Research On Synthesis And Coating Of LiNi_xMn_yCo_1-x-yO₂ Ternary Cathode Materials

Recently,the global energy crisis and environmental destruction have become the major concerns over the years.Electrical energy storage systems enable greater and more effcient use of diffetent energy sources by matching the energy supply with de-mand.So lithium ion batteries have been extensively investigated and widely used;they are not only required to enable the moderately charge/discharge rates applica-tions like mobile phone and portable computer but also to meet an increasing need for new applications such as electric vehicles,which need power sources with both high energy and high power density.Layered LiNixCoyMn1-x-yO2 is of great interest as a promising cathode material for lithium secondary batteries because of its higher theo-retical capacity and better structural stability.However,some problems,such as elec-trolyte corrosion,poor rate capability and high temperature stability,have to be over-come before it is massively applied in the lithium ion battery industry.In this work,the LiNixCoyMn1-x-yO2material having the same layered structure with LiCoO2,was made by co-precipitation method at deffernt Li ratio,Ni/Co/Mn ratio and coating studied.To improve the cycling stability of materials under high-rate and high temperature.This study shows that the exist in the process of precursor oxi-dation and loss,so the molar ratio of Li/(Ni+Co+Mn)is 0.93:1,which is well-formed layered structure and close to theoretical value.In addition,the calcined powder have large value of I(003)/1(104),indicating good ion arrangement and low disorder between Ni2+and Li+.In the different Ni/Co/Mn ratio study,XRD results showed that all three materials had the layered litium transition metal oxide structure(?-NaFeO2 type,space group R3m).SEM characterization of the samples showed that the powder size increases with increasing Ni content,EDS characterization of the sample showe all materials are comply-stoichiometrical.At 4.2V cutoff voltage,LiNi1/3Co1/3Mn1/3O2 shows good capacity ratention in the 0.1C and 1C charge-discharge current,the ca-pacity retention about 88.56%and 80.2%,much more than the other samples about 77.84%and 68.7%in the 0.1C,respectively.And theratio discharge property has ob-vious advantages in the other samples.Surface modification of LiNixCoyMn1-x-yO2 compound with carbon and FeF3 has been attempted with a view to improve the cycling stability,especially upon high temperature and high rate cycling conditions,and HF scavenging effect.Among the surface modified cathodes,carbon coated LiNi1/3CO1/3Mn1/3O2 cathode exhibits ap-preciable specific capacity values of 145.2 mAh·g-1reduce to 132.3 mAh-g-1 with 91.12%capacity retention in the 0.1C current intensity after 50 cycle.Simultaneously,in the high temperature conditions,the discharge capacity deterioration rate of 10.8%and 7.95%are obtained at current densities of 0.1 C and 1C,respectively.But the pris-tine sample capacity deterioration rate of 14.75%and 17.61%are obtained at the same current densities.In addition,the electrochemical impedance spectroscopy(EIS)indicate that such surface modification with decrease of carbon compared to pristine sample.The FeF3 coated LiNi0.4Co0.2Mn0.4O2 decrease the surface impedance,and improve the cycling stability of materials under high-rate and high tempera-ture.Through the experimental results and analysis,the superiority of surface coating in improving the electrochemical properties of LiNixCoyMn1-x-yO2 cathode.