Coating Modification And Cycling Performances Of Electrode Materials For High Capacity Lithium Ion Batteries

Energy shortage and environmental pollution are becoming more and more serious.The development and utilization of new energy is imperative.Compared with the traditional rechargeable battery,lithium-ion batteries have the advantages of high storage capacity,good safety performance and no memory effect.It is widely used in the field of electric vehicles and power grid energy storage.However,there are still a series of problems to be solved before large-scale application.In this paper,based on an in-depth investigation of electrode materials with high capacity for lithium ion batteries,we focus on lithium-rich manganese-based cathode materials(theoretical capacity>250 mAh/g)and nickel-rich ternary cathode materials(theoretical capacity 200 mAh/g).lithium-rich Li 1.i67Ni0.i67Co0.i67Mn0.5O2 cathode material and its coating modification was made based on carbonate coprecipitation,and nickel-rich LiNi0.8Co0.iMn0.iO2 cathode material and its coating modification was made based on hydroxide coprecipitation.The effects of different coating amounts on the morphology and structure of the cathode materials were explored,and the respective cycle performances were studied.The main contents are as follows:1.Lithium-rich Li1.i67Ni0.i67Co0.i67Mn0.5O2 cathode material was synthesized first by carbonate precipitation method.Then a composite material with uniform AIPO4 coating on its particle surfaces was prepared by a pH-controlled chemical deposition process based on Al(NO3)3·6H2O,K2HPO4,hexamethylenetetramine reagents,with citric acid-sodium citrate as buffersolution.The effects of different amount of AIPO4 coating on the phase structure and cycling performance of the Li1.167Ni0.167Co0.167Mn0.5O2 cathode materials have been studied.In comparison,1.0 wt.%AIPO4 coating is the most effective to improve the performances of the cathode material.Experimental results show that the 1.0 wt.%AIPO4 coated material exhibits high initial discharge capacity(265.9 mAh/g at 0.1 C)and excellent capacity retention(with 88.0%retention rate after 150 cycles at 0.5 C).The Li+diffusion rate in 1.0 wt.%AlPO4 coated material is 9.07×10-15 cm2/s,and the electrochemical impedance value is reduced from 152.92 ? to 62.27 ?.The excellent electrochemical performance was attributed to the AlPO4 coating which reduces the side reactions between the electrolyte and the electrode material by preventing their direct contact,thus accelerating lithium ion diffusion and reducing electrochemical resistance.This uniform AlPO4 coating strategy based on adjusting the pH of the solution provides a new idea for the modification of the cathode material for lithium ion batteries.2.The Ni0.8Co0.1Mn0.1(OH)2 precursor was prepared first by the hydroxide co-precipitation method.Then Ni-rich LiNi0.8Co01Mn01O2 cathode material coated with CeO2 was prepared using Ce(NO3)3·6H2O and hexamethylenetetramine as raw materials to coat the precursor and then sintering in solid phase.The phase structure and chemical composition of the material were characterized by XRD,FESEM and XPS and other testings,and their electrochemical performance tests were performed.In comparison,2.0 wt.%CeO2 coating is the most effective to improve the electrochemical performance.The electrochemical impedance was reduced and capacity retention rate are improved significantly.The initial specific discharge capacity at 0.2 C increased from 186.1 mAh/g to 195.8 mAh/g,and the capacity retention rate was 85.7%after 150 cycles at 0.5 C.