A coated modified lithium manganese iron phosphate lithium-ion battery cathode material

Abstract

The application discloses a coated modified lithium manganese iron phosphate lithium ion battery positive electrode material, and preparation steps thereof include the following steps: (1) preparing lithium manganese iron phosphate powder; (2) mixing pyridine and hexafluorophosphoric acid, adding lithium hydroxide and ethanol, and heating in a water bath to obtain a mixture; (3) adding an aqueous solution of indium trichloride, lithium manganese iron phosphate powder and L-malic acid into an ethanol solution of cerium nitrate and n-butyl titanate at the same time, ultrasonic dispersion is carried out, then the mixed solution is laid in a container, water and ethanol are removed by drying and evaporation, calcination is carried out at 120+5 DEG C, then the mixture and selenium acid powder are added and uniformly mixed, calcination is carried out again at 650+5 DEG C, after the completion of the calcination, air cooling is carried out to normal temperature, and the coated modified lithium manganese iron phosphate lithium ion battery positive electrode material is obtained. The positive electrode material prepared by coating and modifying lithium manganese iron phosphate according to the method can significantly improve the discharge specific capacity and capacity retention rate of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials, and particularly to a coated modified lithium manganese iron phosphate lithium-ion battery cathode material. Background Technology

[0002] The positive electrode material of a lithium-ion battery plays a crucial role in its operation, providing the ion source for lithium-ion insertion and extraction between the positive and negative electrodes. Therefore, it must possess the following characteristics: (1) a stable material structure to allow for repeated lithium-ion insertion and extraction and maintain a high cycle life; (2) a high lithium-ion insertion and extraction potential to ensure a high operating voltage output; (3) as many lithium ions as possible to achieve a high battery capacity; (4) high electronic conductivity and lithium-ion diffusion coefficient to maintain a high energy density; (5) stable electrode materials that do not react with other substances; and (6) inexpensive, non-toxic, and easy to synthesize and process. Lithium manganese iron phosphate is a commonly used positive electrode active material for lithium-ion batteries. However, due to its poor stability, lithium manganese iron phosphate requires modification to improve its electrochemical performance. Summary of the Invention

[0003] This invention provides a coated modified lithium iron phosphate lithium-ion battery cathode material, the preparation steps of which include:

[0004] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The ball mill jar is then sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling mixture is dried at 80°C for more than 5 hours to remove the ball milling slurry. Then it is calcined at 300±5°C for 2-3 hours in an argon protective atmosphere. Finally, it is calcined at 650±5°C for more than 5 hours to obtain lithium manganese iron phosphate powder.

[0005] (2) Mix pyridine and hexafluorophosphoric acid, heat in a water bath to 30±2℃ and keep warm for more than 3 hours. Stir the mixture during the heat preservation process. After the heat preservation is completed, add lithium hydroxide and ethanol to the mixture while stirring. After the addition is completed, heat in a water bath to 55±2℃ and keep warm and stir for more than 4 hours. During the heat preservation process, condense and reflux, and then air cool to room temperature to obtain the mixture.

[0006] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; prepare an aqueous solution of indium trichloride; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder and L-malic acid to the solution while stirring. After the addition is completed, stir the mixture and ultrasonically disperse it for more than 2 hours. Then spread the mixture in a container and dry it in an 80°C drying oven to evaporate and remove water and ethanol. After drying, calcine it at 120±5°C for more than 3 hours. Then add the mixture and selenic acid powder and mix evenly. Then calcine it at 650±5°C for more than 5 hours. After calcine, air cool it to room temperature to obtain the coated modified lithium manganese iron phosphate lithium-ion battery cathode material.

[0007] Further, in step (1), the mass ratio of manganese carbonate powder, ferric hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: ferric hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 90~92:20~24:120:35~40:10.

[0008] Further, in step (1), the volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1; the ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, and ball-to-material-to-liquid mass ratio is ball:material:ball milling slurry = 2:1:8.

[0009] Further, in step (2), the molar ratio of the mixture of pyridine and hexafluorophosphate is pyridine:hexafluorophosphate = 1:0.8; the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is lithium hydroxide:ethanol:pyridine = 1.2~1.5g:100mL:4g.

