Research On Modification Of Anode Materials For Lithium Ion Batteries

Over the years,the technology of automotive lithium batteries has gradually matured,and graphite has also occupied the main market of lithium batteries anode because of its low cost and superior performance,but it also has certain defects:the outer layer is easy to peel off,and lithium dendrites are easy to grow,resulting in poor battery magnification and low temperature performance.As a result,a large number of scholars began to think about how to better modify the graphite anode,and the relevant tests proved that ALD technology is a good means of modification.In this paper,starting from the lithium iron phosphate/graphite anode system,the graphite particles and graphite pole pieces are ALD wrapped and modified,and the battery is assembled with modified materials,and the relevant tests show that the low temperature and rate performance of the battery are significantly improved,and the corresponding ALD improvement ideas are proposed for mass production,and the specific research content and results are as follows:(1):Coating experiment on artificial graphite raw materials.The sample heating temperature is set to 125°C,and the optimal number of cycles for a single experiment is 50 times and the number of repetitions is 3times.Materials are characterized using SEM,XRD,EDX,BET,and TEM.The scan showed that the surface of the sample was relatively regular,the structure was superimposed sheet,the edge of the structure was not sharp,the orientation of each wafer was unspecific,and there was a relatively good homogeneous structure.TEM shows that the thickness of the coated Al₂O₃film is about 5 nm.XRD test results show that the graphitization of the sample is very high.The particle size distribution shows that D50 is 14.34 microns,and the particle size distribution range of the material is relatively wide.The relevant CV test shows that the coating of Al₂O₃increases the potential during SEI generation,which is conducive to the thinner thickness of the SEI film layer;the AC impedance curve results show that the coating of Al₂O₃maintains the characteristics before the coating,and the AC impedance is low;the first charge and discharge capacity of the clip cell is 342.9 m Ah/g,and the first Coulomb efficiency is 92.5%.Finally,the design idea of airflow distribution bed ALD equipment is proposed.(2):Coating experiment on coated artificial graphite pole pieces.The sample is heated at 100? and the number of cycles is 80 times.The EDX test results show that the Al₂O₃film formation is uniform to the negative electrode piece by ALD method.Cylindrical 14500 battery first discharge capacity of 567.8 m Ah/g,the first effect of 89.91%;1C charge-discharge 2000 cycle battery can achieve 91.96%capacity retention rate,3C charge-discharge 2000cycle battery can achieve 87.01%capacity retention rate;25Ah soft pack battery different times charge and discharge performance is excellent;-20? low temperature discharge capacity retention rate of 86.2%The 6.5Ah soft pack battery magnification disassembly photo shows that the negative electrode surface is smooth and flat,there is no shadow,and there is no lithium evolution phenomenon;the temperature test of the charge and discharge process of the8.5Ah soft pack battery with different magnifications shows that the temperature rise of the negative ear is very small.The above shows that ALD deposition of Al₂O₃thin film is a better surface coating material for lithium-ion battery anode polar plates.Finally,a roll-to-roll coating mode is proposed,which can improve the speed of winding coating.