Synthesis And Properties Of High-Performance Layered Lithium-Rich Cathode Materials For Lithium Ion Batteries

The development of green and clean energy has become a significant strategic choice to solve the increasingly prominent energy and environmental problems.As one of efficient energy storage and conversion devices,lithium ion batteries have been widely used in electric vehicles,smart power grids and other fields due to their high operating voltage,high energy density,long cycle life and no memory effect.The performance of lithium ion batteries largely depends on the cathode materials.In this research paper,after analyzing and summarizing the research progress and current situation of lithium ion cathode materials,we choose the lithium-rich layered cathode material xLi₂MnO₃·?1-x?LiMO₂?M=Ni,Co,Mn?which has the advantages of high energy density,high voltage,low cost and safety as the research object.Owing to the irreversible transformation from layered structure to the spinel phase upon cycling,the poor cyclic stability and the fast attenuation of voltage of the lithiun-rich layered cathode material are hopefully improved by patassium ion doping.We firstly use KCl as the patassium source to prepare surface K⁺doped Li_1.2Ni_0.2Mn_0.6O₂ material via a facile ball-milling process.This material delivers a high reversible capacity of 260 mAh g^-1 after 100 cycles at 0.1 C(1 C=200 mA g^-1),besides,the voltage decay is alleviated to some extent.Soft X-ray absorption spectroscopy?sXAS?confirms that the existence of K⁺may promote the generation of O₂^2-on the material surface,as well as the reduction of Mn³⁺to Mn²⁺,thereby alleviating the generation of spinel phase upon cycling and improving the cycling stability of this material.On the basis of the research above,we use the precursor of potassium-contained?-MnO₂ to prepare the bulk K⁺doped Li_1.2Ni_0.2Mn_0.6O₂ material,and then we study the effects of different calcination time at 900?on the properties of final material.The results show that the bulk K⁺doped material displays the best electrochemical performance when the sintering time is 12 h,which delivers a high discharge specific capacity of 173.2 mAh g^-1 after 150 cycles at 1 C.By comparing with pristine material,it can be found that potassium bulk doping can greatly inhibit the transformation of layered structure to spinel phase,thus alleviating the voltage attenuation and improving the rate performance and cyclic stability of this material.