Superhydrophilic Solar Evaporator Combined with Ion-Selective Membrane for High-Efficiency Lithium Extraction

Abstract

Inspired by the natural process of transpiration-induced selective water and nutrient absorption, a solar evaporation-driven lithium extraction method has been developed by integrating interfacial evaporation with ion-selective membrane separation, which provides an alternative pathway toward energy-, cost-efficient lithium mining. However, practical implementation is challenging due to the conventional solar evaporator's salt scaling and cavitation problem. To address these problems, a superhydrophilic solar evaporator embedded with a high water-retaining polymer is designed to generate ultrahigh negative pressure (−59 MPa), enabling sustained water flow and inhibiting salt crystallization. Under one sun irradiation (1 kW m⁻²), the evaporator demonstrates a high-water evaporation rate of 2.43 kg m⁻² h⁻¹; it then facilitates the delivery of Li⁺, resulting in lithium enrichment in the evaporator. By optimizing a polyamide (PA)-based ion-selective membrane, the solar-driven lithium extraction system demonstrates excellent Li⁺/Mg²⁺ separation performance, achieving a high separation factor of 15.6. Outdoor experiments demonstrate robust lithium extraction performance when treating salt lake brines, as the superhydrophilic evaporator retains hydration to prevent cavitation and ensure continuous ion enrichment. This research advances material design for solar desalination and selective ion recovery, offering a promising solution to tackle global lithium supply challenges.