Modified p2-type sodium battery positive electrode material, preparation method therefor, and use thereof

Abstract

Provided are a modified P2-type sodium battery positive electrode material, a preparation method therefor, and the use thereof. The preparation method comprises the following steps: concurrent flow addition of a nickel-manganese salt solution, a precipitant solution, and a complexing agent solution into a base solution, and carrying out a coprecipitation reaction to replace the nickel-manganese salt solution with a cobalt salt solution; continuing to carry out a coprecipitation reaction to obtain a sodium battery precursor; mixing and sintering the sodium battery precursor and a sodium source, and separately coating a carbon layer and a metal oxide. The modified P2-type sodium battery positive electrode material prepared using the present method is a P2-type manganese-based layered oxide structure; the battery has excellent cycle performance, rate capability, and material stability, the battery can reduce side reactions with the electrolyte at high potentials, lowers material dissolution and electrolyte consumption, and improves the cycle performance of a material.

Description

A modified P2-type sodium cathode material and its preparation method and application Technical Field

[0001] The present application belongs to the technical field of sodium ion batteries and relates to a modified P2-type sodium battery positive electrode material and its preparation method and application. Background Art

[0002] Sodium-ion batteries, with their abundant raw materials and low cost, have broad application prospects in new large-scale energy storage systems and smart grids. The development of high-performance electrode material systems plays a crucial role in the application of sodium-ion batteries.

[0003] Among the many cathode materials for sodium-ion batteries, layered transition metal oxides have attracted widespread attention due to their simple synthesis methods and controllable composition and structure. The increasing demand for high specific capacity due to technological advancements has made the capacity limitations of traditional cationic redox reaction mechanisms a bottleneck.

[0004] CN115064670A discloses a method for preparing a doped, coated, and modified sodium nickel manganate positive electrode material, comprising the following steps: (1) surface treating the sodium nickel manganate positive electrode material with a hydrogen peroxide solution to obtain a surface-treated sodium nickel manganate positive electrode material; and (2) mixing the surface-treated sodium nickel manganate positive electrode material in step (1) with sodium salt and MgO powder, grinding the mixture, and then calcining the mixture to obtain the doped, coated, and modified sodium nickel manganate positive electrode material.

[0005] CN113845158A discloses a method for preparing a porous spherical structure sodium nickel manganate positive electrode material, comprising the following steps: (1) adding a nickel manganese metal salt solution, a carbonate precipitant solution and a complexing agent solution into a reactor containing a bottom liquid to carry out a co-precipitation reaction to obtain a nickel manganese binary carbonate precursor with a solid structure having different internal and external crystallinity; (2) calcining the nickel manganese binary carbonate precursor with a solid structure to decompose the nickel manganese binary carbonate with a solid structure to obtain a nickel manganese binary oxide precursor with a layered structure; and (3) uniformly mixing the layered nickel manganese binary oxide precursor with a sodium salt and calcining the mixture to obtain the porous spherical structure sodium nickel manganate positive electrode material.

[0006] In the sodium positive electrode material prepared by the above scheme, Mn 3+ / Mn 4+ The working voltage of the redox couple is low, which leads to low energy density of the material, and Mn 3+It is easy to cause distortion when working at low potential, resulting in irreversible capacity decay; the material's structural evolution is complex during the redox reaction, and P2-O2 phase transition is prone to occur when working at high potential, resulting in poor cycle and rate performance; high potential operation is prone to cause serious material / electrolyte side reactions, causing dissolution of electrode materials and continuous consumption of electrolyte; when the material is stored in the air, Na2CO3 or NaHCO3 compounds are easily formed on the surface, which damages its capacity, cycle and rate performance, and increases storage and transportation costs.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of the present application is to provide a modified P2-type sodium battery positive electrode material, a preparation method and application thereof. The modified P2-type sodium battery positive electrode material prepared by the method described in the present application has a P2-type manganese-based layered oxide structure, has excellent cycle performance and rate performance, and has high material stability. It can reduce the side reactions occurring with the electrolyte at high potential, reduce material dissolution and electrolyte consumption, and improve the cycle performance of the material.

