Preparation Of Lithium-rich Ternary Cathode Materials And Investigation

Lithium-ion battery has numerous advantages,such as high density,long cycle life,low cost,environment friendly and so on.Therefore,it has become the main stream energy storage equipment of all kinds of electronic products in the present society.Meanwhile,it has a broad application prospect in the fields of daily life,such as medical military work,aeronautics and astronautics etc.The performance of a lithium-ion battery mainly depends on anode and cathode materials.Cathode material has been proven to be the key to improve the performance of lithium-ion batteries,because the capacity of anode material outclasses cathode material.At present,the energy density of the commercialized cathode materials,such as lithium-iron phosphate,lithium manganate and other materials,is unsatisfactory.Due to the high energy density,lithium-rich ternary layered material has been regarded as one of the best cathode material choice for the next generation of lithium-ion batteries.However,its commercial application has been limited by poor cycle performance,low coulomb efficiency and waste water pollution etc.Consequently,improving the performance and studying a green synthesis technique of lithium-rich ternary layered cathode material have become a hot research topic in the field of lithium ion battery materials.In order to eliminate the environmental pollution during synthesis process,a green synthetic technique by spray drying method for lithium-rich ternary layered cathode materials has been explored in this work.Ammonium bicarbonate,transition metal acetate and lithium hydroxide are used as raw materials,which are all low-cost and environmentally friendly.At the same time,ethanol is used to guarantee the uniformity of the slurry.Lithium-rich ternary layered cathode materials,Li_1.5Ni_0.15Co_0.15Mn_0.7O_2.5,with excellent electrochemical performance have been obtained finially by optimizing the synthesis process and conditions.Moreover,the discharge capacity of the material has been further improved by adding hydroxyethyl cellulose?HEC?.The obtained Li_1.5Ni_0.15Co_0.15Mn_0.7O_2.5has the best discharge capacity of 261mAh·g^-11 at 0.1C.The material also has exellent cycling stability.The capacity of the sample still keeps 229mAh·g^-11 after 75 cycles at 0.1C,which is almost 90%of the capacity retention.On this basis,the effects and usage of different surfactants are studied.When 0.6 wt.%HEC is added in the slurry of raw materials,the structure of material has been a further perfection and the discharge capacity is improved significantly.The sample has a discharge capacity of more than 300 mAh·g^-11 at 0.1C,and 270mAh·g^-11 at 0.5C.The calcination time and temperature are also optimized based on the above conditions.The results show that,the sample has the best electrochemical performance with 265 m Ah·g^-1,when the precursor is calcinated at 450?for 5 hours,and then calcinated again at 890?for 12 hours.In this work XRD,SEM etc are used to characterize the structure of the materials.The relationship between material structure and properties,and the influence of different synthetic processes and conditions on the material structure have been revealed.