Bridging Donor Ligands Enable an Ultrastable Graphite Anode for Sodium-Ion Batteries

Graphite is widely utilized as an anode material in lithium-ion batteries due to its abundance, cost-effectiveness, and excellent structural stability during lithium intercalation and deintercalation, which contribute to a long cycle life. However, graphite is not inherently suitable for sodium-ion batteries (SIBs) due to the limited intercalation properties of sodium ions. To address this, we propose the concept of bridging-donor-ligands, which construct ligand channels and consistently expand the graphite interlayer spacing. Using sodium dicyandiamide (NaDCA) as a model ligand, we demonstrate the formation of abundant ligand channels facilitated by the versatile dicyanamide anion (DCA^-), significantly enhancing the structural robustness of ternary graphite intercalation compounds (t-GICs). Hence, the graphite anode capacity retention is over 94% after 5000 cycles, with an average Coulombic efficiency (CE) exceeding 99.8% in SIBs. This mechanism is versatile and can be extended to other metal-ion battery electrolytes.