Electrochemical properties of LiCoO₂ thin film surface modified by lithium tantalate and lithium niobate coatings

Amorphous lithium tantalate (LTaO)- and lithium niobate (LNbO)-coated LiCoO₂ (LCO) thin film electrodes were fabricated by pulsed laser deposition (PLD). The LTaO- and LNbO-coated LCOs showed lower interfacial resistances and high-rate charge–discharge properties as compared with a bare LCO. The contribution of the LTaO and LNbO coatings to the electrochemical properties was considered using lithium diffusion and surface analysis. Tracer lithium diffusion coefficients (D_Li^⁎) of the LTaO and LNbO thin films were determined by secondary ion mass spectroscopy (SIMS) using ⁶Li and ⁷Li isotopes. Surface analysis of the LTaO- and LNbO-coated LCOs before and after electrochemical measurement was performed using X-ray photoemission spectroscopy (XPS). The LTaO and LNbO thin films indicated fast lithium-ion diffusion; moreover, no degradation of the surface of the LNbO-coated LCO was observed during the electrochemical measurements. Therefore, LNbO is considered an excellent coating material for decreasing interfacial resistance.