阅读说明：本技术 一种氟磷钒酸锂的制备方法及应用 (Preparation method and application of lithium fluorophosphates vanadate ) 是由 郑琼 李先锋 韩建鑫 凌模翔 张华民 于 2019-11-27 设计创作，主要内容包括：本发明提供一种氟磷钒酸锂的制备方法及应用,本发明提出一种两步法制备碳复合均匀、颗粒尺寸均匀的高纯相碳包覆NVPF材料。本发明制备方法第一步将V～(5+)完全还原成V～(3+)的单一反应,第二步将第一步得到的均匀且碳包覆均匀的纳米V-2O-3@C粉末作为前驱体和P源、F源、Na源高温烧结成相,第三步是快速冷却,本发明制备方法在第二步高温烧结后将反应产物置于惰性气氛下快速冷却,一方面避免了得到的产物LiVPO-4F在高温过程的分解,获得的LiVPO-4F具有高的纯度,在应用的时候,实际比容量高；另一方面,也避免了包覆的碳在空气中的氧化,使得合成的LiVPO-4F表面包覆有均匀的碳层,有利于材料电导率和有效比容量的提升。(The invention provides a preparation method and application of lithium fluorophosphates vanadate, and provides a two-step method for preparing a high-purity carbon-coated NVPF material with uniform carbon compounding and uniform particle size. The preparation method of the invention comprises the first step of mixing V 5+ Is completely reduced into V 3+ The second step is to obtain the uniform nano V with uniform carbon coating 2 O 3 The @ C powder is used as a precursor, and is sintered into a phase with a P source, an F source and a Na source at a high temperature, the third step is rapid cooling, and the method is implementedIn the preparation method, after the second step of high-temperature sintering, the reaction product is placed in an inert atmosphere for rapid cooling, so that the obtained product LiVPO is avoided 4 Decomposition of F in a high temperature process to obtain LiVPO 4 F has high purity and high actual specific capacity when applied; on the other hand, oxidation of the coated carbon in air is also avoided, so that the synthesized LiVPO 4 The surface of the F is coated with a uniform carbon layer, which is beneficial to the improvement of the conductivity and the effective specific capacity of the material.)

1. The preparation method of the carbon composite vanadium lithium fluorophosphate electrode material is characterized by comprising the following steps of:

(1) stirring a vanadium source and a carbon source in a solvent at the temperature of 60-90 ℃ for 1-12 h to obtain a mixed solution; drying the mixed solution, and then preserving the heat for 4-24h at the temperature of 600-;

(2) mixing a fluorine source, a phosphorus source, a lithium source and the carbon composite vanadium trioxide, and then preserving the heat for 4-48 at the temperature of 600-1000 ℃ in a non-oxygen atmosphere;

(3) and (3) placing the reaction product obtained in the step (2) in an inert atmosphere for cooling for 30s-5min at the cooling temperature of 0-40 ℃, taking out, crushing and grinding to obtain the carbon composite lithium vanadium fluorophosphate powder.

2. The method according to claim 1, wherein the mass of the carbon source in the step (1) is 30-60% of the mass of the vanadium source.

3. The preparation method according to claim 1, wherein the molar ratio of the fluorine source, the phosphorus source, the lithium source and the carbon composite vanadium trioxide in the step (2) is 0.95-1.05: 1: 0.5.

4. The preparation method according to claim 1, wherein the solvent in step (1) is one or more of water, ethanol, ethylene glycol and butanol.

5. The preparation method according to claim 1, wherein the mass ratio of the solvent to the solid content in the mixed solution in the step (1) is 2-20: 1.

6. The production method according to claim 1,

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

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

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

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

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

7. The preparation method according to claim 1, wherein the non-oxygen atmosphere in step (1) and step (2) is one or a mixture of helium, nitrogen, ammonia and hydrogen.

8. A vanadium lithium fluorophosphate electrode material prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the vanadium lithium fluorophosphate electrode material according to claim 8 in a lithium ion battery.

Technical Field

The invention belongs to the technical field of lithium ion battery electrode materials, and particularly relates to a preparation method and application of lithium fluorophosphates vanadate.

