Electrochemical reactions of AgFeO2 as negative electrode in Li- and Na-ion batteries

AgFeO2 nanoparticles synthesized via precipitation at room temperature are investigated in Li- and Na-ion cells through electrode coatings with an alginate binder. The electrochemical reactions of AgFeO2 with Li+ and Na+ ions, as well as its role as alternative negative electrode in these cell systems are carefully evaluated. Initial Li uptake causes irreversible amorphization of the AgFeO2 structure with concomitant formation of Ag-0 nano particles. Further Li incorporation results in conversion into Fe nanoparticles and Li2O, together with Li-alloying of these Ag-0 clusters. Similar mechanisms are also found upon Na uptake, although such processes are hindered by overpotentials, the capacity and reversibility of the reactions with Na+ ions being not comparable with those of their Li+ counterparts. The behaviour of AgFeO2 at low potentials vs. Li+ /Li displays a synergic pseudo-capacitive charge storage overlapping Li-Ag alloying/de-alloying. This feature is exploited in full cells having deeply lithiated AgFeO2 and LiFePO4 as negative and positive electrodes, respectively. These environmentally friendly iron-based full cells exhibit attractive cycle performances with approximate to 80% capacity retention after 1000 cycles without any electrolyte additive, average round trip efficiency of approximate to 89% and operational voltage of 3.0 V combined with built-in pseudo-capacitive characteristics that enable high cycling rates up to approximate to 25C.