Construction of hierarchical Zn-HHTP/LDH heterostructures for selective and enhanced lithium extraction via capacitive deionization

Abstract

Efficient and sustainable lithium extraction from aqueous resources is vital for advancing next-generation energy storage technologies. However, conventional LiAl-layered double hydroxide (LDH) adsorbents are hindered by low adsorption capacity, sluggish ion transport, and poor regeneration. Here, we present a hierarchically engineered Zn-HHTP/LDH heterostructured electrode, prepared by Zn doping into LiAl-LDH to form LiZnAl-LDH on carbon cloth, followed by in situ coordination with 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to construct a conductive metal–organic framework (c-MOF). The resulting $\pi$-d conjugated interface significantly enhances charge transport, accelerates Li${}^{+}$ diffusion, and increases the density of active sites. When applied in a capacitive deionization (CDI) system, the electrode delivers a high Li${}^{+}$ adsorption capacity (50.25 mg g${}^{-1}$), excellent specific capacitance (198.33 F g${}^{-1}$ in 10 mM LiCl), and superior cycling stability (87.5% capacity retention after 100 cycles). In complex brines, it achieves exceptional selectivity (Li${}^{+}$/Mg${}^{2+}$ = 17.75). Density functional theory and molecular dynamics simulations reveal that the enhanced performance originates from interfacial charge redistribution, a reduced Li${}^{+}$ migration barrier (0.24 eV), and robust Zn-O${}_4$ coordination. This work offers a promising CDI platform and provides mechanistic insights into the rational design of heterostructured electrodes for efficient and selective lithium recovery from challenging aqueous environments.