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

Abstract

A positive electrode active material, which is an example of an embodiment, is a composite oxide represented by the compositional formula LixNayNiaM1-aOd (in the formula, M is at least one element selected from transition metal elements other than Li, Na, and Ni and typical elements, 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 electroneutrality. When 1 L of water is added to 1000 g of the composite oxide, the concentration of the alkali component eluted into the water is less than 700 mmol / L.

Description

Technical Field

[0001] This disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for manufacturing the positive electrode active material, and a non-aqueous electrolyte secondary battery using the positive electrode active material. Background Technology

[0002] In non-aqueous electrolyte secondary batteries such as lithium-ion batteries, the positive electrode active material has a significant impact on battery performance, including input / output characteristics, capacity, and durability. Therefore, much research has been conducted on positive electrode active materials. Generally, lithium transition metal composite oxides containing transition metal elements such as Ni and Mn are used as positive electrode active materials. The types and amounts of elements contained in the lithium transition metal composite oxide, as well as the crystal structure of the composite oxide, have a significant impact on battery performance. Sometimes, even slight changes in these properties can prevent the achievement of target performance.

[0003] For example, Patent Documents 1-3 disclose the use of Na-containing transition metal composite oxides as positive electrode active materials for the purpose of achieving high-capacity and high-durability non-aqueous electrolyte secondary batteries. Furthermore, Patent Documents 4-6 disclose the synthesis of Na-containing transition metal composite oxides by mixing and calcining transition metal oxides, lithium compounds, and sodium compounds.

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent No. 6395051

[0006] Patent Document 2: Japanese Patent No. 6792836

[0007] Patent Document 3: Japanese Patent Application Publication No. 2011-216495

[0008] Patent Document 4: Japanese Patent Application Publication No. 2020-123440

[0009] Patent Document 5: Japanese Patent Application Publication No. 2020-123441

[0010] Patent Document 6: Japanese Patent No. 5904371 Summary of the Invention

[0011] In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion batteries have been used as power sources for vehicle propulsion, requiring further increases in capacity. As disclosed in the aforementioned patent documents, various studies have been conducted on positive electrode active materials, but from the perspective of increasing capacity, existing positive electrode active materials, including those in the aforementioned patent documents, still have considerable room for improvement.

[0012] The positive electrode active material for non-aqueous electrolyte secondary batteries disclosed herein is characterized by being composed of the formula Lix Na y Ni a M 1-a O d The composite oxide is represented by the formula, where M is at least one selected from 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 electroneutrality. When 1L of water is added to 1000g of the composite oxide, the concentration of the alkaline component dissolved in the water is less than 700mmol / L.

[0013] The method for manufacturing the positive electrode active material disclosed herein is characterized by comprising a step of synthesizing a sodium complex oxide, and a step of reacting the sodium complex oxide with a lithium compound to exchange a portion of the Na in the sodium complex oxide for Li, wherein the sodium complex oxide is composed of the formula Na z Ni b M 1-b O e The compound oxide is represented by the formula, where M is at least one selected from transition metal elements and typical elements other than Li, Na, and Ni, z ≥ 0.90, 0.40 ≤ b ≤ 0.95, e is a value that satisfies electroneutrality, and the lithium compound contains at least one selected from lithium hydroxide, lithium carbonate, and lithium bicarbonate.

[0014] The non-aqueous electrolyte secondary battery disclosed herein comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte, all containing the aforementioned positive electrode active material.

[0015] According to the positive electrode active material disclosed herein, high capacity can be achieved in non-aqueous electrolyte secondary batteries. Attached Figure Description

[0016] Figure 1 This is a longitudinal cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method. Detailed Implementation

[0017] The inventors have conducted in-depth research on increasing the capacity of non-aqueous electrolyte secondary batteries. They discovered that by using a lithium-sodium transition metal composite oxide (represented by the above-described composition) as the positive electrode active material, where the concentration of the alkali component dissolved in water is less than 700 mmol / L when 1 L of water is added to 1000 g of the composite oxide, the battery capacity is significantly increased. Furthermore, when the alkali dissolution amount is less than 700 mmol / L, the properties of the positive electrode slurry used in the manufacture of the positive electrode are stable, and productivity is improved. On the other hand, if the alkali dissolution amount is 700 mmol / L or more, undesirable gelation of the positive electrode slurry occurs, making it difficult to use in actual production.

[0018] The positive electrode active material disclosed herein is obtained by exchanging a portion of the Na in the sodium composite oxide with Li after synthesis, leaving a specified amount of Na remaining. Compared to positive electrode active materials synthesized using conventional ion exchange methods, the positive electrode active material of this disclosure has a higher residual Na content. By controlling the residual Na content within a specific range, the battery capacity is significantly improved. It is believed that the specified amount of Na stabilizes the crystal structure of the positive electrode active material, resulting in a substantial increase in capacity.

