Coated sodium ion battery positive electrode material, preparation method thereof and positive plate

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a coated sodium ion battery positive electrode material, a preparation method thereof and a positive plate. The coated sodium ion battery positive electrode material provided by the invention comprises a layered transition metal oxide and a coating layer coated on the surface of the layered transition metal oxide, the coating layer comprises MOn / 2 and NaX, M is selected from one or more of Ni, Mg, Zn, Ca, Cu, Fe, Co, Ti, Zr, W, V, Mn, Y, In and La, X is a halogen element, and n is larger than or equal to 2 and smaller than or equal to 5; the layered transition metal oxide is NayM'zO2 + r. The surface of the layered transition metal oxide is coated with the metal oxide MOn / 2 and the sodium halide NaX, the metal oxide reduces the occurrence of side reactions, the sodium halide NaX can serve as a bridge between an electrolyte and a positive electrode material to carry out sodium ion transmission, and the rate capability is not sacrificed while the cycling stability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a coated sodium ion battery positive electrode material, a preparation method thereof, and a positive electrode sheet. Background Art

[0002] Lithium-ion battery applications remain hot, dominating the market for electric vehicles, energy storage systems, portable electronic devices, and other fields. However, lithium batteries face challenges such as low global abundance of lithium and high raw material costs, which limit their further application.

[0003] Sodium-ion batteries (SIBs) have garnered extensive attention and research due to their abundant and widespread sodium resources and similar operating principles to lithium-ion batteries. Sodium-based layered oxide cathode materials are a key component of SIBs, offering advantages such as low cost and the ability to leverage existing production lines and equipment. Furthermore, SIBs offer excellent safety performance and a wide range of applications, making them highly promising for further development and application.

[0004] However, there are still some shortcomings in the layered oxide positive electrode materials that need to be addressed. For example, the high residual alkali in the positive electrode material is not conducive to the subsequent battery slurry coating process, and the consumption of electrolyte and gas production during battery charging and discharging are serious problems. At the same time, the structural instability of the material during charging and discharging causes battery performance degradation, resulting in the poor cycle performance and rate performance of the prepared sodium-ion battery. Summary of the Invention

[0005] The object of the present invention is to provide a coated sodium ion battery positive electrode material to solve the problems of poor cycle performance and rate performance of existing sodium ion battery positive electrode materials.

[0006] The second object of the present invention is to provide a method for preparing a coated sodium ion battery positive electrode material to solve the problem of poor cycle performance and rate performance of existing sodium ion battery positive electrode materials.

[0007] The third object of the present invention is to provide a positive electrode sheet to solve the problem of poor cycle performance and rate performance of existing sodium ion battery positive electrode materials.

[0008] In order to solve the above technical problems, the technical solution of the coated sodium ion battery positive electrode material of the present invention is:

[0009] A coated sodium ion battery positive electrode material, comprising a layered transition metal oxide and a coating layer coated on the surface of the layered transition metal oxide; the coating layer comprises MO n / 2and NaX, wherein M is selected from one or more of Ni, Mg, Zn, Ca, Cu, Fe, Co, Ti, Zr, W, V, Mn, Y, In, and La, X is a halogen element, 2≤n≤5; the layered transition metal oxide is Na y M' z O 2+r , wherein M' is selected from one or more of Ni, Fe, Mn, Cu, Zn, Mg, Ti, Li, Al, Co, Sn, B, Ca, Y, Zr, W, Nb, and V, 0.5≤y≤1.2, 0≤z≤0.1, and -0.3≤r≤0.3.

[0010] The present invention improves the existing technology and provides a coated sodium ion battery positive electrode material by coating the metal oxide MO on the surface of the layered transition metal oxide. n / 2 and sodium halide NaX to form a surface passivation layer. The metal oxide in the passivation layer avoids the gelation of PVDF glue caused by the alkalinity of the slurry during the slurrying process, effectively improving the processing performance of the material. At the same time, its good electrochemical stability blocks the contact between the positive electrode material and the electrolyte, inhibits the dissolution of transition metals, reduces the occurrence of side reactions, effectively alleviates the corrosion of the electrolyte, ensures the stability of the material structure, and improves the cycle performance and safety performance of the battery. In addition, sodium halide NaX has a high ionic conductivity and can act as a bridge between the electrolyte and the positive electrode material to transport sodium ions, thereby improving the cycle stability of the positive electrode material without sacrificing its rate performance.

