Boosting Conversion of the Si–O Bond by Introducing Fe2+ in Carbon-Coated SiOx for Superior Lithium Storage

SiO_x-based anodes are of great promise for lithium-ion batteries due to their low working potential and high specific capacity. However, several issues involving large volume expansion during the lithiation process, low intrinsic conductivity, and unsatisfactory initial Coulombic efficiency (ICE) hinder their practical application. Here, an Fe-SiO_x@C composite with significantly improved lithium-storage performance was successfully synthesized by combining Fe²⁺ modification with a carbon coating strategy. The results of both experiments and density functional theory calculations confirm that the Fe²⁺ modification not only effectively achieves uniform carbon coating but also weakens the bonding energy of the Si-O bond and boosts reversible lithiation/delithiation reactions, resulting in great improvement in the electrical conductivity, ICE, and reversible specific capacity of the as-obtained Fe-SiO_x@C. Together with the coated carbon, the in situ-generated conductive Fe-based intermediates also ensure the electrical contact of active components, relieve the volume expansion, and maintain the structural integrity of the electrode during cycling. And the Fe-SiO_x@C (x ≈ 1.5) electrode can deliver a high-rate capacity of 354 mA h g^-1 at 2.0 A g^-1 and long-term cycling stability (552.4 mA h g^-1 at 0.5 A g^-1 even after 500 cycles). The findings here provide a facile modification strategy to improve the electrochemical lithium-storage performance of SiO_x-based anodes.