Interlayer-Tailored Alkyl-MXenes for Selective Electrochemical Lithium-Ion Extraction

The efficient and selective extraction of lithium ions from aqueous media is crucial for resource recovery, yet remains challenging due to the chemical similarity of coexisting alkali ions, such as sodium. In this study, we report a two-step electrochemical strategy that utilizes tailored MXene electrodes for lithium ion extraction with enhanced selectivity and extraction rates. By preintercalating hexadecylamine (HDA) and decyltrimethylammonium (C10), which are long-chain organic molecules, into the Ti₃C₂T _<i>x</i> MXene structure, we tailored the interlayer environment to favor lithium ions over sodium ions. The HDA-intercalated MXene demonstrated high Li⁺/Na⁺ selectivity with a lithium ion uptake of 2.2 mmol/L and a suppressed sodium ion uptake (<0.2 mmol/L). Extended cycling revealed that molecular preintercalation modulates ion transport pathways and influences structural and electrochemical stability. Both HDA-Ti₃C₂T _<i>x</i> and C10-Ti₃C₂T _<i>x</i> maintained a lithium ion purity of nearly 100% over 50 cycles.