Method for producing cathode material of lithium iron phosphate battery
Lithium iron phosphate (LiFePO., abbreviated as LFP, also called lithium iron phosphorus) of lithium iron phosphate battery refers to a lithium battery pack that uses lithium iron phosphate as a positive electrode material, and its working principle is the same as that of a lithium battery pack.
The correct chemical formula of LiFePO4 is LiMPO4 (M can be any metal, such as Fe, Co, Mn, Ti, etc.).
Its physical structure is olivine. From the structure point of view, AyMPO4, Li1-xMFePO4, LiFePO4MO, etc. can also be used as cathode materials for lithium-ion batteries.
Its characteristic is that it does not contain precious elements, the price of raw materials is low, and the resources of phosphorus, iron, and lithium are abundant on the earth, so there will be no major problems in the supply of materials.
In addition to the common characteristics of lithium batteries, there are also some unique advantages, such as its moderate working voltage (3.2V), large capacity (170mAh/g), high discharge power, fast charging and cycling Long life (up to 2000 times), high stability in high temperature and high heat environment.
Production method of cathode material for lithium iron phosphate battery
1. Carbothermal reduction method
Carbothermal reduction method is also a kind of high temperature solid phase method. The synthetic methods are relatively easy to industrialize. Most of them use lithium dihydrogen phosphate (LiHPO4), ferric oxide (Fe2O3) or ferric oxide, sucrose as raw materials. After uniform mixing, they are roasted at high temperature and protected by fish gas or nitrogen. To reduce trivalent iron to divalent iron, that is, to synthesize lithium iron phosphate by carbothermal reduction method.
Advantages: It solves the oxidation reaction that may be caused during the mixing and processing of raw materials, makes the synthesis process more reasonable, and improves the conductivity of the material.
Disadvantages: The reaction time is relatively long, the temperature is difficult to control, and the control conditions for product consistency are more stringent, which is difficult to adapt to industrial production.
2. Hydrothermal synthesis method
The hydrothermal synthesis method belongs to the category of wet method. It uses soluble ferrous salt, lithium salt and phosphoric acid as raw materials, and directly under hydrothermal conditions In the synthesis of LiFePO4, due to the low solubility of oxygen in the hydrothermal system, the synthesis of LiFePOA in the hydrothermal system provides an excellent inert environment.
Advantages: The hydrothermal method can prepare ultra-fine particles in the liquid phase, and the raw materials can be mixed at the molecular level. It has the advantages of uniform phase, small powder particle size, simple operation, etc., and has the advantages of easy mass production, good product batch stability, and low-cost and easy-to-obtain raw materials. At the same time, an inert atmosphere is not required during the production process.
Disadvantages: The structure of the product prepared by the water-cooking synthesis method often has iron dislocation, which generates metastable FePO, which affects the chemical and electrochemical properties of the product. At the same time, there are also shortcomings such as uneven particle size, impure phase, large equipment investment (high temperature and high pressure reactor design and manufacture are difficult, and the cost is also high) or the process is more complicated.
3. In addition, sol-gel synthesis method, liquid phase co-precipitation method, microwave synthesis method, etc. are also used in the preparation of LFP raw materials.
These processes have their own advantages and disadvantages, but after the improved process, the first three are more widely used. A123 in the United States and Phostech in Canada adopt the solid phase method, and Valence in the United States adopts the solid phase method. Carbothermal reduction method, LG Chem uses continuous hydrothermal synthesis method.
In the material preparation process, conductive carbon coating is a key technology in the LiFePO2 preparation process. By pre-coating a high-quality conductive carbon layer on the surface of the foil, A123 effectively reduces the internal resistance of the battery and improves the high-rate discharge capacity of the lithium iron phosphate battery.
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