An environmentally friendly and feasible route was creatively put forward to synthesize LiFePO4 using two industrial wastes, Fe-P and CO2 from yellow phosphorus manufacture. LiFePO4 was obtained via a one-step synthesis in which the mixture of Fe1.5P, Li2CO3, and H3PO4 in an appropriate molar ratio was calcined at 800 degrees C for 6 h in CO2. The chemical reaction mechanism was investigated by thermogravimetric and differential scanning calorimetric analysis and X-ray diffraction measurements; thereby, the appropriate synthesis conditions were determined. The electrochemical performances of the synthesized LiFePO4 coated with 5.3 wt % carbon were characterized by charge-discharge tests, cyclic voltammetric experiments, and electrochemical impedance spectroscopic measurements, which indicate high capacity, good cyclic capability, and low impedance. Fe-P waste slag and the greenhouse gas CO2 are successfully converted into the energy materials in this work, which improves the traditional two-step synthesis route and provides a new route of LiFePO4 production.