Exploring the Mechanism of Spontaneous and Lithium-Assisted Graphitic Phase Formation in SiC Nanocrystallites of a High Capacity Li-Ion Battery Anode

Abstract

Herein, we employed first-principles density functional theory calculations to understand the structural, electronic, and magnetic properties of pristine and lithiated zinc blende (ZB) SiC(111) surface slabs. Our calculations on below four layer thick slabs reveal the spontaneous formation of a graphitic SiC layer which mimics the two-dimensional boron nitride structure. Though this monolayer shows a direct band gap, the energy bands in bi- and trilayer slabs are nondegenerated owing to weak van der Waal’s interaction between the layers, and they show indirect band gap for those cases. In a pristine slab, the surface states presented in both sides originate magnetism, and they are coupled antiferromagnetically. Its strength decreases with increasing layer thickness. This magnetism is quenched during lithiation and exfoliation of layers. The latter is observed, even for thicker ZB slabs during lithiation. The average lithium intercalation potential is calculated to be 0.20 V, which is quite comparable with the anodic potential of high capacity SiC nanoparticles as reported in experiment. Thus, the mechanism of lithiation in SiC nanoparticles is proposed to be intercalation, rather than alloying.