Cicada wing‐like hierarchical porous carbon to facilitate the re‐deposition of sulfur for high‐performance lithium‐sulfur batteries

The poor electrical conductivity of elemental sulfur ultimately results in poorer cycle performance, restricting the marketization of lithium-sulfur (Li-S) batteries. Herein, a cicada wing-like bio-derived hierarchical porous carbon (BHPC) derived from economical and common oats was prepared and optimized to facilitate the re-deposition of sulfur in the electrochemical reversible process. Due to the remarkable cicada wing-like thin layer structure and instinctively three-stage nested pores with aperture distribution of micropores, mesopores, and macropores as 35.12%, 27.67%, and 37.21% respectively, the BHPC-4 can mainly provide good conductive network and lots of reactive sites to increase the electro-reaction contact area as well as the effective utilization of sulfur. The bio-derived carbon goes a step further to facilitate the re-uniform distribution of active substances during the cycling and repress the “Shuttling Effect”. The initial discharge specific capacity at 0.1 C is 1554 mA h/g for BHPC-4/S. Furthermore, the BHPC-4/S cathode displayed a capacity decay of 0.096% and above 95% of the Coulombic efficiency over 500 cycles at 0.5 C and supported a terrific cycling stability. Novelty Statement This work investigates BHPC/S employed as cathode for Li-S batteries. Series of bio-derived hierarchical porous carbon (BHPC) were prepared by high-temperature activation carbonization method with low-cost oatmeal as biomass precursor material, KOH as the activator. The SEM images reflect the effect of activator dosage on the morphology of BHPC samples. Among them, the BHPC-4 prepared under optimal conditions displays a three-stage network pore structure with cicada wing-like thin layer. The results of BET reveal that the specific surface area of BHPC-4 is 1531.7 m2/g and the proportions of three kinds of pores in BHPC-4 are 35.12%, 27.67%, 37.21%, respectively. The TEM image further proves the cicada wing-like thin layer structure of BHPC-4, which can provide vast number of active reaction sites and supply a large conductive network. The three-stage network pore structure can accelerate the diffusion and adsorption of electrons and ions, effectively inhibit the dissolution and the “Shuttle Effect” of polysulfide, therefore enhance the utilization of active substance. The lithium polysulfide static adsorption test and UV-vis absorption spectra imply BHPC-4 can capture polysulfide effectively. Besides, the special structure of BHPC-4 can facilitate the re-uniform distribution of active substance during the cycling. So, the BHPC-4/S electrode exhibits a high initial capacity of 1554 mA h/g at 0.1 C. Furthermore, after 500 ultra-long cycles at 0.5 C, the BHPC-4/S remained at 250 mA h/g and the average damping rate is 0.096%/per cycle. The Coulombic efficiency is stable over 95% during cycles. Moreover, it presents a superior rate capability and lower interfacial transfer resistance of 154.6 Ω.