Influence of Zr dopant on microstructural and electrochemical properties of LiCoO2 thin film cathodes by RF sputtering

LiCoO2 thin film cathodes have been well established in Li-ion rechargeable batteries, however, its useful capacity hardly exceeds 50% of the theoretical value. Irreversible structural changes will occur upon exchange of Li ions i.e. >0.5 per unit formula limit, during intercalation/deintercalation reactions. Reportedly, lattice doping phenomenon has noticed an improvement in cyclability of LiCoO2. In this work, the influence of Zr doping on microstructural and electrochemical properties of RF magnetron sputtered LiCoO2 thin film cathodes have been presented. A series of LiZrxCo1−xO2 thin films have been deposited on Au/Ti/SiO2/Si (100) substrates using a Zr-LiCoO2 mosaic target. All the films were deposited at optimized processing conditions. XRD and Raman spectroscopy measurements confirmed the hexagonal layered structure with R3¯m symmetry for Zr doped LiCoO2 film cathodes. The AFM reveals the estimated average grain size is around 50 nm. The cyclic voltammetry studies for these cathodes exhibit narrow potential peak separation of 24 mV and resulting highest diffusion coefficient (D¯Li) of about 1.8 × 10−11 cm2 s−1, respectively. These films exhibited a highest initial discharge capacity of 64.4 μA h cm−2 μm−1 with a capacity retention of 98.5% even after 25 cycles. In non-aqueous region, the cell exhibited an initial discharge capacity of about 65 μA h cm−2 μm−1 with good cycling stability even after 80 cycles, and is observed to be the more promising cathode candidate than the pristine LiCoO2 films.