Ultra-lightweight Ti₃C₂T_x MXene modified separator for Li-S batteries: Thickness regulation enabled polysulfide inhibition and lithium ion transportation

The practical application of lithium-sulfur (Li-S) batteries is limited by the easy dissolution of polysulfides in the electrolyte, resulting in the lithium polysulfide (LPS) shuttle effect. Several two-dimensional (2D) materials with abundant active binding sites and high surface-to-volume ratios have been developed to prepare functional separators that suppress the diffusion of polysulfides. However, the influence of modified layer thickness on Li+ transport has not been considered. Herein, we synthesized individual and multilayered 2D Ti3C2Tx MXene nanosheets and used them to fabricate a series of Ti3C2Tx-PP modified separators. The separators had mass loadings ranging from 0.16 to 0.016 mg cm(-2), which is the lowest value reported for 2D materials to the best of our knowledge. The corresponding reductions in thickness ranged from 1.2 mu m to 100 nm. LPS shuttling was effectively suppressed, even at the lowest mass loading of 0.016 mg cm(-2). Suppression was due to the strong interaction between LPS intermediates and Ti atoms and hydroxyl functional groups on the separator surface. The lithium-ion diffusion coefficient increased with the reduction of Ti3C2Tx layers on the separator. Superior cycling stability and rate performance were attained when the separator with a Ti3C2Tx-PP mass loading of 0.016 mg cm(-2) was incorporated into a Li-S battery. Carbon nanotubes (CNTs) were introduced into the separators to further improve the electrical and Li+ ionic conductivity in the cross-plane direction of the 2D Ti3C2Tx layers. With the ultra-lightweight Ti3C2Tx/CNTs modified PP separator, the cell maintained a capacity of 640 mAh g(-1) after 200 cycles at 1 C with a capacity decay of only 0.079% per cycle. (C) 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.