Reversible electrochemical lithium cycling in a vanadium(IV)- and Niobium(V)-based Wadsley-Roth phase

E. A. Lawrence, M. A. Davenport, R. Devi, Z. Cai, M. Avdeev, J. R. Belnap, J. Liu, H. Alnaser, A. Ho, T. D. Sparks, G. Sai Gautam, J. Allred, and H. Ji; Chem. Mater. 35, 3470-3483 (2023)


Fast charging remains one of the greatest safety challenges in Li-ion batteries due to Li-dendrite growth occurring on graphite anodes if they are lithiated too quickly. The search for high-rate anodes has highlighted materials in the Wadsley–Roth (WR) shear phase family. The relative abundance of V compared with traditional WR compositions of Nb and W makes V-based phases attractive. However, the high voltage and poor reversibility typically associated with V redox have made V-rich WR phases less studied than Nb- and W-rich phases. Here, we show that a new V-rich Wadsley–Roth phase, V7Nb6O29, achieves excellent rate capability and 80% capacity retention after 228 cycles with a relatively low average voltage of 1.76 V vs Li/Li+ compared with other V-rich WR phases. Single-crystal X-ray diffraction reveals a P4/m space group with repeating 2 × 2 × ∞ and 3 × 3 × ∞ blocks of V4+ and Nb5+ octahedra. Combined neutron pair distribution function analysis, X-ray absorption spectroscopy, and density functional theory calculations show that V redox is the primary source of capacity and that cycling stability is provided by the stable octahedral coordination adopted by V4+ in the material.

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