Enhanced Structural and Electrochemical Stability\nof Li and Mg Co-Doped LiMn<sub>2</sub>O<sub>4</sub> Cathodes for Li-Ion\nBatteries with a Mg Source from Bischofite

In\nthis work, Li<sub>1+<i>x</i></sub>Mg<sub><i>y</i></sub>Mn<sub>2–<i>x</i>–<i>y</i></sub>O<sub>4</sub> spinel octahedral nanoparticles doped with Li\nand Mg (<i>x</i> = 0.03, <i>y</i> = 0.00, 0.02,\n0.05, and 0.10) were synthesized by an ultrasound-assisted Pechini-type\nsol–gel process. High-purity Mg(OH)<sub>2</sub>, obtained from\nbischofite (MgCl<sub>2</sub>·6H<sub>2</sub>O), an industrial\nwaste produced during the industrial lithium extraction process, was\nused as a new source of magnesium for this purpose. Electrochemical\nmeasurements were carried out in coin semicells. As the Mg doping\nconcentration increases, the insertion/extraction mechanism of Li\nions changes from a two-phase reaction to a single-phase process in\na solid solution. The discharge capacities of the cathode materials\nincrease until reaching a maximum value of 120.2 mAh g<sup>–1</sup> for <i>y</i> = 0.05 and finally decrease for <i>y</i> = 0.10. The retention capacity exhibited the same behavior after\n100 cycles at a C/3 rate and 18 °C, with the optimum (<i>y</i> = 0.05, 94.0%). The retention capacity dropped by 14%\nat 50 °C. The optimum was successfully applied in pouch cells\nat 50 cycles with similar and stable electrochemical behavior. Therefore,\nboth Mg(OH)<sub>2</sub> and Li<sub>2</sub>CO<sub>3</sub> obtained\nfrom Salar de Atacama are sources of Mg and Li, potential candidates\nin the development of cathode materials with high-rate capability\nand long cycling stability for lithium-ion batteries.