Disorder/order-heterophase VO2 for enhanced lithium storage performance in lithium-ion capacitors

Interfacial engineering has proved to be an effective strategy for improving the performance of electrode materials in many applications. Herein, we report the disorder-order engineering of VO2 nanorods, and construct a crystal core and a surface-amorphized shell heterostructure (denoted as A-VO2) by simple hydrothermal method and reduction reaction, as a promising anode of lithium ion capacitor (LIC). The tunable amorphous layer introduces a large number of oxygen vacancy, which can efficiently improve electronic conductivity and enhance Li ion storage capacity. The crystalline-amorphous heterointerface generated in A-VO2 can significantly reduce the surface energy of VO2 and Li+ diffusion barrier, as well as increase the charge storage sites. The crystalline-amorphous heterogeneous phases work synergistically to facilitate ion and electron transport and maintain structural stability in discharge/charge process. The A-VO2-2 nanorods electrode possesses high capacity of 309 mAh g−1 at 0.1 A g−1 after 300 cycles, obviously larger than the crystalline VO2 electrode. In addition, the LIC, assembled with A-VO2-2 nanorods as anode and commercial active carbon (AC) as cathode, exhibit great energy density of 76.75 and 22.05 W h kg−1 at power density of 195 and 9360 W kg−1. It can remain 38.9 % of the initial capacity after 5000 cycles, demonstrating an instructive paradigm for disorder-order engineering in LIC electrode materials.