In order to reduce the irreversible capacity and enhance the cycling life of the natural graphite anode of lithium ion batteries, a novel modification method was proposed by encapsulation with an ionically conductive co-polymer on the surface of natural graphite particles via radiation-initiated polymerization. The encapsulated graphite shows great improvement in electrochemical performance such as initial coulombic efficiency and cycleability compared with the original natural graphite. Raman spectroscopy indicates that encapsulation with an ionic conductive polymer can depress the structural changes caused by the cointercalation of solvent molecules. Stable electrode impedance during the repeated cycling is revealed by impedance spectra for encapsulated graphite.