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

Abstract

There has been increasing interest in lithium rechargeable batteries, especially microbatteries, with the rapid development of potable electronic equipments and MEMS (Micro-Electro-Mechanical Systems) technology. In this study, lithium manganese oxide, which is a strong candidate for the battery material, is more abundant, stable 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 thermal treatment on the microstructure and electrode characteristics 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. DLC 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.