Composite positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of battery materials, in particular to a composite positive electrode material and a preparation method and application thereof. The composite positive electrode material is of a core-shell structure and comprises an inner core and a coating layer coating the surface of the inner core, wherein the chemical formula of the positive electrode active material is Na < x-a > Li Ni < 1-b-c > M RE < c > O < 2-d > F < d >, and the material of the coating layer comprises Na < 3 > PO < 4 > and Na < 3 > PS < 4 >. The sodium ion battery prepared from the composite positive electrode material not only has high energy density, but also has excellent long-cycle stability, the defects in the prior art are effectively overcome, and a new design idea is provided for development of the sodium ion battery.

Description

Technical Field

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

[0002] With the rapid development of the global economy, the demand for energy increases year by year. Traditional fossil fuels can no longer meet the growing energy demand. The development and utilization of new energy have become the key to solving the energy crisis. As a new energy storage technology, sodium-ion batteries have the advantages of rich raw material resources, high charge and discharge rate, long cycle life, high safety, green environmental protection and recyclability, and have great application potential in various fields.

[0003] The cathode materials for sodium-ion batteries have high theoretical specific capacity and working voltage, and are one of the most potential cathode materials at present. However, they still face many challenges in practical applications. Existing layered oxide cathode materials are prone to structural collapse during charge and discharge due to the insertion and extraction of sodium ions, which reduces the energy density and causes capacity decay; polyanion compound cathode materials are prone to decomposition at high temperatures, affecting the cycle performance of sodium-ion batteries; Prussian blue compound cathode materials are prone to phase transformation during cycling, affecting the stability of the materials.

[0004] Based on this, the research and development of a sodium-ion battery cathode material with stable structure, high energy density and good cycle stability has important practical significance for the development of sodium-ion batteries. Summary of the Invention

[0005] Aiming at the problems of poor structural stability of existing sodium-ion battery cathode materials, which easily lead to a decrease in the energy density and cycle performance of sodium-ion batteries, the present invention provides a composite cathode material, a preparation method thereof, and an application thereof. The composite cathode material has a core-shell structure and includes a cathode active material and a coating layer coated on the surface of the cathode active material. The sodium-ion battery prepared by using the composite cathode material of the present invention can maintain a stable structure during the charge and discharge cycle, ensuring that the sodium-ion battery has a high energy density and long cycle stability, and providing a new design idea for the development of sodium-ion battery cathode materials.

[0006] To achieve the above invention purpose, the present invention provides the following technical solutions: In the first aspect of the present invention, a composite cathode material is provided. The composite cathode material has a core-shell structure and includes a cathode active material and a coating layer coated on the surface of the cathode active material; Wherein, the chemical formula of the cathode active material is Na x-a Li a Ni 1-b-c M b RE c O2-d F d , wherein, M is any one of Mn, Fe, Zn, Zr, Nb, Mo, Cu or Ti; RE is any one of La, Eu or Dy; 0.8 ≤ x ≤ 1, 0 < a ≤ 0.2, 0 < b ≤ 0.3, 0 < c ≤ 0.2, 0 < d ≤ 1; The material of the coating layer includes Na3PO4 and Na3PS4.

[0007] The present invention designs a composite cathode material with a core-shell structure, using the cathode active material with high specific capacity as the core and the coating layer material that can improve the cycle stability of battery materials as the shell. It can not only improve the energy density but also maintain a good capacity retention rate after multiple charge and discharge cycles. The cathode active material is a doped multi-layered metal oxide. The doped elements occupy specific lattice sites, effectively improving the structural stability of the cathode material, reducing the structural changes and phase transitions during charge and discharge, and thus improving the cycle life of the sodium-ion battery. In particular, the incorporation of rare earth elements plays a role in supporting the structure and inhibiting the occurrence of phase transitions. Moreover, since the insertion and extraction of sodium ions will cause volume changes in the material, which may lead to pulverization and structural collapse of the material, rare earth elements can act as a buffer to absorb and disperse the stress generated by volume changes, thereby reducing the risk of structural collapse of the cathode material.

