A polyanion positive electrode material precursor, a preparation method and application thereof
By improving the preparation process, the problems of easy oxidation and impurity phase formation of polyanion cathode material precursors in air were solved, realizing high-purity polyanion cathode materials with excellent electrochemical performance, which are suitable for high-performance sodium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUHAN BISIDI BATTERY MATERIAL CO LTD
- Filing Date
- 2026-04-10
- Publication Date
- 2026-07-24
AI Technical Summary
Existing polyanionic cathode material precursors are easily oxidized in air, leading to deterioration of electrochemical performance, and impurities exist after sintering, resulting in low phase purity.
Anhydrous amorphous products are prepared by mixing sodium, phosphorus and transition metal sources, followed by sand milling, adding reducing agent and complexing agent, reacting in an acidic environment, spray drying and pre-calcining under a protective atmosphere, ensuring uniform distribution of transition metal valence states and avoiding the formation of impurity phases.
A high-purity solid-solution pure-phase polyionic cathode material was obtained, which has excellent electrochemical performance and stability and is suitable for high-performance sodium-ion batteries.
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Figure CN122444148A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of sodium-ion battery technology, and more specifically, relates to a polyanion cathode material precursor, its preparation method and application. Background Technology
[0002] In the sodium-ion battery cathode material system, polyanionic cathode materials stand out for their structural stability, effectively suppressing lattice distortion during charge and discharge. They also possess excellent electrochemical cycle stability, as well as excellent thermal stability, environmental stability, ion transport stability, and long-term storage stability, making them an important development direction for sodium-ion battery cathode materials.
[0003] However, sodium iron phosphate / sodium manganese phosphate materials cannot be synthesized through direct thermal treatment. They are typically prepared using lithium iron phosphate as a raw material via chemical substitution to achieve alkali metal ion replacement. This method suffers from low product yield, high process cost, and low compaction density. While sodium iron pyrophosphate can be synthesized through direct solid-state thermal treatment, it exhibits drawbacks such as a low electrochemical plateau and small specific capacity, resulting in energy density that fails to meet the application requirements of power batteries.
[0004] Cathode materials are one of the key factors determining the overall performance of sodium-ion batteries. To integrate the advantages of phosphate and pyrophosphate materials, mixed phosphate-type polyanionic cathode materials have become an important research direction. Among them, sodium iron pyrophosphate / sodium manganese pyrophosphate are typical solid solution materials, with a narrower phase formation temperature range compared to single-phase phosphate materials. When using conventional synthesis methods, electrochemically inert impurities (such as NaFePO4) are inevitably generated, significantly degrading the electrochemical performance of the material. Furthermore, the polyanionic cathode material precursors prepared by spray drying are easily oxidized when placed in air, leading to the presence of a large amount of trivalent iron impurities in the product, affecting the electrochemical performance of the final product.
[0005] Therefore, there is an urgent need in this field to develop a polyanionic cathode material precursor that can be stably stored in the environment and can ensure the purity of phase formation, so as to provide support for the industrialization of high-performance polyanionic cathode materials. Summary of the Invention
[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide a polyanionic cathode material precursor, its preparation method and application, which aims to solve the problems of poor stability and easy oxidation of the existing polyanionic cathode material precursor in air, and the presence of impurity phases in the polyanionic cathode material obtained after sintering, resulting in low phase purity of the material and deterioration of electrochemical performance.
[0007] To achieve the above objectives, in a first aspect, this application provides a method for preparing a polyanionic cathode material precursor, comprising the following steps: S1. The sodium source, phosphorus source, transition metal M source and solvent are mixed and then milled to obtain a pre-reaction slurry; the transition metal M is one or more of Fe, Mn, Co and Ni. S2. Under acidic conditions, the above pre-reacted slurry is mixed with reducing agent and complexing agent to carry out reduction reaction and complexation reaction to obtain precursor slurry; S3. Spray dry the above precursor slurry to obtain precursor powder; S4. The above precursor powder is pre-calcined under a protective atmosphere to obtain anhydrous amorphous product, namely the above polyanion cathode material precursor.
[0008] Preferably, in step S1, the sodium source is one or more of sodium sulfate, sodium citrate, sodium carbonate, sodium bicarbonate, sodium oxalate, disodium ethylenediaminetetraacetate, sodium formate, sodium acetate, sodium oxalate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium nitrate.
