Microstructure Analysis and Characterization of Li(Ni_(1-x)Co_x)O_2 Thin Film Prepared by Li Diffusion on Ni-Co Alloy Substrates for Cathode Application

摘要

The currently commercialized cathode material for Li ion batteries such as LiCoO_2 exhibited limit to further improve the performance of the batteries, since the employed screen printing method for cathode fabrication is difficult to reduce the thickness and control the microstructure of the oxide layer. In this studies, we have synthesized Li(Ni_(1-x)Co_x)O_2 thin film by utilizing Li-diffusion reaction on the surface of Ni-Co alloy substrates. For the preparation of Ni-Co alloy rod, Ni and 20at.%Co powder were mixed for 24hrs by ball milling, and then pressed into rod-shape by cold-isostatic pressing. The Ni-Co rods were sintered at 1100°C for 6hrs in the reducing atmosphere of Ar 96% and H_2 4%. The sintered Ni-20at%Co rod was cold-rolled into tape at 5% reduction ratio with the final thickness of 100μm, and the recrystallization heat treatment for the development of the cube texture of the rolled Ni alloy tape was carried out at 1000°C in Ar 96% and H_2 4%. After thin layer of metallic Li was deposited on the surface of Ni-Co template using thermal evaporation method in the glove box, the Li/Ni-Co composite tape were heat-treated at 700～850°C for 1～2hrs in oxidizing atmosphere to induce Li-diffusion into Ni-Co substrate and Li(Ni_(0.8)Co_(0.2))O_2 phase formation. The phase evolution of Li(Ni_(0.8)Co_(0.2))O_2 was confirmed by X-ray diffraction and the grain size and morphology of the surface were analyzed by scanning electron microscopy and atomic force microscopy. Also the charge and discharge test were conducted to confirm the electrical characteristics of Li(Ni_(1-x)Co_x)O_2/Ni-Co thin film for the cathode application.