Lithium Ion Battery Cathode Material LiNi <1/3> Sub <1> 3 O ₂ Magnification Performance Improvement Study

has been considered one of the most promising cathode materials for next generation Li-ion batteries due to its low cost, high capacity and stability. Recently, most studies focus on the enhancement of the tap density and cycling performance of LiNi1/3Co1/3Mn1/3O2while less attention has been paid to the rate capability. In order to improve the poor rate capability of the LiNi1/3Co1/3Mn1/3O2, ion doping and forming composites with conductive materials have been undertaken in this paper. The microstructure of the samples were characterized by XRD, SEM and TEM, and the electrochemical properties were tested by cyclic voltammetry and AC impedance test.The precursor of LiNi1/3Co1/3Mn1/3O2was obtained by rheological phase reaction method with Li2CO3,(CH3COO)2Ni·4H2O,(CH3COO)2Co·4H2O,(CH3COO)2Mn·4H2O as raw materials. The optimized condition for the synthesis of LiNi1/3Co1/3Mn1/3O2via rheological phase reaction method is lithium excess of6%and sintering at900℃for8h. Zr-doped and Cl-doped LiNi1/3Co1/3Mn1/3O2mateials were synthesised via rheological phase reaction method, respectively, and both of them showed significantly improved rate capability. Zr-doping could lead to better structural stability, less cation mixing and expanded tunnels for lithium ion migration of the LiNi1/3Co1/3Mn1/3O2. Furthermore, with the increase of the amount of Zr-doping, there formed a Li2Zr03coating layer on the surface of the LiNi1/3Co]/3Mn1/3-xZrxO2, which could protect the electrode material from the electrolyte corrosion. The obtained LiNi1/3Co1/3Mn1/3-0.01Zr0.01O2exhibited the best electrochemical performance, which delivered an initial discharge specific capacity of189mAh/g at0.2C,158mAh/g at1.0C,142mAh/g at2.0C and132mAh/g at3.0C between2.5and4.6V, respectively. Cl-doping could improve the ordering of lamellar structure, suppress cation mixing, expand channels for lithium ion migration and cause changes in the charge state of transition metals. As a result, Cl-doping could lead to the decrease of impedance and enhanced activity of the electrochemical reaction.As semiconductor material, LiNi1/3Co1/3Mn1/3O2suffers the poor electronic conductivity. LiNi1/3Co1/3Mn1/3O2/Graphene and LiNi1/3Co1/3Mn1/3O2/CNTs were prepared by using graphene or carbon nanotubes as conductive material to enhance the cycle performance and rate capability of LiNi1/3Co1/3Mn1/3O2. In order to further enhance the electronic conductivity of LiNi1/3Co1/3Mn1/3O2, a LiNi1/3Co1/3Mn1/3O2/Graphene/CNTs composite was designed by using graphene and carbon nanotubes as conductive materials. The obtained LiNi1/3Co1/3Mn1/3O2/1%CNTs/2%Graphene composite exhibited excellent rate capability, which delivered an initial discharge capacity of156mAh/g at0.2C,145mAh/g at1.0C,126mAh/g at2.0C and111mAh/g at3.0C between2.5and4.6V, respectively. This should be ascribed to the high electronic conductivity of the three-dimensional spatial structure achieved by the combination of one-dimensional carbon nanotubes and two-dimensional graphene.