[0010] To achieve this goal, this application adopts the following technical solutions:

[0011] In a first aspect, the present application provides a method for preparing a modified P2-type sodium cathode material, the preparation method comprising the following steps:

[0012] (1) injecting a nickel-manganese binary salt solution, a precipitant solution, and a complexing agent solution into a bottom liquid in parallel to perform a one-step coprecipitation reaction, replacing the nickel-manganese binary salt solution with a cobalt salt solution while controlling the flow rates of other materials to remain unchanged, and performing a two-step coprecipitation reaction to obtain a sodium electrode precursor;

[0013] (2) mixing the sodium battery precursor with a sodium source and sintering the mixture to obtain a sodium battery positive electrode material;

[0014] (3) mixing the sodium cathode material with a nitrogen-containing carbon source and an alkaline solution, and calcining the mixture at a high temperature to obtain a calcined material;

[0015] (4) The calcined material and the metal oxide are mixed and subjected to heat treatment to obtain the modified P2 type sodium cathode material.

[0016] This application improves the electrochemical performance of the material by adjusting the feed type during the coprecipitation process and coating the surface of the nickel-manganese precursor with cobalt. After mixing and sintering the cobalt-coated nickel-manganese precursor with a sodium source, a P2-type manganese-based layered oxide microstructure is obtained, which constructs microchannels that are conducive to electron / ion transport, thereby improving its electrochemical performance. This application coats the surface of the material with nitrogen-containing carbon materials and metal oxides to prevent the material from absorbing CO2 and H2O, prevent the dissolution of metal ions, and improve the conductivity and ion transport efficiency, thereby improving its cyclic stability.

[0017] In one embodiment, the concentration of the nickel-manganese binary salt solution in step (1) is 1 to 3 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0018] In one embodiment, the molar ratio of nickel to manganese in the nickel-manganese binary salt solution is x:y, 0 <x<1,0<y<1,x+y=1。

[0019] In one embodiment, the precipitant solution comprises sodium hydroxide solution.

[0020] In one embodiment, the mass concentration of the precipitant solution is 10% to 40%, for example, 10%, 15%, 20%, 30% or 40%.

[0021] In one embodiment, the complexing agent solution comprises aqueous ammonia.

[0022] In one embodiment, the mass concentration of the ammonia water is 10-30%, for example, 10%, 15%, 20%, 25% or 30%.

[0023] In one embodiment, the base solution includes a complexing agent.

[0024] In one embodiment, the pH of the base solution is 9 to 13, for example, 9, 10, 11, 12 or 13.

[0025] In one embodiment, the concentration of the cobalt salt solution is 0.3-0.6 mol / L, for example, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.5 mol / L or 0.6 mol / L.

[0026] The concentration of the cobalt salt solution will affect the performance of the modified P2 type sodium battery cathode material. If the concentration of the cobalt salt solution is too high, the performance of the sodium battery cathode material will decrease. If the concentration of the cobalt salt solution is too low, the coating effect will not be achieved.

[0027] In one embodiment, the temperature of the one-step coprecipitation reaction and the two-step coprecipitation reaction in step (1) is independently 40-65°C, for example, 40°C, 45°C, 50°C, 60°C or 65°C.

[0028] In one embodiment, the pH of the one-step co-precipitation reaction and the two-step co-precipitation reaction are independently 9 to 13, for example, 9, 10, 11, 12 or 13.

[0029] In one embodiment, the median particle size of the material in the system after the one-step co-precipitation reaction in step (1) is D501, and the median particle size of the sodium electrode precursor is D502, D502-D501=0.5~1μm, for example: 0.5μm, 0.6μm, 0.8μm, 0.9μm or 1μm, etc.

[0030] In one embodiment, the median particle size D502 of the sodium electrolyte precursor is 5 to 14 μm, for example, 5 μm, 8 μm, 10 μm, 12 μm or 14 μm.

[0031] In one embodiment, the sintering process in step (2) includes one-step sintering and two-step sintering.

[0032] In one embodiment, the temperature of the one-step sintering is 450-550°C, for example, 450°C, 480°C, 500°C, 520°C or 550°C.

[0033] In one embodiment, the one-step sintering time is 6 to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0034] In one embodiment, the temperature of the two-step sintering is 1000-1200°C, for example, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C.

