Improved performance of Al-doped LiMn₂O₄ ion-sieves for Li⁺ adsorption

Al-doped LiAl_xMn_2-xO₄ ion-sieves were optimally synthesized with improved structural stability for Li⁺ adsorption through hydrothermal synthesis method. Firstly, several parameters including the Al³⁺ doping content x, hydrothermal temperature, hydrothermal treatment time and calcination temperature were investigated to optimize the synthesis of LiAl_xMn_2-xO₄ ion-sieves for selecting unique spinel structure with low dissolution loss (R) for Li⁺ adsorption. Then, the pristine LiMn₂O₄ (LMO) and optimized LiAl_0.1Mn_1.9O₄ (LAMO) ion-sieves were comparatively investigated from their microstructure and chemical state to Li⁺ adsorption performance. The desorption ratio of Li⁺, adsorption capacity (Q) and the dissolution losses (R_Mn²⁺ and R_Al³⁺) of the ion-sieves were evaluated by adsorption-desorption experiments. It was found that the maximum equilibrium adsorption capacity Q_LAMO was 27.66 mg g⁻¹ and the desorption ratio of Li⁺ could reach 81.2% after 120 min. Meanwhile, R_Mn²⁺ and R_Al³⁺ of LAMO ion-sieve were very low in the desorption process. Moreover, LAMO ion-sieve also shows excellent stability and repeatability that the LAMO could still maintain a high adsorption capacity (19.5 mg g⁻¹) with very low R_Mn²⁺ (3.71%) and negligible R_Al³⁺ after repeating 5 times adsoprtion-desorption operation.