A sodium ion precursor material, its preparation method and use

Abstract

The present invention provides a sodium ion precursor material, a preparation method thereof and uses thereof. The sodium ion precursor material includes a core and a coating layer located on the surface of the core; the core includes nickel-iron-manganese hydroxide, and the coating layer includes nickel-copper-manganese hydroxide. The sodium ion precursor material provided by the present invention has a nickel-iron-manganese layer with relatively high capacity in the inner layer and a nickel-copper-manganese layer with relatively high stability in the outer layer, which improves the stability of the iron-based sodium ion precursor material and the cathode material, and also enables the copper element to uniformly form a phase in the precursor material and the cathode material of the nickel-iron-manganese system, thereby improving the rate performance and cycle stability of the sodium ion cathode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and relates to a sodium ion precursor material, a preparation method thereof, and uses thereof. Background Art

[0002] Sodium ion batteries show great application prospects in the fields of large-scale energy storage and low-speed electric vehicles due to resource and cost advantages. Layered oxides have a relatively high theoretical capacity and are easy to synthesize, and are one of the most promising cathode materials for sodium ion batteries at present.

[0003] For example, CN112510196A discloses a preparation method of a manganese-based metal oxide cathode, and the production steps include the following: S1, grinding and firing: cobalt tetroxide, nickel oxide, manganese oxide, and sodium carbonate in stoichiometric ratio are ground in an agate mortar, and then fired in a muffle furnace at 500 °C for 3 hours and then heated to 850 °C and fired for 12 h; S2, cooling and isolation: after cooling to room temperature, the obtained solid powder is stored in a glove box under argon protection to isolate air and moisture; S3, cathode coating; S4, preparing materials; S5, stirring and mixing; S6, dropping the slurry; S7, vacuum drying.

[0004] The layered oxide cathode material has the following problems: 1) strong hygroscopicity, which can absorb a large amount of moisture in the air and cause it to fail; 2) after long-term cycling of the battery, the structure of the cathode material is prone to collapse, resulting in loss of electrochemical activity. In order to realize the efficient resource utilization of the layered oxide cathode material and further reduce the cost of sodium ion batteries, it is necessary to electrochemically repair the failed or electrochemically inactive layered oxide cathode material.

[0005] In order to improve the cycle stability and rate performance of the layered oxide sodium battery material, it is usually possible to inhibit the order of transition metals, charge order, and Na+ / vacancy order by preparing multi-element or high-entropy metal oxides.

[0006] Currently reported high-entropy metal oxide sodium battery materials are all synthesized by the high-temperature solid-phase method. For example, CN112467119A discloses a preparation method and application of a layered high-entropy oxide sodium ion battery cathode material, belonging to the field of sodium ion battery cathode materials, and its preparation method adopts the high-temperature solid-phase method. On the one hand, the element distribution is uneven, the morphology is irregular and the consistency is poor, affecting the performance; on the other hand, it is difficult to control impurities, metal foreign objects, etc., which is not suitable for large-scale application. If the coprecipitation method is used, many elements such as copper element are difficult to coprecipitate with nickel and manganese to form a single phase when the doping amount is high.

[0007] Therefore, how to obtain a homogeneous multi-element sodium ion cathode material and improve its electrochemical performance at the same time is a technical problem that needs to be solved urgently. Summary of the Invention

[0008] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a sodium ion precursor material, a preparation method and a use thereof. The present invention provides a sodium ion precursor material, with a nickel-iron-manganese with a relatively high capacity in the inner layer and a nickel-copper-manganese with a relatively high stability in the outer layer, which improves the stability of the iron-based sodium ion precursor material and the cathode material, and also enables the copper element to be uniformly phase-formed in the precursor material and the cathode material of the nickel-iron-manganese system, thereby improving the rate performance and cycle stability of the sodium ion cathode material.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a sodium ion precursor material, which includes a core and a coating layer located on the surface of the core; the core includes nickel-iron-manganese hydroxide, and the coating layer includes nickel-copper-manganese hydroxide.

[0011] The sodium ion precursor material provided by the present invention has a uniform morphology and a stable structure. The core is nickel-iron-manganese with a relatively high capacity, and the outer coating layer is nickel-copper-manganese with a relatively high stability, making full use of the high-capacity characteristics of the iron-based material while also improving its stability, and also enabling the copper element to be uniformly phase-formed in the precursor material and the cathode material of the nickel-iron-manganese system, thereby improving the rate performance and cycle stability of the sodium ion cathode material.

