Electrochemical lithium recovery technologies have emerged as a promising solution for extracting lithium from various sources, including spent lithium-ion batteries, geothermal brines, and seawater. These methods offer advantages over traditional extraction techniques, such as reduced chemical consumption, higher selectivity, and improved sustainability. The three primary electrochemical approaches include lithium-ion capturing electrodes, redox-coupled systems, and electrolytic processes. Each method employs distinct mechanisms, materials, and cell designs to achieve efficient lithium recovery with varying degrees of Faradaic efficiency and energy consumption.

Lithium-ion capturing electrodes rely on intercalation materials that selectively extract lithium ions from a source solution. Among the most studied materials is λ-MnO₂, a spinel-type manganese oxide with a three-dimensional framework that allows reversible lithium insertion and extraction. The process involves applying a voltage to the electrode, driving lithium ions into the host structure while maintaining structural stability. Another notable material is LiFePO₄, which exhibits high lithium selectivity due to its olivine structure. The Faradaic efficiency of these systems typically ranges between 80% and 95%, depending on the electrode material and operating conditions. Cell designs often employ a two-electrode setup, where the capturing electrode works alongside a counter electrode, such as platinum or carbon, in a lithium-containing electrolyte. The energy requirement for this process varies between 5 and 15 Wh per gram of lithium recovered, influenced by factors like solution concentration and current density.

Redox-coupled lithium recovery systems integrate electrochemical ion pumping with redox-active molecules to enhance lithium extraction. These systems often utilize ferrocyanide-based redox couples or organic molecules such as quinones, which undergo reversible oxidation and reduction reactions. During operation, the redox mediator shuttles electrons while lithium ions are selectively transported across ion-exchange membranes. A common cell configuration involves a three-compartment design, with the source solution, recovery chamber, and redox mediator separated by selective membranes. The Faradaic efficiency in these systems can exceed 90%, with energy consumption ranging from 10 to 20 Wh per gram of lithium. The scalability of redox-coupled systems depends on the stability of the redox mediators and the durability of the membranes, which must withstand prolonged cycling without degradation.

Electrolytic approaches for lithium recovery leverage electrochemical cells to precipitate lithium compounds directly from solution. One example is the electrolysis of lithium-containing brines, where lithium hydroxide or lithium carbonate is generated at the cathode. This method often employs bipolar membranes to separate the anode and cathode compartments, preventing unwanted side reactions. The process requires careful control of pH and current density to avoid co-precipitation of impurities such as magnesium or calcium. Energy consumption for electrolytic lithium recovery ranges from 20 to 30 Wh per gram, higher than other electrochemical methods due to the additional energy needed for water splitting and compound formation. However, this approach can achieve high purity levels, making it suitable for battery-grade lithium production.

Electrode materials play a critical role in determining the performance of electrochemical lithium recovery systems. For lithium-ion capturing electrodes, materials like λ-MnO₂ and LiFePO₄ offer high selectivity but differ in kinetics and stability. λ-MnO₂ exhibits fast lithium insertion rates but may suffer from manganese dissolution in acidic conditions. In contrast, LiFePO₄ demonstrates excellent cycling stability but requires precise potential control to avoid iron oxidation. Composite electrodes, combining active materials with conductive additives like carbon black or graphene, improve electronic conductivity and rate capability. Membrane selection is equally important, particularly for redox-coupled and electrolytic systems. Cation-exchange membranes with high lithium selectivity, such as those incorporating sulfonated polymers, are essential for efficient ion transport.

Faradaic efficiency serves as a key metric for evaluating electrochemical lithium recovery technologies. It measures the fraction of charge passed through the system that contributes directly to lithium extraction. High Faradaic efficiency indicates minimal side reactions, such as hydrogen evolution or oxygen reduction, which waste energy and reduce process efficiency. Achieving Faradaic efficiencies above 90% requires optimizing operating parameters such as applied potential, electrolyte composition, and electrode morphology. For instance, excessive voltage can lead to water electrolysis, while insufficient voltage may slow lithium extraction kinetics. System designs that minimize ohmic losses and maximize active surface area further enhance Faradaic efficiency.

Energy requirements for electrochemical lithium recovery depend on multiple factors, including the source lithium concentration, electrode materials, and cell design. Lower lithium concentrations in sources like seawater or dilute brines demand higher energy input due to increased ohmic resistance and slower mass transport. In contrast, concentrated solutions from battery recycling streams enable more efficient recovery with reduced energy consumption. System scalability hinges on the ability to maintain performance at larger electrode areas and higher current densities without significant efficiency losses. Modular cell designs, where multiple units operate in parallel, facilitate industrial deployment by allowing incremental capacity expansion.

Industrial deployment of electrochemical lithium recovery faces challenges related to cost, durability, and integration with existing processes. The capital cost of electrochemical systems remains higher than conventional methods like evaporation ponds, though operational savings from reduced chemical use and waste generation can offset initial investments. Long-term durability requires electrode materials and membranes that withstand thousands of cycles without performance degradation. Integration with battery recycling flowsheets or brine processing plants necessitates compatibility with upstream and downstream unit operations. Despite these challenges, electrochemical lithium recovery offers a sustainable pathway to meet growing lithium demand while minimizing environmental impact. Continued research into advanced materials, system optimization, and scale-up will further enhance the viability of these technologies for industrial applications.