An innovative concept of activation of electrode materials for Li-ion batteries is proposed through the preparation of carbon-phosphorus (P/C) composites. Carbon-encapsulated phosphorus composites can be successfully prepared via a simple route by the vaporization–condensation of red phosphorus onto mesoporous carbon. Surface area measurements and Raman spectroscopy were used for the characterization of the P/C composites, which were then tested as anode materials in Li-ion batteries showing enhanced electrochemical properties. In contrast to what is observed for pure unsupported phosphorus, Li storage in P/C composite occurs through the reversible formation of Li 3P during the discharge process, as clearly evidenced by in situ XRD, leading to capacities greater than 900 mAh g −1 after 20 cycles.