[0009] Preferably, in step S1, the phosphorus source is one or more of phosphoric acid, sodium hypophosphite, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.
[0010] Preferably, in step S1, the transition metal M source is one or more of the oxides, salts and hydrates of the transition metal M.
[0011] Preferably, in step S1, the molar ratio of the sodium source, the transition metal M source, and the phosphorus source is (3~4):(2~3):(3~4).
[0012] Preferably, in step S1, the solvent is one or more of water, alcoholic organic solvents, and ketone organic solvents.
[0013] Preferably, in step S1, the solid content of the pre-reacted slurry is 35wt%~50wt%.
[0014] Preferably, in step S1, the particle size D50 of the particles in the pre-reacted slurry is less than 200 nm.
[0015] Preferably, in step S2, the pH of the acidic environment is 3 to 5.
[0016] Preferably, in step S2, the molar ratio of the reducing agent to the transition metal M source is (0.1~1):1. Preferably, the reducing agent is one or more of ascorbic acid, oxalic acid, and citric acid.
[0017] Preferably, in step S2, the molar ratio of the complexing agent to the transition metal M source is (0.1~1):1. Preferably, the complexing agent is one or more of monoethanolamine, diethanolamine, ethylenediaminetetraacetic acid and its sodium salt, citric acid, and polymaleic anhydride.
[0018] Preferably, in step S2, the temperature of the above reaction is 25°C to 60°C.
[0019] Preferably, in step S3, the feed rate of the spray dryer is 2 rpm to 20 rpm, the inlet air temperature is 110°C to 180°C, and the outlet air temperature is 60°C to 120°C.
[0020] Preferably, in step S4, the protective atmosphere is an inert gas, nitrogen, or a mixture thereof.
[0021] Preferably, in step S4, the pre-firing temperature is 180℃~350℃, and the pre-firing time is 1h~5h.
[0022] Secondly, this application provides a polyanionic cathode material precursor, which is prepared using the above-described preparation method.
[0023] Thirdly, this application provides a polyanionic cathode material obtained by sintering the aforementioned precursor.
[0024] Preferably, the sintering temperature is 450℃~600℃, and the sintering holding time is 4h~8h.
[0025] Fourthly, this application provides a sodium-ion battery comprising the aforementioned polyanion cathode material.
[0026] In summary, the technical solutions conceived in this application have the following main technical advantages compared with the prior art: (1) The preparation method of the polyanionic cathode material precursor provided in this application involves grinding to fully mix the raw materials, then adding a reducing agent and a complexing agent under acidic conditions. Through the synergistic effect of reduction and complexation reactions, the valence distribution of the transition metal M is precisely controlled, so that the molar ratio of divalent M to trivalent M is greater than 1:1 and some transition metal M exists as free ions, achieving atomic-level uniform mixing. This lays the foundation for obtaining a solid solution pure phase product through subsequent high-temperature phase formation. Then, spray drying and pre-calcination are performed to obtain an anhydrous amorphous product, which is the polyanionic cathode material precursor. The preparation method provided in this application effectively solves the problem of easy generation of electrochemically inert impurities during subsequent sintering. Moreover, after the polyanionic cathode material precursor is stored in air for a long time, the polyanionic cathode material obtained by sintering has high phase purity and still has excellent electrochemical performance.
[0027] (2) By sintering the polyanionic cathode material precursor prepared by the above preparation method, a high-purity solid solution pure phase polyanionic cathode material can be obtained. The material has high specific capacity, good cycle stability, and good rate performance, and has excellent electrochemical performance, making it suitable for the industrial application of high-performance sodium-ion batteries. Attached Figure Description
[0028] Figure 1 This is a schematic flowchart of the preparation method of the polyanionic cathode material precursor provided in this application; Figure 2 This is the XRD pattern of the polyanion cathode material prepared in Example 1 of this application; Figure 3 This is the XRD pattern of the polyanion cathode material prepared in Comparative Example 1 of this application; Figure 4 This is a charge-discharge curve of the button battery assembled in Embodiment 1 of this application; Figure 5 This is a charge-discharge curve of the button cell assembled in Comparative Example 1 of this application. Detailed Implementation
[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0030] In the description of this application, it should be understood that the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The symbol " / " in this document indicates that the related objects are in an "or" relationship; for example, A / B means A or B.
[0031] In the description of the embodiments in this application, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.
[0032] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more.
