Sodium-ion positive electrode material and preparation method thereof, secondary battery

Abstract

The application relates to the technical field of material preparation, and discloses a sodium ion positive electrode material, a preparation method thereof, and a secondary battery. α Ni x Fe y M (1‑x‑y) O2, wherein 0.60 < alpha <= 1.00, 0 < x <= 0.50, 0 < y <= 0.50, x + y < 1.00, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, K, Ca, Li, Mo, B, Sn, Si, Nb, Zn, W, Tc, Cd, Pd, Pb, Po, Tl, Ge, Sc, Ru and Rh, the crystal structure is single crystal, the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, and the content of M gradually decreases. The sodium ion positive electrode material is stable in structure, and can realize high capacity and long cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material preparation, and particularly relates to a sodium ion positive electrode material, a preparation method thereof and a secondary battery. BACKGROUND

[0002] Compared with lithium ion batteries, sodium ion batteries have the advantages of rich reserves of raw materials, low price, relatively stable chemical properties and good safety, and are expected to replace lithium ion batteries and enter the market. Among the sodium ion battery positive electrode materials, layered oxides are most concerned due to their high specific capacity and structure similar to that of lithium ion battery positive electrode materials. In order to make the layered oxide material meet the demand of the cycle life of the battery, doping and surface coating in the material body are necessary measures. Through element doping and surface coating, the cycle reversibility of the material can be improved, the reversible capacity can be increased, the sodium ion diffusion dynamics performance can be improved, the properties of the crystal lattice can be changed to some extent, and the crystal lattice stability, electronic conductivity, sodium ion intercalation and deintercalation dynamics performance, etc. can be enhanced. However, the general doping is that the elements are uniformly distributed in the interior of the sodium ion material, so that the surface layer composition is the same as the internal composition, and the material with high chemical activity of the surface layer is easy to react with the electrolyte, so it needs to be coated again. The coating material is usually an oxide such as aluminum oxide, zirconium oxide, titanium oxide, boron oxide, etc. The oxide is a non-active material, which is not conducive to sodium ion conduction and has the risk of peeling off the coating layer, so as to affect the performance of the battery positive electrode material.

[0003] Although there are currently some sodium ion positive electrode materials with uneven distribution of doping elements in the industry, they are usually gradient materials or core-shell materials synthesized in the precursor stage, and after sintering, they are usually polycrystalline structures with large particle sizes. The performance of the prepared sodium ion positive electrode material is not good. SUMMARY

[0004] To solve the above problems, the present application provides a sodium ion positive electrode material, a preparation method thereof and a secondary battery. The present application performs full gradient doping on the sodium ion positive electrode material by solid phase method to form a structure-stable layered material, thereby realizing high capacity and long cycle performance, so that the prepared secondary battery can be applied to large-scale energy storage field as a new generation of energy storage device.

[0005] To achieve the above purpose, the first aspect of the present application provides a sodium ion positive electrode material, the chemical formula of which is Na α Ni x Fe y M (1-x-y)O2, wherein 0.60 < alpha <= 1.00, 0 < x <= 0.50, 0 < y <= 0.50, x + y < 1.00, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, K, Ca, Li, Mo, B, Sn, Si, Nb, Zn, W, Tc, Cd, Pd, Pb, Po, Tl, Ge, Sc, Ru and Rh, the crystal structure is single crystal, and the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, and the content of M gradually decreases.

[0006] Compared with the prior art, the sodium ion positive electrode material has at least the following technical effects.

[0007] Firstly, the sodium ion positive electrode material contains Ni and Fe. Ni is an active metal element in the electrochemical reaction process and can provide more valence changes, thereby improving the specific capacity of the sodium ion positive electrode material. Fe is also an active metal element, and the electrode potential is high, that is, a higher charge and discharge voltage can be provided, thereby realizing a larger energy density.

[0008] Secondly, the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, that is, the active metal elements Ni and Fe are mainly distributed in the inside of the single crystal, so that the stability of the structure of the sodium ion positive electrode material can be maintained.

[0009] Specifically embodied in:

[0010] (1) The contact of the active metal elements Ni and Fe with the electrolyte during the charging and discharging process can be reduced. In particular, when the charging voltage is high, the high oxidizing property of Ni 4+ and Fe 4+ reacts with the electrolyte, resulting in the destruction of the material structure. In addition, the trace doping of M metal ions in the inside of the single crystal structure also better maintains the stability of the internal structure, thereby realizing higher capacity and cycle performance.

[0011] (2) The distribution of such elements can solve the problem of too high residual sodium content on the surface. The M element on the surface can react with the residual sodium to form a sodium ion positive electrode material with low sodium content, so as to improve the processing performance of the material and reduce the gas production and other electrochemical properties of the battery.

[0012] (3) During the charging and discharging process, the volume of the crystal will change. Through such a gradient distribution of the material, the stable structure of the surface layer can inhibit the phase change of the internal material to a certain extent, and at the same time will not cause the surface layer to crack, which helps to improve the electrochemical performance of the material.

[0013] Thirdly, the sodium ion positive electrode material is a single crystal structure, so the particle size is small, the specific surface area is large, and the structural stability is high. The electrical performance of the material is high in specific capacity, excellent in rate performance and long in cycle life.

[0014] In some embodiments, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, Mo, Zn and W.

[0015] In some embodiments, 0.60 < a < 0.90, 0.10 < x < 0.50, 0.10 < y < 0.50.

[0016] In some embodiments, M is Zn and / or Mn, a = 0.85, x = 0.30, y = 0.40.

[0017] In some embodiments, the average particle size of the single crystal is 1.5 μm to 3.0 μm.

[0018] In some embodiments, the specific surface area of the sodium-ion positive electrode material is 0.6 m 2 / g to 1.2 m 2 / g.

