Prepration And Modification Of Single Crystal Nickel-rich Cathode Materials

Lithium-ion batteries are now widely used in electric vehicles,but still face the challenges of energy density and safety issues.Compared with other cathodes,Ni-rich cathode materials（LiNi_xCo_yMn_zO₂,x+y+z=1 and x>0.6）have the advantage of high energy density,which are promising cathode materials.Ni-rich cathodes generate severe micro-cracking during long cycles,resulting in rapid capacity degradation.Single-crystal cathodes can effectively mitigate interfacial side reactions with electrolyte,inhibit the formation of microcracks and extend cycling life.Single crystallization is a significant way to improve the cycling and safety performance of Ni-rich cathode materials.In this work,single-crystal LiNi_0.9Co_0.05Mn_0.05O₂（SC-NCM90）is prepared by short-time high temperature sintering.The prepared SC-NCM90has a high degree of single crystallization and regular particle morphology.Meanwhile,single crystallization of NCM90 effectively inhibits the generation of micro cracks during the cycling,and improves the cycling stability of NCM90 cathode materials.At last,the effects of Zr doping on structure and performance of SC-NCM90 are studied.The main research contents of this thesis are as follows.1.Ni_0.9Co_0.05Mn_0.05（OH）₂precursor is prepared by co-precipitation method and a 15min and 1000 ^oC high-temperature section is introduced in the conventional sintering conditions to prepare single-crystal NCM90 cathode materials.SC-NCM90 has a good single crystal morphology with an initial discharge capacity of 205.1 m Ah g^-1.At the same time,there are no micro cracks appearing in the single crystals cross section after cycling and the cycling stability is significantly improved.The influence of high-temperature section at different positions on the morphology and properties of NCM90 is discussed.The experiments show that the particle is larger and the shape is more octahedron-like when the high temperature section locates earlier,but the degree of Li/Ni mixing also increases,resulting in the decrease of discharge capacity.2.The SC-NCM90 is further modified by Zr doping.The structural and electrochemical properties of SC-NCM90 doped with different concentrations of Zr are compared.It is found that 0.75%Zr doping can stabilize the electrode structure and improve the electrochemical performance of the SC-NCM90.Because the Zr-O bond energy is stronger than the transition metal-oxygen bond energy,Zr doping can stabilize the lattice structure of the material.