Metal decoration of Si particles via high-energy milling for lithium-ion battery anodes†

The solid electrolyte interphase (SEI) of silicon (Si) anodes for lithium-ion batteries has been a major focus of research for over a decade. One key factor influencing the formation and composition of the SEI is the desolvation of solvated Li ions, which involves an associated energy barrier. To address this, we aim to disrupt interfacial processes by decorating the Si surface with metals, which are conventionally used to improve the conductivity of Si. This study investigates the preparation and electrochemical performance of metal-decorated Si powders (Si^M, where M represents Ni, Fe, Ti, Ag, Al, or Y) as anode materials, using a simple high-energy ball milling process. STEM reveals that the resulting Si^M architectures either appear as islands on the Si surface or are integrated into the Si bulk, although X-ray diffraction (XRD) confirms that the Si lattice is essentially unchanged. The inherent high electronic conductivity of the metals contributed to lower electrode resistance revealed through scanning spreading resistance microscopy (SSRM), with Si^Ni achieving the overall lowest resistance at log(R) = 8.7 log(Ω), compared to log(R) = 10.8 log(Ω) for baseline Si, which is also consistent with reduced impedance during cycling. Among the materials studied, Si^Ni, Si^Fe, and Si^Ti demonstrated the most promising performance, reducing overpotential by up to 20 mV, delivering specific capacities above 1000 mAh g⁻¹ at a C/3 rate, and exhibiting improved rate capability. Zeta potential measurements suggest that particles with lower zeta potential correlate with better performance. Finally, SEI analysis of insoluble species using XPS revealed that metal decoration, particularly with Ni, results in a stable SEI characterized by lower inorganic LiF content and increased C–O products compared to the baseline Si at high states of charge, consistent with its enhanced performance.