Li Qi, Liu Zigeng, Zheng Feng, Liu Rui, Lee Jeongjae, Xu Gui-Liang, Zhong Guiming, Hou Xu, Fu Riqiang, Chen Zonghai, Amine Khalil, Mi Jinxiao, Wu Shunqing, Grey Clare P, Yang Yong
State Key Lab of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials and Department of Chemistry, Xiamen University, Xiamen, 361005, China.
Department of Chemistry, University of Cambridge, Lensfield Rd, Cambridge, CB2 1EW, UK.
Angew Chem Int Ed Engl. 2018 Sep 10;57(37):11918-11923. doi: 10.1002/anie.201805555. Epub 2018 Aug 19.
Na FePO F is a promising cathode material for Na-ion batteries owing to its relatively high discharge voltage and excellent cycling performance. Now, the long- and short-range structural evolution of Na FePO F during cycling is studied by in situ high-energy X-ray diffraction (XRD), ex situ solid-state nuclear magnetic resonance (NMR), and first-principles DFT calculations. DFT calculations suggest that the intermediate phase, Na FePO F, adopts the space group of P2 /c, which is a subgroup (P2 /b11, No. 14) of Pbcn (No. 60), the space group of the starting phase, Na FePO F, and this space group provides a good fit to the experimental XRD and NMR results. The two crystallographically unique Na sites in the structure of Na FePO F behave differently during cycling, where the Na ions on the Na2 site are electrochemically active while those on the Na1 site are inert. This study determines the structural evolution and the electrochemical reaction mechanisms of Na FePO F in a Na-ion battery.
由于具有相对较高的放电电压和出色的循环性能，NaFePOF是一种很有前景的钠离子电池正极材料。目前，通过原位高能X射线衍射（XRD）、非原位固态核磁共振（NMR）和第一性原理密度泛函理论（DFT）计算研究了NaFePOF在循环过程中的长程和短程结构演变。DFT计算表明，中间相NaFePOF采用P2/c空间群，它是起始相NaFePOF的空间群Pbcn（编号60）的一个子群（P2/b11，编号14），并且该空间群与实验XRD和NMR结果吻合良好。NaFePOF结构中两个晶体学上独特的Na位点在循环过程中表现不同，其中Na2位点上的Na离子具有电化学活性，而Na1位点上的Na离子是惰性的。本研究确定了NaFePOF在钠离子电池中的结构演变和电化学反应机理。
