A cathode material for sodium-ion batteries, a preparation method thereof, and applications thereof

Abstract

The present invention discloses a cathode material for a sodium-ion battery, a preparation method thereof, and an application thereof. The cathode material for the sodium-ion battery is composed of a Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 core and a CaTiO3 dielectric coating layer coated on the surface of the core. The preparation thereof includes the following steps: (1) mixing a sodium source, a nickel source, and a manganese source according to a stoichiometric ratio and performing ball milling. The milled powder is calcined at 800-900 °C for 15-18 h to obtain an active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2; (2) mixing the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 prepared in step (1) with calcium carbonate and titanium dioxide and performing ball milling, and calcining at 800-900 °C for 9-12 h to obtain the cathode material for the sodium-ion battery. Through the synergistic effect of the CaTiO3 dielectric coating layer and the selective doping of Ca and Ti lattice sites, the cathode material for the sodium-ion battery prepared by the present invention realizes stable anion redox and crystal structure evolution, and exhibits excellent air stability, effectively improving the battery life of the sodium-ion battery under charge and discharge at a high current density.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and particularly relates to a cathode material for a sodium-ion battery, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the rich resources, wide distribution and low cost of metallic sodium, sodium-ion batteries are gradually applied to grid energy storage workstations and electric vehicles, and are considered to be one of the most promising new secondary battery systems. However, sodium-ion batteries still face many challenges in the commercialization process, mainly including the following three aspects: (1) The energy density needs to be improved urgently: Compared with the energy density of lithium-ion batteries (450 Wh kg -1 ) with relatively mature technical processes, the energy density of sodium-ion batteries (200 Wh kg -1 ) is lower and cannot meet the increasing energy demand of current large-scale energy storage systems. (2) Short battery life at high current density: Most of the reported sodium-ion batteries at present have good battery life and high Coulomb efficiency at low current density (10 mA g -1 ). However, at high current density (1000 mA g -1 ), the cathode materials of sodium-ion batteries face problems such as severe crystal structure damage and voltage attenuation, which in turn lead to rapid reduction of battery capacity and extremely poor charge-discharge stability. For the commercial application of sodium-ion batteries in energy storage devices such as electric vehicles or drones that require fast charge and discharge, it is difficult to achieve a long battery life at high current density. (3) Poor air stability: When sodium-ion batteries are in a humid environment, water molecules in the air will chemically react with the cathode materials of sodium-ion batteries, resulting in sodium loss and phase transformation of the cathode materials, thereby reducing the capacity upper limit and cycle stability of the materials.

[0003] Currently, methods such as introducing anion redox at high voltage, regulating the crystal structure of cathode materials, and adding protection on the crystal surface of cathode materials are used to improve problems such as insufficient energy density and poor stability of sodium-ion batteries. For example, surface modification of Na 0.66 Mn 0.54 Ni 0.13 Co 0.13 O2 cathode materials improves the stability of anion redox, and at the same time the energy density is increased to 456.4 Wh Kg -1 , but its cycle stability only increases from 49.1% to 69.3%, and there is still a large room for improvement (Chemical Engineering Journal 2021, 403, 126308); in addition, using Li2TiO3 for Na 0.67 Mn 0.5 Fe 0.5Surface coating with O2 improves the cycling stability (from 59.9% to 81.3%), but has a narrow voltage window (1.5 V to 4.2 V) and cannot fully utilize anion redox to increase the energy density (Angew. Chem. 2022, 134, e202115552). Most of the reported high-energy-density cathode materials with anion redox currently have drawbacks such as rapid capacity decay and short battery life at high voltages, making it difficult to be applied in commercial sodium-ion batteries. On this poor basis, it is very challenging to attempt to achieve a cathode material with high current density charge and discharge and long working life, while also taking into account the air stability of the battery operation.

