(520f) Recovering Metal Ions from Spent Li-Ion Batteries Using Nanoporous Graphene Oxide Membrane

With the growing use of electric cars, lithium-ion batteries (LiBs) become an emerging material and the demand for LiBs is increasing fast. Therefore, the interest in recycling metal ions from spent batteries to recover cathode metal ions is also growing. There are several methods for recycling metal ions such as solvent extraction, electrochemical deposition, chemical precipitation, etc. However, these methods usually require lots of cost and energy and also need some additional processes to obtain ions separately. Accordingly, the membrane separation process capable of separating ions efficiently with low energy and cost becomes quite attractive. Among various materials for membranes, graphene oxide (GO) is being studied frequently because it is easy to control the interlayer spacing and pore size of the membrane with high stability. In previous papers, the ion selectivity of the GO membrane was improved by heat treatment, surface charge change, cross-linking with polymer, etc.

Herein, we tried to fabricate the nanoporous graphene oxide membranes to investigate the ion separation performance by controlling the pore size and interlayer spacing of the membrane. GO membrane was coated by the bar-coating method and used hot-press method to control the d-spacing and nanopore size of the GO. The interlayer spacing of the GO membrane was decreased and nanopores were generated due to the decomposition of oxygen groups by the hot-press method. These hot-pressed GO membranes exhibit different ion permeance phenomena depending on the ion-concentrated solution. In solutions with low ion concentration, the rate of permeation was faster for divalent ions such as Co, Ni, and Mn compared to monovalent ions. However, the membrane shows Li-ion selective in the mixed solution or at high ion concentration. This phenomenon shows that electrostatic interaction by oxygen groups plays a crucial role at low ion concentrations, while size exclusion by interlayer spacing and adsorption of nanopores becomes critical at high concentrations. DFT calculations were employed to further investigate the ion permeation mechanisms. Based on the calculations, it was found that the binding energies between the divalent ions and the nanopores of graphene were high, resulting in a slow rate of ion permeation. Furthermore, the ion selectivity and interlayer stability of the GO membrane were enhanced by using a zwitterionic polymer. When incorporated into a forward osmosis system, the treated GO membrane was capable of continuously separating Li-ions from a simulated mixture solution of spent Li-battery electrodes.