Positive electrode active material for nonaqueous electrolyte secondary battery, method for producing positive electrode active material, and nonaqueous electrolyte secondary battery

Abstract

A positive electrode active material according to an exemplary embodiment of the present invention is a composite oxide represented by a composition formula LixNayNiaM1-aOd, where M is at least one element selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, 0.80≤x≤1.15, 0.02≤y≤0.20, 0.90≤x+y≤1.20, 0.40≤a≤0.95, and d is a value satisfying electrical neutrality. When 1 L of water is added to 1000 g of the composite oxide, the concentration of the alkali component eluted in water is less than 700 mmol / L.

Description

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

[0001] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the positive electrode active material, and a non-aqueous electrolyte secondary battery using the positive electrode active material.

[0002] In non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, the positive electrode active material has a significant effect on battery performance, such as input / output characteristics, capacity, and durability, and therefore has been the subject of extensive research. Lithium transition metal composite oxides containing transition metal elements such as Ni and Mn are generally used as positive electrode active materials. The types and amounts of elements contained in the lithium transition metal composite oxide, as well as the crystalline structure of the composite oxide, significantly affect battery performance, and even slight changes in these physical properties can prevent the desired performance from being achieved.

[0003] For example, Patent Documents 1 to 3 disclose the use of a Na-containing transition metal composite oxide as a positive electrode active material for the purpose of realizing a nonaqueous electrolyte secondary battery with high capacity and excellent durability. Patent Documents 4 to 6 also disclose the synthesis of a Na-containing transition metal composite oxide by mixing and firing a transition metal oxide, a lithium compound, and a sodium compound.

[0004] Japanese Patent No. 6395051 Japanese Patent No. 6792836 JP 2011-216495 A JP 2020-123440 A JP 2020-123441 A Japanese Patent No. 5904371

[0005] In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used as power sources for driving vehicles, and there is a demand for further increases in capacity. As disclosed in the above patent documents, various studies have been conducted on positive electrode active materials, but conventional positive electrode active materials including those disclosed in the above patent documents still have a lot of room for improvement in terms of increasing capacity.

[0006] The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present disclosure has the composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄwherein M is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, 0.80≦x≦1.15, 0.02≦y≦0.20, 0.90≦x+y≦1.20, 0.40≦a≦0.95, and d is a value that satisfies electrical neutrality, and when 1 L of water is added to 1000 g of the composite oxide, the concentration of alkaline components eluted in water is less than 700 mmol / L.

[0007] The method for producing a positive electrode active material according to the present disclosure is a method for producing a positive electrode active material comprising: ｚ Ni ｂ M １－ｂ O ｅ wherein M is at least one element selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, and z≧0.90, 0.40≦b≦0.95, and e is a value satisfying electrical neutrality; and a step of reacting the sodium composite oxide with a lithium compound to exchange a portion of Na in the sodium composite oxide for Li, wherein the lithium compound contains at least one element selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium hydrogencarbonate.

[0008] A non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode containing the above-described positive electrode active material, a negative electrode, and a non-aqueous electrolyte.

[0009] The positive electrode active material according to the present disclosure can achieve a high capacity non-aqueous electrolyte secondary battery.

[0010] 1 is a longitudinal cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention;

[0011] As a result of extensive research aimed at increasing the capacity of non-aqueous electrolyte secondary batteries, the inventors have found that the capacity of a battery can be significantly increased by using, as a positive electrode active material, a lithium-sodium-containing transition metal composite oxide represented by the above composition formula, which has an alkaline component concentration of less than 700 mmol / L when 1 L of water is added to 1000 g of the composite oxide. Furthermore, when the amount of alkaline component eluted is less than 700 mmol / L, the properties of the positive electrode slurry used in the production of a positive electrode are stabilized, improving productivity. On the other hand, when the amount of alkaline component eluted is 700 mmol / L or more, problems such as gelation of the positive electrode slurry occur, making it difficult to use in actual production.