[0004] In summary, designing a cathode material with high energy density, high working current density, and good air stability is crucial for the wide commercial application of sodium-ion batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a cathode material for sodium-ion batteries, its preparation method, and application. The present invention selects Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 as the cathode active material of the battery. By coating the active material with a CaTiO3 dielectric material on the surface and selectively doping Ca and Ti sites in the bulk phase, the crystal structure of the active material is synergistically regulated, the electrochemical performance is improved, and the life of the sodium-ion battery under high current density charge and discharge is effectively extended.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] In the first aspect of the present invention, a cathode material for sodium-ion batteries is provided, which is composed of a Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 core selectively doped with Ca and Ti bulk phase sites and a CaTiO3 dielectric coating layer coated on the surface of the core.

[0008] Further, Ca is doped at the Na site of Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2, and Ti is doped at the Ni and / or Mn sites of Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2.

[0009] Furthermore, the thickness of the CaTiO3 dielectric coating layer is 15 - 25 nm, for example, 20 nm. Since an overly thick coating layer will result in a sluggish sodium ion deintercalation rate, thereby reducing the charge-discharge capacity in the practical application of sodium ion batteries; while an overly thin coating layer is difficult to effectively utilize the dielectric effect of the CaTiO3 material and cannot sufficiently improve the problem of capacity decay of sodium ion batteries; therefore, the thickness of the CaTiO3 dielectric coating layer needs to be controlled within a suitable range, such as 15 - 25 nm.

[0010] In the second aspect of the present invention, there is provided a method for preparing the positive electrode material of the sodium ion battery described in the first aspect, by mixing and ball-milling the active substance Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 with calcium carbonate and titanium dioxide, and calcining at 800 - 900 °C for 9 - 12 h to obtain the positive electrode material of the sodium ion battery.

[0011] Furthermore, the molar ratio of the active substance Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 to calcium carbonate and titanium dioxide is 20 - 30:0.8 - 1.2:0.8 - 1.2.

[0012] Furthermore, the molar ratio of calcium carbonate to titanium dioxide is preferably 1:1.

[0013] Furthermore, the rotation speed of the ball-milling is 400 - 450 rpm, and the ball-milling time is 8 - 16 h.

[0014] Furthermore, the ball-milling is carried out in the presence of an anhydrous organic solvent; by introducing an anhydrous organic solvent for wet milling, it is possible to avoid the inconvenience and loss of material removal caused by static electricity and other reasons after dry milling.

[0015] Furthermore, the volume molar ratio of the anhydrous organic solvent to the active substance Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 is 10 - 15 mL:0.02 - 0.04 mol.

[0016] Furthermore, the anhydrous organic solvent is preferably anhydrous ethanol.

[0017] Furthermore, it also includes a process of drying the ball-milled material to remove the inorganic organic solvent.

[0018] Furthermore, it also includes a process of washing, filtering, and then drying the calcined material under vacuum.

[0019] Furthermore, the active substance Na 2 / 3 Ni 1 / 3 Mn2 / 3 The preparation of O2 includes the following steps:

[0020] (1) Mix and ball-mill a sodium source, a nickel source, and a manganese source according to the stoichiometric ratio of each metal element in the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2.

[0021] (2) Calcinate the powder after ball-milling in step (1) at 800 - 900 °C for 15 - 18 h to obtain the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2.

[0022] Further, in step (1), the sodium source is Na2CO3, NaNO3, Na2O2 or NaOH, the nickel source is NiO, Ni(OH)2 or Ni(NO3)2, and the manganese source is MnO2 or MnCO3.

[0023] Further, in step (1), the rotation speed of the ball-milling is 400 - 450 rpm, and the ball-milling time is 8 - 16 h.

[0024] Further, in step (1), the ball-milling is preferably carried out in the presence of an anhydrous organic solvent.

[0025] The third aspect of the present invention provides a sodium-ion battery, and the positive electrode sheet of the sodium-ion battery includes the positive electrode material of the sodium-ion battery described in the first aspect.

[0026] Further, the sodium-ion battery is composed of a positive electrode sheet, a negative electrode sheet, a glass fiber separator, and an ester-based electrolyte; the side of the positive electrode sheet coated with the active material is adhered to the glass fiber separator, and the other side of the glass fiber separator is adhered to the negative electrode sheet; the integrated positive electrode sheet, glass fiber separator, and negative electrode sheet are hermetically sealed in a battery case.

[0027] Further, the ester-based electrolyte is formed by dissolving NaPF6 in polycarbonate; the concentration of NaPF6 in the ester-based electrolyte is 1 - 5 mol L -1 .

