Preparation And Modification Of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂and LiNi_0.5Co_0.2Mn_0.3O₂Cathode Materials

:The Li-rich Mn-based Li1.2Mn0.54Co0.13Ni0.13O2cathode material has been considered as a promising cathode material for lithium ion battery because of the advantages of high capacity, low cost, low pollution and excellent safety performance. Layered LiNio.5Coo.2Mno.3O2cathode material has been used in large scale because it owns the advatages of LiNiO2, LiCoO2and LiMnO2-However, there are several shortcomings which restrict the further development of these materials. In this dissertation, in addition, to improve its electrochemical properties, Li1.2Mn0.54Co0.13Ni0.13O2and LiNi0.5Co0.2Mn0.3O2cathode materials were prepared and modified.Layered Li-rich Li1.2Mn0.54Co0.13Ni0.13O2cathode material was successfully synthesized via hydroxide co-precipitation, carbonate co-precipitation and spray drying methods. The results show that cathode material synthesized by hydroxide co-precipitation method displays excellent electrochemical performance. When cycled at2.3-4.7V with a current density of12.5mA·g-1at room temperature, Li1.2Mn0.54Co0.13Ni0.13O2delivered an initial discharge capacity of247mAh·g-1, and the capacity retention of98.7%can be maintained after50cycles at0.2C rate. The Mn0.54Ni0.13Co0.13(CO3)0.8precursor was prepared by carbonate co-precipitation. The optimized synthetic conditions were found as-follow:air atmosphere, pH value of8, the temperature is50℃,6h reaction time, C(M2+)=2mol/L, precipitator is Na2CO3and NH4HCO3mixed solution. The structure and electrochemical performance of Li1.2Mn0.54-x/3Ni0.13-x/3Co0.13-x-/3CrxO2materials have been investigated. The result shows that Cr-doping exhibited improved electrochemical performance.The Ni0.5Co0.2Mn0.3(OH)2precursor was prepared by hydroxide co-precipitation. The structure and electrochemical performance of LiNi0.5-x/3Co0.2-x/3Mn0.3-x/3TixO2(0≤x≤0.06) materials have been investigated. The results showed that LiNi0.5-x/3Co0.2-x/3Mn0.3-x/3TixO2(0≤x≤0.06) possessed a typical hexagonal structure. Although the Ti substituted materials showed somewhat lower initial discharge capacity, it exhibited improved cycling performance, high-temperature behavior and storage performance. EDS and XRD provided evidences that Ti substitution protected the electrode from HF attack and maintained the structure stability of electrode. As shown in EIS, Rct values of Ti substituted samples were reduced compared with pristine electrode. It suggested that Ti substitution can improve the kinetic behaviors during charge/discharge process, affecting the electrochemical performance.