Fundamental understanding of the effects of substitution on the reaction mechanism and kinetics in olivine compounds.

摘要

Lithium ion batteries have dominated the portable electronic market in the last decade, and are currently gaining significant attention towards large-scale application in auto industry and load leveling. However, large scale applications have been plagued by cost and safety concerns. For the Li ion battery to gain even greater market share, lower cost and safer electrode materials are required to meet the future demands of both plug in and electric vehicles. Of the electrode materials, LiFePO4 is one of the promising cathodes for the future auto and electric grid industries.;Olivine LiFePO4 has attracted a lot of attention due to its low cost, high stability, environmental benignity and acceptable theoretical capacity. The material however suffers from inherent low electronic conductive and poor Li-ion diffusivity thus hindering its practical application as a possible electrode material of choice. Despite the limitations, Li at present can cycle very well at acceptable rates. The main objective is to gain fundamental understanding of the reaction mechanism of LiFePO4 to understand the fast electrochemical rate capabilities of the poor electronic insulating "two-phase" LiFePO4/FePO4 system. This will help identify the key parameters required to optimize intercalation processes. We initiated a more systematic study of aliovalent and isovalent substitution in olivine-LiFePO 4 to develop a fundamental understanding of: (1) the possibility of aliovalent doping; (2) crystallographic and thermodynamic changes accompanying such substitution; (3) how the substitution affects the reaction mechanism of olivine-LiFePO4, two phase vs. single phase reaction; and (4) how such substitution affects the reaction kinetics.