[0019] Furthermore, in the positive electrode active material disclosed herein, it is believed that Na, controlled within the aforementioned specific range, enters the crystal structure, and even after repeated washing with water, the Na will not dissolve. In contrast, as disclosed in Patent Documents 4-6, in positive electrode active materials synthesized by mixing and calcining transition metal oxides, lithium compounds, and sodium compounds, substantially all Na dissolves upon washing with water. In other words, the positive electrode active material disclosed herein is considered to be a completely different material from the positive electrode active materials disclosed in Patent Documents 4-6.

[0020] Hereinafter, with reference to the accompanying drawings, an example of an embodiment of the positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the positive electrode active material will be described in detail. Furthermore, technical configurations formed by selectively combining the constituent elements of the various embodiments and modifications described below are also included within the scope of this disclosure.

[0021] In the embodiments described below, a non-aqueous electrolyte secondary battery 10 is exemplified as a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer can 16. However, the outer can of the battery is not limited to a cylindrical outer can. Other embodiments of the non-aqueous electrolyte secondary battery of this disclosure include, for example, a square battery with a square outer can, a coin-shaped battery with a coin-shaped outer can, and a pouch-type battery with an outer can composed of a laminated sheet including a metal layer and a resin layer. In addition, the electrode body is not limited to a wound type and may also be a laminated type electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked with a separator.

[0022] Figure 1 This is a cross-sectional view of a non-aqueous electrolyte secondary battery 10, as an example of an implementation. (See attached image.) Figure 1 As shown, the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer casing 16 for housing the electrode body 14 and the non-aqueous electrolyte. The non-aqueous electrolyte secondary battery 10 is, for example, a lithium-ion secondary battery. The electrode body 14 has 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 wound in a spiral shape with the separator 13 in between. The outer casing 16 is a bottomed cylindrical metal container with an axially open end, and the opening of the outer casing 16 is blocked by a sealing body 17. Hereinafter, for ease of explanation, the sealing body 17 side of the battery is referred to as the upper side, and the bottom side of the outer casing 16 is referred to as the lower side.

[0023] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all strip-shaped elongated bodies, which are alternately stacked in the radial direction of the electrode body 14 by being wound into a spiral. To prevent lithium deposition, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the length direction (long side direction) and the width direction (short side direction). The separator 13 is formed to be at least one size larger than the positive electrode 11, for example, two sheets are arranged to sandwich the positive electrode 11. The electrode body 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.

[0024] Insulating plates 18 and 19 are respectively disposed above and below the electrode body 14. Figure 1 In the example shown, the positive lead 20 extends to the sealing body 17 through the through hole in the insulating plate 18, and the negative lead 21 extends to the bottom of the outer can 16 through the outer side of the insulating plate 19. The positive lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cover 27 of the top plate of the sealing body 17, which is electrically connected to the internal terminal plate 23, becomes the positive terminal. The negative lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative terminal.

[0025] A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness of the battery interior. A groove 22 is formed on the outer can 16, a portion of which extends inward from the side portion to support the sealing body 17. The groove 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove 22 and the open end of the outer can 16 that is riveted to the sealing body 17.

[0026] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating component 25, an upper valve body 26, and a cover 27 are stacked sequentially from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulating component 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating component 25 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heating, the lower valve body 24 deforms and ruptures by pushing the upper valve body 26 upwards towards the cover 27, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cover 27.

[0027] The following provides a detailed description of the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte constituting the non-aqueous electrolyte secondary battery 10, especially the positive electrode 11.

[0028] [positive electrode]

[0029] The positive electrode 11 has a positive electrode core and a positive electrode additive 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, aluminum alloy, stainless steel, or titanium, or a thin film of the metal disposed on its surface. The positive electrode additive layer preferably contains a positive electrode active material, a conductive agent, and a binder, and is disposed on both sides of the positive electrode core. The positive electrode 11 can be manufactured, for example, by coating a positive electrode additive 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 additive layer on both sides of the positive electrode core.

[0030] Examples of conductive agents contained in the positive electrode mixture layer include acetylene black, carbon black such as Ketjen black, graphite, carbon nanotubes (CNTs), carbon nanofibers, graphene, metal fibers, metal powders, and conductive whiskers. A single conductive agent or a combination of multiple agents can be used. The content of the conductive agent is not particularly limited, but relative to the mass of the positive electrode mixture layer, it is, for example, 0.1% by mass or more and 5% by mass or less.

[0031] Examples of binders used in the positive electrode binder layer include fluorinated 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 can also be used in combination with carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc. A single binder can be used, or multiple binders can be used in combination. The content of the binder is not particularly limited, but relative to the mass of the positive electrode binder layer, it is, for example, 0.1% by mass or more and 5% by mass or less.

[0032] The positive electrode active material has a crystal structure belonging to space group R-3m and is composed of the formula Li x Na y Ni a M 1-a O d The term represents a lithium-sodium transition metal composite oxide (Li-Na composite oxide). In the formula, M is at least one transition metal element selected from typical elements other than Li, Na, and Ni, with the following values: 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 electroneutrality. The aforementioned Li-Na composite oxide preferably contains Li, Na, and Ni as essential elements, and also contains Mn. Furthermore, the content of metal elements in the composite oxide can be determined using an ICP emission spectrometer (e.g., a CIROS-120 from SPECTRO).

