Preparation And Coating Modification Of Cathode Material LiNi_1/3Co_1/3Mn_1/3O₂ For Lithium-Ion Batteries

In recent years,cathode material LiNi_1/3Co_1/3Mn_1/3O₂?LNCM?of Lithium-ion batteries has attracted a lot of attention because of its low cost,high capacity,and high discharge platform.Nevertheless,LNCM is prone to inhomogeneity owing to its complex composition during the preparation process,cation mixing(Li+ and Ni²⁺)at high temperature calcination process,and low electronic conductivity.Metal ions easily dissolved in electrolyte during the process of charge and discharge.These lead to bad cycle and rate performances.In this paper,we obtained LNCM with homogeneous cation distribution and low cation mixing by co-precipitation and self-template methods,the samples show the superior electrochemical performances.In addition,in order to further improve the electrochemical performances of LNCM,we also prepared LNCM coated by Pr₆O₁1,and the product shows high discharge capacity and good rate performance.The main research contents are as follows:?1?The LNCM microspheres were prepared by co-precipitation method.It is found that the microspheres calcined at 850 °C exhibit more uniform ion distributions and lower cations mixing.The electrochemical test results show that the LNCM?850 °C?microspheres have good cycle performance and high discharge capacity.The first discharge capacity is 174.9 mAh g^-1 at 1 C,and capacity is 136.6 mAh g^-1 when the current density is up to 10 C,which is higher than that reported in most of the literatures.?2?Hollow dumbbell LNCM with good electrochemical performances were synthesized by a simple self-template solid state method,and the influence of calcination time on electrochemical performances was investigated.The results suggest that LNCM?L-2?calcined at 10 h shows good electrochemical performances.L-2 is composed of 100-200 nm particles,and its diameter is about 1.5-2 ?m.The first discharge capacity of L-2 is 155.1 mAh g^-1 at 1 C,and still maintains 107.8 mAh g^-1 after 500 cycles.The initial discharge capacity is 144.7 mAh g^-1 even at 10 C,and also keeps 97 mAh g^-1 after 300 cycles.The hollow dumbbell LNCM cathode material not only ensure the uniformity of the material,but also buffer the volume change,which can improve the rate performance and long cycle performance.Moreover,the cycle life is longer than most of LNCM reported in the literatures.?3?Uniform Pr₆O₁1 conductive layer was coated on LNCM by low cost wet chemical method.The results show that a small amount of Pr₆O₁1 coating does not change the crystal structure of LNCM.Electrochemical results show that 1 wt% Pr₆O₁1-coated sample(M^-1)displays the best electrochemical performances.The initial discharge capacity is 152.3 mAh g^-1 at 10 C?cut-off voltage of 4.6 V?,which is significantly higher than that of the uncoated material(135.2 mAh g^-1).Therefore,the Pr₆O₁1 layer can accelerate the transmission of Li+ ions in the electrode material,alleviate volume expansion in the process of charge and discharge,and improve the discharge capacity and cycle performance of LNCM in high voltage and high current density.