Porous quasi-graphitic carbon sheets for unprecedented sodium storage

The large size of sodium ions (Na+) restricts the choice of electrode materials; therefore, to realize low-cost energy storage systems, exceptional electrodes are required. Here, we have overcome this bottleneck by developing porous quasi-graphitic carbon (PGC) sheets at the surface of water-soluble KCl crystals as a green catalyst. The KCl crystals not only avoid the use of hazardous chemicals but also provide easy manipulation of the structural and surface chemistry of PGC sheets on a large-scale. The as-synthesized PGC sheets are enriched with micropores and amorphous reservoirs, which serve as mass transport channels and storage sites for Na+, respectively. Interestingly, when PGC sheets are employed as an anode in the sodium-ion battery, they showed an excellent reversible specific capacity of 237 mA h g−1 with outstanding cyclic stability by retaining 83.5% capacity after 250 cycles at 0.1 A g−1 at a capacity decay of 0.07% per cycle, while remaining stable up to 550 cycles when tested at 0.5 A g−1. Thus, the simple synthesis and large-scale production of PGC with high sodium storage capacity make it a potential candidate for secondary ion batteries.