Lithium Bond Impact on Lithium Polysulfide Adsorption with Functionalized Carbon Fiber Paper Interlayers for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are of great interest as a promising energy storage device because of their high theoretical capacity and energy density. However, they exhibit poor discharge capacity and capacity retention during long-term cycling because of their inherent drawbacks including the poor conductivity of sulfur and lithium sulfide, the shuttle effect of lithium polysulfides (LiPSs), and the large volume expansion of sulfur to lithium sulfide. An effective approach that can solve these problems is to use an interlayer inserted between the separator and the cathode. Nevertheless, the underlying adsorption mechanism of LiPSs on the interlayer has not yet been widely investigated. Herein, the effect of lithium bond chemistry on the adsorption of LiPSs on the functionalized carbon fiber paper (CFP) interlayer containing hydroxyl, carboxyl, or amide functional groups is investigated by a density functional theory approach. It is found that the functionalized CFP exhibits a strong lithium bond interaction between the Li electron acceptor of LiPSs and the N or O electron donor of the functionalized CFP interlayer. In addition, the correlation between the adsorption energy of LiPSs on the interlayer and the electrochemical performance of LSBs is investigated. The results provide the fundamental understanding of the structure–property relationship for the adsorption of LiPSs on the functional groups of the interlayer, which will be beneficial for the further development of advanced LSBs.