Background

The positive electrode material of a lithium ion battery is the key to determining 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, lithium vanadium fluorophosphate (LiVPO)₄F, abbreviated as LVPF) has a high voltage (4.2V), a high theoretical specific capacity (153mAh/g), a stable structure and is receiving much attention. 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 to form a carbon composite lithium vanadium fluorophosphate compound by a sol-gel method and a solid phase or wet phase ball milling method, 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, in the traditional process of preparing lithium vanadium fluorophosphate by high-temperature sintering, firstly, a sol-gel method is adopted to mix a high-valence vanadium source, a reducing agent, a carbon source, a fluorine source and a phosphorus source together in a liquid phase, mechanical stirring is carried out at a lower temperature (at 100 ℃), namely, a sol-gel reaction process is carried out, finally, a blue-green gel is formed, after drying, impurities are dehydrated under a more than 300 ℃ environment for pre-sintering, and then, the high-temperature sintering is carried out in a range of 600 ℃ and 1000 ℃ to form a phase. Since the sol-gel process is accompanied by some reduction, part of V⁵⁺Is reduced into V⁴⁺The reaction is incomplete due to the lower reaction temperature. So that the precursor for high-temperature sintering is V⁴⁺/V³⁺Of a mixture of (A) and (B), V being generated during high-temperature sintering⁴⁺Reduction to V³⁺Process for growth into LVPF phase, (V)⁴⁺Reduction to V³⁺The reaction only has 1 step, and the carbon coating is carried out firstlyCovering with V³⁺Direct carbon coating) results in uneven carbon coating on the surface of the generated LVPF, and different particle sizes of the products; on the other hand, the conventional high-temperature sintering preparation is subjected to a high-temperature sintering phase formation process within the range of 600-1000 ℃ at the later stage and then needs to be subjected to a slow cooling process, so that the generated LVPF @ C generates a side reaction (LiVPO) at about 500 DEG₄F is very prone to decompose into lithium vanadium phosphate and VF gas), resulting in a reduction in the purity of the LVPF product produced.

Disclosure of Invention

Based on the above background technology, the invention provides a preparation method of high-purity carbon composite lithium vanadium fluorophosphate, which comprises the following steps:

(1) mixing a vanadium source and a carbon source in a solvent, and stirring at 60-90 ℃ for 1-12 h to obtain a mixed solution; drying the mixed solution, and then placing the dried mixed solution into a 600-1000 ℃ tubular furnace filled with a non-oxygen atmosphere for constant temperature heat preservation for 4-24h to obtain carbon composite vanadium trioxide;

(2) uniformly mixing a fluorine source, a phosphorus source, a lithium source and the carbon composite vanadium trioxide (solid phase mixing or liquid phase mixing), and placing the mixture into a 600-plus-1000 ℃ tubular furnace filled with a non-oxygen atmosphere for constant temperature and heat preservation for 4-48 h;

(3) and (3) placing the reaction product obtained in the step (2) in an inert atmosphere for cooling for 30s-5min at the cooling temperature of 0-40 ℃, and then taking out, crushing and grinding to obtain the carbon composite lithium vanadium fluorophosphate.

Based on the technical scheme, the mass of the carbon source is 30-60% of that of the vanadium source;

the molar ratio of the fluorine source to the phosphorus source to the lithium source to the carbon composite vanadium trioxide is 0.95-1.05: 1: 0.5;

wherein the solvent is one or more of water, ethanol, glycol and butanol;

in the mixed solution, the mass ratio of the solvent to the solid content is 2-20: 1;

the vanadium source is a high-valence vanadium source, and is preferably one or a mixture of ammonium metavanadate, vanadium pentoxide and ammonium polyvanadate;

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

the lithium source is one or a mixture of more of lithium hydroxide, lithium carbonate and lithium fluoride;

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

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

the non-oxygen atmosphere is one or a mixture of helium, nitrogen or ammonia and hydrogen;

based on the technical scheme, the invention also provides the carbon composite vanadium lithium fluorophosphate electrode material prepared by the preparation method. The invention also provides an application of the fluorophosphoric acid vanadium lithium electrode material in a lithium ion battery.

