Investigation Of Li_1.20Mo_0.41Cr_0.39O₂ And MoO₂ Electrode Materials

As cathode materials,the layered rock salt-structured Li-Mo-Cr-O has a theoretical capacity of 325 mAh g-1.The cation layers undergo order-disorder transition with discharge/charge cycling.As anode materials,MoO₂ has high capacity and tap density.However,it electric conductivity is low and the Li-storage mechanism is complicated.In this thesis,Li1.20Mo0.41Cr0.39?2 and carbon-coated Li_1.20Mo_0.41Cr_0.39O₂/C have been fabricated through hydrothermal and solid-state reaction mechods.The MoO₂ and MoO₂/graphene composites have been synthesized through hydrothermal and ultrasonic mixing methods.ICP,XRD,SEM and TEM have been employed to characterize their microstructure and composition.In addition,their electrochemical performances as electrode materials for lithium ion batteries have been evaluated.1.Li_1.20Mo_0.41Cr_0.39O₂ has ?-NaFeO₂ type structure with space group R3m.Its cation layers undergo order to disorder transition after the initial charege/discharge cycle,and the disorder degree increases gradually with discharege/charge cycling.2.The electrochemical properties of the Li_1.20Mo_0.41Cr_0.39O₂/C have been improved by the carbon coating.Its initial charge/discharge capacities reach 270.54/200.2 mAh g-1,and the first-cycle coulombic efficiency is 76.6%.The initial charge/discharge capacities of Li_1.20Mo_0.41Cr_0.39O₂ are 250/160 mAh g-1,and the first-cycle coulombic efficiency is 64.6%.3.The rate capability of the Li_1.20Mo_0.41Cr_0.39O₂/C material has been improved.Its reversible capacity recovers to 107.7 mAh g-1 when the current density restores 15 mA g-1 after 50 cycles at different current density.4.The MoO₂ has rutitle structure,and the composition of MoO₂ with graphene has not change its crystal structure.MoO₂ displays secondary aggregation morphology with the primary particle size of ca.10-20 nm.The MoO₂ particles attach to the graphene surface.5.The graphene additives enhance the electrochemical property of MoO₂.The charge/discharge capacities of MoO₂/G-2 reach 314.6/318 mAh g-1 at 1 C?838 mA g-1?,and 197.8 mAh g-1/202.5 mAh g-1 at 5C.The additive of graphene can decrease the charge transfer resistance of the MoO₂/graphene.