Ionic-liquid-derived fluorine-containing carbon surface engineering of LiFePO4 for enhanced electrochemical performance.
Abstract
Lithium iron phosphate (LFP) is a safe and stable cathode material for lithium-ion batteries; however, its relatively low energy density and limited electronic conductivity restrict its use in high-performance applications. Here, a scalable spray drying-assisted lithiation was developed to engineer fluorine-containing carbonaceous surface layers on LFP. Iron phosphate was first synthesized via co-precipitation and subsequently lithiated through a spray drying process in the presence of the ionic liquid [BMIM][PF6], which acts as a multifunctional precursor for in situ carbon coating and fluorine-containing surface species. X-ray diffraction confirmed the formation of phase-pure olivine LFP, while electron microscopy revealed a conformal surface layer of approximately 5 ± 0.8 nm for the optimized material. Raman spectroscopy showed D/G intensity ratios of approximately 1.02 and 0.99 for LFP-20 and LFP-30, respectively, indicating a carbonaceous surface layer with a modestly higher degree of graphitic ordering at the higher [BMIM][PF6] content. X-ray photoelectron spectroscopy and Near Edge X-ray Absorption Fine Structure (NEXAFS) analyses confirmed carbon-containing and fluorine-containing surface species, consistent with the formation of an ionic-liquid-derived interfacial layer. Thermogravimetric analysis estimated carbon contents of approximately 5 and 6 wt% for LFP-20 and LFP-30, respectively. The optimized LFP-30 exhibited a tap density of 1.30 g cm-3 compared with 0.75 g cm-3 for the glucose-derived reference LFP-G. Electrochemically, LFP-30 delivered approximately 160 mAh g-1 at 0.1C, together with improved rate capability and stable cycling performance. These results demonstrate that integrating ionic-liquid-derived surface modification with spray drying-assisted lithiation provides a scalable approach for simultaneously tailoring surface chemistry, electronic transport, and particle packing in LFP cathodes.
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