Mechanism studies of LiFePO₄ cathode material: Lithiation/delithiation process, electrochemical modification and synthetic reaction

Olivine-structured lithium ion phosphate (LiFePO₄) is one of the most competitive candidates for fabricating energy-driven cathode material for sustainable lithium ion battery (LIB) systems. However, the high electrochemical performance is significantly limited by the slow diffusivity of Li-ion in LiFePO₄ (ca. 10^-14 cm² s^-1) together with the low electronic conductivity (ca. 10^-9 S cm^-1), which is the big challenge currently faced by us. To resolve the challenge, many efforts have been directed to the dynamics of the lithiation/delithiation process in Li_xFePO₄ (0 ≤ x ≤ 1), mechanism of electrochemical modification, and synthetic reaction process, which are crucial for the development of high electrochemical performance for LiFePO₄ material. In this review, in order to reflect the recent progress ranging from the very fundamental to practical applications, we specifically focus on the mechanism studies of LiFePO₄ including the lithiation/delithiation process, electrochemical modification and synthetic reaction. Firstly, we highlight the Li-ion diffusion pathway in Li_xFePO₄ and phase translation of Li_xFePO₄. Then, we summarize the modification mechanism of LiFePO₄ with high-rated capability, excellent low-temperature performance and high energy density. Finally, we discuss the synthetic reaction mechanism of high-temperature carbothermal reaction route and low-temperature hydrothermal/solvothermal reaction route.