Doping And New Preparation Technology Research Of Layered Lithium Manganese Oxide

Layered LiMnO₂ that used as an electronic material（cathode） of lithium ion batteries has many merits such as being non-toxic, safe, of high theoretical capacity（approximately 285mAh/g） and other advantages, by which many problems can be improved, therefore it has become a research hotspot in recent years. However, the production process of cathode material was encumbered by its low efficiency, structural instability, poor electrochemical cycle performance and high cost of preparation. This paper focused on improving its electrochemical performance and providing a theoretical basis for commercialization of LiMnO₂ through the optimization of mature technology, investigation of new preparation process of LiMnO₂ and the doped sample. The details were summarized as follows:（1） Monoclinic LiMnO₂, has unitary and relatively harsh synthetic conditions, therefore, the purpose of this paper is to reduce the complexity of synthetic and costing.NaMnO₂ as the research object, the high temperature solid state method to synthesize Mn₂O₃ and anhydrous Na₂CO₃ was used. The different concentration of sodium and manganese, calcination temperature, holding time, and the presence of carbon powder to protect the influence of different structure of α-NaMnO₂ were investigated. Moreover, the α-NaMnO₂ as the precursor to explore through hydrothermal-ion exchange process under different conditions for the m-LiMnO₂ was studied, and optimized the hydrothermal-ion exchange method to good commercial process result in the effect is better than that of reflux distillation method.（2） In the present work, different elements（Cr, Mg, V, Y, Ce, La, Ti, Fe, Ni, Al, S）, doping process, different controlling factors were investigated. The optimal doping process was obtained of different doping element. RE doping, single doping, binary doping and anion doping, even zwitterions doping all achieved that based on the hydrothermal synthesis method. Additionally, the lattice constant of o-LiMnO₂ and changing of it were accurately figured out, meanwhile, the optimal doping ratio for layered structure could be investigated.（3） The purity of o-LiMnO₂ thermal decomposition temperature at about 370℃. Doped samples after thermal decomposition temperature of the different elements are higher than 400℃, some even up to 480℃. Dual doping unit is better in stability improved. Negative ion doping can also have the effect of improvement. Has the strong oxidizing elements or dual doping of o-LiMnO₂ improve the thermal stability of the coordination is more significant.（4） The Cr, Y, Mg, Al, Ni doped samples which synthesized by hydrothermal method was selected and investigated. Based on the products, orthogonal crystal system normal equation and the least square method was used to accurately figure out the lattice constant of o-LiMnO₂, the optimal doping amount（4at%Cr、4at%Y、4at% Al、4at%Ni） and influence of doping to host lattice was confirmed, as well as the result was consistent with theory analysis. Additionally, the difference of o-LiMnO₂ lattice constant which caused by Mg doping were reversely testified the reliability of this method, and 6at %Mg is the optimal Mg doping ratio for layered structure was investigated.（5） Layered o-LiMnO₂, synthesized by mechanical alloying（MA） with LiOH·H2O and Mn2O3 without any inert atmosphere protection at room temperature. In this study, the effects of solid/liquid weight ratio（S/LWR）, ball/powder weight ratio（B/PWR）, Li⁺/Mn³⁺ mole ratio（L/MMR）, MA time（MAT）, process control agent（PCA） and synthesis temperature on the structural properties of layered o-LiMnO₂ were examined, and it was found that the optimum preparation conditions were B/PWR of 40:1, S/LWR of 2:1, L/MMR of 1.5:1, MAT of 10 hrs and PCA of deionized water, at which the pure o-LiMnO₂ with small particle size and lattice parameter could be synthesized.