A halotransition metal phosphate sodium-ion battery cathode material and its preparation method

Abstract

A halotransition metal phosphate-based cathode material for sodium-ion batteries and its preparation method are disclosed. This invention addresses the technical problems of poor purity, uneven conductive carbon coating, and poor performance in existing halotransition metal phosphate materials. The material of this invention consists of a halotransition metal phosphate and carbon coating on its surface; wherein the halotransition metal phosphate is Na3M2(YO4)2O. x X 3‑2x ; 0 ≤ x < 1.5; M = V, Fe, Ti, or Zr; Y = P, S, or Si; X = F, Cl, or Br; Preparation method: The raw materials are initially mixed according to the stoichiometric ratio of halotransition metal phosphates, then mixed with a carbon source, ball-milled, ground, and calcined to obtain the cathode material. This material has high purity, a reversible capacity of 119 mAh / g at 0.2C charge / discharge, and can achieve more than 3000 cycles at 10C. It can be used in the field of sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to sodium-ion battery cathode materials, their preparation methods, and applications, belonging to the field of battery material synthesis technology. Background Technology

[0002] Compared to lithium, sodium is extremely abundant and inexpensive, giving it an advantage in mid- to low-end electric vehicles and energy storage power stations. Its electrochemical performance largely depends on the cathode material. Among various candidate materials, halotransition metal phosphate sodium-ion battery cathode materials (chemical formula Na3M2(YO4)2O) are particularly promising. x X 3-2x (0≤x<1.5; M=V,Fe,Ti,Zr; Y=P,S,Si; X=F,Cl,Br) possesses considerable theoretical specific capacity, and the supporting effect of polyanions slows down the degradation of battery cycle performance, making it a promising class of SIB materials. Currently, researchers are improving the electrochemical performance of halotransition metal phosphate sodium-ion battery cathode materials by introducing highly electronegative halogens. However, it is well known that halogen atoms react with H to form easily volatile halohydrogens, which then overflow from the material lattice. This phenomenon is highly likely to occur during high-temperature calcination. This not only leads to a decrease in sample purity, but the resulting Na3M2(YO4)3 secondary phase also reduces discharge voltage and specific energy, causing a series of negative effects. Therefore, reducing or eliminating halogen volatilization is of great significance, and it is also essential for the large-scale application of SIBs in large-scale energy storage equipment. Summary of the Invention

[0003] This invention aims to address the problems of poor purity and uneven conductive carbon coating caused by halogen volatilization during the preparation of existing halotransition metal phosphate sodium-ion battery cathode materials. It provides a halotransition metal phosphate sodium-ion battery cathode material and its preparation method. The preparation method of this invention improves the purity and electrochemical performance of the halotransition metal phosphate sodium-ion battery cathode material, including specific energy, specific capacity, rate capability, and cycle performance.

[0004] The halotransition metal phosphate-based sodium-ion battery cathode material of the present invention comprises a halotransition metal phosphate matrix and a conductive layer coated on its surface; the general chemical formula of the halotransition metal phosphate is Na3M2(YO4)2O. x X 3-2x ; 0 ≤ x < 1.5; M = V, Fe, Ti, or Zr; Y = P, S, or Si; X = F, Cl, or Br; The surface-coated conductive layer is a carbon layer. This cathode material has high purity and stably exhibits high operating voltage and excellent cycle and rate performance.

[0005] Furthermore, the thickness of the carbon layer is 1–8 nm.

[0006] The preparation method of the above-mentioned halotransition metal phosphate sodium-ion battery cathode material is carried out according to the following steps:

[0007] 1. At room temperature, weigh out the sodium source, transition metal M source, Y source and halogen source according to the stoichiometric ratio of halotransition metal phosphates and transfer them to a ball mill jar. Ball mill at 150-250 r / min for 10 min or grind in a mortar for 20-30 min to perform preliminary mixing and obtain a uniform fine powder.

