Improvement of the electrochemical properties of a LiNi_0.5Co_0.2Mn_0.3O₂ cathode material by SiO₂/reduced graphene oxide double-layer coating.

In this study, two compounds of TiNb₂O₇ and Ti₂Nb₁₀O₂₉ were successfully synthesized by mechanochemical method and post-annealing as an anode material for lithium-ion batteries. The effect of annealing atmosphere on the morphology, particle size, and electrochemical characteristics of two compounds was investigated. For these purposes, the reactive materials were milled under an argon atmosphere with a certain mole ratio. Subsequently, each sample was subjected to annealing treatment in two different atmospheres, namely argon and oxygen. Phase and morphology identifications were carried out by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) to identify the phases and evaluate the morphology of the synthesized samples. The charging and discharging tests were conducted using a battery-analyzing device to evaluate the electrochemical properties of the fabricated anodes. Annealing in different atmospheres resulted in variable discharge capacities so that the two compounds of TiNb₂O₇ and Ti₂Nb₁₀O₂₉ annealed under the argon atmosphere showed a capacity of 60 and 66 mAh/g after 179 cycles, respectively, which had a lower capacity than their counterpart under the oxygen atmosphere. The final capacity of the annealed samples in the oxygen atmosphere is 72 and 74 mAh/g, respectively.

Lithium ion batteries as one of the most important energy storage equipments, have several challenges including capacity drop as number of cycles increases. Cathode particle coating is an effective approach in improvement of electrochemical performance of the batteries. In this study, TiO2-Ag coating was used to improve NCM cathode performance. The microstructure and crystal structure properties of coated NCMs were evaluated by the FE-SEM and XRD. Electrochemical behavior of the batteries was investigated by cycling performance analysis and EIS. TiO2 coating was deposited as a uniform layer and Ag coating was precipitated as dispersed nanoparticles. The results shows that using of TiO2-Ag coating can improve retention up to 75.9%. The FE-SEM and XRD studies of coated and uncoated NCMs after 100 cycles shows a higher crystalline and microstructural stability for coated NCMs. The TiO2 coated sample shows less increase in charge transfer resistance (62.4 %) than uncoated sample (232.9 %). The charge transfer resistance for TiO2 – Ag coated sample decreased significantly.

Separation of lithium and magnesium has always been a challenge due to their similar characteristics. In this regard, a two stage system was designed in which magnesium precipitated with ammonia and then magnesium from a diluted solution was extracted by D2EHPA in the presence of lactic acid. For this purpose, initial concentration of Magnesium, Ammonia volume, pH, Lactic Acid and D2EHPA concentration were the parameters which have been investigated. The result was a high and desirable separation of these two elements. Usage of ammonia will only lead to precipitation of magnesium and a minor co-precipitation of lithium will occur. Presence of lactic acid in the extraction of magnesium by D2EHPA increases the yield of extraction and the highest observed yield for a concentration of 0.41 mol/L of lactic acid and 0.32 mol/L of D2EHPA was 88.6%. It should be noted that the amount of co-extracted lithium has never been more than 3%. Finally, In order to determine the extraction conditions of lithium sole solution, the effects of contact time, pH, D2EHPA concentration and lithium initial concentration have been studied.