Advantageous effects

(1) The first step of the preparation method of the invention is to ensure V⁵⁺Is completely reduced into V³⁺Due to the fact that the reaction sources are all V⁵⁺The reaction rates are basically consistent everywhere, and the obtained V³⁺The size of the intermediate is consistent; simultaneously, a carbon source is simultaneously introduced in the first step, and V is obtained under the condition of consistent reaction₂O₃The @ C particles are quite uniform and are in the shape of nano-particles; the second step is to coat the uniform nano V obtained in the first step with carbon₂O₃The @ C powder is used as a precursor, and is sintered into a phase with a P source, an F source and an Na source at a high temperature, the P source, the F source and the Na source are in a liquid-phase molten state at a high temperature and are uniformly mixed, the obtained product is uniformly distributed particles, and on the other hand, the particle size of the obtained product can be ensured within the nano-particle size range due to the inhibition of the carbon coating layer. Aiming at the problems of non-uniform carbon coating and non-uniform particle size of a product in the high-temperature sintering process, the invention provides a two-step method for preparing a carbon-coated NVPF material with uniform carbon composition and uniform particle size.

(2) Compared with the ordinary slow cooling, the rapid cooling under the inert atmosphere avoids the LiVPO product₄Decomposition of F in a high temperature process (LiVPO)₄F decomposes at about 500 ℃ to form Li₃V₂(PO₄)₃And VF gas), the obtained LiVPO₄F has high purity and high actual specific capacity when applied; on the other hand, oxidation of the coated carbon in air is also avoided, so that the synthesized LiVPO₄The surface of the F is coated with a uniform carbon layer, which is beneficial to the improvement of the conductivity and the effective specific capacity of the material.

Drawings

FIG. 1 is an SEM photograph of examples 1, 2, 4, 6 and comparative examples 3, 4; (a) example 1; (b) example 2; (c) example 4; (d) example 6; (e) comparative example 3; (f) comparative example 4.

Fig. 2 is an XRD pattern of example 1 and comparative examples 1, 2, and 3.

Detailed Description

Example 1

V₂O₃@ C-solid phase high temperature melting-LVPF @ C-fast cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in water, and stirring at 80 ℃ for 10 hours to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and the resultant V₂O₃Mixing and grinding the @ C solid phase, and then placing the mixture into a tube furnace with 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours; then taking out the reaction product immediately, placing the reaction product in argon atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃, then taking out the reaction product, and crushing and grinding the reaction product to obtain LiVPO₄[email protected]。

Example 2

V₂O₃Mixing @ C-liquid phase, drying, and high-temperature sintering-LVPF @ C-quick cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in 100ml of water, and stirring for 10 hours at 80 ℃ to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g ofg ammonium dihydrogen phosphate, 1.198g lithium hydroxide and the resulting V₂O₃@ C is put into 100ml of water together to be heated, stirred and mixed, the heating temperature is 90 ℃, the stirring time is 6 hours, then the mixed solution is put into a 100-DEG oven to be dried for 24 hours, then the mixed solution is taken out, ground and crushed and then put into a tube furnace with 750 ℃ and argon atmosphere to be kept at constant temperature for 8 hours; then taking out the reaction product immediately, placing the reaction product in argon atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃, then taking out the reaction product, and crushing and grinding the reaction product to obtain LiVPO₄[email protected]。

Example 3

V₂O₃@ C (600 degrees) -solid phase high temperature melting-LVPF @ C-quick cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in 100ml of water, and stirring for 10 hours at 80 ℃ to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 600 ℃ and argon atmosphere for constant temperature heat preservation for 10 hours to obtain black V₂O₃@ C; wherein the mass of the citric acid is 50 percent of the mass of the ammonium metavanadate; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and the resultant V₂O₃Mixing and grinding the @ C solid phase, and then placing the mixture into a tube furnace with 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours; then taking out the reaction product immediately, placing the reaction product in argon atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃, then taking out the reaction product, and crushing and grinding the reaction product to obtain LiVPO₄[email protected]。

