Hierarchical electrodes of NiCo ₂ S ₄ nanosheets-anchored sulfur-doped Co ₃ O ₄ nanoneedles with advanced performance for battery-supercapacitor hybrid devices

Binder-free electrodes with core-shell structures have shown great potential in a variety of important energy storage systems. In order to endow the core-shell hierarchical structure with enhanced electrochemical properties, rationally designed and fabricated hierarchical structures with controllable morphology and great electrical conductivity are highly desired. In this work, a uniform dendritic S-Co ₃ O ₄ @NiCo ₂ S ₄ hierarchical structure grown on Ni foam was successfully designed and synthesized via sulfur-doping of Co ₃ O ₄ (S-Co ₃ O ₄ ) as the inner core with enhanced conductivity. The hierarchical electrode exhibited high areal capacity (10.9 mA h cm ⁻² at a current density of 8 mA cm ⁻² ), a good rate performance (72.5% retention after increasing the current densities from 8 to 30 mA cm ⁻² ), and excellent cycling stability (97.3% retention after 5000 cycles). Moreover, a hybrid energy storage battery-supercapacitor device, constructed from a S-Co ₃ O ₄ @NiCo ₂ S ₄ positive electrode and an active carbon (AC) negative electrode, showed high energy density and power density. Contributing to short ion diffusion, large electroactive sites and low contact resistance, our work not only demonstrates a promising electrode for energy storage battery-supercapacitor hybrid (BSH) devices, but also provides an attractive strategy for the design of electrode materials.