The Investigation On Synthesis And Properties Of Core-Shell Structured Lithium Nickel Aluminum Oxide Cathode Materials

As a typical layered structure cathode material of lithium ion battery,LiNi_0.85-x.85-x Co_0.15Al_xO₂exhibits the great application potential for the advantages of high capacity and low cost.In NCA cathode,general y speaking,the higher content of Ni in the cathode,the higher the capacity of the battery,but it reduces the structural stability of the cathode and thus reduces the cycling performance and thermal stability.Co and Al make contributions to stabilizing the structure of the material,the increase of their contents can improve cycling stability and thermal stability but reduce the capacity of the cathode.Therefore,the capacity,cycle life and thermal stability of NCA cathode materials restrict each other,which affects the large-scale application of the materials.According to the above problems,LiNi_0.85-x.85-x Co_0.15Al_x O₂?0?x?0.25?materials were chosen to research in this paper,and the effects of various proportion of Al on the properties of LiNi_0.85-x.85-x Co_0.15Al_x O₂?0?x?0.25?were systematically investigated.Based on the optimizing Al content,NCA cathode material was designed to different core-shell structures,and then the influence of different core-shelle structure designs on the performance of NCA cathodes was further explored.The specific research content as follows:1.The influence of various Al content on the performance of LiNi_0.85-x.85-x Co_0.15Al_xO₂?0?x?0.25?was investigated.A series of LiNi_0.85-x.85-x Co_0.15Al_x O₂?0?x?0.25?with different Al content were synthesized from NaAlO₂ as the aluminium source via co-precipitation and high temperature solid phase method.The element content and distribution of the samples are analyzed,the results show that the designed NCA samples with different Al content have been successfully prepared.According to the structure and electrochemical properties results,the increasing Al content contributes to enhancing the layered structure orderliness and structure stability,decreasing the cation mixing degree of NCA cathode materials,and improving the cycle stability and thermal stability.However,the high Al content will significantly reduce the capacity of the cathode material.Among them,LiNi_0.85Co_0.15Al_0.05O₂ exhibits the relative ly high discharge capacity and good cycle performance and thermal stability.2.Based on the above results,to take into account the high capacity,long life and high thermal stability of NCA cathode materials,a series of core-shell structured cathode materia ls with total component of LiNi_0.8Co_0.15Al_0.05O₂ were designed,synthesized and explored.High-nickel LiNi_0.85Co_0.15O₂ was selected as the core to provide the capacity,Al-contained LiNi_0.85-x.85-x Co_0.15Al_x O₂?0?x?0.25?was selected as the shel s to improve the structure stability.The influence of shell thickness and shell composition on the properties of cathodes was further explored.The results show that all the core-shelled cathode materials exhibit the superior electrochemical properties than the homogenous one.Shell thickness and shell compositio n have the significant impact on the performance of the cathodes.Among the core-shell structured materials,the Li[?Ni0.85Co0.15?2/3?Ni0.7Co0.15Al0.15?1/3]O2 cathode combining the advantage of core with high capacity and shell with high structure stability exhibits the excelle nt electrochemical properties.The results will provide an inspiration and reference for further understanding and designing core-shell structure cathode materials.