Synthesis Of Layered Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂Its Electrochemical Study

As a layered solid-solution material, xLi₂MnO₃·（1x）LiMO₂has manyadvantages such as high specific capacity, excellent cycling performance, low-cost,light pollution and other remarkable electrochemical performances. It has been a newalternative cathode material with high energy density for lithium-ion batteries.However, exsiting of the insulation component of Li2MnO3in the material leads to alow electronic conductivity. As a result, its rate capability is not satisfied. In addition,a thick solid electrolyte interphase （SEI） film would form on the surface of electrodematerial under high charge potential. These problems seriously restrict its wideapplication. In this work, three kinds of Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂（i.e.0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2） materials were prepared by the sol-gel,co-precipitation and solid-phase ball-milling methods. The morphology and crystalstructure of the obtained materials were characterized using scanning electronmicroscopy （SEM） and X-ray diffraction （XRD）, respectively. Their electrochemicalproperties were investigated by using cyclic voltametry （CV） and galvanostaticcharge-discharge measurements.Firstly, we studied the effct of synthesis method on the electrochemicalproperties of layered Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂materials, which were prepared bythe sol-gel, co-precipitation and solid-phase ball-milling methods. XRD resultssuggest that all samples are layered solid-solution materials. Meanwhile, the samplesprepared by the sol-gel and co-precipitation methods have complete lattice andwell-layer structure. The sample prepared by solid-phase ball-milling method has anincomplete solid-solution phenomenon. From SEM images, it can be seen that themorphology of samples varies with the preparation method. The initial dischargecapacities of them are259,255and153mAh·g^-1at0.1C rate when prepared bysol-gel, co-precipitation and solid-pahse ball-milling methods, respectively. Thecorresponding irreversible discharge capacities are95、97and88mAh·g^-1in the firstcycle. At a current density of2C, the initial discharge capacities of samples preparedby the sol-gel and co-precipitation methods are174and166mAh·g^-1, respectively,which are67%and65%of the ones at0.1C.Secondly, the layered material prepared by co-precipitation method was coatedwith2.9wt%AlF₃on the surfaceare. XRD pattern shows that the AlF₃-coating doesn’t change the crystal structure of the Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂. SEM imagesdisplay the morphology of the product changed with AlF₃-coating. Theelectrochemical results indicate that AlF₃-coating can improve its discharge capacity,cycling performance and rate capability. The capacity retention of the coated materialis92%at0.2C rate after50cycles, which is better than that of the un-coated material（74%after45cycles）. Even at a0.5C rate, the coated material delivered a capacityabout94%of the initial one after45cycles higher that the un-coated material （78%）.Moreover, AlF₃-coating enhanced the coulombic efficiency in the first cycle.Electrochemical impedance spectra suggest the AlF₃-coating layer could maintain theSEI film, which formed on the surface of electrode material during charging anddischarging. Therefore, the charge transfer resistance could not increase with cycling.As consequency, the electrochemical performances of the battery were improved.Finally, a series of V₂O₅-Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂composite materials wereprepared by using the sol-gel sample as raw material. The morphology and crystalstructure were characterized using SEM and XRD, respectively. The electrochemicalresults suggest that V₂O₅could effectively reduce the irreversible capacity loss of thesolid solution in the first cycle. When the composite materials contain20wt%ofV₂O₅, they exhibit no irreversible capacity loss in the first cycle.