All-solid-state batteries replacing the flammable liquid electrolyte by a non-flammable solid electrolyte promise significantly enhanced energy density (e.g. by enabling lithium-metal anodes and high-voltage cathodes), fast charging capabilities (e.g. by tolerating higher operating temperatures), and improved operational safety (e.g. by eliminating flammable components). These advantages render all-solid-state batteries very attractive for automotive companies. The dependency of European automotive manufacturers, which contribute substantially to Europe’s economic strength, on batteries from Asia is a major concern also for the European Commission. Consequently the European Commission considers all-solid-state batteries as a pathway to re-establish strong cell manufacturing in Europe. However, there exists currently no all-solid-state battery technology that can compete in terms of performance with today’s lithium-ion batteries.
We developed a non-flammable non-toxic solid electrolyte for all-solid-state batteries based on a novel class of inorganic borate electrolytes offering simultaneously high ionic conductivity (1 mS/cm at 25°C) and a wide electrochemical stability window (>3 V). We successfully demonstrated a 3 V-class battery cell with a sodium metal anode and NaCrO2 cathode achieving remarkable capacity retention of 85% after 250 cycles to 3.2 V. Our results bring this material class to a technology readiness level comparable to the heavily investigated oxide- and sulfide-based solid-state electrolytes investigated intensively e.g. by Samsung, Toyota, VW, etc.
Swiss National Science Foundation, Swiss State Secretariat for Education, Research, and Innovation, Polish-Swiss Research Programme, Horizon 2020
 L. Duchêne, A. Remhof, H. Hagemann, C. Battaglia, Status and prospects of hydroborate electrolytes for all-solid-state batteries, Energy Storage Mater. 2019, in press.
 L. Duchêne, D. H. Kim, Y. B. Song, S. Jun, R. Moury, A. Remhof, H. Hagemann, Y. S. Jung, C. Battaglia, Crystallzation of closo-borate electrolytes from solution enabling infiltration into slurry-casted porous electrodes for all-solid-state batteries, Energy Storage Mater. 2019, in press.
 R. Asakura, L. Duchêne, R.-S. Kühnel, A. Remhof, C. Battaglia, Electrochemical oxidative stability of hydroborate solid-state electrolytes, ACS Appl. Energy Mater. 2019, 2, 6924.
 L. Duchêne, S. Lunghammer, T. Burankova, W.-C. Liao, J. P. Embs, C. Copéret, H. M. R. Wilkening, A. Remhof, H. Hagemann, C. Battaglia, Ionic conduction mechanism in the Na2(B12H12)0.5(B10H10)0.5 closo-borate solid-state electrolyte: interplay of disorder and ion-ion interactions, Chem. Mater. 2019, 31, 3449.
 L. Duchêne, R.-S. Kühnel, E. Stilp, E. Cuervo Reyes, A. Remhof, H. Hagemann, C. Battaglia, A stable 3 V all-solid-state sodium–ion battery based on a closo-borate electrolyte, Energy Environ. Science 2017, 10, 2609.
 Y. Yan, R.-S. Kühnel, A. Remhof, L. Duchêne, E. Cuevo Reyes, D. Rentsch, Z. Lodziana, C. Battaglia, A lithium amide-borohydride solid-state electrolyte with lithium-ion conductivities comparable to liquid electrolytes, Adv. Energy Mater. 2017, 7, 1700294.
 E. Roedern, R.-S. Kühnel, A. Remhof, C. Battaglia, Magnesium ethylenediamine borohydride as solid-state electrolyte for magnesium batteries, Scientific Reports 2017, 7, 46189.
Solid state batteries for tomorrow's electric cars, Empa & Fraunhofer press release, 22.2.2019 (English)