Abstract
A new iron hydroxyl-phosphate, H2Fe14/3(PO4)4(OH)4 has been synthesized under hydrothermal conditions. In this compound, perpendicular chains formed by the face-sharing FeO6 form rod-packing structure. Only about 60% of the chain sites are occupied by iron atoms; other metals, such as manganese, nickel, zinc, can be incorporated into the chain either by filling in the vacancies and/or replacing some of the iron atoms. Reversible insertion and extraction of lithium into this compound shows it to be an excellent cathode material. At current density of 0.1 mA/cm2, 90 % of the theoretical capacity (176 mAh/g) can be obtained. The utilization was reduced to about 70 % on a ten-fold increase of current density. The electrochemical behavior is attributed to the 3-dimensional rod packing structure, where lithium can move freely even at high current densities inside the 3-dimensional framework without altering the host structure. Two of the protons in the lattice may be exchanged by lithium giving Li2Fe14/3(PO4)4(OH)4. These lithium atoms are not removable in electrochemical cycling and similar electrochemical property was found for these two compounds, suggesting an ion-exchange process for the lithiation.
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Song, Y., Zavalij, P.Y. & Stanley Whittingham, M. New Iron (III) Hydroxyl-Phosphate with Rod-packing Structure as Intercalation Materials. MRS Online Proceedings Library 756, 77 (2002). https://doi.org/10.1557/PROC-756-EE7.7
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DOI: https://doi.org/10.1557/PROC-756-EE7.7