Enabling high stability lithium–sulfur batteries by separator modification with chemically bonded functional groups

The inter-electrode shuttle effect of soluble lithium polysulfides (LiPSs) and sluggish sulfur redox kinetics lead to low Coulombic efficiency and poor cycling stability in lithium–sulfur (Li–S) batteries. Separator modification provides a viable approach to addressing these issues. When the separator surface is modified with proper functional groups, the soluble LiPSs can be captured as they diffuse to the separator. Herein, a composite material of transition metal telluride (2H-MoTe2) loaded on MXene nanosheets (MX) is proposed as a separator modification material for Li–S batteries (MX@MoTe2), which is prepared by electrostatic self-assembly. Experiments and theoretical calculations show that MX@MoTe2 has a strong adsorption and reversible conversion effect on LiPSs. The Li–S cells with the MX@MoTe2-modified separator exhibit stable high-rate cycling, with a capacity decay of 0.021% per cycle over 1000 cycles at 5C. In addition, a high area capacity of 7.18 mAh cm−2 is achieved at a high sulfur loading (9.34 mg cm−2) and low electrolyte/sulfur ratio (6.0 μl mg−1). Moreover, the chemically bonded MXene/MoTe2 interface enables interfacial electronic regulation of 2H-MoTe2, which not only strengthens LiPS adsorption but also promotes the deposition and dissolution kinetics of Li2S. This interfacial adsorption/catalytic effect provides useful guidance for designing long-cycle Li–S batteries.