Prussian Blue As Negative and Positive Electrode in Lithium and Sodium-Ion Batteries
We recently reported the performance of Prussian Blue (from now on abbreviated as PB) acting as anode versus lithium in organic media. In the low voltage window of 1.6 - 0.005 V, it exhibits a plateau at ca. 0.9 V and capacities comparable to those observed for graphite (450 mAh/g in the first cycle and 350 mAh/g after 50 cycles at 8.75 mA/g), which are 5 times higher than the theoretically expected for the insertion of 1 Li+ per formula unit through an intercalation mechanism. Based on several evidences observed when ex-situ experiments are carried out in the discharged electrodes, we proposed a conversion (or displacement) mechanism, for the first time reported, as the reaction probably taking place.
On the other hand, the already contrasted performance of the potassium PB as cathode, in combination with the increasing interest in new alternatives to lithium, providing less expensive and more environmentally friendly materials, such as the NIB, led us to consider the sodiated phase of PB, ideally NaFeIIIFeII(CN)6·xH2O, to work as cathode material versus sodium in organic media. The presence of sodium ions in the crystal structure of the pristine material could facilitate the insertion/deinsertion of these alkali ions. Herein, we will present the study on the optimization of the electrochemical behaviour of the sodium system, which shows 2 plateaus at 2.7 and 3.45 V and capacities up to 140 mAh/g, in NIB. The mechanism of insertion/deinsertion will be also discussed.
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