Lithium Ion Battery Dual Anode Materials Lini < Sub > 0.8 < / Sub > Co < Sub > 0.2 < / Sub > O < Sub > 2 < / Sub > Preparation And Modification Of Research

LiNi0.8Co0.2O2was the solid solution of LiCoO2and LiNiO2and had a-NaFeO2layered structure. It was receiving more and more attention and considered a promising candidate for substitution of LiCoO2as the cathode material for lithium-ion batteries owing to its high specific capacity, high energy density, high open-circuit voltage, relatively inexpensive, and good cycle performance.In this thesis, the process conditions of precursor preparing stage and high temperature sintering stage were investigated respectively, in order to improve LiNi0.8Co0.2O2cathode material’s discharge capacity and the stability and security of cycling from the perspective of lower production costs and ease of industrialization. LiNi0.8Co0.2O2cathode material was modified by surface coating Al2O3to improve the cycle stability and security of material. XRD, SEM, TG, Land battery test systems and other characterization and testing means were used to investigate systematically structure, surface morphology and electrochemical performance of LiNi0.8Co0.2O2cathode material.(1) Ni0.8Co0.2(OH)2precursor was prepared by ammonia complexing liquid phase co-precipitation method. The mixed metal ion concentration, precipitant concentration, pH value, reaction temperature, reaction time were investigated to learn what influence they have to distribution and morphology of precursor particle and to determine the optimum conditions for preparation of precursor. Ni0.8Co0.2(OH)2precursor synthesized with optimum conditions had excellent structural, no impurity, uniform distribution, with a spherical morphology, the tap density of1.74g/cm-3.(2) The initially identified sintering program was adopting two sintering stages to prepare LiNi0.8Co0.2O2cathode material and the optimum conditions should be chosen in two temperature range to be investigated,600℃～700℃and720℃～760℃respectively, according to the results of TG analysis of a mixture of the precursor and the lithium source. (3) Combining the results of the analysis of the TG, temperature range of sintering temperature and time were investigated respectively, the influence of sintering environment and lithium ratio on LiNi0.8Co0.2O2structure and electrochemical properties of cathode materials was also investigated. LiNi0.8Co0.2O2, cathode material synthesized by the optimum conditions showed excellent electrochemical performance, the initial discharge capacity was127.80mAh·g-1at0.2C rate between2.7V and4.3V, and the discharge capacity was123.30mAh·g-1after20th cycling. In addition, the result which the structure and performance of LiNi0.8Co0.2O2cathode material emerged strong sensitivity to sintering temperature was varified. Temperature fluctuations made performance of LiNi0.8Co0.2O2cathode material to vary, which affected the consistency of cathode material structure and performance.(4) The influence of the coated amount of Al2O3on the structure and electro--chemical properties of LiNi0.8Co0.2O2cathode material was investigated. The results showed the right amount of Al2O3-coated did not change the layered structure of the material and the surface coating of Al2O3did not inhibit the structural phase transition during cycling. The1.0wt%Al2O3-coatig material showed excellent electrochemical performance, the initial discharge capacity was131.40mAh·g-1at0.2C rate between2.7V and4.3V and the discharge capacity was125.70mAh·g-1after20th cycling, mainly due to the Al2O3layer which reduced cathode material direct contact with the electrolyte and effectively avoided the occurrence of side reactions between the cathode materials and electrolyte.