[0008] 2. Weigh the carbon source and mix it with the fine powder from step 1 in a ball mill jar. Mill the mixture at 400–1200 r / min for 8–12 h to obtain a dry material. The carbon source is an organic acid and its corresponding Lewis base. The organic acid is one or more of citric acid monohydrate, anhydrous citric acid, and ascorbic acid. The Lewis base of citric acid is ammonium citrate, and the Lewis base of ascorbic acid is ascorbic acid amine. The selected organic acid can form a carbon source with a large specific surface area (particulate carbon) during carbonization, making it easier to coat onto the substrate surface. If glucose is used in this step, it is difficult to form a uniform conductive layer on the surface of the phosphate material, therefore the prepared cathode material cannot achieve the expected results. More importantly, the purpose is to introduce the corresponding Lewis base of the organic acid for localized electronic regulation, so that halogen atoms can be stabilized during the initial pre-reaction of the raw materials.

[0009] 3. Transfer the obtained dry material to a mortar and grind it to obtain a powdered precursor;

[0010] 4. The powdered precursor is transferred to a tube furnace and pre-sintered in a flowing inert gas stream. Then, the temperature is raised to 500℃~700℃ and calcined for 5~12 hours. Finally, it is naturally cooled to room temperature with the furnace temperature to obtain the halotransition metal phosphate sodium-ion battery cathode material.

[0011] Furthermore, the transition metal M source mentioned in step two is an ammonium salt or oxide of transition metal M; the Y source is NH4H2YO4 and / or (NH4)2HYO4; the halogen source is NaX and / or NH4X; these raw materials are easy to grind into fine powder, ensuring uniform mixing of raw materials, and forming a uniform halotransition metal phosphate sodium-ion battery cathode material through high-temperature calcination.

[0012] Furthermore, during the ball milling process described in step two, the temperature is maintained at 35–55°C, and this heat preservation process can increase the thoroughness of the solid-phase reaction.

[0013] Furthermore, the ratio of the amount of carbon source to the total amount of transition metal elements mentioned in step two is 1:0.8 to 2.5. The purpose is to allow the dispersed carbon source to penetrate well into the gaps between the precursors, thereby dispersing the precursor particles, preventing agglomeration, and achieving high electronic conductivity.

[0014] Furthermore, the ball milling described in steps one and two is carried out in an air or argon protective atmosphere, with a ball-to-material mass ratio of (10-50):1, and the milling media being agate balls, ZrO2 balls, or stainless steel balls. The purpose is to ensure uniform dispersion of the carbon source.

[0015] Furthermore, the pre-sintering temperature in step four is 350℃~450℃, and the pre-sintering time is 3~5h. The purpose is to allow the carbon source to undergo sufficient thermal decomposition and reduce the volatilization of halogens;

[0016] Furthermore, the heating rate for pre-sintering described in step four is 2–10 °C / min.

[0017] Furthermore, the heating rate for calcination described in step four is 2–10 °C / min.

[0018] Furthermore, the calcination temperature in step four is 550℃~650℃, and the time is 5~8h, in order to ensure that the carbothermic reduction reaction proceeds fully.

[0019] Furthermore, the inert atmosphere mentioned in step four is argon, nitrogen, or a hydrogen-argon mixture, wherein the volume percentage of hydrogen in the hydrogen-argon mixture is 5% to 10%.

[0020] The advantages of this invention over the prior art are as follows:

[0021] (1) This invention proposes a simple Lewis acid-base pair control strategy to stabilize halogen atoms within the material lattice, thereby obtaining pure-phase halotransition metal phosphate sodium-ion battery cathode materials. The halotransition metal phosphate sodium-ion battery cathode materials are synthesized using a solid-state method and high-temperature sintering technology that are easy to control and facilitate large-scale continuous production. The preparation method is simple, easy to operate, and has good reproducibility. This invention controls the local electronic environment and van der Waals forces of transition metals and halogen atoms during the synthesis of halotransition metal phosphate sodium-ion battery cathode materials by selecting appropriate carbon sources and Lewis acid-base pairs, suppressing the inherent volatility of halogen atoms, thereby stabilizing halogen atoms within the lattice of the halotransition metal phosphate sodium-ion battery cathode material. Ultimately, the voltage plateau corresponding to the constant current charge-discharge curve of this type of material shows almost no fluctuation, the transition metal elements undergo redox reactions at higher voltages, and it exhibits excellent long-cycle performance and high energy density. The halotransition metal phosphate sodium fluorophosphate cathode material prepared by this invention has a suppressed low voltage plateau (~3.4V) during constant current charge and discharge, which is beneficial to improving the overall energy density of the battery.

