Heteroatom-Mediated Functional Carbon Engineering for the Simultaneous Enhancement of Graphitization and Interfacial Stability in LiFePO4

Carbon coatings are indispensable for mitigating the intrinsically poor electronic conductivity of olivine LiFePO4 (LFP) cathodes, yet their potential to regulate cathode/electrolyte interfacial chemistry remains comparatively underexplored. Here, we present a multifunctional carbon-engineering strategy in which LiBOB and LiBF4 are incorporated during carbon-layer formation to tailor carbon ordering and surface chemical functionality simultaneously. Raman spectroscopy revealed enhanced graphitic ordering upon addition of the boron-containing precursors, while TOF-SIMS confirmed the preferential incorporation of boron-containing (and, in the case of LiBF4, fluorine-containing) species within the carbon-rich surface region. X-ray diffraction combined with Rietveld refinement further indicated only minor lattice contraction, implying limited incorporation of precursor-derived species into the olivine framework without disruption of the overall crystal structure. The optimized electrodes modified with 0.2 wt % LiBOB and LiBF4 exhibited markedly improved high-rate performance, retaining approximately 66% and 69% of their 0.1 C capacities at 10 C, respectively, compared with ∼53% for pristine LFP. Electrochemical impedance spectroscopy revealed substantially lower charge-transfer resistance after prolonged cycling, and XPS and TOF-SIMS analyses demonstrated that the chemically functionalized carbon layers suppress electrolyte decomposition and promote the formation of a more stable cathode/electrolyte interphase. These interfacial benefits translated into significantly improved cycling stability at elevated temperatures and greater resistance to degradation following storage at 80 °C. Of the two strategies, LiBF4-derived B/F functionalization afforded the most pronounced improvement by coupling enhanced carbon ordering with superior interfacial stabilization. Collectively, these results demonstrate that chemical functionalization can transform conventional carbon coatings from passive conductive layers into multifunctional interfacial architectures that concurrently promote electronic transport, regulate electrolyte decomposition, and enhance the thermal durability of LFP cathodes.