Coating Modification On LiNi_0.8Co_0.1Mn_0.1O₂ Cathode By Ni-Co-Based Oxide For Lithium Ion Batteries

LiNi0.8Co0.1Mn0.1O2(NCM811)is one of the most promising cathode materials for lithium ion batteries,but its poor cycling performance limits application in high-energy density batteries.Therefore,coating modified NCM811 has become a research hotspot.The traditional coating modification design mainly revolves around monometallic oxides,but the modification each monometallic oxide has some limitations due to the single nature.In this thesis,the similarities and differences of monometallic and bimetallic oxides coating modified NCM811 were researched in detail for the first time.NiO,Co3O4,NiO/Co3O4 and NiCo2O4 were respectively coated on the surface of NCM811.Compared with the monometallic oxide coatings,NiCo2O4 coating exhibited better modification effect,which enhance the initial coulombic efficiency(CE)to 82.9%and improve the capacity retention to 91.0%,showing the capacity at 174.3 mAh g-1 after 200 cycles at a current density of 100 mA g-1.The excellent coating modification effect of bimetallic oxide is mainly due to:(1)NiCo2O4 has high electron and ion conductivity,which can provide diffusion channel for lithium ion while conducting electrons;(2)NiCo2O4 has better corrosion resistance,results in lower impedance caused by side reactions and SEI;(3)NiCo2O4 has good mechanical properties,which can accommodate the volume expansion during the cycle and prevent the structural pulverization.Theoretical calculations provide more explanations in three aspects,including mechanical stability,chemical stability and electrical properties.It confirms that NiCo2O4 coating layer has higher electrical conductivity,lower lithium ion diffusion barrier,stronger elastic modulus and lower binding energy with fluorine ions.Excellent comprehensive performance of bimetallic oxide effectively make up disadvantages of monometallic oxides respectively,concluded that the bimetallic oxide coating layer is superior to monometallic oxide.More importantly,this research puts forward a novel idea of coating modified cathode materials for lithium ion batteries,which has profound implications in the design of other bimetallic or polymetallic oxides coatings and even other types of bimetallic coatings,such as sulfides and selenides,in the future.