High electrical conductivity of 3D mesporous carbon nanocage as an efficient polysulfide buffer layer for high sulfur utilization in lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries display a high theoretical energy density compared with commercial lithium-ion batteries (LIBs). However, there are several major challenges including the poor conductivity and large volumetric expansion of sulfur, and the shuttle effect and uncontrollable deposition of lithium polysulfides, which lead to the low sulfur utilization and poor cycle life in practical applications. The fabrication of state-of-the-art separator based on high electrical conductivity of 3D porous carbon is believed to restrain the shuttle effect of lithium polysulfides and control the deposition of lithium sulfide. Herein, we report a kind of 3D mesporous carbon nanocage (PCN) with a high electrical conductivity as an efficient polysulfide buffer layer on PP separator in Li-S batteries for high sulfur utilization. The extraordinary electrical conductivity of the 3D PCN can promote the transformation reaction of Li2S/sulfur-to-lithium polysulfides between PCN separators and sulfur cathode. During charge/discharge, PCN serves as a buffer layer to redistribute the shuttling back of LiPSs owing to its abundant mesoporous structure. Thereby, Li-S batteries using PCN separator shows an extraordinary initial discharge capacity of 1044 mAh g−1 which still remains 652 mAh g−1 after 200 cycles at 1C. This is a significantly boost for sulfur utilization compared with that in Li-S batteries using PP separator. In addition, the advanced Li-S batteries with PCN separators reveal a superior areal capacity (2.5 mAh cm−2) at a high sulfur loading amount of 7.34 mg cm−2, showing the potential in practical application.