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Abstract

Titanium niobium oxides (TNOs) are attractive anode materials for high power density Li-ion batteries. However, the details of capacity storage in TNOs are not fully understood today as it depends on the Ti and Nb composition and their changes in the oxidation state. This is further complicated by a wide variation in gravimetric capacities reported in the literature for TNO anodes. Therefore, in this work, we systematically synthesise TiNb₂O₇, Ti₂Nb₁₀O₂₉, Ti₂Nb₁₄O₃₉, and TiNb₂₄O₆₂ particles using the same solid state reaction approach and report their electrochemical properties via galvanostatic cycling, cyclic voltammetry, and the galvanostatic intermittent titration technique (GITT). Furthermore, we use operando X-ray absorption spectroscopy (XAS) to investigate the redox reactions taking place in each of these compositions, which provides new insights into their charge storage mechanisms. We found that of the materials tested, TiNb₂O₇ anodes show the best cycling and rate performance, which could be related to the higher utilization of Nb redox revealed via operando XAS analysis.