Enhanced Fast-Charging Performance of High-Mass-Loading Mn-Rich Li[Mn_1-xFe_x]PO₄ Cathodes via LiF-Less Cathode–Electrolyte Interphase

Mn-rich Li[Mn_1-xFe_x]PO₄ (LMFP) cathodes are promising candidates for next-generation lithium-ion batteries due to their structural stability and cost-effectiveness. However, under industrially relevant high-mass-loading conditions, they still suffer from severe performance degradation, particularly during fast charging. In this study, we systematically demonstrate that charge-transfer resistance, rather than bulk Li⁺ diffusivity, governs the kinetic limitations of LMFP electrodes with an areal capacity of ∼3.5 mAh cm⁻² (∼23 mg cm⁻² mass loading). Surface analyses reveal that the buildup of electronically and ionically insulating LiF at the cathode–electrolyte interphase (CEI) is the primary cause of sluggish charge transfer, highlighting a previously overlooked detrimental role of LiF. Guided by this insight, we implement an interfacial engineering strategy that suppresses LiF formation at the CEI. Remarkably, the resulting high-mass-loading LMFP cathodes deliver a 1.6-fold increase in capacity at 5C and retain ∼87% of their initial capacity after 100 cycles at 2C. Moreover, operando structural analysis reveals that electrodes with LiF-suppressed CEI maintain a robust single-phase transition during fast cycling, directly linking interfacial LiF suppression to significantly enhanced charge-transfer kinetics. This work highlights the critical importance of CEI engineering in enabling fast-charging Mn-rich olivine cathodes under practical, high-mass-loading conditions.