Method for synthesizing lithium iron manganese phosphate positive electrode material

Abstract

The invention discloses a method for synthesizing a lithium iron manganese phosphate positive electrode material, and belongs to the technical field of lithium batteries. According to the technical scheme, lithium salt, manganese salt, ferric salt and iron powder are mixed, acetylene pressure sintering is conducted in a high-temperature furnace, cooling and screening are conducted, and a finished product is obtained. According to the method, particle gaps are filled with carbon nano-particles, so that the conductivity is improved, the volume is not increased, and the gram volume and the energy density are enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a method for synthesizing a lithium manganese iron phosphate positive electrode material. BACKGROUND

[0002] Lithium manganese iron phosphate batteries are superior to ternary batteries in terms of safety and service life, and their energy density also exceeds that of lithium iron phosphate batteries. In particular, when the molar ratio of manganese to iron reaches 6:4, this material can improve the discharge voltage platform, but too high a manganese content can accelerate the degradation of battery life. However, lithium manganese iron phosphate batteries have certain limitations in practical applications. Although the theoretical discharge platform of lithium manganese iron phosphate batteries is as high as 4V, which is higher than the 3.4V of lithium iron phosphate batteries, the capacity of lithium manganese iron phosphate batteries is limited due to their low conductivity. In addition, the current technology has limited improvement in the electrochemical performance of lithium manganese iron phosphate, resulting in lower actual energy density than lithium iron phosphate batteries.

[0003] Current research mainly focuses on the size of the electrode material particles, the addition ratio of the conductive agent, and the surface carbon coating technology, with the aim of improving the energy density by enhancing the conductivity. Although these methods can increase the energy density to some extent, the effect is not significant. This is mainly because these methods can only improve the conductivity of the particle surface, but the conductivity of the particle interior is not improved, thus failing to achieve the expected improvement effect. Therefore, it is particularly important to further optimize and improve the electrode material of lithium manganese iron phosphate batteries. SUMMARY

[0004] Therefore, the present application provides a method for synthesizing a lithium manganese iron phosphate positive electrode material, which can effectively solve the problem of low conductivity of the electrode material of the existing lithium manganese iron phosphate battery, resulting in low actual energy density. To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] A method for synthesizing a lithium manganese iron phosphate positive electrode material, comprising:

[0006] S1, mixing lithium salt, manganese salt, iron salt and iron powder according to a molar ratio of 1:0.6:0.4:(0.001-0.005) to obtain a uniform mixture, and then placing the mixture in a high-temperature furnace;

[0007] S2, introducing acetylene gas into the furnace, and maintaining the pressure in the furnace between 5 and 10 atmospheres;

[0008] S3, igniting the high-temperature furnace to raise the internal temperature to 550-850℃, and maintaining the constant temperature for 8-12 hours to form an initial material;

[0009] S4, cooling the initial material generated in step S3, and removing the iron after cooling by sieving to obtain a lithium manganese iron phosphate positive electrode material.

[0010] Preferably, in step S2, when the furnace pressure reaches 5 to 10 atmospheres, the pressure needs to be maintained for 1 hour.

[0011] Preferably, in step S2, the high-temperature furnace needs to be first pumped to a vacuum state, then acetylene gas is injected, and this process needs to be repeated more than 3 times.

[0012] Preferably, the particle size of the iron powder used needs to be less than 1 micrometer.

[0013] Preferably, the lithium salt used is lithium carbonate.

[0014] Preferably, the manganese salt used is manganous phosphate.

[0015] Preferably, the iron salt used is ferrous phosphate.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] The present application realizes filling a large amount of carbon nanometer in the internal pores of the lithium iron manganese phosphate positive electrode material particles by mixing lithium salt, manganese salt, iron salt and iron powder and sintering at high temperature, thereby improving the internal conductivity of the particles. This method successfully improves the conductivity without increasing the volume of the material, thereby improving the capacity and overall energy density of each gram of material. DETAILED DESCRIPTION

[0018] The present application discloses a method for synthesizing lithium iron manganese phosphate positive electrode material, comprising:

[0019] S1: mixing lithium salt, manganese salt, iron salt and iron powder according to the molar ratio of 1:0.6:0.4:(0.001-0.005) to obtain a uniform mixture, and then placing the mixture in a high-temperature furnace;

[0020] S2: introducing acetylene gas into the furnace to maintain the pressure in the furnace between 5 and 10 atmospheres;

[0021] S3: igniting the high-temperature furnace to raise the internal temperature to 550 to 850℃, maintaining the constant temperature for 8 to 12 hours to form an initial material;

[0022] S4: cooling the initial material generated in step S3, and removing the iron after cooling by sieving to obtain the lithium iron manganese phosphate positive electrode material.

