The high-temperature β-phase NaMnO2 is a promising material for Na-ion batteries（NIBs） due to its high capacity and abundant resources. However, the synthesis of phase-pure -NaMnO2 is burdensome and costineffective...The high-temperature β-phase NaMnO2 is a promising material for Na-ion batteries（NIBs） due to its high capacity and abundant resources. However, the synthesis of phase-pure -NaMnO2 is burdensome and costineffective because it needs to be sintered under oxygen atmosphere at high temperature and followed by a quenching procedure. Here we first report that the pure β phase can be stabilized by Cu-doping and easily synthesized by replacing a proportion of Mn with Cu via a simplified process including sintering in air and cooling to room temperature naturally. Based on the first-principle calculations, the band gap decreases from 0.7 eV to 0.3 eV, which indicates that the electronic conductivity can be improved by Cu-doping. The designed -NaCu（0.1）Mn（0.9）O2 is applied as cathode in NIBs, exhibiting an energy density of 419 Wh/kg and better performance in terms of rate capability and cycling stability than those in the undoped case.展开更多
β-NaMnO2理论容量高、制备简单,是一种极具应用前景的钠离子电池正极材料.但是由于存在前几次循环容量衰减快的问题,故目前对其容量衰减机制的研究较少.采用传统固相法制备了层状β-NaMnO2钠离子电池正极材料,在10mA/g的电流密度下β-N...β-NaMnO2理论容量高、制备简单,是一种极具应用前景的钠离子电池正极材料.但是由于存在前几次循环容量衰减快的问题,故目前对其容量衰减机制的研究较少.采用传统固相法制备了层状β-NaMnO2钠离子电池正极材料,在10mA/g的电流密度下β-NaMnO2的初始放电比容高达184mA·h/g;10次循环后,容量保持率为73%.为探讨容量衰减原因,用X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscopy,SEM)、高分辨透射电子显微镜(high resolution transmission electron microscopy,HRTEM)、X射线光电子能谱仪(X-ray photoelectron spectroscope,XPS)等手段对材料的成分及结构进行表征.XRD结果显示,在前3次充放电过程中均出现了Na0.91MnO2和Na0.7MnO2的相,而NaMnO2的相消失不见.在充电以后,样品的HRTEM图像上也出现了许多不同取向的纳米晶,伴随着点缺陷和面缺陷的存在.通过XPS进一步检测,发现在充放电过程中Mn的价态发生了变化.展开更多
基金Supported by the National Key Technologies R&D Program of China under Grant No 2016YFB0901500the National Nature Science Foundation of China under Grant Nos 51725206 and 51421002
文摘The high-temperature β-phase NaMnO2 is a promising material for Na-ion batteries（NIBs） due to its high capacity and abundant resources. However, the synthesis of phase-pure -NaMnO2 is burdensome and costineffective because it needs to be sintered under oxygen atmosphere at high temperature and followed by a quenching procedure. Here we first report that the pure β phase can be stabilized by Cu-doping and easily synthesized by replacing a proportion of Mn with Cu via a simplified process including sintering in air and cooling to room temperature naturally. Based on the first-principle calculations, the band gap decreases from 0.7 eV to 0.3 eV, which indicates that the electronic conductivity can be improved by Cu-doping. The designed -NaCu（0.1）Mn（0.9）O2 is applied as cathode in NIBs, exhibiting an energy density of 419 Wh/kg and better performance in terms of rate capability and cycling stability than those in the undoped case.
文摘β-NaMnO2理论容量高、制备简单,是一种极具应用前景的钠离子电池正极材料.但是由于存在前几次循环容量衰减快的问题,故目前对其容量衰减机制的研究较少.采用传统固相法制备了层状β-NaMnO2钠离子电池正极材料,在10mA/g的电流密度下β-NaMnO2的初始放电比容高达184mA·h/g;10次循环后,容量保持率为73%.为探讨容量衰减原因,用X射线衍射(X-ray diffraction,XRD)、扫描电子显微镜(scanning electron microscopy,SEM)、高分辨透射电子显微镜(high resolution transmission electron microscopy,HRTEM)、X射线光电子能谱仪(X-ray photoelectron spectroscope,XPS)等手段对材料的成分及结构进行表征.XRD结果显示,在前3次充放电过程中均出现了Na0.91MnO2和Na0.7MnO2的相,而NaMnO2的相消失不见.在充电以后,样品的HRTEM图像上也出现了许多不同取向的纳米晶,伴随着点缺陷和面缺陷的存在.通过XPS进一步检测,发现在充放电过程中Mn的价态发生了变化.
