High-Entropy MXene as Bifunctional Mediator toward Advanced Li-S Full Batteries.

The development of high-energy-density Li-S batteries (LSBs) is still hindered by the disturbing polysulfide shuttle effect. Herein, with clever combination between "high entropy" and MXene, an HE-MXene doped graphene composite containing multiple element quasi-atoms as bifunctional mediator for separator modification (HE-MXene/G@PP) in LSBs is proposed. The HE-MXene/G@PP offers high electrical conductivity for fast lithium polysulfide (LiPS) redox conversion kinetics, abundant metal active sites for efficient chemisorption with LiPSs, and strong lipophilic characteristics for uniform Li deposition on lithium metal surface. As demonstrated by DFT theoretical calculations, in situ Raman, and DRT results successively, HE-MXene/G@PP efficiently captures LiPSs through synergistic modulation of the cocktail effect and accelerates the LiPSs redox reaction, and the lattice distortion effect effectively induces the homogeneous deposition of dendritic-free lithium. Therefore, this work achieves excellent long-term cycling performance with a decay rate of 0.026%/0.031% per cycle after 1200 cycles at 1 C/2 C. The Li||Li symmetric cell still maintains a stable overpotential after 6000 h under 40 mA cm/40 mAh cm. Furthermore, it delivers favorable cycling stability under 7.8 mg cm and a low E/S ratio of 5.6 μL mg. This strategy provides a rational approach to resolve the sulfur cathode and lithium anode problems simultaneously.