[0033] In the composition formula Li x Na y Ni a M 1-a O d In this process, the molar ratio (y) of Na can be 0.02 or higher and 0.20 or lower (0.02≤y≤0.20), preferably 0.04 or higher, and more preferably 0.06 or higher. The upper limit of the molar ratio (y) of Na is preferably 0.18, and more preferably 0.16. Furthermore, if the molar ratio (y) exceeds 0.20, it is possible that Na ions will be extracted during charging and absorbed by the negative electrode. This will lead to the formation of byproducts through reaction with the non-aqueous electrolyte during charging and discharging, becoming a major cause of reduced charge / discharge capacity and efficiency of the battery.

[0034] An example of a preferred 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, with 0.04≤y≤0.18 or 0.06≤y≤0.16 being preferred. If the molar ratio (y) of Na is within this range, the layered structure of the composite oxide is considered stable, and the improvement in charge-discharge capacity becomes more significant.

[0035] In the composition formula Li x Na y Ni a M 1-a O d In this process, the molar ratio (x) of Li can be 0.80 or higher and 1.15 or lower (0.80≤x≤1.15), preferably 0.82 or higher, and more preferably 0.84 or higher. The upper limit of the molar ratio (x) of Li is preferably 1.00, and more preferably 0.95. An example of a preferred 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 significant.

[0036] In the composition formula Li x Na y Ni a M 1-a O d In this process, the combined molar ratio (x+y) of Li and Na can be 0.90 or higher and 1.20 or lower (0.90≤x+y≤1.20), preferably 0.92 or higher, and more preferably 0.94 or higher. The upper limit of the combined molar ratio (x+y) of Li and Na is preferably 1.10, and more preferably 1.05. An example of a preferred range for the combined molar ratio (x+y) of Li and Na 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 combined molar ratio (x+y) of Li and Na is within this range, the capacity improvement effect becomes more significant.

[0037] In the composition formula Li x Na y Ni a M1-a O d In this process, the molar ratio (a) of Ni can be 0.40 or higher and 0.95 or lower (0.40 ≤ a ≤ 0.95), preferably 0.45 or higher, more preferably 0.50 or higher. The upper limit of the molar ratio (a) of Ni is preferably 0.75, more preferably 0.70. An example of a preferred 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, wherein 0.45 ≤ a ≤ 0.75 or 0.50 ≤ a ≤ 0.70 is preferred. If the molar ratio (a) of Ni is within this range, it is easy to achieve high capacity while suppressing material costs.

[0038] In the composition formula Li x Na y Ni a M 1-a O d In the formula Li, examples of elements containing 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, Bi, etc. M is at least one element selected from these elements. Preferably, it is selected from at least one of Mn, Co, Al, Fe, Ti, Mg, Ca, Sr, and Si, and as mentioned above, it is preferable to contain at least Mn. In the formula Li x Na y Ni a M 1-a O d In the molar ratio (1-a) of M, it 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.

[0039] In the composition formula Li x Na y Ni a M 1-a O d In this context, the molar ratio (d) of O is a value that satisfies electroneutrality. In other words, it is a value that satisfies the valence of O atoms in the positive electrode active material. There are no particular restrictions on the molar ratio (d) of O as long as it satisfies the valence of atoms in the positive electrode active material; for example, it can be d = x + y + 1, or d < x + y + 1, or d > x + y + 1. Especially in the freshly manufactured positive electrode active material, when d < x + y + 1, it represents an oxygen-deficient structure similar to layered rock salt. The preferred molar ratio (d) of O is, for example, 1.8 or higher and 2.3 or lower.

[0040] The positive electrode active material is a Li-Na composite oxide having the composition expressed by the above formula, with the Li-Na composite oxide having a concentration of less than 700 mmol / L of alkali dissolved in water when 1 L of water is added to 1000 g of the composite oxide as the main component. Here, the main component refers to the component with the highest mass percentage among the constituent components of the positive electrode active material. In the positive electrode additive layer, composite oxides other than this Li-Na composite oxide can be used as the positive electrode active material, but the content of this Li-Na composite oxide is preferably 50% by mass or more, and can practically be 100% by mass.

[0041] When 1 L of water is added to 1000 g of Li-Na composite oxide, the concentration of the alkali component dissolved 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 alkali component dissolved is 700 mmol / L or more, poor gelation of the cathode slurry will occur, making it unsuitable for actual production. When the amount of alkali component dissolved is, for example, 100 mmol / L or less, the stability of the cathode slurry becomes particularly good, and high-quality cathode 11 can be produced in actual production. There is no particular limitation on the lower limit of the amount of alkali component dissolved; 10 mmol / L is an example. Excessive removal of the alkali component greatly increases the possibility of alkali metal detachment from the active material, which can sometimes result in capacity degradation or increased resistance.

[0042] Furthermore, the alkaline component mainly originates from Li and Na present on the particle surface that do not enter the crystal structure of the composite oxide. In other words, the Li-Na composite oxide is used after being washed with water until the leaching of this alkaline component is less than 700 mmol / L. Na, which enters the crystal structure of the Li-Na composite oxide, is substantially not dissolved during the washing process, and the molar ratio (y) of Na remains substantially unchanged even after repeated washing. The Li-Na composite oxide satisfies the above compositional formula Li when, for example, it is washed with water until the leaching of this alkaline component is below 100 mmol / L, or substantially zero (the determination limit). x Na y Ni a M 1-a O d Composite oxides.

