Understanding the Behaviors of λ-MnO 2 in Electrochemical Lithium Recovery: Key Limiting Factors and a Route to the Enhanced Performance

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-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 defined 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…