Optimization of Cobalt Loading and Electrode Formulation in Carbon-Coated Si@Co Composite Anodes for Lithium-Ion Batteries

Abstract Silicon is a promising anode material for high-energy-density lithium-ion batteries, but its practical use is hindered by poor electrical conductivity, large volume changes, and progressive structural and interfacial degradation. This study investigated whether Co deposition and carbon coating could improve the electrochemical behavior of nanosilicon and identify suitable Co loading and electrode composition.HF-treated nanosilicon was decorated with different nominal amounts of Co through NaBH₄ reduction and subsequently coated with sucrose-derived carbon to obtain Si@Co/C composites. Their phase composition, morphology, and elemental distribution were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Lithium-storage behavior and interfacial kinetics were evaluated using electrochemical measurements. The crystalline Si framework was retained after Co incorporation. Microscopic and elemental analyses revealed the morphology of the composites and the distribution of Si, Co, and C. The composite containing 5 wt% Co, tested with an active material/Super P/PVDF mass ratio of 6:3:1, achieved the highest initial discharge capacity of approximately 1600 mAh g⁻¹ and showed favorable capacity recovery during rate testing. Its Coulombic efficiency stabilized above 99.5% after the initial cycles. Nevertheless, the reversible capacity decreased to approximately 200 mAh g⁻¹ after 400 cycles, indicating substantial long-term structural degradation. Moderate Co loading and optimization of the electrode formulation improved the initial capacity and reaction kinetics of Si-based composite anodes. Further stabilization of the electrode structure and interfaces is required to achieve durable cycling performance.