Oxygen Vacancies Enhanced NiCo 2 O 4 Nanoarrays on Carbon Cloth as Cathode for Flexible Supercapacitors with Excellent Cycling Stability

Defect engineering such as oxygen vacancy in heterostructured electrode materials has emerged as a promising strategy to improve material performance in energy storage and conversion fields. The most common methods to introduce oxygen vacancies in energy materials usually involve high temperature treatment or strong reducing agents. In this work, we adopted a mild solvothermal treatment method to introduce oxygen vacancies into NiCo2O4 (Vo-NiCo2O4) nanoarrays. Owing to the increased oxygen vacancies and the improved surface area, the as-prepared Vo-NiCo2O4 on carbon cloth (Vo-NiCo2O4@CC) shows a high specific capacitance of 1389 mF cm−2 under the current density of 0.5 mA cm−2, and a remarkable capacitance retention of 93.8 % after 10000 cycles when used as cathode for supercapacitor. Moreover, an aqueous asymmetric supercapacitor was assembled using Vo-NiCo2O4@CC as cathode and AC@CC as anode and this device delivers a high energy density of 43.6 Wh kg−1 at a power density of 281 W kg−1. In addition, the as-assembled quasi-solid state asymmetric supercapacitor exhibits excellent mechanical flexibility and functions well while being bent at large angles or being twisted. This work offers a facile, cost-effective and practical available approach to finely tune the surface property of electrode materials towards flexible energy storage devices for wearable applications.