Identifying the Structural Evolution of the Sodium Ion Battery Na2FePO4F Cathode
Identifying the Structural Evolution of the Sodium Ion Battery Na2FePO4F Cathode
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DOI：
10.1002/anie.201805555
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发表时间：
2018-09-10
影响因子：
16.6
通讯作者：
Yang, Yong
中科院分区：
文献类型：
--
作者：
Li, Qi;Liu, Zigeng;Yang, Yong
Na2FePO4F具有较高的放电电压和良好的循环性能，是一种很有前途的钠离子电池正极材料。目前，通过原位高能x射线衍射（XRD）、原位固态核磁共振（NMR）和第一性原理DFT计算，研究了循环过程中Na2FePO4F的长、短程结构演变。DFT计算表明，中间相Na1.5FePO4F采用的空间群为P2(1)/c，是起始相Na2FePO4F的空间群Pbcn（60）的子群（P2(1)/b11, No. 14），该空间群与实验XRD和NMR结果吻合良好。在循环过程中，Na2FePO4F结构中两个晶体结构独特的Na位点表现不同，其中Na2位点上的Na离子具有电化学活性，而Na1位点上的Na离子具有惰性。本研究确定了Na2FePO4F在钠离子电池中的结构演变和电化学反应机理。
Na2FePO4F 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 Na2FePO4F during cycling is studied by in situ high-energy X-ray diffraction (XRD), exsitu solid-state nuclear magnetic resonance (NMR), and first-principles DFT calculations. DFT calculations suggest that the intermediate phase, Na1.5FePO4F, adopts the space group of P2(1)/c, which is a subgroup (P2(1)/b11, No. 14) of Pbcn (No. 60), the space group of the starting phase, Na2FePO4F, 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 Na2FePO4F 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 Na2FePO4F in a Na-ion battery.