Irreversible Increase in Disorder in Doped Graphene Lithium Ion Battery Anodes during First Discharge

摘要

Heteroatom-doped graphene materials show high capacity as Li-ion battery anodes. However, the Li+ reduction potential in doped graphene anodes varies drastically during charging/discharging, which adversely affects battery performance. The varying reduction potential is conjectured to result from graphene sheets aggregating during electrode preparation into a disordered graphite structure, which demonstrate a similar reduction potential profile. To test this conjecture we measured the disorder during charging/discharging via in situ x-ray diffraction. We find that the doped graphene interlayer spacing irreversibly increases during the first discharge prior to solid electrolyte interphase formation, and commensurate with this phenomena we find an increase in double-layer capacitance, suggesting an increase in surface area. These results imply an increase in disorder during the first discharge, which supports the conjecture that doped graphene batteries resemble disordered graphite. However, a significant disordering occurs during the first discharge and not necessarily during electrode preparation.