[0019] The second aspect of the present application provides a preparation method of a sodium-ion positive electrode material, comprising the steps of:

[0020] (I) preparing a sodium nickel ferrite positive electrode material

[0021] According to the formula amount, a nickel source, an iron source and a sodium source are mixed in water to obtain a mixed solution, and then the mixed solution is ground to obtain a slurry, and the slurry is spray dried to obtain a precursor powder. The precursor powder is subjected to first sintering and first crushing;

[0022] (II) preparing a full-gradient doped sodium-ion positive electrode material

[0023] The M source is mixed in water to obtain a mixed solution, and then the mixed solution is ground to obtain a slurry. The slurry is mixed with the sodium nickel ferrite positive electrode material according to the formula amount, and then spray dried and subjected to second sintering and second crushing,

[0024] and the temperature of the first sintering is lower than that of the second sintering.

[0025] The preparation method of the sodium-ion positive electrode material of the present application is prepared by spray drying and solid-phase sintering. First, a sodium nickel ferrite positive electrode material with a small particle size is prepared, and then a layer of M source material is coated by spray drying. In the solid-phase sintering mode, the M element slowly penetrates into the interior of the material by increasing the sintering temperature, and the Ni and Fe elements occupied by the M element gradually penetrate to the outside of the material, so that a full-gradient doped sodium-ion positive electrode material is formed. This preparation method can prepare small single crystal particles, and the particle size is uniform, the powder and defects are few, and the surface is smooth. At the same time, the preparation material process is simple, the cost is low, and the industrial production can be realized.

[0026] In some embodiments, the nickel source is nickel oxide.

[0027] In some embodiments, the iron source is iron oxide.

[0028] In some embodiments, the M source is an oxide of M, M being at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, K, Ca, Li, Mo, B, Sn, Si, Nb, Zn, W, Tc, Cd, Pd, Pb, Po, Tl, Ge, Sc, Ru and Rh.

[0029] In some embodiments, the sodium source is at least one of NaOH, NaNO3, Na2CO3 and CH3COONa.

[0030] In some embodiments, the molar amount of sodium element in the sodium source is m, the sum of the molar amount of nickel element in the nickel source and the molar amount of iron element in the iron source is n, and m / n is 1.00-1.45:1.

[0031] In some embodiments, the solid content of the mixed solution in step (I) for preparing the sodium nickel ferrite positive electrode material is 20wt.% to 40wt.%.

[0032] In some embodiments, the Dv50 of the slurry in step (I) for preparing the sodium nickel ferrite positive electrode material is 0.2μm to 0.7μm.

[0033] In some embodiments, the inlet air temperature of the spray drying in step (I) for preparing the sodium nickel ferrite positive electrode material is 220℃ to 280℃, and the exhaust air temperature is 80℃ to 100℃.

[0034] In some embodiments, air is introduced during the first sintering process.

[0035] In some embodiments, the temperature of the first sintering is 600℃ to 850℃.

[0036] In some embodiments, the holding time of the first sintering is 5h to 12h.

[0037] In some embodiments, the heating rate of the first sintering is 2℃ / min to 5℃ / min.

[0038] In some embodiments, the first crushing includes sequentially using a rotary wheel mill for coarse crushing and an air jet mill for fine crushing on the product after the first sintering.

[0039] In some embodiments, the Dv50 of the particles after the first crushing is 2.0μm to 4.0μm.

[0040] In some embodiments, the mass ratio of the sodium nickel ferrite positive electrode material to the M source is 1-8:1.

[0041] In some embodiments, the solid content of the mixed solution in step (II) for preparing the full-gradient doped sodium-ion positive electrode material is 5wt.% to 15wt.%.

[0042] In some embodiments, the Dv50 of the slurry in step (II) for preparing the full-gradient doped sodium-ion positive electrode material is 0.1 μm to 0.3 μm.

[0043] In some embodiments, the inlet air temperature of the spray drying in step (II) for preparing the full-gradient doped sodium-ion positive electrode material is 220°C to 280°C, and the exhaust air temperature is 80°C to 100°C.

[0044] In some embodiments, air is introduced during the second sintering process.

[0045] In some embodiments, the temperature of the second sintering is 750°C to 950°C.

[0046] In some embodiments, the holding time of the second sintering is 6h to 16h.

[0047] In some embodiments, the heating rate of the second sintering is 1°C / min to 4°C / min.

[0048] In some embodiments, the second crushing includes sequentially using a rotary wheel mill for coarse crushing and an air jet mill for fine crushing on the product after the second sintering.

[0049] In some embodiments, the Dv50 of the particles after the second crushing is 2.5 μm to 4.5 μm.

[0050] The third aspect of the present application provides a secondary battery, including a positive electrode material, a negative electrode material, and an electrolyte, wherein the positive electrode material includes the sodium-ion positive electrode material described above or the sodium-ion positive electrode material prepared by the method for preparing the sodium-ion positive electrode material described above.

[0051] In some embodiments, the negative electrode material includes a carbon-based negative electrode material and / or a silicon-based negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 SEM image of the sodium-ion positive electrode material prepared for Example 1 of the present application;

[0053] Figure 2 XRD image of the sodium-ion positive electrode material prepared for Example 1 of the present application. DETAILED DESCRIPTION

[0054] The secondary battery of the present application comprises a positive electrode material, a negative electrode material and an electrolyte. The preparation process of the secondary battery is similar to that of a lithium ion battery, i.e. first preparing a positive electrode sheet comprising the positive electrode material, a negative electrode sheet comprising the negative electrode material, then winding or stacking the positive electrode sheet, the negative electrode sheet and a separator into an electrode core, and filling the electrolyte into the shell and sealing the shell.