[0022] This invention synthesizes sodium vanadium fluorophosphate, a halotransition metal phosphate cathode material for sodium-ion batteries, via a solid-state method. The discharge curve shows only two distinguishable voltage plateaus (approximately 4.1V and 3.6V, vs. Na). + / Na), because of the lower voltage plateau (~3.4V, vs. Na) generated by the impurity phase after halogen volatilization. + The / Na) disappears. Furthermore, this low-voltage plateau was observed in the control group, originating from the secondary phase Na3V2(PO4)3, whose presence reduced the average discharge voltage and energy density of the cathode material when fully charged. Data analysis is as follows: its discharge specific capacity at rates of 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, 15.0, 20.0, and 30.0C are 119, 113, 110, 107, 101, 95, 89, 83, and 67 mAh / g, respectively. This material can stably withstand high current density charge-discharge cycles over a long period, retaining a discharge specific capacity of 60 mAh / g after 3000 cycles at a 10C current density. Moreover, its constant current charge-discharge curve at 0.2C indicates that the cathode material undergoes an electrochemical reaction with two voltage plateaus and only minimal voltage polarization.

[0023] (2) This invention incorporates a carbon source that acts as both a coating material and a reducing agent, uniformly coating the material surface with a thickness ranging from 1 to 8 nm. Introducing a Lewis base that matches the carbon source allows for uniform intermolecular interactions through Lewis acid-base pairs, resulting in a more uniform distribution of the carbon source in the precursor material. This leads to an electrode material with a uniform and densely coated surface carbon conductive layer. There are two methods: one is to select a Lewis acid-base pair during the initial pre-solid phase reaction to regulate intermolecular interactions during preparation, and to supplement the ball milling process with heat preservation to ensure a more thorough solid-phase reaction; the other is to change the type of carbon source. Different carbon sources exist in different forms on the surface of the halotransition metal phosphate cathode material. Using an organic acid that easily forms a uniformly coated carbon conductive layer on its surface improves its electronic conductivity. Furthermore, using an organic acid as the carbon source and introducing the corresponding Lewis base allows for a more stable, dense, and highly electronically conductive carbon coating through simple intermolecular forces. Therefore, the halotransition metal phosphate cathode material exhibits superior electronic conductivity and significantly improved rate performance.

[0024] (3) This invention provides a method for the mass production of stable high-voltage and high-energy-density halotransition metal phosphate sodium-ion battery cathode materials, including local electronic structure micro-tuning, carbon source selection, synthesis conditions, process parameters, and operation methods. A carbon source with high electronic conductivity is used, and halogen atoms are stabilized by introducing a Lewis base corresponding to the carbon source, thereby obtaining a high-purity phase of this type of cathode material, ultimately significantly improving the electrochemical performance of this material.

[0025] (4) In the preparation process, the present invention does not require the use of dispersants but directly performs dry solid-phase ball milling, which reduces the production cost. More importantly, it prevents more complex side reactions (such as various complexation reactions) from occurring in the liquid state and prevents the volatilization of halogens, such as fluorine. Attached Figure Description

[0026] Figure 1 XRD patterns of sodium vanadium fluorophosphate prepared in Comparative Example 1 and Example 1;

[0027] Figure 2 The rate performance of sodium vanadium fluorophosphate prepared in Comparative Example 1 in a half-cell with sodium as the counter electrode is shown in the figure.

[0028] Figure 3 The cycling performance of sodium vanadium fluorophosphate prepared for Comparative Example 1 at a current density of 10.0C in a half-cell with sodium as the counter electrode.

[0029] Figure 4 The constant current charge-discharge curve of sodium vanadium fluorophosphate prepared for Comparative Example 1 at 0.2C in a half-cell with sodium as the counter electrode;

[0030] Figure 5 The rate performance of sodium vanadium fluorophosphate, the halotransition metal phosphate cathode material prepared in Example 1, in a half-cell with sodium as the counter electrode is shown in the figure.

