Graphite Co-Intercalation Chemistry in Sodium-Ion Batteries

Lithium ion intercalation chemistry in graphite underpins commercial lithium-ion batteries since 1991. In exploring the potential of cost-effective graphite anodes in alternative battery systems, the conventional intercalation chemistry falls short for Na ions, which exhibited minimal capacity and thermodynamic unfavourability in sodium ion batteries (SIBs). The introduction of an alternative intercalation chemistry involving solvated-Na-ion co-intercalation gives a rebirth to graphite anodes. The co-intercalation chemistry allows appreciable Na ion storage capacities and extraordinary rate capabilities. The fundamental differences between intercalation and co-intercalation chemistries have attracted extensive investigation over the past decade for high-power SIBs. Herein, we focus on the state-of-the-art advances on the co-intercalation chemistry in the SIBs for the purpose of enriching insights into graphite intercalation chemistry. Following our introducing the thermodynamic features of co-intercalation reactions, we will illuminate the electrochemical properties and mechanic issues of co-intercalated graphite, finalized by the perspective challenges and potential resolutions.