Preparation,Modification And Performance Study Of LiNi_0.8Co_0.15Al_0.05O₂ Cathode Material

Among the nickel-rich LiNiO2-based cathode materials for lithium-ion batteries,LiNi0.8Co0.15Al0.05O2 not only owns an excellent discharge capacity,but also has the advantages of low cost and low toxicity.However,the rapid loss of capacity during cycling,poor high-temperature performance and so on have seriously hindered its application in large scale.In this dissertation,the preparation conditions of LiNi0.8Co0.15Al0.05O2 were determined and optimized in this paper,in order to improve its electrochemical properties.The LiNi0.8Co0.15Al0.05O2 cathode material was prepared by co-precipitation and high temperature calcination in this paper,and the effects of pH value,synthesis temperature and the amount of lithium on the crystal structure,the morphology and electrochemical properties of LiNi0.8Co0.15Al0.05O2 were investigated.According to the obtained TG/DSC curve,we determined the pretreatment temperature of the precursor and the range of calcination temperature.When the pH value was 11,the heat treatment temperature was 750℃ and the amount of lithium was 1.02,the sample delivered an initial discharge specific capacity of 169.6mAh/g at 0.2C in the voltage range of 2.7-4.3V.And 80.3%of the initial discharge capacity was maintained after 30 cycles.The precursor of nickel cobalt hydroxide was prepared by a coprecipitation method,then LiNi0.8Co0.15Al0.05O2 was obtained by mixing the precursor with aluminum source and lithium source after calcination at 750℃,and the effects of different aluminum source on the crystal structure,the morphology and electrochemical properties of LiNi0.8Co0.15Al0.05O2 were examined.The result showed that the elements of Ni,Co and A1 were distributed more evenly in samples when using alumina or aluminum isopropoxide as aluminum source.Meanwhile,the crystal structure and electrochemical properties of these samples were improved.The sample prepared with aluminum isopropoxide delivered an initial discharge capacity of 175.7mAh/g,which is 6.1mAh/g higher than the sample prepared with alumina.The capacity retention was increased to 85.2%after 30 cycles,and high-temperature performance and rate capability of the samples were considerably improved.The TiO2 coated LiNi0.8Co0.15Al0.05O2 cathode material was synthesized via a solvothermal method,and the effect of coated-Ti02 amount on the crystal structure,the morphology and electrochemical properties of LiNi0.8Co0.15Al0.05O2 were studied.The initial discharge capacity of TiO2-coated samples were decreased in different degrees,yet the cycling performance were improved.The thickness of coated layer was about 10nm when LiNi0.8Co0.15Al0.05O2 coated with 3wt%TiO2.And the capacity retention was 87.7%after 30 cycles,7.4%higher than uncoated sample.Moreover,the high-temperature performance and rate capability of the samples were considerably improved.