Co-doping induced Mn-vacancy LiMn2O4 based membrane electrode for lithium extraction by electrochemically switched ion permselective process

Abstract

LiMn2O4 (LMO) is considered an effective electroactive material for electrochemical lithium extraction from aqueous solutions. However, the stability issue limits its practical application. Herein, Co-doping induced Mn-vacancy LiMn2O4 (LCMO) powders were synthesized by a high-temperature solid-phase method, which were further applied to prepare an electrochemical permselective membrane electrode for selective lithium-ion extraction. Physicochemical characterizations combining with density functional theory (DFT) calculations revealed that Co-doping at 8a site will induce the formation of Mn vacancies in LMO, which can reduce the content of easily dissolutive trivalent Mn (Mn3+) and lower the Li+ migration energy barrier. As a result, the Li+ permeation flux of optimized LCMO-0.04 (Co: Mn = 0.04: 1.96) based membrane electrode (156.809 mmol·m−2·h−1) was increased by 85.65 % compared to that of LMO-based one (84.461 mmol·m−2·h−1) in an electrochemically switched ion permselective (ESIP) system. The selectivity factors of Li+/ Na+, Li+/Mg2+, Li+/ K+ for the LCMO-0.04 based membrane electrode were up to 10.06, 11.69, and 15.19, which were about twice as high as those for LMO membrane based one. After 1000 circles of cyclic voltammetry (CV) tests, the CV area of the LCMO-0.04 based membrane electrode maintained 91.59 % of the initial value, demonstrating remarkable electrochemical stability.