Synthesize And Study High Voltage LiMn_0.5Ni_0.5O₂ Cathode Material

More and more scientists pay great attention on lithium-ion batteries due to their excellent electrochemical performances,such as high energy and power densities,long lifetime,no memory effect,environment friendliness and low self-discharge comparing with other energy storage devices.So,lithium-ion batteries were used in portable electronics such as laptops,mobile phones and cameras.But lithium-ion batteries are still unable to meet market demand for energy storage devices up to now.Cathode material which is the most important part of lithium-ion batteries plays a critical role in determining the electrochemical properties.Layer LiNi_0.5Mn_0.5O₂ cathode materials have outstanding advantages such as low cost?high voltage?energy and power densities,which attract people's attention.However,LiNi_0.5Mn_0.5O₂ cathode material still has some shortcomings such as poor cyclic performance and rate performance,which stops its application.This study will improve its electrochemical performances by synthesized methods,elements doping and surface coating.In the meantime,we would explore the relationship between the structure and electrochemical performances.To be specific,LiNi_0.5Mn_0.5O₂ will be synthesized by solid state method,sol-gel method,a combination of co-precipitation and solid-state method and a combination of hydrothermaland solid-state method.According to the structure measures and electrochemical tests,the materials were synthesized by a combination of co-precipitation and solid-state method which have good crystallinity,small size and good electrochemical performances.After analyzing the mechanism,we found the materials prepared by a combination of co-precipitation and solid-state method had smaller degree of Li/Ni cation maxing,which is in favor of Li-ion migration.Hence,a combination of co-precipitation and solid-state method was used to synthesize the doping and the pristine cathode materials.The study shows Ca-doping can improve the capacity,cyclic performances and rate performances.We explore the reason found that Ca-doping can lower the degree of Li/Ni cation maxing,improve the structure stability,reduce the resistances and improve the lithium-ion migration rate.In addition,Li₂SiO₃ was used as the coating materials to synthesize Li₂SiO₃@LiNi_0.5Mn_0.5O₂ cathode materials by co-precipitation,hydrothermal and solid-state method.The cathode materials prepared by this method have the uniform coating layer and good crystallinity.The structure shows partial of Si⁴⁺doping into the structure,and the synergistic effect of Si-doping and Li₂SiO₃ coating can effetely improve the electrochemical performances.Then,the reason was explored and found that Si-doping can lower the degree of Li/Ni cation maxing,improve the structure stability,Li₂SiO₃ coating can reduce the agglomeration,speed up the rate of lithium-ion migration and reduce the side reaction.