[0012] The positive electrode active material according to the present disclosure is obtained by synthesizing a sodium composite oxide, then exchanging a portion of the Na in the sodium composite oxide with Li, leaving a predetermined amount of Na. The amount of Na remaining in the positive electrode active material according to the present disclosure is greater than that in positive electrode active materials synthesized by conventional ion exchange methods. By controlling the amount of Na remaining within a specific range, battery capacity is significantly improved. It is believed that the predetermined amount of Na stabilizes the crystalline structure of the positive electrode active material, thereby achieving a significantly higher capacity.

[0013] In addition, in the positive electrode active material according to the present disclosure, it is believed that Na is incorporated into the crystal structure in a concentration controlled within the above-mentioned specific range, and this Na does not leach out even when the positive electrode active material is repeatedly washed with water. In contrast, in the positive electrode active material synthesized by mixing and baking a transition metal oxide, a lithium compound, and a sodium compound as disclosed in Patent Documents 4 to 6, substantially all of the Na is leached out by washing with water. In other words, the positive electrode active material according to the present disclosure and the positive electrode active materials disclosed in Patent Documents 4 to 6 are believed to be completely different materials.

[0014] Hereinafter, with reference to the drawings, an example of an embodiment of a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present disclosure and a non-aqueous 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.

[0015] In the embodiment described below, a nonaqueous electrolyte secondary battery 10 is exemplified, which is a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical outer can 16 with a bottom, but the outer can of the battery is not limited to a cylindrical outer can. Other embodiments of the nonaqueous electrolyte secondary battery according to the present disclosure include, for example, a prismatic battery having a prismatic outer can, a coin-shaped battery having a coin-shaped outer can, and a pouch-shaped battery having an outer can made of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode assembly is not limited to a wound type, and may be a stacked electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0016] FIG. 1 is a cross-sectional view of a 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 outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The nonaqueous electrolyte secondary battery 10 is, for example, a lithium-ion secondary battery. 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 outer can 16 is a cylindrical metal container with a bottom and an open end in the axial direction. The opening of the outer can 16 is closed by a sealing member 17. Hereinafter, for convenience of explanation, the sealing member 17 side of the battery is referred to as the top, and the bottom side of the outer can 16 is referred to as the bottom.

[0017] The positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode assembly 14 are all strip-shaped, long bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length direction (longitudinal direction) and width direction (transverse direction). The separator 13 is formed to be at least slightly larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11. The electrode assembly 14 has 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.

[0018] 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 outer can 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 outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0019] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 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 can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0020] 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.

[0021] 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.

[0022] [Positive Electrode] The positive electrode 11 has 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 that is stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film with such a metal disposed on the surface layer. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably 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 a positive electrode active material, a conductive agent, and a binder onto the positive electrode core, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode core.

[0023] 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% by mass or more and 5% by mass or less with respect to the mass of the positive electrode mixture layer.

[0024] 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.

[0025] The positive electrode active material has a crystal structure belonging to the space group R-3m and has the composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄThe lithium-sodium transition metal composite oxide (Li—Na composite oxide) is represented by the formula: In the formula, M is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, and 0.80≦x≦1.15, 0.02≦y≦0.20, 0.90≦x+y≦1.20, 0.40≦a≦0.95, and d is a value that satisfies electrical neutrality. The Li—Na composite oxide contains Li, Na, and Ni as essential elements, and preferably further contains Mn. The content of metal elements contained in the composite oxide can be measured using an ICP optical emission spectrometer (for example, CIROS-120 manufactured by SPECTRO).

[0026] Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ In the formula, the molar ratio (y) of Na may be 0.02 or more and 0.20 or less (0.02≦y≦0.20), preferably 0.04 or more, more preferably 0.06 or more. The upper limit of the molar ratio (y) of Na is preferably 0.18, more preferably 0.16. If the molar ratio (y) exceeds 0.20, Na ions may be extracted during charging, and the extracted Na ions may be occluded in the negative electrode. This may result in a reaction with the non-aqueous electrolyte during charging and discharging, generating by-products that may reduce the charge / discharge capacity and charge / discharge efficiency of the battery.

