Abstract:

A series of yttrium(III) ion doped layered lithium manganese oxides LiYxMn1-xO2 ( y = 0. 01, 0. 02, 0.03 and 0.05) compounds were synthesized with Na2CO3,(CH3COO)2Mn.2H2O ,CH3COOLi?2H2O and Y2O3 as the starting materials by two step high temperautre solid state reaction and hydrothermal ion exchange method. The Y3+-doping effect on structure and the electrochemical performances of the samples were investigated by XRD, XPS ,cyclic voltammetry and charge-discharge tests. The XRD results show that the samples exhibit the same phase as pure monoclinic sturcture compounds . Electrochemical performances indicate that the yttrium ions can partially replace Mn3+ in monoclinic structure LiMnO2 materials and because the radius of Y3+ is bigger than that of Mn3+ , samples doped with yittrium elements have larger lattice constant comparing with that of undoped sample. Doding enables lithium ion to transport more freely in the three dimensional pathway,and all doped with yittrium elements materials show good cycle stability. Experiments of doping ratio and electrochemistry performance were carried out . The compound LiY0.021Mn0.979O2 obtained exhibited a better performance whose initial discharge specific capacity reached 123.4mAh?g-1 respectively. After 100 cycles, the discharge capacity maintains 212.1mAh?g-1,which is much higher the discharge capacity 138 mAh?g-1 of the undoped monoclinic structure LiMnO2 materials. AC analysis shows lower electrochemical impedance and the diffusibility of lithium ion is clearly improved due to Y3+ doping.

Key words: Monoclinic LiMnO2, Li-ion batteries, cathode material, Yttrium doping, electrochemical behaviors