Electrochemical impedance analysis of the charge transfer mechanism on Li4Ti5O12 surface in the presence or absence of the solid/electrolyte interface film

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A novel three-electrode type cell is developed for highly reliable electrochemical impedance spectroscopy (EIS). A pair of Li4Ti5O12 (LTO) electrodes are placed at both end of the cell, and a lithium counter electrode is inserted between them to assemble a three-electrode-type LTO half-cell. The half-cell is initially discharged to either 0.3 or 1.4 V to prepare the pair of LTO electrodes with or without a solid/electrolyte interface (SEI) film, respectively. The half-cells are reassembled to LTO symmetric cells by removing the central Li electrode without damaging the LTO electrodes. EIS measurements of the symmetric cell indicate impedances associated with charge transfer (RCT) and the SEI film (RSEI) in distinctly different frequency ranges. The temperature dependences of RCT and RSEI are analyzed to clearly understand the influence of the SEI film on the charge transfer mechanism and to explicitly support the common understanding that lithium ions are desolvated at the film/electrolyte interface or inside the film through a different consideration than the conventional one.