A Self-Supported λ-MnO₂ Film Electrode used for Electrochemical Lithium Recovery from Brines

Lithium recovery from an aqueous resource was accelerated by electrochemically driving the transformation of Mn^IV /Mn^III with a spinel λ-MnO₂ film electrode. A λ-MnO₂ electrode without binders or conductive additives is preferred for achieving a large capacity at high current density and long-term cycling capability. In this study, a film of Mn(OH)₂ was first deposited on the surface of Pt or graphite substrates owing to alkalization near the cathode, then it was oxidized to a Mn₃ O₄ film by air, followed by being hydrothermally lithiated to LiMn₂ O₄ spinel and, finally, it was turned into the λ-MnO₂ film electrode through potentiostatic delithiation. The results show that the charging/discharging electric capacity of the fabricated λ-MnO₂ film electrode was up to ≈100 mAh g^-1 at a current density of 50 mA g^-1 in 30 mm Li⁺ aqueous solution, twice that of the λ-MnO₂ powder electrode. Also, 82.3 % lithium capacity remained after 100 cycles of an electrochemically assisted lithium recovery process, indicating high availability and good stability of the λ-MnO₂ spinel on the electrode. The energy consumption for each cycle is estimated to be approximately 1.55±0.09 J, implying that only 4.14 Wh is required for recovery of one mole of lithium ions by this method.