High performance, pH-resistant membranes for efficient lithium recovery from spent batteries

Cation separation under extreme pH is crucial for lithium recovery from spent batteries, but conventional polyamide membranes suffer from pH-induced hydrolysis. Preparation of high performance nanofiltration membranes with excellent pH-resistance remains a challenge. Here we synthesize a high performance nanofiltration membrane (1,4,7,10-Tetraazacyclododecane (TAD)−1,3,5-Tris(bromomethyl)benzene (TBMB) thin film composite membranes (TFCMs)) with excellent pH-stability through interfacial quaternization reaction between TAD and TBMB. Due to the high stability of "C-N" bonds in TAD-TBMB TFCMs, its separation performance is stable even after 70 days immersion in concentrated acid (3 M H2SO4, HNO3, or HCl) and base (3 M NaOH), which is at least 15 times more stable than benchmark commercial membranes. The membrane shows an overall separation performance (11.3 L m−2 h−1 bar−1 (LMHB), RCo2+: 97% in 2 M H2SO4) due to the size sieving and the intensified charge repulsion, outperforming many of the state-of-the-art membranes. Finally, the TAD-TBMB TFCM remains stable during 30-days continuous nanofiltration of 2 M H2SO4 and leachate (2 M H2SO4, ions: 6.2 g L−1) from spent batteries. A highly pH-resistant membrane was prepared by interfacial quaternization reaction, which shows the highest separation performance among analogous membranes and 70-days stability in concentrated acid/base. Meanwhile, Li2CO3 with purity of 99.1% was recovered from acid leachate of spent batteries.