[0010] Further, in step (3), in the ethanol solution of cerium nitrate and tetrabutyl titanate, the concentration of cerium nitrate is 18-26 g / L, the concentration of tetrabutyl titanate is 30-35 g / L, and the solvent is ethanol; in the aqueous solution of indium trichloride, the concentration of indium trichloride is 0.1 mol / L, and the solvent is water.

[0011] Further, in step (3), the ratio of indium trichloride aqueous solution, lithium manganese iron phosphate powder and L-malic acid added to the ethanol solution of cerium nitrate and tetrabutyl titanate is 10 mL: 6-8 mL: 100 g: 1-3 g.

[0012] Further, in step (3), the mass ratio of the mixture and selenic acid powder added to the calcined product at 120±5℃ is calcined product: mixture: selenic acid powder = 100:4~6:1.

[0013] The beneficial effects of the present invention are as follows: the cathode material prepared by coating and modifying lithium manganese iron phosphate using the method described in the present invention can significantly improve the discharge specific capacity and capacity retention rate of the battery. Detailed Implementation

[0014] The present invention will be further described below with reference to the embodiments.

[0015] Example 1

[0016] A modified manganese iron phosphate lithium-ion battery cathode material, the preparation steps of which include:

[0017] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. The mass ratio of manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: iron hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 90:20:120:35:10. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1. Then the ball mill jar is sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, ball material liquid mass ratio is ball: material: ball milling slurry = 2:1:8. The ball milling mixture is dried at 80℃ for 5 h to remove the ball milling slurry. Then it is calcined at 300±5℃ for 2 h in an argon protective atmosphere and then calcined at 650±5℃ for 5 h to obtain lithium manganese iron phosphate powder.

[0018] (2) Pyridine and hexafluorophosphate are mixed, wherein the molar ratio of pyridine to hexafluorophosphate is 1:0.8; the mixture is heated in a water bath to 30±2℃ and kept at that temperature for 3 hours, and the mixture is stirred during the heating process. After the heating process is completed, lithium hydroxide and ethanol are added to the mixture while stirring, wherein the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is 1.2g:100mL:4g; after the addition is completed, the mixture is heated in a water bath to 55±2℃ and kept at that temperature for 4 hours, and the mixture is refluxed during the heating process, and then cooled to room temperature to obtain the mixture.

[0019] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; the concentration of cerium nitrate in the ethanol solution of cerium nitrate and n-butyl titanate is 18 g / L, the concentration of n-butyl titanate is 30 g / L, and the solvent is ethanol; prepare an aqueous solution of indium trichloride; the concentration of indium trichloride in the aqueous solution of indium trichloride is 0.1 mol / L, and the solvent is water; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid to the solution while stirring. The ratio of the amount of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid added to the ethanol solution of cerium nitrate and n-butyl titanate is 18 g / L, the concentration of n-butyl titanate is 30 g / L, and the solvent is ethanol. The mixture was prepared by adding cerium and titanate n-butyl ethanol solution, indium trichloride aqueous solution, lithium manganese iron phosphate powder, and L-malic acid in a ratio of 10 mL: 6 mL: 100 g: 1 g. After addition, the mixture was stirred and ultrasonically dispersed for 2 hours. The mixture was then spread evenly in a container and dried in an oven at 80°C to evaporate and remove water and ethanol. After drying, it was calcined at 120±5°C for 3 hours. Then, the mixture and selenic acid powder were added and mixed evenly. The mass ratio of the mixture to selenic acid powder in the calcined product was calcined product: mixture: selenic acid powder = 100:4:1. The mixture was then calcined at 650±5°C for 5 hours. After calcination, it was air-cooled to room temperature to obtain the coated modified lithium manganese iron phosphate lithium-ion battery cathode material.

[0020] Example 2

[0021] A modified manganese iron phosphate lithium-ion battery cathode material, the preparation steps of which include:

[0022] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. The mass ratio of manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: iron hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 91:22:120:37:10. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1. Then the ball mill jar is sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, ball material liquid mass ratio is ball: material: ball milling slurry = 2:1:8. The ball milling mixture is dried at 80℃ for 5 h to remove the ball milling slurry. Then it is calcined at 300±5℃ for 2 h in an argon protective atmosphere and then calcined at 650±5℃ for 5 h to obtain lithium manganese iron phosphate powder.