[0027] An example of a suitable range for the molar ratio (y) of Na is 0.02≦y≦0.18, 0.02≦y≦0.16, 0.04≦y≦0.20, 0.04≦y≦0.18, 0.04≦y≦0.16, 0.06≦y≦0.20, 0.06≦y≦0.18, or 0.06≦y≦0.16, and among these, 0.04≦y≦0.18 or 0.06≦y≦0.16 is preferred. If the molar ratio (y) of Na is within this range, it is believed that the layered structure of the composite oxide is stabilized, and the effect of improving charge / discharge capacity becomes more significant.

[0028] Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄIn 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. An example of a suitable range of the molar ratio (x) of Li is 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. If the molar ratio (x) of Li is within this range, the capacity improvement effect becomes more pronounced.

[0029] Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ In the formula, the total molar ratio of Li and Na (x + y) may be 0.90 or more and 1.20 or less (0.90≦x + y≦1.20), preferably 0.92 or more, more preferably 0.94 or more. The upper limit of the total molar ratio of Li and Na (x + y) is preferably 1.10, more preferably 1.05. An example of a suitable range for the total molar ratio of Li and Na (x + y) is 0.90≦x + y≦1.10, 0.90≦x + y≦1.05, 0.92≦x + y≦1.20, 0.92≦x + y≦1.10, 0.92≦x + y≦1.05, 0.94≦x + y≦1.20, 0.94≦x + y≦1.10, or 0.94≦x + y≦1.05. If the total molar ratio of Li and Na (x+y) is within this range, the capacity improvement effect becomes more significant.

[0030] Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄIn the formula, the molar ratio (a) of Ni may be 0.40 or more and 0.95 or less (0.40≦a≦0.95), preferably 0.45 or more, more preferably 0.50 or more. The upper limit of the molar ratio (a) of Ni is preferably 0.75, more preferably 0.70. An example of a suitable range of the molar ratio (a) of Ni is 0.40≦a≦0.75, 0.40≦a≦0.70, 0.45≦a≦0.95, 0.45≦a≦0.75, 0.45≦a≦0.70, 0.50≦a≦0.95, 0.50≦a≦0.75, or 0.50≦a≦0.75, and among these, 0.45≦y≦0.75 or 0.50≦y≦0.70 is preferred. If the molar ratio (a) of Ni is within this range, it becomes easy to achieve a high capacity while suppressing material costs.

[0031] Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ In the formula, examples of M include Co, Mn, Al, Be, B, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. M is at least one element selected from these elements. Among these, at least one element selected from the group consisting of Mn, Co, Al, Fe, Ti, Mg, Ca, Sr, and Si is preferred, and as described above, it is preferred to contain at least Mn. The composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ In the formula, the molar ratio (1-a) of M is preferably 0.05 or more and 0.60 or less, more preferably 0.25 or more and 0.55 or less, and particularly preferably 0.30 or more and 0.50 or less.

[0032] Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄIn the formula, the molar ratio (d) of O is a value that satisfies electrical neutrality. In other words, it is a value that satisfies the valence of O in the positive electrode active material. The molar ratio (d) 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, d = x + y + 1, or d < x + y + 1, or d > x + y + 1. In particular, in the positive electrode active material immediately after production, when d < x + y + 1, the layered rock salt structure has a missing oxygen structure. The molar ratio (d) of O is preferably, for example, 1.8 or more and 2.3 or less.

[0033] The positive electrode active material is a Li—Na composite oxide having a composition represented by the above composition formula, and is mainly composed of a Li—Na composite oxide that, when 1 L of water is added to 1000 g of the composite oxide, exhibits an alkaline component eluted in water at a concentration of less than 700 mmol / L. Here, "main component" refers to the component that has the highest mass ratio among the components constituting the positive electrode active material. The positive electrode mixture layer 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%.