[0011] In order to further improve the cycle performance and rate performance of the coated sodium ion battery cathode material, preferably, the MO n / 2 The mass ratio of NaX to Mg is (4-25):10.

[0012] Preferably, the mass of the coating layer is 0.2 to 1.1% of the mass of the layered transition metal oxide.

[0013] The technical solution of the method for preparing the coated sodium ion battery positive electrode material of the present invention is:

[0014] A method for preparing a coated sodium ion battery cathode material comprises the following steps: n After mixing with layered transition metal oxides and sintering, MX n The mass of X is 0.2-0.5 wt% of the layered transition metal oxide; wherein M is selected from one or more of Ni, Mg, Zn, Ca, Cu, Fe, Co, Ti, Zr, W, V, Mn, Y, In, and La; X is a halogen element, 2≤n≤5; the layered transition metal oxide is Na y M' z O 2+r, wherein M' is selected from one or more of Ni, Fe, Mn, Cu, Zn, Mg, Ti, Li, Al, Co, Sn, B, Ca, Y, Zr, W, Nb, and V, 0.5≤y≤1.2, 0≤z≤0.1, and -0.3≤r≤0.3.

[0015] The method for preparing the coated sodium ion battery positive electrode material of the present invention is to control the metal halide MX n The addition ratio is 20%, and the surface residual alkali (such as Na2O, NaOH, Na2CO3) of the positive electrode material is used to react with the metal halide to in situ generate a surface passivation layer including metal oxide and sodium halide. The reaction equation is as follows:

[0016] Na2O+MX n →NaX+MO n / 2

[0017] Na2CO3+MX n →NaX+MO n / 2 +CO2↑

[0018] NaOH+MX n →NaX+MO n / 2 +H2O↑

[0019] Wherein, M is selected from one or more of Ni, Mg, Zn, Ca, Cu, Fe, Co, Ti, Zr, W, V, Mn, Y, In, and La, X is a halogen element, and 2≤n≤5.

[0020] The preparation method provided by the present invention makes full use of the residual alkali on the surface of the positive electrode material, so that the in-situ generated coating layer is in close contact with the positive electrode material, and has better stability than various mechanical mixing methods; and MX n It reacts with the residual alkali on the surface of the positive electrode material, avoiding the gelation of PVDF glue caused by the alkalinity of the slurry during the slurry making process, and effectively improves the processing performance of the material.

[0021] In order to further improve the crystallinity of the coating layer and thus improve the cycle performance, preferably, the holding temperature during sintering is 300-800° C., and the holding time during sintering is 6-8 hours.

[0022] In order to further improve the cycle performance and rate performance at the same time, the holding temperature during sintering is 600-700℃.

[0023] In order to further improve the crystallization performance of the coating layer, preferably, the heating rate during sintering is 1 to 10° C. / min.

[0024] In order to further remove residual alkali on the surface of the layered transition metal oxide and improve battery stability, preferably, the hydroxide content on the surface of the layered transition metal oxide is 3-9%, and the carbonate content is 0.2-0.8%.

[0025] The technical solution of the positive electrode sheet of the present invention is:

[0026] A positive electrode sheet comprises the coated sodium ion battery positive electrode material or the coated sodium ion battery positive electrode material prepared by the method for preparing the coated sodium ion battery positive electrode material.

[0027] The positive electrode sheet provided by the present invention can improve the cycle performance and rate performance of the sodium ion battery by utilizing the coated sodium ion battery positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 XRD patterns at different sintering temperatures in the sintering verification experiment before coating;

[0029] Figure 2 1 is a comparison chart of the cycle performance of Example 1 and Comparative Example 1;

[0030] Figure 3 2 is a comparison chart of the cycle performance of Example 2 and Comparative Example 1;

[0031] Figure 4 1 is a comparison chart of the cycle performance of Example 3 and Comparative Example 1;

[0032] Figure 5 4 is a comparison chart of the cycle performance of Example 4 and Comparative Example 2. DETAILED DESCRIPTION

[0033] The technical concept of the coated sodium ion battery positive electrode material of the present invention is as follows:

[0034] The present invention coats metal oxide MO on the surface of layered transition metal oxide. n / 2 and sodium halide NaX, using MO n / 2 The barrier effect reduces the occurrence of side reactions, and the conductivity of sodium halide NaX is used to transport sodium ions, thereby improving the cycle stability of the positive electrode material without sacrificing its rate performance.

