Study On The Synthesis Of Multi-composite Cathode Material Li(Ni_0.8Co_0.1Mn_0.1)O₂for Lithium Secondary Batteries

As a new kind of cathode material for lithium ion secondary batteries,compared to commercial LiCoO2, nickel, cobalt, manganese multiple oxide Li(Ni0.8Co0.1Mn0.1)O2has some advantages for its high capacity, good cycling performance, low lost, environmental friendly and safety. But it is found that composite distribution is not homogeneous, and the surface morphology of material particles is not uniform during the synthesis of multi-composite oxide material. Improvement of synthetic method must be taken to obtain homogeneous cathode material. Liquid phase method including controlled crystallization co-precipitation and spray pyrolysis is being widely used as appropriate preparation method.Sphere precursor (Ni0.8Co0.1Mn0.1)(OH)2was prepared by controlled crystallization co-precipitation, using NaOH as precipitating agent, NH3·H2O as complexing agent. After follow-up heat treatment of prepared precursor, we obtained high purified sphere Li(Ni0.8Co0.1Mn0.1)O2. The pH of reaction solution, feed rate of mixed salt solution, reaction time, reaction temperature have a great influence on the precursor particle size and surface morphology by controlling the experimental condition of the co-precipitation process. Precursor particles show best surface morphology and size distribution while reaction temperature is50℃,reaction time is20h, the pH of reaction solution is11.0, feed rate of mixed salt solution is12.5mL/h, Optimized synthetic condition was used to prepare (Ni0.8Co0.1Mn0.1)(OH)2precursor. The heat treating condition was optimized, and the cathode materials with good structure and best electrochemical performance were obtained by calcining the precursor and LiNO3at800℃for12.5h. The materials have capacities of about180mAh/g at0.1C.Another work in this thesis was synthesizing Li(Ni0.8Co0.1Mn0.1)O2by spray pyrolysis method. Sulfate and nitrate of nickel, cobalt, and manganese was used as raw materials to prepare sphere precursor. The speed of carrier gas, different kind of mixed salt solution, initial concentration of mixed solution, reaction temperature influence the morphology of precursor particles in different degrees by controlling the experimental condition of the spray pyolysis process.During the spray pyolysis process, more hollow particles appear in the precursor powders while raw material is nitrate, reaction temperature is350℃, initial concentration of mixed solution is0.5mol/L, speed of carrier gas is faster. Appropriate condition is chosen to prepare sphere precursor according to actual requirement. We obtained sphere Li(Ni0.8Co0.1Mn0.1)O2after follow-up calcining the mixture of prepared precursor and LiNO3at800℃for12.5h. The cathode materials show capacities of about120mAh/g at0.1C.