Research On Preparation, Analysis And Performance Of Lithium Manganate As Cathode Materials For Lithium Ion Battery

The characterization and synthesis of spinel Li1+xMn2O4 was studied in the experiment. Li1+xMn2O4 was prepared by solid-state method, sol-gel method and melt-impregnation method, with different sources of lithium (Li2CO3, LiNO3, LiOH·H2O) and manganese (CMD, MnAc2·H2O) at different temperatures and different ratios of Li/Mn, so the conditions of experiment was researched. Process of spinel Li1+xMn2O4 was studied by XRD, SEM and element analysis and so on. On the basis of these, research of the effects of doping and modification on spinel Li1+xMn2O4 material was carried out. Nickel and cobalt was doped according to a certain proportion could produce spinel Li1+xCo0.02Ni0.02Mn1.96O4 at different temperatures with different ratios of Li/Mn.Composite content of lithium, manganese, doped elements of nickel and cobalt and the valence of manganese in lithium ion battery plays an important effect in electrochemical performance. The valence of manganese in lithium manganate is one +3 and one +4, so 3.5 is the perfect state, in which the electrochemical performance is better. However, the selection of conditions such as temperature plays an important effect on the valence state of manganese in the actual production of lithium manganate. For example, the change of temperature so easily leads to the variation of state, causing the difference of electrochemical performance. Therefore, the determination of the state of manganese plays a great significance in studing the capacity attenuation and mechanism of lithium manganate.Firstly, high level of lithium in materials was directly determined with FAAS by preparing a serious of high concentration standard solution, the results have a good accuracy and precision. Secondly, focusing on the determination of average valence state, that is, perchloric acid oxidimetry was used to determine the total content of manganese in materials and the transferred electron of manganese was measured by oxidation-reduction back titration, the two was conbined to calculate the average valence of manganese. The method is simple and rapid in operation, the results are accurate. Thirdly, mixed standard solution matched with the matrix and flame atomic absorption spectrophotometry was used for contious measurement of the doped elements of nickel and colbalt. Avoiding mutual interference between matrix and determined elements.The result is accurate and reliable.The structure and electrochemical performance etc. of cathode material Li1+xMn2O4 and Li1+xNi0.02Co0.02Mn1.96O4 prepared was studied by X-ray diffractometer, scanning electron microscope and battery test equipment. The results showed that the prepared materials are spinel phase and good crystalline, the particles of what are small and distribution uniformity.Using the rate of 0.3C for charging and discharging, showed that the performance of Li1.10Mn2O4 prepared by sol-gel at 700℃for12h was better. On the basis of that, Li1.10Ni0.02Co0.02Mn1.96O4 was synthesized at 800℃for12h, of which the discharge specific capacity decreased significantly but the cycling performance became better. With 0.3C rate, the initial discharge capacity was 114.8mAh/g, the capacity retention rate was 89.4% after 38 cycles. This method is simple, easy to operate relative.