Local structural changes of nano-crystalline ZnFe<inf>2</inf>O<inf>4</inf>during lithiation and de-lithiation studied by X-ray absorption spectroscopy

Publication Type:
Journal Article
Citation:
Electrochimica Acta, 2017, 246 pp. 699 - 706
Issue Date:
2017-08-20
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© 2017 Elsevier Ltd X-ray absorption spectroscopy was carried out to investigate local structural changes around Fe and Zn atoms of the nano-crystalline spinel ferrite ZnFe2O4anode material at various states-of-charge during the 1st and 2nd lithiation/de-lithiation. From the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), we propose a possible structure evolution process of the ZnFe2O4electrode during the 1st discharge and charge cycle. A mixture of metallic iron, ZnO, metallic zinc, LiZn and Li2O phases seem to be formed as the cell is firstly discharged to 0.02 V. Instead of the original ZnFe2O4spinel phase, the metallic iron and zinc particles are re-oxidized to Fe2O3and ZnO phases during the subsequent de-lithiation. A reversible redox reaction between Fe2O3, ZnO and lithium ions is found in the 2nd cycle. The formation of SEI layer in the initial cycles plays a major role in the irreversible capacity of the electrode. The inactive disordered ZnO formed due to the conversion reaction of ZnFe2O4during the 1st lithiation is probably the main reason for the poor electrochemical behavior of the nano-crystalline ZnFe2O4electrode.
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