[0055] The negative electrode sheet is obtained by coating the negative electrode slurry comprising the negative electrode material, a binder and a conductive agent on the negative electrode current collector, drying, cold pressing and die cutting. The mass ratio of the negative electrode material, the binder and the conductive agent can be 75-99:0.1-10:0.1-15. The negative electrode material can be, but is not limited to, a carbon-based material and a silicon-based material. The carbon-based material can be, but is not limited to, a graphite-based material, soft carbon or hard carbon. The silicon-based material can be, but is not limited to, SiO x or carbon-coated SiO x , 0≤x<2. The binder is selected from at least one of polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, styrene-butadiene rubber and acrylated styrene-butadiene rubber. The conductive agent is used to improve the conductivity of the negative electrode, and the conductive agent can be, but is not limited to, carbon black, acetylene black, ketjen black, carbon fiber and other carbon-containing materials, or metal powder or metal fiber materials such as copper, nickel, aluminum, silver, or a mixture thereof. The solvent of the negative electrode slurry can be N-methylpyrrolidone or N-vinylpyrrolidone. The negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal and the like.

[0056] The separator can be a conventional insulating porous polymer film or inorganic porous film, and can be, but is not limited to, a single layer or a combined multi-layer of polypropylene, polyethylene, aramid, polyimide and non-woven fabric separator, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator or a polypropylene / polyethylene / polypropylene three-layer separator. An insulating layer that is ion-permeable and electron-impermeable can also be provided on the separator to prevent short circuit of the secondary battery when thermal shrinkage occurs, and the thickness of the separator is 5-50 μm.

[0057] Similar to lithium-ion batteries, the liquid electrolyte for sodium-ion batteries includes a non-aqueous organic solvent, a sodium salt, and an additive. The non-aqueous organic solvent can be a chain carbonate, a cyclic carbonate, a carboxylic acid ester, or a lactone. The chain carbonate can be dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The cyclic carbonate can be ethylene carbonate, propylene carbonate, or butylene carbonate. The carboxylic acid ester can be methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, or ethyl propionate. The lactone can be γ-butyrolactone, butyrolactone, γ-valerolactone, or γ-hexalactone. The sodium salt can be one or more of NaPF6, NaClO4, NaAlCl4, NaFeCl4, NaSO3CF3, NaBCl4, NaNO3, NaPOF4, NaSCN, NaCN, NaAsF6, NaCF3CO2, NaSbF6, NaC6H5CO2, Na(CH3)C6H4SO3, NaHSO4, and NaB(C6H5)4, and the concentration of the sodium salt is 0.2 M to 2.0 M. An additive can be added to the electrolyte to improve the performance of the battery, and the additive can account for 0.1% to 10% of the mass of the electrolyte. The additive can include, but is not limited to, one or more of ethylene sulfite (GS), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), ethylene sulfate (DTD), 4-methyl ethylene sulfate, 4-propyl ethylene sulfate, propylene sulfate, 4-methyl propylene sulfate, and 4-propyl propylene sulfate.

[0058] The preparation of the positive electrode tab generally includes coating a positive electrode slurry including a positive electrode material, a binder, and a conductive agent on a positive electrode current collector, drying, cold pressing, and die cutting. The mass ratio of the positive electrode material, the binder, and the conductive agent can be 80-99:0.5-10:0.5-10. The binder can be, for example, but is not limited to, at least one of polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinylpyrrolidone, styrene-butadiene rubber, acrylated styrene-butadiene rubber, and epoxy resin. The conductive agent is used to improve the conductivity of the positive electrode, and can be, for example, but is not limited to, a carbon-containing material such as carbon black, acetylene black, ketjen black, carbon fiber, or the like, or a metal powder or metal fiber material such as copper, nickel, aluminum, silver, or the like, or a conductive polymer such as a polyphenylene derivative, or a mixture thereof. The positive electrode current collector can be an aluminum foil. The solvent of the positive electrode slurry can be N-methylpyrrolidone or N-vinylpyrrolidone. The positive electrode material can employ the sodium-ion positive electrode material of the present application.

[0059] The sodium ion positive electrode material of the present application is a single crystal structure and the average particle size is 1.5-3.0 μm. For example, the average particle size of the sodium ion positive electrode material can be, but is not limited to, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm. The specific surface area is 0.6-1.2 m 2 / g. 2 / g. For example, the surface area of the sodium ion positive electrode material can be, but is not limited to, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g.

[0060] As a technical solution of the present application, the chemical formula is Na α Ni x Fe y M (1-x-y) O2, wherein 0.60 < α ≤ 1.00, 0 < x ≤ 0.50, 0 < y ≤ 0.50, x + y < 1.00, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, K, Ca, Li, Mo, B, Sn, Si, Nb, Zn, W, Tc, Cd, Pd, Pb, Po, Tl, Ge, Sc, Ru and Rh, the crystal structure is a single crystal, and the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, and the content of M gradually decreases. For example, α can be, but is not limited to, 0.61, 0.63, 0.65, 0.67, 0.69, 0.71, 0.73, 0.75, 0.77, 079, 0.81, 0.83, 0.85, 0.87, 0.89, 0.91, 0.93, 0.95, 0.97, 0.99, 1.00. x can be, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5. y can be, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5. And x and y are not 0.5 at the same time. In some technical solutions, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, Mo, Zn and W. In another technical solution, M is Zn and / or Mn.

[0061] The preparation method of the sodium ion positive electrode material of the present application comprises the steps of (I) preparing a sodium nickel iron oxide positive electrode material and (II) preparing a full-gradient doped sodium ion positive electrode material.

[0062] The step (I) for preparing the sodium nickel iron oxide positive electrode material comprises: mixing a nickel source, an iron source and a sodium source in water according to a formula amount to obtain a mixed solution, grinding the mixed solution to obtain a slurry, and then spray drying the slurry to obtain a precursor powder; and performing first sintering and first crushing on the precursor powder.

