Synthesis Of Lithium-rich Manganese-based Gradient Layered Oxide Materials By Carbonate

As the next-generation cathodes material for lithium-ion battery,the lithium-rich manganese-based layered oxides,have advantages of high specific capacity and low cost,and wide applications in the future.However,the commercial development of these materials are still hindered by the unclear mechanisms during charging and discharging,the voltage degradation,and poor cycle stability.In this thesis,in order to improve the electrochemical performances of lithium-rich manganese-based layered oxide cathode materials,the carbonate full-concentration gradient lithium-rich manganese-based precursors have been prepared by automatic control continuous reaction devices through designing the material structure and composition.The process of preparation and sintering of carbonate precursors were systematically studied,and the electrochemical performance of the full concentration gradient material was analyzed.The main content of the thesis are as follows:1.The lithium-rich manganese-based layered oxide precursors have been prepared by an automatic controlled continuous reaction device.The influences of the main parameters on the morphology of the precursor were explored,including the type of the base solution,the pH value of the reaction,and the reaction time.The results showed that the carbonate precursor with good sphericity and particle size distribution of 15-25?m could be obtained,when the base solution was 1M ammonia or clean water,the pH value was maintained between 7-8,and the reaction time was not less than 10h.2.According to the above synthesis process of carbonate precursor,based on the low cobalt content material Li_1.2Mn_0.583Ni_0.183Co_0.033O₂,and following the design of the transition metal full concentration gradient,two full concentration gradient precursors have been fabricated,including the gradient changes of transition metal Mn,Ni and stabilization of Co?plan A?,and the changes of all transition metal elements?plan B?.The studies on the sintering process of carbonate precursor,the interdiffusion mechanism of transition metal ions and the electrochemical perfoemances have revealed that the cyclic stability of full concentration gradient lithium-rich manganese-based layered oxide cathode materials are better than the single component Li_1.2Mn_0.583Ni_0.183Co_0.033O₂.Especially,for the materials prepared by Plan A,the capacity retention was 85.4%after 300 cycles at a current density of 200 mA/g,and the lithium ion diffusion coefficient is about 10^-16 cm²s^-1.3.The Ge nanowires were obtained by molten salt electrolysis method,and the Ge nanowire anode can be modified by 10%carbon composition.This anode can keep a specific capacity of 700 mAh/g after 500 cycles at a current density of 500 mA/g.Then the full battery that assembled by combing the Ge-C composite nanowires anode and the full concentration gradient lithium-rich manganese-based layered oxide cathode has good cycle stability,which keeps a capacity retention of 95%after 40 cycles at the current density of 200 mA/g.