Separator Engineering Based on Cl-Terminated MXene Ink: Enhancing Li Diffusion Kinetics with a Highly Stable Double-Halide Solid Electrolyte Interphase.

Separator engineering is a promising route to designing advanced lithium (Li) metal anodes for high-performance Li metal batteries (LMBs). Conventional separators are incapable of regulating the Li diffusion across the solid electrolyte interphase (SEI), leading to severe dendritic deposition. To address this issue, a polypropylene (PP) separator modified by spray coating the Cl-terminated titanium carbonitride MXene ink is designed (PP@TiCNCl). The lithiophilic MXene provides excellent electrolyte wettability and low Li diffusion barriers, finally enhancing the Li diffusion kinetics of excessively stable SEI. The X-ray photoelectron spectroscopy depth profiling as well as cryo-transmission electron microscopy reveals that a gradient SEI hierarchy with evenly distributed LiF and LiCl is spontaneously formed during the electrochemical process. As a consequence, PP@TiCNCl delivers a high Coulombic efficiency (99.15%) coupled with a prolonged lifespan of over 5500 h in half cells and 3100 cycles at 2 C in full cells. This work offers an effective strategy for constructing dendrite-free and Li permeable interfaces toward high-energy-density LMBs.