PPy@NiCo2S4 nanosheets anchored on graphite foam with bicontinuous conductive network for high-areal capacitance and high-rate electrodes

Abstract A three-dimensional (3D) free-standing polypyrrole@NiCo 2 S 4 /GF electrode with internal/external bicontinuous conductive network has been prepared via a two-step hydrothermal process coupled with subsequent in situ polymerization method. The NiCo 2 S 4 nanosheets coated with highly conductive polypyrrole (PPy) shell were uniformly grown on 3D interconnected conductive graphite foam (GF) network. The ultrathin NiCo 2 S 4 nanosheets with 2D layered structure can offer sufficient electrolyte/active materials interface and high capacitance; while GF substrate coupled with PPy conductive shell can serve as an internal/external bicontinuous conductive network, which can greatly enhance the electron transfer rate. The PPy@NiCo 2 S 4 /GF-2 electrode could deliver a high areal specific capacitance of 8.5 F/cm 2 at 1 mA/cm 2 , and a high rate performance of 53% retention can be achieved even under 50 mA/cm 2 . This bicontinuous conductive network fabrication strategy may be applied to high performance energy storage electrodes with industrial-scale.