A compressive-strain-engineered TiO₂/rGO heterojunction as a polysulfide mediator

The practical application of lithium-sulfur batteries (LSBs) is hindered by the polysulfide shuttle effect and sluggish redox kinetics. Herein, we report a compressive strain engineering strategy to develop a TiO₂/reduced graphene oxide (rGO) heterostructure (TNGO) as a high-performance polysulfide mediator for separator modification. The introduced compressive strain in the TiO₂ lattice, confirmed by structural characterizations, effectively enhances polysulfide chemisorption and accelerates Li⁺ diffusion. When coated on a polypropylene separator, the TNGO composite synergistically combines the conductive rGO network with the catalytically active, strained TiO₂. This design simultaneously mitigates the shuttle effect and improves reaction kinetics. Consequently, the LSB with the TNGO-modified separator achieves a high initial capacity of 1072.7 mAh g^-1 at 1C and retains 409.9 mAh g^-1 after 1000 cycles, with a low decay rate of 0.062% per cycle. Even with a high sulfur loading (4.32 mg cm^-2), the cells retain 82.3% of their capacity after 200 cycles at 0.1C. This work demonstrates compressive strain engineering as a novel and powerful strategy for separator modification in LSBs.