Structure-guided interfacial polymerization of AlLi-LDH/polypyrrole electrodes for selective lithium recovery from Mg2+/Li+ mixed brines

Selective lithium recovery from Mg 2+ /Li + mixed brines remains a major challenge because of the similar physicochemical characteristics of competing cations. Although AlLi-layered double hydroxide (AlLi-LDH) is a promising Li + -selective host owing to its structure-dependent affinity for Li + , its poor intrinsic conductivity and possible structural stress during repeated Li + adsorption/desorption limit its practical application in capacitive deionization. Herein, we develop an in-situ structure-guiding strategy to fabricate a polypyrrole-modified AlLi-LDH nanoflower composite AlLi-LDH/PPy for selective Li + recovery in a hybrid capacitive deionization system. In this architecture, the layered AlLi-LDH framework serves as both a Li + -recognition host and a structure-directing scaffold for the interfacial growth of PPy, thereby suppressing disordered polymer aggregation, constructing continuous electron-transport pathways, and enhancing interfacial structural stability. The optimized AlLi-LDH/PPy electrode exhibits improved charge-transfer kinetics, enlarged electrochemically accessible surface area, and favorable Li + storage behavior arising from the synergistic coupling of Li + intercalation in AlLi-LDH and pseudocapacitive contribution from PPy. Under an applied voltage of 1.2 V, the electrode delivers a Li + adsorption capacity of 33.43 mg g −1 . In mixed Mg 2+ /Li + solutions, it retains a discernible preference for Li + , with the separation factor increasing from 6.02 to 7.41 as the Mg 2+ /Li + ratio rises from 1:1 to 5:1, and remaining above 1 even at 10:1. After 30 HCDI cycles, the electrode retained 61.08% of its Li + adsorption capacity, and retained 87.21% of its initial capacity after 100 GCD cycles. This work demonstrates the effectiveness of in-situ oxidative polymerization for regulating conductive-polymer/LDH interfaces and provides a feasible strategy for electrochemical lithium recovery from complex brines.