Electrochemically induced amorphous-to-rock-salt phase transformation in niobium oxide electrode for Li-ion batteries.

Intercalation-type metal oxides are promising negative electrode materials for safe rechargeable lithium-ion batteries due to the reduced risk of Li plating at low voltages. Nevertheless, their lower energy and power density along with cycling instability remain bottlenecks for their implementation, especially for fast-charging applications. Here, we report a nanostructured rock-salt NbO electrode formed through an amorphous-to-crystalline transformation during repeated electrochemical cycling with Li. This electrode can reversibly cycle three lithiums per NbO, corresponding to a capacity of 269 mAh g at 20 mA g, and retains a capacity of 191 mAh g at a high rate of 1 A g. It exhibits superb cycling stability with a capacity of 225 mAh g at 200 mA g for 400 cycles, and a Coulombic efficiency of 99.93%. We attribute the enhanced performance to the cubic rock-salt framework, which promotes low-energy migration paths. Our work suggests that inducing crystallization of amorphous nanomaterials through electrochemical cycling is a promising avenue for creating unconventional high-performance metal oxide electrode materials.