LiCoO2 thin film cathode sputtered onto 500 °C substrate

Abstract

LiCoO2 thin film cathode, which has attracted considerable attention in the past decades due to its promising application in micro-batteries, is commonly produced by magnetron sputtering combined with post-annealing treatment. However, the high temperature treatment hinders its compatibility toward a majority of substrates, while the moderate temperature post-annealing constrains its crystallinity. In this study, LiCoO2 film cathode is sputtered onto the 500 °C substrate. The in-situ annealed LiCoO2 thin film cathode is highly crystallized as hexagonal structure without cubic impurities, exhibiting a capacity retention of 75% at 1 C after 200 cycles and excellent rate performance with 55% of initial capacity at 70 C in liquid electrolyte-based cell. All solid-state thin film Li battery exhibits excellent cycle stability. The excellent electrochemical performance is ascribed to highly crystallized LiCoO2 thin film, which is trigged by high kinetic energy of the sputtered species. On the contrary, the LiCoO2 film fabricated by post-annealing at 500 °C shows much poorer electrochemical performance due to its lower crystallinity, indicating that the annealing mode is crucial for the sputtering. This work provides a new option to deposite high quality LiCoO2 thin film via in situ annealing at a relatively low temperature.