Preparation And Modification Of Ternary Cathode Material NCA

LiNi_0.8Co_0.15Al_0.05O₂（NCA）,a layered ternary material,is considered as one of the most promising cathode materials due to its high energy density and good cycling performance.However,the structural stability and rate performance of NCA materials still need to be improved.In this paper,the optimal synthesis conditions were explored through the condition control of the preparation of precursor by co-precipitation method and the subsequent calcination of lithiation.Mg₃（PO₄）₂ coating and Li₂TiO₃ coating of materials,and the effects of different coating amounts on the properties of NCA materials were explored,and the coating mechanism of different substances was studied and explained.Ni_0.8Co_0.15Al_0.05（OH）₂,a precursor of NCA,was synthesized by coprecipitation method.The effects of different pH,ammonia concentration,lithium content and calcination temperature on the morphology,structure and electrochemical properties of the materials were studied.The optimum synthetic process conditions were determined by multi-condition comparison.XRD and SEM results showed that the pH value of 11,ammonia concentration of 1.5 M,lithium excess of 5%,calcination temperature of 850℃under the above system the the sample exhibited the most optimal layered structure and spherical or class spherical morphology.The results of charging and discharging cycle test indicated that the electrochemical properties of the samples prepared under the above comprehensive conditions were optimal.The initial discharge capacity at 0.1 C could reach 153.64mah/g,and the capacity retention after 100 cycles was 89.25%.NCA materials were prepared under optimal synthesis conditions.Then,Mg²⁺was chelated on the surface of NCA using the chelation of EDTA disodium,and Mg₃（PO₄）₂-coated NCA samples（denoted as Mg₃（PO₄）₂@NCA）were synthesized by centrifugation and secondary sintering after adding phosphorus sources with stoichiometric.By exploring the influence of different cladding amounts on the electrochemical properties of the materials,it can be found that the hexagonal system ofα-NaFeO₂ layer structure remains well after coating.The TEM results showed that the surface of NCA materials is uniformly coated with a layer of Mg₃（PO₄）₂.Electrochemical performance test results showed that 2%Mg₃（PO₄）₂@NCA samples had the best cyclic stability and the best rate performance among the samples with different coating amounts.The results of EIS and CV showed that after 100cycles the increase of the material’s impedance is obviously inhibited,and the polarization is obviously weakened,which is helpful to improve the electrochemical properties of the material.TiO₂ and Li₂CO₃ were successfully adhered to the surface of NCA by ultrasonic dispersion and wet grinding with ethanol,and then the NCA samples coated with Li₂TiO₃（denoted as Li₂TiO₃@NCA）were synthesized by high-temperature calcination.XRD and SEM results showed that different Li₂TiO₃ coating amounts had no effect on the microstructure and macroscopic morphology of NCA materials.Since Li₂TiO₃ itself can be used as an electrode material to contribute capacity during charging and discharging,the influence of coating on the overall capacity loss of the material is reduced.After electrochemical performance test,it can be found that 2%Li₂TiO₃@NCA has the optimal electrochemical stability and higher initial capacity.The zero strain characteristic of Li₂TiO₃ material plays a significant and effective supporting and protection role on the surface of NCA material.After long-term charging and discharging cycles,the material can maintain a good spherical morphology and reduce the corrosion by electrolyte,resulting in serious attenuation of performance.