On the impedance and phase transition of thin film all-solid-state batteries based on the Li4Ti5O12 system

Abstract Model-type thin film all-solid-state batteries (ASSB) of the type Li/”LiPON”/Li 4 Ti 5 O 12 are characterized by impedance spectroscopy as function of the state of charge. Both the contact of Li 4 Ti 5 O 12 (LTO) to the substrate and current collector as well as the Li ion transport through the LTO thin film prove to be important factors for the rate limitation of the cell. The ionic charge transfer resistance between Li 4 Ti 5 O 12 and “LiPON” is proven to not be a rate limiting factor. The impedance measurements are interpreted in terms of the mechanism of phase change in the Li 4 Ti 5 O 12 thin film and the data indicate a solid solution mechanism of phase change. The resulting data are compared to recent results for the Li/”LiPON”/LiCoO 2 system, and several key similarities and differences are highlighted mostly involving the solid electrolyte/Li interface and the degradation thereof. The results are meant to improve the understanding of interfaces in ASSB in general rather than to advance high performance batteries.