Lithium ion sieve modified three-dimensional graphene electrode for selective extraction of lithium by capacitive deionization

Faced with the strong demand of clean energy, development of lithium source is becoming exceedingly vital. Spinel-type manganese oxide (λ-MnO2) is a typical lithium ion sieve material. Herein, the conductive three-dimensional (3D) lithium ion sieve electrode material was fabricated by in-situ growth of λ-MnO2 on 3D reduced graphene oxide (3D-rGO) matrix for Li extraction by capacitive deionization (CDI). The λ-MnO2 modified rGO (λ-MnO2/rGO) retained the 3D network structure with uniform distribution of λ-MnO2 nanosheets on rGO. Electrochemical characterization demonstrated its high conductivity and fast lithium ion diffusion rate. By adjusting the rGO concentration, λ-MnO2 activity was improved significantly. With λ-MnO2/rGO as a positive electrode (activated carbon as negative electrode), the corresponding CDI system was successfully applied for the selective extraction of Li+. The final rGO content in the λ-MnO2/rGO was attained by thermogravity analysis. With the appropriate rGO content (15.5%), the obtained λ-MnO2/rGO electrode achieved the optimal Li+ adsorption amount. The corresponding λ-MnO2/rGO-based CDI cell showed good selectivity and high cycle stability. When applied to the extraction of lithium from synthetic salt lake brine, the electrode also obtained high Li+ adsorption amount with good selectivity.