[0033] The inventors of this application discovered in actual production that the valence state of transition metals in polyanionic cathode materials has a significant impact on the phase formation process of such materials during heat treatment. In the process of preparing polyanionic cathode materials using conventional processes, the inventors attempted to directly spray-dry the mixed raw materials to obtain a hydrated precursor, followed by high-temperature heat treatment to form the phase. However, experimental results showed that when all transition metals in the precursor were in a reduced or oxidized valence state, electrochemically inert impurity phases such as NaFePO4 were easily generated during high-temperature heat treatment, severely affecting the purity of the product. Further research revealed that the hydrated precursor obtained by spray drying is easily oxidized when placed in air, leading to uneven changes in the valence state of the transition metals, resulting in low phase purity and poor batch consistency of the sintered product. Based on this discovery, the inventors made targeted improvements to the preparation process of polyanionic cathode material precursors, specifically providing a method for preparing polyanionic cathode material precursors, such as... Figure 1 As shown, it includes the following steps: S1. The sodium source, phosphorus source, transition metal M source and solvent are mixed and then milled to obtain a pre-reaction slurry; wherein, the transition metal M is one or more of Fe, Mn, Co and Ni; S2. Under an acidic environment, the above pre-reacted slurry is mixed with a reducing agent and a complexing agent to obtain a precursor slurry; S3. Spray dry the above precursor slurry to obtain precursor powder; S4. The above precursor powder is pre-calcined under a protective atmosphere to obtain anhydrous amorphous product, namely the above polyanion cathode material precursor.
[0034] This application first involves mixing and milling the raw materials to ensure thorough mixing and pre-reaction, thereby improving the system's homogeneity. Then, a reducing agent and a complexing agent are added under an acidic environment to synergistically regulate the valence distribution of the transition metal M, ensuring a molar ratio of divalent M to trivalent M greater than 1:1 and that some transition metals exist as free ions. This solves the technical problem in traditional processes where the single or uneven distribution of transition metal valence states easily leads to the formation of electrochemically inert impurities such as NaFePO4 during high-temperature heat treatment, while simultaneously achieving atomic-level uniform mixing. Based on this, spray drying is used to obtain spherical, amorphous precursor powder. Further, pre-calcination under a protective atmosphere removes residual moisture and partially dehydrates and polymerizes the phosphate groups, yielding an anhydrous amorphous product with excellent chemical stability. This completely solves the problems of traditional precursors being easily oxidized in air, having uneven valence states, and resulting in low phase purity of subsequent sintered products.
[0035] In some embodiments, in step S1, the sodium source is one or more of sodium sulfate, sodium citrate, sodium carbonate, sodium bicarbonate, sodium oxalate, disodium ethylenediaminetetraacetate, sodium formate, sodium acetate, sodium oxalate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium nitrate.
[0036] In some embodiments, the phosphorus source is one or more of phosphoric acid, sodium hypophosphite, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.
[0037] In some embodiments, the transition metal M source is one or more of the oxides, salts, and hydrates of the transition metal M. In some embodiments, the salt of the transition metal M is a soluble M salt, including one or more of phosphates, sulfates, nitrates, chlorides, acetates, and oxalates. For example, when the transition metal M is Fe, the Fe source can be selected from, but is not limited to, ferric phosphate, etc.; when the transition metal M is Mn, the Mn source can be selected from, but is not limited to, hydrated manganese iron phosphate, ammonium manganese iron phosphate, manganese acetate, manganese oxalate, etc.
[0038] In some embodiments, in step S1, the molar ratio of the sodium source, the transition metal M source, and the phosphorus source is (3~4):(2~3):(3~4).
[0039] In some embodiments, the solvent is one or more selected from water, alcoholic organic solvents, and ketone organic solvents. The water solvent can be ultrapure water, double-distilled water, deionized water, pure water, distilled water, etc. The alcoholic organic solvent can be selected from, but is not limited to, methanol, ethanol, ethylene glycol, isopropanol, etc. The ketone solvent can be selected from, but is not limited to, acetone, etc.
[0040] In some embodiments, the solid content of the pre-reacted slurry is 35wt% to 50wt%.
[0041] In some embodiments, the particle size D50 of the pre-reacted slurry is less than 200 nm, which can increase the reaction contact area between the raw materials, so that the reaction can proceed quickly and fully. At the same time, it is beneficial for the subsequent added reducing agent and complexing agent to react fully with the surface of the raw materials, and even partially etch into the interior of the raw materials, so that the reduction reaction and complexing reaction can proceed fully.
