Synthesis And Characteristics Of LiNi_0.5Co_0.25Mn_0.25O₂ Cathode Material For Lithium Ion Batteries

LiCoXMnYNi1-X-YO2 are promising candidates of cathode materials for lithium ion batteries. A study on the synthesis, structure and performance of LiNi0.5Co0.25Mn0.25O2 as cathode materials for lithium ion batteries was carried out systemically and in detail through test measures such as TG-DTA, XRD, XPS, SEM, CV, EIS and so on in this dissertation.As the first step of this study, a sol-gel method using citric acid as a chelating agent was developed to synthesize LiNi0.5Co0.25Mn0.25O2. The reaction conditions in sol-gel process, pre-calcination process and calcination process, especially sintering temperature and sintering time in calcinations process, were analyzed and optimized carefully. XRD,XPS,SEM test results indicated: LiNi0.5Co0.25Mn0.25O2 had a typical structure of layered LiNiO2, while its ions arranged better in order and its layered structure was more obvious than LiNiO2; Co and Mn existed in form of +3 and +4 price,respectively,while Ni existed in form of +3 and +4 price and the ratio of content of Ni2+ and Ni3+ was 1:1 in cathode material LiNi0.5Co0.25Mn0.25O2; The material LiNi0.5Co0.25Mn0.25O2 had a well-distributed morphology, and the averge particle was estimated to be almost 0.5μm in diametre.CV test results indicated: there were two couples of peaks at 4.06V/3.63V and 4.29V/4.26V, respectively, in the voltage range of 2.95~4.75V of LiNi0.5Co0.25Mn0.25O2, and the higher peak value of Co4+/Co3+ would enhance the safety and the cycle stability of cathode material LiNi0.5Co0.25Mn0.25O2; Mn as stable body in cathode material LiNi0.5Co0.25Mn0.25O2 was not active; Charge-Discharge test results indicated: The charge-discharge flat of cathode material LiNi0.5Co0.25Mn0.25O2 was not obvious; Operated in the voltage range of 2.95~4.75V and 2.95~4.35V, its initical discharge capability was 202.78mAh·g-1 and 179.23mAh·g-1 , respectively, capacity retention of it was 80.7% and 80.5% after 50 cycles, the charge voltage of LiNi0.5Co0.25Mn0.25O2 was increased from 4.35V to 4.75V, while its capacity retention was not changed and the discharge capability had been increased about 15%. EIS test results indicated: Charged voltage had little effect on the process of Lithium ion moving from electrolyte to...