[0063] In the formula, the precursor is spherical, the nickel source is nickel oxide, the iron source is iron oxide, the M source is an oxide of M, and M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, K, Ca, Li, Mo, B, Sn, Si, Nb, Zn, W, Tc, Cd, Pd, Pb, Po, Tl, Ge, Sc, Ru and Rh. As an example, the M source can be, but is not limited to, at least one of ZrO2, Al2O3, Co3O4, CuO, Y2O3, TiO2, MgO, B2O3, SnO2, SiO2, Nb2O5 and ZnO. The sodium source is at least one of NaOH, NaNO3, Na2CO3 and CH3COONa. The molar amount of sodium in the sodium source is m, the sum of the molar amounts of nickel in the nickel source and iron in the iron source is n, and m / n is 1.00-1.45:1. Controlling the excess of sodium is beneficial for the second sintering. As an example, m / n can be, but is not limited to, 1.00:1, 1.05:1, 1.10:1, 1.15:1, 1.20:1, 1.25:1, 1.30:1, 1.35:1, 1.40:1 or 1.45:1.

[0064] As a technical solution of the present application, the solid content of the mixed solution is 20wt.% to 40wt.%. As an example, the solid content of the mixed solution can be, but is not limited to, 20wt.%, 21wt.%, 23wt.%, 25wt.%, 27wt.%, 29wt.%, 31wt.%, 33wt.%, 35wt.%, 37wt.%, 39wt.% or 40wt.%. The Dv50 of the particles in the slurry is 0.2μm to 0.7μm. As an example, the Dv50 of the particles in the slurry can be, but is not limited to, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm or 0.7μm. The inlet air temperature of the spray drying is 220℃ to 280℃, and the exhaust air temperature is 80℃ to 100℃. As an example, the inlet air temperature can be, but is not limited to, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃ or 280℃, and the exhaust air temperature can be, but is not limited to, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃ or 100℃.

[0065] As a technical solution of the present application, air is introduced during the first sintering process. The temperature of the first sintering is 600-850°C, and the holding time is 5-12h. As an example, the temperature of the first sintering can be but is not limited to 600°C, 640°C, 680°C, 700°C, 730°C, 760°C, 790°C, 820°C, 850°C, and the holding time of the first sintering can be but is not limited to 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h. As another technical solution of the present application, the heating rate of the first sintering is 2-5°C / min, and as an example, the heating rate of the first sintering can be but is not limited to 2°C / min, 3°C / min, 4°C / min, 5°C / min.

[0066] As a technical solution of the present application, the first crushing includes sequentially using a rotary wheel mill for coarse crushing and an air jet mill for fine crushing of the product after the first sintering to a Dv50 of 2.0-4.0μm of the particles, and as an example, the Dv50 of the particles after the first crushing can be but is not limited to 2.0μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm.

[0067] The step (II) for preparing the full-gradient doped sodium-ion positive electrode material includes mixing M source in water to obtain a mixed solution, grinding to obtain a slurry, adding a sodium nickel ferrite positive electrode material according to the formula amount for mixing, spray drying, and sintering and crushing, and the temperature of the first sintering is lower than that of the second sintering.

[0068] The mass ratio of the sodium nickel ferrite positive electrode material and the M source is 1-8:1. As an example, the mass ratio of the sodium nickel ferrite positive electrode material and the M source can be but is not limited to 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1.

[0069] As a technical solution of the present application, the solid content of the mixed solution is 5-15wt.%, and as an example, the solid content of the mixed solution can be but is not limited to 5wt.%, 6wt.%, 7wt.%, 8wt.%, 9wt.%, 10wt.%, 11wt.%, 12wt.%, 13wt.%, 14wt.%, 15wt.%. The Dv50 of the particles in the slurry is 0.1-0.3μm, and as an example, the Dv50 of the particles in the slurry can be but is not limited to 0.1μm, 0.2μm, 0.3μm. The inlet air temperature of the spray drying is 220-280°C, and the exhaust air temperature is 80-100°C, and as an example, the inlet air temperature can be but is not limited to 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, and the exhaust air temperature can be but is not limited to 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, 100°C.

[0070] As a technical solution of the present application, air is introduced during the second sintering process. The temperature of the second sintering is 750-950°C, and the holding time is 6-16h. As an example, the second sintering temperature can be but is not limited to 750°C, 780°C, 800°C, 820°C, 850°C, 880°C, 900°C, 920°C, 950°C, and the holding time of the second sintering can be but is not limited to 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h. As another technical solution of the present application, the heating rate of the second sintering is 2-5°C / min, and as an example, the heating rate of the second sintering can be but is not limited to 2°C / min, 3°C / min, 4°C / min, 5°C / min.

[0071] As a technical solution of the present application, the second crushing includes rough breaking of the product after the second sintering by a rotary wheel mill and fine breaking by an air jet mill to a Dv50 of 2.5-4.5μm, and as an example, the Dv50 of the particles after the second crushing can be but is not limited to 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm.

[0072] To better illustrate the purpose, technical solutions and beneficial effects of the present application, the present application will be further described below in conjunction with specific examples. It should be noted that the following implementation of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0073] Example 1

[0074] The chemical formula of the sodium ion positive electrode material of the present example is Na 0.85 Ni 0.30 Fe 0.40 Zn 0.10 Mn 0.20 O2, which is a single crystal structure, and the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, and the content of Zn and Mn gradually decreases.

[0075] The preparation method of the sodium ion positive electrode material of the present example includes the following steps.

[0076] (I) Preparation of sodium nickel ferrite positive electrode material

[0077] The NiO, Fe2O3 and Na2CO3 (the molar ratio of sodium in Na2CO3 to the sum of the molar amount of Ni and Fe is 1.20:1) were mixed in water to obtain a mixed solution with a solid content of 30%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.5 μm. The slurry was spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C) to obtain spherical precursor powder. The precursor powder was passed through air, and the temperature was increased to 800°C at a heating rate of 2.5°C / min and was kept for 12 h, and was naturally cooled to room temperature to obtain black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium nickel iron oxide positive electrode material with a particle size Dv50 of 2.5 μm.