[0034] When 1 L of water is added to 1000 g of Li—Na composite oxide, the concentration of the alkaline component eluted in the water is preferably 500 mmol / L or less, more preferably 300 mmol / L or less, and particularly preferably 100 mmol / L or less. If the amount of eluted alkaline component is 700 mmol / L or more, problems such as gelation of the positive electrode mixture slurry occur, making it unusable for practical production. If the amount of eluted alkaline component is, for example, 100 mmol / L or less, the stability of the positive electrode mixture slurry is particularly good, and a high-quality positive electrode 11 can be produced even in practical production. The lower limit of the amount of eluted alkaline component is not particularly limited, but is, for example, 10 mmol / L. Excessive removal of the alkaline component is likely to cause alkali metal detachment from the active material, which may result in capacity degradation and increased resistance.

[0035] The alkaline component is mainly due to Li and Na that are not incorporated into the crystalline structure of the composite oxide and are present on the particle surface. In other words, the Li—Na composite oxide is used after being washed with water until the amount of eluted alkaline component is less than 700 mmol / L. The Na incorporated into the crystalline structure of the Li—Na composite oxide is not substantially eluted during the water washing process of the composite oxide, and the molar ratio (y) of Na does not substantially change even if the washing is repeated. For example, when the Li—Na composite oxide is washed with water until the amount of eluted alkaline component is 100 mmol / L or less or substantially 0 (measurement limit), the Li—Na composite oxide has the above composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ It is a composite oxide that satisfies the above.

[0036] The Li—Na composite oxide is, for example, a secondary particle formed by aggregation of a plurality of primary particles. An example of the volume-based median diameter (D50) of the Li—Na composite oxide is 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 integrated value is 50% in the particle size distribution measured by a laser diffraction scattering method. 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 composite oxide is measured in accordance with the BET method (nitrogen adsorption method) described in JIS R1626. If the D50 and BET specific surface area are within the ranges, it is easy to increase the capacity.

[0037] 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 sodium composite oxide, and (2) reacting the sodium composite oxide with a lithium compound to exchange a portion of the Na in the sodium composite oxide for Li. ｚ Ni ｂ M １－ｂ O ｅIn the formula, M is at least one element selected from the group consisting of transition metal elements other than Li, Na, and Ni and typical elements, and z≧0.90, 0.40≦b≦0.95, and e is a value that satisfies electrical neutrality.

[0038] Composition formula Na ｚ Ni ｂ M １－ｂ O ｅ In the formula, M is Li ｘ Na ｙ Ni ａ M １－ａ O ｄ It is the same as M in the formula (1), and preferably contains at least Mn. That is, in step (1), it is preferable to add a manganese raw material. ｚ Ni ｂ M １－ｂ O ｅ In the formula, the molar ratio of Ni (b) and the molar ratio of O (e) are ｘ Na ｙ Ni ａ M １－ａ O ｄ The molar ratio of Na (z) may be 0.90 or more, and is preferably 0.95 or more and 1.05 or less.

[0039] 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 , NaHCO３ , NaOH, NaNO ３ is preferred.

[0040] 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, NiOH, and Ni(OH). ２ , hydroxides such as NiOOH, NiNO ３ Nitrates such as NiCO ３ , Ni ４ CO ３ (OH) ６ (H ２ O) ４ Carbonates such as NiSO ４ Among them, Ni(OH) ２ is preferred.

[0041] 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.

[0042] The mixing ratio of raw materials for the sodium composite oxide is, for example, ｚ Ni ｂ M １－ｂ O ｅ The method for mixing the raw materials is not particularly limited as long as it can mix the raw materials uniformly, and examples thereof include mixing using a known mixer such as a mixer.

