Superion Conductor Na11.1Sn2.1P0.9Se12: Lowering the Activation Barrier of Na+ Conduction in Quaternary 1–4–5–6 Electrolytes

We report on the first quaternary selenide-based Na+ superionic solid electrolyte, Na11.1Sn2.1P0.9Se12 (further denoted as NaSnPSe), which shows virtually the same room temperature Na+ ion conductivity (3.0 mS/cm) as the current record holder for sulfide-based systems, Na11Sn2PS12 (denoted as NaSnPS), but with a considerably lower activation energy of 0.30 eV. Both electrolytes belong to the currently highly topical class of solids comprising group I, IV, V, and VI atoms, which we summarize as 1–4–5–6 electrolytes. Herein, they are compared to each other with regard to their structural characteristics and the resulting ion transport properties. The lower activation energy of Na+ ion transport in NaSnPSe is well in line with the results of speed of sound measurements, Raman spectroscopy, bond-valence site energy calculations, and molecular dynamics simulations, all of which point to a lower lattice rigidity and to weaker Na–chalcogen interactions as compared to NaSnPS.本工作报道了首款基于四元硒化物的钠离子超离子固体电解质Na₁₁.₁Sn₂.₁P₀.₉Se₁₂（下文简称NaSnPSe）。该电解质的室温钠离子电导率可达3.0 mS/cm，与当前硫化物体系的电导率纪录保持者Na₁₁Sn₂PS₁₂（下文简称NaSnPS）几乎持平，但其活化能仅为0.30 eV，显著低于后者。两种电解质均属于当下广受关注的固体电解质类别，其组成包含第I、IV、V、VI族原子，我们将其归纳为1–4–5–6型电解质。本文中，我们针对二者的结构特征与由此衍生的离子传输性能展开对比分析。NaSnPSe更低的钠离子传输活化能，与声速测试、拉曼光谱、键价位点能量计算以及分子动力学模拟的结果高度吻合；上述研究手段均表明，相较于NaSnPS，NaSnPSe具备更低的晶格刚性与更弱的Na-硫族元素相互作用。