A method for preparing a positive electrode material for a sodium ion battery

Abstract

The present invention discloses a method for preparing a positive electrode material for a sodium ion battery, comprising the following steps: (1) weighing nickel-iron-manganese salt to prepare a salt solution S1, a first complexing agent solution C1, a second complexing agent solution C2, and a precipitant alkali solution B1; (2) mixing the salt solution S1 and the first complexing agent solution C1 and adding them to a reactor for reaction; (3) adding the second complexing agent solution C2 to the solution obtained in step 2 for reaction; (4) adding the precipitant alkali solution B1 to the solution obtained in step 3 for precipitation to obtain a precipitate slurry; (5) filtering under positive pressure three times and washing with deionized water to obtain a precursor; (6) transferring the precursor to an oven to obtain a dried precursor; (7) uniformly mixing the precursor and sodium salt to obtain a mixture; and (8) transferring the mixture to a muffle furnace to obtain a positive electrode material. The present invention can effectively control the particle size of the positive electrode material for a sodium ion battery, improve the charge and discharge specific capacity of the material, and has low cost.

Description

Technical Field

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

[0002] The mainstream synthesis method for ternary or layered oxides and their derivative oxides used in the positive electrode materials of lithium-ion batteries and sodium-ion batteries is the co-precipitation method: first, the precursor is synthesized by precipitation, then mixed with lithium salt or sodium salt, and finally calcined at high temperature to obtain the positive electrode material. In the synthesis process of the positive electrode material precursor, a precipitant and a complexing agent are generally used at the same time. The precipitant is mainly sodium hydroxide, sodium carbonate or sodium oxalate, and the complexing agent is mainly ammonia water. For example, the patent (application number: CN202410063503.7) uses sodium hydroxide and sodium carbonate precipitants to obtain a precursor material with uniform Cu element distribution and high tap density. The pH is always controlled at a relatively high level during the entire precipitation process of the patent. In order to control the particle size, the whole process lasts for a long time. For example, the reaction time in Example 1 is as long as 100h, which will significantly increase the production cost. The patent does not list the electrochemical properties of the material. The patent (application number: CN202311819923.5) uses a combination of sodium hydroxide and ammonia water and sodium bicarbonate as the sodium source to synthesize NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the obtained material is a single crystal material with good particle size dispersion and uniform morphology, but the specific capacity of the material is less than 80mAh / g. Patent (application number: CN202210714671.9) uses sodium hydroxide as a precipitant and ammonia as a complexing agent, combined with a supergravity mixer and spray drying process to prepare NaNi 1 / 3 Fe 1 / 3Mn 1 / 3O2 materials offer excellent properties, but their preparation process is complex. Traditional precipitation methods typically use a strong base to react with metal ions, resulting in a rapid precipitation rate. Even with ammonia as a complexing agent, the strong alkalinity of ammonia can cause excessive precipitation, leading to the aggregation of large particles. To ensure uniform concentration within the reactor, a suitable reactor and high agitation speed are required. The addition process must also be slow and the feed concentration kept as low as possible to avoid localized high reactant concentrations, which can lead to uneven and low-density particles. These factors lead to low efficiency in the production of precursors using stirred tanks, bulky production equipment, and a need for improved product consistency. Urea cannot directly provide the hydroxide or carbonate ions required for precipitation, rather than through hydrolysis, effectively compensating for the shortcomings of traditional strong bases. As a precipitant, urea forms a stable complex with metal ions through a complex hydrogen-bonding network. Upon heating, it slowly decomposes to produce ammonia gas, which causes the metal ions to lose their complexes and gradually form an insoluble precipitate, resulting in finer particles. For example, patent application number CN201810598272.4 uses urea as a precipitant and water and ethanol as a mixed solvent, resulting in a highly consistent synthesized material. However, due to the slow hydrolysis of urea, a high-temperature hydrothermal reaction is required to promote the decomposition of urea to produce a precursor. This results in a relatively long reaction time, low production efficiency, and theoretically low yield. Therefore, there is an urgent need to develop a cathode material preparation method that can effectively control the particle size of the cathode material, achieve high charge-discharge specific capacity, high yield, and low synthesis cost. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing a positive electrode material for a sodium ion battery, which can effectively control the particle size of the positive electrode material for a sodium ion battery, improve the charge and discharge specific capacity of the material, and has a low cost.

