Abstract
New sodium-based battery concepts require solid electrolytes as ion conducting separators. Besides NaSICON and β-Al2O3 in the Na2O-R2O3-SiO2 system (R = rare earth), a rarely noticed glass-ceramic solid electrolyte with the composition Na5RSi4O12 (N5-type) exists. The present study addresses the investigation of the ionic conductivity of Na5RSi4O12 solid electrolytes sintered from pre-crystallized glass-ceramic powders. The sintering behavior (optical dilatometry), the microstructure (SEM/EDX), and phase composition (XRD), as well as electrochemical properties (impedance spectroscopy), were investigated. To evaluate the effect of the ionic radii, Y, Sm and Gd rare elements were chosen. All compositions were successfully synthesized to fully densified compacts having the corresponding conducting N5-type phase as the main component. The densification behavior was in agreement with the melting point, which decreased with increasing ionic radii and specific cell volume. Alternatively, the ionic conductivities of N5-phases decreased from Y to Gd and Sm containing samples. The highest ionic conductivity of 1.82 × 10−3 S cm−1 at 20 °C was obtained for Na5YSi4O12 composition. The impact of grain boundaries and bulk conductivity on measured values is discussed. A powder-based synthesis method of this glass-ceramic solid electrolyte using different rare earth elements opens possibilities for optimizing ionic conductivity and scalable technological processing by tape casting.
Highlights
Fraunhofer Institute for Ceramic Technology and Systems Fraunhofer IKTS, Winterbergstrasse 28, Department of Chemical Engineering (Integrated Engineering) & Center for the SMART Energy Platform, College of Engineering, Kyung Hee University, 1732 Deogyeong-daero, Giheung, Abstract: New sodium-based battery concepts require solid electrolytes as ion conducting separators
Since in this study we focus on the conductivities of the respective N5 phases and assess the N16.5 phase as non-conductive according to the current state of knowledge, we assume, as a first approximation, a 2-phase structure, of which only the N5-phase contributes to conductivity
According to our previous studies on the Y-substituted type of this material (N5-Y), it has been found that a pre-crystallization of the parental glass of this material (N5-Y), it has been found that a pre-crystallization of the parental glass powder prior to the sintering of compact specimens is advantageous in achieving dense powder prior to the sintering of compact specimens is advantageous in achieving dense microstructures [28]
Summary
Fraunhofer Institute for Ceramic Technology and Systems Fraunhofer IKTS, Winterbergstrasse 28, Department of Chemical Engineering (Integrated Engineering) & Center for the SMART Energy Platform, College of Engineering, Kyung Hee University, 1732 Deogyeong-daero, Giheung, Abstract: New sodium-based battery concepts require solid electrolytes as ion conducting separators. The present study addresses the investigation of the ionic conductivity of Na5 RSi4 O12 solid electrolytes sintered from pre-crystallized glass-ceramic powders. A powder-based synthesis method of this glass-ceramic solid electrolyte using different rare earth elements opens possibilities for optimizing ionic conductivity and scalable technological processing by tape casting. The most advanced Na-ion batteries are the Na-S and the Na-NiCl2 (ZEBRA) Both cells operate at high temperatures of about 300 ◦ C to ensure that the electrode materials are in a molten state [4,5]. The progress of ambient temperature sodium-ion batteries published maps and institutional affiliations
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