Influence Of Electrochemical Performance Of Modified NCM811 Cathode Material

As the main power battery of new energy vehicles,lithium-ion batteries have the advantages of high energy density,high voltage,environmental protection and safety,and are favored by all parties.Among the various components of lithium-ion batteries,the cathode material is undoubtedly the most critical part,and lithium nickel cobalt manganese oxide(NCM,Li Ni_xCo_yMn_1-x-yO₂,0.8?x<1,02.With its high specific capacity,high cycle performance of Li Co O₂and high safety performance of Li Mn O₂,it is currently the most promising ternary cathode material for lithium-ion batteries in large-scale applications.Lithium-ion ternary cathode materials can potentially meet the sustainability,environmental friendliness and high energy density required by the next generation of LIBs.However,there are many defects in the ternary cathode material.The capacity and potential of the nickel-rich layered oxide NCM deteriorate rapidly during long-term cycling,which inevitably affects the stable output of energy.The frequent use of coating and doping strategies can improve the conductivity,surface structure and internal framework of the ternary cathode material,and improve the performance of lithium-ion batteries.It is of great significance for the better and faster application of lithium-ion batteries in real life.value.Based on this,the main research content of this paper is:(1)Use the reflux method to coat aluminum acetylacetonate on the surface of NCM811.After a series of electrochemical tests,the coated material is proved Significantly improve the electrochemical performance of the material.After 300 cycles,the discharge capacity of the modified NCM811 is 130.5 m Ah g^-1,and the capacity retention rate is 75.05%,which is significantly higher than that of the NCM811 sample.At the same time,during the coating process,Partial doping of aluminum ions into NCM811 expands the cell spacing of the material,facilitates the insertion and extraction of lithium ions,and brings better electrochemical performance.(2)Through the method of modifying the surface of the positive electrode,the residual-OH on the surface of the electrode material of the lithium-ion battery and the metal zirconium acetylacetonate are adsorbed to the surface of the material through the chemical bond M-O bond in acetone to achieve the interface monomolecular layer modification.result.After the electrochemical test,the cycle performance and rate performance of the coated modified material are better than the original material.Different from aluminum acetylacetonate coated NCM811,since the ion radius of zirconium is larger than that of aluminum,during the surface coating process,more ions are doped into NCM811,and the cell spacing formed is larger,which is more beneficial The insertion and extraction of lithium ions brings better electrochemical performance.(3)The LiFePO₄ coated NCM811 was prepared by a simple ball milling method,and the influence of different coating amounts of LiFePO₄on the electrochemical performance of NCM811 was studied in detail.When the coating amount of LiFePO₄is 1 wt%,the material can maintain good cycle stability,good rate performance and thermal stability.The capacity retention rate of the material after 300 cycles is 61.6%,which is significantly better than the48.63%of NCM811.EIS results show that LFP modification can effectively reduce RSEI(from 46.37 to 32.13?)and RCT(from 155.9 to 113.5?),and promote the migration of Li⁺.The electrochemical cycling performance of 811 and 1 wt%coated 811 materials was tested at50?and 1C current density.Although the initial capacity of the NCM811 original material was higher than the 1 LFP coated material,it was after 200 cycles,The capacity retention rate of 1 LFP is 76.25%,and the capacity is 132.3 m Ah g^-1,which is much higher than the 58.15%and 110.2 m Ah g^-1of 811.The coating of 1 wt%LiFePO₄is beneficial to improve the thermal stability of the battery cathode.The above results indicate that LiFePO₄coating NCM811 is beneficial for improving the electrochemical performance of the material,and it is worthy of further study.