Enhancing Li-storage ability of FeC2O4 anode enabled by oxygen-vacancy-enriched amorphous carbon microspheres compositing via hydrogen bonding interactions

Iron oxalate (α-FeC₂O₄), with a stable Li⁺ diffusion pathway, exhibits excellent cycling stability but is limited in commercial applications due to its low electronic conductivity. To overcome this issure, we introduced an organic β-cyclodextrin (β-CD) compound with partial oxygen functional groups after thermal decomposition, to prepare an amorphous carbon microspheres (AMCs) composite. Considering the stable sustaining force supported by crystal water between FeC₂O₄·2H₂O interlayer, a unique composite technology with α-FeC₂O₄ and AMCs through the interactions of hydrogen bonds (FCO/AMCs) was proposed. By adjusting the solvent ratio, FCO/AMCs 1:3 with high concentration of oxygen vacancies and conductive network established by AMCs, exhibits excellent discharge specific capacity of 1183.78 mAh g^-1 at current density of 1 A g^-1 after 1000 cycles and stable cycling performance with the capacity retention rate of 72.8% even over 750 cycles at 5 A g^-1. Based on the catalytic effect of oxygen vacancies and faster average Li⁺ diffusion rate, FCO/AMCs 1:3 electrode also shows higher exchange current density (j₀ = 2.35 × 10^-3 A cm^-2) and apparent electron transfer rate constant (k_app = 1.02 cm s^-1), leading higher reversibility. Additionally, an in-depth analysis of kinetic parameters Li-ion tendentious behavior differences in transformation reactions, reveals that more oxygen vacancies can promote the ionization of Fe⁰, releasing more spin-polarized electrons to form spin-polarized capacitance. This research provides a novel strategy on carbon compositing and offers more comprehensive understanding of the kinetic processes involved in the oxalate-based anode material.