The effect of relative permittivity of surface supporting materials for high-speed rechargeable LiCoO₂ cathode film

We previously reported that the BaTiO₃(BTO)-LiCoO₂(LCO)-electrolyte triple-phase interface (TPI) could play an important role in C-rate enhancement, however, why this supporting material is effective for high performance remains unknown. We focus on the relative permittivity of supporting materials using finite element method calculations and experiments. Calculations revealed that the electric field near the TPI was reinforced as the relative permittivity of supporting materials increased. Experimentally, we prepared nanodots and micropads deposited on LCO thin film using BTO and CeO₂ as supporting materials to evaluate electrochemical properties and SEI formation mechanisms, respectively. High C-rate performance was improved by the introduction of CeO₂ and BTO nanodots; however, only the BTO nanodots deposited on LCO could work at 100C. In addition, SEI around the TPI was quite thin around CeO₂ and BTO pads, although 10 and 300 nm SEI were observed at the non-pad area of CeO₂ and BTO, respectively. This indicated that the Li⁺ motion between electrolyte and electrode could be accelerated depending on the relative permittivity of supporting materials. The low SEI around the TPI of both the CeO₂ and BTO pads suggested that the main reactions of Li⁺ insertion/de-insertion into/from LCO might be dominant around the TPI area.