The effects of BaTiO₃ nanodots density support on epitaxial LiCoO₂ thin-film for high-speed rechargeability

LiCoO₂ (LCO) is one of the most promising cathode materials for Li ion batteries (LIBs). However, LCO shows a rate-limiting step of Li⁺ migration between electrode and electrolyte interfaces, requiring LIBs to be charged under low-current conditions. For next generation batteries, it will be necessary to meet the demand for a shorter charging-time. We investigated a support method for the LCO surface to improve high C-rate performance, and revealed that the Li⁺ intercalation/de-intercalation reaction into/from LCO was accelerated by the introduction of a BaTiO₃-LCO-electrolyte interface (triple-phase interface; TPI), due to the electric field concentration near the TPI. In this report, we investigate the dependence of high C-rate performance on the density of surface BaTiO₃ nanodots using epitaxial LiCoO₂ thin films created via pulsed laser deposition (PLD). As the number of nanodots increased, so did discharge capacity at 50C, becoming saturated at surface coverage over 22%. However, at 100C, the discharge capacity decreased at surface coverage over 40%. These results indicate that coalescence of nanodots reduces not only the TPI length but also the electrochemically active range at quite high C-rate. Therefore, we infer that optimal surface coverage should be varied depending on the C-rate.