Nickel-cobalt based aqueous flexible solid state supercapacitors with high energy density by controllable surface modification

An available strategy is rationally designed to modify the electrode surfaces with specific electric property based on the controllable surface modifications. In this way, the substitution of oxygen with sulfur can be realized on the surfaces of nickel-cobalt-based molybdate with low temperature chemical vapor deposition method, in which the structures are well-retained. The obtained electrode materials after sulfuration at low temperature are transformed to be nickel-cobalt-based molybdate which is covered with a thin layer of sulfides. Compared with NixCoyMoO4 precursor, the formation of nanocrystalline particles (5-10nm in size) on the surfaces of the nanosheets after sulfuration will supply much more electrochemical active centers, facilitating the improvement the electrochemical performance of the electrode materials. The oxides-sulfides electrode (NixCoyMoO4@MoS2/CoS/NiS)exhibits a good specific capacity of 1689F g(-1), satisfactory cycle performance with an outstanding retention (90.6%) after 5000 cycles. Besides, an excellent retention of the capacitances (85.3%) can be maintained as the current density is high to be 30 A g(-1). Furthermore, the corresponding flexible all-solid-state battery hybrid supercapacitor is developed with the energy density high to be 60.4 W h kg(-1) at 800.6 W kg(-1) and remarkable stability (94.4% retention) after 5000 cycles.