[0035] The method for preparing the coated sodium ion battery positive electrode material provided by the present invention comprises the following steps: n After mixing with layered transition metal oxides and secondary sintering, MX nThe mass of X is 0.2-0.5 wt% of the layered transition metal oxide; wherein M is selected from one or more of Ni, Mg, Zn, Ca, Cu, Fe, Co, Ti, Zr, W, V, Mn, Y, In, and La; X is a halogen element, 2≤n≤5; the layered transition metal oxide is Na y M' z O 2+r , wherein M' is selected from one or more of Ni, Fe, Mn, Cu, Zn, Mg, Ti, Li, Al, Co, Sn, B, Ca, Y, Zr, W, Nb, and V, 0.5≤y≤1.2, 0≤z≤0.1, and -0.3≤r≤0.3.

[0036] In a specific embodiment, the layered transition metal oxide is prepared using existing technology, specifically, sodium carbonate and M(OH)2 are obtained by single sintering, wherein M is a transition metal; the molar ratio of sodium ions in sodium carbonate to the transition metal in M(OH)2 is (1-2): (1-2); the single sintering temperature is 800-1000°C, and the single sintering time is 10-20h.

[0037] It can be understood that the structure of the layered transition metal oxide is P2 type or O3 type.

[0038] In a specific embodiment, the layered transition metal oxide is of O3 type, and O3 type includes NaNi 0.333 Fe 0.333 Mn 0.333 O2 and NaNi 0.2 Fe 0.3 Mn 0.3 Zn 0.1 O2.

[0039] In a specific embodiment, the primary sintering is performed in an oxygen-containing atmosphere; the secondary sintering is performed in air or an inert gas; and the inert atmosphere is selected from one of nitrogen and argon.

[0040] In a specific embodiment, the positive electrode sheet is prepared from a coated sodium ion battery positive electrode material, a conductive agent, and a binder in a mass ratio of (80-90): (5-10): (5-10).

[0041] The embodiments of the present invention are further described below with reference to specific examples. Unless otherwise specified, the chemical reagents involved in the following examples are all commercially available conventional products.

[0042] 1. Specific embodiments of the coated sodium ion battery positive electrode material and preparation method thereof of the present invention

[0043] Example 1

[0044] The preparation method of the coated sodium ion battery positive electrode material of this embodiment is as follows:

[0045] (1) Sodium carbonate (analytical grade), Ni 0.333 Fe 0.333 Mn 0.333 (OH)2 was mixed evenly in proportion to meet the molar ratio of sodium ions in sodium carbonate to total transition metal elements (Ni, Fe, Mn) of 1:1, and mixed into material A to be fired by a high-speed and low-speed combination mixing method. Material A to be fired was placed in a sagger and placed in a box-type atmosphere furnace with compressed air. The temperature was raised to 900℃ at a heating rate of 5℃ / min and sintered at a constant temperature for 15h. The temperature was naturally cooled to room temperature and crushed and sieved to obtain NaNi 0.333 Fe 0.333 Mn 0.333 Layered transition metal oxides of O2.

[0046] (2) 100g of layered transition metal oxide NaNi 0.333 Fe 0.333 Mn 0.333 O2 and 0.55g ZnF2 (calculated based on the mass of the fluorine element, the added amount is 2000ppm of the layered transition metal oxide) are mixed evenly; in an air atmosphere, the temperature is raised to 350°C at 5°C / min, and sintered at 350°C for 6h, and then cooled to obtain a coated sodium ion battery positive electrode material.

[0047] The coated sodium ion battery positive electrode material obtained in this embodiment is the coated sodium ion battery positive electrode material provided by the present invention, including layered transition metal oxide NaNi 0.333 Fe 0.333 Mn 0.333 O2 and a coating layer coated on the surface of the layered transition metal oxide; the coating layer is ZnO and NaF; the solid electrolyte membrane, i.e., the coating layer, has a thickness of 20 nm, the mass of the coating layer is 0.77% wt of the mass of the layered transition metal oxide, and the weight ratio of ZnO to NaF is 9.69:10.

[0048] Example 2

[0049] The preparation method of the coated sodium ion battery positive electrode material in this embodiment is basically the same as that in Example 1, except that: in step (2), the temperature is raised to 600°C at a heating rate of 2°C / min and sintered at 600°C for 6h.