[0008] The coating layer material, as a physical barrier, can effectively prevent the side reaction between the electrode material and the electrolyte, reduce the risk of damage to the structure of the cathode active material, maintain the structural integrity of the cathode active material, and thus improve the cycle stability of the cathode material. The composite cathode material provided by the present invention has excellent structural stability. The sodium-ion battery prepared by using it has a high energy density and long cycle stability, solving the problems of poor structural stability of the existing sodium-ion battery cathode material, which easily leads to a decrease in the energy density and cycle performance of the sodium-ion battery.

[0009] Preferably, the mass ratio of Na3PO4 to Na3PS4 in the coating layer is 1:0.8 - 1:1.2.

[0010] Preferably, the thickness of the coating layer is 2 nm - 10 nm.

[0011] More preferably, the thickness of the coating layer is 5 nm - 10 nm.

[0012] The preferred coating layer can not only inhibit the side reaction between the cathode active material and the electrolyte, reduce the dissolution and structural damage of the cathode active material, thereby improving the capacity retention rate and cycle stability of the battery.

[0013] Preferably, the cathode active material is Na 0.8Li 0.1 Ni 0.7 Mn 0.2 La 0.1 O 1.4 F 0.6 、Na 0.7 Li 0.2 Ni 0.55 Zn 0.35 Eu 0.1 OF、Na 0.75 Li 0.25 Ni 0.6 Zr 0.2 Dy 0.1 O 1.3 F 0.7 、Na 0.75 Li 0.05 Ni 0.55 Fe 0.3 La 0.1 5O 1.25 F 0.75 Or Na 0.7 Li 0.1 Ni 0.5 Cu 0.3 Eu 0.2 O 1.2 F 0.8 .

[0014] Preferably, the method for preparing the positive electrode active material comprises the following steps: According to the designed ratio, the sodium source, lithium source, nickel source, M source, RE source and fluorine source are uniformly mixed to obtain a mixed inorganic material; the mixed inorganic material is wet ball-milled, and then heated to 700° C.-1200° C. for calcination and grinding to obtain the positive electrode active material.

[0015] Further preferably, the solvent for the wet ball milling is anhydrous ethanol; and the mass volume ratio of the mixed inorganic material to the solvent is 1g:4mL-1g:8mL.

[0016] Preferably, the diameter of the ball milling beads in the wet ball milling is 100 μm-500 μm; the ball-to-material ratio is 5:1-10:1; the rotation speed is 600 rpm-900 rpm; and the ball milling time is 1 h-3 h.

[0017] Preferably, the calcination time is 10h-15h.

[0018] Preferably, the temperature is raised to 700°C-1200°C by programmed heating, with a heating rate of 3°C / min-8°C / min.

[0019] Preferably, the sodium source is sodium fluoride or sodium carbonate.

[0020] Preferably, the lithium source is lithium carbonate or lithium fluoride.

[0021] Preferably, the nickel source is nickel carbonate or nickel oxide.

[0022] Preferably, the M source is any one of manganese carbonate, manganese dioxide, iron carbonate, iron oxide, zinc carbonate, zinc oxide, zirconium carbonate, zirconium oxide, niobium carbonate, niobium oxide, molybdenum carbonate, molybdenum oxide, copper carbonate, copper oxide or titanium dioxide.

[0023] Preferably, the RE source is any one of lanthanum oxide, europium oxide or dysprosium oxide.

[0024] Preferably, the fluorine source is sodium fluoride or lithium fluoride.

[0025] In a second aspect of the present invention, a method for preparing the composite cathode material is provided, including the following steps: weighing the cathode active material, Na3PO4 and Na3PS4 according to the designed ratio, mixing them evenly, and performing fusion coating to obtain a coated material; under an inert atmosphere, heating the coated material to 300°C - 500°C for sintering, and then cooling to obtain the composite cathode material.