[0043] The aforementioned Li-Na composite oxides are, for example, secondary particles formed by the aggregation of multiple primary particles. An example of the median particle size (D50) on a volume basis for Li-Na composite oxides is either 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 that represents 50% of the total volume in the particle size distribution determined by laser diffraction scattering. The BET specific surface area of ​​the Li-Na composite oxide is, for example, 0.1 m². 2 / g or more and 10m 2 / g or less, or 0.5m 2 / g or more and 5m 2 / g or less. The BET specific surface area of ​​the composite oxide was determined according to the BET method (nitrogen adsorption method) as described in JIS R1626. If D50 and BET specific surface area are within this range, high capacity can be easily achieved.

[0044] The Li-Na composite oxide is produced through the following steps: (1) mixing and calcining sodium and nickel raw materials to synthesize the sodium composite oxide; (2) reacting the sodium composite oxide with a lithium compound to exchange a portion of the Na in the sodium composite oxide for Li. In step (1), the sodium composite oxide is synthesized, which is composed of the formula Na z Ni b M 1-b O e The compound oxide is represented by the formula, where M is at least one selected from transition metal elements and typical elements other than Li, Na, and Ni, z ≥ 0.90, 0.40 ≤ b ≤ 0.95, and e is a value that satisfies electroneutrality.

[0045] In the composition formula Na z Ni b M 1-b O e In this context, M and the above-mentioned composition Li x Na y Ni a M 1-a O d The M is the same, and it is preferred to contain at least Mn. That is, in step (1), it is preferred to add manganese raw material. In addition, in the composition formula Na z Ni b M 1-b O e In the above composition formula, the molar ratio of Ni (b) and the molar ratio of O (e) are respectively related to the above composition formula Li x Na y Ni a M 1-a O d a and d are the same. The molar ratio (z) of Na can be 0.90 or higher, preferably 0.95 or higher and 1.05 or lower.

[0046] The sodium raw material used is selected from at least one of metallic sodium and sodium compounds. As for the sodium compound, there are no particular limitations as long as it contains Na; examples include acetates of CH3COONa, CH3COONa・3H2O, nitrates of NaNO3, sulfates of Na2SO4, carbonates of Na2CO3, bicarbonates of NaHCO3, hydroxides of NaOH, and oxides of Na2O and Na2O2. Among these, Na2CO3, NaHCO3, NaOH, and NaNO3 are preferred.

[0047] The nickel raw material used is selected from at least one of metallic nickel and nickel compounds. As for the nickel compound, there are no particular limitations as long as it contains Ni; examples include oxides of NiO, hydroxides of NiOH, Ni(OH)2, and NiOOH, nitrates of NiNO3, carbonates of NiCO3 and Ni4CO3(OH)6(H2O)4, and sulfates of NiSO4. Ni(OH)2 is preferred.

[0048] The manganese raw material used is selected from at least one of metallic manganese and manganese compounds. As for the manganese compound, there are no particular limitations as long as it contains Mn, and examples include oxides of MnO, Mn2O3, Mn3O4, MnO2, etc., hydroxides of Mn(OH)2, MnOOH, etc., carbonates of MnCO3, nitrates of Mn(NO3)2, sulfates of MnSO4, etc. Among these, Mn(OH)2 is preferred.

[0049] Regarding the mixing ratio of raw materials for sodium complex oxides, for example, to satisfy the above composition formula Na z Ni b M 1-b O e The mixing method can be set in any way that can evenly mix the raw materials. There are no particular limitations, and it is possible to use a known mixer or other mixer for example.

[0050] The mixture of the above-mentioned raw materials is fired in a firing furnace in the atmosphere or with 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 heating 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 more. Here, the firing time refers to the time from when the firing furnace reaches the firing temperature until the end of firing and cooling begins. The fired product is then rapidly cooled in the atmosphere, for example, by removing it from the firing furnace.

[0051] In step (2), a portion of the Na in the sodium complex oxide is exchanged for Li. That is, the Li exchange needs to be carried out with a residual amount of Na. As a preferred method for exchanging Na for Li, a method of adding a molten salt bed of lithium salt to the sodium complex oxide and heating it can be cited. The lithium salt can be, for example, at least one selected from lithium nitrate, lithium sulfate, lithium chloride, lithium carbonate, lithium hydroxide, lithium iodide and lithium bromide, preferably at least one selected from lithium hydroxide, lithium carbonate and lithium bicarbonate, and more preferably lithium hydroxide.

[0052] Lithium hydroxide can be anhydrous or hydrated. By using at least one selected from lithium hydroxide, lithium carbonate, and lithium bicarbonate, especially lithium hydroxide, in the lithium molten salt, a specified amount of Na residue can be easily maintained, and the molar ratio (y) of Na can be controlled within the aforementioned range. When lithium hydroxide is used in the lithium molten salt, the molar ratio of lithium hydroxide relative to the total molar 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, in the lithium molten salt, it is possible to use substantially only lithium hydroxide.

