超临界溶剂热合成纳米磷酸铁锂晶体生长机制探究

At present, the growth mechanism of supercritical solvothermal synthetic lithium iron phosphate(LiFePO₄)nanocrystals and the influence of reaction parameters are not clear. Given this circumstance, LiFePO₄powder with average particle size of 68-85 nm is prepared by supercritical solvothermal synthesis at reaction temperature of 340-400 ℃. The crystal structure and particle size of the product are characterized and analyzed, and the apparent activation energy and growth mechanism of LiFePO₄nanocrystals growth process are evaluated. On this basis, the growth kinetics of LiFePO₄nanocrystals is established. The results show that the growth process of nano LiFePO₄in supercritical solvent plays a dominant role in the final crystal size, and the growth process is controlled by the surface reaction, which conforms to the multinucleus-controlled second-order growth kinetics. In electrochemical performance tests, sample obtained at 400 ℃ delivers an initial discharge specific capacity of 153.5 mA·h/g at 0.1C(C referring to charge and discharge rates of the battery), and the capacity retention is 68.3% at 5C. Impurities(Li3Fe2(PO4)3 and Fe3(PO₄)2)in the samples obtained at the reaction temperature of 340 ℃ results in severe battery polarization. In high-speed charge-discharge, critical capacity decay is witnessed, ending up with a capacity retention of only 46.9% at 5C. This study reveals the growth mechanism of LiFePO4 nanocrystals synthesized by supercritical solvothermal method, and lays a theoretical foundation for the subsequent process parameter optimization and even industrial application.