Abstract
Nano-oxides and hydroxides generate great interest as promising positive electrode materials for the development of high energy density supercapacitors. However, their usually limited ionic and electronic conductivities significantly decrease their energy storage performances when increasing the electrode's mass loading. Here, we report on a sonochemical approach to functionalize the surface of Co(OH)2 nanomaterials by EmimBF4 ionic liquid that greatly improves the stability and the electrochemical performances of high mass loading electrodes (13 mg cm−2). This surface functionalization boosts the transport properties and strongly enhances the capacity as well as the capacity retention at higher current densities compared to basic Co(OH)2 (e.g. 113.5 C g−1 vs 59.2 C g−1 at 1 A g−1). Additionally, the protective layer formed by the ionic liquid stabilizes the electrode material upon cycling in KOH aqueous electrolyte and protects the material from oxidation upon open-air storage.