[0012] In the present invention, if there is no coating layer and the copper element is directly located in the core, it will lead to a decrease in cycle stability; if the substances of the core and the coating layer are exchanged with each other, the purpose of improving capacity and cycle stability cannot be achieved.

[0013] Preferably, the thickness of the coating layer is 0.3 to 1.5 μm, such as 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm or 1.5 μm, etc.

[0014] In the present invention, if the thickness of the coating layer is too thick, that is, too much nickel-copper-manganese hydroxide is added, it is not conducive to the exertion of capacity; if the thickness is too thin, there will be a problem of poor cycle stability.

[0015] Preferably, the D50 of the core is 3 to 18 μm, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm or 18 μm, etc.

[0016] In the present invention, if the D50 of the core is too small, it will affect the tap density, and if the D50 is too large, it will lead to a low capacity.

[0017] Preferably, the nickel-iron-manganese hydroxide and the nickel-copper-manganese hydroxide further include doping elements.

[0018] In the sodium-ion precursor provided by the present invention, after adding doping elements, a substance with more than five elements is obtained, thereby obtaining a high-entropy sodium-ion cathode material, which is beneficial to improving the cycle stability and rate performance of the battery.

[0019] Preferably, the doping element includes any one or a combination of at least two of Mg, Al, Zn, Ti, Zr or W.

[0020] Preferably, the doping amount of the doping element in the sodium-ion precursor is 500-10000 ppm, such as 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm or 10000 ppm, etc.

[0021] In the present invention, if the doping amount of the doping element is too much, the material capacity will be affected.

[0022] In the second aspect, the present invention provides a preparation method of the sodium-ion precursor material as described in the first aspect, and the preparation method includes the following steps:

[0023] (1) The nickel-iron-manganese mixed salt solution, the precipitant solution and the complexing agent solution are added to the bottom liquid in a co-current manner to carry out a coprecipitation reaction to obtain a core.

[0024] (2) After obtaining the core with the target particle size in step (1), the nickel-iron-manganese mixed salt solution is replaced with a nickel-iron-copper mixed salt solution and the coprecipitation reaction is continued to obtain the sodium-ion precursor material.

[0025] The preparation method provided by the present invention first forms nickel-iron-manganese spheres and then precipitates nickel-copper-manganese, overcoming the problem that copper is difficult to coprecipitate homogeneously with nickel-iron-manganese. The copper content can be greatly increased, and a sodium-ion precursor material with a stable core-shell structure is obtained. The further sintered sodium-ion material has a high capacity and good stability, and its rate performance and cycle performance are improved.

[0026] In the present invention, only by adopting the method of first obtaining nickel-iron-manganese hydroxide and then precipitating nickel-copper-manganese hydroxide can the problem that copper is difficult to coprecipitate homogeneously with nickel-iron-manganese be effectively solved, and the core-shell structure can also stabilize the structure of the core, that is, the structure of the precursor material and the method complement each other and influence each other.

[0027] Preferably, the nickel-iron-manganese mixed salt solution in step (1) further includes a reducing agent.

[0028] In the present invention, the reducing agent is used to prevent the oxidation of ferrous ions in the nickel-iron-manganese mixed salt solution to ferric ions, and the type of the reducing agent is an acidic reducing agent, such as VC.

[0029] Preferably, the molar concentration of the nickel-iron-manganese mixed salt solution in step (1) is 0.5 - 2.5 mol / L, such as 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L or 2.5 mol / L, etc.

[0030] Preferably, the pH value of the bottom solution in step (1) is 9 - 11, such as 9, 9.3, 9.5, 9.8, 10, 10.3, 10.5, 10.8 or 11, etc.

[0031] Preferably, the bottom solution in step (1) comprises a precipitant, a complexing agent and water.

[0032] In the present invention, the preparation method of the bottom solution is a conventional technical means, including but not limited to:

[0033] Add pure water accounting for 1 / 3 - 3 / 4 of the volume of the reaction kettle into the reaction kettle, introduce N 2 Protect and start stirring, then add the precipitant and the complexing agent, adjust the pH value and the concentration of the complexing agent to obtain the required bottom solution.

[0034] Preferably, the mass concentration of the complexing agent in the bottom solution in step (1) is 10 - 20 g / L, such as 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L or 20 g / L, etc.

[0035] Preferably, the raw materials added in parallel flow in step (1) further include a doping agent solution.

[0036] Preferably, the temperature of the coprecipitation reaction in step (1) is 40 - 70 °C, such as 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C or 70 °C, etc.

