Understanding the Cathodic Overpotential in LiMn₂O₄ Electrodes for Lithium Recovery from Brines in a Continuous Flow-by Electrochemical Reactor

With the growing demand for battery materials, lithium recovery from alternative natural resources has gained attention, especially from geothermal sources by the direct lithium extraction (DLE) method. For DLE technology to be economically attractive, a challenging brine depletion of 90% should be attempted, requiring a thorough understanding of the recovery system under high concentration gradients. In this work, the impact of current density and brine concentration on the capacity of electrodes with different mass loading, 30 and 10 mg cm −2 , was studied for a continuous electrochemical ion-pumping system. The cathodic overpotential was decomposed with analytical expressions into the individual contributions of surface and concentration overpotential, as well as the equilibrium potential at the inlet (LiCl 30 mM and NaCl 1.3 M) and outlet (LiCl 3 mM and NaCl 1.3 M) of a continuous electrochemical flow-by reactor. The largest potential shift from reactor inlet to outlet was found to be due to the equilibrium potential, followed by the concentration overpotential. All of the derived equations were experimentally validated, providing key insights for optimizing electrochemical lithium extraction under real operational conditions.