Electrochemical behavior of LiFePO₄ thin film prepared by RF magnetron sputtering in Li₂ SO₄ aqueous electrolyte

LiFePO₄ films were deposited on Au/Si substrate by radio-frequency magnetron sputtering. The effect of annealing on the crystallization and morphology of LiFePO₄ thin film has been investigated. X-ray diffraction revealed that the films through annealing were well crystallized compared with as-deposited films. The surface morphology of the thin film was also observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Electrochemical tests in 1M Li₂SO₄ showed that the annealed thin film in 500°C exhibits larger Li-ion diffusion coefficient (3.46 × 10^-7 cm²s^-1) than as-deposited film and powder. Furthermore, cyclic voltammetry demonstrate a well-defined lithium intercalation/deintercalation reaction at around 0.45 V versus SCE (i.e., 3.6 V versus Li⁺/Li), suggesting that the annealed LiFePO₄ thin film is a promising candidate cathode film for lithium microbatteries.