[0050] The coated sodium ion battery positive electrode material obtained in this embodiment is the coated sodium ion battery positive electrode material provided by the present invention, including layered transition metal oxide NaNi 0.333 Fe 0.333 Mn 0.333O2 and a coating layer coated on the surface of the layered transition metal oxide; the coating layer is ZnO and NaF; the coating layer thickness is 16nm; the mass of the coating layer is 0.83% of the mass of the layered transition metal oxide; the mass ratio of ZnO to NaF in the coating layer is 9.69:10.

[0051] Example 3

[0052] The step (1) of the method for preparing the coated sodium ion battery positive electrode material of this embodiment is basically the same as that of Example 1, except for step (2);

[0053] (2) Weigh 100g NaNi 0.333 Fe 0.333 Mn 0.333 The O2 compound and 0.82gMgF2 (calculated based on the mass of the fluorine element, the added amount is 5000ppm of the layered transition metal oxide) are mixed evenly, heated to 750℃ at 8℃ / min under a nitrogen atmosphere, sintered at 750℃ for 6h, and cooled to obtain a coated sodium ion battery positive electrode material.

[0054] The coated sodium ion battery positive electrode material obtained in this embodiment is the coated sodium ion battery positive electrode material provided by the present invention, including layered transition metal oxide NaNi 0.333 Fe 0.333 Mn 0.333 O2 and a coating layer coated on the surface of the layered transition metal oxide; the coating layer is MgO and NaF; the solid electrolyte membrane, i.e., the coating layer, has a thickness of 19 nm, the mass of the coating layer is 1.07% wt of the mass of the layered transition metal oxide, and the weight ratio of MgO to NaF is 4.8:10.

[0055] Example 4

[0056] The preparation method of the coated sodium ion battery positive electrode material of this embodiment is as follows:

[0057] (1) Sodium carbonate (analytical grade), Ni 0.2 Fe 0.3 Mn 0.3 Zn 0.1 (OH)2 was mixed evenly in proportion to meet the molar ratio of sodium ions in sodium carbonate to total transition metal elements (Ni, Fe, Mn, Zn) of 1:1, and mixed into material A to be fired by a high-speed and low-speed mixing method. Material A to be fired was placed in a sagger and placed in a box-type atmosphere furnace with compressed air. The temperature was raised to 900°C at a heating rate of 5°C / min and sintered at a constant temperature for 15h. The temperature was naturally cooled to room temperature and crushed and sieved to obtain NaNi 0.2 Fe 0.3 Mn 0.3 Zn 0.1Layered transition metal oxides of O2.

[0058] (2) Weigh 100g NaNi 0.2 Fe 0.3 Mn 0.3 Zn 0.1 The O2 compound and 0.34g ZrCl4 (calculated based on the mass of the chlorine element, the added amount is 2060ppm of the layered transition metal oxide) are mixed evenly, heated to 600℃ at 3℃ / min under an argon atmosphere, sintered at 600℃ for 8h, and cooled to obtain a coated sodium ion battery positive electrode material.

[0059] The coated sodium ion battery positive electrode material obtained in this embodiment is the coated sodium ion battery positive electrode material provided by the present invention, including layered transition metal oxide NaNi 0.333 Fe 0.333 Mn 0.333 O2 and a coating layer coated on the surface of the layered transition metal oxide; the coating layer is ZrO2 and NaCl; the solid electrolyte membrane thickness is 7nm, the coating layer mass is 0.26%wt of the layered transition metal oxide mass, and the weight ratio of ZrO2 to NaCl is 21:10.

[0060] 2. Specific Embodiments of the Positive Electrode Sheet of the Present Invention

[0061] Example 5

[0062] The preparation method of the positive electrode sheet of this embodiment is as follows: the coated sodium ion battery positive electrode material of Example 1 or 2, the conductive agent SP, and the binder PVDF are mixed in a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) solution is added. The mixture is stirred by a homogenizer to obtain a slurry, which is evenly coated on the current collector aluminum foil and dried at a drying temperature of 120°C for 2 hours; and cut into small discs with a diameter of 12 mm, i.e., the positive electrode sheet.

[0063] 3. Comparative Examples

[0064] Comparative Example 1

[0065] The positive electrode material of the sodium ion battery in this comparative example is NaNi obtained in step (1) of Example 1. 0.333 Fe 0.333 Mn 0.333 O2.

