Preparation of Silicon Nanosheet/Reduced Graphene Oxide Heterostructures and Their Application as Anodes for Li-Ion Batteries

Silicon (Si) is a promising material for Li-ion battery anodes due to its theoretical specific capacity, which is more than 10 times higher than that of carbon-based materials. However, the substantial volume change (up to 300%) during charge and discharge cycles necessitates the formation of a robust interface between the current collector and the silicon to accommodate this expansion and contraction. In this study, we fabricated silicon nanosheet (Si NS)/reduced graphene oxide (rGO) heterostructures and evaluated their performance as anodes in Li-ion batteries. The fabricated anodes demonstrated a discharge capacity of approximately 2400 mAh/g, corresponding to 60% of silicon's theoretical capacity, and operated stably for over 100 cycles. This high capacity is attributed to the formation of a robust interface where strong electronic and lithium interactions occur rapidly, not through point-to-point interactions between particles, but through face-to-face heterojunctions between the two-dimensional materials.
Among various anode materials for lithium-ion batteries, silicon is considered a next-generation material due to its high theoretical specific capacity (4200 mAh/g when fully lithiated to Li_4.4Si) and relatively low discharge potential (0.1 to 0.4 V vs. Li/Li⁺). However, electrodes made from silicon materials face challenges in maintaining contact with conductive additives and current collectors due to volume expansion during lithiation. Therefore, an appropriate electrode design that enhances cycle stability and rate performance is essential for silicon-based batteries.
In this study, we prepared silicon nanosheets by exfoliating calcium silicide, which was then used to create heterojunctions with reduced graphene oxide. In this system, the reduced graphene oxide functions as the current collector. The heterostructures were prepared as follows: First, CaSi₂ was reacted with an excess amount of hydrochloric acid for two days to exchange the interlayer calcium with protons. Subsequently, the product was treated with sodium dodecyl sulfate solution to exfoliate the layered structure into monolayer silicon nanosheets. Atomic Force Microscopy (AFM) measurements revealed that the resultant silicon materials had a sheet-like structure with a lateral dimension of 1 µm and a thickness of 4 nm. To create the conductive carbon matrix, a GO dispersion was prepared and thoroughly mixed with the Si NS dispersion. The mixture was then freeze-dried and thermally reduced under a hydrogen atmosphere, resulting in a matrix with uniformly dispersed silicon nanosheets within the rGO nanosheets. To evaluate the electrochemical performance of the fabricated anode materials, half-cells were constructed using lithium foil as the counter electrode and subjected to charge-discharge tests.