Highly selective lithium extraction from salt lake via carbon-coated lithium vanadium phosphate capacitive electrode

Abstract

<p>Recently, with the rapid development of lithium-ion batteries and electric vehicles, the demand for lithium resources in the world has undoubtedly greatly intensified. Based on the advantages of high selectivity and low energy consumption, capacitive deionization (CDI) technology is well-suited for the selective extraction of lithium resources from salt lakes. Herein, carbon-coated Li₃V₂(PO₄)₃ (LVP@C) is developed as a cathode electrode for the first time by using a hybrid CDI device to selectively extract Li⁺ ions from salt lake brine, due to its high theoretical capacity and excellent cycling capacity. The electrochemical (de)intercalation mechanism of Li⁺ ions in the LVP@C has been evaluated by electrochemical, X-ray photoelectron spectroscopy (XPS), and <em>in-situ</em> X-ray diffraction (XRD) techniques, demonstrating a reversible transition of the V valence state during electrosorption/desorption based on Faradaic redox reaction. The optimized LVP@2C delivers a maximum Li⁺ electrosorption capacity of 25.8 mg g⁻¹, and still maintains a high retention of 78 % even after 50 cycles. The LVP@2C has lithium selectivity coefficients of 444.7 and 351.2 at high Mg-Li ratios of 1:5 and high Na-Li ratios of 1:15. Density Functional Theory (DFT) calculations further reveal that the selective electrosorption mechanism in the LVP@2C electrode is mostly ascribed to the smaller hydrated ionic radius and lower ionic diffusion energy barrier of Li⁺ ions in comparison with Mg²⁺ ions. Finally, the effectiveness evaluation of the lithium selective extraction from the brine of a natural salt lake in Tibet indicates that the LVP@2C has highly selective electrosorption of lithium (α_(Li/Mg) = 187.50, α_(Li/K) = 136.11, α_(Li/Na) = 116.88, α_(Li/Ca) = 4.92) and can serve as a potential electrode for the extraction of lithium from salt lake brine.<br></p>