Manganese-rich lithium manganese iron phosphate (LiMnxFe1-xPO4) cathodes are promising candidates for next-generation energy storage due to their high energy density; however, they are often hindered by sluggish electronic and ionic kinetics. In this study, we demonstrate a synergistic molecular priming strategy using a combination of long-chain polyethylene glycol (PEG) and sucrose to precisely tailor the interfacial carbon coating of LiMn0.7Fe0.3PO4(LMFP). Interfacial analyses reveal that PEG acts as a decisive molecular spacer, effectively disrupting sucrose self-aggregation via hydrogen bonding and promoting the conformal and lateral spreading of the carbon sources over the LMFP precursor surface. Upon calcination, this pre-organized organic layer transforms into a seamless, long-range conductive network while refining the primary crystallite size to ~45 nm. Consequently, the optimized LMFP electrode exhibits exceptional high-rate capability, retaining 86.25% of its initial capacity at a 10 C discharge rate. This work provides fundamental mechanistic insights into molecular-level interfacial design, offering a versatile pathway to overcome kinetic barriers in high-power lithium-ion battery materials.