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), R_Co2+: 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.