In situ impedance analysis on BaTiO3-LiCoO2 composite cathodes for lithium ion batteries

摘要

In situ electrochemical impedance spectroscopy (EIS) was undertaken to investigate the contribution of a ferroelectric artificial solid electrolyte interface (SEI) to the enhancement of the rate capability of lithium ion batteries. Resistance elements, consisting of the cell reactions, the resistance of the electrolyte, R-sol, that of the Li metal anode reaction, R-Li, and the charge transfer resistance, R-ct, were measured. A small ferroelectric BaTiO3 (BT) load, similar to 1 mol %, notably reduced R-ct and R-sol compared with bare LiCoO2 (LC), indicating that loaded ferroelectric BT SEIs effectively promote Li inter/deintercalation into and from the active material, LC, and restrict cobalt ion dissolution into the electrolyte liquid. Lower R-ct and R-sol resulted in a significantly higher capacity retention ratio at a 10C rate compared with the initial cycle for small BT load, similar to 1 mol %. The capacity retention dropped rapidly, accompanied by a slight increase in R-ct for larger BT loads, 5 and 15 mol %, which may be attributed to the thicker BT layer and the existence of the impurity phase, BaCO3. These results imply that the ferroelectric SEI affected the kinetics of mobile Li ions at the cathode-electrolyte interface, significantly enhancing the rate capability. (C) 2015 The Japan Society of Applied Physics