[0043] The mixture of raw materials is fired in a firing furnace in the atmosphere or in an oxygen stream. The firing 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. When the firing temperature is 750°C or higher and 850°C or lower, the firing time is preferably 20 hours or longer. Here, the firing time means the time from when the temperature of the firing furnace reaches the firing temperature to when firing ends and cooling begins. The fired product is, for example, rapidly cooled in the atmosphere by being removed from the firing furnace.

[0044] In step (2), a portion of the Na in the sodium 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 bed of a lithium salt to the sodium composite oxide and heating it. As the lithium salt, for example, at least one selected from the group consisting of lithium nitrate, lithium sulfate, lithium chloride, lithium carbonate, lithium hydroxide, lithium iodide, and lithium bromide is used. However, it is preferable to use at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium hydrogencarbonate, and it is more preferable to use lithium hydroxide.

[0045] Lithium hydroxide may be anhydrous or hydrated. By using at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium hydrogencarbonate, particularly lithium hydroxide, as the lithium molten salt, it becomes easy to leave a predetermined amount of Na, and the molar ratio (y) of Na can be controlled within the above range. When lithium hydroxide is used as the lithium molten salt, the molar ratio of lithium hydroxide to the total moles of the lithium molten salt is preferably 25 mol% or more, more preferably 50 mol% or more, and even more preferably 75 mol% or more. Furthermore, the lithium molten salt may essentially contain only lithium hydroxide.

[0046] In the step (2), the mixing ratio of the Na composite oxide and the lithium molten salt can be appropriately set depending on the ratio of lithium hydroxide contained in the lithium molten salt. 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, for example, 0.8 or more and 1.2 or less in the molar ratio of Li in the lithium molten salt to Na in the Na composite oxide (Li / Na), and the above composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ It is preferable that the content of Li and Na is set so as to satisfy the preferable content of Li and Na in the above range.

[0047] 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 material is cooled. The cooling method is not particularly limited, and may be, for example, natural cooling (cooling in a furnace).

[0048] The product after ion exchange is washed with water to remove alkaline components (Li, Na) present on the particle surface. In the water washing step, a solvent such as ethanol or methanol may be used in combination. The product after water washing is 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. As described above, the product after ion exchange is washed with water until the amount of eluted alkaline components becomes less than 700 mmol / L.

[0049] [Negative Electrode] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode core can be a foil of a metal stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film with such a metal disposed on its surface. The negative electrode mixture layer contains a negative electrode active material and a binder and is preferably provided on both sides of the negative electrode core. The negative electrode 12 can be fabricated, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core. Metallic lithium foil can also be used as the negative electrode 12. Alternatively, the negative electrode 12 may be composed only of a negative electrode core, with metallic lithium being deposited on the core surface during battery charging.

[0050] The negative electrode active material is not particularly limited as long as it reversibly absorbs and releases lithium ions, and generally, carbon materials such as graphite are used. Furthermore, elements that alloy with Li, such as Si and Sn, or materials containing such elements may also be used as the negative electrode active material. Among these, silicon-containing materials containing Si are preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, may also be used as the negative electrode active material. One type of negative electrode active material may be used alone, or multiple types may be used in combination.

[0051] The carbon material functioning as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. Among them, it is preferable to use artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, and amorphous graphite, or a mixture thereof. Examples of the silicon-containing material functioning as the negative electrode active material include silicon alloys, silicon compounds, and Si-containing composite materials. A suitable silicon-containing material is a composite particle containing an ion-conducting phase and a Si phase dispersed in the ion-conducting phase.

[0052] As with the positive electrode 11, the binder contained in the negative electrode mixture layer can be a fluororesin, an olefin resin, PAN, a polyimide, a polyamide, an acrylic resin, or the like. However, polyvinyl acetate, styrene-butadiene rubber (SBR), or the like may also be used. Among these, SBR is preferable. A single binder may be used, or multiple binders may be used in combination. The negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. These function as thickeners in the negative electrode mixture slurry. The binder content 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 negative electrode mixture layer. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0053] [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.

