Structure and electrochemical performances of NiCo hydroxide with anion exchange by carbonates for hybrid supercapacitor

Abstract Transition metal‐based hydroxides have received much attention as promising electrode materials for hybrid supercapacitors (HSCs). In this work, we report the effects of anion exchange on the structure and electrochemical performances of NiCo hydroxides when controlling the amount of carbonate added during the hydrothermal process. Structural investigations of NiCo hydroxides found that the incorporation of carbonate additives significantly affects the morphology, also causing a change in crystalline phase, which transform from a layered double hydroxide (LDH) to a carbonate hydroxide (CH). The CH electrode incorporating 3 mmol of Na 2 CO 3 (CH‐S3) exhibits superior electrochemical performance, achieving a maximum specific capacitance of 2130 F g ‒1 at a current density of 2 A g ‒1 , attributed to the optimized concentration of the carbonate additive. Moreover, HSCs consisting of CH‐S3//activated carbon were assembled and found to possess a maximum energy density of 56.2 Wh kg −1 at a power density of 425 W kg −1 , along with outstanding stability during 5000 cycles. Therefore, we propose that an efficient energy storage device can be implemented through the proposed facile approach with an anion exchange step.