[0026] Preferably, the specific steps of the fusion coating are as follows: first coating the mixture at 400°C - 500°C and 300 rpm - 800 rpm for 50 min - 80 min; then coating at 300°C - 400°C and 200 rpm - 500 rpm for 4 h - 6 h.

[0027] The present invention uses the fusion coating method to coat the cathode active material, promoting the construction of a more efficient sodium ion transport channel between the coating material and the cathode active material, effectively enhancing the conductivity and stability of the composite cathode material, and thus improving the cycle stability of the sodium ion battery.

[0028] Preferably, the temperature is raised to 300°C - 500°C in a programmed heating manner, and the heating rate is 3°C / min - 5°C / min.

[0029] Preferably, the sintering time is 4 h - 6 h.

[0030] Preferably, the cooling is carried out in a programmed cooling manner, and the cooling rate is 5°C / min - 10°C / min.

[0031] In a third aspect of the present invention, an application of the composite cathode material or the composite cathode material prepared by using the method for preparing the composite cathode material in the preparation of sodium ion batteries is provided.

[0032] In summary, the present invention provides a composite cathode material with a core-shell structure, including a cathode active material and a coating layer coated on the surface of the cathode active material. The sodium-ion battery prepared by using the composite cathode material of the present invention can maintain structural stability during the charge and discharge cycle, ensuring that the sodium-ion battery has a high energy density and long cycle stability. After testing, the sodium-ion battery prepared by using the composite cathode material provided by the present invention still has a capacity retention rate of 84.1% after 500 cycles, providing a new design idea for the development of sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a scanning electron microscope image of the composite cathode material described in each example. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] Example 1 This example provides a composite cathode material, which specifically includes the following content: The composite cathode material has a core-shell structure and includes a cathode active material and a coating layer with a thickness of 7 nm coated on the surface of the cathode active material; Among them, the chemical formula of the cathode active material is Na 0.8 Li 0.1 Ni 0.7 Mn 0.2 La 0.1 O 1.4 F 0.6 ; The coating layer material is Na3PO4 and Na3PS4 with a mass ratio of 1:1.

[0036] The preparation method of the composite cathode material is as follows: Step 1: According to the designed ratio, 0.5345 g of sodium carbonate, 0.1850 g of lithium carbonate, 2.6141 g of nickel oxide, 0.8651 g of manganese dioxide, 0.8154 g of lanthanum oxide and 1.2852 g of sodium fluoride are mixed evenly to obtain a mixed inorganic material; the mixed inorganic material is put into a planetary ball mill, 30 mL of anhydrous ethanol is added, ball milling beads with a diameter of 250 μm are used, and the mixed inorganic material is wet ball milled for 2 h at a ball-to-material ratio of 8:1 and a rotation speed of 800 rpm, dried at 90 °C for 20 min, and the dried mixed inorganic material is sent into a muffle furnace and calcined at a heating rate of 5 °C / min to 850 °C for 12 h, and then ground to obtain the positive electrode active material.

[0037] Step 2: 5 g of the positive electrode active material, 0.1752 g of Na3PO4 and 0.1752 g of Na3PS4 are mixed evenly and subjected to fusion coating. First, the mixture is coated at 450 °C and 600 rpm for 60 min; then coated at 350 °C and 400 rpm for 5 h to obtain a coated material; in an inert atmosphere, the coated material is heated to 450 °C at a heating rate of 4 °C / min and sintered for 5 h. After sintering, it is cooled to room temperature at a cooling rate of 6 °C / min to obtain a composite positive electrode material.

