Study On Preparation And Modification Of Spherical LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials

Layer rich nickel LiNi_0.8Co_0.1Mn_0.1O₂ cathode material has the advantage of higher capacity,better rate performance and its cost is far lower compared with LiCoO₂,which has a promising prospect.The precursor Ni_0.8Co_0.1Mn_0.1?OH?₂ was synthesized by co-precipitation method,and the cathode material LiNi_0.8Co_0.01Mn_0.1O₂ was achieved by sintering at high temperature.Nano ZinO was modified on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ via sol-gel process.The conclusion are drawn as follows:The best synthetic conditions were found as.the concentration of aqueous ammonia solution was 1.5 mol/L.the value of pH was 10.5-10.6 and the reaction time was 16 h.The precursor showed good sphericity,uniform particle size about 8 ?m under the best conditions.The LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials was prepared by sintering the precursor and Li2CO3,which showed the best electrochemical properties.The LiNi_0.8Co_0.1Mn_0.1O₂ was achieved by sintering at 750? for 16 h,which had low cation mixing,good layer structure and spherical shape.The highest discharge capacity of the materials is 20_0.1,187.1,173.9 and 161.7 mAh g-1 in 3.0-4.3 V at 0.2,1.2 and 5 C,respectively.The capacity retention rate in the 50th cycle was 84.6%at 1 C.The chemical diffusion coefficients of lithium ion.DLi,in LiNi_0.8Co_0.1Mn_0.1O₂ were determined by cyclic voltammogral?CV?at different scanning rates,the result showed the DLi of oxidation and reduction peaks is 2.52×10-11 and 1.48×10-11cm2/s,respectively.Electrochemical impedance spectroscopy?EIS?demonstrated that the SEI film on the surface of electrode was destroyed.interfacial impedance and charge transfer resistance increased as the cycle index being increased.The discharge capacity and cycle performance were getting worse.The nano ZnO was modified on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ cathode materials.The XRD sho\wed the structure of the LiNi_0.8Co_0.1Mn_0.1O₂ was untouched by the modification of ZnO.The SEM,EDS and TEM demonstrated that the Zno was uniformly distributed on the surface of the cathode materials as nano particles,the sizes was from 50-200 nm.Both the nano ZnO and LiNi_0.8Co_0.1Mn_0.1O₂ had higher crystallinity.When the mass percent of modified ZnO was 1%,the electrochemical properties of LiNi_0.8Co_0.1Mn_0.1O₂ is best.The capacity retention rate was 93.0%after 50th cycle in 3.0-4.3 V at 1 C,while the pristine was only 84.6%.the highest discharge capacity of modified materials increased 1.40%.2.14%,5.23%and 6.06%at 0.2,1,2 and 5 C,respectively.CV proved that lithium ion intercalation and deintercalation on the modified materials increased the reversibility of electrode.The chemical diffusion coefficients of lithium ion of oxidation and reduction peaks for pristine and modified is 2.52×10-11,1.48×10-11 and 3.41×10-11 1.51×10-11 cm2/s.EIS showed that the interfacial impedance and charge transfer resistance remarkably decreased because of nano ZnO modification,the stability of electrode and electronic conductivity were improved,Which would be advantageous for lithium ion intercalation and deintercalation.The electrochemical properties of LiNi_0.8Co_0.1Mn_0.1O₂ was greatly improved.