$\beta $-NaMnO$_{2}$理论容量高、制备简单, 是一种极具应用前景的钠离子电池正极材料. 但是由于存在前几次循环容量衰减快的问题, 故目前对其容量衰减机制的研究较少. 采用传统固相法制备了层状$\beta $-NaMnO$_{2}$钠离子电池正极材料, 在10 mA/g的电流密度下$\beta $-NaMnO$_{2}$的初始放电比容高达184 mA$\cdot$h/g; 10次循环后, 容量保持率为73%. 为探讨容量衰减原因, 用X射线衍射(X-ray diffraction, XRD)、扫描电子显微镜(scanning electron microscopy, SEM)、高分辨透射电子显微镜(high resolution transmission electron microscopy, HRTEM)、X射线光电子能谱仪(X-ray photoelectron spectroscope, XPS)等手段对材料的成分及结构进行表征. XRD结果显示, 在前3次充放电过程中均出现了Na$_{0.91}$MnO$_{2}$和Na$_{0.7}$MnO$_{2}$的相, 而NaMnO$_{2}$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.

Due to its easy synthesis process and high theoretical capacity, layered $\beta $-NaMnO$_{2}$ is considered as a potential cathode material in sodium ion battery. However, studies on its capacity degradation in the first several cycles are rare. In this article, $\beta $-NaMnO$_{2}$ was prepared by a solid state method, which had a high initial discharge capacity of 184 mA$\cdot$h/g at 10 mA/g with a capacity retention of 73% after 10 cycles. The mechanism of capacity degradation was investigated based on X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscope (XPS). Phase transformation was recorded by XRD in the first three cycles, showing appearance of Na$_{0.91}$MnO$_{2}$ and Na$_{0.7}$MnO$_{2}$ in the discharge process with low crystallinity instead recrystallization of NaMnO$_{2}$. The proportion of disorder structure increased upon Na$^+$-ion extraction, associated with a loss of crystallinity as evidenced by HRTEM observation. XPS further explained the valence variation of Mn in different phases in the cycling.