With the continuous rapid growth in the volume of spent lithium-ion batteries, developing an environmentally friendly, cost-effective, and efficient recycling process for cathode materials has become a key scientific challenge for the sustainable development of the new energy industry. Conventional hydrometallurgical recycling technologies typically rely on strong acids combined with external reducing or oxidizing agents, which lead to high reagent consumption and operating costs while generating large volumes of metal-containing wastewater, posing significant environmental and disposal challenges. Therefore, it is of great scientific and practical significance to develop a novel recycling process that eliminates the need for external chemical additives while enabling the synergistic recovery of multiple components. In this study, an additive-free recycling strategy based on an intrinsic synergistic redox mechanism is proposed for a mixed system of spent LiFePO₄ (S-LFP) and LiMn₂O₄ (S-LMO). This approach fully utilizes the electrochemical potential difference between different electrode materials to drive spontaneous electron transfer reactions under mildly acidic conditions, with acid consumption reduced by nearly half compared to conventional methods. Specifically, Fe²⁺ ions are first leached from S-LFP and act as intrinsic reducing agents in the solution; these Fe²⁺ ions subsequently reduce Mn³⁺ to Mn²⁺ in S-LMO, thereby promoting the efficient co-leaching of Mn and Li. This process achieves the synergistic recycling of the spent materials, reaching nearly 100% leaching efficiency for Mn and Li under mild conditions (20 ℃, 40 min), demonstrating excellent reaction kinetics and synergistic effects. Concurrently, Fe species are selectively converted into insoluble FePO₄ precipitates, allowing for easy solid-liquid separation. The resulting FePO₄ can directly serve as a precursor for the regeneration of LiFePO₄ (R-LFP). The leachate is further processed by adjusting the pH with ammonia to precipitate Mn(OH)₂, followed by the addition of Na₂CO₃ to obtain Li₂CO₃, thereby achieving the full recovery and reuse of Fe, Mn, Li, and P elements. The regenerated R-LFP exhibits a uniform spherical morphology with a narrow particle size distribution and a well-preserved crystal structure. Electrochemical testing reveals that the regenerated material delivers an excellent discharge capacity of 135.0 mA·h/g and a capacity retention of 99.4% after 200 charge-discharge cycles, indicating outstanding cycling stability and structural reversibility. This work systematically elucidates the self-driven redox mechanism between spent electrode materials and achieves closed-loop recovery of all constituent elements along with the regeneration of high-value-added materials. The entire process relies solely on spontaneous electron transfer between the waste materials, without the need for external oxidizing or reducing agents, significantly lowering energy consumption, reagent usage, and secondary pollution. The proposed synergistic redox strategy overcomes the limitations of conventional hydrometallurgical processes and provides a new theoretical foundation and practical pathway for the green, efficient, and sustainable recycling of multi-component spent lithium-ion batteries, showing great potential for large-scale industrial application.