Lithium has emerged as a critical raw material because of its indispensable role in the energy transition, especially in manufacturing lithium-ion batteries for electric vehicles and portable devices. However, 95% of such batteries are discarded without recycling once they reach the end of their life. When recycled, the batteries are shredded to form a black mass, which is leached by sulfuric acid. The resulting leachate contains transition cations such as nickel, cobalt, and manganese, besides Li. Thus, it is necessary to separate these elements, which is typically achieved through successive precipitation by increasing the pH of the leachate. However, this process results in a 40-60% loss of lithium which is the last element to be recovered.

Flow Electrode Capacitive Deionization (FCDI) is a very recent electromembrane desalination technology which employs flow electrodes (carbon slurries) to remove ions from saline water. We hypothesised that replacing standard cation exchange membranes with lithium-selective ones could allow for lithium recovery from brines and spent Li-ion batteries. In this talk, the journey behind the creation of Lithium Membrane Flow Capacitive Deionization (Li-MFCDI) [1] will be disclosed.

Several key challenges were addressed to optimise the FCDI/Li-MFCDI performance regarding energy efficiency and the possibility of scale-up. Polymeric lithium-selective membranes were developed [2] to overcome the limitations of ceramic membranes, which are brittle and expensive, limiting their scalability. Another challenge in FCDI and Li-MFCDI is to maintain the uninterrupted flow of carbon slurry electrodes while preventing channel blockage. In this context, the design of flow electrode channels was investigated experimentally and by computational fluid dynamics (CFD), considering the shear-thinning behaviour of flow electrodes [3]. Furthermore, innovations, including the utilisation of 3D-printed flow electrode gaskets as a substitute for the state-of-the-art computer numerical control (CNC) milled graphite current collectors, were explored to improve system scalability and efficiency. The research also assessed various operational modes under the same operating conditions to identify the most efficient operational mode for continuous and scalable desalination or lithium recovery. Finally, several different activated carbons were tested in the FCDI system to hunt out the best material for flow electrodes to enhance performance, scalability, and overall system efficiency.