Understanding the Behaviors of λ-MnO_2 in Electrochemical Lithium Recovery: Key Limiting Factors and a Route to the Enhanced Performance

摘要

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 /l-MnO_2 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-MnO_2 originating from different limiting factors for lithium recovery are denned with regard to the rate of Li~+ supply from the electrolyte: depleted, transition, and saturated regions. By characterization of λ-MnO_2 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.