In situ generated bilayer functional coatings on manganese-rich LiMn0.84Fe0.15Mg0.01PO4 for high-rate lithium-ion batteries

Abstract

The poor lithium-ion-diffusion kinetics and low electronic conductivity of LiMn_0.85Fe_0.15PO₄ cathode materials substantially hinder their practical utilization for rechargeable lithium-ion batteries. In the present study, an in situ-generated Li₃PO₄ and carbon dual-surface-coating strategy was employed during the one-pot preparation process to produce LiMn_0.84Fe_0.15Mg_0.01PO₄ cathode materials. Specifically, a uniform Li₃PO₄ nano-coating was obtained by adjusting the molar ratio of excess Li and P to 3 : 1 to accelerate lithium-ion-diffusion and stabilize the structure. Meanwhile, the homogeneous carbon nano-coating was utilized to construct a conductive carbon network from a composite carbon source consisting of citric acid and polyethylene glycol 400 (PEG 400). The dual coatings with different functional roles synergistically improved the electronic conductivity (8.9 × 10⁻³ S cm⁻¹) and lithium-ion-diffusion coefficient (10⁻¹¹ to 10⁻¹² cm² s⁻¹), while effectively inhibiting manganese dissolution. The modified L_1.03MFMP_1.01 exhibited excellent lithium-storage properties, especially rate property, with a discharge specific capacity of up to 83.8 mA h g⁻¹ at 10C. Ex situ XRD measurements further demonstrated the structural stability and high reversibility of L_1.03MFMP_1.01 during the charge–discharge process. The strategy of in situ generated bilayer functional coatings also provides insights into improving the rate performance of other phosphate-based electrode materials.