Cathode performance in sustainable Na-ion full-cells: Layered oxides versus polyanionic chemistry

During the last decades, sodium-ion batteries (SIBs) have drawn interest since sodium resources are abundant, inexpensive, and available around the earth's crust. Nonetheless, this effort has been mainly focused on half-cell configurations, a preliminary step to evaluate which materials are suitable for future SIBs full-cells. Up to date, few works related to hard carbon (HC)-based SIBs full-cells have been published, and the irreversibility of the HC anode first cycle is still an issue to be solved. Herein, two positive material electrodes, a polyanionic compound (Na 3 V 2 O 2 (PO 4 ) 2 F@C) and a layered oxide (Na 2/3 Mn 0.8 Fe 0.1 Ti 0.1 O 2 ), were selected due to their favorable theoretical specific capacity and high operating potential. Moreover, the chosen sacrificial salt, to compensate for the Na + loss for the formation of the Solid Electrolyte Interface (SEI), was Na 2 C 3 O 5 because of its non-flammable nature and easy process to fully remove the structural water from the hydrated precursor. In full-cell studies using the sacrificial salt, Na 3 V 2 O 2 (PO 4 ) 2 F@C demonstrates excellent long-term cycling stability, retaining 91% of its initial capacity with a discharge capacity of ∼105 mAh g −1 after 200 cycles at 130 mA g −1 . This research highlights the electrochemical properties and sustainability of these systems, underscoring the potential for developing greener and more environmentally friendly battery alternatives.