High-capacity lithium-containing alloy anodes (e.g., Li_4.4Si, Li_4.4Sn, and Li₃P) enable lithium-free cathodes (e.g., Sulfur, V₂O₅, and FeF₃) to produce next-generation lithium-ion batteries (LIBs) with high energy density. Herein, we design a Li₃P/C nanocomposite with Li₃P ultrafine nanodomains embedded in micrometer-scale porous carbon particles. Benefiting from the unique micro/nanostructure of the Li₃P/C nanocomposite, electrons transfer rapidly through the conductive pathway provided by the porous carbon framework and the volume change between Li₃P and P is confined in the nanopores of the carbon, which avoids the collapse of the whole Li₃P/C composite particles. As expected, the as-achieved Li₃P/C nanocomposite provided a high available lithium-ion capacity of 791 mAh/g (calculated based on the mass of Li₃P/C) at 0.1 C during the initial delithiation process. Meanwhile, the Li₃P/C nanocomposite showed 75% of its 0.5 C capacity at 6 C and stable cycling stability.