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

Well-crystallized and electrochemically active Li 1 - x Ni 1+ x O 2 and LiCoO 2 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 LiCoO 2 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, Li 1 - x Ni 1+ x O 2 films can only be effectively prepared in a single synthetic step from nickel plates. Such different activation methods required for the preparation of LiCoO 2 and Li 1 - x Ni 1+ x O 2 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).