Strong adsorption of lithium polysulfides on ethylenediamine-functionalized carbon fiber paper interlayer providing excellent capacity retention of lithium-sulfur batteries

Abstract

Lithium-sulfur batteries (LSBs) are widely investigated since they have rather high theoretical capacity (1675 mAh g−1) and specific energy (∼2600 Wh kg−1). However, their poor capacity retention limits their practical use. Herein, sulfur-loaded activated carbon was used as the cathode of LSB. The functionalized carbon fiber paper (CFP) containing carboxyl and amide groups was used as an interlayer of LSB. With these designs of the LSB, it can provide excellent charge storage performance with high capacity retention. The LSB using ethylenediamine (EDA)-functionalized CFP interlayer exhibits an outstanding initial discharge capacity of 1800 mAh g−1 and 1472 mAh g−1 after the stable SEI formation with ca. 92% capacity retention and low degradation rate of 0.046% per cycle after 200 cycles at 1C. A strong adsorption capacity of polysulfide and amide functional group of EDA-functionalized CFP reduces the shuttle mechanism phenomenon. The density functional theory calculation shows that EDA-functionalized CFP can strongly bind high order polysulfides (Li2Sn, 4 ≤ n ≤ 8) when compared to other functional groups. Furthermore, the fully charged LSB cell with ca. 3.5 mg cm−2 sulfur loading content on the cathode can practically supply electricity to a nominal 3-V spinning motor for 25 min demonstrating the practical use of our as-fabricated LSB.