[0038] Example 2 This example provides a composite positive electrode material, which specifically includes the following content: The composite positive electrode material has a core-shell structure, including a positive electrode active material and a coating layer with a thickness of 5 nm coated on the surface of the positive electrode active material; Among them, the chemical formula of the positive electrode active material is Na 0.7 Li 0.2 Ni 0.55 Zn 0.35 Eu 0.1 OF; the coating layer material is Na3PO4 and Na3PS4 with a mass ratio of 1:0.9.

[0039] The preparation method of the composite positive electrode material is as follows: Step 1: According to the designed ratio, 0.3695 g of lithium carbonate, 2.0540 g of nickel oxide, 1.4243 g of zinc oxide, 0.8795 g of europium oxide and 2.0995 g of sodium fluoride are mixed evenly to obtain a mixed inorganic material; the mixed inorganic material is put into a planetary ball mill, 35 mL of anhydrous ethanol is added, milling beads with a diameter of 300 μm are used, and the mixed inorganic material is wet-milled for 2 h at a ball-to-material ratio of 10:1 and a rotation speed of 800 rpm, dried at 90 °C for 20 min, and the dried mixed inorganic material is sent into a muffle furnace and calcined at a heating rate of 5 °C / min to 900 °C for 11 h, and then ground to obtain the positive electrode active material.

[0040] Step 2: 5 g of the positive electrode active material, 0.1651 g of Na3PO4 and 0.1352 g of Na3PS4 are mixed evenly and subjected to fusion coating. First, the mixed material is coated at 420 °C and 750 rpm for 80 min; then coated at 360 °C and 400 rpm for 6 h to obtain a coated material; in an inert atmosphere, the coated material is heated to 400 °C at a heating rate of 5 °C / min and sintered for 5 h. After sintering, it is cooled to room temperature at a cooling rate of 5 °C / min to obtain a composite positive electrode material.

[0041] Example 3 This example provides a composite positive electrode material, which specifically includes the following content: The composite positive electrode material has a core-shell structure, including a positive electrode active material and a coating layer with a thickness of 7 nm coated on the surface of the positive electrode active material; Among them, the chemical formula of the positive electrode active material is Na 0.75 Li 0.25 Ni 0.6 Zr 0.2 Dy 0.1 O 1.3 F 0.7 ; the coating layer material is Na3PO4 and Na3PS4 with a mass ratio of 1:1.1.

[0042] The preparation method of the composite positive electrode material is as follows: Step 1: According to the designed ratio, 0.1325 g of sodium carbonate, 0.4618 g of lithium carbonate, 2.2407 g of nickel oxide, 1.2322 g of zirconium oxide, 0.9325 g of dysprosium oxide and 1.4697 g of sodium fluoride are mixed evenly to obtain a mixed inorganic material; the mixed inorganic material is put into a planetary ball mill, 28 mL of absolute ethanol is added, ball milling beads with a diameter of 400 μm are used, and the mixed inorganic material is wet ball milled for 2 h at a ball-to-material ratio of 6:1 and a rotation speed of 800 rpm, dried at 90 °C for 20 min, and the dried mixed inorganic material is sent into a muffle furnace and calcined at a heating rate of 5 °C / min to 1150 °C for 11 h, and then ground to obtain the positive electrode active material.

[0043] Step 2: 5 g of the positive electrode active material, 0.1547 g of Na3PO4 and 0.1702 g of Na3PS4 are mixed evenly and subjected to fusion coating. First, the mixture is coated at 400 °C and 800 rpm for 75 min; then coated at 400 °C and 300 rpm for 6 h to obtain a coated material; in an inert atmosphere, the coated material is heated to 390 °C at a heating rate of 3 °C / min and sintered for 5 h. After sintering, it is cooled to room temperature at a cooling rate of 10 °C / min to obtain a composite positive electrode material.

