Low-Temperature Growth of Hard Carbon with Graphite Crystal for Sodium-Ion Storage with High Initial Coulombic Efficiency: A General Method

Practical application of hard carbon materials in sodium-ion batteries (SIBs) is largely limited by their low initial coulombic efficiency (ICE), which may be improved by increasing the graphitization degree. However, biomass-derived hard carbon is usually nongraphitizable and extremely difficult to graphitize by direct heating even at 3000 degrees C. Herein, a general strategy is reported for fabricating hard carbon materials with graphite crystals at 1300 degrees C promoted by external graphite that serves as a crystal template for the growth of graphite crystals. The graphite crystals enable the contacted pseudographitic domains with a high-level ordered structure, large domain size, and low defects, leading to an enhanced ICE. The obtained hard carbon materials with graphite crystals, using the carbonized eggshell membranes, and sucrose-derived microsphere as precursors, achieve very high ICE of 89% and 91% with reversible capacity of 310 and 301 mA h g(-1), respectively. Therefore, using external graphite to promote high-level ordering pseudographitic domains at low temperature is quite useful to improve ICE for SIB applications.