １－ａ－ｂ M2 ｃ M3 ｄ O ｅ wherein M1 is at least one selected from the group consisting of Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, B, Ga, In, P, Hf, Co, and Al; M2 is at least one selected from the group consisting of alkali metals excluding Li and Na, alkaline earth metals, and La; M3 is at least one selected from the group consisting of Ta, Nb, Mo, Zr, and Sb; and 0.8≦x≦1.15, 0<y≦0.2, 0<z≦0.2, 0.8<x+y≦1.35, 0<a≦1, 0≦b<1, 0≦1−a−b<1, 0<c≦1, 0≦d≦1, and e is a value satisfying electrical neutrality.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, which has an O3-type layered rock salt structure.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein M1 contains at least one element selected from the group consisting of Al and Co.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the a satisfies 0.3≦a≦1.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the a satisfies 0.4≦a≦0.

9.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein y satisfies 0.05≦y≦0.

2.

7. The BET specific surface area is 2 m ２ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the SiO2 content is 1 / g or more.

8. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, a negative electrode, and a non-aqueous electrolyte.

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