Preparation And Modification Of LiNi_0.5Co_0.2Mn_0.3O₂ Cathode Materials With Long Life-span And High Rate Performance For Lithium-ion Batteries

The cathode material determines the cost and electrochemical performance of lithium-ion battery,so development of high performance?high discharge specific capacity,long cycle performance and high operating voltage?,low cost and pollution-free cathode material for lithium-ion battery is very significant.Although the ternary cathode material has been commercialized,the current utilization of it is only half of its theoretical specific capacity and its cycle performance is also not ideal,so modifications are needed.The modifications of the ternary cathode material are mainly in two aspects:one is to increase the discharge specific capacity;the other is to improve the long-term cycle performance.In this paper,the precursor was prepared and modified by a simple carbonate co-precipitation method to obtain improved LiNi_0.5Co_0.2Mn_0.3O₂ cathode material.Al?OH?₃coating was applied to the surface of the precursor and then calcined at a high temperature,which makes LiNi_0.5Co_0.2Mn_0.3O₂ obtain the effect of Al³⁺-doping and LiAlO₂-coating in one step.F127 surfactant was added to change the morphology during the synthesis process,followed with F-doping modification to improve the electrochemical performance of LiNi_0.5Co_0.2Mn_0.3O₂.XRD,TEM,SEM,XPS and GSAS structural refinement methods were used to characterize the modified materials.The electrochemical properties of the modified materials were tested by means of charge-discharge test,cyclic voltammetry test and AC impedance test.The specific research work is as follows:?1?LiNi_0.5Co_0.2Mn_0.3O₂ was modified by coating Al?OH?₃ on the surface of the precursor,which is different form the conventional coating method.This precursor coating method enables the product to obtain the effect of Al³⁺-doping and LiAlO₂-coating in one step and makes the coating layer uniformly and completely coated on the surface of the active material.Among all the samples,2wt%Al modified sample shows better electrochemical performance.Under the current density of 0.5 C and the high cut-off voltage of 4.6 V,2wt%Al modified sample shows high capacity retention of 82.08%after 200 cycles.2 wt%Al modified sample also owns high discharge capacity of 142.73 mAh g^-1 at a large current density of 10 C,while that of the pristine sample is only 98.46 mAh g^-1.?2?The electrochemical performance of LiNi_0.5Co_0.2Mn_0.3O₂ material was improved by the combined modification of F127 surfactant and F-doping.The use of F127 surfactant increases the structural integrity and crystallinity of the product.Further F element doping stabilizes the material structure,enlarges layer spacing and hence improves the electrochemical performance.After modification,F127-NCMF sample shows high capacity retention of 79.04%after 500 cycles at 10 C,while that of the pristine sample is only 13.17%of the initial capacity after 200 cycles.The SEM,XRD,and TEM tests of the cycled electrode show that F127-NCMF sample exhibited better cycle performance due to its more stable structure than the other two samples.