阅读说明：本技术 一种一步法制备的钒基聚阴离子型化合物及应用 (Vanadium-based polyanion compound prepared by one-step method and application thereof ) 是由 郑琼 李先锋 凌模翔 韩建鑫 张华民 于 2019-11-27 设计创作，主要内容包括：本发明提供一种一步法制备的钒基聚阴离子型化合物及应用,原料均在高温熔融下反应,无需前期复杂工艺,直接在高温下呈液态熔融混合,原材料之间发生分子级别的混合,混合充分均匀,同时高温下反应能垒降低,可迅速反应获得分布均匀的纳米片状碳复合钒基聚阴离子型化合物；由于高温烧结后产物在惰性气体中快速冷却,避免了高温过程中氟磷酸钒基聚阴离子型化合物的分解,产物具有很高的纯度。由其组装电池的初始比容量接近理论比容量,电池倍率性能得到大幅提高。该方法为高性能氟磷酸钒基聚阴离子型化合物的高效合成及其在钠离子电池中的应用提供了新策略。(The invention provides a vanadium-based polyanionic compound prepared by a one-step method and application thereof, wherein raw materials are all reacted under high-temperature melting, a complex process at the early stage is not needed, the raw materials are directly melted and mixed in a liquid state at high temperature, the raw materials are mixed at a molecular level, the mixing is fully and uniformly, meanwhile, the reaction energy barrier is reduced at high temperature, and the nano flaky carbon composite vanadium-based polyanionic compound with uniform distribution can be quickly obtained through reaction; because the product after high-temperature sintering is rapidly cooled in inert gas, the decomposition of the vanadium fluorophosphate polyanion compound is avoided in the high-temperature process, and the product has high purity. The initial specific capacity of the assembled battery is close to the theoretical specific capacity, and the multiplying power performance of the battery is greatly improved. The method provides a new strategy for the efficient synthesis of the high-performance vanadium fluorophosphate polyanion compound and the application of the high-performance vanadium fluorophosphate polyanion compound in the sodium-ion battery.)

1. A method for preparing a vanadium-based polyanionic compound, comprising the steps of:

(1) mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a sodium source or a lithium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

(2) and (2) placing the reaction product obtained in the step (1) in an inert atmosphere for cooling for 30s-5min at the temperature of 0-40 ℃ to obtain the vanadium-based polyanion compound.

2. The preparation method according to claim 1, wherein the product cooled in step (2) is ball milled in a high-energy ball mill at a rotation speed of 300-.

3. The production method according to claim 1,

when the vanadium-based polyanionic compound is sodium vanadium monofluorophosphate (NaVPO)₄F) Mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a sodium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

the molar ratio of the sodium source to the vanadium source to the phosphorus source to the fluorine source is 1-1.2: 1:1: 1-1.5;

the mass of the carbon source is 30-60% of the total mass of the vanadium source, the sodium source, the fluorine source and the phosphorus source.

4. The production method according to claim 1,

when the vanadium-based polyanionic compound is lithium vanadium monofluorophosphate (LiVPO)₄F) Mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a lithium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

the stoichiometric ratio of the lithium source, the vanadium source, the phosphorus source and the fluorine source is 1-1.2: 1:1: 1-1.5;

the mass of the carbon source is 30-60% of the total mass of the vanadium source, the lithium source, the fluorine source and the phosphorus source.

5. The production method according to claim 1,

when the vanadium-based polyanionic compound is sodium vanadium triphosphate Na₃V₂(PO₄)₂F₃Mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a sodium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

the stoichiometric ratio of the sodium source to the vanadium source to the phosphorus source to the fluorine source is 3-3.5: 2:2: 3-3.8.

The mass of the carbon source is 30-60% of the total mass of the vanadium source, the sodium source, the fluorine source and the phosphorus source.