[0053] In step (2), the mixing ratio of Na composite oxide and lithium molten salt can be appropriately set according to the proportion of lithium hydroxide contained in the lithium molten salt. When only lithium hydroxide is used in the lithium molten salt, the molar ratio (Li / Na) of Li in the lithium molten salt to Na in the Na composite oxide is, for example, 0.8 or more and 1.2 or less, preferably satisfying the above-mentioned composition formula Li. x Na y Ni a M 1-a O d The optimal content of Li and Na in the solution is set by means of setting the preferred content.

[0054] The heating temperature in the Li exchange process 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 proceeds rapidly, potentially resulting in an uneven reaction. On the other hand, if the heating temperature is below 200°C, the reaction cannot proceed sufficiently, easily leaving excess Na residue. Regarding the heating treatment time, for example, after reaching the target heating treatment temperature at a heating rate of 3.0°C / min or higher and 8.0°C / min or lower, it is set to 3 hours or higher and 10 hours or lower. After heating treatment, cooling is performed. Furthermore, the cooling method is not particularly limited, for example, natural cooling (furnace cooling).

[0055] To remove the alkaline components (Li, Na) present on the particle surface, the products after ion exchange are washed with water. Solvents such as ethanol or methanol can be used in the washing process. By drying the washed products, Li-Na composite oxides are obtained. The drying atmosphere after washing can be atmospheric or vacuum, with no particular limitation. Alternatively, a second heating treatment or a second washing treatment can be performed after washing. As described above, the products after ion exchange are washed with water until the leaching amount of the aforementioned alkaline components is less than 700 mmol / L.

[0056] [negative electrode]

[0057] The negative electrode 12 has a negative electrode core and a negative electrode additive layer disposed on the negative electrode core. The negative electrode core can be made of a metal foil stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a thin film of the metal disposed on its surface. The negative electrode additive layer preferably contains a negative electrode active material and a binder, and is disposed on both sides of the negative electrode core. The negative electrode 12 can be manufactured, for example, by coating a negative electrode additive slurry containing a negative electrode active material and a binder onto the negative electrode core, drying the coating, and then compressing it to form a negative electrode additive layer on both sides of the negative electrode core. Alternatively, lithium metal foil can also be used as the negative electrode 12. Alternatively, the negative electrode 12 can be composed only of the negative electrode core, with lithium metal deposited on the surface of the core during battery charging.

[0058] There are no particular limitations on the negative electrode active material as long as it can reversibly absorb and release lithium ions; carbon materials such as graphite are generally used. Alternatively, elements alloyed with Li, such as Si and Sn, or materials containing these elements can be used as negative electrode active materials. Silicon-containing materials containing Si are preferred. Additionally, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, can also be used as a negative electrode active material. A single negative electrode active material can be used, or multiple materials can be used in combination.

[0059] Carbon materials that function as negative electrode active materials are, for example, at least one selected from natural graphite, artificial graphite, soft carbon, and hard carbon. Among these, artificial graphite such as bulk artificial graphite (MAG) and graphitized mesophase carbon microspheres (MCMB), natural graphite such as flake graphite, bulk graphite, and amorphous graphite, or mixtures thereof, are preferred. Silicon-containing materials that function as negative electrode active materials include, for example, silicon alloys, silicon compounds, and Si-containing composite materials. Suitable silicon-containing materials are composite particles comprising an ion-conducting phase and a Si phase dispersed within the ion-conducting phase.

[0060] Similar to the case of positive electrode 11, the binder contained in the negative electrode binder layer can also be fluoropolymers, olefin resins, PAN, polyimide, polyamide, acrylic resin, etc., or polyvinyl acetate, styrene-butadiene rubber (SBR), etc. SBR is preferred. A single binder or multiple binders can be used. Furthermore, the negative electrode binder layer preferably contains CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. These act as thickeners in the negative electrode binder slurry. The binder content is not particularly limited, but relative to the mass of the negative electrode binder layer, it is, for example, 0.1% by mass or more and 5% by mass or less. Additionally, the negative electrode binder layer may contain conductive agents such as CNTs.

[0061] [Diaphragm]

[0062] The diaphragm 13 is made of a porous sheet material with ion permeability and insulation properties. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Preferred materials for the diaphragm 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The diaphragm 13 can be a single-layer structure or a multi-layer structure. Furthermore, a resin layer with high heat resistance, such as aramid resin, can be formed on the surface of the diaphragm 13.

[0063] At the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12, a filler layer containing inorganic filler can be formed. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. The filler layer can be formed by coating a slurry containing the filler onto the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0064] [Non-aqueous electrolytes]

[0065] Non-aqueous electrolytes possess ionic conductivity (e.g., lithium-ion conductivity). Non-aqueous electrolytes can be liquid electrolytes (electrolytes) or solid electrolytes.

