Producing battery‐grade lithium hydroxide: A bipolar membrane with lower water dissociation barriers

Abstract Bipolar membrane electrodialysis (BMED) promises to convert Li 2 SO 4 into LiOH, but suffers from inefficient interfacial water dissociation and insufficient alkaline stability. Herein, an interface‐engineered bipolar membrane (BPM) was developed using an alkaline lignin‐modified Ti 3 C 2 T x (AL‐Ti 3 C 2 T x ) interlayer. Grafting alkaline lignin onto Ti 3 C 2 T x introduced hydroxyl‐rich sites and improved hydrophilicity, thereby facilitating water dissociation. The optimized BPM (sulfonated polysulfone cation exchange layer/AL‐Ti 3 C 2 T x interlayer/N‐methylpiperidine‐quaternized poly(2,6‐dimethyl‐1,4‐phenylene oxide) anion exchange layer) achieved a transmembrane voltage of 0.97 V at 115 mA·cm −2 and a current efficiency of 99.52%, outperforming commercial BP‐1 and SSBP‐1 membranes. DFT indicated that AL‐Ti 3 C 2 T x reduces the water dissociation energy barrier to 0.26 versus 0.47 eV for pristine Ti 3 C 2 T x . In BMED, the membrane enabled efficient conversion of Li 2 SO 4 into high‐purity LiOH (>99.7%) with a total energy cost of 2.95 $·kg −1 . This work demonstrates a biomass‐enabled MXene interfacial design for high‐performance BPMs and sustainable lithium chemical production.