Research On Lithium Sodium Manganese Oxides As A New Kind Of Cathode Material For Lithium Ion Batteries

Li-Mn-O compounds are promising candidates for cathode materials for lithium ion batteries because of their low cost, low toxicity and abundant resources. However, the problem of structural instability limits the development of the LiMnO2in large-scale application. A new type of cathode material for lithium ion batteries layered sodium-lithium manganese oxides with a general formula LixNa1-xMnO2was explored in this thesis. It was synthesized by substituting Li with Na in conventional LiMnO2cathode material. The thesis studies its synthesis route in detail and bring forward a comprehensive evaluation of the feasibility of its application as a cathode material.Layered LixNa1-xMnO2cathode materials had been synthesized by solid-state methods. The influences of synthesis conditions, such as ratio of Li and Na, calcination temperature, raw material on the structure and performance have been investigated. The optimal conditions for preparing LixNa1-xMnO2can be summarized as follows:the spherical Mn3O4as Mn-source, the reaction temperature of600℃, x=0.25. The Lio.25Na0.75Mn02has a high initial discharge specific capacity of269mAh/g,89%of which is maintained after40cycles at0.1C. The work mechanism of the material in lithium ion batteries was studied through different analytical methods. The ICP and XRD analysis of the cycled material show that sodium ions are taken off from the structure in the charging-discharging process and the material converts to a structure similar to Li2MnO3.Li0.25Na0.75MnO2was mixed with different lithium salts for ion exchange, showing that the sodium ion could be replaced by the lithium ion, and the original structure changed to Li2Mn03structure. The cycle performance of the exchanged samples deteriorated, and the capacity retention after39cycles is78%for the ion exchange sample with LiNO3. When Li0.25Na0.75MnO2is used as cathode materials in the sodium ion battery system, the initial discharge specific capacity is93mAh/g, the first coulomb efficiency is only55%. The Li0.25Na0.75MnO2is used as cathode material in the "Li0.25Na0.75MnO2//Li4Ti5O12" cell and the initial discharge specific capacity is141mAh/g. In the "Li0.25Na0.75MnO2/C" battery system, the cathode material displays a low discharge capacity and poor cycle performance.