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

With the development of society,people have higher requirements for the driving range of electric vehicles,which means that the energy density of lithium-ion batteries has higher requirements.Traditional cathode materials have been unable to meet people's needs.LiNi_0.8Co_0.1Mn_0.1O₂,a nickel-rich ternary cathode material,is considered to be a promising cathode material for lithium-ion batteries due to its high capacity,high energy density and low cost.However,LiNi_0.8Co_0.1Mn_0.1O₂ easily reacts with the electrolyte during charge and discharge,resulting in poor cycle performance,large polarization,and rapid voltage decay.In order to improve the electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂,this paper designed a lithium ion conductor coating layer and used two coating methods to modify the surface coating of LiNi_0.8Co_0.1Mn_0.1O₂.The introduction of the coating layer can avoid direct contact of LiNi_0.8Co_0.1Mn_0.1O₂ with the electrolyte and reduce side reactions;On the other hand,the introduced lithium ion conductor is beneficial to improve the lithium ion transmission rate of the interface.The electrochemical stability of the coated LiNi_0.8Co_0.1Mn_0.1O₂ has been greatly improved.The specific work is as follows:?1?For the preparation of LiNi_0.8Co_0.1Mn_0.1O₂ by the traditional alkaline coprecipitation method,it is necessary to strictly control the harsh conditions such as pH,temperature and inert atmosphere,and the equipment is expensive.We have developed a simple acid co-precipitation method to prepare LiNi_0.8Co_0.1Mn_0.1O₂,the preparation process does not need to control pH and inert gas protection,and can be operated at normal temperature.The specific process is as follows:Firstly,the rod-shaped MC₂O₄·2H₂O?M=Ni,Co,Mn?precursor was prepared by acid co-precipitation method,and the rod-shaped LiNi_0.8Co_0.1Mn_0.1O₂ was obtained by high temperature calcination with lithium salt.The assembled battery was subjected to electrochemical test.The initial discharge capacity of the sample was 183.2 mAh g^-1,and the capacity retention rate was 77.4%after 100 cycles of 0.5 C current.?2?In order to improve the electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂,we introduced different thicknesses of Li-Ti-O coating on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ by co-precipitation method,and studied different coating ratios.The electrochemical properties of the sample show that the introduction of Li-Ti-O lithium ion conductor coating improves the rate performance of LiNi_0.8Co_0.1Mn_0.1O₂,alleviates the voltage decay and polarization of the electrode during cycles,and improves the cycling stability,in which 3wt%Li-Ti-O coated LiNi_0.8Co_0.1Mn_0.1O₂ has the best electrochemical performance?cycling stability of 84.8%?.?3?In order to further improve the quality of the coating,we use solvothermal method to react the crystal water of the precursor of the rod-shaped MC₂O₄·2H₂O?M=Ni,Co,Mn?with tetrabutyl titanate.A thin and uniform Li-Ti-O coating layer was formed on the surface of LiNi_0.8Co_0.1Mn_0.1O₂.Electrochemical test results show that the capacity retention of 3 mol%Li-Ti-O coated LiNi_0.8Co_0.1Mn_0.1O₂ is 88.6%after 100 cycles of 0.5 C charge and discharge current.The introduction of Li-Ti-O coating layer greatly reduces the polarization of the LiNi_0.8Co_0.1Mn_0.1O₂ cathode material and the voltage decay during the cycles.In addition,the coating layer is also beneficial to improve the high temperature performance of the battery.The capacity retention rate of 3 mol%Li-Ti-O coated LiNi_0.8Co_0.1Mn_0.1O₂ after 50 cycles at65°C is 81.1%.It is higher than LiNi_0.8Co_0.1Mn_0.1O₂?52.0%?.