RF-sputtered LiCoO2 thick films: microstructure and electrochemical performance as cathodes in aqueous and nonaqueous microbatteries

摘要

Films of LiCoO2 are prepared on metallized silicon substrates using RF-magnetron sputtering technique. The microstructural properties of the films are investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelec-tron spectroscopy, and atomic force microscopy. The films deposited at a substrate temperature of 250 °C with subsequent annealing at 650 °C exhibited hexagonal layered structure with Kim symmetry. The kinetics of lithium ions in LiCoO2 film cathode host matrix and its cycleability are studied in aqueous Pt//LiCoO2 and nonaqueous Li// LiCoO2 cell. Both the electrochemical cells at same current density of 50 μA cm~(-2) delivered the same initial discharge capacity of about 60 ixA hcm~(-2) μrn~(-1) with a chemical diffusion coefficient of ca. 10~(-11) cm2 s~(-1) for Li~+ ions. The capacity fade rates for the Pt//LiCoO2 and Li//LiCoO2 cells, in average are 3.0 and 0.15% per cycle, respectively, for the first 20 cycles. The Pt//LiCoO2 cell is found to be advantageous for small number of cycles and is cost effective than the Li//LiCoO2 cell.