Waste coffee grounds-derived carbon: Nanoarchitectured pore-structure regulation for sustainable room-temperature sodium–sulfur batteries

A systematic comparison has been made of three different porous carbon structures derived from waste coffee grounds to investigate the effect of carbon porosity on the electrochemical performance of RT Na–S batteries. The differences in their electrochemical performances were investigated in relation to the pore size distribution and the presence of sulfur molecules (Sn, 2 ≤ n ≤ 8) in the pores. We demonstrated that the hierarchically porous structure resulted in good rate capability and superior cycling stability. In particular, optimized carbon with micro-, meso-, and macroporous structures is beneficial because of its excellent wettability and kinetic accessibility. The optimized carbon structure with an appropriate sulfur content exhibited significantly higher capacity retention and long cycle stability in RT Na–S batteries. In addition, the reaction mechanisms have been investigated in combination with X-ray photoelectron spectroscopy measurements during the discharge process. The study established a relevance between the exact regulation of the pore structure of the carbon materials and their electrochemical performance, and also built a correlation between waste biomass and high-effective energy storage materials, which can inspire the rational design of porous carbon structures for further development of the highly efficient, cost-effective and sustainable RT Na–S batteries.