Amorphous Sub‐Stoichiometric Silicon Carbide (a‐SiCx) Particles From the Gas Phase for Battery Applications

ABSTRACT Capacity fading during cycling remains a significant challenge for silicon‐based anode materials in Li‐ion batteries. Amorphous, sub‐stoichiometric silicon carbide (a‐SiC x ) nanoparticles have proven to be more stable than pure silicon, albeit with lower lithiation capacities. The incorporation of carbon during the nanoparticle synthesis is highly effective in the suppression of crystalline phases during both synthesis and cycling. In this study, a‐SiC x materials with varying carbon concentrations (up to 22 wt.%) were produced via gas‐phase synthesis in a hot‐wall reactor. The primary objective is to understand the mechanism of carbon incorporation into the silicon particles, and secondly its impact on material properties and battery performance. Based on extensive materials science investigations and NMR analyses, we have determined that carbon is incorporated together with hydrogen, which further promotes amorphization. Furthermore, cycling analysis shows a strongly increased stability with 85% retention after 200 cycles for materials with more than 10 wt.% carbon, probably mainly due to a reduced buildup of internal resistances and reduced volume expansion. Furthermore, crystalline Si‐Li‐phases cannot be formed in this material during lithiation enabling deep lithiations, and Coulombic efficiency is increased. These results suggest that a‐SiC x is a promising alternative to pure silicon as an anode material.