Niobium Doping Of Nickel Rich NCM Concentration Gradient Ternary Cathode Materials

As the market places higher and higher requirements on the energy density and endurance of lithium-ion battery cathode materials,high-nickel ternary materials have gradually received more attention.As the Ni content of the system increases,the specific capacity of the ternary material increases,but the lithium-nickel mixing becomes serious,the stability decreases.In addition,the material alkaline behaves higher and easier to absorb water.Therefore,the modification of high nickel ternary materials has become the research hotspot in recent years.Based on the existing co-precipitation synthesis process,this article uses Nb element to dope the high nickel ternary materials,and explores the influence of doping method,doping amount,type of Nb source and particle size of Nb source on the modification effect.And the mechanism of Nb element doping in high nickel ternary materials(Li Ni_0.8Co_0.1Mn_0.1O₂,NCM811)are preliminary explored.The subject explored the effect of the doping method.The liquid-phase precipitation method and the solid-phase calcination method were used to dope in the same proportion.The discharge specific capacity of material prepared by the latter was164.90 m Ah/g at 1 C rate,which is better than the former（137.90 m Ah/g at 1 C rate）,and its preparation cost is lower,so the solid-phase calcination method was determined to be the better doping method.The influence of the doping amount was explored.It was set as 1%and 3%.The results showed that overall discharge specific capacity decreased 20 m Ah/g approximately at 1 C rate when the doping amount was increased to 3%,and it couldn’t improve the cycle stability much.The effect of Nb sources used for doping was explored,three grades of Nb sources including optical grade niobium pentoxide（OG）,hydrated niobium pentoxide（HY340）and niobium oxyphosphate（Nb P）with doping amount of 1%were uesd.The results indicated that the discharge specific capacity has decreased after doping of HY340 and Nb P,its discharge specific capacity at 1 C rate were 147.90 m Ah/g and 147.10 m Ah/g respectively,while the OG doping materials behave increased discharge specific capacity（167.90 m Ah/g）and cycle stability.The doping effects of optical grade niobium pentoxide with different particle sizes were compared,it could be found that the XRD peak strength became weaker when the smaller particle size Nb₂O₅doped to the system,and the microscopic morphology characterized by SEM was also different.The most important thing is that the discharge specific capacity decreased larger（15 m Ah/g）,which may due to the incorporation of more Nb elements into the crystal lattice,leading to a certain degree of damage to the ion order and not conducive to Li⁺diffusion.All in all,this subject conducts Nb doping modification research on the high-nickel ternary material NCM-811,optimizes the doping method,doping amount,niobium source and the particle size of niobium source.The results show that proper doping has little impact on the specific discharge capacity,but its cycle stability have been greatly improved.The capacity of 1%Nb₂O₅doping material in 1 C rate after 100 cycles at room temperature has not decreased at all,which is superior to intrinsic materials.In addition,the results indicate that Nb doping can expand the lattice parameters and interlayer distance,reduce the generation of Ni²⁺and the degree of lithium-nickel mixing,slow down the appearance of micro-cracks and particle breakage during the cycles,and improves cycle stability.