(Invited) Reversible Co-Intercalation of Sodium and Solvent in Graphite

Graphite is a universal host materials that can accommodate various guest species in its galleries. Its capability of reversible lithium de/intercalation facilitates graphite as a standard anode for lithium ion batteries, while the thermodynamic instability of sodium intercalation made it not suitable for sodium ion batteries. We recently discovered that reversible solvated-Na ion intercalation enables graphite to become a promising anode for sodium ion batteries. As a continuous effort to exploit the graphite as an anode in sodium ion batteries, here we investigate the solvated-Na intercalation mechanism through in operando X-ray diffraction analysis, electrochemical titration, real-time observation of graphite expansion and density functional theory-based calculations. This work demonstrates the formation of first-stage graphite intercalation compound where the solvated-Na ions are doubly stacked in parallel with graphene layers. We further provide insights on tuning energy storage potentials of solvated ion intercalation electrodes by introducing various solvents.