[0066] Comparative Example 2

[0067] The preparation method of the sodium ion battery positive electrode material of this comparative example is as follows:

[0068] Sodium carbonate (analytical grade), Ni 0.2 Fe 0.3 Mn0.3 Zn 0.1 (OH)2 was mixed evenly in proportion to meet the molar ratio of sodium ions in sodium carbonate to total transition metal elements (Ni, Fe, Mn, Zn) of 1:1, and mixed into material B to be fired by a high-speed and low-speed combination mixing method. Material B to be fired was placed in a sagger and placed in a box-type atmosphere furnace with air atmosphere. The temperature was raised to 900℃ at a heating rate of 5℃ / min and sintered at a constant temperature for 15h. The temperature was naturally cooled to room temperature and crushed and sieved to obtain NaNi 0.2 Fe 0.3 Mn 0.3 Zn 0.1 Layered transition metal oxides of O2.

[0069] The layered transition metal oxide NaNi obtained in this comparative example 0.2 Fe 0.3 Mn 0.3 Zn 0.1 O2 is the positive electrode material of the sodium ion battery in this comparative example.

[0070] IV. Experimental Examples

[0071] (1) Sintering verification experiment before coating

[0072] Weigh 12.60g Na2CO3 and 12.40g ZnF2 and mix them evenly to obtain a mixture. Weigh 3 portions of 6g each of the mixture and place them in crucibles in a muffle furnace. Heat to 350℃, 600℃, and 800℃ and sinter for 30min respectively. Then take out the samples, sieve them, and perform X-ray diffraction test. The XRD patterns at different sintering temperatures are shown in Figure 2. Figure 1 As shown, it is the intensity (intensity)-2θ angle (Two-Theta) curve, from Figure 1 It can be seen that the peaks of ZnO and NaF appear when the sintering temperature is 350℃, that is, at this temperature, Na2CO3 and ZnF2 have reacted to form ZnO and NaF, but the crystallinity of the product is poor; after increasing the sintering temperature to 800℃, the peak width of the XRD spectrum is narrow, that is, ZnO and NaF with good crystallinity are obtained.

[0073] (2) Performance testing

[0074] Charge and discharge test:

[0075] The sodium ion cathode materials from the examples and comparative examples were fabricated into positive electrode sheets using the method of Example 3. Button cells were assembled in an argon glove box. A 15.6 mm sodium metal sheet was used as the negative electrode. A sodium hexafluorophosphate (NaPF6) / ethylene carbonate (EC) / diethyl carbonate (DEC) solution was prepared in appropriate proportions as the electrolyte. A glass fiber separator was used to assemble the CR2032 button cells. Charge and discharge tests were conducted using constant current / constant voltage charging and constant current discharge modes at current densities of 0.1 / 0.5 / 1C, with charge and discharge cutoff voltages ranging from 2 to 4 V.

[0076] Residual alkali content test:

[0077] The sodium ion positive electrode materials of the embodiment and the comparative example were tested for residual alkali content using the residual alkali content test method (GB / T 41704-2022) in the lithium ion battery positive electrode material detection method.

[0078] The cycle performance comparison diagrams of Examples 1-4 and Comparative Example 1 are shown as follows: Figure 2-5 As shown in Table 1, the discharge capacity, capacity retention rate after 50 cycles and surface residual alkali content of the sodium ion batteries made of the positive electrode materials of the embodiment and the comparative example are shown in Table 1. Figure 2-5 As can be seen from Table 1, although the first-week discharge capacity of the battery made of the sodium ion positive electrode material of Example 1 is 129.90 mAh / g at 0.1C, it is lower than that of the uncoated NaNi 0.333 Fe 0.333 Mn 0.333 O2 (Comparative Example 1), but its capacity retention rate after 50 cycles is 105.48%, which is much higher than that of Comparative Example 1. The first-week discharge capacity of Example 2 is 141.00 mAh / g, slightly higher than that of the uncoated NaNi 0.333 Fe 0.333 Mn 0.333 The capacity retention rate of O2 is 96.73%, which is significantly higher than 89.22% of Comparative Example 1. The first week discharge capacity of Example 3 is 133.50 mAh / g, which is lower than that of the uncoated NaNi 0.333 Fe 0.333 Mn 0.333 O2 (ie, comparative example 1), but its capacity retention rate is 98.08%, much higher than that of comparative example 1. Similarly, the first week discharge capacity of Example 4 is 146.00 mAh / g, which is comparable to that of the uncoated NaNi 0.2 Fe 0.3 Mn 0.3 Zn 0.1 O2 (ie, comparative example 2) is basically the same, but its capacity retention rate is 94.09%, which is much higher than 85.26% of comparative example 2.

