焙烧气氛对LiNi0.5Mn0.5O2中Li/Ni混排及电化学性能的影响

摘要

Layered LiNi0.5Mn0.5O2 was synthesized by a solid state reaction method under air or oxygen atmosphere.The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), and charge-discharge tests.The results show that the LiNi0.5Mn0.5O2 synthesized by the solid state reaction method under both air and oxygen atmospheres give a pure phase and good crystallinity, however, their electrochemical performance differs.The material synthesized under oxygen gives better electrochemical performance including a higher first discharge capacity and better cycle stability.At a rate of 0.1C the first discharge capacity of the material synthesized under oxygen was found to be 178 mAh·g-1.After 50 charge and discharge cycles the discharge capacity was still 165 mAh·g-1 giving a capacity retention rate of 92.7％.For the material synthesized under air, the first discharge capacity at a rate of 0.1C was found to be 164 mAh·g-1.After 50 charge and discharge cycles, the discharge capacity was 137 mAh·g-1 giving a capacity retention rate of 83.5％.The reason for the material synthesized under oxygen having better electrochemical performance than the material synthesized under air is due to the oxygen atmosphere suppressing the Li/Ni exchange ratio in LiNi0.5Mn0.5O2.%用固相法分别在氧气和空气气氛下合成了层状锂离子电池正极材料LiNi0.5Mn0.5O2,采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、电化学阻抗谱(EIS)及充放电性能测试对其结构、形貌和电化学性质进行表征,用Rietveld精修计算晶体结构中的Li/Ni混排率,研究了混排率与电化学性能的关系.结果显示,在不同的焙烧气氛下均能合成出纯相和结晶性良好的LiNi0.5Mn0.5O2,但两种材料在电化学性能上存在一定的差异.氧气气氛下焙烧合成的材料在首次放电容量,循环稳定性方面均优于空气气氛下合成的材料,在0.1 C充放电条件下氧气气氛下焙烧得到的LiNi0.5Mn0.5O2材料首次放电容量达到178 mAh·g-1,充放电循环50圈后容量为165 mAh·g-1,容量保持率为92.7%;而在空气气氛下焙烧得到的LiNi0.5Mn0.5O2材料首次放电容量为164mAh.g-1,充放电循环50圈后容量为137 mAh·g-1,容量保持率为83.5%.氧气气氛下合成的材料具有较优的电化学性能可归因于氧气气氛下焙烧合成的LiNi0.5Mn0.5O2具有较小的Li/Ni混排率.