Jeudi 12 juillet 2018
Salle de Conférences
Séminaire Romain MOURY
Université de Genève

Development and characterizations of closo-borate-based
solid electrolyte for Na all-solid-state batteries

Romain Moury*1, Angelina Gigante1, Arndt Remhof2, Zbigniew Lodziana3, Leo
Duchene2, and H. Hagemann1
1Department of Physical Chemistry, University of Geneva, Quai E. Ansermet 30, CH-1211 Geneva 4, Switzerland.
2 Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
3INP, Polish Academy of Sciences, 31-342 Kraków, Poland

All-solid-state batteries promise higher energy and power density, wider working temperature and electrochemical windows and safer approach compare to batteries using organic liquid electrolyte. Recently sodium dodecahydro-closo-dodecaborate (Na2B12H12) was found to be superionic conductor above its temperature of phase transition (0.1 S/cm at 529K) [1]. This discovery has triggered intensive researches aiming to find strategies to decrease the phase transition temperature to room temperature. Among the strategies, the solid-solution Na2[(B12H12)0.5(B10H10)0.5] has demonstrated to be a remarkable good ionic conductor at room temperature with a conductivity of 1 mS/cm owing to its cubic close packing [2]. Moreover, it was demonstrated that Na2[(B12H12)0.5(B10H10)0.5] solid-state electrolyte can be employed to build a 3V battery stable for at least 250 cycles [3]. However, the main roadblock for the development of closo-borates as solid electrolyte is their expensive and unsafe syntheses. Our main purposes then, were to develop a new and safe procedure to decrease the production price and structurally characterise them. In a first part, I will show a 4 steps scalable procedure allowing to produce Na2[(B12H12)0.5(B10H10)0.5] solid-state electrolyte without the use of any toxic boranes and staring with the cheapest borohydride available on the market sodium borohydride (NaBH4) [4]. In a second part, I will present the high-pressure and high temperature Powder X-Ray Diffraction results performed on Na2B12H12 to gain insight the structural properties of this materials and extract physical properties as the bulk modulus and the Coefficient of the Thermal Expansion (CTE). I will show that Na2B12H12 undergoes to two first order displacive phase transitions P21/cPbcaPnnm and describe the mechanism. Moreover, with a group-theoretical analysis, Iwill attempt to rationalize the irreversible nature of the first transition.
[1] T. J. Udovic et al., Chem. Commun. 50 (2014) 3750.
[2] Duchene, L., et al., Chem. Comm. 53 (2017) 4195.
[3] Duchene, L., et al., Energy Environ. Sci. 10 (2017) 2609.
[4] Moury R.,* et al., Chem. Mater. In preparation.

Conférence : Romain MOURY – 12/7/2018
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