[0004] In order to solve the above technical problems, the present invention provides a method for preparing a positive electrode material for a sodium ion battery, comprising the following steps:

[0005] (1) Weighing nickel-iron-manganese salt to prepare salt solution S1, preparing first complexing agent solution C1, preparing second complexing agent solution C2, and preparing precipitant alkali solution B1;

[0006] (2) mixing the salt solution S1 and the first complexing agent solution C1 into a reactor to react;

[0007] (3) adding the second complexing agent solution C2 to the solution obtained in step 2 to carry out a reaction;

[0008] (4) adding the precipitant alkali solution B1 to the solution obtained in step 3 to precipitate and obtain a precipitate slurry;

[0009] (5) positive pressure filtration three times and washing with deionized water to obtain a precursor;

[0010] (6) transferring the precursor to an oven to obtain a dry precursor;

[0011] (7) uniformly mixing the precursor and the sodium salt to obtain a mixture;

[0012] (8) The mixture is transferred to a muffle furnace for reaction to obtain a positive electrode material.

[0013] Furthermore, the reaction conditions of step 2 are: stirring at 60-100° C. for 0.5 h-20 h, and pH=4-6.

[0014] Furthermore, the reaction conditions of step 3 are: stirring at 60-100° C. for 0.5 h to 20 h, and pH=6-8.5.

[0015] Furthermore, the reaction conditions of step 4 are: pH=8.5-13, temperature of 60-100° C., and stirring for 0.5 h-20 h.

[0016] Furthermore, the reaction conditions of step 6 are: temperature 40°C-200°C, and drying time 1h-20h.

[0017] Furthermore, the reaction conditions of step 8 are: in an air atmosphere, heating to 400-700°C at a heating rate of 1-10°C / min and pre-calcining for 1-10h, and then heating to 800-1100°C at a heating rate of 1-10°C / min and calcining for 5-30h.

[0018] Beneficial effects of the invention: This patent proposes a new method for preparing a positive electrode material for a battery. This method improves upon the traditional coprecipitation method by employing a dual complexing agent method using urea and ammonia to gradually complex the salt solution ions. Finally, a precipitant is added for precipitation. This method effectively controls the precipitation rate and synthesizes a layered oxide material with a more uniform particle size distribution. The synthesized material exhibits higher specific capacity and initial coulombic efficiency. The hydrothermal reaction temperature used in this patent is lower than the traditional method, making it easier to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an SEM image of the positive electrode material of Example 1 of the present invention.

[0020] Figure 2 This is an SEM image of the positive electrode material of Comparative Example 1 of the present invention.

[0021] Figure 3 1 is a graph showing the first charge and discharge curves of the positive electrode materials obtained in Example 1 and Comparative Example 1 of the present invention.

[0022] Figure 4 It is an experimental data diagram of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0025] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0026] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0027] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0028] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0029] Reference Figures 1 to 4 As shown, the present invention discloses a method for preparing a positive electrode material for a sodium ion battery, comprising the following steps: (1) weighing nickel iron manganese salt to prepare a salt solution S1, a first complexing agent solution C1, a second complexing agent solution C2, and a precipitant alkali solution B1; (2) mixing the salt solution S1 and the first complexing agent solution C1 and adding them to a reactor for reaction; (3) adding the second complexing agent solution C2 to the solution obtained in step 2 for reaction; (4) adding the precipitant alkali solution B1 to the solution obtained in step 3 for precipitation to obtain a precipitate slurry; (5) filtering under positive pressure three times and washing with deionized water to obtain a precursor; (6) transferring the precursor to an oven to obtain a dried precursor; (7) mixing the precursor and the sodium salt to obtain a mixture; and (8) transferring the mixture to a muffle furnace for reaction to obtain a positive electrode material.

[0030] The reaction conditions are as follows: the reaction conditions of step 2 are: stirring at a temperature of 60-100°C for 0.5h-20h, and a pH of 4-6; the reaction conditions of step 3 are: stirring at a temperature of 60-100°C for 0.5h-20h, and a pH of 6-8.5; the reaction conditions of step 4 are: pH of 8.5-13, and stirring at a temperature of 60-100°C for 0.5h-20h; the reaction conditions of step 6 are: temperature of 40°C-200°C, and drying for 1h-20h; the reaction conditions of step 8 are: in an air atmosphere, heating to 400-700°C at a rate of 1-10°C / min and pre-calcining for 1-10h, and then heating to 800-1100°C at a rate of 1-10°C / min and calcining for 5-30h.