[0078] (II) Preparation of a sodium ion positive electrode material with full gradient doping

[0079] ZnO and MnO2 were mixed in water to obtain a mixed solution with a solid content of 8 wt.%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.2 μm. The sodium nickel iron oxide positive electrode material was added for mixing, and the mass ratio of the sodium nickel iron oxide positive electrode material to the dopant (ZnO and MnO2) was 1.9:1. The mixture was spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C). Air was passed through, and the temperature was increased to 900°C at a heating rate of 2.5°C / min and was kept for 10 h, and was naturally cooled to room temperature to obtain black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium ion positive electrode material with full gradient doping with a particle size Dv50 of 3.0 μm.

[0080] The prepared sodium ion positive electrode material was subjected to SEM and XRD tests, and the results are shown in Figure 1 and Figure 2 It can be seen from the results of Figure 1 that the prepared sodium ion positive electrode material is a single crystal structure, and the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, and the content of Zn and Mn ions gradually decreases. The average particle size is about 1.7 μm, the surface of the material is very smooth, there is no fine powder, and the residual alkali content is low. Figure 2 The XRD of

[0081] Example 2

[0082] The chemical formula of the sodium ion positive electrode material of this example is Na 0.80 Ni 0.50 Fe 0.30 Cu0.10 Mn 0.10 O2, which is a single crystal structure, and from the surface of the single crystal to the inside, the content of Ni and Fe gradually increases, and the content of Cu and Mn gradually decreases.

[0083] The preparation method of the sodium ion positive electrode material of the embodiment comprises the following steps.

[0084] (I) Preparation of sodium nickel ferrite positive electrode material

[0085] According to the formula amount, NiO, Fe2O3 and Na2CO3 (the molar ratio of sodium in Na2CO3 to the sum of the molar amount of Ni and Fe is 1.00:1) are mixed in water to obtain a mixed solution with a solid content of 30%, the mixed solution is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.5 μm, and the slurry is spray dried (the spray inlet air temperature is 220°C, and the spray exhaust air temperature is 90°C) to obtain spherical precursor powder. The precursor powder is passed through air, the temperature is raised to 800°C at a heating rate of 2.5°C / min and kept for 12h, and naturally cooled to room temperature to obtain a black blocky material, which is then sequentially subjected to rotary wheel grinding and jet mill crushing to obtain a sodium nickel ferrite positive electrode material with a particle size Dv50 of 2.5 μm.

[0086] (II) Preparation of full gradient doped sodium ion positive electrode material

[0087] CuO and MnO2 are mixed in water to obtain a mixed solution with a solid content of 10wt.%, the mixed solution is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.2 μm, and the mixed solution is mixed with a sodium nickel ferrite positive electrode material (the mass ratio of the sodium nickel ferrite positive electrode material to the dopant (CuO and MnO2) is 5.3:1), and then spray dried (the spray inlet air temperature is 220°C, and the spray exhaust air temperature is 90°C). Air is passed through again, the temperature is raised to 850°C at a heating rate of 2.5°C / min and kept for 10h, and naturally cooled to room temperature to obtain a black blocky material, which is then sequentially subjected to rotary wheel grinding and jet mill crushing to obtain a full gradient doped sodium ion positive electrode material with a particle size Dv50 of 2.8 μm.

[0088] Example 3

[0089] The chemical formula of the sodium ion positive electrode material of the embodiment is Na 0.85 Ni 0.30 Fe 0.40 Zn 0.10 Mn 0.20 O2, which is a single crystal structure, and from the surface of the single crystal to the inside, the content of Ni and Fe gradually increases, and the content of Cu and Mn gradually decreases.

[0090] The preparation method of the sodium ion positive electrode material of the embodiment comprises the following steps.

[0091] (I) Preparation of sodium nickel iron oxide positive electrode material

[0092] The molar amount of sodium in NiO, Fe2O3 and CH3COONa and the sum of the molar amount of Ni and Fe are mixed in water according to the formula amount, and the ratio is 1.45:1. The mixture is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.5 μm. The slurry is spray dried (the spray inlet air temperature is 220°C, and the spray exhaust air temperature is 90°C) to obtain spherical precursor powder. The precursor powder is passed through air, and the temperature is raised to 800°C at a heating rate of 2.5°C / min and kept for 12h, and naturally cooled to room temperature to obtain a black block material. The black block material is then sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium nickel iron oxide positive electrode material with a particle size Dv50 of 2.6 μm.

[0093] (II) Preparation of full-gradient doped sodium ion positive electrode material

[0094] ZnO and MnO2 are mixed in water to obtain a mixture, and the solid content of the mixture is 8wt.%. The mixture is added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.2 μm. The sodium nickel iron oxide positive electrode material (the mass ratio of the sodium nickel iron oxide positive electrode material to the dopant (ZnO and MnO2) is 1.8:1) is mixed and then spray dried (the spray inlet air temperature is 220°C, and the spray exhaust air temperature is 90°C). Air is then passed through, and the temperature is raised to 900°C at a heating rate of 2.5°C / min and kept for 10h, and naturally cooled to room temperature to obtain a black block material. The black block material is then sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a full-gradient doped sodium ion positive electrode material with a particle size Dv50 of 3.5 μm.

[0095] Example 4

[0096] The chemical formula of the sodium ion positive electrode material of the embodiment is Na 0.75 Ni 0.35 Fe 0.35 Zn 0.15 Mn 0.15 O2, which is a single crystal structure, and the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, and the content of Zn and Mn gradually decreases.

[0097] The preparation method of the sodium ion positive electrode material of the embodiment comprises the following steps.

[0098] (I) Preparation of sodium nickel iron oxide positive electrode material

[0099] The NiO, Fe2O3 and Na2CO3 (the molar ratio of sodium in Na2CO3 to the sum of the molar amount of Ni and Fe is 1.05:1) were mixed in water to obtain a mixed solution with a solid content of 25%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.5 μm. The slurry was spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C) to obtain spherical precursor powder. The precursor powder was passed through air, and the temperature was increased to 800°C at a heating rate of 2.5°C / min and maintained for 12 h, and then naturally cooled to room temperature to obtain a black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium nickel iron oxide positive electrode material with a particle size Dv50 of 2.5 μm.

