The transport properties and the underlying coordination structure of a ternary electrolyte consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1,2-dimethoxyethane (DME), and 1,3-dioxolane (DOL) is studied over a wide concentration range up to a Solvent-in-Salt (SiS) electrolyte. Among other advantages for next-generation battery application, SiS electrolytes offer high lithium transference numbers (tLi) of 0.73. We analyze the transport mechanism by electrophoretic NMR (eNMR), providing mobilities µi of all species. Intriguingly, in the SiS region, the mobility of the neutral species DME exceeds the cation mobility (µ_DME > µ_Li), suggesting a heterogeneous transport mechanism, where the Li⁺ mobility is averaged over different species. Based on Raman spectroscopy, NMR spectroscopy and MD simulations, we derive a model for a concentration-dependent Li⁺ coordination environment with a heterogeneous Li⁺ coordination in the SiS region, where the 1^st coordination shell either consists of TFSI^- and DOL only, or of DME, TFSI^-, and DOL. Lithium ions partially coordinated by DME migrate faster in an electric field, in contrast to lithium ions solely coordinated by anions and DOL molecules, explaining the peculiarity of the rapidly migrating neutral DME molecules. Further, DME is identified as an exclusive bidentate ligand, while TFSI^- and DOL act as bridging ligands coordinating different Li⁺ ions. Thus, Li⁺ coordination heterogeneity is the basis for Li⁺ transport heterogeneity and for achieving very high Li⁺ transference numbers. In addition, an effective dynamic decoupling of Li⁺ and anions occurs with an Onsager coefficient σ_+- ≈ 0. These results provide a deeper understanding of the very efficient lithium ion transport in SiS electrolytes with potential to bring further improvements for battery applications.

中文翻译：

---

盐溶剂电解质中的异质锂配位可实现高锂迁移数

研究了由双(三氟甲磺酰基)亚胺锂 (LiTFSI)、1,2-二甲氧基乙烷 (DME) 和 1,3-二氧戊环 (DOL) 组成的三元电解质在较宽浓度范围内的输运特性和基础配位结构盐包溶剂 (SiS) 电解质。除下一代电池应用的其他优势外，SiS 电解质还具有 0.73 的高锂迁移数 (tLi)。我们通过电泳核磁共振 (eNMR) 分析传输机制，提供所有物种的迁移率 µi。有趣的是，在 SiS 区域，中性物质 DME 的迁移率超过了阳离子迁移率 (μ _DME > µ _Li )，这表明存在异质传输机制，其中 Li ⁺迁移率在不同物种上取平均值。基于拉曼光谱、核磁共振光谱和 MD 模拟，我们推导出了SiS 区域中具有异质 Li ^{+配位的浓度依赖性 Li +}配位环境模型，其中第^{一个配位壳仅由 TFSI -}和 DOL组成，或 DME、TFSI ^-和 DOL。与仅由阴离子和 DOL 分子配位的锂离子相比，由 DME 部分配位的锂离子在电场中迁移得更快，这解释了快速迁移的中性 DME 分子的特殊性。此外，DME 被认为是唯一的双齿配体，而 TFSI ^-和 DOL 则充当协调不同 Li ⁺离子的桥配体。因此，Li ^{+配位异质性是Li +}传输异质性和实现非常高的Li ⁺转移数的基础。此外，Li ⁺和阴离子的有效动态解耦发生在 Onsager 系数 σ _+- ≈ 0 的情况下。这些结果提供了对 SiS 电解质中非常高效的锂​​离子传输的更深入的了解，并有可能为电池应用带来进一步的改进。