Modulated synthesis of nickel copper bimetallic compounds by ammonium fluoride-based complex as novel active materials of battery supercapacitor hybrids

Bimetallic compounds have attracted much attention as efficient active materials of battery supercapacitor hybrid (BSH), owing to their multiple redox states, high electrical conductivity, and simply synthesis process. Nickel-based compounds offer high theoretical capacities, while copper-based compounds provide high electrical conductivity. The energy storage performance can be further enhanced designing favorable morphologies, which can be influenced by the incorporation of structure directing agents (SDAs) such as NH₄BF₄ and NH₄HF₂. In this study, nickel and copper bimetallic compounds are synthesized as active materials of BSHs in a novel environment containing metal salts, NH₄BF₄, NH₄HF₂, and 2-methylmidozole. The effects of the Cu to Ni ratio on material and electrochemical properties are investigated. To enhance the electrochemical contributions of nickel, which has higher theoretical capacities, the reaction time for copper ions is reduced. The optimal bimetallic (CuNi13) electrode achieves the highest specific capacitance (C_F) of 1758.0 F/g, corresponding to a capacity of 791.1C/g at 1 A/g, due to the higher nickel content and smaller sheet sizes. The BSH assembled using the CuNi13 and reduced graphene oxide electrodes demonstrates a maximum energy density of 109.1 Wh/kg at 1071 kW/kg. The C_F retention of 85.5% and Coulombic efficiency of 93.6% are also maintained after 10,000 cycles.