L. Wang, X. Zhang*, C. Li, Y.N. Xu, Y.B. An, W.J. Liu, T. Hu, S. Yi, K. Wang, X.Z. Sun, Y. Gong, Z.-S. Wu*, Y.W. Ma*

Chemical Engineering Journal, 2023, 468.

DOI: 10.1016/j.cej.2023.143507 [PDF]

Orthorhombic niobium pentoxide (T-Nb2O5) is widely acknowledged as a fast pseudocapacitive material. Nevertheless, its application is hindered by the narrow voltage window (1-3 V vs. Li/Li+), due to the irreversible phase transformation and sluggish kinetics upon deep lithiation. Herein, we demonstrate a unique method for introducing Nb vacancies in T-Nb2O5 nanoparticles via amine-assisted oxidative etching of Nb2CTx MXene, providing extra storage sites and improving structural flexibility by introducing cationic defects. Subsequently reduced graphene oxide (rGO) is employed as substrate to disperse T-Nb2O5 nanoparticles and construct T-Nb2O5/rGO nanohybrids. Through multiple characterizations and computational simulations, the ability of T-Nb2O5/rGO to realize rapid and stable multi-electron transfer lithium storage is witnessed. Owing to the enrichment of Nb vacancies and nanoparticle morphology, even when voltage window of 0.01-3 V (vs. Li/Li+) is extended, T-Nb2O5 exhibits a pseudocapacitive mechanism and integrity of partial crystal structure; effectively tackling the structural collapse and sluggish kinetics of T-Nb2O5. Consequently, the T-Nb2O5/rGO anode shows a superior rate capacity (148 mAh/g at 10 A/g), and cycling stability (3000 cycles at 5 A/g). Notably, the as-assembled lithium-ion capacitors achieve a high energy density of 123.7 Wh/kg, a power density of 22.5 kW/kg, and a capacity retention of 83.6% after 20000 cycles.