[0031] Figure 6 The graph shows the cycling performance of sodium vanadium fluorophosphate, a halotransition metal phosphate cathode material prepared in Example 1, at a current density of 10.0C in a half-cell with sodium as the counter electrode.

[0032] Figure 7 The constant current charge-discharge curve of sodium vanadium fluorophosphate, the cathode material of halotransition metal phosphate prepared in Example 1, at 0.2C in a half-cell with sodium as the counter electrode.

[0033] Figure 8 Scanning electron microscope image of sodium vanadium fluorophosphate prepared for Comparative Example 1 in a half-cell with sodium as the counter electrode.

[0034] Figure 9 SEM image of sodium vanadium fluorophosphate, the halotransition metal phosphate cathode material prepared in Example 1, in a half-cell with sodium as the counter electrode.

[0035] Figure 10 Transmission electron microscopy image of sodium vanadium fluorophosphate prepared for Comparative Example 1 in a half-cell with sodium as the counter electrode.

[0036] Figure 11 The image shows a TEM image of sodium vanadium fluorophosphate, the cathode material of a halotransition metal phosphate sodium-ion battery prepared in Example 1, in a half-cell with sodium as the counter electrode. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0038] Comparative Example 1: This example prepares sodium vanadium fluorophosphate as a control, with the chemical formula Na3V2(PO4)2F3. The preparation method of this material is carried out according to the following steps:

[0039] 1. At room temperature, weigh 0.9540g of anhydrous sodium carbonate, 1.4038g of ammonium metavanadate, 1.3800g of ammonium dihydrogen phosphate, and 0.6667g of ammonium fluoride according to the stoichiometric ratio of Na3V2(PO4)2F3 and transfer them to a ball mill jar. Agate balls are selected as the ball milling media, and the ball-to-material mass ratio is 30:1. Ball mill at 200r / min for 10min to perform preliminary mixing and obtain a uniform fine powder.

[0040] 2. Using citric acid monohydrate solid (molecular formula: C6H8O7·H2O) as a carbon source, 2.5218 g of citric acid monohydrate solid was weighed and mixed with the fine powder obtained in step 1 to obtain a light yellow powder; the ratio of the amount of citric acid monohydrate to the total molar amount of transition metal elements was 1:1; the light yellow powder was placed in a ball mill, agate balls were selected as the milling media, the ball-to-material mass ratio was 30:1, and the ball milling was carried out at a speed of 800 r / min for 12 h, with the temperature maintained at 40℃ during the ball milling process, to obtain dry material; ball milling effectively reduced the particle size of large intermediates and obtained a precursor with a uniform composition;

[0041] 3. Transfer the dry material prepared in step 2 to a mortar and grind for 30 minutes to obtain a powdered precursor;

[0042] 4. The powdered precursor is transferred to a tube furnace and pre-sintered at 400°C for 4 hours under a flowing high-purity argon protective atmosphere at a heating rate of 2°C / min. Then, it is calcined at 600°C for 6 hours at a heating rate of 2°C / min. The furnace is then allowed to cool naturally to room temperature to obtain sodium vanadium fluorophosphate, a halotransition metal phosphate cathode material for sodium-ion batteries.

[0043] Example 1: This example describes the preparation of sodium vanadium fluorophosphate, a halotransition metal phosphate cathode material for sodium-ion batteries, with the chemical formula Na3V2(PO4)2F3. The preparation method of this material is as follows:

[0044] 1. At room temperature, weigh 0.9540g of anhydrous sodium carbonate, 1.4038g of ammonium metavanadate, 1.3800g of ammonium dihydrogen phosphate, and 0.6667g of ammonium fluoride according to the stoichiometric ratio of Na3V2(PO4)2F3 and transfer them to a ball mill jar. Agate balls are selected as the ball milling media, and the ball-to-material mass ratio is 30:1. Ball mill at 200r / min for 10min to perform preliminary mixing and obtain a uniform fine powder.

