Preparation And Doping Modification Of Lithium Cathode Material Li₂MnO₃·LiMnO₂

Lithium cathode materials?LCM?Li₂MnO₃·LiMnO₂ are composite material on nanoscale.They own the advantages of high energy density,good cyclability and low cost.Which would make them to be widely applied in the next-generation lithium-ion batteries.Nevertheless,some problems such as capacity decay in the first cycle,poor rate capability and degradation of discharge voltage must be resolved.To improve the electrochemical of LCM,we have studied to take charge of these disadvantages.The main contents are listed as following:Firstly,Li₂MnO₃·LiMnO₂ cathod material was prepared using the MnCO3 microspheres as the percurser,which generated from the reaction of MnAc2 with NH4HCO3,and followed annealing at different temperatrues with Li OH salt.From XRD patterns,one can see that the as-prepared samples possess layered structure.Effect of temperature on the electrochemical properties was studied.It is found that the sample annealed at 500° C possesses the best electrochemical performance.This sample can deliver the initial capacities of 345 and 253 mAh g^-1 when charged and discharged at 0.1C rate,respectively.It retained the corresponding capacities of 254 and 218 mAh g^-1 after 50 cycles.Unfortunately,its rate capability is unsatisfied due to low electron/ion conductivity.Therefore,some works need to be carried out to improve the electrochemical performance of the Li₂MnO₃·LiMnO₂ cathod material.Secondly,the Li₂MnO₃·LiMnO₂ was doped with K+ cations to improve its electrochemical performance.The Li₂MnO₃·LiMnO₂ cathode materials doped with various amounts of K+ ions were prepared by a hydrothermal method.The obtained materials are in nanowire shape with a slight aggregation.The overlapped nanowires formed interparatrating structure for Li+ ion diffusion,which shortens the diffusion distance of Li+ ion.As a result,the rate capability of the sample was improved.It is found from XRD patterns,K+ ions have doped into the interlayer of the Li₂MnO₃·LiMnO₂ crystals from the galvanostatic charge-discharge measurements,one can see that material.Sample displayed the best electrochemical performance.It can deliver the initial capacity of 362 and 273 mAh g^-1 when charged-discharged,respectively.And retain the capacity of 214 and 209 mAh g^-1 after 50 cycles.The capacity retention is 76% for this sample which is higher than that of undoped sample by 72%.Moreover,it can still deliver a capacity of 126 mAh g^-1 at 1 C rate.The results suggested that K-doping could improve the cycle performance and ratecapability of the Li₂MnO₃·LiMnO₂ cathode material.Finally,Li₂MnO₃·LiMnO₂ cathode material was modified by doping of F anions using the nanowires MnO2 precursor that prepared by hydrothermal method.In the fabrication process,a certain amount of LiF was introduced to replace LiOH to produce the Li₂MnO₃·LiMnO₂ samples?F=0,0.005,0.01,0.02?.From the XRD patterns,it can be seen that the layered structure of Li2MnO3.Characteristic diffraction peaks being to hardly changed their location,but their intensities decreased with the doping amount of F-anions.Based on the electrochemical measurement,the F=0.01 Li₂MnO₃·LiMnO₂ is found to possess the best electrochemical properties.It can delicer initial capacity of 359 and 269 mAh g^-1 when charged-discharged at 0.1 C rate,respectively.The capacity retention for this sample is 59% after 50 cycles at 0.1C rate,and discharge capacity at 2 C rate is 85 mAh g^-1.After cycled at various rates,the results indicated that the electrochemical properties of the Li₂MnO₃·LiMnO₂cathode material could imprived by doping of F-anions.