Controllable Assembly of Hybrid Electrodes by Electrophoretic Deposition for High-Performance Battery-Supercapacitor Hybrid Devices

Hybrid electrodes, which are made of a physical (electrical double layer) storage component and a chemical (battery-type) material, have shown great potential in battery-supercapacitor hybrid (BSH) devices. Here, we present an approach which is based on electrophoretic deposition (EPD) as a means of assembling a binder-free, high-performance BSH device. Ketjenblack (KB) used as the physical storage material and NiCo₂O₄ (NCO) as the chemical storage compound were dispersed in the presence of Ni²⁺. The latter assisted in positively charging the surface of both materials and thus resulted in similar deposition rates by EPD on nickel foam (NF). This enabled us to nicely control the NCO to KB ratio in the hybrid electrode and optimize its performance. In this binder-free hybrid electrode, the KB chains served as a fast electron path providing high conductivity for the NCO electroactive material. More importantly, the KB chains could remain in contact with NCO coping with the mechanical stress during the electrochemical reaction. As a result, the optimized hybrid electrode showed high specific capacity (460 C g^-1 at 1 A g^-1) and excellent cycling performance (82.5% retention after 15 000 cycles). The BSH device was assembled with the hybrid electrode (NF/NCO-KB) as positive and activated carbon as negative electrodes, and exhibited high energy density of 53.0 Wh kg^-1 at power density of 746 W kg^-1 and outstanding cycling performance of 88.6% retention after 10 000 cycles.