Preparation And Modification Of Ni-rich Cathode Materials For Lithium Ion Batteries

The ternary layered material LiNi_0.8Co_0.1Mn_0.1O₂ has a high nickel content,leading to a high degree of lithium-nickel mixture,poor cycling performance and high residual lithium content on the surface.Aiming at these problems,the structure and electrochemical properties of the ternary layered material LiNi_0.8Co_0.1Mn_0.1O₂ have been studied from the synthetic methods and material coating modification:LiNi_0.8Co_0.1Mn_0.1O₂ cathode material has been prepared by a sol-gel method with oxalic acid as a complexing agent.By comparing the materials synthesized at different calcination temperatures,the sample calcined at 800°C?AC@NCM-800?has a better layered structure and a lower lithium-nickel mixture.The microstructure of the material is a secondary fluffy structure composed of primary particles.This hierarchical structure is beneficial for exhibiting better electrochemical performance.Take AC@NCM-800 as an instance,the specific capacity for the first cycle is 197.4 mAh·g^-1 at a current density of0.1C;and the specific capacity for the first cycle and the 50^th cycles are respectively 179.3mAh·g^-1 and 154.0 mAh·g^-11 at the current density of 1 C;namely,the capacity retention rate is 85.9%.LiNi_0.8Co_0.1Mn_0.1O₂ cathode material has been synthesized with the help of a carbon gel that is formed by using resorcinol and formaldehyde in a water bath heating process.The effects of different calcination temperatures on the physical and chemical properties of the LiNi_0.8Co_0.1Mn_0.1O₂ materials have been investigated.The Experiments results show that a carbon gel precursor formed by the resorcinol and formaldehyde in the water bath heating process,and the carbon gel combines with metal ions to ensure that the reactants are mixed uniformly.The cathode material calcined at 800°C?RF@NCM-800?has the best electrochemical performance.For example,the RF@NCM-800 has a specific capacity of 178.6 mAh·g^-1 for the first cycle,the coulombic efficiency can reach 83.4%.After 50cycles,the RF@NCM-800 also retains the discharge specific capacity of 141.8 mAh·g^-1.Therefore,the material shows excellent first discharge specific capacity and better cycle performance.The surface of LiNi_0.8Co_0.1Mn_0.1O₂ cathode is formed a layer of Co₃O₄ coating utilizing Co?NO?₂·6H₂O as coated material,the membrane formation and coagulation of polyvinylpyrrolidone?PVP?.The effects of different coatings on the electrochemical properties of LiNi_0.8Co_0.1Mn_0.1O₂ cathode have been explored.The experimental results show that coating of 1%Co₃O₄ can weaken the side reaction between the cathode and the electrolyte,reduce the residual alkali content on the surface of the cathode,and improve its cycle performance.For 1%NCM(LiNi_0.8Co_0.1Mn_0.1O₂ cathode coated by 1%Co₃O₄),the discharge specific capacity for the first cycle is 176.5 mAh·g^-1,and it can maintain 142.6mAh·g^-1 after 100 cycles at the current density of 1C;that is its capacity retention rate is80.8%.