K-gradient doping to stabilize the spinel structure of Li1.6Mn1.6O4for 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; Li(1.6)Mn(1.6)O(4)is one of them. However, Mn(3+)exists in the Li(1.6)Mn(1.6)O(4)precursor due to incomplete reaction during syntheses, and the disproportionation reaction of Mn(3+)inevitably results in Mn dissolution during lithium adsorption and desorption. The stable recycling and structural stability of Li(1.6)Mn(1.6)O(4)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 Mn(3+)and improvement in the structural stability of the adsorbent.