Studies On Modification And Electrochemical Performance Of High Nickel Ternary Cathode Material LiNi_0.8Co_0.1Mn_0.1O₂

Layered LiNi_xCo_yMn_1-x-yO₂ has attracted more attention due to its high discharge specific capacity,but the poor cycle performance caused by poor structural stability limits its wide application.In this paper,the lithiation,doping and coating of LiNi_0.8Co_0.1Mn_0.1O₂ materials were studied.The product structure was measured by crystal structure and morphology.The electrochemical performance of materials was evaluated by cyclic performance,rate performance,cyclic voltammetry curve and alternating current impedance.During the lithiation of LiNi_0.8Co_0.1Mn_0.1O₂ materials,the structure,morphology,and electrochemical performance of the cathode materials prepared by different calcination temperatures and lithium ratios were mainly explored.The results show that the fixed lithium ratio,with the increase of the calcination temperature,the size of the secondary particles will gradually grow,and the crystal structure of the material is improved.When the calcination temperature reaches 800°C,the material has a better morphology and a higher discharge specific capacity,and exhibits excellent cycle performance and rate performance.The sintering of the secondary particles occurs when the temperature continues to rise,which destroys the structure of material,leading to a significant increase in cation mixing and a sharp fading in capacity.Additionally,by fixing the calcination temperature,the effects of different lithium ratios on the properties of the materials were studied.When the lithium ratio is relatively low,the lithium element volatilizes during the calcination process,makes it easier for Ni²⁺to enter the Lilayer and causes Li/Ni mixing.With the increase of lithium ratio,the Li/Ni mixing phenomenon is suppressed,the initial discharge capacity of the material increases and the irreversible loss decreases.When the lithium ratio is 1.07:1,the LiNi_0.8Co_0.1Mn_0.1O₂ material has the highest discharge specific capacity of 176.1 m Ah·g^-1 and the best rate performance.After the lithium ratio exceeds 1.07:1,too much residual lithium on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ material will also affect the performance of the electrode material.Therefore,the optimal calcination temperature is 800℃,and the optimal lithium ratio is 1.07:1.On this basis,the study of LiNi_0.8Co_0.1Mn_0.1O₂ material doped with sodium and coated with lithium molybdate was carried out.In the study of LiNi_0.8Co_0.1Mn_0.1O₂ material doping,Na element was successfully doped into LiNi_0.8Co_0.1Mn_0.1O₂ by solid-state method,and the effect of Na doping on the performance of LiNi_0.8Co_0.1Mn_0.1O₂ was explored.The results show that Na element doping can effectively reduce the Li/Ni mixing and improve the structural stability of the material.Li_0.97Na_0.03Ni_0.8Co_0.1Mn_0.1O₂ material shows excellent rate performance.When the voltage increases to 10 C(1 C=200 m A·g^-1),the discharge specific capacity of the modified material reaches 140.5 m Ah·g^-1,while that of the unmodified material is only 125.5 m Ah·g^-1.When the current intensity decreases from 10 C to 0.5 C,the discharge specific capacity of Li_0.97Na_0.03Ni_0.8Co_0.1Mn_0.1O₂ is also higher than that of the undoped sample.Li_0.97Na_0.03Ni_0.8Co_0.1Mn_0.1O₂ also shows excellent cycle performance under high current density.In the voltage range of 2.8～4.3 V,the capacity retention of the doped sample can reach 64.33%after 100 cycles at 10 C,while the undoped is only 35.01%.By testing the CV curve and EIS during battery cycling,it is found that the presence of Na ions can effectively suppress electrode polarization and improve lithium ion diffusion,therefore,the electrochemical performance of the material is improved.Finally,the effect of lithium molybdate coating on the properties of LiNi_0.8Co_0.1Mn_0.1O₂materials was studied.The results show that the coated material shows better electrochemical performance,the polarization phenomenon and irreversible capacity loss are reduced.The presence of the Li₂Mo O₄ coating eliminates"dead lithium"on the surface and provides a"protective shell"for the LiNi_0.8Co_0.1Mn_0.1O₂ material,which suppresses the occurrence of side reactions and reduce the erosion of core materials by HF.Although the initial specific discharge capacity of the coated samples is only 165.8 m Ah·g^-1,the capacity retention rate is as high as90.59%after 100 cycles at 1 C,which is significantly higher than that of the uncoated ones.Additionally,the electrode after disassembly was disassembled and tested.It is found that the solid electrolyte interface film（SEI）on the surface of the coated sample is significantly thinner than that of the uncoated,which indicates that the formation of the film reduces the interface impedance.