Study Of Synthesis And Modification Of LiNi_0.5Mn_1.5O₄Cathode Material With Rare Earth Element Doping

LiNi0.5Mn1.5O4is considered as one of the most promising cathodematerials for its high theoretical capacity of147mAhg^-1and highdischarge plateau at4.7V. In this paper, the preparation conditions andrare earth elements （Ce, Sm, Y） doping of LiNi0.5Mn1.5O4wereinvestigated. The structure, morphology and electrochemical properties ofthe as-prepared materials were studied by XRD and SEM, galvanostaticcharge-disaharge, cyclic voltammetry （CV） and andAC impedance.The influence of prefiring process and calcination temperatures on theelectrochemical performances, structure, and morphology ofLiNi0.5Mn1.5O4synthesized by sol-gel method was studied. The optimumpreparation conditions was that LiNi0.5Mn1.5O4was prefired at450℃withlow heating rate of2℃/min for5h and calcinated at850℃for16h.The initial discharge capacity of sample was139.1mAhg^-1and122.9mAhg^-1, and the capacity after100cycles was139.1mAhg^-1and107.1mAhg^-1, at0.2C and1C, respectively. However, the cell rate performancewas poor.The structure and electrochemical performances of rare earth elements （Ce, Sm and Y） doped LiNi0.5Mn1.5O4were studied. The resultsshowed that the Ce and Sm doping reduced the electrochemicalperformance. However, the Y doping improved the rate performance andcycle retention. LiNi_0.49Mn_1.49Y_0.02O₄had high discharge capacity andgood cycle stability. The initial discharge capacity was126.5mAhg^-1and125.5mAhg^-1, the discharge capacity after100cycles was129.6mAhg^-1,122.5mAhg^-1at0.2C and1C, respectively. At higher rate, such as3C and10C, the initial discharge capacity was110.5mAhg^-1and109.2mAhg^-1,the discharge capacity after90cycles was109.6mAhg^-1and95.3mAhg^-1,respectively. AC impedance indicated that LiNi_0.49Mn_1.49Y_0.02O₄electrodehad the lower impedance value during cycling.