钠离子电池正极材料Na2MnPO4F的^23Na MAS NMR谱研究

^(23)Na MAS NMR Spectroscopic Study of Na_2MnPO_4F as Cathode Material for Sodium-Ion Battery

Na2MnPO4F材料是一种很有发展前景的钠离子电池正极材料,本文通过非原位XRD和固体核磁共振技术研究该材料充放电结构变化(晶体结构与局域Na位).非原位XRD测试发现,充电过程在2θ为31°和36°左右出现新的衍射峰,表明钠脱出后电极上有中间相物质生成.23Na MAS NMR谱图的-209 ppm、-258 ppm和-295 ppm三个谱峰分别对应于该材料结构中Na1+Na2位、Na3位和Na4位.非原位23Na MAS NMR谱研究发现,充电过程中-209ppm处信号峰面积比例减小,表明Na1和Na2位的Na比Na3和Na4位先脱出.充电至4.2 V,-132 ppm和-330 ppm处出现中间相物质的信号峰;而放电过程则相反.

The Na2MnPO4F is one of the promising cathode materials for the sodium ion batteries.In the paper,we employed the ex situ X-ray diffraction and solid state NMR techniques to study the charge and discharge processes of this material,including the crystal structure and sodium sites changes.The ex situ X-ray diffraction patterns showed that two new diffraction peaks could be observed at 31° and 36° indicating an intermediate phase formed with the extraction of Na＋.From the 23Na MAS NMR spectrum of the material,three peaks were seen at -209 ppm,-258 ppm and -295 ppm,which can be assigned to Na1＋Na2,Na3 and Na4 sites in the crystal structure,respectively.The ex situ solid state NMR study demonstrated that the Na＋in Na1 and Na2 sites deintercalated firstly compared to Na3 and Na4 sites.The signal peaks of intermediate phase appeared at -132 ppm and -330 ppm when charging to 4.2 V.The opposite phenomenon occurred during the discharge process.