Nitrogen-doped microporous carbon with narrow pore size distribution as sulfur host to encapsulate small sulfur molecules for highly stable lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) battery with high theoretical energy density has been considered as an important energy storage system. However, its application has been limited by low cycling stability and rapid capacity decay due to the shuttle of lithium polysulfide (Li2Sn, n > 5). These problems can be solved using small sulfur molecules (S2–4) as the active material, while synthesis of carbon hosts with suitable pores size and narrow pore distribution to encapsulate small sulfur molecules are still challenging. Here, we report a novel nitrogen-doping microporous carbon (NDMC) sulfur host with narrow micropore unimodal size distribution centered at 0.57 nm. By accommodating small sulfur molecules (S2–4) within the subnanopores of NDMC, the formation and shuttle of soluble lithium polysulfide (LiPS) can be avoided. The cathode shows only a long potential plateau due to the direct conversion from S2–4 to Li2S. In carbonate-based electrolyte, the NDMC/S-2 cathode remains a stable and reversible capacity of 902 mAh g−1 at 0.2 C with 100% Coulombic efficiency after 500 cycles, and capacity fading per cycle is only around 0.02%. Besides, an excellent capacity of 511.8 mAh g−1 is achieved even at an ultrahigh rate of 10 C, demonstrating a superior rate capability performance. This NDMC/S composite also shows excellent cycling stability in ether-based electrolyte. All the above demonstrate the NDMC has great potential application in Li-S batteries.