[0031] Example 1:

[0032] Take nickel sulfate heptahydrate, ferrous sulfate heptahydrate and manganese sulfate monohydrate, and prepare a 1L salt solution S1 with a total salt solution concentration of 1 mol / L, wherein the molar ratio of Ni, Fe and Mn is 1:1:1. Prepare a urea complexing agent solution C1 with a concentration of 10 mol / L. Prepare an ammonia complexing agent solution C2 with a concentration of 1.5 mol / L. Prepare a sodium hydroxide precipitant solution B2 with a concentration of 4.5 mol / L. (2) Mix the salt solution S1 and the urea solution C1 and add them to the reactor. Stir for 3 hours at 70°C, at which point the pH is 5.5. (3) Add the ammonia solution C2 to the solution in (2) at a rate of 5 mL / min. Stir for 0.5 hours at 80°C, at which point the pH is 8.0. (4) Add the sodium hydroxide solution B2 to the solution in (3) at a rate of 5 mL / min until the pH is 11.0. Stir for sufficient reaction at 80°C for 5 hours to obtain a precipitated slurry. (5) The precipitated slurry was filtered three times under positive pressure and washed with deionized water three times to obtain a yellowish-brown precursor. (6) The precursor was transferred to an oven and dried at 100°C for 10 hours to obtain a dry precursor. (7) The dry precursor was mixed with sodium carbonate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 (8) The mixture was transferred to a muffle furnace and heated to 550°C at a rate of 3°C / min in air atmosphere and pre-calcined for 5 h. The temperature was then increased to 900°C at a rate of 3°C / min and calcined for 20 h to obtain the positive electrode material C-1.

[0033] Example 2:

[0034] Take nickel nitrate hexahydrate, iron nitrate nonahydrate and manganese nitrate tetrahydrate, and prepare a 1L salt solution S1 with a total salt solution concentration of 1 mol / L, wherein the molar ratio of Ni, Fe and Mn is 1:1:1. Prepare a urea complexing agent solution C1 with a concentration of 5 mol / L. Prepare an ammonia complexing agent solution C2 with a concentration of 1.5 mol / L. Prepare a sodium hydroxide precipitant solution B2 with a concentration of 4.5 mol / L. (2) Mix the salt solution S1 and the urea solution C1 and add them to the reactor. Stir for 3 hours at 90°C and pH = 6.0. (3) Add the ammonia solution C2 to the solution in (2) at a rate of 5 mL / min. Stir for 0.5 hours at 80°C and pH = 8.0. (4) Add the sodium hydroxide solution B2 to the solution in (3) at a rate of 5 mL / min until the pH = 11.0. Stir and react for 5 hours at 80°C to obtain a precipitate slurry. (5) The precipitated slurry was filtered three times under positive pressure and washed with deionized water three times to obtain a yellowish-brown precursor. (6) The precursor was transferred to an oven and dried at 100°C for 10 hours to obtain a dry precursor. (7) The dry precursor was mixed with sodium carbonate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 (8) The mixture was transferred to a muffle furnace and heated to 550°C at a rate of 3°C / min in air atmosphere and pre-calcined for 5 h. The temperature was then increased to 900°C at a rate of 3°C / min and calcined for 20 h to obtain the positive electrode material C-2.

[0035] Example 3:

[0036] Take nickel chloride hexahydrate, ferrous chloride dihydrate and manganese chloride tetrahydrate and prepare a 1L salt solution S1 with a total salt solution concentration of 1 mol / L, wherein the molar ratio of Ni, Fe and Mn is 1:1:1. Prepare a urea complexing agent solution C1 with a concentration of 10 mol / L. Prepare an ammonia complexing agent solution C2 with a concentration of 3.0 mol / L. Prepare a sodium hydroxide precipitant solution B2 with a concentration of 4.5 mol / L. (2) Mix the salt solution S1 and the urea solution C1 and add them to the reactor. Stir for 3 hours at 70°C and pH = 4.5. (3) Add the ammonia solution C2 to the solution in (2) at a rate of 5 mL / min. Stir for 0.5 hours at 80°C and pH = 7.5. (4) Add the sodium hydroxide solution B2 to the solution in (3) at a rate of 5 mL / min until the pH = 12.0. Stir and react for 5 hours at 80°C to obtain a precipitate slurry. (5) The precipitated slurry was filtered three times under positive pressure and washed with deionized water three times to obtain a yellowish-brown precursor. (6) The precursor was transferred to an oven and dried at 100°C for 10 hours to obtain a dry precursor. (7) The dry precursor was mixed with sodium carbonate (NaNi1 / 3 Fe 1 / 3 Mn 1 / 3 (8) The mixture was transferred to a muffle furnace and heated to 550°C at a rate of 3°C / min in air atmosphere and pre-calcined for 5 h. The temperature was then increased to 900°C at a rate of 3°C / min and calcined for 20 h to obtain the positive electrode material C-3.

