A Solution-Processable High-Modulus Crystalline Artificial Solid Electrolyte Interphase for Practical Lithium Metal Batteries

The solid electrolyte interphase (SEI) has been identified as a key challenge for Li metal anodes. The brittle and inhomogeneous native SEI generated by parasitic reactions between Li and liquid electrolytes can devastate battery performance; therefore, artificial SEIs (ASEIs) have been proposed as an effective strategy to replace native SEIs. Herein, as a collaboration between academia and industrial R&D teams, a multifunctional (crystalline, high modulus, and robust, Li+ ion conductive, electrolyte-blocking, and solution processable) ASEI material, LiAl-FBD (where "FBD" refers to 2,2,3,3-tetrafluoro-1,4-butanediol), for improving Li metal battery performance is designed and synthesized. The LiAl-FBD crystal structure consists of Al3+ ions bridged by FBD2- ligands to form anion clusters while Li+ ions are loosely bound at the periphery, enabling an Li+ ion conductivity of 9.4 x 10(-6) S cm(-1). The fluorinated, short ligands endow LiAl-FBD with electrolyte phobicity and high modulus. The ASEI is found to prevent side reactions and extend the cycle life of Li metal electrodes. Specifically, pairing LiAl-FBD coated 50 mu m thick Li with industrial 3.5 mAh cm(-2) NMC811 cathode and 2.8 mu L mAh(-1) lean electrolyte, the Li metal full cells show superior cycle life compared to bare ones, achieving 250 cycles at 1 mA cm(-2).