[0023] Example 1

[0024] S1: mixing lithium carbonate, manganous phosphate, ferrous phosphate and iron powder according to the molar ratio of 1:0.6:0.4:0.001 to ensure uniform mixing to form a mixture, and sending the mixture into a high-temperature furnace;

[0025] S2: Vacuum extraction of the high-temperature furnace, followed by acetylene gas filling, which is repeated at least three times. At the last acetylene filling, the gas pressure in the high-temperature furnace is adjusted to 5 atmospheres, and the pressure is maintained for 1 hour;

[0026] S3: Start heating the high-temperature furnace, and raise the temperature in the furnace to 550°C, and maintain the temperature for 8 hours to prepare the preliminary material;

[0027] S4: Cool the preliminary material obtained in step S3, and after cooling, screen to remove iron powder, and finally obtain the lithium manganese iron phosphate positive electrode material.

[0028] Example 2

[0029] S1: Mix lithium carbonate, manganese phosphate, ferrous phosphate, and iron powder in a molar ratio of 1:0.6:0.4:0.002 to form a mixture, and send the mixture into a high-temperature furnace;

[0030] S2: Vacuum treatment of the high-temperature furnace, followed by acetylene gas filling, which is repeated at least three times. At the last acetylene filling, the gas pressure in the high-temperature furnace is adjusted to 5 atmospheres, and the pressure is maintained for 1 hour;

[0031] S3: Start heating the high-temperature furnace, and raise the temperature in the furnace to 550°C, and maintain the temperature for 8 hours to prepare the preliminary material;

[0032] S4: Cool the preliminary material obtained in step S3, and after cooling, screen to remove iron powder, and finally obtain the lithium manganese iron phosphate positive electrode material.

[0033] Example 3

[0034] S1: Mix lithium carbonate, manganese phosphate, ferrous phosphate, and iron powder in a molar ratio of 1:0.6:0.4:0.003 to form a mixture, and send the mixture into a high-temperature furnace;

[0035] S2: Vacuum treatment of the high-temperature furnace, followed by acetylene gas filling, which is repeated at least three times. At the last acetylene filling, the gas pressure in the high-temperature furnace is adjusted to 5 atmospheres, and the pressure is maintained for 1 hour;

[0036] S3: Start heating the high-temperature furnace, and raise the temperature in the furnace to 550°C, and maintain the temperature for 8 hours to prepare the preliminary material;

[0037] S4: Cool the preliminary material obtained in step S3, and after cooling, screen to remove iron powder, and finally obtain the lithium manganese iron phosphate positive electrode material.

Claims

1. A method for synthesizing lithium manganese iron phosphate cathode material, comprising: S1 is mixed with lithium salt, manganese salt, iron salt and iron powder in a molar ratio of 1:0.6:0.4:(0.001-0.005) to obtain a homogeneous mixture, which is then placed in a high-temperature furnace. S2 introduces acetylene gas into the furnace to maintain the furnace pressure between 5 and 10 atmospheres. S3 ignites the high-temperature furnace, raising the internal temperature to 550 to 850°C and maintaining it at a constant temperature for 8 to 12 hours to form the initial material; S4 cools the initial material generated in step S3, and removes iron by sieving after cooling to obtain lithium manganese iron phosphate cathode material.

2. The method for synthesizing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S2, when the pressure inside the furnace reaches 5 to 10 atmospheres, this pressure needs to be maintained for 1 hour.

3. The method for synthesizing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, In step S2, the high-temperature furnace must first be evacuated to a vacuum state, and then acetylene gas must be injected. This process must be repeated more than three times.

4. The method for synthesizing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The iron powder used must have a particle size of less than 1 micrometer.

5. The method for synthesizing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The lithium salt used is lithium carbonate.

6. The method for synthesizing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The manganese salt used is manganese phosphate.

7. The method for synthesizing lithium manganese iron phosphate cathode material as described in claim 1, characterized in that, The iron salt used is ferrous phosphate.