Single-Crystal Nano-Subunits Assembled Accordion-Shape WNb 2 O 8 Framework with High Ionic/Electronic Conductivities towards Li-Ion Capacitors.

Recently, Li-ion capacitors (LICs) have drawn tremendous attention due to their high energy/power density along with long cycle life. Nevertheless, the slow kinetics and stability of the involved anodes as bottleneck barriers always result in the modest properties of devices. The exploration of advanced anodes with both high ionic and electronic conductivities as well as structural stability thus becomes more significant for practical applications of LICs. Herein, a single-crystal nano-subunits assembled hierarchical accordion-shape WNb 2 O 8 micro-/nano framework is first designed via a one-step scalable strategy with the multi-layered Nb 2 CT x as a precursor. The underlying solid solution Li-storage mechanism of the WNb 2 O 8 just with a volumetric expansion of ≈1.5% is proposed with in situ analysis. Benefiting from congenitally crystallographic merits, single-crystalline characteristic, and open accordion-like architecture, the resultant WNb 2 O 8 as a robust anode platform is endowed with fast electron/ion transport capability and multi-electron redox contributions from W/Nb, and accordingly, delivers a reversible capacity of ≈135.5 mAh g -1 at a high rate of 2.0 A g -1 . The WNb 2 O 8 assembled LICs exhibit an energy density of ≈33.0 Wh kg -1 at 9 kW kg -1 , coupled with remarkable electrochemical stability. The work provides meaningful insights into the rational design and construction of advanced bimetallic niobium oxides for next-generation LICs.