Hard carbon-coated natural graphite electrodes for high-energy and power lithium-ion capacitors

Hard carbon-coated natural graphite materials have been prepared and evaluated as a negative electrode for high-energy and high-power lithium-ion capacitors. The graphite surface was coated with hard carbon by using polyacrylonitrile as a precursor, which was confirmed by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The hard carbon coating on natural graphite particles significantly affects the electrochemical characteristics of lithium-ion capacitors. The full-cell using the hard carbon-coated graphite electrode showed much higher energy and power densities than those with pristine natural graphite and hard carbon electrodes, respectively. Furthermore, the hard carbon-coated graphite electrode exhibited an enhanced cycle performance with a capacity retention of 74.6% after 10,000 cycles, higher than those of pristine natural graphite (33.3%) and the mixture of hard carbon and natural graphite (51.4%). The results clearly indicate that the hard carbon-coated graphite electrode is suitable as a negative electrode material for high-energy and highpower lithium-ion capacitors.