Enhanced storage capability by biomass-derived porous carbon for lithium-ion and sodium-ion battery anodes

Efficient electrodes with impressive storage capability and fast ion transfer rate are urgently needed to meet the demand for higher energy/power densities and longer life cycles and large rate powering devices. Through a simple freeze-drying and annealing process, nitrogen-containing porous carbon materials with a hierarchical porous structure and enlarged lattice spacing between graphene layers are synthesized. Benefiting from an improvement in the electrochemical activity, porosity, conductive network and mechanical stability, the porous carbon used as anodes for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) exhibits an excellent storage capability, rate performance, and cyclability. Apple carbon exhibits a high capacity of 1050 mA h g^-1, and celery carbon shows the reversible capacities of 990 mA h g^-1 at 0.1 A g^-1 after the 200th cycle as LIBs anodes. For SIBs, a high capacity of 438 mA h g^-1 is obtained after 200 cycles for apple carbon and 451 mA h g^-1 for celery carbon. It is noteworthy that celery carbon shows a capacity retention of 94% between the 50th to 200th cycling. Further analysis on the structure characterization and charging curves reveal that celery carbon has a high N content, dilated intergraphene spacing, and an intrinsically hierarchical porous structure, which are capable of reversibly accumulating sodium ions through surface adsorption and sodium intercalation. Also, the electrochemical impedance spectroscopy (EIS) reveals that celery carbon has a low charge-transfer resistance, the enhanced cyclability and rate performance might be attributed to convenient ion diffusion in the electrode.