Recovery of lithium by pseudocapacitive electrodes in capacitive deionization

Lithium is a crucial component in rechargeable lithium-ion batteries for many applications, including the powering of electric vehicles and stationary energy storage systems. This investigation focused on two hybrid pseudocapacitive materials, the polystyrene sulfonate-MXene composite (PM) and the sodium titanate/graphene oxide composite (NG), for lithium ions recovery from aqueous Li⁺ resources. This was achieved by selectively removing unwanted divalent Ca²⁺ and Mg²⁺ ions, as well as monovalent K⁺ ions, through capacitive deionization (CDI) using a single-cell system, resulting in a final solution enriched with Li⁺ ions. Based on the ion selectivity order observed previously as Mg²⁺≈ Ca²⁺ > K⁺ > Li⁺, a series of CDI experiments were conducted with sequential steps to remove more selective ions first and to obtain a lithium-enriched solution with higher purity and maximum extracted fraction. Both PM and NG electrodes demonstrated promising performance when tested in binary, ternary, and quaternary ionic solutions with the recovered lithium solution purity in the range of 59.09 %-95.94 % and 59.75 %-77.17 %, respectively. Further, the highest enrichment factor values observed were S_Li+,Mg2+; 268.1 for PM and S_Li+,Ca2+; 44.25, for NG electrodes. The PSS-modified MXene composite electrode in obtaining the Li⁺ solution with the highest purity when separated Ca²⁺ from a binary solution. These findings offer valuable insights into the selective electrosorption of divalent ions over lithium ions through the utilization of ion intercalation pseudocapacitive nanocomposite electrodes. The obtained results hold significance in advancing novel non-precipitation techniques for the recovery of lithium ions from aqueous lithium resources.