Study On The Mechanism Of Low Content Doping Elements In Nickelrich Ternary Cathode Materials

Lithium-ion batteries are widely used in various electric energy storage devices due to its many advantages such as stable working voltage,high energy density,and long life.The positive electrode material has a decisive influence on the battery’s operating voltage,energy density and other performance,which are the bottleneck for the further improvement of the battery performance nowadays.Compared with other cathode materials,ternary cathode materials have the advantages of high capacity,low cost,and environmental friendliness,which are current research hotspots.In recent years,with the further pursuit of cost and energy density,ternary materials have gradually developed in the direction of rich nickel.However,the specific mechanism by which low-doping elements Mn/Al and Co play a role in nickel-rich ternary materials is still unclear.In order to clarify the mechanism of low doping elements and point out the direction of further improvement of material properties,this paper compares and studies the performances of the two groups of LiNi_0.8Co_0.1Mn_0.1O₂ and LiNi_0.85Co_0.1Al_0.05O₂,as well as LiNi_0.8Co_0.1Mn_0.1O₂ and LiNi_0.8Co_0.15Mn_0.05O₂materials.This research mainly includes the following two aspects:（1）In order to clarify the difference in the mechanism of Mn/Al,the two most commonly used nickel-rich ternary cathode materials,LiNi_0.8Co_0.1Mn_0.1O₂ and LiNi_0.85Co_0.1Al_0.05O₂,were synthesized by the co-precipitation method.Through the characterization of the phase composition and simulation calculation analysis of the two materials before and after the cycle,it is found that the low-doping element Mn/Al enhances the stability of the transition metal layer,effectively inhibits the migration and dissolution of Ni element during the long cycle of the material,thereby ensuring the long cycle life of the material.At the same time,since the bonding stability of Mn to O in the transition metal layer of the nickel-based material is weaker than that of Al to O,this causes the Mn in LiNi_0.8Co_0.1Mn_0.1O₂ to be more likely to dissolve during the cycle,which intensifies the Li/Ni anti-occupancy defects and irreversible phase transitions in the material.（2）In order to clarify the mechanism of Co,two nickel-rich ternary cathode materials with the same Ni content,LiNi_0.8Co_0.1Mn_0.1O₂ and LiNi_0.8Co_0.15Mn_0.05O₂,were synthesized by co-precipitation method.It is found that the structural stability of LiNi_0.8Co_0.15Mn_0.05O₂ with higher Co content is better than that of LiNi_0.8Co_0.1Mn_0.1O₂when the voltage exceeds 4.3 V during charge and discharge cycles.This is because the incorporation of more Co atoms inhibits the lattice shrinkage of the material more effectively during the delithiation process,so that the lattice expansion of the material in the deep delithiation process in the direction perpendicular to the lithium layer is slowed down.As a result,the material plays an improved structural stability under high voltage.Therefore,LiNi_0.8Co_0.15Mn_0.05O₂ has a slighter volume expansion effect than LiNi_0.8Co_0.1Mn_0.1O₂ during the cycle,which prevents serious cracks in the material particles,thereby avoiding the continuous decomposition of the electrolyte,and effectively alleviating the continuous increase in interface impedance to ensure the rapid transmission of lithium ions.In summary,the trace doping element of Mn/Al in the high-nickel ternary material mainly plays a role in stabilizing the transition metal layer of the material,which can inhibit the migration and precipitation of Ni atoms in the transition metal layer during the long cycle,but this inhibitory effect of Al is more significant than that of Mn.The incorporation of Co element can effectively inhibit the expansion of the lattice in the direction perpendicular to the lithium layer during the delithiation of the material,resulting in an improved stability of the nickel-rich ternary material under high voltage.