Researchers at Wuhan University in China have developed a new electrochemical cell, PANI/Li_xMn₂O₄, for selective recovery of Li⁺ ions from brine water with high impurity cations (K⁺, Na⁺, Mg²⁺, etc).

The cell can simultaneously extract LiCl from a simulated brine with a high average current efficiency of 95%, energy consumption of 3.95 Wh mol^‐1 LiCl and a strong cycle ability with 70.8% capacity retention over 200 cycles. This method avoids using additional chemicals, offering a high efficiency, pollution‐free technology for Li⁺ extraction from brine waters. A paper on their work is published in the journal ChemSusChem.

The global demand for lithium has dramatically increased during the past decade, mostly due to the rapid growth of lithium-ion battery markets from portable electronics to large scale electric vehicles and electric energy storage applications. As predicted, average annual growth of global lithium consumption would still be ~10 % in near future. Consequently, the stable supply of lithium resources has become an issue of increasing concern.

Lithium is now obtained mostly from lithium ores and brine lakes. Lithium extraction from ores suffers from high energy consumption and technical complexities, which include high temperature calcination, subsequent dissolution and difficult elemental separation. For these reasons, most of the lithium (~ 80%) recovers currently from brine lakes by a “lime soda evaporation process”. In this process, brine water is pumped into shallow ponds for one-year-long solar evaporation to precipitate out the chlorides and sulfates of K⁺, Na⁺, Mg²⁺ and Ca²⁺ and then treated with excess lime to remove magnesium and finally with sodium carbonate to produce the insoluble lithium carbonate. However, this lime soda evaporation method is only techno-economically feasible for the brine lakes with low Mg/Li ratios and with suitable climate conditions.

To separate Li from the brines with high Mg/Li ratios, several methods, such as ion sieve adsorption, solvent extraction and electrochemical separation, have been widely employed. Though several ion sieves such as manganese oxides and titanium oxides have a high selectivity for Li⁺ extraction, but they are difficult for large scale application owing to their low adsorption capacity and efficiency. Similarly, solvent extraction of Li⁺ ions using diketone, organophosphorus, or crown ethers as extractants offers a high separation efficiency of Li⁺ ions from brines, but the industrial application of these extractants is limited due to their high cost.

… In this work, we investigate the selectivity of spinel Li_xMn₂O₄ positive electrode for Li⁺ insertion and performance of PANI negative electrode for the capture of Cl^- ions, and then built a PANI/Li_xMn₂O₄ cell for the recovery of lithium from brines. When compared with the previously reported electrochemical methods, offering a promising approach for direct recovery of LiCl from brine lakes.

—Zhao et al.

The structure of polyaniline (PANI) allows the doping of this material with chloride ions to a high degree, benefiting the extraction, and allowing lithium chloride salts to form more readily in the extraction process. The spinel structure of the mineral component of the cell allows the ready insertion of lithium ions into the material.

Schematic illustration of the extraction of LiCl from brine water and the release of LiCl from the PANI/Li_xMn₂O₄ cell. Zhao et al.

Resources

• Zhao, A. , Liu, J. , Ai, X. , Yang, H. and Cao, Y. (2019), “Highly Selective and Pollution‐free Electrochemical Extraction of Lithium by a Polyaniline/Li_xMn₂O₄ Cell.” ChemSusChem. doi: 10.1002/cssc.201803045