Surface Modification And Electrochemical Performance Of Ni-Rich Cathode Material (LiNi_0.6Co_0.2Mn_0.2O₂) For Lithium Ion Battery

In recent decades,due to increasing attention to global warming,greenhouse gas emissions,and the depletion of fossil fuels,electric vehicles?EV?have received widespread attention.Considering the reduction of CO₂ emissions and global environmental issues,electric vehicles have been widely accepted by the automotive industry.Lithium-ion batteries are lightweight,fast charging,high energy density,low self discharge,and long life.They have attracted widespread attention in electric vehicle applications.The rapid expansion of the electric vehicle market has imposed more stringent requirements on the energy density of the cathode material.LiNi_0.6Co_0.2Mn_0.2O₂,as a high energy density cathode material for lithium-ion batteries,has a good market prospect.Compared with traditional anode materials such as LiFePO₄ and LiCoO₂,it has a higher energy density.However,LiNi_0.6Co_0.2Mn_0.2O₂?NCM?,a nickel-rich cathode material,still has a series of problems that need to be solved,such as the serious loss of discharge capacity for the first time,the storage environment is extremely harsh,and the phase change is prone to occur during cycling.As a result,their service life is severely limited.In view of the above-mentioned series of problems,in this paper,we use coating to modify the nickel-rich anode material LiNi_0.6Co_0.2Mn_0.2O₂,and study its electrochemical performance.The results are as follows:?1?Preparation and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂@Al₂O₃composite.In this study,we used a sol-gel method to synthesize an alumina?Al₂O₃?coating on the surface of NCM materials.Our research shows that Al₂O₃ coating significantly improves the capacity retention and rate performance of NCM on lithium ion batteries,and its resistance to moisture in the air is significantly improved.Constant current charge and discharge tests show that the 2 wt%Al₂O₃ coated samples have the best electrochemical performance.It provides a discharge capacity of 175 mAh/g in a potential window of 1 C rate and a potential window of 2.7-4.3 V,which is better than171 mAh/g of the raw material,and its capacity retention rate after 500 cycles is 80%,which is higher than 70%of the raw material.In addition,the best sample has a high rate capacity of 152 mAh/g at a 10 C rate,and the value is much higher than the original sample.The physical characterization results show that the improved electrochemical performance can be attributed to the synergistic effect of Al₂O₃coating and Al doping.The enlarged interlayer spacing produced by replacing Li⁺with Al³⁺facilitates lithium ion diffusion.In addition,the Al₂O₃ protective layer can hinder the contact between the electrolyte and the active material,so that the corrosion of the electrode structure is effectively reduced,thereby suppressing the increase in impedance during the cycle.?2?Preparation and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂@LiAlO₂composite.In this study,we introduced a small amount of LiAlO₂ on the surface of NCM through a combination of freeze-drying and high-temperature solid-phase methods to improve its rate and cycle performance.X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,high-resolution transmission electron microscopy?HRTEM?,and energy dispersive spectroscopy?EDS?results confirmed that the LiAlO₂ coating was firmly wrapped on the NCM surface.Modified NCM has excellent rate performance and excellent cycle retention.Specifically,the NCM material coated with 3 mol%LiAlO₂ showed a discharge capacity of 163 mAh/g at a rate of 10 C,and 84.0%Capacity retention rate after 500 cycles at a rate of 1 C?2.7-4.5 V?.The capacity retention rate of the original NCM was only 41.2%.It's excellent electrochemical performance is attributed to the LiAlO₂ surface coating.During the cyclic charging/discharging,it suppresses the interface side reaction between the active material and the electrolyte,enhances the lithium ion diffusion between the electrode/electrolyte interface and prevents the active material from being crushed.?3?Preparation and electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂@Li₂TiO₃composite.In this study,we introduced a small amount of Li₂TiO₃ on the surface of NCM through a combination of freeze-drying and high-temperature solid-phase methods to improve its rate and cycle performance.Transmission electron microscopy?TEM?analysis showed that the spherical particles were completely covered by crystalline Li₂TiO₃ with an average thickness of 5 nm.Electrochemical tests show that compared with the original material,the modified NCM material has excellent reversible capacity,good cycle performance and rate characteristics,and has a higher lithium ion diffusion coefficient and a better differential capacity curve.In particular,after 1mol%Li₂TiO₃ modified NCM sample was subjected to 500 high voltage cycles?cutoff charge of 4.5 V?at a rate of 1 C,the capacity retention rate reached 84.4%.The improved electrochemical performance is attributed to the removal of lithium residues and the unique Li₂TiO₃ structure.It is said that the removal of lithium residues can reduce the side reactions between Li₂O and the electrolyte,while the unique Li₂TiO₃ structure can buffer the core and shell volume changes during cycling,enhance the lithium ion diffusion ability of the composite,and combine the Li₂TiO₃coating and Ti doping miscellaneous advantages.