[0028] Further, the preparation method of the positive electrode sheet includes the following steps:

[0029] (1) Mix and grind the positive electrode material of the sodium-ion battery, the carbon material, and the binder described in the first aspect to obtain a mixture, and then mix and stir evenly with a solvent to obtain a slurry; the mass ratio of the positive electrode material of the sodium-ion battery, the carbon material, and the binder in the mixture is 7 - 8:1 - 2:1 - 2;

[0030] (2) Uniformly coat the mixed slurry prepared in step (1) on one side of the carbon-coated aluminum foil, and obtain the positive electrode sheet after vacuum drying.

[0031] Furthermore, in step (1), the carbon material is preferably one or more of conductive carbon black, acetylene black, Ketjen black, activated carbon, carbon nanotubes, graphene, porous carbon, carbon nanofibers; the binder is preferably polyvinylidene fluoride and / or polytetrafluoroethylene; the solvent is preferably one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide.

[0032] Furthermore, in step (2), the temperature of the vacuum drying is 80 - 120 °C, and the time is 8 - 12 h.

[0033] The beneficial effects of the present invention are as follows:

[0034] 1. The present invention uses Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 with anion redox as the positive electrode active material, and obtains a sodium-ion battery positive electrode material by coating the surface of the positive electrode active material with a CaTiO3 dielectric material and selectively doping Ca and Ti sites in the bulk phase; the CaTiO3 dielectric material coating layer of the sodium-ion battery positive electrode material effectively regulates the stability of anion redox through dielectric polarization, which helps the battery to achieve stable charge and discharge at high energy density; in addition, the selective doping of Ca and Ti bulk phase sites can more reasonably and effectively stabilize the crystal structure of the positive electrode material during charge and discharge, so that the battery still has the advantage of "long battery life" under "high current density charge and discharge"; under the synergistic effect of the above CaTiO3 dielectric material coating layer and Ca and Ti bulk phase doping, the problems of crystal structure damage and voltage attenuation of the sodium-ion positive electrode material under high current density are effectively improved, and a long battery life under high current density charge and discharge is achieved; at a current density as high as 1730 mAh g -1 and a wide voltage window of 1.5 - 4.5 V, the battery still has a capacity retention rate of 85.5% after 500 cycles.

[0035] 2. The CaTiO3 dielectric material prepared on the surface of the positive electrode material in the present invention not only stabilizes the anion redox, but also effectively blocks the adverse effects of water molecules in the air on the internal positive electrode material, improving the air stability of the positive electrode material; after soaking the sodium-ion battery positive electrode material prepared in the present invention in water for 24 hours, the crystal form of the positive electrode material does not change and still maintains a good crystal structure. Description of the Drawings

[0036] Figure 1 X-ray diffraction pattern of the sodium-ion battery positive electrode material prepared in Example 1;

[0037] Figure 2 Transmission electron microscopy image of the positive electrode material of the sodium-ion battery prepared in Example 1;

[0038] Figure 3 High-resolution transmission electron microscopy image of the positive electrode material of the sodium-ion battery prepared in Example 1;

[0039] Figure 4 X-ray diffraction refinement pattern of the positive electrode material of the sodium-ion battery prepared in Example 1;

[0040] Figure 5 Active substance Na 2 / 3 Ni 1 / 3 Mn 2 / 3 X-ray diffraction spectra of NiMnO2 as the active substance of the positive electrode of the sodium-ion battery and the positive electrode material of the sodium-ion battery before and after soaking in water for 24 h;

[0041] Figure 6 First three-cycle electrochemical curves of the comparative battery and the modified battery in Example 3 at 0.1C;

[0042] Figure 7 Cycling performance graphs of the comparative battery and the modified battery in Example 3 at 10C. Detailed implementation manners

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of this invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0044] The present invention will be further described below in conjunction with specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0045] Example 1

[0046] This example relates to the preparation of a positive electrode material for a sodium-ion battery. Using Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 as the positive electrode active substance, surface CaTiO3 dielectric material coating and bulk Ca and Ti site selective doping are carried out on the positive electrode active substance to obtain the positive electrode material of the sodium-ion battery; the specific preparation process is as follows:

