Metastable Cation-Disordered Niobium Tungsten Oxides as Li-ion Battery Anode Materials

Metastable cation-disordered compounds have greatly expanded the synthesizable compositions of solid-state materials and drawn sharp attention among battery electrochemists. While such a strategy has been very successful in a few well-known structures, such as rock salts, metastable cation-disordered materials for other structural types, especially for non-close packed structures, are peculiarly underexplored. In this work, we develop a new series of fully cation-disordered metastable niobium tungsten oxides with a simple structure, and name this new structural type anti-Li3N. Furthermore, we find that metastable anti-Li3N NWOs transform to a cation-disordered cubic structure when applied as a Li-ion battery anode, highlighting an intriguing non-close packed to close packed conversion between two cation-disordered phases, as evidenced in various physicochemical characterizations, in terms of diffraction, electronic, and vibrational structures. This work enriches the structural and compositional space of niobium tungsten oxide families, cation-disordered solid-state materials, and the working mechanisms of Li-ion battery anodes.