[0035] In one embodiment, the two-step sintering time is 20 to 30 hours, for example, 20 hours, 22 hours, 25 hours, 28 hours or 30 hours.

[0036] In one embodiment, the pH of the alkaline solution in step (3) is 8 to 9, for example, 8, 8.2, 8.5, 8.8 or 9.

[0037] In one embodiment, the nitrogen-containing carbon source comprises polydopamine.

[0038] In one embodiment, the mass ratio of the sodium cathode material to the nitrogen-containing carbon source is (500-1000):1, for example: 500:1, 600:1, 800:1, 900:1 or 1000:1, etc.

[0039] The mass ratio of sodium battery positive electrode material and polydopamine is controlled at 500-1000:1, and the performance of the sodium battery positive electrode material is better. If the amount of polydopamine added is too high, the stability of the positive electrode material will decrease. If the amount of polydopamine added is too low, its effect will be small, and the performance of the sodium battery positive electrode will be reduced.

[0040] In one embodiment, the high temperature calcination treatment is performed at a temperature of 1000-1200°C, for example, 1000°C, 1050°C, 1100°C, 1150°C or 1200°C.

[0041] In one embodiment, the high temperature calcination treatment time is 20 to 30 hours, for example, 20 hours, 22 hours, 25 hours, 28 hours or 30 hours.

[0042] In one embodiment, the metal oxide in step (4) includes at least one of Al2O3, ZrO2 or MnO2.

[0043] In one embodiment, the mass ratio of the calcined material to the metal oxide is (600-1000):1, for example: 600:1, 700:1, 800:1, 900:1 or 1000:1, etc.

[0044] In one embodiment, the heat treatment temperature is 700-1300°C, for example, 700°C, 800°C, 1000°C, 1100°C or 1300°C.

[0045] In one embodiment, the heat treatment time is 8 to 20 hours, for example, 8 hours, 10 hours, 12 hours, 15 hours or 20 hours.

[0046] In a second aspect, the present application provides a modified P2-type sodium battery positive electrode material, which is prepared by the method described in the first aspect.

[0047] In a third aspect, the present application provides a positive electrode plate, which comprises the modified P2-type sodium battery positive electrode material as described in the second aspect.

[0048] In a fourth aspect, the present application provides a sodium ion battery, which comprises the positive electrode sheet as described in the third aspect.

[0049] Compared with the prior art, this application has the following beneficial effects:

[0050] (1) The modified P2-type sodium battery positive electrode material prepared by the method described in the present application has a P2-type manganese-based layered oxide structure, which has excellent cycle performance and rate performance. The material has high stability, can reduce the side reactions occurring with the electrolyte at high potential, reduce material dissolution and electrolyte consumption, and improve the cycle performance of the material.

[0051] (2) The first efficiency of the battery made of the modified P2-type sodium battery positive electrode material described in this application can reach more than 83.4%, the first discharge capacity can reach more than 112.9 mAh / g, and the capacity retention rate after 50 cycles can reach more than 98.3%.

[0052] Still other aspects will become apparent upon reading and understanding the detailed description. DETAILED DESCRIPTION

[0053] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0054] Example 1

[0055] This embodiment provides a modified P2-type sodium battery cathode material. The preparation method of the modified P2-type sodium battery cathode material is as follows:

[0056] (1) A 2 mol / L sulfate solution (i.e., nickel-manganese binary salt solution) was prepared according to a molar ratio of Ni:Mn=6:4, a 32% NaOH solution and an 18% ammonia solution were prepared, 600 L of pure water was added to the reactor, and then ammonia was added to make the pH value of the bottom liquid reach about 10.0. The temperature of the reactor was maintained at 56°C, and N2 was introduced throughout the reaction to prevent oxidation. The nickel-manganese binary salt solution was uniformly added to the reactor at a feeding rate of 40 L / h. At the same time, a mixed solution of ammonia and alkali solution was added to control the pH value of the reaction environment between 10.4 and 10.6. The stirring was turned on at a speed of 300 rpm. The particle size reached 7 μm. The nickel-manganese binary salt solution was replaced with a cobalt sulfate solution with a concentration of 0.6 mol / L, and the coprecipitation reaction was continued to obtain a sodium electrode precursor with a D50 of 8 μm.

