Strauss Florian, Rousse Gwenaëlle, Sougrati Moulay Tahar, Dalla Corte Daniel Alves, Courty Matthieu, Dominko Robert, Tarascon Jean-Marie
National Institute of Chemistry , Hajdrihova 19, SI-1000 Ljubljana, Slovenia.
Sorbonne Universités - UPMC Univ Paris 06 , 4 Place Jussieu, F-75005 Paris, France.
Inorg Chem. 2016 Dec 19;55(24):12775-12782. doi: 10.1021/acs.inorgchem.6b02070. Epub 2016 Nov 23.
In the search for new cathode materials for sodium ion batteries, the exploration of polyanionic compounds has led to attractive candidates in terms of high redox potential and cycling stability. Herein we report the synthesis of the two new sodium transition-metal pentaborates NaMBO (M = Fe, Co), where NaFeBO represents the first sodium iron borate reported at present. By means of synchrotron X-ray diffraction, we reveal a layered structure consisting of pentaborate BO groups connected through M in tetrahedral coordination, providing possible three-dimensional Na-ion migration pathways. Inspired by these structural features, we examined the electrochemical performances versus sodium and showed that NaFeBO is active at an average potential of 2.5 V vs Na/Na, correlated to the Fe/Fe redox couple as deduced from ex situ Mössbauer measurements. This contrasts with the case for NaCoBO, which is electrochemically inactive. Moreover, we show that their electrochemical performances are kinetically limited, as deduced by complementary ac/dc conductivity measurements, hence confirming once again the complexity in designing high-performance borate-based electrodes.
在寻找钠离子电池新型正极材料的过程中，对聚阴离子化合物的探索已产生了在高氧化还原电位和循环稳定性方面颇具吸引力的候选材料。在此，我们报告了两种新型钠过渡金属五硼酸盐NaMBO（M = Fe，Co）的合成，其中NaFeBO是目前报道的首例钠铁硼酸盐。通过同步辐射X射线衍射，我们揭示了一种层状结构，该结构由通过处于四面体配位的M连接的五硼酸盐BO基团组成，提供了可能的三维钠离子迁移途径。受这些结构特征的启发，我们研究了它们相对于钠的电化学性能，结果表明，NaFeBO在相对于Na/Na平均电位为2.5 V时具有活性，这与通过非原位穆斯堡尔测量推断出的Fe/Fe氧化还原对相关。这与NaCoBO的情况形成对比，NaCoBO在电化学上是惰性的。此外，正如通过互补的交流/直流电导率测量所推断的那样，我们表明它们的电化学性能受到动力学限制，从而再次证实了设计高性能硼酸盐基电极的复杂性。
