High-Voltage Cycling Stability in ZnF2-Encapsulated Li(Mn0.6Fe0.4)PO4 Cathode

Abstract

Li(MnxFe1–x)PO4 (LMFP) is a Co/Ni free, 4 V class cathode material for cost-sensitive electric vehicles and grid-scale energy storage. However, fully accessing its capacity and energy density requires ≥4.5 V operation, which accelerates electrolyte oxidation and Mn/Fe dissolution, driving impedance growth, voltage fade, and capacity loss. In this work, LMFP powder is rationally engineered with a conformal ZnF2 coating via atomic layer deposition (ALD), and its electrochemistry is comprehensively investigated. Under demanding cycling conditions (1000 cycles, 2.5–4.5 V vs Li/Li+; discharge @1C and 5C), the LMFP@ZnF2 cathode demonstrates >22% higher capacity retention than its pristine counterpart. Postmortem analyses reveal that ZnF2 encapsulation facilitates the formation of a thin, uniform, and F-, Li-, and P-enriched cathode–electrolyte interphase (CEI) that preserves the Mn/Fe stoichiometry and mitigates particle pulverization. Compared to the organic-rich CEI in the pristine-LMFP cathode, the robust inorganic-dominated CEI in LMFP@ZnF2 was found to be instrumental in promoting high-voltage stability and mechanical integrity of the cathode. Overall, this research presents a scientifically grounded and industry-relevant strategy for stabilizing LMFP-cathode operation at high voltages and aligns with global sustainability goals.