[0042] In some embodiments, the molar ratio of divalent M to trivalent M in the precursor slurry is greater than 1:1. This is to ensure that divalent M dominates in the solution, improving the stability of the precursor in air and thus enhancing the phase purity and electrochemical performance of the product. When the molar ratio of divalent M to trivalent M is too small, the stability of the precursor decreases, resulting in a higher concentration of trivalent iron impurities in the product, which cannot provide redox sites and consequently deteriorates the electrochemical performance.
[0043] In some embodiments, in step S2, the pH of the acidic environment is 3 to 5.
[0044] It is understood that this application does not specifically limit the type of reducing agent in step S2, and all reducing agents disclosed in the prior art suitable for the reduction of transition metal M are applicable to this application. In some embodiments, in step S2, the reducing agent includes, but is not limited to, one or more of ascorbic acid, oxalic acid, and citric acid. In some embodiments, the molar ratio of the reducing agent to the transition metal M source is (0.1~1):1.
[0045] In some embodiments, in step S2, the complexing agent is one or more of monoethanolamine, diethanolamine, ethylenediaminetetraacetic acid and its sodium salt, citric acid, and polymaleic anhydride. The complexing agent used in this application can affect the coordination environment of the transition metal and also serves as a carbon source. In some embodiments, the molar ratio of the complexing agent to the transition metal M source is (0.1~1):1.
[0046] In some implementation methods, step S2 further includes the addition of a surfactant capable of improving the dispersibility of each raw material in the solvent system. Exemplary examples of such surfactants include, but are not limited to, one or more of the following: oleic acid, sodium oleate, stearic acid, sodium stearate, sodium citrate, sodium alginate, citric acid, ascorbic acid, polyvinylpyrrolidone, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, ammonium dodecyl sulfate, dodecyl phosphate, hexadecyltrimethylammonium bromide, sodium diisooctyl succinate sulfonate, and polyoxyethylene stearate.
[0047] In some embodiments, the reaction temperature in step S2 is 25°C to 60°C. In some embodiments, to increase the reaction rate and ensure the reaction proceeds fully, the reaction can be carried out under stirring conditions. In some embodiments, the stirring speed is 300 to 800 rpm. It is understood that those skilled in the art can adapt the stirring speed according to the actual production scale, and all such adjustments are within the scope of protection of this application.
[0048] In some embodiments, in step S3, the feed rate of the spray drying process is 2~20 rpm, the inlet air temperature is 110℃~180℃, and the outlet air temperature is 60℃~120℃. The spray drying process using the aforementioned inlet and outlet air temperatures and feed rate ensures stable moisture evaporation, avoids the formation of large pores, and ensures that the precursor is uniformly dispersed micron-sized spherical particles.
[0049] In some embodiments, in step S4, the protective atmosphere is an inert gas, nitrogen, or a mixture thereof, the pre-firing temperature is 180°C to 350°C, and the pre-firing time is 1 hour to 5 hours.
[0050] This application also provides a polyanionic cathode material precursor, which is prepared by the above-described preparation method.
[0051] The precursor prepared in this application, after sintering, yields a high-purity solid-solution pure-phase polyanionic cathode material with excellent electrochemical performance, suitable for industrial applications in high-performance sodium-ion batteries. Based on this, this application also provides a polyanionic cathode material obtained by sintering the aforementioned precursor.
[0052] In some embodiments, the sintering temperature is 450℃~600℃, and the sintering holding time is 4h~8h.
[0053] On the other hand, this application also provides a sodium-ion battery comprising the aforementioned polyanion cathode material.
[0054] It should be understood that materials of the same or similar type, model, quality, properties, or function as the reagents and instruments used in the following embodiments can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.