[0037] Preferably, the pH value of the coprecipitation reaction in step (1) is 10 - 11, such as 10, 10.3, 10.5, 10.8 or 11, etc.

[0038] Preferably, the stirring speed of the coprecipitation reaction in step (1) is 200 - 500 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, etc.

[0039] Preferably, the nickel-copper-manganese mixed salt solution in step (2) further includes a reducing agent.

[0040] Preferably, the molar concentration of the nickel-copper-manganese mixed salt solution in step (2) is 0.5 to 2.5 mol / L, such as 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L, etc.

[0041] Preferably, the raw materials in the coprecipitation reaction process in step (2) further include a dopant solution.

[0042] As a preferred technical solution, the preparation method includes the following steps:

[0043] (1) A nickel-iron-manganese mixed salt solution, a precipitant solution, a dopant solution, and a complexing agent solution with a molar concentration of 0.5 to 2.5 mol / L are added to the bottom liquid in a co-current manner, maintaining the pH value at 10 to 11, and carrying out a coprecipitation reaction at 40 to 70 °C at 200 to 500 rpm to obtain a core;

[0044] (2) After obtaining the core in step (1), the nickel-iron-manganese mixed salt solution is replaced with a nickel-iron-copper mixed salt solution and the coprecipitation reaction is continued to obtain the sodium ion precursor material;

[0045] Among them, the nickel-iron-manganese mixed salt solution in step (1) further includes a reducing agent; the nickel-copper-manganese mixed salt solution in step (2) further includes a reducing agent.

[0046] In the third aspect, the present invention provides a sodium ion oxide cathode material, which is obtained by mixing and sintering the sodium ion precursor material as described in the first aspect with a sodium source;

[0047] The sodium ion oxide cathode material includes a core and a coating layer on the surface of the core; the core includes nickel-iron-manganese-sodium oxide, and the coating layer includes nickel-copper-manganese-sodium oxide.

[0048] Preferably, the sintering temperature is 800 to 1000 °C.

[0049] Preferably, the sintering time is 10 to 20 h.

[0050] Preferably, the nickel-iron-manganese-sodium oxide and the nickel-copper-manganese-sodium oxide further include doping elements.

[0051] In the fourth aspect, the present invention further provides a sodium ion battery, which includes the sodium ion oxide cathode material as described in the third aspect.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The sodium ion precursor material provided by the present invention has a uniform morphology and a stable structure. The core is nickel iron manganese with a relatively high capacity, and the outer coating is nickel copper manganese with relatively high stability. The high-capacity characteristics of the iron-based material are fully utilized while its stability is improved. During the preparation process, nickel iron manganese is first formed into spheres and then nickel copper manganese is precipitated, overcoming the problem that copper is difficult to precipitate homogeneously with nickel iron manganese, which can greatly increase the copper content and thus improve the rate performance and cycle stability of the sodium ion cathode material. The positive electrode in the sodium ion battery is prepared from the precursor material provided by the present invention, and the D50 of the core of the precursor is 3-18 μm, and the thickness of the coating layer is in the range of 0.3-1.5 μm. At a discharge voltage of 2.0-4.0 V, the first discharge specific capacity of the battery can reach more than 146.1 mAh / g at 0.1C, the rate performance at 1C / 0.1C can reach more than 96.1%, and the capacity retention rate can reach more than 95.3% after charging and discharging at 0.1C / 0.1C for the first cycle and then cycling 50 times at 0.5C / 1C. Detailed Embodiments

[0054] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0055] Example 1

[0056] This example provides a sodium ion precursor material. The sodium ion precursor material includes a core (D50 is 3 μm) and a coating layer (thickness is 0.3 μm) coated on the surface of the core. The core is magnesium-doped nickel iron manganese hydroxide (the molar ratio of Ni, Fe, and Mn is 1:1:1), and the coating layer is magnesium-doped nickel copper manganese hydroxide (the molar ratio of Ni, Cu, and Mn is 1:1:1). Among them, the doping amount of magnesium in the precursor material is 1000 ppm.