6. The preparation method according to any one of claims 1 to 5, wherein the inert atmosphere gas is one or a mixture of helium and nitrogen;

the sodium source is at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate and sodium fluoride;

the vanadium source is at least one of ammonium metavanadate, vanadium pentoxide, ammonium polyvanadate, vanadium trioxide and vanadium dioxide;

the phosphorus source is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid;

the carbon source is at least one of citric acid, oxalic acid, ascorbic acid, glucose, sucrose, fructose and polyethylene glycol;

the fluorine source is at least one of hydrogen fluoride, lithium fluoride, sodium fluoride and polytetrafluoroethylene.

7. A vanadium-based polyanion-based compound produced by the production method according to claim 1.

8. Use of the vanadium-based polyanionic compound according to claim 7 as a positive electrode material in a lithium ion battery or a sodium ion battery.

Technical Field

The invention relates to the technical field of electrode materials of lithium/sodium ion batteries, in particular to a preparation method and application of a vanadium-based polyanion compound for a lithium/sodium ion battery.

Technical Field

The positive electrode material of a lithium ion battery or a sodium ion battery is the key to determine the energy density of the battery. The preferred positive electrode material should have a high operating voltage, high capacity and a stable structure. Among the numerous positive electrode materials, the vanadium fluorophosphate-based polyanion compound, vanadium lithium fluorophosphate (LiVPO)₄F, LVPF for short), sodium vanadium monofluorophosphate (NaVPO4F, NVPF for short), and sodium vanadium trifluoride phosphate (Na)₃V₂(PO₄)₂F₃NVPF for short₃) Has high voltage (4.2V, 3.4V and 3.9V respectively), high theoretical specific capacity (153 mAh/g, 143mAh/g and 128mAh/g respectively), and stable structure. However, the intrinsic conductivity of the compound is low, so that the performance of the compound is limited. In order to improve the conductivity of the material, a common method is to add a carbon source in the processes of a sol-gel method and a solid phase or wet phase ball milling method to form a carbon composite vanadium fluorophosphate-based compound, so that the conductivity of the material is improved to a certain extent, and the rate capability and the effective capacity of the battery are improved. However, the above method still has the defects that the sol-gel method needs to select water or ethanol or a mixture as a solvent, the solvent needs to fully dissolve and stir the raw materials at a temperature of about 100 ℃, and then the raw materials are dried and ground to form a primary process, and the carbon composite product is formed by sintering the raw materials at a high temperature for a long time in an inert atmosphere and slowly cooling the raw materials in a later stage; the high-energy ball milling is needed to reduce the particle size of raw materials and promote the mixing of the raw materials in the early stage of solid phase ball milling or wet phase ball milling, and the carbon composite product is formed by long-time high-temperature sintering and slow cooling in inert atmosphere in the later stage. The early-stage mixing of the two preparation methods is low-temperature liquid phase mixing or solid phase mixing, the mixing is insufficient, and the formed intermediate is V⁴⁺And V³⁺A mixed valence state of (a); in the later-stage high-temperature sintering process of the intermediate, on one hand, the intermediate is accompanied with the reduction reaction of vanadium with valence 4, on the other hand, a carbon composite process occurs, so that the particle size of a carbon composite compound sintered into a phase is large, generally in a micron level, and the appearance is irregular. In addition, the high-temperature sintering process is subjected to a slow cooling process, and the generated product is easy to generate side reaction (the product is decomposed into VF gas) at about 500 ℃, so that the purity of the prepared product is reduced.

Disclosure of Invention

Based on the background technology, the invention provides a method for preparing a nano flaky vanadium-based polyanionic electrode material by one-step high-temperature melting, raw materials are reacted under the high-temperature melting, a complex process in the early stage is not needed, the raw materials are directly melted and mixed in a liquid state at high temperature, the raw materials are mixed at a molecular level, the mixing is fully and uniformly, meanwhile, the reaction energy barrier is reduced at high temperature, and the nano flaky carbon composite vanadium-based polyanionic compound with uniform distribution can be obtained by rapid reaction; because the product after high-temperature sintering is rapidly cooled in inert gas, the decomposition of the vanadium fluorophosphate polyanion compound is avoided in the high-temperature process, and the product has high purity. The initial specific capacity of the assembled battery is close to the theoretical specific capacity, and the multiplying power performance of the battery is greatly improved. The method provides a new strategy for the efficient synthesis of the high-performance vanadium fluorophosphate polyanion compound and the application of the high-performance vanadium fluorophosphate polyanion compound in the sodium-ion battery.

