Because the cathode material of a high nickel system is very sensitive to the preparation environment, battery environment, storage environment (temperature, humidity, oxygen value). Therefore, to find a suitable preparation system that has a certain reference value for the industrialization of the whole high nickel system cathode material. The preparation method has a great influence on the microstructure and electrochemical properties of the high nickel layered materials. Common preparation methods are high-temperature solid-phase method, co-precipitation method, sol-gel method, spray drying method, and combustion method.
1. Preparation of NCA
CaO through the conventional co-precipitation method (0≤x≤0.2) cathode material LiNi0.8Co0.2-xAlx02. First, the nitrate of nickel, cobalt, and aluminum was prepared into a mixture solution of 2mol/L and dropped to 4mol/L ammonia to adjust the pH to 8.5. Then, the sodium hydroxide solution was dropped to adjust the pH to 11. Then, the washing precipitate of PVP dispersant was added, filtered, and dried to obtain the nickel-cobalt-A1 hydroxide precursor. By the molar ratio of Li/Me = 1.05, mixed LiOH and precursor, in the 600 ℃ 6 hours after calcining, placed in the oxygen flow calcined at 750 ℃ for 8 ~ 24 hours, for calcining LiNi0.8 Co0.2 - xAlx02 0.750 ℃ 16 sample preparation NCA ħ displays 160.8 ma/highest initial discharge capacity of g and 89% of the initial coulombic efficiency and 40 times cycle after the discharge capacity is 150 mah/g.
Han prepared a sol by means of sol to gel method at 140℃. The liNi0.8Co0.2-xAlx02 powder can be obtained by calcination at 800℃. The results showed that no matter how much Al (x≤0.05) was contained, the powder was a single-phase layered structure compound. In addition, it is found that with the increase of Al, the capacity of the initial discharge environment of the material decreases, but the technical performance of charge and discharge becomes better. Ju et al. [8] used Ni, Co, Al nitrate as raw materials, citric acid, and ethylene glycol as chelating agents to prepare Ni-Co-A1-O precursors by traditional spray pyrolysis. After calcination at 800℃ for 0.5 ~ 12 h with LiOH, the obtained NCA materials developed spherical surface morphology with an average level size of 1.1μm. The discharge capacity has been up to 200 mAh/g and has its own good circulation system performance, high-temperature performance, and rate improvement performance.
Hu [9]NCA cathode material prepared by co-precipitation method has a charge and discharge current density of 0.2C... The material has a discharge specific capacity of 196mAh/g, which remains 96.1% after 50 cycles. Chung et al. [10] coated amorphous carbon with a thickness of 2~3nm on the surface of NCA by chemisorption. The carbon coating effectively inhibits the reaction between the matrix material and the HF in the electrolyte, improves the thermal stability of the matrix material, and improves its electrochemical performance under high current. In fact, electrochemical inert materials are used to modify LiNi02 based cathode materials for lithium-ion batteries. Although the performance and safety of the cycle are improved, the discharge specific capacity and energy density are reduced. Kim et al. [11] prepared A1F3 surface phase modified NCA cathode materials by precipitation method. After 50 cycles, the capacity retention rate of the matrix material is only 86.5%, while that of the modified material is 96%, which improves the rate performance and thermal stability of the modified material.
Xi prepared NCM811 positive electrode structure material by adding acetic acid with a transition metal and different lithium sources under different economic conditions. The results show that the technical performance of NCM811 samples has a significant difference. The specific capacity of the samples with LiOH•H2O or LiO3 as lithium sources can not be lower than that of Li2CO3. Li2CO3, transition, and metal acetate were pretreated at 550℃ and sintered at 800℃. The electrochemical system performance of the sample was the best. The highest market capacity and average data capacity of the first 20 cycles were 200.8 mA•h/g and 188.1 mA•h/g at 0.2C ratio.
Lu prepared NCM811 cathode materials by sol-gel method and co-precipitation method respectively and studied the effects of these two methods on the properties of the materials. The results show that, compared with the co-precipitation method, the particle size of NCM811 cathode material prepared by sol-gel method is hexahedral structure, particle size concentration is about 500nm, the layered structure is obvious, cation mixing degree and particle agglomeration degree is low, but the vibration density is high, the first discharge specific capacity is 200.2mA·h/g, at 0.5°C after 50 cycles, the capacity retention rate is 82.2%.
The bear. The prepared LiF NCM811 in-situ coating material, 2 is the result of EDX analysis of NCM811 material coating. As shown in Fig. 2, NCM811's uniformly distributed LiF surface layer of LiF effectively hindered the added HF with the electrode when the capacity-retention ratio was high for the performance of the uncoated 10.4% material after 200 cycles and the side reaction of 60 degrees. Compared with the same material without coating] C temperature cycle performance.
The performance of high nickel cathode materials depends largely on the size and morphology of the particles, so the preparation technology and methods are mostly focused on the uniform distribution and dispersion of raw materials from different enterprises to obtain spherical particles with small size and large specific surface area. The combination of the co-precipitation method and the high-temperature solid-phase method is the mainstream ideological method at present. In the early stage, the raw materials are mixed evenly, the prepared materials have a uniform particle size, regular surface morphology, and the learning process is easier to manage and control. It is the main analysis method of industrial social production in China at present. Compared with the coprecipitation method, the spray drying process is simpler and the preparation speed is faster. The morphology of the material obtained by the spray drying method is as good as that obtained by the coprecipitation method, which has the potential for further research.
