Regulation preferred crystal plane and oxygen vacancy of CoWO4 with morphology remolding to boost electrochemical performances for battery-supercapacitor hybrid device electrode

Crystal plane engineering and defect engineering are feasible approaches to tune the electrochemical performance of nanocmaterials. Herein, a carambola-like CoWO4 microsphere with preferred crystal planes and oxygen vacancies is synthesized by a microwave-assisted hydrothermal process together with post annealing treatment. The in-depth observation on microstructure and electrochemical tests suggest that it is the new preferred crystal planes and oxygen vacancies in CoWO4 that improves conductivity and reaction activity to lead to a much higher capacity. Further density functional theory (DFT) analysis reveals that tuning the preferred crystal plane and introduction of oxygen vacancy into CoWO4 not only effectively enhance electronic conductivity, but also promote OH− adsorption/desorption, and reduce electronic transmission barrier. As a result, the as-obtained carambola-like CoWO4 microsphere with preferred crystal planes and oxygen vacancies delivers high specific capacity (493.7 C g−1/137.1 mA h g−1 at 1 A g−1) with superior rate capability (148.6 C g−1/41.3 mA h g−1 at 15 A g−1). Moreover, the cycling-induced morphology evolution lead to unconventional capacity increasing during cycling. The as-fabricated A-CoWO4//6 M KOH//activated carbon (AC) BSH device exhibits a maximum energy density of 27.5 Wh kg−1 at 1031.4 W kg−1 and 95.7% capacity retention after 12000 cycles. This work provides a possible way to improve the electrochemical performances of other metal oxide electrodes with low-capacity and irreversibility.