Khadija El Kindoussy, Rachid Oubaki, Ikram Bouaakil, Youssef Samih, Mouad Dahbi, Jones Alami, Mohammed Makha, University Mohammed VI Polytechnic, Benguerir, Morocco
The anode plays a crucial role in determining the performance of lithium-ion batteries and has evolved from conventional graphite to silicon-based materials, which offer a much higher theoretical capacity (4200 mAhg^-1). However, the practical application of silicon is limited by its significant volume expansion during cycling, leading to rapid electrode degradation. Si/C composite anodes represent a promising strategy to mitigate this challenge by combining silicon’s high capacity with the structural stability provided by carbon. The latter mitigates the drawbacks of silicon anodes by buffering volume changes and by enhancing the electrical conductivity. The carbon matrix also improves structural integrity, enabling better cycling stability of lithium-ion batteries. Unlike conventional methods that often lack control of the structure and reproducibility, Physical Vapor Deposition offers precise control over film composition, thickness, and microstructure, enabling the fabrication of uniform and well adherent films.
In our study, Si/C thin films were deposited using Direct Current Magnetron Sputtering (DcMS) and High-Power Impulse Magnetron Sputtering (HiPIMS) in a reactive atmosphere containing acetylene (C₂H₂) to investigate the effect of the silicon-to-carbon ratio on the structural, mechanical, and electrochemical properties of thin film anodes. HiPIMS-deposited films exhibited higher density, finer grain structure, smoother surfaces, and superior mechanical properties compared to their DcMS counterparts. Electrochemical characterization showed that HiPIMS Si-rich anodes generally offered higher initial capacity but suffered from faster capacity fading, whereas DcMS anodes exhibited slightly lower initial efficiency but improved cycling stability, likely due to their lower film density acting as a more compliant buffer against silicon expansion. Increasing the carbon content in HiPIMS-deposited films led to better capacity retention at the expense of initial capacity and efficiency. In contrast, DcMS films with higher carbon content showed poorer electrochemical performance, which was attributed to oxygen incorporation that irreversibly traps lithium, leading to a reduction in the capacity.