Extracting lithium electrochemically from seawater has the potential to resolve any future lithium shortage. However, electrochemical extraction only functions efficiently in high lithium concentration solutions. Herein, we discovered that lithium extraction is temperature and concentration dependent. Lithium extraction capacity (i.e., the mass of lithium extracted from the source solutions) and speed (i.e., the lithium extraction rate) in electrochemical extraction can be increased significantly in heated source solutions, especially at low lithium concentrations (e.g., < 3 mM) and high Na+/Li+ molar ratios (e.g., >1000). Comprehensive material characterization and mechanistic analyses revealed that the improved lithium extraction originates from boosted kinetics rather than thermodynamic equilibrium shifts. A higher temperature (i.e., 60 oC) mitigates the activation polarization of lithium intercalation, decreases charge transfer resistances, and improves lithium diffusion. Based on these understandings, we demonstrated that a thermally assisted electrochemical lithium extraction process could achieve rapid (36.8 mg g-1 day-1) and selective (51.79% purity) lithium extraction from simulated seawater with an ultrahigh Na+/Li+ molar ratio of 20,000. The integrated thermally regenerative electrochemical cycle can harvest thermal energy in heated source solutions, enabling a low electrical energy consumption (11.3-16.0 Wh mol-1 lithium). Furthermore, the coupled thermal-driven membrane process in the system can also produce freshwater (13.2 kg m-2 h-1) as a byproduct. Given abundant low-grade thermal energy availability, the thermally assisted electrochemical lithium extraction process has excellent potential to realize mining lithium from seawater.
Keywords: Electrochemical lithium extraction; Membrane distillation; Seawater; Thermally regenerative electrochemical cycle; Waste heat utilization.
Copyright © 2022 Elsevier Ltd. All rights reserved.