[0023] (2) Pyridine and hexafluorophosphate are mixed, wherein the molar ratio of pyridine to hexafluorophosphate is 1:0.8; the mixture is heated in a water bath to 30±2℃ and kept at that temperature for 3 hours, and the mixture is stirred during the heating process. After the heating process is completed, lithium hydroxide and ethanol are added to the mixture while stirring, wherein the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is 1.3g:100mL:4g; after the addition is completed, the mixture is heated in a water bath to 55±2℃ and kept at that temperature for 4 hours, and the mixture is refluxed during the heating process, and then cooled to room temperature to obtain the mixture.

[0024] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; the concentration of cerium nitrate in the ethanol solution of cerium nitrate and n-butyl titanate is 20 g / L, the concentration of n-butyl titanate is 32 g / L, and the solvent is ethanol; prepare an aqueous solution of indium trichloride; the concentration of indium trichloride in the aqueous solution of indium trichloride is 0.1 mol / L, and the solvent is water; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid to the solution while stirring. The ratio of the amount of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid added to the ethanol solution of cerium nitrate and n-butyl titanate is 1:1. The mixture was prepared by adding cerium and titanate n-butyl ethanol solution, indium trichloride aqueous solution, lithium manganese iron phosphate powder, and L-malic acid in a ratio of 10 mL: 7 mL: 100 g: 2 g. After addition, the mixture was stirred and ultrasonically dispersed for 2 hours. The mixture was then spread evenly in a container and dried in an oven at 80°C to evaporate and remove water and ethanol. After drying, it was calcined at 120±5°C for 3 hours. Then, the mixture and selenic acid powder were added and mixed evenly. The mass ratio of the mixture to selenic acid powder in the calcined product was calcined product: mixture: selenic acid powder = 100:5:1. The mixture was then calcined at 650±5°C for 5 hours. After calcination, it was air-cooled to room temperature to obtain the coated modified lithium manganese iron phosphate lithium-ion battery cathode material.

[0025] Example 3

[0026] A modified manganese iron phosphate lithium-ion battery cathode material, the preparation steps of which include:

[0027] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. The mass ratio of manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: iron hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 91:22:120:38:10. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1. Then the ball mill jar is sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, ball material liquid mass ratio is ball: material: ball milling slurry = 2:1:8. The ball milling mixture is dried at 80℃ for 5 h to remove the ball milling slurry. Then it is calcined at 300±5℃ for 2 h in an argon protective atmosphere and then calcined at 650±5℃ for 5 h to obtain lithium manganese iron phosphate powder.

[0028] (2) Pyridine and hexafluorophosphate are mixed, wherein the molar ratio of pyridine to hexafluorophosphate is 1:0.8; the mixture is heated in a water bath to 30±2℃ and kept at that temperature for 3 hours, and the mixture is stirred during the heating process. After the heating process is completed, lithium hydroxide and ethanol are added to the mixture while stirring, wherein the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is 1.4g:100mL:4g; after the addition is completed, the mixture is heated in a water bath to 55±2℃ and kept at that temperature for 4 hours, and the mixture is refluxed during the heating process, and then cooled to room temperature to obtain the mixture.

[0029] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; the concentration of cerium nitrate in the ethanol solution of cerium nitrate and n-butyl titanate is 22 g / L, the concentration of n-butyl titanate is 34 g / L, and the solvent is ethanol; prepare an aqueous solution of indium trichloride; the concentration of indium trichloride in the aqueous solution of indium trichloride is 0.1 mol / L, and the solvent is water; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid to the solution while stirring. The ratio of the amount of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid added to the ethanol solution of cerium nitrate and n-butyl titanate is 1:1. The mixture was prepared by adding cerium and titanate n-butyl ethanol solution, indium trichloride aqueous solution, lithium manganese iron phosphate powder, and L-malic acid in a ratio of 10 mL: 7 mL: 100 g: 2 g. After addition, the mixture was stirred and ultrasonically dispersed for 2 hours. The mixture was then spread evenly in a container and dried in an oven at 80°C to evaporate and remove water and ethanol. After drying, it was calcined at 120±5°C for 3 hours. Then, the mixture and selenic acid powder were added and mixed evenly. The mass ratio of the mixture to selenic acid powder in the calcined product was calcined product: mixture: selenic acid powder = 100:5:1. The mixture was then calcined at 650±5°C for 5 hours. After calcination, it was air-cooled to room temperature to obtain the coated modified lithium manganese iron phosphate lithium-ion battery cathode material.

