Ideally realized sodium-ion capacitor via irreversible oxidation of sodium azide to pre-metalate the anodic host

• Published in: Journal of power sources 2024-07, Vol.609, p.234637, Article 234637
• Main Authors: Parejo-Tovar, Andres, Béguin, François
• Format: Article
• Language: English
• Subjects: Activated carbon EDL electrode; Hard carbon pre-sodiation; Irreversible oxidation; Nitrogen gas by-product; Sodium azide sacrificial material; Sodium-ion capacitor
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2024.234637

Herein, sodium azide (NaN3) is used as sacrificial cathodic material to address the metal deficiency issues in the anodic host of sodium-ion capacitors (NICs). Electrochemical online mass spectroscopy at C/40 (C theoretical capacity of NaN3) on a NaN3–C65 electrode percolated by carbon black (C65 conductive additive) demonstrates a complete irreversibility of the oxidation process, with the evolution of N2 (1.5 mol for 1 mol of NaN3) as sole by-product. Gas adsorption analysis at 77 K on pristine and oxidized NaN3-AC (AC = activated carbon) electrodes reveals a noteworthy regeneration of the porous texture of activated carbon after oxidation. Laminated NaN3-AC//HCM cells (HCM: hard carbon) were prepared, and sodium was transferred to the HCM negative electrode by electrochemical oxidation of NaN3, giving rise to AC//NaxHCM sodium-ion capacitors. Over a voltage range from 2.0 V to 3.8 V, the NICs demonstrated impressive capacitance retention of 90%, and energy efficiency of 95% after 15,000 galvanostatic cycles. In terms of energy and power performance, the NICs exhibited output energy of 38 Wh kg−1 up to 4 kW kg−1. These results demonstrate that sodium azide is an ideal “zero dead mass” sacrificial material holding the potential for the one-step realization of cost-effective NICs presenting attractive electrochemical characteristics. •A precursor cell is realized with an activated carbon/sodium azide positive electrode.•Sodium azide is used as sacrificial cathodic material for the sodiation of hard carbon.•Sodium azide is electrochemically oxidized to transfer sodium to hard carbon.•The only product of electrochemical oxidation of sodium azide is nitrogen.•The activated carbon//sodium doped hard carbon cell displays excellent life span.