Hierarchical ZnCo2O4-ZnO/ZnCo2O4 core-shell microarchitecture as pseudocapacitive material with ultra-high rate capability and enhanced cyclic stability for asymmetric supercapacitors

Abstract

Compared with materials for electric double layer capacitors, pseudocapacitive electrode materials have the disadvantage of poor cyclic stability, which is expected to be improved via reasonably designing material microarchitecture. In this work, the hierarchical ZnCo2O4-ZnO/ZnCo2O4 core–shell microarchitecture composite was constructed directly on Ni foam by a two-step solvothermal pathway and calcination. In particular, by growing porous ZnCo2O4 nanosheets on the surface of ZnCo2O4-ZnO microsphere, the pseudocapacitance was significantly enhanced. In addition, this superior configuration provided a stable space structure and highly exposed surface/interface with abundant electrochemical reaction sites, to ensure both the long-term cyclic stability and the diffusion and transfer of electrolyte ions in fast redox kinetics. Consequently, the as-prepared pseudocapacitive material possessed a high specific capacity (2487F g−1 at 1 A g−1), ultrahigh rate capability of 2110F g−1 at 20 A g−1, striking pseudocapacitance contribution (∼95% at 1.0 mV s−1), and ultra-long cycle stability (6000 cycles with 93.3% of capacitance retention). Furthermore, the assembled aqueous asymmetric supercapacitor demonstrated a high energy density of 55.46 W h kg−1 at 1500 W kg−1. The overall results offered a promising approach for rationally designing pseudocapacitive electrode materials with abundant surface/interface active sites for high-performance supercapacitors.