Halogen-Bonding\nNanoarchitectonics in Supramolecular\nPlasticizers for Breaking the Trade-Off between Ion Transport and\nMechanical Strength of Polymer Electrolytes for High-Voltage Li-Metal\nBatteries

The\nlow ionic conductivity of poly(ethylene oxide) (PEO)-based\npolymer electrolytes at room temperature impedes their practical applications.\nThe addition of a plasticizer into polymer electrolytes could significantly\npromote ion transport while inevitably decreasing their mechanical\nstrength. Herein, we report a supramolecular plasticizer (SMP) to\nbreak the trade-off effect between ionic conductivity and mechanical\nproperties in PEO-based polymer electrolytes. Accordingly, the SMP\nis constructed by tetraethylene glycol dimethyl ether (G4) and SbF<sub>3</sub> through halogen bonds. The SMP-plasticized PEO electrolyte\n(PEO/SMP) presents a simultaneously enhanced ionic conductivity of\n2.4 × 10<sup>–4</sup> S cm<sup>–1</sup> (25 °C)\nand a high mechanical strength of 8.1 MPa, compared to those of pristine\nPEO-based electrolytes. Benefiting from the halogen bonds between\nG4 and SbF<sub>3</sub>, the Li–O coordination in PEO/SMP is\nevidently weakened, and thus rapid Li<sup>+</sup> transport is achieved.\nFurthermore, the PEO/SMP electrolyte possesses a wide electrochemical\nstability window of 4.5 V and, importantly, derives an inorganic-rich\nSEI with a low interfacial resistance on a lithium metal surface.\nBy using PEO/SMP, the lithium-metal battery with the LiNi<sub>0.5</sub>Co<sub>0.2</sub>Mn<sub>0.3</sub>O<sub>2</sub> cathode exhibits a\ngood rate and long-term cycling performance with a capacity retention\nof 75.3% (500 cycles). This work offers a rational guideline for the\ndesign of polymer electrolytes suitable for high-performance lithium-metal\nbatteries.