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 high‐power lithium‐ion capacitors.