[0045] II. Using citric acid monohydrate solid (C6H8O7·H2O) and ammonium citrate (C6H 11 (NO7) Lewis acid-base pairs act as both carbon source and reducing agent. 1.7651 g of citric acid monohydrate solid and 0.8757 g of ammonium citrate were weighed and mixed with the fine powder obtained in step one to obtain a pale yellow powder. The ratio of the total amount of Lewis acid-base pairs to the total molar amount of transition metal elements was 1:1. The pale yellow powder was placed in a ball mill, with agate balls as the milling media and a ball-to-material mass ratio of 30:1. The mill was run at 800 r / min for 12 h, with the temperature maintained at 40℃ during the milling process, to obtain dry material. Ball milling effectively reduced the particle size of large intermediates and obtained a precursor with a uniform composition.

[0046] 3. Transfer the dry material prepared in step 2 to a mortar and grind for 30 minutes to obtain a powdered precursor;

[0047] 4. The powdered precursor is transferred to a tube furnace and pre-sintered at 400°C for 4 hours under a flowing high-purity argon protective atmosphere at a heating rate of 2°C / min. Then, it is calcined at 600°C for 6 hours at a heating rate of 2°C / min. The furnace is then allowed to cool naturally to room temperature to obtain sodium vanadium fluorophosphate, a halotransition metal phosphate cathode material for sodium-ion batteries.

[0048] Figure 1 XRD patterns of sodium vanadium fluorophosphate prepared in Comparative Example 1 and Example 1. Figure 1 It can be seen that the sodium vanadium fluorophosphate prepared in Comparative Example 1 has a non-negligible impurity phase. Comparison revealed that these impurity peaks correspond to the standard PDF card of the Na3V2(PO4)3 phase. In contrast, the XRD pattern of the sodium vanadium fluorophosphate prepared in Example 1 only showed signal peaks of the Na3V2(PO4)2F3 phase, and these impurity phases were not detected, proving that the generation of impurity phases was suppressed, and high-purity sodium vanadium fluorophosphate was successfully prepared.

[0049] Both the sodium vanadium fluorophosphate prepared in Comparative Example 1 and the sodium vanadium fluorophosphate prepared in Example 1 were assembled into simulated coin cells. The electrochemical performance of the resulting coin cells was tested in the voltage range of 2.5–4.4 V.

[0050] Figure 2 The rate performance graph of sodium vanadium fluorophosphate prepared in Comparative Example 1 in a half-cell with sodium as the counter electrode is shown. Figure 2 As can be seen, within the voltage range of 2.5-4.4V, the sodium vanadium fluorophosphate prepared in Comparative Example 1 exhibits poor rate performance and discharge specific capacity. Specifically, the battery assembled with this cathode material has an initial discharge specific capacity of 90mAh / g at 10.0C.

[0051] Figure 3 The cycling performance of sodium vanadium fluorophosphate prepared for Comparative Example 1 at a current density of 10.0C in a half-cell with sodium as the counter electrode is shown in the figure. Figure 3 As can be seen, in the cycle performance test within the voltage range of 2.5-4.4V, the self-assembled half-cell of sodium vanadium fluorophosphate prepared in Comparative Example 1 showed 105, 102, 100, 98, 94, 90, 85, 79, and 66 mAh / g at rates of 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, 15.0, 20.0, and 30.0C, respectively. This material can withstand long-term stable high current density charge and discharge, and only 53 mAh / g of discharge specific capacity was retained after 3000 cycles at a current density of 10.0C.

[0052] Figure 4 The constant current charge-discharge curves of sodium vanadium fluorophosphate prepared in Comparative Example 1 at 0.2C in a half-cell with sodium as the counter electrode are shown. Figure 4 It can be seen that the sodium vanadium fluorophosphate cathode material prepared in Comparative Example 1 with citric acid as the carbon source was subjected to constant current charge-discharge test in the voltage range of 2.5-4.4V. Its voltage plateau was tilted and a low voltage plateau was generated by the Na3V2(PO4)3 impurity phase. This impurity phase was generated by the loss of halogen element F during the preparation process.

