Relating Structure to Electrochemistry: In-Situ Studies of Fe[Fe(CN)6] As Cathode Materials for Rechargeable Li- and Na-Ion Batteries

The Prussian blue type compound Fe[Fe(CN)₆] is investigated as a cathode material for use in rechargeable Li- and Na-ion batteries. The structural changes following electrochemical Li⁺ and Na⁺ ion insertion during charge-discharge cycles were followed using in-situ X-ray and neutron powder diffraction techniques.^1-3

The electrochemical performance of Fe[Fe(CN)₆] has been investigated for both Li⁺ and Na⁺ ions with capacities of 100 and 115 mA h g^-1 respectively. Further investigations of the Na-ion cells for Fe[Fe(CN)₆] show the capacity to depend on the heating temperature used in preparing the cathode material. Fe[Fe(CN)₆] heated at 110 °C shows the highest capacity of 115 mA h g^-1, with capacity fading to 75 mA h g^-1 when the framework is heated at 150 °C. Cells containing samples of Fe[Fe(CN)₆] heated at 110 °C show excellent capacity retention of more than 99% after 50 cycles.

In-situ synchrotron X-ray diffraction has been performed for the Na-ion cells, while in-situneutron diffraction studies were carried out on Li-ion cells. In both cases, these allow for the direct correlation of structural changes to the cathode material and the observed electrochemical properties, as both are collected simultaneously.

(1)        Roberts, M.; Biendicho, J. J.; Hull, S.; Beran, P.; Gustafsson, T.; Svensson, G.; Edström, K. Journal of Power Sources 2013, 226, 249.

(2)        Sharma, N.; Peterson, V. J. Solid State Electrochem. 2012, 16, 1849.

(3)        Bergstöm, Ö.; Andersson, A. M.; Edström, K.; Gustafsson, T. J. Appl. Crystallogr. 1998, 31, 823.