[0055] The following are examples and comparative examples: Example 1 The method for preparing the polyanionic cathode material provided in this embodiment includes the following steps: (1) Weigh out ferric phosphate (iron source), sodium dihydrogen phosphate (phosphorus and sodium source), and sodium carbonate (sodium source) according to the stoichiometric ratio of Na4Fe3(PO4)2P2O7, then add deionized water, place the mixture in a closed stirring tank, grind and circulate twice to fully pre-react, and obtain a pre-reacted slurry with a particle D50 of 180nm. Then add citric acid (complexing agent), ascorbic acid (reducing agent), and PVP-30 (surfactant), wherein the molar ratio of citric acid to ferric phosphate is 0.5:1, the molar ratio of ascorbic acid to ferric phosphate is 0.5:1, the amount of PVP-30 is 30g, then adjust the pH of the slurry to 4.0, and carry out reduction and complexation reactions at 40℃ and stirring speed of 500rpm for 12h to obtain the precursor slurry. The overall color of the slurry changed from the initial yellow to dark green, meaning that the molar ratio of ferrous iron to ferric iron was greater than 1:1, and some iron existed in the form of free ions.
[0056] (2) The above precursor slurry is fed into a centrifugal spray dryer, and the feed rate is set to 10 rpm, the inlet air temperature is 180°C, and the outlet air temperature is 120°C for spray drying. After treatment, spherical non-crystalline amorphous particles are obtained, which are the precursor powder.
[0057] (3) The above precursor powder is placed in a rotary tube furnace and pre-calcined at 300°C for 2 hours at a rate of 5°C / min in an argon atmosphere. After natural cooling, an anhydrous amorphous product is obtained, which is the precursor of polyanionic cathode material.
[0058] (4) The above-mentioned polyanion cathode material precursor was placed in a shallow bowl, stacked in multiple layers, and placed in an argon atmosphere. It was sintered at 470°C for 8 hours and then cooled naturally to obtain the polyanion cathode material.
[0059] Figure 2 This is the XRD pattern of the polyanion cathode material prepared in this embodiment. It can be seen that there are no impurity phase peaks in the XRD diffraction curve, indicating that the polyanion cathode material is a solid solution pure phase.
[0060] Example 2 The preparation method of the polyanionic cathode material provided in this embodiment is the same as that in embodiment 1, except that the molar ratio of ascorbic acid and iron phosphate in step (1) is 0.1:1.
[0061] Example 3 The preparation method of the polyanionic cathode material provided in this embodiment is the same as that in embodiment 1, except that the molar ratio of ascorbic acid and iron phosphate in step (1) is 1:1.
[0062] Comparative Example 1 The preparation method of the polyanionic cathode material provided in this comparative example includes the following steps: (1) Weigh out ferric phosphate (iron source), sodium dihydrogen phosphate (phosphorus source), and sodium carbonate (sodium source) according to the stoichiometric ratio of Na4Fe3(PO4)2P2O7, then add deionized water, place the mixture in a closed stirring tank, grind and circulate twice to fully pre-react, and obtain a pre-reacted slurry with a particle D50 of 180nm. Then add citric acid (complexing agent) and PVP-30 (surfactant), wherein the molar ratio of citric acid to ferric phosphate is 0.5:1, and the amount of PVP-30 is 30g. Then adjust the pH of the slurry to 4.0, and react at 40℃ and a stirring speed of 500rpm for 12h to obtain the precursor slurry.
[0063] (2) The above slurry was spray-dried, pre-calcined and sintered according to the method provided in Example 1 to obtain polyanion cathode material.
[0064] Figure 3 The XRD pattern of the polyanion cathode material prepared in this comparative example shows that there are obvious impurity peaks, indicating that the polyanion cathode material prepared in Comparative Example 1 contains impurity phases.
[0065] Electrochemical performance testing: The polyanion cathode materials prepared in the above embodiments and the polyanion cathode materials prepared in the comparative example were respectively mixed with conductive agent (Super-P, Ketjen Black), binder PVDF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) in an 8:1:1 ratio to form slurries. These slurries were coated onto aluminum foil and dried to obtain a sodium-ion battery cathode sheet. Metallic sodium was used as the counter electrode, and a glass fiber membrane was selected as the separator. A mixed solution of 1 mol / L NaPF6 and ethylene carbonate (EC): dimethyl carbonate (DEC) = 1:1 vol.% was used as the electrolyte. The coin cells were assembled in a glove box under an argon atmosphere with a water content below 1 ppm. The assembled coin cells were then subjected to constant current charge-discharge tests at a current density of 0.1C (12.9 mAh / g). The test results are shown in [Figure number missing]. Figure 4 , Figure 5 Table 1.
[0066] Table 1. Electrochemical performance of polyanionic cathode materials prepared in the examples and comparative examples.
