Abstract
Lithium-sulfur battery (LSB) is a promising candidate as a conventional lithium-ion battery replacement due to its high theoretical specific capacity and high energy density together with additional advantages of low cost, abundance, and environment friendliness. However, LSB still suffers from many issues including natural insulator of active sulfur and final product of Li2S, polysulfide shuttle effect, and 80% volume expansion during cycling which are causes of capacity fading in the LSB. To fix the mentioned issues as well as improve performances of LSB, carbon interlayer has introduced between a sulfur cathode and separator to suppress lithium polysulfide diffusion and act as an upper current collector. Here, we prepare surface modified carbon fiber paper (CFP) via a simple amide coupling reaction with various amine reactants to study the effect of functional groups on the surface of the CFP on LSB performances. LSB with modified CFPs as interlayers show significant higher specific capacity than LSB without interlayer due to the chemisorption ability between functional groups on the CFP surfaces and lithium polysulfide intermediates. The LSB with modified CFP by 4-aminobenzoic acid interlayer exhibits the highest specific capacity along with long cyclability observed from high capacity retention of 88.5% and Coulombic efficiency above 98% after 200 cycles. Furthermore, the lithium polysulfide chemisorption capabilities of each functional group are fundamentally explained via density functional theory (DFT) calculations through the binding energy between functional groups and polysulfide intermediates. More interestingly, we also prove that the excellent performance of the LSB with 4-aminobenzoic acid interlayer is due to the strong lithium bond of S-L...O coupled with hydrogen bond of S...H-O.