A method of preparing carbon-coated cuprous oxide, including: (1) preparing a liquid polyacrylonitrile (LPAN) solution, stirring the LPAN solution to yield a cyclized polyacrylonitrile solution; (2) heating the cyclized LPAN solution to yield a thermally-oxidized polyacrylonitrile (OPAN); (3) mixing the thermally-oxidized polyacrylonitrile with a copper compound to yield a mixture, and adding to the mixture a hydrophilic solvent or a hydrophobic solvent, thus yielding a polyacrylonitrile coated copper compound; (4) drying the polyacrylonitrile coated copper compound in an oven until the solvent is evaporated completely and the polyacrylonitrile coated on the copper compound is crosslinked to form a solid, where yielding a carbonized precursor coated copper compound; and (5) calcining the carbonized precursor coated copper compound in the presence of an inert gas flow of between 10 and 500 mL/min.