Preparation method of lithium iron phosphate of cathode material of lithium ion secondary battery

Abstract

The invention provides a preparation method of lithium iron phosphate of a cathode material of a lithium ion secondary battery, which comprises the following steps: well mixing a trivalent iron source, a carbon source, a phosphate source, a lithium source, and doped ions, performing working procedures such as drying and the like to obtain a lithium iron phosphate precursor mixture, heating the mixture in reducing atmosphere with a heating rate of 0.1-10 DEG C / min, calcining the mixture at 200-800 DEG C for 5-25 hours, cooling the mixture to room temperature in the furnace, grinding the mixture to obtain the cathode material of a lithium ion electrode. The preparation method has simple process, and low cost, and the prepared cathode material of a lithium electrode has good discharge and cycle performance; the process parameters are easy to control; the batch has good stability; and the preparation method is suitable for large-scale industrial production.

Description

technical field [0001] The invention belongs to the field of preparation of positive electrode materials of lithium ion batteries, and in particular relates to a method for preparing lithium iron phosphate, a positive electrode material of lithium ion secondary batteries, by using a trivalent iron source. technical background [0002] Olivine LiFePO 4 Because of its low cost, environmental friendliness, long cycle life, good thermal stability and high safety performance, it is considered to be one of the best cathode materials for lithium-ion power batteries. [0003] Although LiFePO 4 It has many advantages, but it also has the following two disadvantages that hinder its practical application: (1) low electronic conductivity and lithium ion diffusion rate, resulting in initial capacity loss and poor high-rate charge-discharge performance; (2) ) during the synthesis of LiFePO 4 It is difficult to control the purity of Fe, even if the synthesis conditions are strictly cont...

AI Technical Summary

Problems solved by technology

[0003] Although LiFePO 4 It has many advantages, but it also has the following two disadvantages that hinder its practical application: (1) low electronic conductivity and lithium ion diffusion rate, resulting in initial capacity loss and poor high-rate charge-discharge performance; (2) ) during the synthesis of LiFePO 4 It is difficult to control the purity of Fe, even if the synthesis conditions are strictly controlled, it is still impossible to completely avoid Fe 3+ is oxidized, and most of the researches currently use the more expensive Fe 3+ The compound is used as iron source, which increases the preparation cost

(3) LiFePO 4 The tap density is lower, resulting in a lower volume specific energy

However, it is difficult to design and manufacture large-scale high-temperature and high-pressure reactors, and the cost is high, and it is often necessary to add twice as much Li salt as a precipitant during the synthesis process, which increases the preparation cost

[0007] Patent CN200410017382.5 adopts low-priced ferric source and one-step solid phase synthesis of carbon-coated lithium iron phosphate simplifies the process and reduces the cost. Carbon coating can well solve the problem of poor conductivity of lithium iron phosphate , the 0.2C discharge capacity is 157mAh / g, but the conductivity inside the lithium iron phosphate lattice has not changed, and the 1C discharge capacity is 124mAh / g, which is still a long way from large-scale industrialization

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