In order to solve the technical problems, the invention adopts the following specific technical scheme:

the invention provides a method for preparing a vanadium-based polyanion compound by a one-step method, which specifically comprises the following steps:

(1) mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a sodium source or a lithium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

(2) and (2) placing the reaction product in the step (1) in an inert atmosphere for rapid cooling for 30s-5min at the cooling temperature of 0-40 ℃ to obtain the vanadium-based polyanion compound.

Based on the technical scheme, preferably, the cooled product is placed in a high-energy ball mill for high-speed ball milling at the rotating speed of 300-.

Based on the above technical scheme, preferably, when the vanadium-based polyanionic compound is sodium vanadium monofluorophosphate (NaVPO)₄F) Mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a sodium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

the molar ratio of the sodium source to the vanadium source to the phosphorus source to the fluorine source is 1-1.2: 1:1: 1-1.5;

the mass of the carbon source is 30-60% of the total mass of the vanadium source, the sodium source, the fluorine source and the phosphorus source.

Based on the above technical scheme, preferably, when the vanadium-based polyanionic compound is lithium vanadium monofluorophosphate (LiVPO)₄F) Mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a lithium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

the stoichiometric ratio of the lithium source, the vanadium source, the phosphorus source and the fluorine source is 1-1.2: 1:1: 1-1.5;

the mass of the carbon source is 30-60% of the total mass of the vanadium source, the lithium source, the fluorine source and the phosphorus source.

Based on the technical scheme, preferably, when the vanadium-based polyanionic compound is sodium vanadium triphosphate Na₃V₂(PO₄)₂F₃Mixing a vanadium source, a phosphorus source, a carbon source, a fluorine source and a sodium source, and keeping the mixture at the temperature of 600-1000 ℃ for 1-10 h in an inert atmosphere;

the stoichiometric ratio of the sodium source to the vanadium source to the phosphorus source to the fluorine source is 3-3.5: 2:2: 3-3.8.

The mass of the carbon source is 30-60% of the total mass of the vanadium source, the sodium source, the fluorine source and the phosphorus source.

Based on the technical scheme, preferably, the inert atmosphere gas is one or a mixture of helium and nitrogen;

the sodium source is one or a mixture of sodium hydroxide, sodium carbonate, sodium bicarbonate and sodium fluoride;

the vanadium source is one or a mixture of more of ammonium metavanadate, vanadium pentoxide, ammonium polyvanadate, vanadium trioxide and vanadium dioxide;

the phosphorus source is one or a mixture of more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid;

the carbon source is one or a mixture of more of citric acid, oxalic acid, ascorbic acid, glucose, sucrose, fructose and polyethylene glycol;

the fluorine source is one or a mixture of more of hydrogen fluoride, lithium fluoride, sodium fluoride and polytetrafluoroethylene.

Based on the technical scheme, preferably, the vanadium source is one or a mixture of ammonium metavanadate, vanadium pentoxide and ammonium polyvanadate.

The invention also provides a vanadium-based polyanion compound prepared by the preparation method.

The invention also provides an application of the vanadium-based polyanion compound, and the vanadium-based polyanion compound is used as a positive electrode material in a lithium ion battery or a sodium ion battery.

Advantageous effects

(1) The invention provides a method for preparing a nano flaky vanadium-based polyanionic electrode material by one-step high-temperature melting, raw materials are reacted under the high-temperature melting, a previous complex process is not needed, the raw materials are directly mixed in a molten liquid state at high temperature, the raw materials are mixed at a molecular level, the mixing is fully and uniformly, meanwhile, the reaction energy barrier is reduced at high temperature, and the nano flaky carbon composite vanadium-based polyanionic compound with uniform distribution can be quickly obtained by reaction.

