Preparation And Modification Of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials For Li-ion Batteries

Lithium ion batteries have been widely applied in power and energy storage systems owing to high energy density,long cycle life and good safety performance.Lithium nickle cobalt manganese oxide is recognized to be one of the most promising cathode material due to its high energy density,good cycling performance and thermal stability.In this thesis,nickel-rich oxide LiNi_0.8Co_0.1Mn_0.1O₂ was chosen as the research object.LiNi_0.8Co_0.1Mn_0.1O₂was synthesized via co-precipitation method.Some important parameters and conditions in the preparation process,such as calcination temperature and Li sources were researched to study their influence on the electrochemical performance of the prepared LiNi_0.8Co_0.1Mn_0.1O₂material.On this basis,the electrochemical properties of the material were improved by surface coating.The structure and morphology of the product was analyzed with XRD and SEM,respectively.The electrochemical mechanisms were characterized by electrochemical impedance spectroscopy and cyclic voltammetry test.The specific experiments are as follows:Firstly,the study confirms that the specific electrochemical properties of LiNi_0.8Co_0.1Mn_0.1O₂ synthesized with different Li source have certain differences.The sample obtained with lithium acetate exhibits the lowest discharge capacity at 0.2C rate.While LiNi_0.8Co_0.1Mn_0.1O₂ synthesized with nitrate lithium and lithium carbonate as Li source have little difference,both of which are higher than the sample synthesized with lithium acetate as Li source.Secondly,the effect of different calcination conditions on the electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂ cathode material is studied.The XRD spectras of the materials are almost identical at different calcination temperatures and different calcination times.At the same calcination temperature,the initial charge/discharge capacity and coulombic efficiency of the cathode material calcined for 12h are lower than that of calcined for 20h.At the same calcination time?20h?,LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials calcined at 750?and 850?are compared.After 35 cycles,the discharge capacity of the material calcined at 750?maintains at 169.4mAh/g with a retention of 87.6%,while that calcined at850?maintains at 162.1mAh/g with a retention of 85.4%.It is concluded that the cycling stability and the rate performance of the sample calcined at 750?is better than that calcined at 850?.Therefore,calcination for 20h at 750?is the optimal condition for preparation of LiNi_0.8Co_0.1Mn_0.1O₂ cathode material.Finally,LiNi_0.8Co_0.1Mn_0.1O₂ was further coated by different amounts of Al₂O₃ via wet coating method.X-ray diffraction patterns show that the main structure of modified materials maintain the layered structure with well crystallinity.No impure peaks are found in XRD patterns,indicating that the coating layer is amorphous structure.The SEM results further exhibit that morphology do not change much after 1wt%coating.Particle distribution is uniform,but a little agglomeration appeared when Al₂O₃ coating amount increased to 3wt%and 5wt%.Electrochemical tests show that coated materials have better electrochemical performance than the bare material.The CV results indicate that the Al₂O₃ coating materials have reduced electrochemical polarization.Consequently,the sample with 1wt%Al₂O₃coating exhibit the best electrochemical performance and rate capability.