Polyethylenimine Expanded Graphite Oxide Enables High Sulfur Loading and Long-Term Stability of Lithium-Sulfur Batteries

Abstract

To realize practical lithium-sulfur batteries (LSBs) with long cycling life, designing cathode hosts with a high specific surface area (SSA) is recognized as an efficient way to trap the soluble polysulfides. However, it is also blamed for diminishing the volumetric energy density and being susceptible to side reactions. Herein, polyethylenimine intercalated graphite oxide (PEI-GO) with a low SSA of 4.6 m² g^-1 and enlarged interlayer spacing of 13 Å is proposed as a superior sulfur host, which enables homogeneous distribution of high sulfur content (73%) and facilitates Li⁺ transfer in thick sulfur electrode. LSBs with a moderate sulfur loading (3.4 mg S cm^-2 ) achieve an initial capacity of 1157 and 668 mAh g^-1 after 500 cycles at 0.5 C. Even when the sulfur loading is increased to 7.3 mg cm^-2 , the electrode still delivers a high areal capacity of 4.7 mAh cm^-2 (641 mAh g^-1 ) after 200 cycles at 0.2 C. The excellent electrochemical properties of PEI-GO are mainly attributed to the homogeneous distribution of sulfur in PEI-GO and the strong chemical interactions between polysulfides and amine groups, which can mitigate the loss of active phases and contribute to the better cycling stability.

Keywords: graphite oxide; high sulfur content; intercalation; lithium-sulfur batteries; low specific surface area.