Carbon nanofilms of less than 20nm in thickness were prepared on alumina nanoparticles by pyrolysis of a citric acid precursor to test high-rate charging anode material in lithium ion battery. The electrochemical reaction mechanism of the anode was investigated by changing the voltage from 1.5V to 0.01V with a counter Li metal electrode. The specific capacity of ∼20nm thick carbon nanofilm was 2180mAhg−1, much larger than those of conventional carbon anode materials. The high capacity of carbon nanofilm was attributed to adsorption of Li ion multi-layers on carbon nanofilm surfaces and adsorption on defects, functional groups or micropores of amorphous carbon, in addition to Li intercalation in hard carbons. Very short diffusion path length from ∼20nm ultrathin film (∼20nm) with high specific capacitance was mainly responsible for achieving high-rate charging performance while maintaining reasonable charging capacity compared to soft carbon. The fabricated anode with ∼20nm thick carbon film on alumina nanoparticles improved the specific charging capacity by 9.4% at 1C rate and 8.3% at 10C rate compared to conventional soft carbon.