Electrolyte-dependent lithium intercalation in Chlorine-Terminated MXenes synthesized via molten salt etching

MXenes are two-dimensional materials with a wide range of applications. The electrochemical properties of these materials are largely determined by their surface terminations (functional groups). Traditionally, hydrofluoric acid (HF) is used for MXene synthesis, which typically results in -O, -F, and -OH surface terminations. However, these groups can limit the MXene's conductivity, stability, electrochemical behavior, and chemical reactivity. In this study, we synthesized multilayer Ti₃C₂Cl₂ MXenes via a molten salt etching route using ZnCl₂, a method that enables the controlled introduction of chlorine surface terminations instead of conventional HF-based approaches. We systematically investigated the lithium-ion intercalation behavior of these chlorine-terminated MXenes (MS-Ti₃C₂Cl₂) in organic electrolytes—DMSO, PC, and ACN—employing a three-electrode Swagelok cell configuration. Electrochemical analysis showed that electrolyte composition strongly affects Li⁺ intercalation behavior. PC enabled pseudocapacitive storage via full desolvation, while DMSO offered high Coulombic efficiency (~100%) with mixed kinetics. ACN caused solvated Li⁺ co-intercalation and poor performance. b-value analysis indicated diffusion-controlled behavior in DMSO (b = 0.663) versus capacitive dominance in ACN (b = 0.884). These results highlight the critical role of termination chemistry and solvent choice in optimizing MXene electrodes for advanced energy storage with customized interfacial properties.