[0054] 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.

[0055] [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.

[0056] 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).

[0057] 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).

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0063] 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.

[0064] 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.

[0065] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0066] Example 1 Preparation of Cathode Active Material A hydroxide containing Ni and Mn in a 1:1 molar ratio and sodium carbonate were mixed in a molar ratio of Ni:Mn:Na = 0.5:0.5:1.05. The resulting mixture was heated at a heating rate of 1 ° C. / min, calcined in air at 800 ° C. for 24 hours, and then rapidly cooled in air to obtain a Na-containing composite oxide. Next, lithium hydroxide and a Na-containing composite oxide were mixed in a molar ratio of Li:Na = 1:1. The resulting mixture was heated at a heating rate of 2 ° C. / min and then heated in air at 300 ° C. for 2 hours. The product was then cooled at a cooling rate of 2 ° C. / min, washed with water, and then heat-treated in vacuum at 160 ° C. for 4 hours to obtain a Li-Na composite oxide (cathode active material).

[0067] The product after the ion exchange treatment was washed with water by adding 1 L of water per 1000 g of the product, stirring, and then performing solid-liquid separation using a centrifuge. In Example 1, this water washing was repeated three times. This water washing step removes alkaline components that had adhered to the surface of the product during the ion exchange step, etc.

[0068] The composition of the obtained Li-Na composite oxide was analyzed using an ICP optical emission spectrometer (CIROS-120 manufactured by Spectro). As a result, the ratio of the total molar amount of Li and Na to the molar amount of metal elements Me excluding Li and Na in the composite oxide ((Li+Na) / Me) was 0.984, and the ratio of the molar amount of Na to the molar amount of metal element Me in the composite oxide (Na / Me) was 0.130. That is, the composition formula of the Li-Na composite oxide is Li ０．８５４ Na ０．１３０ Ni ０．５ Mn ０．５ O ２ is.

[0069] [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 slurry was applied to a positive electrode core made of aluminum foil, and the coating film was dried. The coating film was then rolled with a rolling roller to obtain a positive electrode having a positive electrode mixture layer formed on the positive electrode core.

[0070] [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 water to a concentration of 1 mol / liter to prepare a non-aqueous electrolyte solution.

[0071] [Preparation of Test Cell] A metal lithium 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).

[0072] Example 2 A positive electrode active material and a test cell were produced in the same manner as in Example 1, except that the product after the ion exchange treatment was washed with water twice. Composition analysis of the resulting positive electrode active material revealed that (Li+Na) / Me was 0.950 and Na / Me was 0.137.

[0073] Comparative Example 1 A positive electrode active material and a test cell were produced in the same manner as in Example 1, except that 1 L of water per 1000 g of the product after ion exchange was added to the product, followed by stirring and then washing with water by suction filtration to separate the solid and liquid. Composition analysis of the resulting positive electrode active material revealed that the (Li+Na) / Me ratio was 0.993 and the Na / Me ratio was 0.142.

[0074] Comparative Example 2 A positive electrode active material and a test cell were produced in the same manner as in Comparative Example 1, except that a mixture of lithium nitrate and lithium chloride in a molar mass ratio of 88:12 was used instead of lithium hydroxide as the Li raw material added in the ion exchange step of the Na-containing composite oxide. Composition analysis of the obtained positive electrode active material revealed that (Li+Na) / Me was 0.929 and Na / Me was 0.010.

[0075] Comparative Example 3: A hydroxide containing Ni and Mn in a 1:1 molar ratio, lithium hydroxide, and sodium carbonate were mixed in a molar ratio of Ni:Mn:Li:Na = 0.5:0.5:1.10:0.05. The resulting mixture was heated at a temperature increase rate of 1°C / min, calcined in air at 800°C for 24 hours, and then rapidly cooled in air to obtain a Li-Na composite oxide. The composite oxide was then washed with water in the same manner as in Comparative Example 1 and heat-treated in vacuum at 160°C for 4 hours to obtain a Li-Na composite oxide (cathode active material). Composition analysis of the resulting cathode active material revealed that the (Li + Na) / Me ratio was 1.117 and the Na / Me ratio was 0.017.

