Synthesis And Properties Of High Nickel Ternary Cathode Material LiNi_0.8Co_0.1Mn_0.1O₂ Coated With Graphene/CNTs

The high nickel ternary cathode material LiNi_0.8Co_0.1Mn_0.1O₂ has a high theoretical specific capacity and low cost due to its high Ni content,and it has great development prospects as lithium ion battery cathode material.However,the mixed arrangement of Ni2+ and Li+,and the low Co and Mn content lead to poor cycling stability and rate performance of the material.Graphene and CNTs have excellent electrical conductivity and a large specific surface area.In this paper,graphene and CNTs was coated with LiNi_0.8Co_0.1Mn_0.1O₂.LiNi_0.8Co_0.1Mn_0.1O₂ was prepared by high temperature sintering method.Graphene and CNTs were pretreated separately.The graphene and CNTs were coated on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ by using ultrasonic technology and liquid phase self-aggregation method.The structure and morphology of LiNi_0.8Co_0.1Mn_0.1O₂,graphene/LiNi_0.8Co_0.1Mn_0.1O₂ composite,CNTs/LiNi_0.8Co_0.1Mn_0.1O₂ composites and graphene/CNTs/LiNi_0.8Co_0.1Mn_0.1O₂ composites were studied by XRD,SEM,FTIR and TEM characterization methods.The electrochemical properties of these materials were studied by charge-discharge property test,CV and EIS.The effects of graphene and CNTs coating and coating amount on LiNi_0.8Co_0.1Mn_0.1O₂ were investigated.The experimental results showed that LiNi_0.8Co_0.1Mn_0.1O₂ can be successfully coated with graphene and CNTs by this method.The crystal structure and morphology of LiNi_0.8Co_0.1Mn_0.1O₂ were not affected by the coating of graphene and CNTs.The optimal coating amounts of graphene and CNTs were 0.8%and 0.5%.The first charge-discharge specific capacity of 0.8%-graphene/LiNi_0.8Co_0.1Mn_0.1O₂ composites at 0.1 C were 222.85,208.93 mAh/g.The specific capacity of 0.5%-CNTs/LiNi_0.8Co_0.1Mn_0.1O₂ composites at the first charge-discharge at 0.1 C were 229.36,215.587 mAh/g.And the first charge-discharge specific capacity of LiNi_0.8Co_0.1Mn_0.1O₂ were 209.90,190.16 mAh/g.The graphene/LiNi_0.8Co_0.1Mn_0.1O₂ composites with coating content of 0.8%can give off 205.18 mAh/g after 100 cycles at 0.1 C.CNTs/LiNi_0.8Co_0.1Mn_0.1O₂ composites with coating content of 0.5%can give off 191.36 mAh/g after 100 cycles at 0.1 C.At the same condition,the capacity retention of LiNi_0.8Co_0.1Mn_0.1O₂ was only 86.5%after 100 cycles.LiNi_0.8Co_0.1Mn_0.1O₂ was coated with 0.8%graphene and 0.5%CNTs.TEM tests on graphene,CNTs and graphene/CNTs showed that the edges of graphene was wrinkled and the tubular structure of CNTs was good.One-dimensional tubular CNTs was interspersed between two-dimensional sheets of graphene to form a good three-dimensional network structure.The first charge-discharge specific capacity of graphene/CNTs/LiNi_0.8Co_0.1Mn_0.1O₂ composites were 229.10,217.33 mAh/g.And the cycle performance,multiplier performance were also improved.The results of CV and EIS of graphene/CNTs/LiNi_0.8Co_0.1Mn_0.1O₂ composites showed that the polarization of LiNio.8Co0.1Mn0.1O2 during charge-discharge was reduced by the coating of graphene and CNTs,and the impedance of the electrode material was reduced.In addition,the graphene/CNTs have an excellent of co-coating modification.Graphene and CNTs are coated on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ to form a 3D network structure that facilitates the transfer of Li+,and graphene and CNTs form a "protective barrier" to inhibit the side reaction of the electrolyte to LiNi_0.8Co_0.1Mn_0.1O₂.They can improve the electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂.