Electrochemical performance of magnetron sputter deposited LiFePO 4-Ag composite thin film cathodes

Abstract

LiFePO 4 thin films have been sputtered from a pure LiFePO 4 target onto Ag/SS, Ag/Si 3N 4/Si and Si 3N 4/Si substrates. All of the deposited films were annealed at 973 K for 1 hr in H 2/Ar (5 %) atmosphere. Substrate induced microstructural and crystallographic evolutions have been observed by a scanning electron microscope and X-ray diffraction. Energy dispersion spectra and X-ray photoelectron spectra revealed that Ag was mixed in the LiFePO 4 films deposited on Ag under layers. Ceramic metal composite thin films were obtained. The film conductivity (1 × 10 − 3 Scm − 1 ) is therefore elevated by an order of six, compared with pure LiFePO 4 (10 − 9 Scm − 1 ). The electrochemical measurements of the LiFePO 4-Ag films showed a flat plateau at 3.4 V (v.s. Li/Li +) and a reversible capacity of 80 mAh/g. Optimization of Ag contents may further improve the discharge capacity.