[0030] Example 4

[0031] A modified manganese iron phosphate lithium-ion battery cathode material, the preparation steps of which include:

[0032] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. The mass ratio of manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: iron hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 92:24:120:40:10. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1. Then the ball mill jar is sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, ball material liquid mass ratio is ball: material: ball milling slurry = 2:1:8. The ball milling mixture is dried at 80℃ for 5 h to remove the ball milling slurry. Then it is calcined at 300±5℃ for 2 h in an argon protective atmosphere and then calcined at 650±5℃ for 5 h to obtain lithium manganese iron phosphate powder.

[0033] (2) Pyridine and hexafluorophosphate are mixed, wherein the molar ratio of pyridine to hexafluorophosphate is 1:0.8; the mixture is heated in a water bath to 30±2℃ and kept at that temperature for 3 hours, and the mixture is stirred during the heating process. After the heating process is completed, lithium hydroxide and ethanol are added to the mixture while stirring, wherein the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is 1.5g:100mL:4g; after the addition is completed, the mixture is heated in a water bath to 55±2℃ and kept at that temperature for 4 hours, and the mixture is refluxed during the heating process, and then cooled to room temperature to obtain the mixture.

[0034] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; the concentration of cerium nitrate in the ethanol solution of cerium nitrate and n-butyl titanate is 26 g / L, the concentration of n-butyl titanate is 35 g / L, and the solvent is ethanol; prepare an aqueous solution of indium trichloride; the concentration of indium trichloride in the aqueous solution of indium trichloride is 0.1 mol / L, and the solvent is water; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid to the solution while stirring. The ratio of the amount of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid added to the ethanol solution of cerium nitrate and n-butyl titanate is 1:1. The mixture was prepared by adding cerium and titanate n-butyl ethanol solution, indium trichloride aqueous solution, lithium manganese iron phosphate powder, and L-malic acid in a ratio of 10 mL: 8 mL: 100 g: 3 g. After addition, the mixture was stirred and ultrasonically dispersed for 2 hours. The mixture was then spread evenly in a container and dried in an oven at 80°C to evaporate and remove water and ethanol. After drying, it was calcined at 120±5°C for 3 hours. Then, the mixture and selenic acid powder were added and mixed evenly. The mass ratio of the mixture to selenic acid powder in the calcined product was calcined product: mixture: selenic acid powder = 100:6:1. The mixture was then calcined at 650±5°C for 5 hours. After calcination, it was air-cooled to room temperature to obtain the coated modified lithium manganese iron phosphate lithium-ion battery cathode material.

[0035] Comparative Example 1

[0036] A comparative lithium-ion battery cathode material, the preparation steps of which include:

[0037] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. The mass ratio of manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: iron hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 91:22:120:37:10. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1. Then the ball mill jar is sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, ball material liquid mass ratio is ball: material: ball milling slurry = 2:1:8. The ball milling mixture is dried at 80℃ for 5 h to remove the ball milling slurry. Then it is calcined at 300±5℃ for 2 h in an argon protective atmosphere and then calcined at 650±5℃ for 5 h to obtain lithium manganese iron phosphate powder.

[0038] (2) The mixture of lithium hydroxide and ethanol was used as the mixture of this comparative example. The mixing mass ratio was lithium hydroxide: ethanol = 1.3g: 100mL. The mixture was heated in a water bath to 55±2℃ and stirred for 4h. During the heat preservation process, the mixture was refluxed and then cooled to room temperature to obtain the mixture of this comparative example.