[0057] (2) mixing the sodium battery precursor with sodium carbonate according to Na / M=1.1, first heating to 500°C and keeping the temperature for 8 hours, then continuing to heat to about 1100°C and keeping the temperature for 24 hours to obtain a sodium battery positive electrode material;

[0058] (3) placing the sodium cathode material in an alkaline solution with a pH of 8.5 and adding polydopamine and mixing uniformly, wherein the mass ratio of the sodium cathode material to the polydopamine is 700:1, and calcining at 1100° C. for 24 h to obtain a calcined material;

[0059] (4) The calcined material was fully mixed with Al2O3 in a ball mill at a mass ratio of 800:1, and then placed in a roller kiln for heat treatment at 1000°C in an air atmosphere for 12 hours to obtain the modified P2-type sodium cathode material.

[0060] Example 2

[0061] This embodiment provides a modified P2-type sodium battery cathode material. The preparation method of the modified P2-type sodium battery cathode material is as follows:

[0062] (1) A 1 mol / L sulfate solution (i.e., nickel-manganese binary salt solution) was prepared according to a molar ratio of Ni:Mn=6:4, a 10% NaOH solution and a 30% ammonia solution were prepared, 600 L of pure water was added to the reactor, and then ammonia was added to make the pH value of the bottom liquid reach about 10.0. The temperature of the reactor was maintained at 45°C, and N2 was introduced throughout the reaction to prevent oxidation. The nickel-manganese binary salt solution was uniformly added to the reactor at a feeding rate of 40 L / h. At the same time, a mixed solution of ammonia and alkali solution was added to control the pH value of the reaction environment between 9.5 and 9.8. The stirring was turned on at a speed of 300 rpm. The particle size reached 4.5 μm. The nickel-manganese binary salt solution was replaced with a cobalt sulfate solution with a concentration of 0.4 mol / L, and the coprecipitation reaction was continued to obtain a sodium electrode precursor with a D50 of 5 μm.

[0063] (2) mixing the sodium battery precursor with sodium carbonate according to Na / M=1.1, first heating to 450°C and keeping the temperature for 10 hours, then continuing to heat to about 1000°C and keeping the temperature for 30 hours to obtain a sodium battery positive electrode material;

[0064] (3) placing the sodium cathode material in an alkaline solution with a pH of 8 and adding polydopamine and mixing uniformly, wherein the mass ratio of the sodium cathode material to the polydopamine is 500:1, and calcining at 1000° C. for 30 h to obtain a calcined material;

[0065] (4) The calcined material was fully mixed with ZrO2 in a ball mill at a mass ratio of 600:1, and placed in a roller kiln for heat treatment at 700°C in an air atmosphere for 20 hours to obtain the modified P2 type sodium cathode material.

[0066] Example 3

[0067] This embodiment provides a modified P2-type sodium battery cathode material. The preparation method of the modified P2-type sodium battery cathode material is as follows:

[0068] (1) A 3 mol / L sulfate solution (i.e., nickel-manganese binary salt solution) was prepared according to a molar ratio of Ni:Mn=6:4, a 40% NaOH solution and a 10% ammonia solution were prepared, 600 L of pure water was added to the reactor, and then ammonia was added to make the pH value of the bottom liquid reach about 12.0. The temperature of the reactor was maintained at 56°C, and N2 was introduced throughout the reaction to prevent oxidation. The nickel-manganese binary salt solution was uniformly added to the reactor at a feeding rate of 40 L / h. At the same time, a mixed solution of ammonia and alkali solution was added to control the pH value of the reaction environment between 11.8 and 12.3. The stirring was turned on at a speed of 300 rpm. The particle size reached 13.2 μm. The nickel-manganese binary salt solution was replaced with a cobalt sulfate solution with a concentration of 0.5 mol / L, and the coprecipitation reaction was continued to obtain a sodium electrode precursor with a D50 of 14 μm.