[0047] (1) Positive electrode active substance Na 2 / 3 Ni 1 / 3 Mn 2 / 3Preparation of O2 powder: Weigh 0.01 mol of Na2CO3, 0.01 mol of NiO, and 0.02 mol of MnCO3 into a ball milling jar, and uniformly powder them on a ball mill at 400 revolutions per minute for 12 h. Transfer the mixed powder sample after mixing to a porcelain boat, and calcine it in a muffle furnace at 900 °C for 15 h in an air atmosphere to obtain a black powder. Filter, wash, and dry the black powder with absolute ethanol to obtain the active substance Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 powder.

[0048] (2) Preparation of the cathode material for sodium-ion batteries: Weigh 0.01 mol of the Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 powder, 0.4 mmol of CaCO3, and 0.4 mmol of TiO2 into a ball milling jar, add 10 ml of absolute ethanol, and then seal the ball milling jar with adhesive tape. Subsequently, wet mill it on a ball mill at 400 revolutions per minute for 12 h. Dry the wet-milled slurry in an oven at 60 °C, and then transfer it to a porcelain boat. Calcinate it in a muffle furnace at 900 °C for 9 h in an air atmosphere to obtain a black powder. Filter, wash, and dry the black powder with absolute ethanol to obtain the active substance Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 with surface CaTiO3 dielectric coating and bulk Ca and Ti site selective doping modification, that is, the cathode material for sodium-ion batteries.

[0049] Perform X-ray diffraction characterization on the prepared cathode material for sodium-ion batteries, and the characterization results are as Figure 1 shown (the experimental data in the figure is the cathode material for sodium-ion batteries prepared in this example, PDF#00-054-0894Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2, PDF#00-001-1055CaTiO3 are the standard XRD spectra of Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 and CaTiO3 respectively), and it can be seen from the figure that the main diffraction peaks of the cathode material for sodium-ion batteries prepared in this example all belong to Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2, and at the same time, the diffraction peaks belonging to CaTiO3 can be observed.

[0050] Perform transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) characterization on the prepared cathode material for sodium-ion batteries. Figure 2TEM image of the cathode material for sodium-ion batteries. As can be seen from the figure, an obvious coating layer can be observed on the surface of the active material; Figure 3 HRTEM image of the cathode material for sodium-ion batteries. As can be seen from the figure, the thickness of the coating layer on the surface of the cathode material for sodium-ion batteries prepared in this example is about 20 nm, and the lattice fringes of the coating layer belong to the (220) crystal plane of the CaTiO3 material.

[0051] Figure 4 X-ray diffraction refinement pattern of the cathode material for sodium-ion batteries. The refinement results are shown in Table 1 below:

[0052] Table 1 Refinement data of the cathode material for sodium-ion batteries

[0053] atom site x y z Occ. Na1 2d 0.33333 0.66667 0.75000 0.406 Na2 2b 0 0 0.25000 0.253 Ca1 2d 0.33333 0.66667 0.75000 0.012 Ca2 2b 0 0 0.25000 0.003 Ni 2a 0 0 0 0.347 Mn 2a 0 0 0 0.667 Ti 2a 0 0 0 0.014 O 4f 0.33333 0.66667 0.08648 1.000

[0054] According to the above refinement results, the mass ratio of the coating layer CaTiO3 in the cathode material for sodium-ion batteries can be calculated to be 4.04 wt%, and the mass ratio of the core active material is 95.96 wt%; in addition, it can be seen from the refinement results that Ca is doped at the Na site and Ti is doped at the transition metal Ni or Mn site in the core active material. The space group of the core active material is p63 / mmc, and the unit cell parameters are: α = β = 90°, γ = 120°.

[0055] From the above characterization data, it can be seen that the core of the cathode material for sodium-ion batteries prepared in this example is Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 with selective doping of Ca and Ti bulk phase points, and the outer layer is a CaTiO3 coating layer.

