Sodium‐ and Potassium‐Hydrate Melts Containing Asymmetric Imide Anions for High‐Voltage Aqueous Batteries

• Published in: Angewandte Chemie 2019-10, Vol.131 (40), p.14340-14345
• Main Authors: Zheng, Qifeng, Miura, Shota, Miyazaki, Kasumi, Ko, Seongjae, Watanabe, Eriko, Okoshi, Masaki, Chou, Chien‐Pin, Nishimura, Yoshifumi, Nakai, Hiromi, Kamiya, Takeshi, Honda, Tsunetoshi, Akikusa, Jun, Yamada, Yuki, Yamada, Atsuo
• Format: Article
• Language: English
• Subjects: Alkali metals; Anions; Aqueous electrolytes; Asymmetrische Imid-Anionen; Asymmetry; Batteries; Chemistry; Electric potential; Electrochemical potential; Electrochemistry; Elektrochemie; Flux density; Hydrate; Lithium-ion batteries; Melts; Potassium; Potassium channels (voltage-gated); Potentialfenster-Erweiterung; Rechargeable batteries; Salts; Sodium; Sodium channels (voltage-gated); Voltage; Wasserbasierte Batterien; Water chemistry
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201908830

Aqueous Na‐ or K‐ion batteries could virtually eliminate the safety and cost concerns raised from Li‐ion batteries, but their widespread applications have generally suffered from narrow electrochemical potential window (ca. 1.23 V) of aqueous electrolytes that leads to low energy density. Herein, by exploring optimized eutectic systems of Na and K salts with asymmetric imide anions, we discovered, for the first time, room‐temperature hydrate melts for Na and K systems, which are the second and third alkali metal hydrate melts reported since the first discovery of Li hydrate melt by our group in 2016. The newly discovered Na‐ and K‐ hydrate melts could significantly extend the potential window up to 2.7 and 2.5 V (at Pt electrode), respectively, owing to the merit that almost all water molecules participate in the Na+ or K+ hydration shells. As a proof‐of‐concept, a prototype Na3V2(PO4)2F3|NaTi2(PO4)3 aqueous Na‐ion full‐cell with the Na‐hydrate‐melt electrolyte delivers an average discharge voltage of 1.75 V, that is among the highest value ever reported for all aqueous Na‐ion batteries. Raumtemperatur‐Hydratschmelzen für Na‐ und K‐Systeme wurden bei Untersuchungen optimierter eutektischer Systeme von Na‐ und K‐Salzen mit asymmetrischen Imid‐Anionen erstmals entdeckt. Die Ergebnisse führen zu einer signifikanten Erweiterung des Potentialfensters und zeigen neue Möglichkeiten für wässrige Elektrolyte in der Anwendung in sicheren Hochspannungsbatterien auf.