Charge-Transfer Kinetics of The Solid-Electrolyte Interphase on Li4 Ti5 O12 Thin-Film Electrodes

Abstract

Charge-transfer kinetics between electrodes and electrolytes critically determines the performance of lithium-ion batteries (LIBs). Lithium titanate defect spinel (Li₄ Ti₅ O₁₂ , LTO) is a safe and durable anode material, but its relatively low energy density limits the range of applications. Utilizing the low potential region of LTO is a straightforward strategy for increasing energy density. However, the electrochemical characteristics of LTO at low potentials and the properties of the solid-electrolyte interphase (SEI) on LTO are not well understood. Here, we investigate the charge-transfer kinetics of the SEI formed between model LTO thin-film electrodes and organic electrolytes with distinct solvation ability using AC impedance spectroscopy whereas their stability was assessed by cyclic voltammetry of ferrocene. With the SEI film on LTO, the Li⁺ desolvation was rate-determining step but with larger activation energies, which showed a strong dependence on the solvation ability of electrolyte. The activation energies of desolvation for the fluoroethylene carbonate+dimethyl carbonate- and ethylene carbonate+diethyl carbonate-based systems increased from 35 and 55 to 44 and 67 kJ mol^-1 , respectively, and that for the propylene carbonate-based system did not noticeably change at around 67 kJ mol^-1 . In addition, the SEI passivation of LTO was much slower than that of graphite, and the rate also strongly depended on the solvation ability of the electrolyte. Understanding the surface properties of LTO at low potentials opens the door for high-energy-density LTO-based LIBs.

Keywords: Li4Ti5O12; desolvation; lithium-ion batteries; organic electrolytes; solid-electrolyte interphase.