[0066] Liquid electrolytes (electrolytes) may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents may include, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these solvents. The non-aqueous solvent may contain halogen-substituted derivatives in which at least a portion of the hydrogen atoms has been replaced by halogen atoms such as fluorine. Examples of halogen-substituted derivatives include fluorocyclic carbonates such as fluoroethylene carbonate (FEC), fluorochain carbonates, and fluorochain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0067] Examples of the aforementioned esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate; chain carbonates such as dimethyl carbonate (DMC), methyl ethyl 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).

[0068] Examples of the aforementioned ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eudesmol, crown ethers, 1,2-dimethoxyethane diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and dihexyl ether. Ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, 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, tetraethylene glycol dimethyl ether, and other chain ethers.

[0069] The preferred electrolyte salt is a lithium salt. Examples of lithium salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB. 10 Cl 10Examples of lithium salts include lower aliphatic carboxylic acids such as lithium Cl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium tetrafluoro(oxalate)phosphate. Examples of borates include lithium bis(oxalate)borate (LiBOB) and lithium difluoro(oxalate)borate (LiDFOB). Examples of imide salts include lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium trifluoromethanesulfonyl-nonafluorobutanesulfonylimide (LiN(CF3SO2)(C4F9SO2)), and lithium bis(pentafluoroethanesulfonyl)imide (LiN(C2F5SO2)2). Among these, LiPF6 is preferred from the perspectives of ionic conductivity and electrochemical stability. The concentration of lithium salt, for example, relative to 1L of non-aqueous solvent, can be less than 4 moles, less than 3 moles, preferably less than 1.8 moles, more preferably more than 0.8 moles and less than 1.8 moles.

[0070] Non-aqueous electrolytes may contain additives. Examples of additives include unsaturated carbonates, acid anhydrides, phenolic compounds, benzene compounds, nitrile compounds, isocyanate compounds, sulpholactone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0071] 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, vinylvinylene carbonate, and divinylvinylene carbonate. One type of unsaturated cyclic carbonate can be used alone, or in combination of two or more. In unsaturated cyclic carbonates, some hydrogen atoms can be replaced by fluorine atoms. The acid anhydride can be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, preferably an anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0072] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0073] Examples of nitrile compounds include adiponitrile, heptanonitrile, propionitrile, and succinate. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bis(methyl isocyanate)cyclohexane (BIMCH). Examples of sulcolone compounds include propane sulcolone and propene sulcolone. Examples of sulfuric acid compounds include vinyl sulfate, ethylene sulfate, dimethyl sulfate, and lithium fluorosulfate. Examples of borate compounds include trimethylborate and tris(trimethylsilyl)borate. Examples of phosphate compounds include trimethyl phosphate and tris(trimethylsilyl) phosphate. Examples of phosphite compounds include trimethyl phosphite and tris(trimethylsilyl) phosphite.

[0074] As a solid electrolyte, examples include solid or gel-like polymer electrolytes and inorganic solid electrolytes. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Polymer electrolytes may contain, for example, lithium salts and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As a matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent can be used. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins.

[0075] Example

[0076] The present disclosure will be further illustrated below by way of examples, but the present disclosure is not limited to these examples.

[0077] <Example 1>

[0078] [Preparation of positive electrode active material]

[0079] A Ni- and Mn-containing hydroxide in a 1:1 molar ratio and sodium carbonate in a Ni:Mn:Na molar ratio of 0.5:0.5:1.05 were mixed. The resulting mixture was heated at 1 °C / min and calcined in air at 800 °C for 24 hours, followed by rapid cooling in air to obtain a Na-containing composite oxide. Next, lithium hydroxide and the Na-containing composite oxide were mixed in a Li:Na molar ratio of 1:1. The resulting mixture was heated at 2 °C / min in air at 300 °C for 2 hours. The product was then cooled at 2 °C / min, washed with water, and then heated in a vacuum at 160 °C for 4 hours to obtain a Li-Na composite oxide (positive electrode active material).

[0080] The product after ion exchange treatment was washed by adding 1 L of water to every 1000 g of product, stirring, and then separating the solid and liquid components using a centrifuge. In Example 1, this washing was repeated three times. This washing process removes the alkaline components that adhere to the surface of the product during the ion exchange process.

[0081] The composition of the obtained Li-Na composite oxide was analyzed using an ICP emission spectrometer (SPECTRO CIROS-120). The results showed that the ratio of the total molar amount of Li and Na in the composite oxide to the molar amount of the metal element Me (excluding Li and Na) ((Li+Na) / Me) was 0.984, and the ratio of the molar amount of Na in the composite oxide to the molar amount of the metal element Me (Na / Me) was 0.130. Therefore, the composition formula of the Li-Na composite oxide is Li... 0.854 Na 0.130 Ni 0.5 Mn 0.5 O2.

[0082] [The production of the positive electrode]

[0083] The aforementioned Li-Na composite oxide was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a solid content mass ratio of 92:5:3, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare a positive electrode slurry. This positive electrode slurry was coated onto a positive electrode core made of aluminum foil. After the coating dried, it was calendered using calendering rollers to obtain a positive electrode with a positive electrode slurry layer formed on the positive electrode core.

[0084] [Preparation of non-aqueous electrolytes]

[0085] A non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / L in a mixed solvent consisting of ethylene fluorocarbonate (FEC) and methyl propionate (FMP) in a volume ratio of 1:3.

