Abstract: Co-free lithium-rich manganese-based oxides (LRMOs), which offer energy densities over 1000 Wh·kg⁻¹ and low raw material cost, are attractive cathode candidates for next generation high-energy density lithium-ion batteries (LIBs). Nonetheless, their practical application is hindered by their high initial irreversible capacity, capacity and voltage decay, and voltage hysteresis. Herein, a novel iron phosphide modification strategy is presented, where Fe₃P is incorporated into the bulk phase of the Li_1.2Ni_0.2Mn_0.6O₂ (LNMO) cathode material during its fabrication process of high-temperature calcination of the precursor after spray drying. This regulation stabilizes the crystal lattice of LNMO, promotes the formation of a robust cathode–electrolyte interphase, and mitigates decomposition of the electrolyte, thereby significantly enhancing the cycling stability and rate capability. Consequently, the modified LNMO achieves a capacity of 179 mAh·g⁻¹ (98% capacity retention) after 450 cycles at 1C (1C = 200 mA·g⁻¹), and 82% capacity retention after 1000 cycles at 5C. The regulatory strategy is facile and straightforward contributes superior electrochemical performance for LNMO cathode materials, which has potential for wide-ranging applications.