Supercritical CO₂-Assisted SiO_x/Carbon Multi-Layer Coating on Si Anode for Lithium-Ion Batteries

Supercritical CO₂ (SCCO₂), characterized by gas-like diffusivity, low surface tension, and excellent mass transfer properties, is applied to create a SiO_x/carbon multi-layer coating on Si particles. Interaction of SCCO₂ with Si produces a continuous SiO_x layer, which can buffer Si volume change during lithiation/delithiation. In addition, a conformal carbon film is deposited around the Si@SiO_x core. Compared to the carbon film produced via a conventional wet-chemical method, the SCCO₂-deposited carbon has significantly fewer oxygen-containing functional groups and thus higher electronic conductivity. Three types of carbon precursors, namely, glucose, sucrose, and citric acid, in the SCCO₂ syntheses are compared. An eco-friendly, cost-effective, and scalable SCCO₂ process is thus developed for the single-step production of a unique Si@SiO_x@C anode for Li-ion batteries. The sample prepared using the glucose precursor shows the highest tap density, the lowest charge transfer resistance, and the best Li⁺ transport kinetics among the electrodes, resulting in a high specific capacity of 918 mAh g⁻¹ at 5 A g⁻¹. After 300 charge–discharge cycles, the electrode retains its integrity and the accumulation of the solid electrolyte interphase is low. The great potential of the proposed SCCO₂ synthesis and composite anode for Li-ion battery applications is demonstrated.