[0039] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; the concentration of cerium nitrate in the ethanol solution of cerium nitrate and n-butyl titanate is 20 g / L, the concentration of n-butyl titanate is 32 g / L, and the solvent is ethanol; prepare an aqueous solution of indium trichloride; the concentration of indium trichloride in the aqueous solution of indium trichloride is 0.1 mol / L, and the solvent is water; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid to the solution while stirring. The ratio of the amounts of the aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid added to the ethanol solution of cerium nitrate and n-butyl titanate is as follows: The mixture consisted of an ethanol solution of cerium nitrate and n-butyl titanate, an aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid in a ratio of 10 mL: 7 mL: 100 g: 2 g. After adding the materials, the mixture was stirred and ultrasonically dispersed for 2 hours. The mixture was then spread evenly in a container and dried in an oven at 80°C to evaporate and remove water and ethanol. After drying, it was calcined at 120±5°C for 3 hours. Then, the mixture and selenic acid powder were added and mixed evenly. The mass ratio of the mixture to selenic acid powder in the calcined product was calcined product: mixture: selenic acid powder = 100:5:1. The mixture was then calcined at 650±5°C for 5 hours. After calcination, it was air-cooled to room temperature to obtain the lithium-ion battery cathode material described in this comparative example.

[0040] Comparative Example 2

[0041] A comparative lithium-ion battery cathode material, the preparation steps of which include:

[0042] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. The mass ratio of manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: iron hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 91:22:120:37:10. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1. Then the ball mill jar is sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, ball material liquid mass ratio is ball: material: ball milling slurry = 2:1:8. The ball milling mixture is dried at 80℃ for 5 h to remove the ball milling slurry. Then it is calcined at 300±5℃ for 2 h in an argon protective atmosphere and then calcined at 650±5℃ for 5 h to obtain lithium manganese iron phosphate powder.

[0043] (2) Pyridine and hexafluorophosphate are mixed, wherein the molar ratio of pyridine to hexafluorophosphate is 1:0.8; the mixture is heated in a water bath to 30±2℃ and kept at that temperature for 3 hours, and the mixture is stirred during the heating process. After the heating process is completed, lithium hydroxide and ethanol are added to the mixture while stirring, wherein the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is 1.3g:100mL:4g; after the addition is completed, the mixture is heated in a water bath to 55±2℃ and kept at that temperature for 4 hours, and the mixture is refluxed during the heating process, and then cooled to room temperature to obtain the mixture.

[0044] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; the concentration of cerium nitrate in the ethanol solution of cerium nitrate and n-butyl titanate is 20 g / L, the concentration of n-butyl titanate is 32 g / L, and the solvent is ethanol; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add lithium manganese iron phosphate powder and L-malic acid to the solution while stirring. The ratio of lithium manganese iron phosphate powder to L-malic acid added to the ethanol solution of cerium nitrate and n-butyl titanate is ethanol solution of cerium nitrate and n-butyl titanate: lithium manganese iron phosphate powder: L- Malic acid = 10mL:100g:2g; after adding the materials, stir the mixture and ultrasonically disperse it for 2 hours. Then, spread the mixture evenly in a container and dry it in an 80℃ drying oven to evaporate and remove water and ethanol. After drying, calcine it at 120±5℃ for 3 hours. Then, add the mixture and selenic acid powder and mix evenly. The mass ratio of the mixture and selenic acid powder added to the calcined product is calcined product: mixture: selenic acid powder = 100:5:1. Then, calcine it at 650±5℃ for 5 hours. After calcination, air cool it to room temperature to obtain the lithium-ion battery cathode material described in this comparative example.

[0045] Comparative Example 3

[0046] A comparative lithium-ion battery cathode material, the preparation steps of which include:

[0047] (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. The mass ratio of manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: iron hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 91:22:120:37:10. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1. Then the ball mill jar is sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, ball material liquid mass ratio is ball: material: ball milling slurry = 2:1:8. The ball milling mixture is dried at 80℃ for 5 h to remove the ball milling slurry. Then it is calcined at 300±5℃ for 2 h in an argon protective atmosphere and then calcined at 650±5℃ for 5 h to obtain lithium manganese iron phosphate powder.