[0100] (II) Preparation of a sodium ion positive electrode material with full gradient doping

[0101] ZnO and MnO2 were mixed in water to obtain a mixed solution with a solid content of 10 wt.%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.2 μm. The slurry was mixed with a sodium nickel iron oxide positive electrode material (the mass ratio of the sodium nickel iron oxide positive electrode material to the dopant (ZnO and MnO2) was 3.25:1), and then spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C). The mixture was passed through air, and the temperature was increased to 900°C at a heating rate of 2.5°C / min and maintained for 10 h, and then naturally cooled to room temperature to obtain a black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium ion positive electrode material with full gradient doping with a particle size Dv50 of 3.0 μm.

[0102] Example 5

[0103] The sodium ion positive electrode material of the present example has a chemical formula of Na 0.85 Ni 0.30 Fe 0.40 Zn 0.10 Mn 0.20 O2, which is a single crystal structure, and the content of Ni and Fe gradually increases from the surface to the inside of the single crystal, and the content of Zn and Mn gradually decreases.

[0104] The method for preparing the sodium ion positive electrode material of the present example comprises the following steps.

[0105] (I) Preparation of a sodium nickel iron oxide positive electrode material

[0106] The NiO, Fe2O3 and Na2CO3 (the molar ratio of sodium in Na2CO3 to the sum of the molar amount of Ni and Fe is 1.20:1) were mixed in water to obtain a mixed solution with a solid content of 30%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.6 μm. The slurry was spray dried (the spray inlet air temperature was 250°C, and the spray exhaust air temperature was 85°C) to obtain spherical precursor powder. The precursor powder was heated in air at a heating rate of 3.5°C / min to 850°C and maintained for 10 h, and then naturally cooled to room temperature to obtain a black block material. The black block material was sequentially subjected to a rotary wheel mill and an air jet mill to obtain a sodium nickel manganese oxide positive electrode material with a particle size Dv50 of 2.0 μm.

[0107] (II) Preparation of a sodium ion positive electrode material with full gradient doping

[0108] ZnO and MnO2 were mixed in water to obtain a mixed solution with a solid content of 8 wt.%. The mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.1 μm. Sodium nickel manganese oxide positive electrode material (the mass ratio of the sodium nickel manganese oxide positive electrode material to the dopant (ZnO and MnO2) was 3.2:1) was added and mixed, and then spray dried (the spray inlet air temperature was 240°C, and the spray exhaust air temperature was 100°C). The material was heated in air at a heating rate of 2.0°C / min to 950°C and maintained for 8 h, and then naturally cooled to room temperature to obtain a black block material. The black block material was sequentially subjected to a rotary wheel mill and an air jet mill to obtain a sodium ion positive electrode material with full gradient doping with a particle size Dv50 of 2.6 μm.

[0109] Comparative Example 1

[0110] The sodium ion positive electrode material of the present example has a chemical formula of Na 0.85 Ni 0.30 Mn 0.40 Zn 0.10 Fe 0.20 O2, which is a single crystal structure, and the content of Ni and Mn gradually increases from the surface to the inside of the single crystal, and the content of Zn and Fe gradually decreases.

[0111] The method for preparing the sodium ion positive electrode material of the present example comprises the following steps.

[0112] (I) Preparation of a sodium nickel manganese oxide positive electrode material

[0113] The NiO, MnO2 and Na2CO3 (the molar ratio of sodium in Na2CO3 to the sum of the molar amount of Ni and Fe is 1.20:1) were mixed in water to obtain a mixed solution with a solid content of 30%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.5 μm. The slurry was spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C) to obtain spherical precursor powder. The precursor powder was passed through air, and the temperature was raised to 800°C at a heating rate of 2.5°C / min and maintained for 12 h, and then naturally cooled to room temperature to obtain a black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium nickel manganese oxide positive electrode material with a particle size Dv50 of 2.5 μm.

[0114] (II) Preparation of a sodium ion positive electrode material with full gradient doping

[0115] ZnO and Fe2O3 were mixed in water to obtain a mixed solution with a solid content of 8 wt.%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.2 μm. Sodium nickel manganese oxide positive electrode material was added (the mass ratio of the sodium nickel manganese oxide positive electrode material to the dopant (ZnO and Fe2O3) was 3.15:1) for mixing, and then spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C). Air was passed through, and the temperature was raised to 900°C at a heating rate of 2.5°C / min and maintained for 10 h, and then naturally cooled to room temperature to obtain a black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium ion positive electrode material with full gradient doping with a particle size Dv50 of 3.0 μm.

[0116] Comparative Example 2

[0117] The chemical formula of the sodium ion positive electrode material of the present example is Na 0.85 Ni 0.3 Fe 0.4 Zn 0.1 Mn 0.2 O2, which is a single crystal structure, and from the surface of the single crystal to the inside, there are a partially uniform gradient doping region and an internal undoped region.

[0118] The preparation method of the sodium ion positive electrode material of the present example includes the following steps.

[0119] (I) Preparation of a sodium nickel manganese oxide positive electrode material

[0120] The NiO, Fe2O3 and Na2CO3 (the molar ratio of sodium in Na2CO3 to the sum of the molar amount of Ni and Fe is 1.20:1) were mixed in water to obtain a mixed solution with a solid content of 30%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle Dv50 of 0.5 μm. The slurry was spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C) to obtain spherical precursor powder. The precursor powder was passed through air, and the temperature was raised to 950°C at a heating rate of 2.5°C / min and maintained for 12 h, and then naturally cooled to room temperature to obtain a black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium nickel ferrite positive electrode material with a particle size Dv50 of 4.0 μm.

