Synthesis And Modification Of LiNi_0.6Co_0.2Mn_0.2O₂ As A Cathode Material For Lithium-ion Batteries

Nickel-rich layered LiNiO.6C0.2Mn0.2O2 material has emerged as a promising one for applications in lithium ion batteries owing to its considerable capacity within a relatively low cut-off voltage range (<4.3 V). In this paper, the influence of calcining atmosphere (oxygen or air) was studied to optimize the synthesis conditions and the prepared LiNi0.6Co0.2Mn0.2O2 powers were coated by Al2O3 and graphene to improve its electrochemical performances, furthermore, improved electrochemical performances of LiCoO2 material within a high cut-off voltage range (4.5 V) was studied.Layered Ni-rich LiNiO.6Co0.2Mn0.2O2 materials were prepared by calcining the mixture of Ni0.6Co0.2Mno.2(OH)2 precursor (co-precipitation method) and Li salts(Li2CO3). Two different caicination atmosphere (air and oxygen) were adopted to obtain final two samples of LNCMO-A (air) and LNCMO-O (oxygen) to individually investigate the influence of oxygen instead of air atmosphere on the structure and electrochemical behavior of the LNCMO materials. XRD and SEM results showed the LNCMO-O sample possessed relatively smaller Li+/Ni2+ cation mixing, better layer-structure ordering and smaller primary particle size. The electrochemical charge/discharge test results showed the LNCMO-O sample exhibited superior discharge capacity (184.6 mAh·g-1 at 0.1C), higher initial coulombic efficiency (84.2%),higher cycling retention (91.4% after 100 cycles at 0.5C) and promoted rate performance. Further XPS, CV and EIS analyses on the promotion mechanism demonstrated that the oxygen-atmosphere calcination was important and beneficial to improve the electrochemical performance for Ni-rich LiNi0.6Co0.2Mn0.2O2 material.LiNi0.6Co0.2Mn0.2O2 powers were coated with uniform Al2O3 film through homogeneous precipitation method with urea as precipitant. XRD results showed the 1% Al2O3-coated LiNi0.6Co0.2Mn0.2O2 sample had better hexagonal ?-NaFeO2 layered structure. TEM images showed a uniform Al2O3 layer was formed on the LiNi0.6Co0.2Mn0.2O2 surface. The electrochemical tests showed the 1% Al2O3-coated LiNi0.6Co0.2Mn0.2O2 sample exhibited higher discharge capacity, excellent cycling performance and rate performance.The LiNi0.6Co0.2Mn0.2O2/RGO composites were prepared by hydrothermal method.XRD results showed the crystal structure of LiNi0 6Co0.2Mn0.2O2 material was not changed after coating grapheme and the 2.5% RGO-coated LiNi0.6Co0.2Mn0.2O2 sample had better hexagonal ?-NaFeO2 layered structure. TEM images showed a amorphous RGO layer was formed on the LiNi0.6Co0.2Mn0.2O2 surface. The electrochemical tests showed the 2.5% RGO-coated LiNI0.6Co0.2Mn0.2O2 sample exhibited excellent cycling performance and rate performance.LiCoO2 powers were prepared by high temperature solid state method with Co3O4 and Li2CO3 as raw materials. (LiNi0.5Mn1.5O4)0.2(LiCoO2)0.8 composites were prepared by sulfate co-precipitation process. XRD results showed the crystal structure of(LiNi0.5Mn1.5O4)0.2(LiCoO2)0.8 composite was different from that of LiCoO2 material.SEM images showed the primary particles of composites were closed to spherical and its agglomeration degree was higher. The electrochemical tests showed the(LiNi0.5Mn1.5O4)0.2(LiCoO2)0.8 composites exhibited better cycling performance (90.2%after 50 cycles at 0.5C) and rate performance. The results from CV indicated that the(LiNi0.5Mn1.5O4)0.2(LiCoO2)0.8 composites possessed better structural stability and reversibility during cycling.