Graphite/electrolyte interface formed in LiBOB-based electrolytes. II. Potential dependence of surface chemistry on graphitic anodes

In an attempt to depict a dynamic picture of solid electrolyte interface (SEI) formation on a graphitic anode surface during the initial forming cycle, we employed X-ray photoelectron spectroscopy in combination with a "pre-formation" technique to establish the dependence of the surface chemistry on the forming potential of the anode. A progressive transition in the is electron binding energies of the major elements was observed as the lithiation proceeded. However, the surface chemical species as well as their abundances seemed to stabilize around 0.55 V and remained constant during the subsequent delithiation process, indicating that a stable SEI exists thereafter. Integrating the information revealed by different analyses, we believe that the reductive decomposition of the BOB- anion starts at ca. 1.00 V, while the effective protection of the graphene surface by SEI is available after the anode is lithiated below the potential of 0.55 V vs. Li.