[0057] The preparation method of the sodium ion precursor material is as follows:

[0058] (1) A nickel iron manganese mixed sulfate solution (the molar ratio of nickel iron manganese is 1:1:1) with a molar concentration of 2 mol / L containing a reducing agent, a magnesium sulfate solution with a molar concentration of 0.01 mol / L, a sodium hydroxide solution (mass concentration 32%), and an ammonia water solution with a mass concentration of 15% are added to the bottom liquid in parallel (the pH value in the bottom liquid is 11, and the concentration of ammonia water is 10 g / L), maintaining a reaction environment with a pH value of 10.5, and carrying out a coprecipitation reaction at 50 °C with a rotation speed of 500 rpm. When D50 reaches 3 μm, the feeding is stopped to obtain the core;

[0059] (2) After obtaining the core, replace the nickel-iron-manganese mixed sulfate solution with a nickel-copper-manganese mixed sulfate solution containing a reducing agent with a molar concentration of 2 mol / L, keep other raw materials unchanged, and add them in parallel flow to the bottom liquid to continue the coprecipitation reaction until D50 reaches 3.6 μm. The materials in the kettle are centrifugally washed, dried, and sieved to obtain the sodium ion precursor material.

[0060] Example 2

[0061] This example provides a sodium ion precursor material. The sodium ion precursor material includes a core (D50 is 10 μm) and a coating layer (thickness is 0.5 μm) coated on the surface of the core. The core is a zirconium-doped nickel-iron-manganese hydroxide (the molar ratio of Ni, Fe, and Mn is 4:2:4, Ni / Fe / Mn 40 / 20 / 40), and the coating layer is a zirconium-doped nickel-copper-manganese hydroxide (the molar ratio of Ni, Cu, and Mn is 4:2:4). Among them, the doping amount of zirconium in the precursor material is 3000 ppm.

[0062] The preparation method of the sodium ion precursor material is as follows:

[0063] (1) Add a nickel-iron-manganese mixed sulfate solution (the molar ratio of nickel, iron, and manganese is 4:2:4) with a molar concentration of 0.5 mol / L containing a reducing agent, a zirconium sulfate solution with a molar concentration of 0.01 mol / L, a sodium hydroxide solution (mass concentration 32%), and an ammonia water solution with a mass concentration of 16% in parallel flow to the bottom liquid (the pH value in the bottom liquid is 10, and the concentration of ammonia water is 15 g / L), maintain a reaction environment with a pH value of 10, and carry out the coprecipitation reaction at 70 °C with a rotation speed of 300 rpm. Stop feeding when D50 reaches 10 μm to obtain the core.

[0064] (2) After obtaining the core, replace the nickel-iron-manganese mixed sulfate solution with a nickel-copper-manganese mixed sulfate solution containing a reducing agent with a molar concentration of 0.5 mol / L, keep other raw materials unchanged, and add them in parallel flow to the bottom liquid to continue the coprecipitation reaction until D50 reaches 11 μm. The materials in the kettle are centrifugally washed, dried, and sieved to obtain the sodium ion precursor material.

[0065] Example 3

[0066] This example provides a sodium ion precursor material. The sodium ion precursor material includes a core (D50 is 18 μm) and a coating layer (thickness is 1.5 μm) coated on the surface of the core. The core is an aluminum-doped nickel-iron-manganese hydroxide (the molar ratio of Ni, Fe, and Mn is 5:2:3), and the coating layer is an aluminum-doped nickel-copper-manganese hydroxide (the molar ratio of Ni, Cu, and Mn is 5:2:3). Among them, the doping amount of aluminum in the precursor material is 5000 ppm.

[0067] The preparation method of the sodium ion precursor material is as follows:

[0068] (1) A nickel-iron-manganese mixed sulfate solution (with a molar ratio of nickel:iron:manganese of 5:2:3) with a molar concentration of 2.5 mol / L containing a reducing agent, a sodium aluminate solution with a molar concentration of 0.05 mol / L, a sodium hydroxide solution (with a mass concentration of 32%), and an ammonia water solution with a mass concentration of 15% are added to the bottom liquid in parallel (the pH value in the bottom liquid is 9, and the concentration of ammonia water is 10 g / L). A reaction environment with a pH value of 10.5 is maintained, and a coprecipitation reaction is carried out at 40 °C with a rotation speed of 200 rpm. When D50 reaches 18 μm, the feeding is stopped to obtain the core;

[0069] (2) After obtaining the core, the nickel-iron-manganese mixed sulfate solution is replaced with a nickel-copper-manganese mixed sulfate solution with a molar concentration of 2.5 mol / L containing a reducing agent, and other raw materials remain unchanged. The solution is added to the bottom liquid in parallel and the coprecipitation reaction is continued until D50 reaches 21 μm. The materials in the kettle are centrifuged, washed, dried, and sieved to obtain the sodium ion precursor material.