[0121] (II) Preparation of a doped sodium ion positive electrode material

[0122] ZnO and MnO2 were mixed in water to obtain a mixed solution with a solid content of 8 wt.%, and the mixed solution was added to a sand mill for fine grinding to obtain a slurry with a particle Dv50 of 0.2 μm. The slurry was mixed with a sodium nickel ferrite positive electrode material (the mass ratio of the sodium nickel ferrite positive electrode material to the dopant (ZnO and MnO2) was 3.2:1), and then spray dried (the spray inlet air temperature was 220°C, and the spray exhaust air temperature was 90°C). The mixture was passed through air, and the temperature was raised to 900°C at a heating rate of 2.5°C / min and maintained for 10 h, and then naturally cooled to room temperature to obtain a black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a doped sodium ion positive electrode material with a particle size Dv50 of 5.0 μm.

[0123] Comparative Example 3

[0124] The chemical formula of the sodium ion positive electrode material of the present example is Na 0.85 Ni 0.43 Fe 0.57 O2@Zn / Mn (i.e. Na 0.85 Ni 0.43 Fe 0.57 O2@Zn / Mn coated with Zn and Mn), which is a single crystal structure, and Zn and Mn are distributed on the surface of the single crystal particles.

[0125] The preparation method of the sodium ion positive electrode material of the present example comprises the following steps.

[0126] (I) Preparation of a sodium nickel ferrite positive electrode material

[0127] The NiO, Fe2O3and Na2CO3(the molar ratio of sodium in Na2CO3to the sum of the molar amounts of Ni and Fe is 1.20:1) were mixed in water to obtain a mixture with a solid content of 30%, and the mixture was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.5 μm. The slurry was spray dried (the spray inlet temperature was 220°C, and the spray exhaust temperature was 90°C) to obtain spherical precursor powder. The precursor powder was heated in air at a rate of 2.5°C / min to 800°C and maintained for 12 h, and then naturally cooled to room temperature to obtain black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a sodium nickel iron oxide positive electrode material with a particle size Dv50 of 2.5 μm.

[0128] (II) Preparation of coated sodium ion positive electrode material

[0129] ZnO and MnO2were mixed in water to obtain a mixture (the molar ratio of Zn to Mn was 1:2), and the solid content of the mixture was 8 wt.%. The mixture was added to a sand mill for fine grinding to obtain a slurry with a particle size Dv50 of 0.2 μm. Sodium nickel iron oxide positive electrode material (the mass ratio of the sodium nickel iron oxide positive electrode material to the dopant (ZnO and MnO2) was 3.2:1) was added for mixing, and then spray dried (the spray inlet temperature was 220°C, and the spray exhaust temperature was 90°C). The mixture was heated in air at a rate of 2.5°C / min to 500°C and maintained for 10 h, and then naturally cooled to room temperature to obtain black blocky material. The black blocky material was sequentially subjected to a rotary wheel mill and an air jet mill for crushing to obtain a coated sodium ion positive electrode material with a particle size Dv50 of 3.0 μm.

[0130] The average particle size of the sodium ion positive electrode materials of Examples 1 to 5 and Comparative Examples 1 to 3 was measured using a particle size analyzer, the specific surface area was tested using a Micromeritics surface area analyzer 3020, and the electrochemical performance was tested, and the results are shown in Table 1.

[0131] Electrochemical performance test: The sodium ion positive electrode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were respectively taken as active material, mixed with a binder PVDF and a conductive agent (Super-P) according to a mass ratio of 95:1.5:3.5, and a proper amount of N-vinyl pyrrolidone was added as a solvent to make a slurry, which was coated on an aluminum foil and dried in vacuum and rolled to prepare a negative electrode sheet. With lithium metal as a counter electrode, 1 mol / L LiPF6 and a three-component mixed solvent of EC:DMC:EMC = 1:1:1 (v / v) were mixed to form an electrolyte, and a polypropylene microporous membrane was used as a separator to assemble a CR2032 type button cell in an inert gas glove box. The charge-discharge test of the button cell was performed on a battery test system of Wuhan Blue Electronic Co., Ltd. At 25°C, 0.1C constant current charging was performed to 0.01V, then 0.02C constant current discharging was performed to 0.005V, and finally 0.1C constant current charging was performed to 4.0V. The capacity charged to 4.0V was the initial specific discharge capacity, the ratio of the discharge capacity to the charge capacity was the initial charge-discharge efficiency, and the corresponding discharge specific capacity of the 100th cycle was obtained after 100 cycles, and the charge-discharge efficiency of the 100th cycle was calculated.

[0132] Table 1: Electrochemical performance and physical properties of each example and comparative example

[0133]

[0134]

[0135] As can be seen from the results in Table 1, compared with Comparative Examples 1 to 3, the sodium ion positive electrode materials of Examples 1 to 5 have small particle size and large specific surface area, and still have high initial specific discharge capacity and initial charge-discharge efficiency at a high voltage of 4.0V, which are significantly higher than the specific capacity and efficiency of the sodium ion positive electrode materials in Comparative Examples 1 to 3, indicating that more sodium ions participate in the reaction and intercalation during the charge-discharge process of the sodium ion positive electrode materials of Examples 1 to 5, which indicates that the sodium ion positive electrode materials of Examples 1 to 5 have good kinetic performance, i.e. good rate performance. After 100 cycles, the specific capacity and charge-discharge efficiency of the materials are high, indicating that the sodium ion positive electrode materials have good cycle performance and less side reactions on the surface of the materials. This is mainly because the content of Ni and Fe gradually increases from the surface to the inside of the material by solid-phase doping in the present application, and the content of the doping element M gradually decreases, which can maintain the stability of the structure of the sodium ion positive electrode material and reduce the contact between the active metal elements Ni and Fe and the electrolyte during the charge-discharge process.

