Tailorable metal–organic framework based thin film nanocomposite membrane for lithium recovery from wasted batteries

This paper presents a tailorable method for the preparation of hierarchically structured membranes for efficient lithium recovery. Firstly, a metal–organic framework (MOF), namely MIL-101 (Cr), is grafted with different ionic liquids (ILs) onto its coordinate unsaturated site (CUS). The modified MOF (IL-MOF) is then used as nanoparticles to fabricate the flexible hydrophilic polyvinylidene fluoride (PVDF) based thin film nanocomposite (TFN) membrane. Secondly, comprehensive characterizations of both the nanoparticle and the IL-MOF based TFN membrane are carried out. Thirdly, lithium recovery is performed experimentally using simulated lithium-ion batteries (LIBs) leaching solution with the as-synthesized membrane. The first order ageing test of TFN membrane is conducted by MOF detachment tendency investigation and ILs leaching tendency evaluation. The results show that IL-MOF nanoparticles have a significant effect on lithium recovery. Compared with the original membrane, the IL-MOF-TFN membrane exhibits a fourfold lithium selectivity enhancement for $S_{{\mathrm{Li}}^{+},{\mathrm{Mn}}^{2+}}$ (from 1.73 to 8.91), $S_{{\mathrm{Li}}^{+},{\mathrm{Co}}^{2+}}$ (from 1.75 to 9.94) and $S_{{\mathrm{Li}}^{+},{\mathrm{Ni}}^{2+}}$ (from 1.69 to 10.09), as well as improved regeneration behavior, permeability (up to 45.0 L/(m²·h·bar)) and antifouling performance (flux recovery rate FRR up to 96.39 %). It is found that 98.9 % of the lithium was recovered from the feed solution over five repeated filtration cycles with maintained membrane integrity. This work highlights the advances in the design, modification and integration of MOFs into mechanically and chemically stable membrane technology for lithium recovery.