| For all-solid-state batteries using sulfide solid electrolytes,the main factors limiting their applications include the chemical and electrochemical stability of the sulfide electrolyte itself,and the stability of the interface between the electrolyte and the electrode.When using high nickel material as the cathode active material,the irreversible phase change during cycling will lead to the volume changes of the cathode.This will further reduce the contact between the cathode and the solid electrolyte.What’s more,the side reactions that occur at the interface will continue to accumulate at the interface.This reduces the ion conductivity,resulting in irreversible capacity loss and rapid performance degradation.In order to optimize the interface between the cathode and the solid electrolyte,atomic layer deposition(ALD)technology is used in this paper.Niobium ethoxide and lithium tert-butoxide are selected as sources to deposit on the single crystal LiNi0.8Co0.1Mn0.1O2(NCM811)material.Through infrared spectroscopy(IR)and X-ray photoelectron spectroscopy(XPS)technology,combined with electrochemical characterization,the influence of the coating layer on the surface of LiNi0.8Co0.1Mn0.1O2(NCM811)before and after cycling was explored.Experiments show that the coating layer with a thickness of about 5 nm can significantly reduce the increase in impedance of the battery during resting and cycling by inhibiting side reactions at the cathode/solid electrolyte interface.From the surface morphology characterization of the material annealed at 400℃ the surface of the particles becomes smoother.This reduces the contact resistance to a certain extent.At the same time,the coating layer can reduce the surface impurities of the cathode,inhibit the side reactions of the cathode/solid electrolyte interface and the oxidation decomposition reaction of the solid electrolyte itself.This can significantly increase the battery capacity(the firstcycle discharge capacity at 0.1C is as high as 205.4 mAh g-1)and cycle stability(capacity retention rate remains 90.3%after 100 cycles at 0.3C),and shows a good rate performance(115 mAh g-1 at 1C).Subsequently,in order to optimize the ALD process,this article explored the effects of the two coating parameters of the deposition process,the number of coating turns and the ratio of Li/Nb sub-cycles.Experiments show that the growth rate of the coating layer obtained by ALD is about lnm/cycle,and when the number of coating cycles is 4 and the Li/Nb sub-cycle ratio is 1:2,the first cycle efficiency of the battery reaches 76.6%.And after 130 cycles at 0.3C,there still remains a high capacity retention rate of 91.0%.At the same time,during the investigation of the parameter setting in the coating process,It is also found that within a certain range,the number of the coating cycle mainly affects the cycling retention rate of the battery,while the different Li/Nb sub-cycle ratio mainly affects its discharge specific capacity.Since the LiNbO3 coated by ALD is in an amorphous state,annealing at different temperatures can transform the coating layer to a crystalline state.In order to explore the suitable heat treatment temperature of the ALD coating,the coating was annealed at different temperatures.The experiment found that after annealed under 400℃ the coating layer basically transforms into crystalline state,which avoids Nb doping into the crystal lattice caused by annealing at higher temperature(500℃ and above),and also avoids the amorphous coating that has not been completely transformed in lower temperature(300.℃).The uniform coating layer of 400-ALDNCM effectively reduces the interface impedance,inhibits the H2-H3 phase transition,and exhibits excellent cycle and rate performance. |
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