[0044] Example 4 This example provides a composite positive electrode material, which specifically includes the following content: The composite positive electrode material has a core-shell structure and includes a positive electrode active material and a coating layer with a thickness of 8 nm coated on the surface of the positive electrode active material; Among them, the chemical formula of the positive electrode active material is Na 0.75 Li 0.05 Ni 0.55 Fe 0.3 La 0.15 O 1.25 F 0.75 ; the coating layer material is Na3PO4 and Na3PS4 with a mass ratio of 1:1.

[0045] The preparation method of the composite positive electrode material is as follows: Step 1: According to the designed ratio, 0.0923 g of lithium carbonate, 2.0539 g of nickel oxide, 1.1977 g of iron oxide, 1.2218 g of lanthanum oxide and 1.5746 g of sodium fluoride are mixed evenly to obtain a mixed inorganic material; the mixed inorganic material is put into a planetary ball mill, 30 mL of absolute ethanol is added, and ball milling beads with a diameter of 250 μm are used. The mixed inorganic material is wet ball milled at a ball-to-material ratio of 8:1 and a rotation speed of 800 rpm for 2 h, dried at 90 °C for 20 min, and the dried mixed inorganic material is sent into a muffle furnace and heated to 1050 °C at a heating rate of 6 °C / min for calcination for 12 h, and then ground to obtain the positive electrode active material.

[0046] Step 2: 5 g of the positive electrode active material, 0.1841 g of Na3PO4 and 0.1841 g of Na3PS4 are mixed evenly and subjected to fusion coating. First, the mixed material is coated at 480 °C and 500 rpm for 60 min; then coated at 360 °C and 500 rpm for 5 h to obtain a coated material; in an inert atmosphere, the coated material is heated to 500 °C at a heating rate of 4 °C / min for sintering for 5 h. After sintering, it is cooled to room temperature at a cooling rate of 6 °C / min to obtain a composite positive electrode material.

[0047] Example 5 This example provides a composite positive electrode material, which specifically includes the following content: The composite positive electrode material has a core-shell structure and includes a positive electrode active material and a coating layer with a thickness of 10 nm coated on the surface of the positive electrode active material; Among them, the chemical formula of the positive electrode active material is Na 0.7 Li 0.1 Ni 0.5 Cu 0.3 Eu 0.2 O 1.2 F 0.8 ; the coating layer material is Na3PO4 and Na3PS4 with a mass ratio of 1:1.2.

[0048] The preparation method of the composite positive electrode material is as follows: Step 1: According to the designed ratio, 0.2649 g of sodium carbonate, 0.1847 g of lithium carbonate, 1.8673 g of nickel oxide, 1.2151 g of copper oxide, 0.8798 g of europium oxide and 1.6796 g of sodium fluoride are mixed evenly to obtain a mixed inorganic material; the mixed inorganic material is put into a planetary ball mill, 30 mL of absolute ethanol is added, ball milling beads with a diameter of 500 μm are used, and the mixed inorganic material is wet-milled at a ball-to-material ratio of 5:1 and a rotation speed of 900 rpm for 2 h, dried at 90 °C for 20 min, and the dried mixed inorganic material is sent into a muffle furnace and calcined at a heating rate of 4 °C / min to 920 °C for 12 h, and then ground to obtain the positive electrode active material.

[0049] Step 2: 5 g of the positive electrode active material, 0.1931 g of Na3PO4 and 0.2318 g of Na3PS4 are mixed evenly and subjected to fusion coating. First, the mixed material is coated at 450 °C and 400 rpm for 60 min; then coated at 330 °C and 500 rpm for 5 h to obtain a coated material; in an inert atmosphere, the coated material is heated to 420 °C at a heating rate of 4 °C / min and sintered for 6 h. After sintering, it is cooled to room temperature at a cooling rate of 10 °C / min to obtain a composite positive electrode material.

[0050] Comparative Example 1 This comparative example provides a composite positive electrode material, which is different from Example 1 in that: lanthanum oxide in the positive electrode active material is replaced with an equimolar amount of erbium oxide, and other components and parameters remain unchanged, which will not be elaborated here.

