Fabrication in a Single Synthetic Step of Electrochemically Active LiMO₂ (M = Ni and Co) Thin-Film Electrodes Using Soft Solution Processing at 20−200 °C

Abstract

Well-crystallized and electrochemically active Li1-xNi1+xO2 and LiCoO2 thin-film electrodes for lithium rechargeable microbatteries can be fabricated in a single synthetic step using an economical, less energy consuming, and environmentally friendly “Soft Solution Processing” method in a concentrated LiOH solution at fixed temperatures between 20 and 200 °C without any postsynthesis annealing. While the purely hydrothermal treatment of cobalt plates directly leads to the formation of LiCoO2 films, Ni(OH)2 films on nickel plates are fabricated under the same hydrothermal conditions. By using the electrochemical−hydrothermal approach under supplementary galvanostatic charge with the same hydrothermal conditions, Li1-xNi1+xO2 films can only be effectively prepared in a single synthetic step from nickel plates. Such different activation methods required for the preparation of LiCoO2 and Li1-xNi1+xO2 films respectively can be ascribed to the different metal cation valencies between dissolved nickel species (that contain divalent nickel) and dissolved cobalt species (that should possess trivalent cobalt).