Understanding ion intercalation of LiMn2O4 in brine for electrochemical detection of Li+

Abstract

Lithium-ion detection is necessary for extraction of lithium. Electrochemical sensors based on spinel LiMn₂O₄/λ-MnO₂ are expected to enable low-cost detection of lithium ions. Many studies demonstrate preferential intercalation of lithium ions, but little research has been done on how the differences in intercalation between lithium and other ions arise. Here, the differences in intercalation were identified by electrochemical impedance spectroscopy. Lithium ions were preferentially intercalated into λ-MnO₂ because of low charge transfer impedance. The apparent diffusion coefficient of sodium or potassium ions was one order of magnitude lower than that of lithium ions, while that of magnesium or calcium ions was two orders of magnitude lower. Therefore, insignificant intercalation of sodium, magnesium, potassium, and calcium ions slowed down diffusion of lithium ions through the channel and obstructed lithium-ion intercalation. The concentration of lithium ions was detected in brine of Baqiancuo Salt Lake by stripping voltammetry using λ-MnO₂ and an average recovery of 95.0 % was achieved. This study gives insights into ion intercalation of LiMn₂O₄ in brine, which favors improvement of lithium-ion sensor based on LiMn₂O₄. In addition, the investigation facilitates understanding of the selectivity of similar materials (e.g., LiFePO₄ and Prussian blue analogous) in intercalation process.