[0067] As shown in Table 1, compared to Comparative Example 1, the polyanion cathode material prepared in this application exhibits superior electrochemical performance. In terms of specific capacity, Example 1 shows a charging specific capacity of 102 mAh / g and a discharging specific capacity of 99 mAh / g, representing increases of 21.4% and 22.2% respectively compared to Comparative Example 1 (84 mAh / g and 81 mAh / g). This indicates that the material can achieve higher energy density and effectively improve the battery life of sodium-ion batteries. Simultaneously, Example 1 achieves an initial coulombic efficiency of 97.1%, higher than the 96.4% of Comparative Example 1, indicating fewer irreversible side reactions during the first charge-discharge process, higher utilization of active materials, less initial capacity loss, and better reversibility. In summary, the polyanion cathode material provided in this application achieves significant improvements in both specific capacity and initial coulombic efficiency, possessing outstanding advantages of high specific capacity and high initial efficiency, making it more suitable for the industrialization needs of high-performance sodium-ion batteries.
[0068] Furthermore, in actual production, the polyanionic cathode material precursor prepared in step (3) of Example 1 above is stored in air for a period of time (1 week), and then sintered to obtain a polyanionic cathode material with high phase purity and still maintaining excellent electrochemical performance.
[0069] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A method for preparing a polyanionic cathode material precursor, characterized in that, Includes the following steps: S1. The sodium source, phosphorus source, transition metal M source and solvent are mixed and then milled to obtain a pre-reaction slurry; the transition metal M is one or more of Fe, Mn, Co and Ni; S2. Under an acidic environment, the pre-reacted slurry is mixed with a reducing agent and a complexing agent to carry out reduction and complexation reactions to obtain a precursor slurry. S3. Spray dry the precursor slurry to obtain precursor powder; S4. The precursor powder is pre-calcined under a protective atmosphere to obtain an anhydrous amorphous product, namely the polyanion cathode material precursor.
2. The preparation method according to claim 1, characterized in that, In step S1, the sodium source is one or more of the following: sodium sulfate, sodium citrate, sodium carbonate, sodium bicarbonate, sodium bioxalate, disodium ethylenediaminetetraacetate, sodium formate, sodium acetate, sodium oxalate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium nitrate; and / or, The phosphorus source is one or more of phosphoric acid, sodium hypophosphite, monoammonium hydrogen phosphate, diammonium hydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, sodium monoammonium phosphate, sodium diammonium phosphate, and disodium hydrogen phosphate; and / or, The transition metal M source is one or more of the oxides, salts, and hydrates of the transition metal M; and / or, The molar ratio of the sodium source, the transition metal M source, and the phosphorus source is (3~4):(2~3):(3~4); and / or, The solvent is one or more selected from water, alcoholic organic solvents, and ketone organic solvents; and / or, The solid content of the pre-reacted slurry is 35wt%~50wt%; and / or, The particle size D50 of the pre-reacted slurry is less than 200 nm.
3. The preparation method according to claim 2, characterized in that, The pH of the acidic environment is 3-5; and / or, The molar ratio of the reducing agent to the transition metal M source is (0.1~1):1; and / or, The molar ratio of the complexing agent to the transition metal M source is (0.1~1):
1.
4. The preparation method according to claim 3, characterized in that, The reducing agent is one or more of ascorbic acid, oxalic acid, and citric acid; and / or... The complexing agent is one or more of monoethanolamine, diethanolamine, ethylenediaminetetraacetic acid and its sodium salt, citric acid, and polymaleic anhydride.
5. The preparation method according to claim 3, characterized in that, In step S2, the reaction temperature is 25℃~60℃.
6. The preparation method according to claim 1, characterized in that, In step S3, the feed rate of the spray dryer is 2 rpm to 20 rpm, the inlet air temperature is 110℃ to 180℃, and the outlet air temperature is 60℃ to 120℃; and / or, In step S4, the protective atmosphere is an inert gas, nitrogen, or a mixture thereof, the pre-firing temperature is 180℃~350℃, and the pre-firing time is 1h~5h.
7. A polyanionic cathode material precursor, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.
8. A polyanionic cathode material, characterized in that, It is obtained by sintering the precursor as described in claim 7.
9. The polyanionic cathode material according to claim 8, characterized in that, The sintering temperature is 450℃~600℃; and / or the sintering holding time is 4h~8h.
10. A sodium-ion battery, characterized in that, Includes the polyanionic cathode material as described in claim 8 or 9.