Degradation mechanisms in low-voltage Wadsley-Roth TiNb2O7 electrodes upon cycling with Li

Abstract

Drawing more and more interest, Wadsley-Roth phases, and more specifically titanium-niobium oxide (TNO), are considered as serious competitor for Li₄Ti₅O₁₂ exhibiting a higher capacity and thus a larger specific energy. Many groups report advanced synthesis route for this material but only little consideration was given to the study of the lithiation and degradation mechanisms. In this work, we report an astonishing evolution in the cycling performance of TiNb₂O₇, synthesized with a normal solid-state route, displaying a strong variation of performances at high rates depending on its cycling history. To understand the underlying phenomena, we carried out many investigations, in particular by confronting in situ and post mortem X-ray diffraction with neutrons diffraction results. RAMAN spectroscopy and HRSTEM experiments were also performed to push further the understanding of degradation mechanisms.