Characterization of Sputter-Deposited LiCoO₂ Thin Film Grown on NASICON-type Electrolyte for Application in...

All-solid-state Li-rechargeable batteries using a 500 nm-thick LiCoO₂ (LCO) film deposited on two NASICON-type solid electrolyte substrates, LICGC (OHARA Inc.) and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), are constructed. The postdeposition annealing temperature prior to the cell assembly is critical to produce a stable sharp LCO/electrolyte interface and to develop a strong crystallographic texture in the LCO film, conducive to migration of Li ions. Although the cells deliver a limited discharge capacity, the cells cycled stably for 50 cycles. The analysis of the LCO/electrolyte interfaces after cycling demonstrates that the sharp interface, once formed by proper thermal annealing, will remain stable without any evidence for contamination and with minimal intermixing of the constituent elements during cycling. Hence, although ionic conductivity of the NASICON-type solid electrolyte is lower than that of the sulfide electrolytes, the NACSICON-type electrolytes will maintain a stable interface in contact with a LCO cathode, which should be beneficial to improving the capacity retention as well as the rate capability of the all-solid state cell.