The reaction mechanism of FeSb2 as anode for sodium-ion batteries
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Univ. of Tennessee Space Inst. (UTSI), Tullahoma, TN (United States)
The electrochemical reaction of FeSb2 with Na is reported for the first time. The first discharge (sodiation) potential profile of FeSb2 is characterized by a gentle slope centered at 0.25 V. During charge (Na removal) and the subsequent discharge, the main reaction takes place near 0.7 V and 0.4 V, respectively. The reversible storage capacity amounts to 360 mA h g-1, which is smaller than the theoretical value of 537 mA h g-1. The reaction, studied by ex situ and in situ X-ray diffraction, is found to proceed by the consumption of crystalline FeSb2 to form an amorphous phase. Upon further sodiation, the formation of nanocrystalline Na3Sb domains is evidenced. During desodiation, Na3Sb domains convert into an amorphous phase. The chemical environment of Fe, probed by 57Fe Mo ssbauer spectroscopy, undergoes significant changes during the reaction. During sodiation, the well-resolved doublet of FeSb2 with an isomer shift around 0.45 mm s-1 and a quadrupole splitting of 1.26 mm s-1 is gradually converted into a doublet line centered at about 0.15 mm s1 along with a singlet line around 0 mm s-1. The former signal results from the formation of a Fe-rich FexSb alloy with an estimated composition of Fe4Sb while the latter signal corresponds to superparamagnetic Fe due to the formation of nanosized pure Fe domains. Interestingly the signal of Fe4Sb remains unaltered during desodiation. This mechanism is substantially different than that observed during the reaction with Li. The irreversible formation of a Fe-rich Fe4Sb alloy and the absence of full desodiation of Sb domains explain the lower than theoretical practical storage capacity.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1185578
- Journal Information:
- Physical Chemistry Chemical Physics. PCCP, Vol. 16, Issue 20; ISSN 1463-9076
- Publisher:
- Royal Society of ChemistryCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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