The Study Of XLi₂MnO₃·?1-x?Li[Ni_0.5Co_0.2Mn_0.3]O₂ Core-Shell Structured As Cathode Materials For Lithium-Ion Batteries

As the application of lithium-ion batteries continues to expand to higher energy consumption devices,such as electrical energy storage systems?EES?and electric vehicles?EVs?,the development of higher energy density electrode materials is becoming more essential.Although NCM layered ternary materials have some advantages by elemental synergies,it cannot meet the requirements of high performance lithium-ion battery recently.Lithium-rich layered materials which can accommodate more than one unit of Li per molecule,attracted the most attention in the recent years.The goal of this article is to synthesize a core-shell like structured composite cathode material.The core is Li[Ni_0.5Co_0.2Mn_0.3]O₂ which has a high-content of Ni,while the shell is Li₂MnO₃ which could stabilize the particles.In order to obtain the best ratio of xLi₂MnO₃·?1-x?Li[Ni_0.5Co_0.2Mn_0.3]O₂ core-shell structured material,the ratio of 0.25,0.33 and 0.50 were synthesized by a ball milling-annealing process.The structure of Li₂MnO₃ was identified by the mean of XRD.The electrochemical performance showed that the material exhibited the highest discharge capacity when the synthesis ratio was 0.33.The constant current tests were carried out in the voltage range of 2.0⁴.8 V with the current of 20 mA/g.The cell exhibited an initial discharge capacity of 181.3 mAh/g with 88.9%capacity retention after 50 cycles.Smaller sized Li₂MnO₃ particles synthesized by PVP sol-gel method were used to improve the core-shell structure.TEM and SEAD were used to detect both Li₂MnO₃and Li[Ni_0.5Co_0.2Mn_0.3]O₂ in LMO₂?s?sample.The result showed the material exhibited excellent structurall compatibility.The constant current tests were carried out under the same conditions as before.And cell exhibited a discharge capacity of 240.7 mAh/g which was better than the LMO₂?l?cell.The diffusion coefficient of the lithium-ion and charge transfer resistance were studied by electrochemical work station to analyze the different performance between LMO₂?s?and LMO₂?l?cell.The result showed that the diffusion of lithium-ions can be reduced by the thickness of shell and the smaller size of Li₂MnO₃ which exhibited a higher discharge capacity.In order to increase the electronic conductivity of LMO?s?,the carbon coated LMO₂?s?was synthesized by using glucose,acetylene black and polyving akohol as carbon source.The results showed that LMO₂?s?@C1?carbon source of acetylene black?had the best rate performance.The constant current tests were carried out in the voltage range of 2.0⁴.8 V with the current of 200 mA/g.The cell exhibited an initial discharge capacity of 226.5 mAh/g,and reached a capacity of 155.4 mAh/g even after 50 cycles.