Modification And Application Of High-nickel Layered Materials For Lithium-ion Batteries

In the 2020s,with the advent of the new energy era,lithium ion batteries are increasingly widely used,including mobile digital products,electric vehicles,hybrid vehicles and so on.The development of lithium ion battery has become the top priority of the new energy industry,especially the electric vehicle power battery field which is widely expected and favored by people.Higher range and higher energy density of electric vehicles have become the pursuit direction of power batteries.The high nickel ternary cathode material can make up for the low upper limit of energy density of lithium iron phosphate,so it becomes a more promising cathode material for lithium ion batteries.This paper will start from the existing problems of high nickel ternary materials,take LiNi_0.8Co_0.1Mn_0.1O₂(NCM811)as the base material,optimize its preparation method and process conditions,find the internal relationship between the special phase behavior of NCM811 and poor cycle stability,and design effective modification strategies.It provides a new idea for the modification and production process of NCM811 and higher nickel content ternary layered materials.This topic includes the following contents:(1)The first work is to synthesize NCM811 by different methods.In previous work,it was found that polyethylene glycol(PEG)assisted solvothermal method can control the growth of phosphate cathode material precursors along a specific[010]direction.The first method to synthesize NCM811 is to prepare NCM811 precursor Ni_0.8Co_0.1Mn_0.1(OH)₂ by PEG flux thermal method.By controlling the volume ratio of PEG to water,the precursor can grow towards the spherical morphology.After mixing lithium,NCM811 particles were sintered at high temperature.It was found that the morphology of precursor was related to PEG/water ratio,and the particle size was related to reaction temperature.The second method is oxalate coprecipitation.The morphology of NCM811 precursor is needle-like by changing the coprecipitation temperature and aging time.The reaction system of this method is neutral,so the influence of p H on coprecipitation is ignored.Different types of NCM811 were successfully synthesized by the two synthetic methods,which laid a foundation for further research on the modification of high nickel layered materials.(2)Nickel-rich layered materials are the most commercially valuable materials for power batteries.However,due to the presence of Ni³⁺,the lattice degradation of high ni ternary materials is particularly serious during the cycling process.In this experiment,lini_0.8-XCo_0.1+XMn_0.1O₂ was prepared with the increase of cobalt content(x=0.02,0.04,0.06).Through electrochemical test,X-ray diffraction analysis,constant-current intermittent titration,Rietvel refinement and other characterization methods,the effect of increased cobalt content on nickel-rich layered materials was explained.With the increase of cobalt content,the reverse phase transformation of 4.2 V is inhibited,and the material exhibits good stability during the cycle.Encouragingly,with increased cobalt content,the samples showed excellent cycling and rate properties,REDOX inhomogeneity and impedance reduction,and high initial Coulomb efficiency.On this basis,lin I _0.82Co_0.12Mn_0.06O₂ layered material with high nickel and cobalt properties was synthesized.This study confirms the complex and indispensable role of cobalt and provides a cobalt-rich strategy for the design of Ni-rich layered materials.(3)In this study,a Rich-Ni high-Co layered material has a core-shell structure design,in which LiNi_0.82Co_0.12Mn_0.06O₂(NCM-Ni82)as the core wrapped in aluminum shell by doping LiNi_0.735 Co_0.15 Mn_0.1Al_0.015 O₂ to form the hybrid particles LiNi_0.795Co_0.13Mn_0.07Al_0.005O₂(NCM-HA).The NCM-HA module was divided into the core part NCM-Ni82 and the monohybrid part(NCM-HS)without Al.Then,all the modules were compared with the original LiNi_0.8Co_0.1Mn_0.1O₂ by various characterization methods to reveal the superiority of the design.Core-shell structure can prevent micro-crack diffusion caused by lattice shrinkage with high cobalt content,and improve the morphological strength of the cathode material,so that the cathode material can give full play to the excellent stable cycling performance brought by the significant cation order degree of Co rich treatment.The capacity retention rate of the excellent cathode material NCM-HA is still 83.3%after 200 cycles,while that of the original material is 55.42%and that of the commercial material is 48.88%.In addition,NCM-HA successfully inhibited the unsteady phase transition of layered materials at4.2 V and reduced the degree of polarization during the cycling process.This study provides a new strategy for the modification of cobalt-rich nickel-rich layered materials.