(2) Compared with the common natural cooling, the invention can avoid the decomposition of the obtained product, namely the vanadium fluorophosphate polyanion compound in the high-temperature process, such as: NVPF and LVPF materials are decomposed into NVP/LVP and VF gases in a high-temperature process; on the other hand, the oxidation of the coated carbon in the air is avoided, so that the synthesized vanadium fluorophosphate polyanion compound material has a purer crystal phase and high actual specific capacity in application.

(3) The initial specific capacity of the battery assembled by the vanadium-based polyanion compound is close to the theoretical specific capacity, the multiplying power performance of the battery is greatly improved due to the small particles of the vanadium-based polyanion compound material and the uniform coating of the surface of the vanadium-based polyanion compound material on the high-conductivity carbon layer, and the method provides a new strategy for the efficient synthesis of the high-performance vanadium-based polyanion compound and the application of the high-performance vanadium-based polyanion compound in the sodium ion battery.

Drawings

FIG. 1 is SEM pictures of example 1(a), comparative example 1(c), comparative example 2(d), and comparative example 3 (b);

fig. 2 is XRD patterns of example 1, comparative example 2, and comparative example 3.

Detailed Description

Example 1

LiVPO₄[email protected]：

Uniformly mixing 0.06mol of lithium hydroxide, 0.06mol of ammonium metavanadate, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, then placing the mixture in a corundum crucible, placing the corundum crucible in a tubular furnace with a helium atmosphere at 850 ℃, keeping the temperature for 3 hours, and calcining at high temperature; and then placing the reaction product in a helium atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃. Then placing the obtained product in a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h to obtain LiVPO₄F @ C powder;

example 2

NaVPO₄[email protected]：

Uniformly mixing 0.06mol of sodium hydroxide, 0.06mol of ammonium metavanadate, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, then placing the mixture in a corundum crucible, placing the corundum crucible in a tubular furnace with a helium atmosphere at 850 ℃, keeping the temperature for 5 hours, and calcining at high temperature; and then placing the reaction product in a helium atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃. Then putting the obtained product into a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h, and then obtaining NaVPO₄F @ C powder;

example 3

Na₃V₂(PO₄)₂F₃@C

Uniformly mixing 0.06mol of sodium hydroxide, 0.04mol of ammonium metavanadate, 0.04mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.04mol of citric acid, placing the mixture in a corundum crucible, and then placing the corundum crucible into a tubular furnace which is at 850 ℃ and is filled with helium atmosphere to keep the temperature for 5 hours for high-temperature calcination; and then placing the reaction product in a helium atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃. Then putting the obtained product into a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h to obtain Na₃V₂(PO₄)₂F₃@ C powder;

example 4

LiVPO₄[email protected]：

Uniformly mixing 0.06mol of lithium hydroxide, 0.06mol of ammonium metavanadate, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, then placing the mixture in a corundum crucible, placing the corundum crucible in a 600 ℃ tubular furnace with helium atmosphere, and keeping the temperature for 3 hours to perform high-temperature calcination; and then placing the reaction product in a helium atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃. Then placing the obtained product in a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h to obtain LiVPO₄F @ C powder;

example 5

LiVPO₄[email protected]：

Uniformly mixing 0.06mol of lithium hydroxide, 0.06mol of ammonium metavanadate, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, then placing the mixture in a corundum crucible, placing the corundum crucible in a tubular furnace with 1000 ℃ and helium atmosphere, and keeping the temperature for 3 hours to perform high-temperature calcination; and then placing the reaction product in a helium atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃. Then placing the obtained product in a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h to obtain LiVPO₄F @ C powder;

