Design of nickel cobalt oxide and nickel cobalt oxide@nickel molybdenum oxide battery-type materials for flexible solid-state battery supercapacitor hybrids

The flexible solid-state battery supercapacitor hybrid (SBS) is one of the promising energy storage devices for wearable electronic devices. Surface properties of active materials play important roles on electrolyte/active material interaction and energy storage ability. This work applies nickel cobalt oxide (NiCo2O4) and nickel cobalt oxide@nickel molybdenum oxide (NiCo2O4@NiMoO4) as the active material for SBS. Effects of structure directing agents (SDA) and substrates on surface properties and energy storage abilities of active materials are investigated. SDA has less influence on active material morphology while Ni foam with higher electrical conductivity is preferable as substrate. The best energy storage ability is obtained for SBS with NiCo2O4@NiMoO4 electrode prepared using ammonium fluoride with capacity of 0.68 mAh/cm(2) and the maximum energy density of 70.78 Wh/kg at 3.25 kW/kg. Excellent bending ability for the device with nearly no capacitance decay under 150 bending is attained. Capacitance retention of 80% and Coulombic efficiency of higher than 95% are achieved for SBS measured in 5000 times charging/discharging process. This work firstly relates surface property of active materials to energy storage ability of SBS. It is expected that more efficient active materials and better energy storage ability can be eventually achieved by understanding effects of synthesizing parameters.