[0086] [Construction of Experimental Units]

[0087] Using lithium foil as the negative electrode, the positive and negative electrodes are arranged opposite each other through a separator to form an electrode body. The electrode body and the non-aqueous electrolyte are placed in a coin-shaped outer container, and the opening of the outer container is sealed with a gasket and a sealing body to create a test unit (non-aqueous electrolyte secondary battery).

[0088] <Example 2>

[0089] Except for changing the number of water washes of the product after ion exchange treatment to 2, the positive electrode active material and test unit were prepared in the same manner as in Example 1. The composition of the obtained positive electrode active material was analyzed, and the results showed that (Li+Na) / Me was 0.950 and Na / Me was 0.137.

[0090] <Comparative Example 1>

[0091] After ion exchange, 1 L of water was added to every 1000 g of product and stirred. The product was then washed with water using a solid-liquid separation method via vacuum filtration. Otherwise, the positive electrode active material and experimental unit were prepared in the same manner as in Example 1. Compositional analysis of the obtained positive electrode active material showed that (Li+Na) / Me was 0.993 and Na / Me was 0.142.

[0092] <Comparative Example 2>

[0093] As the Li raw material added in the ion exchange process of the Na-containing composite oxide, lithium hydroxide was replaced by a substance prepared by mixing lithium nitrate and lithium chloride in a molar mass ratio of 88:12. Otherwise, the positive electrode active material and test unit were prepared in the same manner as in Comparative Example 1. Compositional analysis of the obtained positive electrode active material showed that (Li+Na) / Me was 0.929 and Na / Me was 0.010.

[0094] <Comparative Example 3>

[0095] A Ni-Mn hydroxide, lithium hydroxide, and sodium carbonate were mixed in a 1:1 molar ratio with a Ni:Mn:Li:Na molar ratio of 0.5:0.5:1.10:0.05. The resulting mixture was heated at a rate of 1 °C / min and calcined in air at 800 °C for 24 hours, followed by rapid cooling in air to obtain a Li-Na composite oxide. The composite oxide was then washed with water using the same method as in Comparative Example 1 and heated in a vacuum at 160 °C for 4 hours to obtain the Li-Na composite oxide (positive electrode active material). Compositional analysis of the obtained positive electrode active material showed that (Li+Na) / Me was 1.117 and Na / Me was 0.017.

[0096] <Comparative Example 4>

[0097] In the ion exchange process of the Na-containing composite oxide, lithium hydroxide and the Na-containing composite oxide were mixed at a molar ratio of Li:Na = 0.8:1. Otherwise, the positive electrode active material and test unit were prepared in the same manner as in Comparative Example 1. Compositional analysis of the obtained positive electrode active material showed that (Li+Na) / Me was 0.737 and Na / Me was 0.311.

[0098] <Comparative Example 5>

[0099] Except that the Li-Na composite oxide synthesized in Comparative Example 3 was washed twice with water using the same method as in Comparative Example 1, the positive electrode active material and test unit were prepared in the same manner as in Comparative Example 3. The composition of the obtained positive electrode active material was analyzed, and the results showed that (Li+Na) / Me was 1.110 and Na / Me was less than 0.001.

[0100] <Reference Example>

[0101] A Ni and Mn hydroxide in a 1:1 molar ratio and lithium hydroxide in a Ni:Mn:Li molar ratio of 0.5:0.5:1.09 were mixed. The resulting mixture was heated at a heating rate of 1 °C / min and calcined in air at 800 °C for 24 hours, followed by rapid cooling in air to obtain a Li composite oxide. The composite oxide was then washed with water using the same method as in Comparative Example 1 and heated in a vacuum at 160 °C for 4 hours to obtain the Li composite oxide (positive electrode active material). Compositional analysis of the obtained positive electrode active material showed a Li / Me ratio of 1.09.

[0102] For each embodiment and comparative example, the leaching amount of the alkaline component of the positive electrode active material, the discharge capacity of the test unit, and the properties of the positive electrode slurry were evaluated using the methods described below. The evaluation results, along with the synthesis method of the positive electrode active material, the (Li+Na) / Me ratio, and the Na / Me values, are shown in Table 1.

[0103] [Evaluation of the dissolution amount of alkaline components]

[0104] In each of the positive electrode active materials in the examples and comparative examples, 1L of water was added to every 1000g of active material, and solid-liquid separation was performed. The concentration (dissolution amount) of the alkaline component (Li+Na) in the filtrate was determined by ICP emission spectroscopy.

[0105] [Evaluation of discharge capacity]

[0106] Each test unit of the examples and comparative examples was charged at a constant current of 0.2C at 25°C until the battery voltage reached 4.5V, and then charged at a constant voltage of 4.5V until the current value reached 0.02C. After a 20-minute pause, the battery was discharged at a constant current of 0.2C until the battery voltage reached 2.5V, and the discharge capacity was calculated.

[0107] [Evaluation of the positive electrode mixture slurry]

[0108] The cathode slurries prepared during the production of the examples and comparative examples were left to stand at 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.