comparative example 1

Preparation of LiVPO by sol-gel method₄[email protected]：

Uniformly mixing 0.06mol of lithium hydroxide, 0.06mol of ammonium metavanadate, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, putting the mixture into a 500ml beaker, adding 250ml of deionized water to dissolve the mixture to form dark blue sol, and putting the obtained sol into a water bath kettle at the temperature of 90 ℃ to heat and stir for 12 hours to form blue-green gel; putting the obtained gel-state substance into a 100-degree oven, drying for 12h, taking out water, and grinding and crushing to form a reaction precursor; then placing the obtained precursor into a 350-degree oven for pre-sintering, taking out and grinding for 30min to obtain a reaction intermediate; then placing the mixture into a tube furnace with the atmosphere of helium gas at 850 ℃ for high-temperature sintering for 8h, and taking out the product after the product is slowly cooled to room temperature in the tube furnace to obtain LiVPO₄F @ C powder;

comparative example 2

Preparation of LiVPO by solid-phase ball milling method₄[email protected]：

Uniformly mixing 0.03mol of vanadium pentoxide, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of lithium fluoride and 0.06mol of citric acid, putting the mixture into a high-energy ball mill, carrying out high-speed ball milling for 5 hours at the ball milling rotating speed of 500r/min, taking out the ball-milled material, putting the ball-milled material into a 350-DEG C oven for presintering, taking out the material after the material is slowly cooled to the room temperature in a tubular furnace, and grinding the material for 30 minutes to obtain a reaction intermediate; then placing the reaction intermediate into a tube furnace with helium atmosphere at 850 ℃ for high-temperature sintering for 8h, and taking out the product after slowly cooling the product to room temperature in the tube furnace to obtain LiVPO₄F @ C powder;

comparative example 3LiVPO₄[email protected]：

Uniformly mixing 0.06mol of lithium hydroxide, 0.06mol of ammonium metavanadate, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, then placing the mixture into a tubular furnace which is filled with a corundum crucible and is filled with helium gas at 850 ℃ for constant-temperature heat preservation for 3 hours for high-temperature calcination, and taking out the material after the material is slowly cooled (5 ℃ per minute) to room temperature in the tubular furnace; placing the obtained product in a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h, and then obtaining the LiVPO₄F @ C powder;

comparative example 4

NaVPO₄[email protected]：

Uniformly mixing 0.06mol of sodium hydroxide, 0.06mol of ammonium metavanadate, 0.06mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, then placing the mixture into a tubular furnace which is filled with a corundum crucible and is filled with helium gas at 850 ℃ for constant-temperature heat preservation for 3 hours for high-temperature calcination, and taking out the material after the material is slowly cooled (5 ℃ per minute) to room temperature in the tubular furnace; placing the obtained product in a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h, and then obtaining the NaVPO₄F @ C powder;

comparative example 5

Na₃V₂(PO₄)₂F₃@C：

Uniformly mixing 0.06mol of sodium hydroxide, 0.04mol of ammonium metavanadate, 0.04mol of ammonium dihydrogen phosphate, 0.06mol of ammonium fluoride and 0.06mol of citric acid, then placing the mixture into a tubular furnace which is filled with a corundum crucible and is filled with helium gas at 850 ℃ for constant-temperature heat preservation for 3 hours for high-temperature calcination, and taking out the material after the material is slowly cooled (5 ℃ per minute) to room temperature in the tubular furnace; placing the obtained product in a high-energy ball mill for high-speed ball milling at the rotating speed of 600r/min for 12h, and then obtaining Na₃V₂(PO₄)₂F₃And (3) powder.

