Preparation method of high-conductivity lithium iron phosphate cathode material

Abstract

The invention provides a preparation method of a high-conductivity lithium iron phosphate cathode material. The preparation method comprises the steps of: adding a doping compound into phosphoric acid and trivalent ferric salt solution, separately adding a pyrolytic carbon source and a carbonization accelerator in two manners, adding alkaline solution, controlling the pH of the system to be within 1-4, reacting for a period of time, washing and drying so as to obtain a ferric phosphate precursor; and mixing a lithium source, the precursor, the pyrolytic carbon source and the carbonization accelerator, stirring (or ball milling), drying in vacuum, thermally treating and grinding so as to prepare the doped carbon-wrapping lithium iron phosphate. The doping compound, the pyrolytic carbon source and the carbonization accelerator are added when the ferric phosphate precursor is prepared, the electric conductivity of lithium iron phosphate intracells and the electric conductivity among particles are improved, and the electrochemical performance of the lithium iron phosphate intracells is obviously improved at a high rate; and moreover, ferrous iron at high price is not used any more, so that the production cost is greatly lowered.

Description

technical field [0001] The invention relates to a preparation method of a positive electrode material of a lithium ion battery, in particular to a preparation method of a lithium iron phosphate positive electrode material. Background technique [0002] The commonly used cathode active materials for lithium-ion batteries are LiCoO 2 , LiMn 2 o 4 and LiFePO 4 , Among them, because lithium iron phosphate material has many advantages such as stable structure, good thermal stability, low raw material cost, low toxicity, environmental friendliness, good safety performance and good high temperature performance, it is a kind of positive electrode active material with great potential. In particular, its oxidation exothermic temperature exceeds 400°C, and it has excellent thermal stability. [0003] But LiFePO 4 The electronic conductivity is low, only 10 -9 ~10 -10 S / cm, thus the rate performance is poor, which limits its application. Generally, methods such as carbon coating...

AI Technical Summary

Problems solved by technology

However, most of the pure phase FePO 4 , to prepare doped and carbon-encapsulated LiFePO by adding doping elements and carbon sources when mixed with Li sources 4 / C; these doping elements and carbon sources are surrounded by FePO 4 The periphery, in the subsequent heat treatment forms LiFePO 4 In the process of / C, it is difficult for the inside of the core to enter the interior of the particles in large quantities only by the diffusion of ions and carbon during the sintering process, and only a very small amount of doped metal elements and carbon sources enter the surface layer, so the conductivity is low. High; although the electrochemical performance at low rates is also good, the performance at higher rates is not fundamentally improved