Study On Synthesis And Electrochemical Properties Of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂Lithium-rich Cathode Material

The manganese-based solid solution xLi[Li_1/3Mn_2/3]O₂·（1–x）LiMO₂（M aretransition metal ions） has been focused widely and investigated extensively byscientists and researchers because of its high specific capacity, good thermalstability, clean environment and low cost, etc. In recent years, one of the promisingmaterials of lithium-rich, Li[Li（0.2）Mn₍0.54_Ni_0.13Co_0.13]O₂(x=0.5, and M=Mn1/3Ni1/3Co_1/3), has been chose as an object of my thesis research. The synthesis and surfacemodification coating have been studied in depth in order to improve its dischargecapacity and cycle performance. Firstly, the cathode material of lithium-rich, Li[Li0.2Mn0.54Ni0.13Co_0.13]O₂, has been synthesized by co-precipitation method. And itsstructure has been characterized and analyzed through XRD, SEM, XPS and ICP, ect.The electrochemical properties have been studied through the charge-dischargetesting, etc. Meanwhile, the important synthesis condition parameters ofLi[Li（0.2）Mn₍0.54_Ni_0.13Co_0.13]O₂, such as sintering time, sintering temperature and thelithium source, have been optimized. Also influence of them on their structure andelectrochemical properties were discussed and researched.The final optimizationresults show that the material which has the layered structure and goodelectrochemical performance could be prepared at900℃for18h when takingLi2CO3as the lithium source. In the current rate of0.1C, the initial dischargespecific capacity of the material is267.2mAh/g and its coulombic efficiency is76.7%; After50cycle laps the discharge specific capacity still remains236.9mAh/g and its rate of capacity retention is88.7%.In order to improve the electrochemical properties of cathode material, theprepared Li[Li（0.2）Mn₍0.54_Ni_0.13Co_0.13]O₂was coated with Al₂O₃and graphene to makea modification. Firstly, the Al₂O₃coating was chose, and the amount of coating is0.25wt%and1wt%, respectively. As for0.25wt%Al₂O₃, the first discharge specificcapacity under the0.1C is282.6mAh/g, which increases by15.4mAh/g whencompared with the bare one. And its initial coulombic efficiency is78.6%, whichalso increased by1.9%. Regarding the1wt%Al₂O₃coating, the first dischargespecific capacity under the0.1C is290.2mAh/g, which increases by23mAh/gcompared with the bare. And its initial coulombic efficiency is78.7%, which alsoincreased by2%. Meanwhile after Al₂O₃-coated its magnification performance hasbeen greatly improved, especially when the coating amount is1wt%. SoAl₂O₃-coating improved obviously electrochemical properties of the preparedmaterials. Secondly, the graphene coating was chose, and the mass ratio of the cathodematerial and the graphene was2:100and6:100respectively. When the mass ratiowas2:100, the first discharge specific capacity of synthetic material under0.1C is296.9mAh/g, which improved29.7mAh/g compared with the bare. And its initialcoulombic efficiency is77.8%, which also increases by1.1%.When the mass ratio was6:100, the first discharge specific capacity of thesynthetic material under0.1C is316.0mAh/g, which improved48.8mAh/g comparedwith the bare. And its initial coulombic efficiency is72.5%, which also reduces by4.2%.