[0056] Air stability study

[0057] The active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 prepared in this example and the cathode material for sodium-ion batteries are immersed in water at room temperature for 24 h, and the crystal structures of the materials before and after immersion are characterized. The results are as Figure 5 shown. The diffraction peak intensity of the active material Na 2 / 3 Ni 1 / 3Mn 2 / 3 O2 decreases significantly after being immersed in water for 24 h, and a peak envelope appears, indicating that the crystallinity of the material becomes poor ( Figure 5 a); while the diffraction peak intensity and peak shape of the cathode material for sodium-ion batteries prepared in this example do not change after being immersed in water for 24 h ( Figure 5 b), indicating that the cathode material for sodium-ion batteries has good air stability.

[0058] Example 2

[0059] This example relates to the preparation of a cathode material for a sodium-ion battery. Using Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 as the cathode active material, the surface of the cathode active material is coated with CaTiO3 dielectric material and the Ca and Ti sites in the bulk phase are selectively doped to obtain the cathode material for the sodium-ion battery. The specific preparation process is as follows:

[0060] (1) Preparation of the cathode active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 powder: Weigh 0.02 mol of Na2CO3, 0.02 mol of NiO and 0.04 mol of MnCO3 into a ball milling jar, and uniformly powder them on a ball mill at 450 revolutions per minute for 12 h. Transfer the mixed powder sample after mixing to a porcelain boat, and calcine it in a muffle furnace at 900 °C for 18 h in an air atmosphere to obtain a black powder. Filter, wash and dry the black powder with absolute ethanol to obtain the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 powder.

[0061] (2) Preparation of the cathode material for the sodium-ion battery: Weigh 0.02 mol of the Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 powder prepared in the above step (1), 0.8 mmol of CaCO3 and 0.8 mmol of TiO2 into a ball milling jar, add 10 ml of absolute ethanol, then seal the ball milling jar with adhesive tape, and then wet mill it on a ball mill at 450 revolutions per minute for 10 h. Dry the wet milled slurry in an oven at 60 °C, then transfer it to a porcelain boat, and calcine it in a muffle furnace at 900 °C for 12 h in an air atmosphere to obtain a black powder. Filter, wash and dry the black powder with absolute ethanol to obtain the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 with surface CaTiO3 dielectric coating and selective doping modification of Ca and Ti bulk phase sites, that is, the cathode material for the sodium-ion battery.

[0062] Example 3

[0063] This example relates to the preparation of a sodium-ion battery. The specific preparation process is as follows:

[0064] (1) Preparation of the positive electrode sheet: The active material, acetylene black, and polytetrafluoroethylene are mixed and ground evenly according to a mass ratio of 8:1:1 to obtain a mixture. The mixture is mixed and stirred evenly with N-methylpyrrolidone solvent to obtain a slurry. The amount of the N-methylpyrrolidone solvent is limited to completely dissolve the binder and evenly disperse the carbon material in the mixture to form a slurry. The slurry is evenly coated on one side of the carbon-coated aluminum foil and vacuum-insulated in a vacuum oven at 120 °C for 12 h to obtain a modified battery positive electrode material.

[0065] (2) Assembly of the sodium-ion battery: The side of the positive electrode sheet prepared in step (1) coated with the active material is bonded to the glass fiber separator, and the other side of the glass fiber separator is bonded to the negative electrode sheet. The negative electrode sheet is metallic sodium. The integrally bonded positive electrode sheet, glass fiber separator, and negative electrode sheet are hermetically sealed in a battery case, and 180 μL of electrolyte is added dropwise. The electrolyte is an electrolyte formed by dissolving NaPF6 in polycarbonate, and the concentration of NaPF6 is 1 mol L -1 . After sealing, the assembly of the sodium-ion battery is completed.

[0066] The above-mentioned active material is the positive electrode material of the sodium-ion battery prepared in Example 1 to obtain a modified battery; the active material is replaced with an equal amount of Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 powder to obtain a comparative battery.

[0067] Electrochemical performance and cycle performance tests

[0068] The above-mentioned modified battery and comparative battery are respectively installed on the battery clips of the Blue Power BT2000 battery test device, and the electrochemical performance and cycle performance tests are carried out by controlling through the Blue Power battery test program. The voltage window of the electrochemical test is set to 1.5 - 4.5 V; the number of cycles of the cycle test is set to 500 cycles; the theoretical capacity of the battery is set to 1 C = 173 mAhg -1 ; the battery needs to be static for 8 - 12 h before the electrochemical test to allow the electrolyte to fully infiltrate the inside of the battery.

