Fe 3+ -Derived Boosted Charge Transfer in an FeSi 4 P 4 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 FeSi ₄ P ₄ -carbon nanotube (FSPC) and reduced-FeSi ₄ P ₄ -carbon nanotube (R-FSPC) heterostructures. The FSPC contains abundant Fe ³⁺ cations and negligible pore contents, whereas R-FSPC predominantly comprises Fe ²⁺ and an abundance of nanopores and vacancies. The copious amount of Fe ³⁺ 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 _3.75 Si phases and the aggregation of discharging/recharging products and guarantees the reformation of FeSi ₄ P ₄ 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.