Leo Duchene1 2 Ruben-Simon Kühnel1 Eduardo Cuervo Reyes1 Daniel Rentsch3 Arndt Remhof1 Hans Hagemann2 Corsin Battaglia1

1, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, , Switzerland
2, University of Geneva, Geneva, , Switzerland
3, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, , Switzerland

All-solid-state sodium-ion batteries promise to simultaneously yield higher energy density, improved safety, and lower cost as compared to state-of-the-art lithium-ion technologies based on organic liquid electrolytes. A competitive all-solid-state battery requires a solid-state electrolyte with high ionic conductivity near room temperature and high thermal and electrochemical stability. Meeting these three requirements simultaneously represents a major challenge. In fact, research focus has recently shifted from merely conductivity improvement of the electrolyte to interface engineering for the implementation in all-solid cells.
In this regard, we will present a new sodium-ion conductor, namely Na2(B12H12)0.5(B10H10)0.5, that simultaneously offers high sodium ion conductivity of 0.9 mS cm-1 at 20 °C, excellent thermal stability up to at least 300 °C, and importantly a large electrochemical stability window of 3 V including stability versus metallic sodium enabling long-term striping and plating and the use of a sodium metal anode [1]. In addition, we will discuss strategies to enable a 3 V all-solid-state battery based on Na2(B12H12)0.5(B10H10)0.5 and demonstrate first cycling results (85% capacity retention after 250 cycles at C/5).
Our results demonstrate that closo-borate based electrolytes and particularly Na2(B12H12)0.5(B10H10)0.5 could pave the way towards safe and long-life all-solid-state batteries.

[1] Duchêne, L.; Kühnel, R.-S.; Rentsch, D.; Remhof, A.; Hagemann, H.; Battaglia, C. A Highly Stable Sodium Solid-State Electrolyte Based on a Dodeca/deca-Borate Equimolar Mixture. Chem. Commun. 2017, 53 (30), 4195–4198.