[0076] Comparative Example 4 A positive electrode active material and a test cell were produced in the same manner as in Comparative Example 1, except that in the ion exchange step of the Na-containing composite oxide, lithium hydroxide and the Na-containing composite oxide were mixed in a molar ratio of Li:Na=0.8:1. Composition analysis of the obtained positive electrode active material revealed that (Li+Na) / Me was 0.737 and Na / Me was 0.311.

[0077] Comparative Example 5 A positive electrode active material and a test cell were produced in the same manner as in Comparative Example 3, except that the Li—Na composite oxide synthesized in Comparative Example 3 was washed twice with water in the same manner as in Comparative Example 1. Composition analysis of the obtained positive electrode active material revealed that (Li+Na) / Me was 1.110 and Na / Me was 0.001 or less.

[0078] <Reference Example> A hydroxide containing Ni and Mn in a 1:1 molar ratio was mixed with lithium hydroxide in a molar ratio of Ni:Mn:Li = 0.5:0.5:1.09, and the resulting mixture was heated at a temperature increase rate of 1°C / min, calcined in air at 800°C for 24 hours, and then quenched in air to obtain a Li composite oxide. The composite oxide was then washed with water in the same manner as in Comparative Example 1 and heat-treated in vacuum at 160°C for 4 hours to obtain a Li composite oxide (cathode active material). Composition analysis of the resulting cathode active material revealed that the Li / Me ratio was 1.09.

[0079] For each example and comparative example, the amount of alkaline component eluted from the positive electrode active material, the discharge capacity of the test cell, and the properties of the positive electrode mixture slurry were evaluated by the following methods. The evaluation results are shown in Table 1, along with the synthesis method of the positive electrode active material, the (Li+Na) / Me ratio, and the Na / Me ratio.

[0080] [Evaluation of the Amount of Leached Alkaline Component] To each of the positive electrode active materials of the Examples and Comparative Examples, 1 L of water was added per 1000 g of the active material, followed by solid-liquid separation. The concentration (amount of leaching) of the alkaline components (Li+Na) in the filtrate was measured using ICP emission spectroscopy.

[0081] [Evaluation of Discharge Capacity] Each test cell of the Examples and Comparative Examples was charged at a constant current of 0.2 C at 25° C. until the battery voltage reached 4.5 V, and then charged at a constant voltage of 4.5 V until the current value reached 0.02 C. After a 20-minute rest, the test cell was discharged at a constant current of 0.2 C until the battery voltage reached 2.5 V, and the discharge capacity was determined.

[0082] [Evaluation of Positive Electrode Mixture Slurry] The positive electrode mixture slurries prepared when producing the positive electrodes of the Examples and Comparative Examples were left to stand in an environment of 25°C for 7 days, and the changes in the properties of the slurries were observed. The evaluation results shown in Table 1 are as follows: Good: No change Bad: The slurry gelled

[0083]

[0084] As shown in Table 1, the test cells of the examples have higher capacities than the test cells of Comparative Examples 2 to 5 and the Reference Example. Specifically, by using a Li—Na composite oxide as the positive electrode active material, in which the (Li + Na) / Me ratio is 0.90 or more and 1.20 or less, and the residual amount of Na is controlled so that the Na / Me ratio is 0.02 or more and 0.20 or less, the discharge capacity can be significantly improved. When the Na / Me ratio of the positive electrode active material is less than 0.02 (Comparative Examples 2 and 3 and the Reference Example), or when the Na / Me ratio exceeds 0.02 (Comparative Example 4), the discharge capacity is significantly lower than that of the test cells of the examples. Furthermore, when a positive electrode active material with an alkaline component elution amount of 700 mmol / L or more is used (Comparative Examples 1 and 2), the stability of the positive electrode mixture slurry is poor, making it unsuitable for practical production.

