The urgent need to mitigate climate change is accelerating the global transition toward renewable energy systems, which in turn is driving an unprecedented demand for energy storage materials. Among these, lithium has become a critical resource for enabling large-scale electrification and supporting the decarbonization of the energy sector. The presence of lithium-bearing geothermal reservoirs in Germany offers a unique opportunity for domestic lithium production, contributing to resource security and reducing dependence on imports. In this context, electrochemical lithium ion pumping (ELIP) has emerged as a promising direct lithium extraction (DLE) technology. Its main advantages lie in high selectivity, potential energy efficiency, and compatibility with diverse brine chemistries. Nevertheless, ELIP still faces significant challenges related to its scalability and to the inherently low lithium concentrations found in natural geothermal brines. Addressing these limitations requires a combined understanding of electrode materials, reactor design, and process operation. This thesis investigates the development of a lithium recovery system based on the ELIP concept, following a stepwise approach from the characterization of active materials to process-level implementation. The first part provides a comprehensive review of ELIP technologies and their working principles, outlining the rationale for selecting the LiMn₂O₄/λ-MnO₂ (LMO) rocking-chair configuration as the focus of this work. Based on this selection, experimental efforts were directed toward developing and characterizing composite LMO electrodes and evaluating the electrochemical performance of the rocking-chair system under conditions representative of geothermal brines. Composite LMO electrodes with different mass loadings were prepared, and their lithium (de)intercalation behavior was examined in a circulating Flow-By reactor using an artificial brine containing 30 mM Li and 1.3 M Na, which reproduces the Na/Li ratio present in geothermal brines from the Upper Rhine Graben. Lithium selectivity was evaluated both at the electrode level and in the full LMO rocking-chair system in the presence of competing cations found in geothermal brines. Key performance indicators, including energy consumption per mole of lithium extracted, Faradaic efficiency, and lithium separation factor with respect to impurity ions, were quantified to assess both the energy efficiency and separation performance of the complete system under controlled Flow-By operation. Building upon this foundation, a continuous-flow reactor concept was designed and experimentally validated to demonstrate lithium extraction under conditions simulating the progressive lithium depletion that occurs during brine circulation. In this design, the reactor is divided into functional zones that are tailored to local variations in lithium concentration, mitigating mass transport limitations while reducing the overall electrode area required for high lithium recovery. This zoned configuration allowed up to 90 % lithium recovery from artificial geothermal brine. Process-level parameters such as brine hydrodynamics and reactor retained volume were analyzed, providing criteria for scaling up the electrochemical unit within hybrid geothermal plants. Finally, a detailed electrochemical analysis was carried out to optimize the cathodic process, identified as a primary constraint on overall system performance. Cyclic voltammetry and electrochemical impedance spectroscopy, combined with a transmission line model for porous electrodes, were used together with systematic variations in electrode mass loading and hydrodynamic conditions to deconvolute the contributions of equilibrium potential, as well as surface and concentration overpotentials. These findings provide quantitative insight into the energy and electrode capacity losses occurring under depleted brine conditions and establish a framework for improving both energy and material efficiency of future large-scale ELIP systems. Overall, this work bridges the gap between laboratory proof of concept and process-level design, laying the scientific and engineering foundations for scalable electrochemical direct lithium extraction from geothermal brines.
Clara Ines Roggerone (Thu,) studied this question.