Fe³⁺-Derived Boosted Charge Transfer in an FeSi₄P₄ Anode for Ultradurable Li-Ion Batteries

Ion and electron transportation determine the electrochemical performance of anodes in metal-ion batteries. This study demonstrates the advantage of charge transfer over mass transport in ensuring ultrastable electrochemical performance. Additionally, charge transfer governs the quality, composition, and morphology of a solid–electrolyte interphase (SEI) film. We develop FeSi4P4-carbon nanotube (FSPC) and reduced-FeSi4P4-carbon nanotube (R-FSPC) heterostructures. The FSPC contains abundant Fe3+ cations and negligible pore contents, whereas R-FSPC predominantly comprises Fe2+ and an abundance of nanopores and vacancies. The copious amount of Fe3+ ions in FSPC significantly improves charge transfer during Li-ion battery tests and leads to the formation of a thin monotonic SEI film. This prevents the formation of detrimental LiP and crystalline-Li3.75Si phases and the aggregation of discharging/recharging products and guarantees the reformation of FeSi4P4 nanocrystals during delithiation. Thus, FSPC delivers a high initial Coulombic efficiency (>90%), exceptional rate capability (616 mAh g–1 at 15 A g–1), and ultrastable symmetric/asymmetric cycling performance (>1000 cycles at ultrahigh current densities). This study deepens our understanding of the effects of electron transport on regulating the structural and electrochemical properties of electrode materials in high-performance batteries.