[0051] Comparative Example 2 This comparative example provides a composite positive electrode material, which is different from Example 1 in that: manganese dioxide in the positive electrode active material is replaced with an equimolar amount of cobalt oxide, and other components and parameters remain unchanged, which will not be elaborated here.

[0052] Comparative Example 3 This comparative example provides a composite positive electrode material, which is different from Example 1 in that: lanthanum oxide in the positive electrode active material is replaced with an equimolar amount of zinc oxide, and other components and parameters remain unchanged, which will not be elaborated here.

[0053] Comparative Example 4 This comparative example provides a composite positive electrode material, which is different from Example 1 in that: lithium carbonate in the positive electrode active material is replaced with an equimolar amount of potassium carbonate, and other components and parameters remain unchanged, which will not be elaborated here.

[0054] Comparative Example 5 This comparative example provides a composite cathode material, which is different from that of Example 1 in that: the doping of rare earth elements is omitted in the cathode active material, and its chemical formula is Na 0.8 Li 0.1 Ni 0.8 Mn 0.2 O 1.3 F 0.7 , and other components and parameters remain unchanged, which will not be elaborated here.

[0055] Comparative Example 6 This comparative example provides a composite cathode material, which is different from that of Example 1 in that: the coating material is replaced with an equal amount of Na3PO4, and other components and parameters remain unchanged, which will not be elaborated here.

[0056] Comparative Example 7 This comparative example provides a composite cathode material, which is different from that of Example 1 in that: the coating material is replaced with an equal amount of Na3PS4, and other components and parameters remain unchanged, which will not be elaborated here.

[0057] To further demonstrate the technical effects of the present invention, the present invention conducts application performance tests on the composite cathode materials obtained in Examples 1-5 and Comparative Examples 1-7, and prepares each composite cathode material into a sodium-ion battery, and the specific production steps are as shown in the test example.

[0058] Test Example The composite cathode material, conductive carbon black and polyvinylidene fluoride are mixed evenly in a mass ratio of 90:5:5, coated on an aluminum foil to make a positive electrode sheet, a sodium sheet is used as the negative electrode sheet, polypropylene is used as the separator, NaClO4 is used as the electrolyte salt, ethylene carbonate, propylene carbonate and fluoroethylene carbonate are used as the electrolyte solvents, the electrolyte concentration is 1 mol / L, and under an inert atmosphere, a button cell is assembled.

[0059] The present invention conducts electrical performance tests on the button cells obtained in the test example, and the charge and discharge voltage is 2.0V - 4.3V. The first cycle is tested for charge and discharge at a rate of 0.1C, and then the cycle charge and discharge tests are carried out at a rate of 0.5C for 200 cycles and 500 cycles. The unit is: mAh / g, and the capacity retention rate is the ratio of the capacity of the battery in the 200th and 500th cycles to the capacity of the first cycle; the test results are shown in Table 1.

[0060] Table 1 Electrochemical performance test results of button cells prepared using the composite cathode materials obtained in each example and comparative example

[0061] As can be seen from Table 1, the sodium-ion batteries prepared using the composite cathode materials obtained in Examples 1-5 have excellent performance. In particular, for Example 1, the initial discharge specific capacity at 0.1C is as high as 175.5 mAh / g; after 200 cycles, the discharge specific capacity at 0.5C is as high as 154.8 mAh / g, and the capacity retention rate is as high as 88.2%; after 500 cycles, the discharge specific capacity at 0.5C is as high as 147.6 mAh / g, and the capacity retention rate is as high as 84.1%.

[0062] According to Figure 1 it can be seen that the composite cathode material provided by the present invention has a core-shell structure, wherein the coating layer is a mixture of Na3PO4 and Na3PS4, and the core is Na x-a Li a Ni 1-b-c M b RE c O 2-d F d positive electrode active material; the composite cathode material has a high energy density and excellent cycle stability, effectively making up for the deficiencies of the prior art.

