Structural Distortion in the Wadsley‐Roth Niobium Molybdenum Oxide Phase Triggering Extraordinarily Stable Battery Performance

with superior electrochemical Li-ion storage performance, including an ultralong cycling lifespan of at least 15000 cycles. During electrochemical cycling, a reversible single-phase solid-solution reaction with lithiated intermediate solid solutions is demonstrated using in situ X-ray diffraction, with the valence and short-range structural changes of the electrode probed by in situ Nb and Mo K-edge X-ray absorption spectroscopy. This work reveals that the superior stability of niobium molybdenum oxides is underpinned by changes in octahedral distortion during electrochemical reactions, and we report an in-depth understanding of how this stabilizes the oxide structure during cycling with implications for future long-life battery material design.