[0048] (2) Pyridine and hexafluorophosphate are mixed, wherein the molar ratio of pyridine to hexafluorophosphate is 1:0.8; the mixture is heated in a water bath to 30±2℃ and kept at that temperature for 3 hours, and the mixture is stirred during the heating process. After the heating process is completed, lithium hydroxide and ethanol are added to the mixture while stirring, wherein the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is 1.3g:100mL:4g; after the addition is completed, the mixture is heated in a water bath to 55±2℃ and kept at that temperature for 4 hours, and the mixture is refluxed during the heating process, and then cooled to room temperature to obtain the mixture.

[0049] (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; the concentration of cerium nitrate in the ethanol solution of cerium nitrate and n-butyl titanate is 20 g / L, the concentration of n-butyl titanate is 32 g / L, and the solvent is ethanol; prepare an aqueous solution of indium trichloride; the concentration of indium trichloride in the aqueous solution of indium trichloride is 0.1 mol / L, and the solvent is water; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid to the solution while stirring. The ratio of L-malic acid was 10 mL: 7 mL: 100 g: 2 g for an ethanol solution of cerium nitrate and tetrabutyl titanate, an aqueous solution of indium trichloride, lithium manganese iron phosphate powder, and L-malic acid. After adding the materials, the mixture was stirred and ultrasonically dispersed for 2 hours. The mixture was then spread evenly in a container and dried in an oven at 80°C to evaporate and remove water and ethanol. After drying, it was calcined at 120±5°C for 3 hours. Then, the additive was added and mixed evenly. The mass ratio of the additive to the calcined product was 100:5. The mixture was then calcined at 650±5°C for 5 hours. After calcination, it was air-cooled to room temperature to obtain the lithium-ion battery cathode material described in this comparative example.

[0050] Example 5

[0051] The positive electrode materials prepared by the methods described in the above embodiments and comparative examples were used to prepare experimental CR2032 coin cells, and then electrochemical tests were conducted on the cells. First, polyvinylidene fluoride (PVDF) was dissolved in N-methylpyrrolidone (N-methylpyrrolidone) at a mass ratio of 1:22 to prepare a PVDF solution. Then, the positive electrode materials, carbon black conductive agent, and PVDF solution prepared by the methods described in the above embodiments and comparative examples were mixed to form a slurry. The mass ratio of positive electrode material, carbon black conductive agent, and PVDF solution was 8:1:1. The slurry was coated on a clean aluminum foil, dried at 80°C for 5 hours, pressed into sheets, and then dried in an 80°C drying oven for 10 hours to obtain a positive electrode sheet with a thickness of 0.2 mm. A test battery was assembled using lithium metal sheets as the negative electrode, commercially available monolayer polypropylene as the separator, and 1 mol / L LiPF6 as the electrolyte (ethylene carbonate: dimethyl carbonate volume ratio in the solvent was 1:1). The battery was placed in an argon atmosphere before the experiment. The battery was then charged at a constant current of 1C to 4.5V on an electrochemical workstation, placed in a constant current environment for 2 minutes, and then discharged at a constant current of 1C to 2.5V, completing one constant current charge-discharge cycle. After 100 charge-discharge cycles, the discharge specific capacity of the battery was obtained, and the capacity retention rate was calculated. The results are shown in Table 1.

[0052] As shown in Table 1, the cathode material prepared by coating and modifying lithium manganese iron phosphate using the method described in this invention can significantly improve the discharge specific capacity and capacity retention rate of the battery. This is mainly because the coating process inhibits the side reactions on the surface of the cathode material and enhances its stability. Furthermore, the coating modification process can partially fill the defects and gaps on the surface of the lithium manganese iron phosphate cathode material, preventing the electrolyte from corroding the cathode material. This invention, by doping indium and selenium into the coating layer and subjecting it to fluorination, can significantly improve the lithium-ion transfer rate in the coating layer, promote lithium-ion migration, and exhibit excellent electrochemical performance.