Example 4

V₂O₃@ C (1000 degree) -solid phase high temperature melting-LVPF @ C-quick cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in 100ml of water, and stirring for 10 hours at 80 ℃ to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 1000 ℃ and argon atmosphere for constant temperature heat preservation for 6 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and the resultant V₂O₃Mixing and grinding the @ C solid phase, and then placing the mixture into a tube furnace with 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours; subsequently subjecting the reaction product toImmediately taking out, placing in an argon atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃, then taking out a reaction product, and crushing and grinding to obtain LiVPO₄[email protected]。

Example 5

V₂O₃@ C-solid phase high temperature melting (600 degree) -LVPF @ C-fast cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in 100ml of water, and stirring for 10 hours at 80 ℃ to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and the resultant V₂O₃Mixing and grinding the @ C solid phase, and then placing the mixture into a tube furnace with 600 ℃ and argon atmosphere for constant temperature preservation for 10 hours; then taking out the reaction product immediately, placing the reaction product in argon atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃, then taking out the reaction product, and crushing and grinding the reaction product to obtain LiVPO₄[email protected]。

Example 6

V₂O₃@ C (600 degrees) -solid phase high temperature melting (1000 degrees) -LVPF @ C-quick cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in 100ml of water, and stirring for 10 hours at 80 ℃ to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and the resultant V₂O₃Mixing and grinding the @ C solid phase, and then placing the mixture into a tube furnace with 1000 ℃ and argon atmosphere for constant temperature preservation for 6 hours; then taking out the reaction product immediately, placing the reaction product in argon atmosphere for rapid cooling for 1min at the cooling temperature of 25 ℃, then taking out the reaction product, and crushing and grinding the reaction product to obtain LiVPO₄[email protected]。

Comparative example 1

V₂O₃@ C-solid phase high temperature melting-LVPF @ C-slow cooling

5.85g of ammonium metavanadate anddissolving 2.9g of citric acid in water, mixing, and stirring at 80 ℃ for 10 hours to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and the resultant V₂O₃Mixing and grinding the @ C solid phase, and then placing the mixture into a tube furnace with 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours; then slowly cooling the reaction product in a tubular furnace at a cooling rate of 5 ℃ per minute, taking out the product after cooling to room temperature, and grinding the powder to obtain LiVPO₄[email protected]。

Comparative example 2

V₂O₃Mixing @ C-liquid phase, drying, and sintering at high temperature-LVPF @ C-slow cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in 100ml of water, and stirring for 10 hours at 80 ℃ to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and the resultant V₂O₃@ C is put into 100ml of water together to be heated, stirred and mixed, the heating temperature is 90 ℃, the stirring time is 6 hours, then the mixed solution is put into a 100-DEG oven to be dried for 24 hours, then the mixed solution is taken out, ground and crushed and then put into a tube furnace with 750 ℃ and argon atmosphere to be kept at constant temperature for 8 hours; then slowly cooling the reaction product in a tubular furnace at a cooling rate of 5 ℃ per minute, taking out the product after cooling to room temperature, and grinding the powder to obtain LiVPO₄[email protected]。

Comparative example 3

Conventional sol-gel method-LVPF @ C-slow cooling

Dissolving and mixing 5.85g of ammonium metavanadate, 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide and 2.9g of citric acid in 100ml of water, and stirring at 80 ℃ for 10 hours to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tubular furnace with 350 ℃ and argon atmosphere for constant temperature and heat preservation for 5 hours for pre-carbonization to obtain an intermediate; taking out the intermediate, grinding, placing in an argon atmosphere at 750 DEG CKeeping the temperature of the tube furnace for 8 hours at constant temperature; then slowly cooling the reaction product in a tubular furnace at a cooling rate of 5 ℃ per minute, taking out the reaction product after cooling to room temperature, and grinding to obtain LiVPO₄[email protected]。

Comparative example 4

V₂O₃Mixing @ C (first carbon coating) -liquid phase (adding carbon source, second carbon coating), drying, and sintering at high temperature-LVPF @ C @ C-slow cooling

