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

Abstract

In this work, Li_1+xMg_yMn_2–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.