Micrometer-scale single crystalline particles of niobium titanium oxide enabling an Ah-level pouch cell with superior fast-charging capability.

Wadsley-Roth phase niobium titanium oxide (TiNbO) is widely regarded as a promising anode candidate for fast-charging lithium-ion batteries due to its safe working potential and doubled capacity in comparison to the commercial fast-charging anode material (lithium titanium oxide, LiTiO). Although good fast charge/discharge performance was shown for nanostructured TiNbO, the small size would cause the low electrode compensation density and energy density of batteries, as well as parasitic reactions. Fundamental understanding of the electrochemical lithium insertion/extraction process and the structural evolution for the micrometer-scale single crystalline TiNbO (MSC-TiNbO) could provide insights to understand its inherent properties and possibility for fast-charging application. Here, we revealed the highly reversible structural evolution of the MSC-TiNbO during the lithiation/delithiation processes. Interestingly, an ion-conductive lithium niobate interphase was formed on the MSC-TiNbO surface during the formation cycle, which could facilitate fast ion diffusion on the material surface and support fast electrochemical reaction kinetics. Experimentally, the MSC-TiNbO delivered a high reversible capacity of 291.9 mA h g at 0.5C with a high initial Coulombic efficiency (>95%), and showed superb rate capability with a reasonable capacity of 55.6 mA h g under a high current density of 40C. An Ah-level pouch cell with a lithium cobalt oxide (LiCoO) cathode exhibited 91.5% capacity retention at 3C charging rate, which revealed the significant role of high crystallinity and formation of an ion conductive nano-interphase in realizing fast charging capability of practical TiNbO-based lithium-ion batteries.