Fast phase transformation of micrometer-scale single-crystal TiNb2O7 anode for Ah-level fast-charging laminated pouch cell

The Wadsley-Roth phase TiNb₂O₇ (TNO) has been identified as a promising anode material with potential for high safety and fast-charging lithium-ion batteries (LIBs), arising from its competitive theoretical specific capacity and secure operational potential. Despite the significant advancements in specific capacity, fast charging, and longevity at the coin cell level, a comprehensive understanding and realization of the fast-charging capability and corresponding cycling stability of the TNO under practical application conditions (such as a pouch cell with an anode capacity exceeding 2 mAh cm⁻²) continues to be elusive. In this study, we explore a simple, scalable solid-phase carbon source melt strategy to fabricate the kilogram-level micrometer-scale single-crystal TNO particles enveloped by an ultrathin carbon coating layer of <5 nm (TNO@C). The in-situ X-ray diffraction (XRD) measurement of the LiCoO₂||TNO@C laminated pouch cell (anode mass loading of ∼10 mg cm⁻²) under fast charging/discharging conditions with the combination of material characterizations and electrochemical analysis reveals a fast, yet stable crystal structure evolution for the micrometer-scale single-crystal TNO@C with only 7.03% fluctuation in unit cell volume value, which is indicative of fast reaction kinetics. The Ah-level laminated LiCoO₂||TNO@C pouch cell achieved 80.8% charge within 6 min (10 C) and retained 85.3% capacity after 1000 cycles at the charging current density of 6 C (10 min), far surpassing all the results in previous publications. The straightforward synthetic approach for the micrometer-scale single-crystal TNO@C, coupled with a clear understanding of reaction kinetics and rapid crystal structure evolution, paves the way for the practical application of the micrometer-scale single-crystal TNO@C anode material for fast charging LIBs.