[0070] Example 4

[0071] The difference between this example and Example 1 is that the sodium ion precursor material provided in this example is not doped with magnesium element, and magnesium sulfate solution is not added in the preparation method.

[0072] The rest of the preparation methods and parameters are the same as those in Example 1.

[0073] Example 5

[0074] The difference between this example and Example 1 is that D50 of the core of the sodium ion precursor material in this example is 2 μm, and the coprecipitation time is adjusted adaptively in the preparation method.

[0075] The rest of the preparation methods and parameters are the same as those in Example 1.

[0076] Example 6

[0077] The difference between this example and Example 1 is that D50 of the core of the sodium ion precursor material in this example is 20 μm, and the coprecipitation time is adjusted adaptively in the preparation method.

[0078] The rest of the preparation methods and parameters are the same as those in Example 1.

[0079] Example 7

[0080] The difference between this example and Example 1 is that the thickness of the coating layer of the sodium ion precursor material in this example is 2 μm, and the coprecipitation time is adjusted adaptively in the preparation method.

[0081] The rest of the preparation methods and parameters are the same as those in Example 1.

[0082] Example 8

[0083] The difference between this example and Example 1 is that the thickness of the coating layer of the sodium ion precursor material in this example is 0.1 um, and the coprecipitation time is adjusted adaptively in the preparation method.

[0084] The remaining preparation methods and parameters are the same as those in Example 1.

[0085] Comparative Example 1

[0086] The difference between this comparative example and Example 1 is that the sodium ion precursor material in this comparative example is magnesium-doped nickel-iron-copper-manganese hydroxide (the molar ratio of Ni, Fe, Cu, and Mn is 33.3:25.1:8.2:33.3), that is, it is a non-core-shell structure; a mixed sulfate solution of nickel, iron, manganese, and copper is selected for coprecipitation reaction in the preparation method.

[0087] The remaining preparation methods and parameters are the same as those in Example 1.

[0088] Comparative Example 2

[0089] The difference between this comparative example and Example 1 is that the inner core material and the coating layer material are exchanged with each other in this comparative example, and the materials in the preparation method are also exchanged with each other.

[0090] The remaining preparation methods and parameters are the same as those in Example 1.

[0091] Mix the sodium ion precursor materials provided in Examples 1-8 and Comparative Examples 1-2 with sodium carbonate, sinter at 1000 °C for 12 h, and the obtained material is pulverized to obtain a sodium ion oxide cathode material.

[0092] Prepare a positive electrode sheet from the sodium ion oxide cathode material, and use a sodium sheet as the counter electrode to prepare a button cell.

[0093] Perform electrochemical performance tests on the batteries provided in Examples 1-8 and Comparative Examples 1-2. The test conditions are charge-discharge voltage of 2.0-4.0 V, charge-discharge test at 0.1C / 0.1C for the first cycle, and then cycle 50 times at 0.5C / 1C. The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] It can be seen from the data results of Example 1 and Example 4 that without doping, both the rate performance and the cycling performance decrease significantly.

[0097] From the data results of Example 1 and Examples 5 and 6, it can be seen that if the core particle size is too small, the cycling performance will decrease, while if the particle size is too large, it will affect the capacity and rate performance.

[0098] From the data results of Example 1 and Examples 7 and 8, it can be seen that if the thickness of the coating layer is too thick, the capacity and rate performance will significantly decrease, while if the thickness is too thin, it is not conducive to improving the cycling performance.

[0099] From the data results of Example 1 and Comparative Example 1, it can be seen that for the non-core-shell structure, that is, copper element is directly doped into nickel iron manganese, it is impossible to significantly improve the comprehensive performance such as capacity, rate and cycling performance.

[0100] From the data results of Example 1 and Comparative Example 2, it can be seen that when the core is nickel copper manganese and the coating layer is nickel iron manganese, not only the cycling performance cannot be improved, but on the contrary, the capacity decay will be accelerated.

[0101] In summary, the sodium ion precursor material provided by the present invention has uniform morphology and stable structure. The core is nickel iron manganese with relatively high capacity, and the outer coating layer is nickel copper manganese with relatively high stability. It makes full use of the high-capacity characteristics of the iron-based material and at the same time improves its stability. During the preparation process, nickel iron manganese is first formed into spheres and then nickel copper manganese is precipitated, overcoming the problem that copper is difficult to precipitate homogeneously with nickel iron manganese, which can greatly increase the copper content and thus improve the rate performance and cycling stability of the sodium ion cathode material. The positive electrode in the sodium ion battery is prepared from the precursor material provided by the present invention, and the D50 of the core of the precursor is 3-18 μm, and the thickness of the coating layer is in the range of 0.3-1.5 μm. At a discharge voltage of 2.0-4.0 V, the first discharge specific capacity of the battery at 0.1C can reach more than 146.1 mAh / g, the rate performance at 1C / 0.1C can reach more than 96.1%, and the capacity retention rate after charging and discharging at 0.1C / 0.1C for the first cycle and then cycling 50 times at 0.5C / 1C can reach more than 95.3%.

