Modification And Electrochemical Performance Of High Nickel Ternary Cathode Material

The Ni-rich ternary cathode material LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）is considered one of the most promising cathode materials due to its high discharge capacity and working voltage.However,the poor cycling stability and safety limit the widespread application of NCM811,mainly due to its inherent structural instability and high surface reactivity during the lithium removal process.Based on this,this article proposes various simple and effective modification strategies to optimize and modify NCM811,improving its high potential electrochemical performance and revealing its modification mechanism.The specific research content is as follows:（1）The NCM811 electrode sheet was modified with graphene as a whole coating.The cycling performance and rate performance of the graphene-coated sample were significantly higher than those of the unmodified sample,indicating that the graphene coating layer has a protective effect on the electrode sheet,inhibiting the electrode/electrolyte interface side reactions,alleviating secondary particle fragmentation,and maintaining the structural stability of the electrode sheet.In addition,the graphene coating layer can effectively inhibit the c-axis expansion of NCM811,thus stabilizing the electrode structure.（2）The LiCoPO₄layer was coated on the surface of NCM811 particles.1.0 wt%LiCoPO₄-coated sample still had a capacity of 156.5 mAh g^-1after 100 cycles in the high voltage range of 3-4.6 V,with a capacity retention rate of 87.47%,while the capacity of NCM sample was only 96.9 mAh g^-1after 100 cycles,with a corresponding capacity retention rate of 55.90%.The LiCoPO₄coating layer inhibits the side reaction between NCM811 and electrolyte and reduces the charge transfer impedance on the surface of the material;on the other hand,it effectively inhibits the grain boundary cracking caused by internal stress,prevents particle fragmentation and stabilizes the crystal structure of NCM811.（3）NCM811 particles were coated with La_0.7Sr_0.3CoO₃by sol-gel method.The electrochemical test results showed that the sample with 1%coating amount could maintain a discharge capacity of 174.5 mAh g^-1after 100 cycles in the voltage range of3-4.5 V,with a capacity retention rate of 90.74%.The presence of La_0.7Sr_0.3CoO₃optimized the lithium ion and electron migration environment of the ternary cathode material,suppressed surface side reactions and surface structural phase changes,and reduced polarization phenomena and stabilized the structure of NCM811,thereby improving the electrochemical performance of NCM811.