[0079] In addition, the surface residual alkali content of the positive electrode materials of Examples 1-3 is significantly lower than that of Comparative Example 1. Similarly, the surface residual alkali content of the positive electrode material of Example 4 is also significantly lower than that of Comparative Example 2, indicating that the preparation method of the present invention can significantly reduce the surface residual alkali.

[0080] Table 1 Performance test results of positive electrode materials of Examples and Comparative Examples

[0081]

[0082] The coated sodium ion battery positive electrode material of the present invention has significantly improved buckling cycle performance, that is, the obtained oxide and sodium halide coated positive electrode material inhibits the side reaction between the positive electrode material and the electrolyte during the charge and discharge process; at the same time, the present invention effectively reduces the surface residual alkali of the layered oxide positive electrode material through chemical reaction.

[0083] The coated sodium-ion battery cathode material provided by the present invention can be obtained by mixed sintering, and the coating compound used is inexpensive, reducing material costs. This layered oxide cathode material can be widely used in power, energy storage systems, portable storage devices, as well as mid- and low-end electric vehicles and trams.

[0084] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A coated sodium ion battery cathode material, characterized in that: It comprises a layered transition metal oxide and a coating layer coated on the surface of the layered transition metal oxide; the coating layer comprises MO n / 2 and NaX, wherein M is selected from one or more of Ni, Mg, Zn, Ca, Cu, Fe, Co, Ti, Zr, W, V, Mn, Y, In, and La, X is a halogen element, 2≤n≤5; the layered transition metal oxide is Na y M' z O 2+r , wherein M' is selected from one or more of Ni, Fe, Mn, Cu, Zn, Mg, Ti, Li, Al, Co, Sn, B, Ca, Y, Zr, W, Nb, and V, 0.5≤y≤1.2, 0≤z≤0.1, and -0.3≤r≤0.

3.

2. The coated sodium ion battery positive electrode material according to claim 1, wherein The MO n / 2 The mass ratio of NaX to Mg is (4~25):

10.

3. The coated sodium ion battery positive electrode material according to claim 1 or 2, characterized in that The mass of the coating layer is 0.2-1.1% of the mass of the layered transition metal oxide.

4. A method for preparing a coated sodium ion battery positive electrode material according to any one of claims 1 to 3, characterized in that: The following steps are involved: MX n After mixing with layered transition metal oxides and sintering, MX n The mass of X is 0.2-0.5wt% of the layered transition metal oxide; wherein M is selected from one or more of Ni, Mg, Zn, Ca, Cu, Fe, Co, Ti, Zr, W, V, Mn, Y, In, and La; X is a halogen element, 2≤n≤5; the layered transition metal oxide is Na y M' z O 2+r , wherein M' is selected from one or more of Ni, Fe, Mn, Cu, Zn, Mg, Ti, Li, Al, Co, Sn, B, Ca, Y, Zr, W, Nb, and V, 0.5≤y≤1.2, 0≤z≤0.1, and -0.3≤r≤0.

3.

5. The method for preparing the coated sodium ion battery positive electrode material according to claim 4, wherein: The holding temperature during sintering is 300~800℃, and the holding time during sintering is 6~8h.

6. The method for preparing the coated sodium ion battery positive electrode material according to claim 5, wherein: The holding temperature during sintering is 600~700℃.

7. The method for preparing a coated sodium ion battery cathode material according to claim 4, wherein: The heating rate during sintering is 1~10℃ / min.

8. The method for preparing a coated sodium ion battery cathode material according to claim 4, wherein: The surface hydroxide content of the layered transition metal oxide is 3~9%, and the carbonate content is 0.2~0.8%.

9. A positive electrode sheet, characterized in that: The invention relates to a coated sodium ion battery positive electrode material according to any one of claims 1 to 3 or a coated sodium ion battery positive electrode material prepared by the method for preparing the coated sodium ion battery positive electrode material according to any one of claims 4 to 8.

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