[0102] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a sodium ion precursor material, characterized in that, the sodium ion precursor material includes a core and a coating layer located on the surface of the core; the core includes nickel iron manganese hydroxide, and the coating layer includes nickel copper manganese hydroxide; the thickness of the coating layer is 0.3 - 0.9 μm; the nickel iron manganese hydroxide and the nickel copper manganese hydroxide also include doping elements; the doping elements are any one or a combination of at least two of Mg, Ti or Zr; the doping amount of the doping elements in the sodium ion precursor is 1000 - 5000 ppm; the preparation method of the sodium ion precursor material includes the following steps: (1) A nickel iron manganese mixed salt solution, a precipitant solution, a complexing agent solution and a dopant solution are added to a bottom liquid in a co - current manner for a coprecipitation reaction to obtain a core; (2) After obtaining the core in step (1), the nickel iron manganese mixed salt solution is replaced with a nickel copper manganese mixed salt solution and the coprecipitation reaction is continued to obtain the sodium ion precursor material.

2. The preparation method according to claim 1, characterized in that, the D50 of the core is 3 - 18 μm.

3. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the nickel iron manganese mixed salt solution in step (1) further includes a reducing agent.

4. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the molar concentration of the nickel iron manganese mixed salt solution in step (1) is 0.5 - 2.5 mol / L.

5. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the pH value of the bottom liquid in step (1) is 9 - 11.

6. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the bottom liquid in step (1) includes a precipitant, a complexing agent and water.

7. The preparation method of the sodium ion precursor material according to claim 6, characterized in that, the mass concentration of the complexing agent in the bottom liquid in step (1) is 10 - 20 g / L.

8. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the temperature of the coprecipitation reaction in step (1) is 40 - 70 °C.

9. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the pH value of the coprecipitation reaction in step (1) is 10 - 11.

10. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the stirring speed of the coprecipitation reaction in step (1) is 200 - 500 rpm.

11. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the nickel copper manganese mixed salt solution in step (2) further includes a reducing agent.

12. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the molar concentration of the nickel copper manganese mixed salt solution in step (2) is 0.5 - 2.5 mol / L.

13. The preparation method of the sodium ion precursor material according to claim 1, characterized in that, the preparation method includes the following steps: (1) A nickel-iron-manganese mixed salt solution with a molar concentration of 0.5 to 2.5 mol / L, a precipitant solution, a dopant solution, and a complexing agent solution are added to the bottom liquid in parallel flow, maintaining the pH value at 10 to 11, and a coprecipitation reaction is carried out at 40 to 70 °C at 200 to 500 rpm to obtain the core; (2) After obtaining the core described in step (1), the nickel-iron-manganese mixed salt solution is replaced with a nickel-copper-manganese mixed salt solution and the coprecipitation reaction is continued to obtain the sodium ion precursor material; Among them, the nickel-iron-manganese mixed salt solution in step (1) further includes a reducing agent; the nickel-copper-manganese mixed salt solution in step (2) further includes a reducing agent, and the raw materials in the coprecipitation reaction process in step (2) further include a dopant solution.

14. A sodium ion oxide cathode material, characterized in that, the sodium ion oxide cathode material is obtained by mixing and sintering the sodium ion precursor material prepared by the preparation method according to any one of claims 1-13; the sodium ion oxide cathode material includes a core and a coating layer on the surface of the core; the core includes nickel-iron-manganese sodium oxide, and the coating layer includes nickel-copper-manganese sodium oxide; the nickel-iron-manganese sodium oxide and the nickel-copper-manganese sodium oxide further include doping elements.

15. The sodium ion oxide cathode material according to claim 14, characterized in that, the sintering temperature is 800 to 1000 °C.

16. The sodium ion oxide cathode material according to claim 14, characterized in that, the sintering time is 10 to 20 h.

17. A sodium ion battery, characterized in that, the sodium ion battery includes the sodium ion oxide cathode material according to any one of claims 14-16.

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