[0037] Example 4:

[0038] Take nickel acetate tetrahydrate, ferrous acetate tetrahydrate and manganese acetate sulfate tetrahydrate and prepare a 1L salt solution S1 with a total salt solution concentration of 1 mol / L, wherein the molar ratio of Ni, Fe and Mn is 1:1:1. Prepare a urea complexing agent solution C1 with a concentration of 10 mol / L. Prepare an ammonia complexing agent solution C2 with a concentration of 1.5 mol / L. Prepare a sodium hydroxide precipitant solution B2 with a concentration of 4.5 mol / L. (2) Mix the salt solution S1 and urea solution C1 and add them to the reactor. Stir for 3 hours at 70°C and pH = 6.0. (3) Add ammonia solution C2 to the solution in (2) at a rate of 5 mL / min. Stir for 0.5 hours at 80°C and pH = 8.0. (4) Add sodium hydroxide solution B2 to the solution in (3) at a rate of 5 mL / min until pH = 9.0. Stir for sufficient reaction at 80°C for 5 hours to obtain a precipitated slurry. (5) The precipitated slurry was filtered three times under positive pressure and washed with deionized water three times to obtain a yellowish-brown precursor. (6) The precursor was transferred to an oven and dried at 100°C for 10 hours to obtain a dry precursor. (7) The dry precursor was mixed with sodium carbonate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 (8) The mixture was transferred to a muffle furnace and heated to 550°C at a rate of 3°C / min in air atmosphere and pre-calcined for 5 h. The temperature was then increased to 900°C at a rate of 3°C / min and calcined for 20 h to obtain the positive electrode material C-4.

[0039] Example 5:

[0040] Take nickel sulfate heptahydrate, ferrous sulfate heptahydrate and manganese sulfate monohydrate, and prepare a 1L salt solution S1 with a total salt solution concentration of 1 mol / L, wherein the molar ratio of Ni, Fe and Mn is 1:1:1. Prepare a urea complexing agent solution C1 with a concentration of 10 mol / L. Prepare an ammonia complexing agent solution C2 with a concentration of 1.5 mol / L. Prepare a sodium hydroxide precipitant solution B2 with a concentration of 4.5 mol / L. (2) Mix the salt solution S1 and the urea solution C1 and add them to the reactor. Stir for 1 hour at 80°C and pH = 6.0. (3) Add the ammonia solution C2 to the solution in (2) at a rate of 5 mL / min. Stir for 0.5 hour at 80°C and pH = 8.0. (4) Add the sodium hydroxide solution B2 to the solution in (3) at a rate of 5 mL / min until the pH = 12.0. Stir for sufficient reaction at 80°C for 0.5 hour to obtain a precipitated slurry. (5) The precipitated slurry was filtered 3 times under positive pressure and washed 3 times with deionized water to obtain a yellowish-brown precursor. (6) The precursor was transferred to an oven and dried at 100°C for 10 hours to obtain a dry precursor. (7) The dry precursor was mixed with sodium carbonate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 (8) The mixture was transferred to a muffle furnace and heated to 550°C at a rate of 3°C / min in air atmosphere and pre-calcined for 5 h. The temperature was then increased to 900°C at a rate of 3°C / min and calcined for 20 h to obtain the positive electrode material C-5.

[0041] Example 6:

[0042] Take nickel sulfate heptahydrate, ferrous sulfate heptahydrate and manganese sulfate monohydrate, and prepare a 1L salt solution S1 with a total salt solution concentration of 1 mol / L, wherein the molar ratio of Ni, Fe and Mn is 1:1:1. Prepare a urea complexing agent solution C1 with a concentration of 10 mol / L. Prepare an ammonia complexing agent solution C2 with a concentration of 1.5 mol / L. Prepare a sodium carbonate precipitant solution B2 with a concentration of 4 mol / L. (2) Mix the salt solution S1 and the urea solution C1 and add them to the reactor. Stir for 3 hours at 70°C and pH = 6.2. (3) Add the ammonia solution C2 to the solution in (2) at a rate of 5 mL / min. Stir for 0.5 hours at 80°C and pH = 8.5. (4) Add the sodium carbonate solution B2 to the solution in (3) at a rate of 5 mL / min until the pH is 9.5. Stir and react for 5 hours at 80°C to obtain a precipitate slurry. (5) The precipitated slurry was filtered three times under positive pressure and washed with deionized water three times to obtain a yellowish-brown precursor. (6) The precursor was transferred to an oven and dried at 100°C for 10 hours to obtain a dry precursor. (7) The dry precursor was mixed with sodium carbonate (NaNi1 / 3 Fe 1 / 3 Mn 1 / 3 (8) The mixture was transferred to a muffle furnace and heated to 550°C at a rate of 3°C / min in air atmosphere and pre-calcined for 5 h. The temperature was then increased to 900°C at a rate of 3°C / min and calcined for 20 h to obtain the positive electrode material C-6.