[0085] As can be seen from Comparative Examples 3 and 5, most of the Na is eluted by washing with water from the cathode active material obtained by the synthesis method of mixing and baking a transition metal raw material, a Li raw material, and a Na raw material. In other words, the cathode active materials of Comparative Examples 3 and 5 and the cathode active materials of the Examples are considered to be completely different materials, and when the cathode active materials of Comparative Examples 3 and 5 are used, a high capacity battery cannot be achieved.

[0086] The present disclosure is further illustrated by the following embodiments: Structure 1: Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ wherein M is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, and 0.80≦x≦1.15, 0.02≦y≦0.20, 0.90≦x+y≦1.20, 0.40≦a≦0.95, and d is a value that satisfies electrical neutrality, and when 1 L of water is added to 1000 g of the composite oxide, the concentration of alkaline components eluted in water is less than 700 mmol / L. ｘ Na ｙ Ni ａ M １－ａ O ｄ The positive electrode active material for a non-aqueous electrolyte secondary battery according to the first aspect of the present invention, wherein the molar ratio (a) of Ni is 0.50≦a≦0.70. ｘ Na ｙ Ni ａ M １－ａ O ｄ In the formula (1), the molar ratio (y) of Na is 0.06≦y≦0.16. ｘ Na ｙ Ni ａ M １－ａ O ｄwherein M is at least one selected from the group consisting of Mn, Co, Al, Fe, Ti, Mg, Ca, Sr, and Si. Aspect 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Aspects 1 to 4, wherein, when 1 L of water is added to 1000 g of the composite oxide, the concentration of an alkaline component eluted in water is 500 mmol / L or less. Aspect 6: A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: ｚ Ni ｂ M １－ｂ O ｅ wherein M is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, and z≧0.90, 0.40≦b≦0.95, and e is a value satisfying electrical neutrality; and reacting the sodium composite oxide with a lithium compound to exchange a portion of the Na in the sodium composite oxide for Li, wherein the lithium compound contains at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium hydrogencarbonate.Configuration 7: A non-aqueous electrolyte secondary battery comprising: a positive electrode containing the positive electrode active material according to any one of Configurations 1 to 5, a negative electrode, and a non-aqueous electrolyte.

[0087] 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. Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ wherein M is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, 0.80≦x≦1.15, 0.02≦y≦0.20, 0.90≦x+y≦1.20, 0.40≦a≦0.95, and d are values ​​satisfying electrical neutrality, and when 1 L of water is added to 1000 g of the composite oxide, a concentration of an alkaline component eluted in water is less than 700 mmol / L.

2. Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the molar ratio (a) of Ni is 0.50≦a≦0.

70.

3. Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the molar ratio (y) of Na is 0.06≦y≦0.

16.

4. Composition formula Li ｘ Na ｙ Ni ａ M １－ａ O ｄ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein M is at least one selected from the group consisting of Mn, Co, Al, Fe, Ti, Mg, Ca, Sr, and Si.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein when 1 L of water is added to 1000 g of said composite oxide, the concentration of an alkaline component eluted in water is 500 mmol / L or less.

6. A method for producing a positive electrode active material for use in a non-aqueous electrolyte secondary battery, comprising the steps of: ｚ Ni ｂ M １－ｂ O ｅ wherein M is at least one selected from the group consisting of transition metal elements and typical elements other than Li, Na, and Ni, and z≧0.90, 0.40≦b≦0.95, and e is a value satisfying electrical neutrality; and a step of reacting the sodium composite oxide with a lithium compound to exchange a portion of Na in the sodium composite oxide for Li, wherein the lithium compound includes at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium hydrogen carbonate.

7. A non-aqueous electrolyte secondary battery comprising: a positive electrode containing the positive electrode active material according to any one of claims 1 to 5; a negative electrode; and a non-aqueous electrolyte.