Abstract
The rational design of high performance sodium solid electrolytes is one of the key challenges in modern battery research. In this work, we identify new sodium ion conductors in the substitution series Na5-xAl1-xSixS4 (0 ≤ x ≤ 1), which are entirely based on earth-abundant elements. These compounds exhibit conductivities ranging from 1.64 · 10−7 for Na4SiS4 to 2.04 · 10−5 for Na8.5(AlS4)0.5(SiS4)1.5 (x = 0.75). We determined the crystal structures of the Na+-ion conductors Na4SiS4 as well as hitherto unknown Na5AlS4 and Na9(AlS4)(SiS4). Na+-ion conduction pathways were calculated by bond valence energy landscape (BVEL) calculations for all new structures highlighting the influence of the local coordination symmetry of sodium ions on the energy landscape within this family. Our findings show that the interplay of charge carrier concentration and low site symmetry of sodium ions can enhance the conductivity by several orders of magnitude.
Highlights
In recent years, all-solid-state batteries (ASSB) have garnered attention as promising candidates for future battery applications in large scale mobility systems, such as electric vehicles (Goodenough, 2012; Janek and Zeier, 2016; Kato et al, 2016)
We present the crystal structures of Na5AlS4, Na4SiS4, and Na9(AlS4)(SiS4) and investigate their Na+-ion migration pathways by bond valence energy landscape (BVEL)
From all samples in the Na5-xAl1-xSixS4 (0 ≤ x ≤ 1) aliovalent substitution series powder X-ray diffractograms (PXRDs) were measured to study the crystallinity and phase composition
Summary
All-solid-state batteries (ASSB) have garnered attention as promising candidates for future battery applications in large scale mobility systems, such as electric vehicles (Goodenough, 2012; Janek and Zeier, 2016; Kato et al, 2016). This is due to safety issues arising from liquid electrolytes applied in conventional lithium-ion batteries. To be applicable for battery systems, the implemented solid electrolytes are required to show high ionic and low electronic conductivity, along with high electrochemical and structural stability, as well as low production costs (Lotsch and Maier, 2017).
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