Hydrophilic Modification Using Polydopamine on Core–Shell Li1.6Mn1.6O4@Carbon Electrodes for Lithium Extraction from Lake Brine

Lithium extraction from salt-lake brine is important to ensure a sustainable supply of lithium and meet its increasing demand for use in electric vehicles and large-scale energy storage devices. However, it remains challenging to separate Li+ ions from coexisting ions in the brine. Here, we propose a combined strategy of a core–shell structure and hydrophilic modification of a Li1.6Mn1.6O4 electrode to efficiently extract lithium from brine with a high sodium ion content. Core–shell Li1.6Mn1.6O4@carbon was derived from polydopamine-encapsulated Li1.6Mn1.6O4 via calcination. The ∼2 nm carbon shell protects Mn from leaching during lithium extraction. Compared with bare Li1.6Mn1.6O4, the lithium extraction capacity of the modified electrode increases from 20 to 39.6 mg/g in a brine with a high Na–Li ratio (Na/Li = 44.78 by weight). The coating of polydopamine on the Li1.6Mn1.6O4@carbon electrode reduces the water contact angle from 119 to 86.9°, resulting in a hydrophilic surface. Using an electrochemical adsorption method, the lithium extraction capacity and desorption ratio reach 65.6 mg/g and 86.0%, respectively, which are superior to the performance of the current membrane capacitive deionization and electrochemical method. The modified electrode shows high lithium-ion selectivity and excellent stability due to the reversible redox reactions during lithium extraction/release. The strategy proposed here provides insights into the structural design of electrodes for the highly efficient separation of lithium from brine.