Simultaneously Exfoliated Boron-Doped Graphene Sheets To Encapsulate Sulfur for Applications in Lithium–Sulfur Batteries

Heteroatom-doped high-quality graphene is highly effective in encapsulating sulfur (S) and fabricating a high-performance electrode for lithium–sulfur (Li-S) batteries. Herein, simultaneously exfoliated boron-doped graphene sheets (B-EEGs) are prepared via electrochemical exfoliation of graphite in a 1.0 mol L –1 Li bis(oxalato)borate (LiBOB)/dimethyl methylphosphonate (DMMP) electrolyte. The obtained B-EEG possesses high quality with a large planar size of ∼11 μm, few structure defects of I D /I G = 0.26, and low oxygen content of 7.93%. After B-EEG is used to encapsulate S through an in situ deposition route, the S@B-EEG with an S content of 72.5% displays a high initial discharge capacity of 1476 mAh g –1 at 0.1 C. Compared to a conventional S@thermally reduced graphene oxide (S@T-RGO) composite, the S@B-EEG composite exhibits a high capability of 1018 mAh g –1 at 1 C and excellent capacity retention of 838 mAh g –1 after 130 cycles. On one hand, the excellent electrochemical performances of S@B-EEG are primarily attributed to the few defects and big planar size of B-EEG, which is helpful for increasing the conductivity of S and suppressing the shuttle of long-chain polysulfides. On the other hand, the doped boron atoms as active sites can efficiently trap polysulfides by chemical adsorption.