Irreversible lithium loss in the initial cycles appreciably reduces the energy density of lithium-ion batteries. Prelithiation is an effective way to compensate for such lithium loss, but current methods suffer from either the instability or low capacity of prelithiation reagents. Lithium oxalate (Li₂C₂O₄) has shown great potential as a lithium-compensation material because of its high theoretical capacity (equivalent to lithium metal), low cost, and air stability. However, the practical applications of Li₂C₂O₄ are limited by its low electrochemical activity and high critical decomposition voltage. In this study, we performed the prelithiation of a low-voltage cathode by using Mo₂C catalysis and nano-Li₂C₂O₄. Results show that the Mo₂C catalyst changes the electron cloud distribution around Li₂C₂O₄ and greatly reduces the activation energy, thereby significantly accelerating the lithium release from Li₂C₂O₄. The nano-Li₂C₂O₄ prepared by freeze-drying shows accelerated ionic and electronic conduction as well as close contact with Mo₂C. Benefiting from the synergistic effect, the decomposition potential of Li₂C₂O₄ is decreased by 0.5 V with an efficiency close to 100%. The LiCoO₂∥SiO full cell empowered with the nano-Li₂C₂O₄/Mo₂C prelithiation composite demonstrates 46.9% higher capacity than the control and thus has great potential for practical applications.