Preparation And Modification Of Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material

Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）cathode materials have been extensively utilized due to their superior energy density,high discharge capacity and wide operating voltage.However,rapid capacity decay and inferior rate capability hinder the practical utilization of NCM811 in lithium-ion batteries.In this study,a two-step sol-gel method was successfully employed to synthesize pure NCM811.XRD and SEM were applied to scientifically study the influence of sintering temperature,holding time and lithium amount on the phase structure and micromorphology of NCM811.Moreover,multichannel galvanostatic system and electrochemical workstation were carried out to test charge-discharge performance and EIS.The results clarified that NCM811 synthesized at 750℃for 15 h with lithium amount of 1.09exhibited the best developed layered structure,appropriate particle size,uniformly distributed particles and minimum charge transfer impedance.Meanwhile,NCM811demonstrated dominant electrochemical properties with 176.3 m Ah/g at 1 C and capacity retained over 79%after 100 cycles.The discharge capacity at 5 C is 108.3 m Ah/g.Nb⁵⁺with strong Nb-O bonding energy（753 k J/mol）,optimal radius（0.64（?））and high valence state was introduced into NCM811 structure.Multichannel galvanostatic system,CV and EIS were employed to determine the optimal doping amount.In addition,XRD,SEM,TEM,EDS and XPS were utilized to investigate the influence of Nb doping on electrochemical performance of NCM811 and its internal mechanism.Consequently,NCM811 with 1%（N2）doping amount of Nb⁵⁺exhibited dominate performance.To be specific,the structural stability was remarkably improved and polarization degree was significantly reduced.Besides,N2 sample exhibited minimal Li/Ni mixing and maximum D⁺_Li.Furthermore,N2 rendered splendid performance with discharge capacity of 181.6m Ah/g,cyclic retention rate of 94.55%(2.7-4.3 V,100^th)and rate capability of 151.5m Ah/g at 5 C.NCM811 was modified by Sm.With an optimal modification amount（S2 sample）,Sm³⁺was successfully doped into the crystal lattice of NCM811 and Sm₂O₃ coating layer was uniformly formed on the surface of the cathode.The results indicated that lattice distance of NCM811 was enlarged,conductivity was improved and impedance was reduced by Sm modification.What’s more,Sm modification was able to stabilize the crystal structure of NCM811,inhibit the erosion of electrolyte on cathode effectively and restrain the side reactions between NCM811 and electrolyte.As a result,S2 sample exhibited the highest initial discharge capacity of 184.2 m Ah/g（1 C）,remarkable capacity retention rate of 94.19%(2.7-4.3 V,100^th)and superior rate capability of 152.2 m Ah/g at5C.It is noteworthy that when the cut off voltage was enhanced to 4.5 V,the cyclic retention rate of S2 is still as high as 91.46%.