The structural design and electrochemical performances of tetrahedral encapsulated silicon and reduced graphene oxide-polydopamine film composites for anode materials

Abstract

Si has emerged as the most promising anode material due to its high theoretical capacity, low voltage platform and cost effectiveness. However, Si-based materials are inherently less electrically conductive due to their large volume change, resulting in a significant reduction in cycling performance. In order to improve the electrochemical properties of Si, the orthotetrahedral MOF structure has been used as a shell template and encapsulated the Si within the structure (Si@Co), followed by the combination of polydopamine (PDA) and reduced graphene oxide (RGO) to form a flexible network nanofilm (PDA-RGO), finally the two synergistic interactions form the Si@Co/NC@C composite. The effects of Co and PDA at different concentrations on the electrochemical properties of the composites are discussed. The as-prepared core-shell structure design can significantly suppress the volume change of Si-based anode material during the process of lithiation/delithiation, and enhance its cyclic stability. The PDA-RGO network films can increase Li⁺ transport channels and provide more active sites to reduce particle agglomeration. The small amount of N atoms present in 2-methylimidazole (2-MIM) and PDA can provide some of the defect sites to adsorb some of the Li⁺ and improve the conductivity of the electrode materials. The experimental results show that Si@Co/NC@C has the best electrochemical performance with an ICE of 71.62 %. It exhibits a specific capacity of 1621.38 mAh g⁻¹ for charging, a specific capacity of 724.2 mAh g⁻¹ after 500 cycles at a current density of 0.5 A g⁻¹ and a specific capacity of 630.12 mAh g⁻¹ at 5 A g⁻¹.