Dissolving and mixing 5.85g of ammonium metavanadate and 2.9g of citric acid in 100ml of water, and stirring for 10 hours at 80 ℃ to obtain a mixed solution; drying the mixed solution, grinding the obtained powder, and placing the powder into a tube furnace with the temperature of 750 ℃ and argon atmosphere for constant temperature and heat preservation for 8 hours to obtain black V₂O₃@ C; 1.85g of ammonium fluoride, 5.75g of ammonium dihydrogen phosphate, 1.198g of lithium hydroxide, 0.65g of sucrose and the resultant V₂O₃@ C is put into 100ml of water together to be heated, stirred and mixed, the heating temperature is 90 ℃, the stirring time is 6 hours, then the mixed solution is put into a 100-DEG oven to be dried for 24 hours, then the mixed solution is taken out, ground and crushed and then put into a tube furnace with 750 ℃ and argon atmosphere to be kept at constant temperature for 8 hours; then slowly cooling the reaction product in a tubular furnace at a cooling rate of 5 ℃ per minute, taking out the reaction product after cooling to room temperature, and grinding to obtain LiVPO₄[email protected]。

Description of the embodiments

Examples 1, 3, 4, 5 and 6 of the present invention are all V prepared by a sol-gel method₂O₃After the @ C is subjected to solid-phase mixing and high-temperature sintering, the LiVPO is quickly cooled and prepared₄F @ C material. From the SEM picture (FIG. 1), it can be seen that the preparation of V by the sol-gel method is changed₂O₃The sintering temperature of @ C (600 degrees, 750 degrees and 1000 degrees) or the solid-phase mixing high-temperature sintering temperature (600 degrees, 750 degrees and 1000 degrees) can obtain LiVPO of the nano-particles₄F @ C material. And the reaction product is rapidly cooled to room temperature in inert atmosphere after being sintered at high temperature, so that LiVPO is effectively avoided₄F is decomposed into lithium vanadium phosphate and VF gas at about 500 ℃ to obtain LiVPO₄XRD of F @ C is essentially free of impurity phases. The coated carbon is also sufficiently protected due to the protection of the inert atmosphere, so thatThe uniformly coated carbon prepared from sol-gel was well preserved. The specific capacities of the lithium ion battery assembled by the electrode at 0.1C are respectively 135mAh/g, 142mAh/g, 145mAh/g, 138mAh/g, 151mAh/g and 148mAh/g, and the specific capacities of 115mAh/g, 128mAh/g, 120mAh/g, 118mAh/g, 130mAh/g and 126mAh/g are respectively realized at a high multiplying power of 5C. The excellent battery performance is shown.

Examples 1, 2 (melt + fast cool after mixing solid and liquid phases):

examples 1 and 2 are the preparation of V by the sol-gel method₂O₃The LiVPO is prepared by mixing solid phase and liquid phase after @ C, sintering at high temperature and quickly cooling₄F @ C material. As can be seen from the SEM image, the LiVPO of the nanoparticles can be obtained by changing the solid phase or liquid phase mixing mode₄F @ C material. In both examples 1 and 2, the reaction product is rapidly cooled to room temperature in an inert atmosphere after being sintered at high temperature, so that LiVPO is effectively avoided₄F is decomposed into lithium vanadium phosphate and VF gas at about 500 ℃ to obtain LiVPO₄The XRD of F @ C is substantially free of diffraction peaks of the hetero-phase. Because of the protection of the inert atmosphere, the coated carbon is also fully protected, so that the uniformly coated carbon prepared by the sol-gel is well preserved. The lithium ion batteries assembled from the electrodes of examples 1 and 2 had specific capacities of 135mAh/g and 143mAh/g at 0.1C, and 115mAh/g and 125mAh/g at a high rate of 5C, respectively, and exhibited excellent battery performance.

Example 1 and comparative example 1: (solid phase + fast and slow Cooling)

Example 1 and comparative example 1 are both V prepared by a sol-gel process₂O₃After @ C is subjected to solid-phase mixing and high-temperature sintering, the obtained LiVPO is prepared₄F @ C material. However, example 1 was rapidly cooled to room temperature in an inert atmosphere, and comparative example 1 was slowly cooled to room temperature in an inert atmosphere, since LiVPO occurred while the reaction product was slowly cooled in an inert atmosphere₄F decomposed to lithium vanadium phosphate and VF gas at around 500 degrees, so that LiVPO obtained in comparative example 1₄The XRD of F @ C has more impurity phases, so that the effective specific capacity of the material is lower. Lithium ion batteries assembled from the electrodes of example 1 and comparative example 1The specific capacity at 0.1C is 135mAh/g and 112mAh/g respectively.

