The synthesis conditions for good spinel compounds are quite stringent. First, it must be an oxygen stoichiometric compound; second, it needs to be doped with different kinds of ions, including lithium ions, so that the charge-discharge process in the entire 4V region is a single-phase reaction. The ideal spinel chemical composition is Li1+χMyMn2-x-yO4. In order to obtain a discharge capacity of about 100mA·h/g, 0<x<0.06 and 0.03V<0.15 must be maintained, where M is excluding lithium ions One or more metal ions; if the counter electrode is lithium metal, the cycle performance of the spinel compound is very good even in the electrolyte environment of 60 °C. However, it is well known that the deposition of manganese ions in Li-ion batteries hinders the intercalation and extraction of Li ions in the carbon anode, and the dissolved manganese ions will lead to the deterioration of the cycling performance of the carbon anode, which in turn affects the cycling performance of Li-ion batteries. Again, since the deterioration of the negative electrode is obvious in the high temperature electrolyte environment, the dissolved amount of manganese must be reduced.
Researchers have developed a new method for the synthesis of spinel-type cathode materials (two-step heating method: 900~1000°C in the initial stage, and 600~800°C in the second step), and have successfully prepared the Spinel material for three conditions.
Spinel crystals with a low specific surface area are formed during the first heating process, which is very effective in reducing the amount of manganese dissolved in the electrolyte. It can be proved by chemical analysis that during the second heating step, the oxygen-depleted spinel can absorb oxygen to form an oxygen-stoichiometric spinel. However, it is very important to prepare the spinel in the first-step synthesis to minimize the amount of oxygen depletion in this process, so that it can be easily converted into an oxygen-stoichiometric spinel in the second-step synthesis. Based on the above, manganese, aluminum, nickel, cobalt ions are suitable metal ions for doping.
Figure 1 shows the cycling performance of Mg-doped spinel materials at 60 °C. It is evident that the oxygen stoichiometric spinel exhibits excellent cycling performance.
The spinel compound prepared by this method at about 1000°C has a manganese ion concentration of only about 3 μg/mL even if it is continuously immersed in the electrolyte for 4 weeks at 60°C, which is obviously higher than that at 800°C. The 100 μg/mL concentration of the prepared LiMn2O4 is much lower. The dissolving amount of manganese in spinel can be reduced to 1/30 by the first heating process, therefore, the high temperature characteristics of Li-ion batteries using this spinel cathode material and graphite anode are significantly improved, as shown in Figure 2. Show.