US-12620579-B2 - Method for preparing carbon-coated lithium iron phosphate material from ferrous phosphate

US12620579B2US 12620579 B2US12620579 B2US 12620579B2US-12620579-B2

Abstract

The present disclosure relates to the technical field of lithium ion battery cathode materials, and particularly discloses a method for preparing a carbon-coated lithium iron phosphate material from ferrous phosphate. The method comprises: mixing self-made ferrous phosphate with a carbon source, and sintering at a low temperature under nitrogen to remove a part of crystal water to obtain carbon-coated ferrous phosphate with a small amount of crystal water; evenly mixing ferrous phosphate with a lithium source, a phosphorus source and multiple carbon sources, and adjusting until a proper iron-to-phosphorus ratio is 0.960-0.975 and a carbon content is 1.5%-1.8%; subsequently drying slurry to obtain material powder; and sintering the material powder through a two-stage temperature rising curve, naturally cooling and then pulverizing to obtain the carbon-coated lithium iron phosphate material. The nano lithium iron phosphate material prepared by the method has high compaction, high capacity and long cycle performance.

Inventors

Ji Yang
Xiong Wang
Hongfu Qi
Yihua Wei
Jie Sun
Zhonglin He
Jianhao He
Haijuan Liu
Hao Li
Menghua Yu
Zhengchuang Cheng

Assignees

HUBEI RT ADVANCED MATERIALS GROUP COMPANY LIMITED

Dates

Publication Date: 20260505
Application Date: 20221101
Priority Date: 20220322

Claims (8)

1 . A method for preparing a carbon-coated lithium iron phosphate material from ferrous phosphate, comprising the following steps: S1 carrying out ball milling on ferrous phosphate containing water of crystallization and a carbon source to obtain powder; S2 sintering the powder obtained in step S1 at a protective atmosphere to remove a part of the water of crystallization to obtain carbon-coated ferrous phosphate containing water of crystallization; wherein the sintering temperature is 250-400° C.; S3 evenly mixing the carbon-coated ferrous phosphate containing water of crystallization obtained in step S2 with a solid phase phosphorus source, a liquid phase phosphorus source, a carbon source and a dispersant to obtain mixed slurry; and S4 drying the mixed slurry obtained in step S3, then sintering the dried slurry at an inert atmosphere, followed by naturally cooling and pulverizing, so as to obtain the carbon-coated nano lithium iron phosphate material.
2 . The method according to claim 1 , wherein in step S1, in the ferrous phosphate containing water of crystallization, a Fe/p molar ratio is 1.46-1.50; a mass ratio of the carbon source to ferrous phosphate is 0.02-0.035:1.
3 . The method according to claim 1 , wherein in step S1, the carbon source is an organic carbon source which is one or more of glucose, PEG, saccharose, starch or citric acid, and the ball milling mode is wet ball milling or dry ball milling.
4 . The method according to claim 1 , wherein in step S2, a gas used in the protective atmosphere is at least one of nitrogen, argon or helium; the sintering time is 3-6 h; in the carbon-coated ferrous phosphate containing water of crystallization, the chemical formula of ferrous phosphate is Fe3(PO4)2*xH2O, wherein x=2-4.
5 . The method according to claim 1 , wherein in step S3, the solid phase phosphorus source is lithium phosphate; the liquid phase phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid, the carbon sources are the organic carbon source or an inorganic carbon source, the dispersant is water, and an iron-to-phosphorus molar ratio in the mixed slurry is 0.960-0.975.
6 . The method according to claim 5 , wherein the organic carbon source is one or more of glucose, PEG, saccharose, starch or citric acid, the inorganic carbon source is one or more of acetylene black, graphite, Super-P and carbon nanotubes, and the iron-to-phosphorus ratio in the mixed slurry is 0.960-0.975.
7 . The method according to claim 1 , wherein in step S4, the drying mode is one or more of spray drying, forced air drying or vacuum drying; a gas for spray drying is at least one of nitrogen, argon and helium, an inlet air temperature for spray drying is 130-150° C., and an outlet air temperature for spray drying is 80-100° C.
8 . The method according to claim 1 , wherein in step S4, the gas used in the inert atmosphere is at least one of nitrogen, argon and helium; the sintering process is divided into two stages, the first-stage temperature is 750-770° C., the preservation time is 7 h, the second-stage temperature is 760-780° C., and the preservation time is 1 h; the powder is pulverized to a particle size of 0.8-3 μm after being sintered.

