Electrochemical properties of diamond-like-carbon coated LiMn2O4 thin films for microbatteries

Abstract

There has been increasing interest in lithium rechargeable batteries, especially microbatteris, with the rapid development of porable electronic equipments and MEMS (Micro-Electro-Mechanical Systems) technology. In this study, lithium managanese oxide, which is strong candidate for the battery material, is more abundant, satble in the ambient state and less toxic than the other oxides such as lithium nickel oxides and lithium cobalt oxides, was deposited by rf magnetron sputter. The effect of htermal treament on the microstructure and electrode characteristic of the lithium manganese oxide cathode was investigated. In an electrochemical experiment using liquid electrolyte, half cell failure was caused by manganese dissolution, degradation of the electrolyte materials during charging/discharging process etc. In this research we focus on the interface reaction problem that would affect the cyclability and lifetime of the microbattery. In order to reduce the interface reaction during operation, we introduced a DLC (Diamond-like-Carbon) film that has high electrical resistivity, mechanical hardness and chemical stability. DCL films were deposited on sputtered lithium manganese oxide electrodes by ECRCVD (Electron Cyclotron Resonance Chemical Vapor Deposition). A DLC-top-layer LiMn2O4 film was more stable during the charging.discharging reaction and showed higher discharge capacity over a wide voltage window than the uncoated LiMn2O4 film.