Fast and Durable Lithium Storage Enabled by Tuning Entropy in Wadsley–Roth Phase Titanium Niobium Oxides

Abstract

Wadsley–Roth phase titanium niobium oxides have received considerable interest as anodes for lithium ion batteries. However, the volume expansion and sluggish ion/electron transport kinetics retard its application in grid scale. Here, fast and durable lithium storage in entropy-stabilized Fe0.4Ti1.6Nb10O28.8 (FTNO) is enabled by tuning entropy via Fe substitution. By increasing the entropy, a reduction of the calcination temperature to form a phase pure material is achieved, leading to a reduced grain size and, therefore, a shortening of Li+ pathway along the diffusion channels. Furthermore, in situ X-ray diffraction reveals that the increased entropy leads to the decreased expansion along a–axis, which stabilizes the lithium intercalation channel. Density functional theory modeling indicates the origin to be the more stable Fe-O bond as compared to Ti-O bond. As a result, the rate performance is significantly enhanced exhibiting a reversible capacity of 73.7 mAh g−1 at 50 C for FTNO as compared to 37.9 mAh g−1 for its TNO counterpart. Besides, durable cycling is achieved by FTNO, which delivers a discharge capacity of 130.0 mAh g−1 after 6000 cycles at 10 C. Finally, the potential impact for practical application of FTNO anodes has been demonstrated by successfully constructing fast charging and stable LiFePO4‖FTNO full cells.