[0053] Table 1

[0054]

[0055]

[0056] The technical solutions provided by the present invention have been described in detail above. For those skilled in the art, there will be changes in specific implementation methods and application scope based on the ideas of the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A coated modified lithium iron phosphate lithium-ion battery cathode material, characterized in that, The preparation steps include: (1) Manganese carbonate powder, iron hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose are mixed in a ball mill jar to form a mixture. A mixture of ethanol and ethylene glycol is added to the mixture as a ball milling slurry. The ball mill jar is then sealed and wet ball milling is performed to obtain a ball milling mixture. The ball milling mixture is dried at 80°C for more than 5 hours to remove the ball milling slurry. Then it is calcined at 300±5°C for 2-3 hours in an argon protective atmosphere. Finally, it is calcined at 650±5°C for more than 5 hours to obtain lithium manganese iron phosphate powder. (2) Mix pyridine and hexafluorophosphoric acid, heat in a water bath to 30±2℃ and keep warm for more than 3 hours. Stir the mixture during the heat preservation process. After the heat preservation is completed, add lithium hydroxide and ethanol to the mixture while stirring. After the addition is completed, heat in a water bath to 55±2℃ and keep warm and stir for more than 4 hours. During the heat preservation process, condense and reflux, and then air cool to room temperature to obtain the mixture. (3) Prepare an ethanol solution of cerium nitrate and n-butyl titanate; prepare an aqueous solution of indium trichloride; stir the ethanol solution of cerium nitrate and n-butyl titanate, and then simultaneously add the aqueous solution of indium trichloride, lithium manganese iron phosphate powder and L-malic acid to the solution while stirring. After the addition is completed, stir the mixture and ultrasonically disperse it for more than 2 hours. Then spread the mixture in a container and dry it in an 80°C drying oven to evaporate and remove water and ethanol. After drying, calcine it at 120±5°C for more than 3 hours. Then add the mixture and selenic acid powder and mix evenly. Then calcine it at 650±5°C for more than 5 hours. After calcine, air cool it to room temperature to obtain the coated modified lithium manganese iron phosphate lithium-ion battery cathode material.

2. The coated modified lithium iron phosphate lithium-ion battery cathode material according to claim 1, characterized in that, In step (1), the mass ratio of manganese carbonate powder, ferric hydroxide powder, ammonium dihydrogen phosphate powder, lithium carbonate powder and sucrose is manganese carbonate powder: ferric hydroxide powder: ammonium dihydrogen phosphate powder: lithium carbonate powder: sucrose = 90-92: 20-24: 120: 35-40:

10.

3. The coated modified manganese iron phosphate lithium-ion battery cathode material according to claim 1, characterized in that, In step (1), the volume ratio of ethanol to ethylene glycol in the ball milling slurry is 9:1; the ball milling process is as follows: ball milling speed 400 r / min, ball milling time 5 h, and ball-to-material-to-liquid mass ratio is ball:material:ball milling slurry = 2:1:

8.

4. The coated modified manganese iron lithium phosphate lithium-ion battery cathode material according to claim 1, characterized in that, In step (2), the molar ratio of pyridine to hexafluorophosphate is pyridine:hexafluorophosphate = 1:0.8; the ratio of the amount of lithium hydroxide and ethanol added to the amount of pyridine mixed is lithium hydroxide:ethanol:pyridine = 1.2~1.5g:100mL:4g.

5. The coated modified manganese iron phosphate lithium-ion battery cathode material according to claim 1, characterized in that, In step (3), the concentration of cerium nitrate in the ethanol solution of cerium nitrate and tetrabutyl titanate is 18-26 g / L, the concentration of tetrabutyl titanate is 30-35 g / L, and the solvent is ethanol; the concentration of indium trichloride in the aqueous solution is 0.1 mol / L, and the solvent is water.

6. The coated modified manganese iron lithium battery cathode material according to claim 1, characterized in that, In step (3), the ratio of indium trichloride aqueous solution, lithium manganese iron phosphate powder and L-malic acid added to the ethanol solution of cerium nitrate and tetrabutyl titanate is 10 mL: 6-8 mL: 100 g: 1-3 g.

7. The coated modified manganese iron lithium phosphate lithium-ion battery cathode material according to claim 1, characterized in that, In step (3), the mass ratio of the mixture and selenic acid powder added to the calcined product at 120±5℃ is calcined product: mixture: selenic acid powder = 100:4~6:1.

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