Enhanced Lithiation of Doped 6H Silicon Carbide (0001) via High Temperature Vacuum Growth of Epitaxial Graphene

The electrochemical lithiation capacity of 6H silicon carbide (0001) is found to increase by over 1 order of magnitude following graphitization at 1350 degrees C in ultrahigh vacuum. Through several control experiments, this Li-ion capacity enhancement is correlated with SiC substrate doping and removal of the native oxide surface layer by thermal annealing, which renders both the bulk and surface electrically conductive. Characterization via multiple depth-resolved spectroscopies shows that lithium penetrates the activated SiC upon lithiation, the bulk lattice spacing does not appreciably change, and the surface structure remains largely intact. The electron energy-loss spectroscopy (EELS) extracted compositional ratio of Li to Si is approximately 1:1, which indicates an intrinsic bulk Li capacity in activated SiC of 670 mAh g(-1). In addition, inelastic X-ray scattering spectra show changes in the Si chemical bonding configuration due to lithiation. X-ray scattering data show a decrease in the SiC Bragg peak intensity during lithiation, suggesting changes to the bulk crystallinity, whereas the emergence of a diffuse scattering feature suggests that lithiation is associated with the development of substrate defects. Overall, these results illustrate that the electrochemical capacity of a traditionally inert refractory material can be increased substantially via surface modification, thus suggesting a new strategy for improving the performance of next generation Li-ion battery electrodes.