[0053] Figure 5 This is a rate performance graph of sodium vanadium fluorophosphate, the halotransition metal phosphate cathode material prepared in Example 1, in a half-cell with sodium as the counter electrode. Figure 5 It can be seen that the sodium vanadium fluorophosphate obtained by this preparation method exhibits good rate performance as a cathode material, which demonstrates the feasibility of the strategy of obtaining pure-phase halotransition metal phosphate sodium-ion battery cathode materials by regulating Lewis acid-base pairs. Figure 5 It can be seen that the rate performance of the sodium vanadium fluorophosphate cathode material prepared in Example 1 is improved, exhibiting higher specific capacity under various charge and discharge conditions. Specifically, the specific capacities of the obtained coin-type sodium-ion batteries at rates of 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, 15.0, 20.0, and 30.0C are 119, 113, 110, 107, 101, 95, 89, 83, and 67 mAh / g, respectively. A reversible capacity of 67 mAh / g can be observed during constant current charge and discharge at a high current density of 10.0C.

[0054] Figure 6 The graph shows the cycling performance of sodium vanadium fluorophosphate, a halotransition metal phosphate cathode material prepared in Example 1, at a current density of 10.0C in a half-cell with sodium as the counter electrode. From... Figure 6 It can be seen that the material can be charged and discharged at high current density for a long time and still retains a discharge specific capacity of 60mAh / g after 3000 cycles at a current density of 10.0C.

[0055] Figure 7 The image shows the constant current charge-discharge curves at 0.2C for sodium vanadium fluorophosphate, the halotransition metal phosphate cathode material prepared in Example 1, in a half-cell with sodium as the counter electrode. Figure 7 It can be seen that the sodium vanadium fluorophosphate cathode material prepared in Example 1, which uses Lewis acid-base pairs as a common carbon source, exhibits a more stable voltage plateau during constant current charge-discharge testing within the voltage range of 2.5-4.4V, and the low voltage plateau caused by the Na3V2(PO4)3 impurity phase disappears.

[0056] Figure 8SEM image of sodium vanadium fluorophosphate prepared in Comparative Example 1 in a half-cell with sodium as the counter electrode. Figure 8 It can be seen that the sodium vanadium fluorophosphate cathode material prepared in Comparative Example 1, which uses citric acid as the carbon source, has a lot of pores on its surface. This indicates that the carbon coating layer is not dense enough, which will reduce the electronic conductivity of the electrode material.

[0057] Figure 9 This is a SEM image of sodium vanadium fluorophosphate, the halotransition metal phosphate cathode material prepared in Example 1, in a half-cell with sodium as the counter electrode. Figure 9 It can be seen that, compared with Comparative Example 1, the sodium vanadium fluorophosphate cathode material prepared in Example 1, using ammonium citrate and citric acid as carbon sources, has fewer surface pores and a denser carbon coating layer, thus improving the electronic conductivity of the electrode material. This improvement in electronic conductivity is also related to that of Comparative Example 1. Figure 4 Example 1 Figure 7 The constant current charge-discharge curves of the obtained cathode materials corroborate each other, with the latter showing smaller voltage polarization at a current density of 0.2C.

[0058] Figure 10 TEM image of sodium vanadium fluorophosphate prepared for Comparative Example 1 in a half-cell with sodium as the counter electrode. Figure 10 It can be seen that the sodium vanadium fluorophosphate cathode material prepared in Comparative Example 1 with only citric acid as the carbon source has a thin and uneven conductive carbon coating layer on its substrate surface. This will cause the substrate material to be exposed to the outside and reduce the electronic conductivity of the electrode material.

[0059] Figure 11 This is a TEM image of sodium vanadium fluorophosphate, the halotransition metal phosphate cathode material prepared in Example 1, in a half-cell with sodium as the counter electrode. Figure 11 As can be seen, compared with Comparative Example 1, the carbon coating layer on the surface of the sodium vanadium fluorophosphate cathode material prepared in Example 1, which uses ammonium citrate and citric acid as carbon sources, is equal to and meets the thickness requirements of the surface carbon coating, so that the substrate material can exhibit better electronic conductivity while ensuring that it is completely coated with conductive carbon.

