Ultra-stable and high-performance battery-capacitor hybrid device via in situ heterojunction optimisation coupled...

Efficient aqueous battery-capacitor hybrid devices combine the benefits of supercapacitors and batteries, achieving exceptional energy density, superior power density, and long-term cycling stability while maintaining excellent safety performance. However, achieving a high degree of matching between battery-type positive electrodes and capacitor-type negative electrodes remains a major challenge. Here, we present an in situ heterojunction optimisation strategy to construct a heterojunction structure composed of a nickel cobalt-based layered double hydroxide (NiCo-LDH) flake and spinel nickel cobalt oxide (NiCo₂O₄) wire on nickel foam (NF) substrate (NC-NCO@NF). This battery-type electrode provided abundant active sites and an ultra-high specific capacity (2840.2 F g^-1 at 0.5 A/g). Meanwhile, a capacitor-type electrode was fabricated by the in situ growth of fragmented reduced graphene oxide thin sheets with multiple edge defects on nickel foam (FrGO@NF), offering excellent conductivity and sufficient multi-edge active sites for fast ion diffusion and charge transport. Benefitting from the high degree of synergy and compatibility between the capacitor-type negative electrode and battery-type positive electrode, an efficient aqueous hybrid device fabricated with an NC-NCO@NF anode and FrGO@NF cathode demonstrated a wide operating voltage range (1.5 V), superior energy-power density (105.6 Wh kg^-1 at 750 W kg^-1) density, and ultra-stable cycling performance (98.6% capacity retention after 14,000 cycles, corresponding to 2000 h). This study not only provides a novel strategy for electrode material design and device architecture construction, but also establishes a solid experimental and theoretical foundation for the advancement and practical implementation of high-performance energy storage systems.