Tuning solvation behavior within electric double layer via halogenated MXene for reliable lithium metal batteries

Solid electrolyte interphase (SEI)/electrolyte interface is critical in determining the lithium (Li) plating/stripping behavior. The solvation structure of Li-ion is well understood in the bulk electrolyte. Still, the mechanism of how SEI components affect the Li-ion solvation structure and desolvation energy barrier at the SEI/electrolyte interface is still unclear. Herein, Ti₃C₂ Maxine with single halogenated terminations (−Cl, −Br, −I) are synthesized and used as a model system, because their surface terminations induce a double halide-rich SEI formation (LiF and LiCl/LiBr/LiI). We examine the influence of the interaction strength between different Li halides and Li-ion on coordination number of Li ions and distribution of Li ions within the inner Helmholtz plane (IHP). A solvation sheath with a low solvent coordination number forms near the IHP of the LiBr interphase, improving the kinetics of Li deposition. Accordingly, half-cells utilising Li-carbon fiber/Ti₃C₂Br₂ electrodes exhibit a long lifespan of 12,000 h (1 mA cm⁻², 1 mAh cm⁻²). A pouch cell comprising Li-carbon fiber/Ti₃C₂Br₂ anode and LiFePO₄ cathode displays a capacity retention rate of 97 % after 300 cycles even at a low negative to positive electrode capacity ratio of 2.26. Our research provides crucial principles for the design of SEI components in Li metal batteries.