Synthesis And Modification Of Spherical Spinel Lithium Manganese Cathode Materials

Recent years, the spinel LiMn2O4has been considered as the most promising cathode material. Compared with the other materials, LiMn2O4has the more abundant resources, lower cost, higher voltage and better safety. However, the LiMn2O4suffers fast capacity fading during cycling, which is the major obstacle to its further commercialization. The synthesis of the spherical LiMn2O4, ion doping and surface modification are concerned in this thesis.The spherical LiMn2O4powder is synthesized from the coprecipitation and solid state method. The Mg and F codoped LiMn2O4samples are synthesized through solid state reaction route with the MgF2as the dopant. The results reveal that the LiMg0.1Mn1.9O3.8F0.2showed the highest initial discharge capacity of121.1mAh g-1, the capacity retention is still89.2%after400cycles at a rate of1C, at55℃.The Y2O3coated LiMn2O4is prepared from the sample precipitation method. The effects of the coating amount on the structural and electrochemical properties are investigated in detail. It has been found that the1wt.%Y2O3-coated LiMn2O4electrode shows excellent cycling performance with76.7%capacity retention after500cycles at1C at55℃.The graphene/Y2O3/LiMn2O4hybrid is firstly synthesized through mixing the as-synthesized Y/LMO powder and graphene oxide aqueous suspension and then anneal at600℃in Ar. The results demonstrat all the samples are highly crystallized and the particle sizes are uniform. The graphene/Y2O3/LiMn2O4hybrid shows the initial discharge capacity of129.3mAh g-1, and the capacity retention is still89.3%even after500cycles at a rate of1C and at55℃.