Cation Vacancy-Boosted Lewis Acid-Base Interactions in a Polymer Electrolyte for High-Performance Lithium Metal Batteries.

Polymer electrolytes have gained extensive attention owing to their high flexibility, easy processibility, intrinsic safety, and compatibility with current fabrication technologies. However, their low ionic conductivity and lithium transference number have largely impaired their real application. Herein, novel two-dimensional clay nanosheets with abundant cation vacancies are created and incorporated in a poly(ethylene oxide) (PEO)/poly(vinylidene fluoride-co-hexafluoropropylene)-blended polymer-based electrolyte. The characterization and simulation results reveal that the cation vacancies not only provide lithium ions with additional Lewis acid-base interaction sites but also protect the PEO chains from being oxidized by excess lithium ions, which enhances the dissociation of lithium salts and the hopping mechanism of lithium ions. Benefiting from this, the polymer electrolyte shows a high ionic conductivity of 2.6 × 10-3 S cm-1 at 27 °C, a large Li+ transference number up to 0.77, and a wide electrochemical stability window of 4.9 V. Furthermore, the LiFePO4∥Li coin cell with such a polymer electrolyte delivers a high specific capacity of 145 mA h g-1 with an initial Coulombic efficiency of 99.9% and a capacity retention of 97.3% after 100 cycles at ambient temperature, as well as a superior rate performance. When pairing with high-voltage cathodes LiCoO2 and LiNi0.5Mn1.5O4, the corresponding cells also exhibit favorable electrochemical stability and a high capacity retention. In addition, the LiFePO4∥Li pouch cells display high safety even under rigorous conditions including corner-cut, bending, and nail-penetration.