The Jahn-Teller Effect for Amorphization of Molybdenum Trioxide towards High-Performance Fiber Supercapacitor.

Amorphous pseudocapacitive nanomaterials are highly desired in energy storage applications for their disordered crystal structures, fast electrochemical dynamics, and outstanding cyclic stability, yet hardly achievable using the state-of-the-art synthetic strategies. Herein, for the first time, high capacitive fiber electrodes embedded with nanosized amorphous molybdenum trioxide (A-MoO3-x) featuring an average particle diameter of ~20 nm and rich oxygen vacancies are obtained via a top-down method using α-MoO3 bulk belts as the precursors. The Jahn-Teller distortion in MoO6 octahedra due to the doubly degenerate ground state of Mo5+, which can be continuously strengthened by oxygen vacancies, triggers the phase transformation of α-MoO3 bulk belts (up to 30 μm long and 500 nm wide). The optimized fibrous electrode exhibits among the highest volumetric performance with a specific capacitance (C V ) of 921.5 F cm-3 under 0.3 A cm-3, endowing the fiber-based weaveable supercapacitor superior C V and E V (energy density) of 107.0 F cm-3 and 9.5 mWh cm-3, respectively, together with excellent cyclic stability, mechanical robustness, and rate capability. This work demonstrates a promising strategy for synthesizing nanosized amorphous materials in a scalable, cost-effective, and controllable manner.