[0043] Comparative Example 1: The complexing agent urea in Example 1 was removed to obtain the positive electrode material CC-1.

[0044] Comparative Example 2: The complexing agent ammonia water in Example 1 was removed to obtain the positive electrode material CC-2.

[0045] Comparative Example 3: A complexing agent, ammonia water, and a precipitant were prepared into a mixed solution to obtain a positive electrode material CC-3.

[0046] Comparative Example 4: Complexing agent urea and complexing agent ammonia water were prepared into a mixed solution to obtain the positive electrode material CC-4.

[0047] Battery assembly and testing

[0048] The positive electrode materials prepared in different examples and reference examples, along with conductive carbon black, PVDF, and NMP, were mixed in a mass ratio of 18:1:1:20, stirred for 5 hours, coated onto aluminum foil, and dried in a vacuum drying oven at 100°C for 20 hours. The resulting electrode sheets were cut into 12 mm diameter pieces, the sheet mass was weighed, and the coating mass was calculated. The resulting pieces served as the positive electrode, and a metal sodium sheet served as the negative electrode. The electrolyte consisted of 1 M NaPF6, DMC:EC:EMC (1:1:1 vol%), and the separator was a glass fiber separator (GF / D). The cells were assembled into CR2032 coin cells in an argon-filled glove box. The cells were allowed to rest for 24 hours before charge and discharge tests were conducted at a rate of 0.2C, 25°C, and a voltage range of 2.0-4.0 V.

[0049] This patent uses a dual-complexing agent method, first treating the salt solution with a first complexing agent, then treating the solution with a second complexing agent, and finally adding a precipitant to complete the precipitation process. This three-step reaction method synthesizes a layered oxide material with a more uniform particle size distribution, resulting in a higher specific capacity and initial coulombic efficiency. The hydrothermal reaction temperature used in this patent is lower than that of traditional urea hydrolysis methods, making it easier to industrialize.

[0050] Depend on Figure 1 and 2 By comparison, it can be seen that the particle size distribution of the positive electrode material synthesized by the improved co-precipitation method of the present invention is more uniform. Figure 3 It shows that the positive electrode material of Example 1 has higher charge and discharge specific capacity and first efficiency than the positive electrode material of Comparative Example 1. Figure 4The electrode quality, thickness and electrochemical performance test results of the embodiments of the present invention and the comparative examples are listed in detail. It can be found that the positive electrode material prepared in the embodiments of the present invention has better overall performance than the comparative examples. Figure 4 The five electrode information prepared in Example 1 and Comparative Example 1 are listed, including the electrode quality and electrode thickness. It can be seen that the quality and thickness stability of the electrode coated in Example 1 are better. This is because the particle size distribution of the positive electrode material in Example 1 is relatively uniform, so the prepared slurry has better uniformity.

[0051] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for preparing a positive electrode material for a sodium ion battery, characterized in that: The steps include: (1) Weighing nickel-iron-manganese salt to prepare salt solution S1, preparing first complexing agent solution C1, preparing second complexing agent solution C2, and preparing precipitant alkali solution B1; (2) mixing the salt solution S1 and the first complexing agent solution C1 into a reactor to react; (3) adding the second complexing agent solution C2 to the solution obtained in step 2 to carry out a reaction; (4) adding the precipitant alkali solution B1 to the solution obtained in step 3 to precipitate and obtain a precipitate slurry; (5) positive pressure filtration three times and washing with deionized water to obtain a precursor; (6) transferring the precursor to an oven to obtain a dry precursor; (7) uniformly mixing the precursor and the sodium salt to obtain a mixture; (8) transferring the mixture to a muffle furnace for reaction to obtain a positive electrode material; The reaction conditions of step 2 are: stirring at 60-100°C for 0.5h-20h, pH = 4-6; The reaction conditions of step 3 are: stirring at 60-100°C for 0.5h-20h, pH = 6-8.5; The reaction conditions of step 4 are: pH = 8.5-13, stirring at 60-100°C for 0.5h-20h; The first complexing agent is urea, and the second complexing agent is ammonia water; The reaction conditions of step 6 are: temperature 40°C-200°C, drying 1h-20h; The reaction conditions of step 8 are: in an air atmosphere, heating to 400-700° C. at a heating rate of 1-10° C. / min and pre-calcining for 1-10 hours, and then heating to 800-1100° C. at a heating rate of 1-10° C. / min and calcining for 5-30 hours.

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