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

Abstract

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.