[0069] (2) mixing the sodium battery precursor with sodium carbonate according to Na / M=1.1, first heating to 550°C and keeping the temperature for 8 hours, then continuing to heat to about 1200°C and keeping the temperature for 20 hours to obtain a sodium battery positive electrode material;

[0070] (3) placing the sodium cathode material in an alkaline solution with a pH of 9 and adding polydopamine and mixing them uniformly, wherein the mass ratio of the sodium cathode material to the polydopamine is 900:1, and calcining the mixture at 1200° C. for 20 h to obtain a calcined material;

[0071] (4) The calcined material was fully mixed with MnO2 in a ball mill at a mass ratio of 1000:1, and placed in a roller kiln for heat treatment at 1300°C in an air atmosphere for 8 hours to obtain the modified P2 type sodium cathode material.

[0072] Example 4

[0073] The only difference between this embodiment and embodiment 1 is that the concentration of the cobalt salt solution is 0.8 mol / L, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0074] Example 5

[0075] The only difference between this embodiment and embodiment 1 is that the concentration of the cobalt salt solution is 0.1 mol / L, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0076] Example 6

[0077] The only difference between this embodiment and embodiment 1 is that the mass ratio of the sodium cathode material to polydopamine is 1100:1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0078] Example 7

[0079] The only difference between this embodiment and embodiment 1 is that the mass ratio of the sodium cathode material to polydopamine is 400:1, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0080] Comparative Example 1

[0081] The only difference between this comparative example and Example 1 is that no cobalt salt solution is added, and other conditions and parameters are exactly the same as those in Example 1.

[0082] Comparative Example 2

[0083] The only difference between this comparative example and Example 1 is that polydopamine is not coated, and other conditions and parameters are exactly the same as those in Example 1.

[0084] Comparative Example 3

[0085] The only difference between this comparative example and Example 1 is that the metal oxide is not coated, and other conditions and parameters are exactly the same as those in Example 1.

[0086] Performance testing:

[0087] The positive electrode materials obtained in the examples and comparative examples were used to prepare button batteries. The specific preparation method was as follows: a slurry was applied at a ratio of 90 (main material): 5 (polyvinylidene fluoride PVDF): 5 (conductive agent acetylene black) to form a pole piece, a metal lithium sheet was used as a counter electrode, the diaphragm model was Celgard 2500, and a 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (the volume ratio of EC to DMC was 1:1) was used as the electrolyte. CR2032 button batteries were assembled in an argon glove box (wherein water <0.01 ppm and oxygen <0.01 ppm). Finally, the batteries were placed in a blue electric test system for electrical performance testing.

[0088] The electrical performance test conditions are as follows: charge and discharge voltage range 2.0V-4.8V, test temperature 25°C, 0.1C / 0.1C cycle for 1 week to test the initial charge and discharge capacity of the battery, and use this to calculate the first efficiency, and 1C / 1C cycle for 50 weeks to test the cycle performance of the battery. The results are shown in Table 1 below.

[0089] Table 1

[0090] As can be seen from Table 1, from Examples 1-3, the first efficiency of the battery made of the modified P2-type sodium battery positive electrode material described in this application can reach more than 83.4%, the first discharge capacity can reach more than 112.9 mAh / g, and the capacity retention rate after 50 cycles can reach more than 98.3%.

[0091] By comparing Example 1 with Examples 4-5, it can be seen that during the preparation process of the modified P2-type sodium-based positive electrode material described in the present application, the concentration of the cobalt salt solution will affect its performance. When the concentration of the cobalt salt solution is controlled at 0.3 to 0.6 mol / L, the performance of the sodium-based positive electrode material obtained is better. If the concentration of the cobalt salt solution is too high, the performance of the sodium-based positive electrode material will be reduced. If the concentration of the cobalt salt solution is too low, the coating effect will not be achieved.

[0092] By comparison of Example 1 and Examples 6-7, it can be seen that in the preparation process of the modified P2-type sodium-type positive electrode material described in the present application, the mass ratio of the sodium-type positive electrode material and polydopamine will affect its performance. The mass ratio of the sodium-type positive electrode material and polydopamine is controlled at 500 to 1000:1, and the performance of the sodium-type positive electrode material is better. If the amount of polydopamine added is too high, the stability of the positive electrode material will decrease. If the amount of polydopamine added is too low, its effect is not significant, but the performance of the sodium-type positive electrode will be reduced.

