Spin-State Engineering of Manganese Boosts the Electrochemical Performance of LiFe0.2Mn0.8PO4 Cathodes.

Olivine-type lithium manganese iron phosphates (LMFPs) have been regarded as promising cathodes for high-energy-density lithium-ion batteries owing to an additional potential plateau at 4 V; however, the poor cycle stability arising from the Jahn-Teller distortion of Mn3+ hinders their practical applications. In this work, high-entropy doping has been proposed to reduce the spin state of Mn2+ in LMFP from a high-spin to an intermediate-spin configuration. The spin-state reduction not only eliminates the intrinsic driving force for Jahn-Teller distortion but also strengthens the stability of the Mn-O bond. Additionally, experimental data and theoretical calculations demonstrate that the reduced spin state of Mn2+ can narrow the bandgap, optimize ion transport pathways, and accelerate Li+ extraction-insertion kinetics within the high-entropy-doped LMFP. The refined LiMn0.65Mg0.03Ca0.03Zn0.03Cu0.03Nb0.03Fe0.2PO4 (HE-LMFP) cathode can demonstrate a remarkable capacity retention of 96.2% after 10,000 cycles at 10 C, along with outstanding rate performance (64.7 mAh g-1 at 50 C) and great commercial application potential (82.5% retention over 1000 cycles at 0.5 C in a 1.5 Ah pouch cell). Our spin-modulation strategy provides a general design principle for suppressing the Jahn-Teller distortion in manganese-based cathodes, thereby promoting the development of next-generation high-energy-density lithium-ion batteries.