Insights into Formation and Li-Storage Mechanisms of Hierarchical Accordion-Shape Orthorhombic CuNb2O6 toward Lithium-Ion Capacitors as an Anode-Active Material

The orthorhombic CuNb2O6 (O-CNO) is established as a competitive anode for lithium-ion capacitors (LICs) owing to its attractive compositional/structural merits. However, the high-temperature synthesis (> 900 & DEG;C) and controversial charge-storage mechanism always limit its applications. Herein, we develop a low-temperature strategy to fabricate a nano-blocks-constructed hierarchical accordional O-CNO framework by employing multilayered Nb2CTx as the niobium source. The intrinsic stress-induced formation/transformation mechanism of the monoclinic CuNb2O6 to O-CNO is tentatively put forward. Furthermore, the integrated phase conversion and solid solution lithium-storage mechanism is reasonably unveiled with comprehensive in(ex) situ characterizations. Thanks to its unique structural merits and lithium-storage process, the resulted O-CNO anode is endowed with a large capacity of 150.3 mAh g(-1) at 2.0 A g(-1), along with long-duration cycling behaviors. Furthermore, the constructed O-CNO-based LICs exhibit a high energy (138.9 Wh kg(-1)) and power (4.0 kW kg(-1)) densities with a modest cycling stability (15.8% capacity degradation after 3000 consecutive cycles). More meaningfully, the in-depth insights into the formation and charge-storage process here can promote the extensive development of binary metal Nb-based oxides for advanced LICs.

Automated summary

In this study, we developed a low-temperature strategy to synthesize a nano-blocks-constructed hierarchical O-CNO anode using multilayered Nb2CTx as the niobium source. The phase conversion and solid solution lithium-storage mechanism of O-CNO were unveiled through comprehensive in(ex) situ characterizations. The resulted O-CNO anode exhibited high capacity, long cycling stability, and high energy and power densities in LICs.