Sequential Additive Engineering Enables Uniform Carbon Coating and Enhanced Interfacial Properties in LiFe_1–<i>x</i>Mn_<i>x</i>PO₄ Cathodes

The electrochemical performance of lithium manganese iron phosphate (LiFe_1-<i>x</i>Mn_<i>x</i>PO₄, LMFP) cathodes remains limited by inefficient electron transport and unstable electrode-electrolyte interfaces. While surface carbon coating is a widely adopted strategy, its interfacial quality is often dictated by the uncontrolled assembly of carbon precursors. Here we uncover the critical role of additive sequence in controlling the interfacial carbon architecture of LMFP. By introducing poly(ethylene glycol) (PEG) before glucose during the construction of carbon coatings, a coordinated adsorption layer is formed, guiding uniform precursor assembly and enabling the in situ formation of a dense, relatively ordered structure carbon shell upon calcination. This pathway enhances both interfacial integrity and electronic connectivity. The resulting cathode delivers a high initial discharge capacity of 161 mAh/g at 0.1 C and 113 mAh/g after 400 cycles at 1 C, and nearly doubled electronic conductivity and Li⁺ diffusivity compared to conventional routes. This work establishes reaction sequence as a powerful synthetic lever─beyond composition or carbon source type─for engineering interfacial structures. It opens a generalizable approach for tuning surface chemistry and boosting performance in carbon-coated phosphate cathodes and other electrode materials.