Surface trace doping of Na enhancing structure stability and adsorption properties of Li_1.6Mn_1.6O₄ for Li⁺ recovery

Li_1.6Mn_1.6O₄ (LMO) is a dominant adsorbent for lithium recovery from solutions resulted from its high theoretical adsorption uptake and a low loss rate of Mn, which can potentially be further improved by trace doping. We achieve stable cycling and high adsorption capacity of Li_1.6Mn_1.6O₄ from aqueous lithium resources through surface trace doping of Na (LMO-Na). The dissolution of Mn is reduced from 5.4% (before doping) to 4.4%, and the adsorption uptake is increased from 33.5 mg/g to 33.9 mg/g at Li⁺ concentration of 24 mmol/L. In addition, first-principles calculations further confirm that Na substitutes for Li at 16d sites, leading to an improvement of the Li⁺ uptake rate and stabilizing the Mn cations in the compound. With the help of Na doping, the undesired dissolution of Mn in the cycling process is inhibited, which may result from reducing the content of the low valent Mn³⁺ and improving the structural stability of the adsorbent. The effect of the Na substitution on adsorption capacity and structure stability is discussed.