Preparation And Electrochemical Performance Of NCM In Lithium Ion Batteries

The R&D of lithium ion power battery with high energy and power density is one of effective strategies to relieve the issues of the current society on energy and environment nowadays.The key technological problem about lithium ion power batter with high energy and power density depends on seeking for the appropriate cathode materials.Recently,the layered LiNi_xCo_yMn_zO₂ with the synergistic advantage among LiCoO₂、LiNiO₂ and LiMnO₂ has been widely paid attention in lithium ion powder battery industry due to high specific capacity,outstanding cycling performance and good thermal stability.Specially,LiNi_xCo_yMn_zO₂ with high Ni ratio has inspired the great interest of researcher because of the quite high specific capacity due to high Ni content.However,the morphology,size,uniform and easy Li/Ni disorder of the LiNi_xCo_yMn_z O₂ cathode materials affect significantly its electrochemical performance,which is determined by the preparation method and condition.Therefore,the suitable preparation method to prepare the uniform spherical nanomaterial is of pivotal importance to the implementation of industrialization of LiNi_xCo_yMn_zO₂ cathode material.The technological conditions were explored to prepare LiNi_xCo_yMn_zO₂ cathode material by the co-precipitation method,hydrothermal method combined with high temperature solid phase method and sol-gel method in this thesis.The electrochemical performance of the as-obtained LiNi_xCo_yMn_z O₂ cathode material was investigated to elucidate the advantage of various preparation method.Furthermore,the electrochemical performance of the LiNi_xCo_yMn_zO₂ cathode material with high Ni ratio prepared by sol-gel method was investigated as well.The details are as following:1.The LiNi_1/3Co_1/3Mn_1/3O₂ spherical uniform particles were prepared successfully by hydroxide co-precipitation method and their electrochemical performances were investigated.The results show that the as-obtained cathode materials deliver an initial specific capacity of 139.1 mAh/g at a current density of 400 mA/g and the capacity retention rate is up to 93%when cycled after 30 cycles.The good cycling performance is obtained although the initial specific capacity is not much high,indicating the good stability of the as-obtained cathode materials by co-precipitation method.2.The hollow LiNi_1/3Co_1/3Mn_1/3O₂ spherical uniform particles were fabricated successfully by a hydrothermal method combined with solid phase method at high temperature and their electrochemical performances were investigated.The results indicate that the as-obtained cathode materials present a high initial specific capacity of 185 mAh/g at a current density of 400 mA/g,which is attributed to short path of electronic transportation and lithium-ion diffusion due to the unique hollow structured materials,indicating the serious effect of material morphology on the electrochemical performance.3.The LiNi_1/3Co_1/3Mn_1/3O₂ uniform nanoparticles were prepared successfully by sol-gel method and their electrochemical performances were investigated.The results show that the as-obtained cathode materials deliver an initial specific capacity of as high as198.6 mAh/g at a current density of 100 mA/g and the specific discharge capacity also remains 116.2 mAh/g when cycled after 100 cycles,revealing that the sol-gel method is potential in preparing the ternary cathode materials with excellent electrochemical performance.4.The LiNi_0.8Co_0.1Mn_0.1O₂ with high Ni content cathode material was prepared successfully by sol-gel method and its electrochemical performance was investigated.The results show the as-obtained cathode materials with high Ni content deliver an initial discharge specific capacity of as high as 201.6 mAh/g whilst the outstanding cycling performance and high rate capability is obtained,indicating that the ternary cathode materials with high Ni content could be prepared by sol-gel method.