Study On Preparation And Performance Of LiNi_xCo_yAl_1-x-yO₂ Cathode Material

As with all of nickel-based cathode materials, Li(Ni-Co-Al)O2 has attracted considerable attention, because of its high voltage platform and high capacity.However, the thermal stability in charge-discharge test is as poor as homogeneity and repeatability in preparation process. In order to reduce the impact of secondary factors,such as calcination temperature and Li content, and improve the influence of main factor(Ni:Co:Al), the most reasonable and stable preparation method is found out. By the best preparation conditions,LiNixCoyAl1-x-yO2 cathode materials are prepared.Electrochemical performance and thermal stability of LiNixCoyAl1-x-yO2 materials are compared to find the best Ni:Co:Al. The results show that:(1). Three different methods of adding Li cause different performance.Solid-liquid hybrid method of preparation would lead to the most stable crystallization process and the lowest impact of secondary factors. In addition,LiNi0.8Co0.15Al0.05O2 cathodes, prepared by solid state method, show a better electrochemical performance with 185.7mAh/g of initial discharge capacity. But the influence of calcination temperature and Li source on crystallization process is strong.The maximum specific capacity difference is nearly 60mAh/g. LiNi0.8Co0.15Al0.05O2 cathodes,prepared by liquid phase method, have the best electrochemical performance,showing 189.4mAh/g of initial discharge capacity with 89.2% capacity retention. However, calcination temperature has a significant impact, indicating poor chemical stability of crystallization process. The most reasonable preparation conditions are affirmed as follows: CH3CH2OH as solvent, liquid phase addition of LiNO3 with molar ratio to M of 1:1, then the first step calcination, adding LiOH H2O with molar ratio of 0.1:1 by solid state method, the second step calcination.(2). LiNixCoyAl1-x-yO2 series materials were prepared by solid-liquid hybrid method. In all of these materials, LiNi0.8Co0.15Al0.05O2 and LiNi0.8Co0.1Al0.1O2 secondary particles have the best surface morphology. During 2.5 ?4.3V,charge-discharge performance of LiNi0.8Co0.15Al0.05O2 material is far beyond the others, showing 181.8mAh/g of initial discharge capacity with 95.72% capacity retention. furthermore, the results show that capacity retention would decrease with the increase of Co/Al co-doping, while R ct and D Li also become worse, which indicate the electrochemical compatibility of Co and A1 is poor. During 2.7?4.5V,properties of LiNi0.8Co0.1Al0.1O2 material are better than other materials, showing 182.2mAh/g of initial discharge capacity with 30.6mAh/g capacity fading after 50 cycles,which indicate LiNi0.8Co0.1Al0.1O2 has the best thermal stability with electrolyte. But the TG-DTA test indicates that, in the absence of electrolytes,thermal stability is increasing with Co/Al doping concentration. The results also turn out that LiNixCoyAl1-x-yO2 powders do not generate heat although they may have decomposed at elevated temperatures.