Solar-Powered Redox Adsorption Method for Round-the-Clock Direct Lithium Extraction from Low-Grade Brines

Electrochemical lithium (Li) extraction from low-grade brines is challenged by maintaining high Li selectivity at practically relevant extraction rates while enabling off-grid, round-the-clock operation in remote, infrastructure-deficient regions. Here we propose a solar-powered redox adsorption method (SRAM), in which dissolved, regenerable electron carriers (ECs) deliver electrons to dispersed olivine iron phosphate (o-FePO₄) adsorbents. In SRAM, EC-mediated electron transfer enables electrochemically effective use of dispersed o-FePO₄ adsorbents, while interfacial charge accumulation and electric double layer (EDL) formation may hinder further access of ECs to the adsorbent surface, thereby moderating local electron flux and suppressing competing-ion intercalation. As a result, SRAM achieves a high extraction rate of 40 mA mmol^-1 o-FePO₄ while maintaining high selectivity (separation factors of 700 for Li⁺/Na⁺ and 2400 for Li⁺/Mg²⁺) from low-grade brines (70 ppm Li⁺). Meanwhile, ECs function as integrated chemical energy-storage media that can buffer intermittent photovoltaic input and temporally decouple charging from Li extraction, enabling solar-buffered day-night operation without an external electrical storage unit. Field demonstrations support stable operation (∼9 mg Li g^-1 h^-1) and provide a lab-scale validation through 50-L raw brine processing. Our work establishes EC-mediated electron transfer as a promising strategy for sustainable Li recovery from previously untapped low-grade brines.