[0060] This invention relates to the preparation of halotransition metal phosphate sodium-ion battery cathode materials. A carbon source, acting as both a coating material and a reducing agent, is added to uniformly coat the material surface with a thickness ranging from 1 to 8 nm. Furthermore, a Lewis base corresponding to the Lewis acid carbon source is introduced to stabilize halogen atoms during the preparation process, resulting in high electronic conductivity and operating voltage. The preparation process eliminates the need for solvent mixing; instead, raw materials are directly mixed using a dry method, reducing production costs. More importantly, this method prevents side reactions between the solvent and other reagents and inhibits the volatilization of halogen atoms.

[0061] This invention synthesizes a high-energy-density, uniformly carbon-coated matrix halotransition metal phosphate sodium-ion battery cathode material. The material has high purity, which significantly improves the working voltage and enables it to exhibit excellent rate performance and long-cycle stability, demonstrating superior electrochemical performance. The preparation process of this invention is simple, economical, practical, and reproducible. The obtained material has high energy and power density and broad application scenarios.

Claims

1. A method for preparing a halogenated transition metal phosphate sodium-ion battery cathode material, characterized in that, The method is carried out according to the following steps: I. At room temperature, the sodium source, the transition metal M source, the Y source and the halogen source are weighed according to the stoichiometric ratio of the halogenated transition metal phosphate, and are transferred into a ball mill jar for 10 minutes of ball milling at 150-250 r / min or into a mortar for 20-30 minutes of grinding, to carry out preliminary mixing, to obtain a uniform fine powder; II. The carbon source is weighed and mixed with the fine powder of step I in a ball mill jar, and is ball-milled at a speed of 400-1200 r / min for 8-12 hours to obtain a dry material; wherein the carbon source is an organic acid and a Lewis base corresponding to the organic acid; the organic acid is one or more of citric acid monohydrate, anhydrous citric acid and ascorbic acid, the Lewis base of citric acid is ammonium citrate, and the Lewis base of ascorbic acid is ascorbic acid amine; III. The obtained dry material is transferred into a mortar and is ground to obtain a powder-shaped precursor; Four, the powder precursor is transferred to a tube furnace, pre-sintered in a flowing inert gas stream, then continue to heat to 500-700℃ calcination 5-12h, and finally with the tube furnace temperature natural cooling to room temperature, to get halogenated transition metal phosphate sodium-ion battery anode material; the material is composed of a substrate halogenated transition metal phosphate and its surface coated conductive layer; the halogenated transition metal phosphate chemical formula is Na3M2(YO4)2O x X 3-2x ; 0≤x<1.5; M=V, Fe, Ti or Zr; Y=P, S or Si; X=F, Cl or Br; the surface coated conductive layer is a carbon layer with a thickness of 1-8nm.

2. The method for preparing a halotransition metal phosphate sodium-ion battery cathode material according to claim 1, characterized in that, In step II, the transition metal M source is an ammonium salt of the transition metal M or an oxide of the transition metal M; the Y source is NH4H2YO4 and / or (NH4)2HYO4; and the halogen source is NaX and / or NH4X.

3. A method of producing a halogenated transition metal phosphate-based sodium-ion battery cathode material according to claim 1 or 2, characterized in that, In the ball milling process in step II, the temperature is maintained at 35-55℃.

4. The method of claim 1 or 2, wherein the method is characterized by, In step II, the ratio of the amount of substance of the carbon source to the total amount of substance of the transition metal elements is 1:0.8-2.

5.

5. The method of claim 1 or 2, wherein the method is characterized by, In steps I and II, the ball milling is carried out in an air or argon protective atmosphere, the ball-to-material mass ratio is (10-50):1, and the ball milling medium is aagate ball, ZrO2 ball or stainless steel ball.

6. The method of claim 1 or 2, wherein the method is characterized by, In step IV, the pre-sintering temperature is 350-450℃, and the pre-sintering time is 3-5 hours.

7. The method of claim 1 or 2, wherein the method is characterized by, In step IV, the pre-sintering temperature is 350-450℃, and the pre-sintering time is 3-5 hours.

8. The method of claim 1 or 2, wherein the method is characterized by, In step IV, the pre-sintering temperature is 350-450℃, and the pre-sintering time is 3-5 hours.

9. The method of claim 1 or 2, wherein the method is characterized by, In step IV, the calcination temperature is 550-650℃, and the time is 5-8 hours.

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