LiNi_0.95Co_0.02Mn_0.03O₂ Cathode Materials Synthesis And Surface Modification

Ni-rich cathode materials have become one of the most promising cathode materials for lithium-ion batteries due to its high energy density and low manufacturing cost.However,poor cycle stability hinders the commercialization of the cathode materials.In this thesis,LiNi0.95Co0.2Mn0.3O2 cathode materials were successfully synthesized by co-precipitation method combined with high temperature solid phase method,and the effect of preparation parameters on Ni-rich cathode materials was investigated.Then,LiNi_0.95Co_0.02Mn_0.03O₂ cathode materials were treated with NH3,and the influence of NH3 treatment on the interface structure of materials and the improvement mechanism of electrochemical performance were investigated.（1）In the process of preparing Ni0.95Co0.02Mn0.03（OH）2 by co-precipitation method,pH determines the nucleation rate of the precursor during the reaction.The amm onia concentration mainly affects the growth rate of the precursor.The reaction time significantly affects the sphericity and size of the precursor.In the synthesis process of LiNi_0.95Co_0.02Mn_0.03O₂ cathode material by solid-state method,the sintering temperature and sintering time have a significant effect on the primary particle size of the ternary cathode material.The higher temperature causes the primary particle to grow,which leads to the growth of the lithium ions diffusion path and the decrease of the electrochemical performance of the material.Lower sintering temperature or shorter sintering time will lead to a series of problems such as incomplete lattice development.The amount of excess lithium and oxygen flow have significant effects on the crystal structure development Based on the above rules,the first discharge capacity of the cathode material prepared by adjusting process parameters is 225.1 mAh g-1 at current density of 0.2 C,and the initial coulombic efficiency is 89.9%.（2）LiNi_0.95Co_0.02Mn_0.03O₂ cathode material was treated with MH3,physical characterization results show that the material generated NiO phase at materials surface,compared with the unmodified material,inactive NiO phase enhance interfaces stability between LiNi_0.95Co_0.02Mn_0.03O₂ material and electrolyte.The electrochemical characterization results show that the modified sample has a significant improvement in electrochemical performance.After 200 cycles at 1 C,the capacity retention of LiNi_0.95Co_0.02Mn_0.03O₂ increases from 67.6% to 81.1%.