| In recent years,due to the advantages including high energy density,light weight,environment friendly,low self-discharge of lithium ion battery,efforts have been devoted to develop new energy vehicles,which will greatly promote the development of lithium-ion battery industry and related technology.As the core component of new energy vehicles,Li ion battery has become the biggest contributor to overcome the "mileage anxiety".Therefore,the cathode material of Nickel rich system with higher energy density has become an inevitable choice.Among a large number of rich nickel cathode materials,larger capacity and balanced performance makes LiNi0.8Co0.15Al0.05O2 the earliest and most widely used material.However,the problem of cyclic capacity degradation and safety of LiNi0.8Co0.15Al0.05O2 has been the main reason for limiting the extension.Covering material design to degradation mechanism study,this paper has studied the problem of LiNi0.8Co0.15Al0.05O2 cyclic capacity degradation.First,the spherical Ni0.8Co0.15(OH)1.9 precursor with high solid density,regular morphology and uniform particle size distribution has been synthesized by co-precipitation method.The effect of coprecipitation process on the structure,morphology,density and particle size distribution of the precursor has also been discussed.The results show significant effect of the reaction conditions on the precursor and cathode material morphology,structure and properties.Secondly,cathode material with low cation mixing degree and good cycling performance has been synthesized through systematic optimization of the solid-state reaction process.The effect of process parameters(sintering temperature,sintering time,sintering temperature,sintering time,with lithium and oxygen flow rate)on the cathode material structure,morphology and electrochemical performance has been studied in details.The relationship of process-structure-performance has been established gradually.The results show that the crystallinity of LiNi0.8Co0.15Al0.05O2 increased with sintering temperature and sintering temperature increasing,calcining time and sintering time,it increases first and then decreases with increasing cation mixing,calcining temperature and sintering temperature increasing,calcining time and sintering.Higher lithium content promotes the reaction equilibrium toward the cathode material.The crystallinity of the material increases first and then decreases with the lithium content.The cation mixing row first decreases and then increases with lithium content.With the increase of oxygen flow rate,the mass transfer efficiency and the oxidation degree of nickel increased,and the decomposition and loss of oxygen was inhibited,and the cationic mixed discharge decreased first and then increased.On the basis of former work,the stability of the positive electrode material is improved by various elements doping modification,and the mechanism of different doping elements is studied.Bi-functional titanium modification of LiNi0.8Co0.15Al0.05O2 has improved cycle stability significantly by doping and coating.The oxidation of Ni2+ has been induced by higher valence of Ti4+,and the electron concentration of ontology has been improved by space charge compensation effect.The stability of the crystal structure has been improved by higher boding energy of Ti-O.The stability of the structure is further enhanced by Nb doping with stronger space charge effect due to more bonding electrons of Nb.At the same time,there is little benefit to the electrochemical performance of LiNi0.8Co0.15Al0.05O2 through Ce4+ doping,which may attribute to its same bonding electron amount of Ti4+ but larger radius of Ce4+.LiNi0.8Co0.15Al0.05O2 has been doped by more electronegative fluorine,the stability of the layered structure can be improved by stronger ionic bond,thus improving the stability of the cycle.Proper ionic radius with strong space charge effect of cation doping can effectively improve the structure and surface stability,broaden the lithium ion channel.Doping with high electronegativity anion can improve the bonding energy of metal-anion and the stability of structure,and finally improve the electrochemical performance of battery.Thermally stable submicron Li Mn2O4 has been synthesized with industrial Al doped Mn3O4 and Li2CO3.The effects of solid state reaction process on Li Mn2O4 morphology,crystal structure and electrochemical properties has been system studied in details.And then,the blend cathode electrode was prepared by mixing LiNi0.8Co0.15Al0.05O2 and LiMn2O4 with different proportions.The effect of proportions on physical properties and the intercalated-li kinetic mechanism has been studied.Lithium-ion diffusion and transformation has been improved by better rate capability and gap distribution of LiMn2O4 particles,which thereby inhibiting accumulation of dramatic change of lattice structure stress and avoiding the particle break into isolated islands.By logical and systematical design of the source(precursor)and the base unit(lattice structure),the cycle stability of LiNi0.8Co0.15Al0.05O2 has been enhanced.The effect of fabrication process,elemental doping and blend cathode electrode on the structure,morphology and lithium transport mechanism of LiNi0.8Co0.15Al0.05O2 has been thoroughly discussed and analyzed,which will inspire further study and contribute to practical applications. |
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