Macro-microporous carbon with a three-dimensional channel skeleton derived from waste sunflower seed shells for sustainable room-temperature sodium sulfur batteries

Abstract

Macro-microporous carbon (MMC), with a three-dimensional channel skeleton and co-doping of heteroatoms derived from waste sunflower seed shells, was synthesized through a facile chemical-activation process. The three-dimensional channel skeleton with a macroporous structure of the MMC formed an interwoven carbon network that effectively improved the electrical conductivity and facilitated the transfer of Na+ in the cell by allowing the electrolyte to permeate easily. The micropores (<0.7 nm) of the MMC are the main sulfur host and serve to trap the small sulfur molecules (<0.5 nm) within the pores, resulting in excellent electrochemical performance in room-temperature sodium sulfur (RT Na–S) batteries with a carbonate-based electrolyte. The co-doping of heteroatoms (N, O) in the MMC matrix can create an active site that improves the electrical conductivity and builds an interaction with sulfur species to inhibit polysulfide shuttling. The confinement of sulfur through these physical and chemical mechanisms results in a high initial discharge capacity of 1598 mAh g−1 at 0.1 C and a superior capacity retention of 330 mAh g−1 after 510 cycles at 1 C. This study provides an attractive material derived from biomass for low-cost and sustainable RT Na–S batteries.