[0109] Good: No change

[0110] Bad: Slurry gelation

[0111] Table 1

[0112]

[0113] As shown in Table 1, the test unit of the Examples exhibits a higher capacity compared to the test units of Comparative Examples 2-5 and the Reference Examples. Specifically, by using Li-Na composite oxides as the positive electrode active material, where the residual Na content is controlled to be (Li+Na) / Me between 0.90 and 1.20 and Na / Me between 0.02 and 0.20, 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, 3, and the Reference Examples), or when the Na / Me ratio exceeds 0.02 (Comparative Example 4), the discharge capacity is significantly reduced compared to the test units of the Examples. Furthermore, when using a positive electrode active material with an alkali leaching amount of 700 mmol / L or more (Comparative Examples 1 and 2), the stability of the positive electrode slurry is poor, making it unsuitable for actual production.

[0114] As can be seen from Comparative Examples 3 and 5, the positive electrode active material obtained by the synthesis method of mixing transition metal raw materials, Li raw materials and Na raw materials and then calcining them, almost all of the Na is dissolved by washing with water. In other words, it is considered that the positive electrode active materials of Comparative Examples 3 and 5 are completely different materials from the positive electrode active materials of the Examples, and it is impossible to achieve high battery capacity when using the positive electrode active materials of Comparative Examples 3 and 5.

[0115] The present disclosure will be further described through the following embodiments.

[0116] Technical Composition 1: A positive electrode active material for non-aqueous electrolyte secondary batteries, composed of Li x Na y Ni a M 1- a O d The compound oxide is represented by the formula, where M is at least one selected from 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 electroneutrality.

[0117] When 1L of water is added to 1000g of the composite oxide, the concentration of the alkaline component dissolved in the water is less than 700mmol / L.

[0118] Technical Configuration 2: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Technical Configuration 1, in the formula Li x Na y Ni a M 1-a O d In this case, the molar ratio (a) of Ni is 0.50≤a≤0.70.

[0119] Technical Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Technical Configuration 1 or 2, in the formula Li x Na y Ni a M 1-a O d In this case, the molar ratio (y) of Na is 0.06 ≤ y ≤ 0.16.

[0120] Technical configuration 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of technical configurations 1 to 3, in the formula Li x Na y Ni a M 1-a O d In this context, M is selected from at least one of Mn, Co, Al, Fe, Ti, Mg, Ca, Sr, and Si.

[0121] Technical configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of technical configurations 1 to 4, when 1L of water is added to 1000g of the composite oxide, has a concentration of alkaline components dissolved in the water of 500mmol / L or less.

[0122] Technical Component 6: A method for manufacturing a positive electrode active material, which is a method for manufacturing a positive electrode active material used in a non-aqueous electrolyte secondary battery, including a step of synthesizing a sodium composite oxide, and a step of 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 sodium composite oxide is composed of the formula Na z Ni b M 1-b O e The compound oxide is represented by the formula, where M is at least one selected from transition metal elements and typical elements other than Li, Na, and Ni, z ≥ 0.90, 0.40 ≤ b ≤ 0.95, e is a value that satisfies electroneutrality, and the lithium compound contains at least one selected from lithium hydroxide, lithium carbonate, and lithium bicarbonate.

[0123] Technical configuration 7: A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises the positive electrode active material as described in any one of technical configurations 1 to 5.

[0124] Explanation of reference numerals in the attached figures

[0125] 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 lead, 21 Negative lead, 22 Tank, 23 Internal terminal board, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket.

Claims

1. A positive electrode active material for non-aqueous electrolyte secondary batteries, comprising the formula Li x Na y Ni a M 1-a O d The compound oxide is represented by the formula, where M is at least one selected from 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 electroneutrality. When 1L of water is added to 1000g of the composite oxide, the concentration of the alkaline component dissolved in the water is less than 700mmol / L.

2. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, In the composition formula Li x Na y Ni a M 1-a O d In this case, the molar ratio of Ni, a, is 0.50 ≤ a ≤ 0.

70.

3. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, In the composition formula Li x Na y Ni a M 1-a O d In this case, the molar ratio of Na, y, is 0.06 ≤ y ≤ 0.

16.

4. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1, In the composition formula Li x Na y Ni a M 1-a O d In this context, M is selected from at least one 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, When 1L of water is added to 1000g of the composite oxide, the concentration of the alkaline component dissolved in the water is less than 500mmol / L.

6. A method for manufacturing a positive electrode active material, which is a method for manufacturing a positive electrode active material used in a non-aqueous electrolyte secondary battery, comprising a step of synthesizing a sodium composite oxide, and a step of reacting the sodium composite oxide with a lithium compound to exchange a portion of the Na in the sodium composite oxide for Li. The sodium composite oxide is composed of the formula Na z Ni b M 1-b O e The compound oxide is represented by the formula, where M is at least one selected from transition metal elements and typical elements other than Li, Na, and Ni, z ≥ 0.90, 0.40 ≤ b ≤ 0.95, and e is a value that satisfies electroneutrality. The lithium compound comprises at least one selected from lithium hydroxide, lithium carbonate, and lithium bicarbonate.

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

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