Electrochemically constructing V-doped BiFeO3 nanoflake network anodes for flexible asymmetric micro-supercapacitors

Abstract

Bismuth ferrite (BiFeO3) with high specific capacity and wide voltage window, fundamentally stores charge through the reversible redox reactions of cations, but usually suffers from poor rate capability and bad cycling stability, due to its densely-packed crystal structure and multi-electron redox reaction kinetics. We present a novel route to regulate nanoflake network architectures and oxygen vacancy defects of BiFeO3 through V doping and electrochemical induction without annealing. After consecutive charge/discharge process of BiFe0.95V0.05O3 fabricated by electrochemical deposition, the cycled BiFe0.95V0.05O3 (c-BiFe0.95V0.05O3) retains better structural stability and more oxygen vacancies than those of the annealed BiFe0.95V0.05O3, revealing the outstanding superiority of electrochemical induction. The c-BiFe0.95V0.05O3 electrode provides high rate capability and Li+ diffusion coefficient, mainly attributed to its nanoflake network architecture and abundant oxygen vacancies. The first-principle calculation demonstrates V doping and oxygen vacancies can enhance built-in electric field and construct fast ion transport channels for boosting rate capability. Based on the c-BiFe0.95V0.05O3 anode and the PPyHG (polypyrrole hydrogel) cathode, flexible asymmetric micro-supercapacitors can deliver an extremely wide voltage window of 2.3 V and a high areal energy density of 7.33 µWh cm−2 at 63.7 µW cm−2, reflecting its huge potential for flexible energy storage micro-devices.