[0093] By comparing Example 1 and Comparative Example 1, it can be seen that the present application adjusts the type of feed in the coprecipitation process to coat cobalt on the surface of the nickel-manganese precursor, thereby obtaining a microstructure of a P2-type manganese-based layered oxide, constructing microchannels that are conducive to electron / ion transmission, and thus improving its electrochemical performance.

[0094] By comparing Example 1 with Comparative Examples 2-3, it can be seen that the present application coats the surface of the material with carbon material or oxide to prevent the material from absorbing CO2 and H2O, prevent the dissolution of metal ions, and improve the electrical conductivity and ion transmission efficiency, thereby improving its cycle stability.

[0095] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. Preparation method of modified P2-type sodium battery cathode material, including the following steps: (1) Inject the nickel-manganese binary salt solution, precipitant solution, and complexing agent solution into the bottom liquid in parallel flow to carry out a one-step coprecipitation reaction. Replace the nickel-manganese binary salt solution with a cobalt salt solution, and control the flow rates of other materials to remain unchanged to carry out a two-step coprecipitation reaction to obtain a sodium battery precursor; (2) Mix the sodium battery precursor with a sodium source and perform a sintering treatment to obtain a sodium battery cathode material; (3) Mix the sodium battery cathode material with a nitrogen-containing carbon source and an alkaline solution, and perform a high-temperature calcination treatment to obtain a calcined material; (4) Mix the calcined material with a metal oxide and perform a heat treatment to obtain the modified P2-type sodium battery cathode material.

2. The preparation method according to claim 1, wherein, the concentration of the nickel-manganese binary salt solution in step (1) is 1-3 mol / L; optionally, the molar ratio of nickel to manganese in the nickel-manganese binary salt solution is x:y, 0 < x < 1, 0 < y < 1, and x + y = 1; optionally, the precipitant solution includes a sodium hydroxide solution; optionally, the mass concentration of the precipitant solution is 10-40%; optionally, the complexing agent solution includes ammonia water; optionally, the mass concentration of the ammonia water is 10-30%; optionally, the bottom liquid includes a complexing agent; optionally, the pH of the bottom liquid is 9-13; optionally, the concentration of the cobalt salt solution is 0.3-0.6 mol / L.

3. The preparation method according to claim 1 or 2, wherein, the temperature of the one-step coprecipitation reaction and the two-step coprecipitation reaction in step (1) is independently 40-65 °C; optionally, the pH of the one-step coprecipitation reaction and the two-step coprecipitation reaction is independently 9-13.

4. The preparation method according to any one of claims 1-3, wherein, The median particle size of the materials in the system after the one-step coprecipitation reaction described in step (1) is D50 1 , and the median particle size of the sodium-ion battery precursor is D50 2 , D50 2 -D50 1 = 0.5 - 1 μm; Optionally, the median particle size D50 of the sodium-ion precursor 2 is 5 to 14 μm.

5. The preparation method according to any one of claims 1-4, wherein, the sintering treatment in step (2) includes one-step sintering and two-step sintering; optionally, the temperature of the one-step sintering is 450-550 °C; optionally, the time of the one-step sintering is 6-10 h; optionally, the temperature of the two-step sintering is 1000-1200 °C; optionally, the time of the two-step sintering is 20-30 h.

6. The preparation method according to any one of claims 1-5, wherein, the pH of the alkaline solution in step (3) is 8-9; optionally, the nitrogen-containing carbon source includes polydopamine; optionally, the mass ratio of the sodium battery cathode material to the nitrogen-containing carbon source is (500-1000):1; optionally, the temperature of the high-temperature calcination treatment is 1000-1200 °C; optionally, the time of the high-temperature calcination treatment is 20-30 h.

7. The preparation method according to any one of claims 1-6, wherein, The metal oxide described in step (4) includes Al 2 O 3 , ZrO 2 , or MnO 2 and at least one of them; optionally, the mass ratio of the calcined material to the metal oxide is (600-1000):1; optionally, the temperature of the heat treatment is 700-1300 °C; optionally, the time of the heat treatment is 8-20 h.

8. A modified P2-type sodium battery cathode material prepared by the method according to any one of claims 1-7.

9. A positive electrode sheet comprising the modified P2-type sodium battery positive electrode material as described in claim 8.

10. A sodium ion battery comprising the positive electrode sheet as described in claim 9.

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