Description of the embodiments

Examples 1(LVPF) and comparative examples 1 (sol gel), 2 (solid phase ball milling), 3 (high temperature melting-slow cooling) were all LiVPO₄According to the SEM image of FIG. 1, the preparation method of F @ C shows that example 1 and comparative example 3 prepared by the method are relatively regular nano flaky shapes, and comparative example 1 and comparative example 2 prepared by sol-gel and solid-phase ball milling are micron-sized particles and have relatively serious particle agglomeration. According to the analysis of XRD result in figure 2, LiVPO prepared by the invention₄F @ C (example 1) has very high purity and is substantially free of impurity peaks, but impurity peaks of lithium vanadium phosphate (impurity peaks are shown by oval circles in FIG. 2) are observed in comparative examples 1, 2 and 3, mainly due to the sol-gel method, the solid-phase ball milling method and the LiVPO prepared by high-temperature melting-slow cooling₄F @ C undergoes slow cooling after high-temperature sinteringThe LiVPO is very easy to occur in the process of cooling to about 400-₄F is decomposed into VF gas and LVP side reaction, the slower the temperature reduction is, the more serious the side reaction is, so that the prepared LiVPO₄The F @ C crystal phase was not pure and more LVP impurities appeared. Thus, the capacity and rate performance of the cells assembled from the electrodes of example 1 and comparative examples 1, 2, and 3 are shown differently, with example 1 having an effective specific capacity of 145mAg/g at 0.1C, while comparative examples 1, 2, and 3 having specific capacities of only 110mAh/g, 106mAh/g, and 120mAh/g, respectively, at 0.1C due to the presence of more impurities; since example 1 is a nano-platelet, the charge transfer path is reduced, and the resistance is smaller than that of comparative examples 1 and 2, thus having higher rate capability, at a high rate of 5C, example 1 still has a specific capacity of 131mAh/g, while comparative examples 1 and 2 only have specific capacities of 70mAh/g and 82 mAh/g.

Likewise, example 2(NVPF) and comparative example 4 (high temperature melt-slow cool) are both NaVPO₄Preparation method of F @ C, since the preparation of the invention and the preparation of the comparative example 4 both undergo a high-temperature liquid-phase melting process, the NaVPO obtained is prepared₄F @ C are all in a nano-sheet shape; however, according to the analysis of XRD crystal phase, the NaVPO prepared by the invention₄F @ C (example 2) had a very high purity with essentially no impurity peaks, but impurity peaks were observed for sodium vanadium phosphate in comparative example 4. The capacity of the cells assembled from the electrodes of example 2 and comparative example 4 are shown differently, with example 2 having an effective specific capacity of 138mAg/g at 0.1C, while comparative example 4 has a specific capacity of only 108 mAh/g;

likewise, example 3(NVPF3) and comparative example 5 (high temperature melt-slow cool) are both Na₃V₂(PO₄)₂F₃Production method of @ C, since production of the present invention and that of comparative example 5 were both subjected to a high-temperature liquid-phase melting process, Na was produced₃V₂(PO₄)₂F₃@ C is in the shape of nano-sheet; however, according to the analysis of XRD crystal phase, the Na prepared by the invention₃V₂(PO₄)₂F₃@ C (example 3) has very high purity, essentially no impurity peaks, but impurity peaks of sodium vanadium phosphate are observed for comparative example 5. Cell capacity assembled from electrodes of example 3 and comparative example 5The capacity performance was different, with example 3 having an effective specific capacity of 125mAg/g at 0.1C, while comparative example 5 has a specific capacity of only 105 mAh/g;

examples 1, 4, 5(LVPF prepared by sintering at different temperatures) and comparative example 3 (high temperature melting-slow cooling) are all LiVPO₄The preparation method of F @ C, in the preparation process of the invention, nano-flaky LiVPO is obtained under the conditions of sintering temperatures of 600, 850 and 1000 DEG C₄F @ C, and the analysis of the XRD crystal phase shows that the LiVPO prepared by the method₄F @ C (examples 1, 4, 5) all had a higher purity with essentially no impurity peaks, whereas impurity peaks for lithium vanadium phosphate were observed for comparative example 3. The capacity of the cells assembled from the electrodes of examples 1, 4, 5 and comparative example 3 are shown differently, the cells assembled from the electrodes of examples 1, 4, 5 have effective specific capacities of 145mAh/g, 141mAh/g, 149mAh/g, respectively, at 0.1C, while comparative example 3 has a specific capacity of only 120 mAh/g.