Example 2 and comparative example 2: (liquid phase + fast slow cooling):

example 2 and comparative example 2 were both prepared by a sol-gel method to obtain V₂O₃The LiVPO is prepared after the @ C is mixed with liquid phase and sintered at high temperature₄F @ C material. However, example 2 was rapidly cooled to room temperature in an inert atmosphere, and comparative example 2 was slowly cooled to room temperature in an inert atmosphere, since LiVPO occurred while the reaction product was slowly cooled in an inert atmosphere₄F decomposed to lithium vanadium phosphate and VF gas at around 500 degrees, so that LiVPO obtained in comparative example 2₄The XRD of F @ C has more impurity phases, so that the effective specific capacity of the material is lower. The specific capacities of the lithium ion batteries assembled from the electrodes of example 2 and comparative example 2 at 0.1C were 143mAh/g and 105mAh/g, respectively.

Examples 1, 2 and comparative example 3 (sol gel slow cool):

example 1, example 2 and comparative example 3 electrode prepared by conventional sol-gel method, the latter is cooled slowly to room temperature in inert atmosphere after the second high temperature sintering, because the reaction product is cooled slowly in inert atmosphere and side reaction of LiVPO4F decomposing into lithium vanadium phosphate and VF gas at about 500 degree, so that the XRD of LiVPO4F @ C obtained in comparative example 3 has more impurity phase and impure crystalline phase. And since the first step of the sol-gel process is accompanied by a degree of reduction, part of V⁵⁺Is reduced into V⁴⁺The reaction is incomplete due to the lower reaction temperature. So that the precursor of the second high-temperature sintering is V⁴⁺/V³⁺Of a mixture of (A) and (B), V being generated during high-temperature sintering⁴⁺Reduction to V³⁺Growing into LiVPO₄Process of phase F, (V)⁴⁺Reduction to V³⁺The reaction only has 1 step, and carbon coating is firstly carried out, V³⁺Direct carbon coating) such that LiVPO is produced₄The carbon coating on the surface of F is not uniform, the particles of the product are also larger, and SEM shows that compared with the examples 1 and 2, the particles of the comparative example 3 are micron-sized, and the carbon coating is not uniform. The two reasons result in the lower effective specific capacity of the material.The specific capacities of the lithium ion batteries assembled from the electrodes of examples 1 and 2 and comparative example 3 at 0.1C were 135mAh/g, 143mAh/g and 106mAh/g, respectively.

Examples 1, 2 and comparative example 4 (double carbon coating + slow cooling):

example 1, example 2 and double carbon coated comparative example 4 electrode comparison, comparative example 4 first step achieved V₂O₃The first carbon coating is carried out, then, when ammonium fluoride and ammonium dihydrogen phosphate are added, cane sugar is added again to serve as a carbon source, and the second carbon coating of LiVPO4F @ C @ C is realized through high-temperature sintering. The increase in the thickness of the carbon coating layer of the surface of comparative example 4 to 6nm or more, compared to examples 1 and 2 (surface carbon coating layer of 3nm), causes an increase in the charge transfer resistance of the material surface, resulting in an increase in the internal resistance of the battery, causing a decrease in the rate performance of the battery. In addition, in comparative example 4, LiVPO is very likely to occur when the alloy is slowly cooled to room temperature in an inert atmosphere after being sintered at high temperature₄F decomposed to lithium vanadium phosphate and VF gas at around 500 degrees, so that LiVPO obtained in comparative example 4 was obtained₄The XRD of F @ C has more impurity phases, so that the effective specific capacity of the material is lower. The specific capacities of the lithium ion batteries assembled from the electrodes of examples 1 and 2 and comparative example 4 at 0.1C were 135mAh/g, 143mAh/g and 109mAh/g, respectively, and at a high rate of 5C, 115mAh/g, 125mAh/g and 86mAh/g, respectively. The rate performance and effective specific capacity of comparative example 4 are both reduced compared to examples 1, 2.