[0136] In Comparative Example 1, zinc and iron were used as doping elements, and iron was mainly concentrated on the surface layer of the single crystal material, which had high activity and was easy to react with the electrolyte, so the charge-discharge performance and cycle performance were not good.

[0137] In the comparative example 2, the sintering of the sodium nickel iron oxide positive electrode material prepared at 950℃ is already complete, and when the solid phase doping is carried out at a slightly lower temperature of 900℃, it is difficult for zinc and manganese to penetrate into the interior of the single crystal particles, and they mainly gather on the surface of the single crystal particles and the inner layer close to the surface, i.e. there are a part of uniform gradient doping regions and internal undoped regions, so the particle size is large, and the charge-discharge performance and cycle performance are also poor.

[0138] In the comparative example 3, the sodium nickel iron oxide positive electrode material is prepared at 800℃, and the temperature of the solid phase reaction is only 500℃, so ZnO and MnO2 mainly form a coating layer on the surface of the sodium nickel iron oxide positive electrode material instead of doping, so the charge-discharge performance and cycle performance are poor.

[0139] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not a limitation on the protection scope of the present application, although the present application has been described in detail with reference to the preferred embodiments, but it is not limited to the examples listed in the embodiments, and those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for producing a sodium-ion positive electrode material, characterized by, The chemical formula of the sodium ion positive electrode material is Na α Ni x Fe y M (1-x-y) O2, wherein 0.60 < α ≤ 1.00, 0 < x ≤ 0.50, 0 < y ≤ 0.50, x + y < 1.00, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, Ca, Mo, Sn, Nb, Zn, W, Tc, Cd, Pd, Pb, Po, Tl, Ge, Sc, Ru and Rh, the crystal structure is single crystal, and from the surface to the inside of the single crystal, the content of Ni and Fe gradually increases, and the content of M gradually decreases, comprising the steps of: (I) Preparation of sodium nickel iron oxide positive electrode material According to the formula, the nickel source, iron source and sodium source are mixed in water to obtain a mixed solution, then the slurry is grinded and spray dried to obtain a precursor powder, and the precursor powder is subjected to a first sintering at 600-850 DEG C, and a first crushing to obtain a particle with a Dv50 of 2.0-4.0 μm; (II) Preparation of full gradient doped sodium ion positive electrode material The M source is mixed in water to obtain a mixed solution, grinded to obtain a slurry, and mixed with the sodium nickel iron oxide positive electrode material according to the formula, then spray dried and subjected to a second sintering at 750-950 DEG C, and a second crushing to obtain a particle with a Dv50 of 2.5-4.5 μm, and the temperature of the first sintering is lower than that of the second sintering.

2. The method for preparing the sodium-ion cathode material according to claim 1, characterized in that, It comprises at least one of the following features (1) to (20): (1) The nickel source is nickel oxide; (2) The iron source is iron oxide; (3) The M source is an oxide of M, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, Ca, Mo, Sn, Nb, Zn, W, Tc, Cd, Pd, Pb, Po, Tl, Ge, Sc, Ru and Rh; (4) The sodium source is at least one of NaOH, NaNO3, Na2CO3 and CH3COONa; (5) The molar amount of sodium in the sodium source is m, the sum of the molar amount of nickel in the nickel source and the molar amount of iron in the iron source is n, and m / n is 1.00-1.45:1; (6) The solid content of the mixed solution in step (I) is 20-40 wt.%; (7) The Dv50 of the slurry in step (I) is 0.2-0.7 μm; (8) The inlet air temperature of the spray drying in step (I) is 220-280 DEG C, and the exhaust air temperature is 80-100 DEG C; (9) Air is introduced during the first sintering; (10) The holding time of the first sintering is 5-12 h; (11) The heating rate of the first sintering is 2-5 DEG C / min; (12) The first crushing includes rough breaking of the product after the first sintering by a rotary wheel mill and fine breaking by an air jet mill; (13) The mass ratio of the sodium nickel iron oxide positive electrode material to the M source is 1-8:1; (14) The solid content of the mixed solution in step (II) is 5-15 wt.%; (15) The Dv50 of the slurry in step (II) is 0.1-0.3 μm; (16) The inlet air temperature of the spray drying in step (II) is 220-280 DEG C, and the exhaust air temperature is 80-100 DEG C; (17) Air is introduced during the second sintering; (18) The holding time of the second sintering is 6-16 h; (19) the second sintering has a temperature increasing rate of 1-4 ℃ / min; (20) the second crushing comprises sequentially performing coarse crushing on the product after the second sintering by using a rotary wheel mill and performing fine crushing by using an air flow mill.

3. The sodium-ion cathode material prepared by the method according to claim 1 or 2, characterized in that, M is at least one of Zr, Al, Co, Cu, Sr, Y, Mn, Ti, Mg, Mo, Zn and W.

4. The sodium-ion cathode material prepared by the method of claim 1 or 2, wherein the sodium-ion cathode material is characterized in that, 0.60 < α ≤ 0.90, 0.10 ≤ x < 0.50, 0.10 ≤ y < 0.

50.

5. The sodium-ion cathode material prepared according to the method of claim 1 or 2, characterized in that, M is Zn and / or Mn, α = 0.85, x = 0.30, y = 0.

40.

6. The sodium-ion cathode material prepared by the method of claim 1 or 2, wherein the sodium-ion cathode material is characterized in that, The average particle size of the single crystal is 1.5-3.0 μm.

7. The sodium-ion cathode material prepared according to the method of claim 1 or 2, wherein, The specific surface area of the sodium-ion positive electrode material is 0.6 m 2 / g to 1.2 m 2 / g.

8. A secondary battery comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized by, The positive electrode material comprises a sodium ion positive electrode material prepared by the preparation method of the sodium ion positive electrode material in any one of claims 1-2 or the sodium ion positive electrode material in any one of claims 3-7.

9. The secondary battery according to claim 8, characterized by The negative electrode material comprises a carbon-based negative electrode material and / or a silicon-based negative electrode material.

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