Lithium-rich Manganese-based Li[Ni X LiElectrochemical Properties And Structural Analysis Of 1/3-2x/3 Mn 2/3-x/3 ]O 2 (x=0.2, 0.3, 0.4) Materials

Lithium-manganese-rich nickel manganese oxides are regarded as highly potential to be of the electrode materials applied on electric cars cathode material and energy storage system in the future,which is by virtue of its own advantages,such as low prices,environmentally friendly,high performance,etc.However,the internal structure of this materials is unstable when it is charged-discharged at high voltage,therefore the capacity fade was emerged,which is harmful to the long-term use of the battery,so we must understand the capacity fade mechanism of the lithium-manganese-rich nickel manganese oxides.In this paper,three components of Li[Ni_xLi_?1/3-2x/3?Mn_?2/3-x/3?]O₂?x=0.2,0.3,0.4?was prepared by a co-precipitation method.We study the charging process,cycling process and different charge and discharge voltage state of these materials,eventually the internal reasons of the capacity attenuation was learned.Details are as follows:The Ni_aMn_b?OH?₂ precursor was prepared by co-precipitation.The optimal synthesis conditions were determined for different materials respectively.The morphology,crysta l structure and electrochemical properties of different cathode materials were tested and compared to find the similarities and differences of the three components cathode materials.The results demonstrate that Li[Ni_0.2Li_0.2Mn_0.2]O₂ materials have the best crystal structure and electrochemical performance.The layered crystalline structure of the resulting compound in the charging process and circling process was characterized by powder X-ray diffraction?XRD?and high-resolution transmission electron?TEM?micrographs.The results demonstrate that the hexagonal phase was transformed into a hexagonal NiO₂ and an orthorhombic Mn O2 when the charging voltage reached 4.7V.With the increase of cycle numbers,Li₂O was extracted from Li₂MnO₃ component in the cycling period.In addition,the spinel-like phase?cubic?was generated in the cathode materials and became more and more after certain circles.To study the differences of structural changes of the cathode materials charged-discharged at different voltage,XRD and electrochemical tests were applied on the study.The research shows that the charging-discharging voltage is higher,the less time was spent on the extraction of Li₂O from Li₂MnO₃ component in the cathode materials.So the tructural damage is more severe,the spinel-like phase is easier to be produced,that's why the discahrge capacity went up at the initial cycles and then attenuated rapidly at the high voltage.