K-gradient doping to stabilize the spinel structure of Li1.6Mn1.6O4 for Li+ recovery.

Lithium-rich spinel lithium manganese oxide (LMO) compounds are one kind of promising adsorbents for lithium recovery from brine due to their high capacity and low Mn dissolution; Li1.6Mn1.6O4 is one of them. However, Mn3+ exists in the Li1.6Mn1.6O4 precursor due to incomplete reaction during syntheses, and the disproportionation reaction of Mn3+ inevitably results in Mn dissolution during lithium adsorption and desorption. The stable recycling and structural stability of Li1.6Mn1.6O4 were improved in aqueous lithium resources through K-gradient doping (LMO-K). The dissolution of Mn is reduced to 4.0% from 5.4% (before doping) and the adsorption capacity is kept at high capacity (31.6 mg g-1) at a low Li+ concentration of 12 mmol L-1. In addition, first-principles calculations further confirm that K substitutes for Li at 16d sites, leading to the stabilization of the Mn cations in the compound. With the help of K doping, the undesired dissolution of Mn in the cycle process is inhibited, which may be due to the reduction in the content of Mn3+ and improvement in the structural stability of the adsorbent.