In this work, a convenient and efficient one-step solid-phase synthesis method (SPS) is successfully developed for the preparation of NixPy@C nanocomposites under an ambient atmosphere. By controlling the synthesizing temperature, carbon-coated Ni2P, Ni5P4, and NiP2 nanocomposites can be facilely synthesized. The solid-phase synthesized NixPy@C nanocomposites exhibit high charge storage capability and good cycle stability. A high specific capacity of over 197.2 mAh g-1 (709.9 C g−1) is achieved at a current density of 1 A g-1 for the optimal nanocomposite NiP2@C. The assembled hybrid supercapacitor device based on the NiP2@C nanocomposite and an interconnected hierarchical porous carbon (NiP2@C//IHPC) delivers a specific energy of up to 50.38 Wh kg-1 at a specific power of 0.89 kW kg-1. More than 83.8% of initial specific capacity is retained after 20000 cycles. This method is proved to be a reliable strategy for simple preparation of high-performance transition metal phosphides for energy storage devices.