Interface-dictated kinetics in Fe-metal organic framework–derived Fe₃O₄: Diffusion vs. capacitive storage across solid and liquid electrolytes

초록

All-solid-state batteries promise safer, higher-energy storage, yet interfacial kinetics often obscure the intrinsic behavior of conversion anodes. Here we establish a clean, additive- and binder-free platform to interrogate these effects by fabricating ultrathin Fe₃O₄ films derived from an Fe-MOF precursor via alternating-current electrophoretic deposition (AC-EPD). Identical Fe₃O₄ electrodes were evaluated in two architectures: a solid-state Li/Li₁₊ₓAlₓTi₂₋ₓ (PO₄)₃ (LATP)/Fe₃O₄ cell and a liquid-electrolyte Li/LiPF₆/Fe₃O₄ cell. Cyclic voltammetry across multiple scan rates reveals a striking divergence in charge-storage mechanisms. In the LATP cell the response is diffusion-controlled (b ≈ 0.5), consistent with slower Li+ transport in the ceramic and/or elevated resistance at the rigid Fe₃O₄/LATP solid–solid interface. In contrast, the liquid-electrolyte cell exhibits capacitive-dominant behavior (b → 0.9), attributed to facile Li+ transport, superior wetting, and pseudocapacitive contributions. Galvanostatic cycling shows a large initial fade from solid electrolyte interphase formation and irreversible conversion in the ultrathin films, followed by rate-induced stabilization. These results demonstrate that the apparent kinetics of Fe₃O₄ are governed as much by electrolyte identity and interfacial structure as by the anode itself. AC-EPD provides a versatile route to well-defined thin films that isolate electrolyte effects, offering a practical framework for rationally pairing conversion anodes with solid- or liquid-electrolyte systems. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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