Analyze the process of synthesizing lithium battery cathode material by solid phase method
What is a solid phase method for synthesizing lithium battery cathode materials, such as lithium manganese oxide, that is, lithium salts (such as LiCO3, LiNO3, LiOH·H2O, etc.) and manganese salts [such as MnCO3, Mn(NO3)2, etc.] or manganese oxides. (such as electrolytic MnO2, Mn2O3, Mn3O4, etc.) After grinding and mixing in a certain way, it is fired at a high temperature for a long time, and a solid phase reaction occurs directly. It is characterized in that the solid raw material mixture is directly reacted in a solid form. In order to ensure a sufficient reaction rate, the solid material must be heated to above 750 degrees. For the solid phase synthesis reaction of lithium manganese oxide, at least three phases of lithium salt, manganese dioxide and lithium manganese oxide are present. During the solid phase reaction between the solid phase mixtures, atoms or ions need to pass through the interface of the various phases and pass through the phase regions of each phase, which forms atoms or ions in multiple solid phases. Interacting diffusion, therefore, kinetic factors play a decisive role in the reaction rate.
Since a large amount of microstructure rearrangement is involved in the formation of the product LiMn2O4 in the reaction, which involves the breaking and recombination of chemical bonds, the atoms or ions undergo a considerable distance (on the atomic scale). Therefore, a sufficiently high temperature is required to diffuse these atoms or ions to a new reaction interface, and at the same time, a high temperature solid phase reaction is required by electric heating or microwave heating.
The high-temperature solid phase method was used to synthesize the spinel-type cathode material LiMn20 with LieCO3 as the lithium source, chemical MnO2 (CMD) and electrochemical Mn02 (EMD) as the manganese source, and ethanol water mixture as the dispersion medium. The specific method is as follows: weigh a certain proportion of LieCO3 and MnO2, mechanically mix and grind, then add a certain proportion of ethanol/water mixed solution, soak for 24h under stirring to obtain a colloidal mixture, and evaporate to dryness at 100 degrees. It was dried under vacuum for 2 h, ground to a fine powder, then pre-baked at 550 ° C for several hours in air, calcined at about 650 ° C for several hours, and finally calcined at 750 ° for more than ten hours, and naturally cooled to obtain a sample.
The materials were characterized by XRD, BET, TEM and electrochemical tests. The results show that the samples prepared at 750 °C have a good spinel structure with specific surface areas of about 420 m/g and 220 m/g, respectively, and the product has a uniform particle size distribution with an average particle size of 200 nm. Constant current charge and discharge under conditions of 4×10 A/cm2 and 3.0~4.35V, the first discharge capacity is greater than 110 mA·h/g, the efficiency is greater than 90%, and the cycle reversibility is good.
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