Enhanced Structural and Electrochemical Stability of Li and Mg Co-Doped LiMn₂O₄ Cathodes for Li-Ion Batteries with a Mg Source from Bischofite

In this work, Li1+xMgyMn2–x–yO4 spinel octahedral nanoparticles doped with Li and Mg (x = 0.03, y = 0.00, 0.02, 0.05, and 0.10) were synthesized by an ultrasound-assisted Pechini-type sol–gel process. High-purity Mg(OH)2, obtained from bischofite (MgCl2·6H2O), an industrial waste produced during the industrial lithium extraction process, was used as a new source of magnesium for this purpose. Electrochemical measurements were carried out in coin semicells. As the Mg doping concentration increases, the insertion/extraction mechanism of Li ions changes from a two-phase reaction to a single-phase process in a solid solution. The discharge capacities of the cathode materials increase until reaching a maximum value of 120.2 mAh g–1 for y = 0.05 and finally decrease for y = 0.10. The retention capacity exhibited the same behavior after 100 cycles at a C/3 rate and 18 °C, with the optimum (y = 0.05, 94.0%). The retention capacity dropped by 14% at 50 °C. The optimum was successfully applied in pouch cells at 50 cycles with similar and stable electrochemical behavior. Therefore, both Mg(OH)2 and Li2CO3 obtained from Salar de Atacama are sources of Mg and Li, potential candidates in the development of cathode materials with high-rate capability and long cycling stability for lithium-ion batteries.