Hollow porous carbon spheres for high initial coulombic efficiency and low-potential sodium ion storage.

It is critical to develop carbon material anodes with high initial Coulombic efficiency and energy density for sodium ion batteries. Herein, a novel mushroom spore with chitin as carbon precursor is first reported for energy storage, and its special porous spherical structure, fine structure and oxygen functional groups can be accurately controlled by carbonization temperature. The hollow porous carbon spheres obtained from mushroom spore at 1400 °C have appropriate porous structure, d spacing (0.364 nm), 7.12% oxygen content and ultra-low specific surface area of 5.5 m g. It could obtain 81.2% initial Coulombic efficiency and has reversible discharge capacity of 411.1 mA h g, wherein about 75% (308 mA h g) of its total capacity is derived from low-potential plateau (below 0.1 V Na/Na), and the capacity is 384.5 mA h g after 50 cycles. Furthermore, Density functional theory calculation showed that the residual oxygen functional groups (CO) in carbon materials are beneficial to sodium into graphite-like layers, and graphite-like layers spacing is smaller than the reported unadulterated carbon with 0.37 nm. Therefore, the excellent electrochemical performance and low-cost of natural mushroom spore derived hollow porous carbon spheres provide advantages for sodium ion batteries in large-scale storage devices.