Preparation And Modification Of Ni-rich Cobalt-Free LiNi_0.8Mn_0.2O₂ Cathode Material

The transformation from Ni-rich LiNi_1-x-yCo_xMn_yO₂ cathodes research to Ni-rich Co-free LiNi_1-xMn_xO₂ cathodes is considered an effective solution to reduce the cost of cathode materials.However,severe Li⁺/Ni²⁺mixing,structural instability,poor cycling stability,and thermal stability are the main obstacles to its practical application.Based on this,the effects of bulk doping and surface coating on the structure and electrochemical performance of Ni-rich Co-free LiNi_0.8Mn_0.2O₂ material were studied in this paper.Firstly,LiNi_0.8Mn_0.2-xAl_xO₂（0≤x≤0.2）materials were synthesized by co-precipitation combined with the high-temperature solid-state method.The influence of Al content on the properties of Ni-rich LiNi_0.8Mn_0.2O₂ cathode material was investigated.The results of chemical composition and element analysis of the samples indicate that the designed Al-doped cathode materials with different contents have been successfully prepared.The material structure and electrochemical test results showed that the increase in Al content can enhance the layered structure orderliness,reduce the Li⁺/Ni²⁺mixing,inhibit the H2-H3 phase transition,reduce polarization,and reduce the charge transfer resistance,which is conducive to improving the electrochemical performance of the material.However,excessive Al doping can lead to the formation of a secondary phase,significantly reducing the capacity and performance of the cathode.Among them,LiNi_0.8Mn_0.15Al_0.05O₂ material exhibits the best electrochemical performance,with a discharge capacity of 183.1 m Ah g^-1 for the first cycle at 3-4.3 V,0.1 C,and a capacity retention of 91.97%after 300 cycles at 0.5 C while the discharge capacity of the undoped material under the same conditions is 179.1 m A g^-1 and the capacity retention is 78.06%.Secondly,LiNi_0.8Mn_0.2O₂ was coated with boron oxide and aluminum oxide respectively,and its influence on the properties of LiNi_0.8Mn_0.2O₂ cathode material was studied.The result shows that boron oxide coating does not alter the main structure of LiNi_0.8Mn_0.2O₂ and can effectively improve the cycling performance and reduce the charge transfer resistance of the material.When the coating amount is 1wt.%,the cathode material has the best performance,with a discharge capacity of 174.7 m A g^-1for the first cycle at 3-4.3 V,0.1 C,and a capacity retention of 98.24%after 300 cycles at 0.5 C.In addition,boron oxide coating can significantly improve the cycling performance of LiNi_0.8Mn_0.2O₂ cathode material at high voltage,with capacity retention is 85.61%after 300 cycles at 3-4.5 V,0.5 C.Aluminum oxide coating does not change the morphology and crystal structure of pristine material.Adding Li OH appropriately during the coating process can improve the electrochemical performance of the material.Under the studied conditions,the cathode has the best performance when the aluminum oxide coating amount is 1 wt.%,and the Li OH addition amount is 5 mol/%,with a discharge capacity of 186.8 m A g^-1 for the first cycle at 3-4.3 V,0.1 C,and a capacity retention of 96.66%after 300 cycles at 0.5 C.The improvement of electrochemical performance of cathode materials coated with boron oxide and aluminum oxide is related to the fact that the coating can effectively reduce the side reaction between active electrodes and electrolyte,inhibit the dissolution of transition metal ions,and improve the structural stability of cathodes.In summary,this paper focuses on the Ni-rich Co-free LiNi_0.8Mn_0.2O₂ cathode material modified by doping and coating methods.Under the conditions studied,doping and coating did not change the main structure of the layered materials.Among them,Al doping can reduce the Li⁺/Ni²⁺mixing,inhibit the phase transformation in the electrochemical reaction process,and improve the structural stability of the material.Boron oxide and aluminum oxide coating can protect cathode materials from the corrosion of electrolyte and improve the interface and structural stability of cathode materials.These studies provide a reference for improving the performance of LiNi_0.8Mn_0.2O₂ cathode materials.