Tuning the Closed Pore Structure of Hard Carbons with the Highest Na Storage Capacity

Abstract

High-capacity anode materials are one of the bottlenecks to further improve the energy density of Na-ion batteries (NIBs). Except for introducing more defects to increase the sloping capacity, tuning the closed porous structure to boost the plateau capacity is another direction. Here by adopting phenol-formaldehyde resin (PF) as the carbon precursor and ethanol (EtOH) as the pore-forming agent, through precise chemical regulation of their relative content during a solvothermal process before further carbonization, carbon anodes with appropriate microstructure are achieved. It is found that the function of EtOH rests on generating steam vapor to create a pore cavity among cross-linked matrixes. The obtained optimal anodes exhibit a high Na storage capacity of ca. 410 mAh/g. When pairing with an O3-NaNi1/3Fe1/3Mn1/3O2 cathode, the full cell delivers a high initial Coulombic efficiency of 83% and energy density of ca. 300 Wh/kg. The proposed chemical regulation approach via a pore-forming strategy is simple and practical to enable high-energy-density NIBs.