[0069] One charge-discharge cycle process of the battery during the electrochemical test: First, charge at a current density of 10 C to 4.5 V, then static for 10 s, and then discharge at a current density of 10 C to 1.5 V and static for 10 s. This is taken as one cycle.

[0070] The first three-cycle electrochemical curves of the above-mentioned comparative battery and modified battery at 0.1 C are respectively as Figure 6 a, Figure 6 b shown. The charge-discharge behavior above 4.0 V in the figure can be attributed to anion charge-discharge, providing additional capacity and increasing the energy density; from Figure 6 a and Figure 6It can be seen from the comparison that the modified battery has a more stable anion redox behavior.

[0071] The cycling performance of the above-mentioned comparison battery and modified battery at 10C is as follows Figure 7 a, Figure 7 shown in b. When cycling about 300 times, the Coulomb efficiency of the comparison battery becomes unstable, and the capacity retention rate of the comparison battery decreases sharply with the increase of the number of cycles. When cycling about 400 times, the battery capacity approaches 0; while the modified battery cycles 500 times at 10C, its Coulomb efficiency remains stable and is greater than 99%, and the battery capacity is 85.5% of the initial capacity after cycling 500 times. Under high current density charge and discharge, it shows a high capacity retention rate and effectively extends the service life of the battery under high current density.

[0072] The above-described embodiments are merely preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A cathode material for a sodium-ion battery, characterized in that, Na selectively doped with Ca and Ti bulk phase points 2 / 3 Ni 1 / 3Mn 2 / 3 It consists of an O2 core and a CaTiO3 dielectric coating layer covering the surface of the core; The positive electrode material of the sodium-ion battery is prepared by the following method: Mix the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 with calcium carbonate and titanium dioxide, and ball-mill them. Then calcine the mixture at 800-900 °C for 9-12 h to obtain the positive electrode material of the sodium-ion battery; the molar ratio of the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 to calcium carbonate and titanium dioxide is 20-30:0.8-1.2:0.8-1.

2.

2. The cathode material for a sodium-ion battery according to claim 1, wherein Ca doping in Na 2 / 3 Ni 1 / 3 Mn 2 / 3 site of Na in O2, Ti doping in Na 2 / 3 Ni 1 / 3 Mn 2 / 3 sites of Ni and / or Mn in O2.

3. The cathode material for a sodium-ion battery according to claim 1, characterized in that The layer thickness of the CaTiO3 dielectric coating is 15 - 25 nm.

4. The cathode material for a sodium-ion battery according to claim 1, characterized in that, The rotation speed of the ball milling is 400 - 450 rpm, and the ball milling time is 8 - 16 h.

5. The cathode material for a sodium-ion battery according to claim 1, characterized in that, The molar ratio of the calcium carbonate to the titanium dioxide is 1:

1.

6. The cathode material for a sodium-ion battery according to claim 1, characterized in that The ball milling is carried out in the presence of an anhydrous organic solvent.

7. The cathode material for a sodium-ion battery according to claim 1, characterized in that, The active substance Na 2 / 3 Ni 1 / 3Mn 2 / 3 The preparation method of O2 comprises the following steps: (1) Mix and ball-mill a sodium source, a nickel source, and a manganese source according to the stoichiometric ratio of each metal element in the active material Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2; (2) Calcinate the powder after ball milling in step (1) at 800 - 900 °C for 15 - 18 h to obtain the active substance Na 2 / 3Ni 1 / 3 Mn 2 / 3 O2.

8. The cathode material for a sodium-ion battery according to claim 7, characterized in that, The sodium source is Na2CO3, NaNO3, Na2O2 or NaOH, the nickel source is NiO, Ni(OH)2 or Ni(NO3)2, and the manganese source is MnO2 or MnCO3.

9. A sodium-ion battery, characterized in that, The positive electrode sheet of the sodium ion battery comprises the sodium ion battery positive electrode material according to any one of claims 1 - 8.

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