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-Li_3.75Si 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.