[0063] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite cathode material has a core-shell structure and includes a cathode active material and a coating layer coated on the surface of the cathode active material; Among them, the chemical formula of the positive electrode active material is Na x-a Li a Ni 1-b-c M b RE c O 2-d F d , where M is any one of Mn, Fe, Zn, Zr, Nb, Mo, Cu or Ti; RE is any one of La, Eu or Dy; 0.8 ≤ x ≤ 1, 0 < a ≤ 0.2, 0 < b ≤ 0.3, 0 < c ≤ 0.2, 0 < d ≤ 1; The material of the coating layer includes Na3PO4 and Na3PS4.

2. The composite cathode material according to claim 1, wherein The mass ratio of Na3PO4 to Na3PS4 in the coating layer is 1:0.8 - 1:1.2; and / or The thickness of the coating layer is 2 nm - 10 nm.

3. The composite cathode material according to claim 1, wherein Stated positive active substance properties Na 0.8 Li 0.1 Ni 0. 7Mn 0.2 La 0.1 O 1.4 F 0.6 , Na 0.7 Li 0.2 Ni 0.55 Zinc 0.35 EU 0.1 OF, Na 0.75 Li 0.25 Ni 0.6 Zr 0.2 Dy 0.1 O 1.3 F 0.7 , Na 0.75 Li 0.05 Ni 0.55 Fe 0.3 La 0.15 O 1.25 F 0.75 Or 0.7 Li 0.1 Ni 0.5 Cu 0.3 EU 0.2 O 1.2 F 0.8 .

4. The composite cathode material according to claim 1 or 3, characterized in that, The preparation method of the cathode active material includes the following steps: According to the designed ratio, mix a sodium source, a lithium source, a nickel source, an M source, a RE source, and a fluorine source evenly to obtain a mixed inorganic material; after wet ball milling the mixed inorganic material, heat it to 700°C - 1200°C for calcination and grinding to obtain the cathode active material.

5. The composite cathode material according to claim 4, wherein The solvent for the wet ball milling is anhydrous ethanol; the mass-volume ratio of the mixed inorganic material to the solvent is 1 g:2 mL - 1 g:4 mL; and / or The diameter of the ball milling beads for the wet ball milling is 100 μm - 500 μm; the ball-to-material ratio is 5:1 - 10:1; the rotation speed is 600 rpm - 900 rpm; the ball milling time is 1 h - 3 h.

6. The composite cathode material according to claim 4, characterized in that, The calcination time is 10 h - 15 h; and / or Heat it to 700°C - 1200°C in a programmed heating manner, and the heating rate is 3°C / min - 8°C / min.

7. A method for preparing a composite cathode material according to any one of claims 1-6, characterized in that, It includes the following steps: Weigh the cathode active material, Na3PO4, and Na3PS4 according to the designed ratio, mix them evenly, and perform fusion coating to obtain a coated material; under an inert atmosphere, heat the coated material to 300°C - 500°C for sintering and then cool it to obtain the composite cathode material.

8. The preparation method of the composite cathode material according to claim 7, characterized in that, The specific steps of the fusion coating are: first coat the mixture at 400°C - 500°C and 300 rpm - 800 rpm for 50 min - 80 min; then coat it at 300°C - 400°C and 200 rpm - 500 rpm for 4 h - 6 h.

9. The preparation method of the composite cathode material according to claim 7, characterized in that, Heat it to 300°C - 500°C in a programmed heating manner, and the heating rate is 3°C / min - 5°C / min; and / or The sintering time is 4 h - 6 h; and / or Cool it in a programmed cooling manner, and the cooling rate is 5°C / min - 10°C / min.

10. Application of a composite cathode material according to any one of claims 1 - 6 or a composite cathode material prepared by using the preparation method of a composite cathode material according to any one of claims 7 - 9 in the preparation of a sodium ion battery.

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