Description

TECHNICAL FIELD The present disclosure belongs to the technical field of lithium ion battery electrode materials, and particularly relates to a method for preparing a carbon-coated lithium iron phosphate material from ferrous phosphate. BACKGROUND A lithium iron phosphate material with an olivine structure has relatively high theoretical capacity of 170 mAh/g and relatively high discharge voltage of 3.4V, lithium ion deinterlacing has little effect on its solid structure during the charging and discharging. The lithium iron phosphate material, due to long cyclic life, rich resources, low price, small environment pollution, good chemical stability and other advantages, is considered as one of the most valuable lithium ion battery cathode materials. Through the self-made ferrous phosphate material, hydrated ferrous phosphate raw materials with different iron-to-phosphorus ratios can be prepared, an organic carbon source is coated, low-temperature sintering is carried out at the atmosphere of nitrogen, in such the way, a part of crystal water is removed to increase the original iron-to-phosphorus ratio and improve the utilization rate of raw materials, thereby improving the quality of a finished product; meanwhile, the organic carbon source is decomposed so that the surface of the ferrous phosphate material is coated with a conductive carbon layer, thereby improving the conductivity of the material. Addition of a solid phase phosphorus source which is lithium phosphate and a liquid phase phosphorus source which is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid not only can provide a stable frame structure for synthesis of lithium iron phosphate but also allows phosphorus sources to be evenly mixed. It is found from results that the carbon-coated ferrous phosphate containing a small amount of crystal water has higher discharge capacity and longer cyclic life compared with the traditional lithium iron phosphate material. SUMMARY The objective of the present disclosure is to provide a method for preparing a lithium iron phosphate material from ferrous phosphate in order to solve the problem of high lithium iron phosphate material cost. According to the method of the present disclosure, a precursor is treated to remove a part of crystal water, and a carbon layer with good conductivity is coated, so as to obtain a carbon-coated ferrous phosphate material; then by adding the lithium source, the iron source, the phosphorus source and the carbon source, a low-cost high-capacity long-cycle lithium iron phosphate material is prepared. In order to realize the above objective, the present disclosure adopts the following technical solution: Provided is a method for preparing a lithium iron phosphate material from ferrous phosphate, comprising the following steps: (1) carrying out ball milling on ferrous phosphate containing crystal water and a carbon source to obtain powder;(2) sintering the powder obtained in step (1) at a protective atmosphere to remove a part of crystal water to obtain carbon-coated ferrous phosphate containing crystal water;(3) evenly mixing the carbon-coated ferrous phosphate containing crystal water obtained in step (2) with lithium phosphate, a solid phase phosphorus source, a liquid phase phosphorus source, a carbon source and a dispersant to obtain mixed slurry; and(4) drying the mixed slurry obtained in step (3), then sintering the dried slurry at an inert atmosphere, followed by naturally cooling and pulverizing, so as to obtain the carbon-coated nano lithium iron phosphate material. Preferably, in step (1), in the ferrous phosphate containing crystal water, Fe/p is 1.46-1.50. Preferably, in step (1), the carbon source is an organic carbon source which is one or more of glucose, polyethylene glycol (PEG), saccharose, starch or citric acid, and the ball milling mode is wet ball milling or dry ball milling More preferably, the organic carbon source is PEG. Preferably, in step (2), a gas used in the protective atmosphere is at least one of nitrogen, argon or helium; the sintering temperature is 250-400° C., and the sintering time is 3-6 h, more preferably the sintering temperature is 300-400° C., and the sintering time is 3-5 h; in the carbon-coated ferrous phosphate containing crystal water, the chemical formula of ferrous phosphate is Fe3(PO4)2*xH2O, wherein x=2−4. Preferably, in step (3), the solid phase phosphorus source is lithium phosphate; the liquid phase phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphoric acid, the carbon sources are the organic carbon source and an inorganic carbon source, the dispersant is water, and an iron-to-phosphorus ratio in the mixed slurry is 0.960-0.975. Preferably, in step (3), the organic carbon source is one or more of glucose, PEG, saccharose, starch or citric acid, more preferably one or two of glucose or PEG; the inorganic carbon source is one or mo