Understanding the Behaviors of λ-MnO₂ in Electrochemical Lithium Recovery: Key Limiting Factors and a Route to the Enhanced Performance

Abstract

Recently developed electrochemical lithium recovery systems, whose operation principle mimics that of lithium-ion battery, enable selective recovery of lithium from source waters with a wide range of lithium ions (Li⁺) concentrations; however, physicochemical behaviors of the key component-Li⁺-selective electrode-in realistic operation conditions have been poorly understood. Herein, we report an investigation on a λ-MnO₂ electrode during the electrochemical lithium recovery process with regards to the Li⁺ concentration in source water and operation rate of the system. Three distinctive stages of λ-MnO₂ originating from different limiting factors for lithium recovery are defined with regard to the rate of Li⁺ supply from the electrolyte: depleted, transition, and saturated regions. By characterization of λ-MnO₂ at different stages using diverse X-ray techniques, the importance of Li⁺ concentration in the vicinity of the electrode surface is revealed. On the basis of this understanding, increasing the density of the electrode/electrolyte interface is suggested as a realistic and general route to enhance the overall lithium recovery performance and is experimentally corroborated at a wide range of operation environments.