电解质浓度对Gold / LITFSI-DMSO溶液界面溶剂化结构的影响,The Journal of Physical Chemistry C

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电解质浓度对Gold / LITFSI-DMSO溶液界面溶剂化结构的影响
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-05-13 , DOI: 10.1021/acs.jpcc.0c00827
Lei Wang _{1,

2} , Kohei Uosaki ₂ , Hidenori Noguchi _{1,

2}

Affiliation

在锂金属电池中使用高浓度电解质能够有效地抑制锂负极上锂枝晶的生长。必须解决低浓度和高浓度电解质在电解质/电极界面处的溶剂化结构问题，以了解电还原稳定性和固-电解质中间相（SEI）的形成。使用表面增强拉曼光谱法研究了各种电解质浓度下双（三氟甲烷磺酰基）酰亚胺锂（LITFSI）-二甲基亚砜（DMSO）在金模型电极上的浓度依赖性溶剂化结构。在低浓度下，发现游离的DMSO和TFSI ^–被化学吸附在金表面，形成吸附层。其中，TFSI ^–通过对ν（Au–O）键的观察，其氧原子被化学吸附。此外，在金表面化学吸附的TFSI ^–与低浓度电解质中的Li ⁺不协调。随着浓度逐渐增加至2.31 M，化学吸附的TFSI ^–开始与Li ^+配位。当LITFSI浓度进一步增加到2.31 M以上时，吸附层中将不存在化学吸附的DMSO。相反，化学吸附的TFSI ^–成为唯一的物种。化学吸附的TFSI ^–建议与Li ⁺配合使用它的两个氧如此高的浓度使它的配位饱和。一旦施加电场，浓度高于2.31 M的电解质中不含DMSO的吸附层可能有助于形成致密且均匀的SEI，这有助于改善电池的长期循环性。

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Effect of Electrolyte Concentration on the Solvation Structure of Gold/LITFSI–DMSO Solution Interface

The use of high-concentration electrolytes in lithium metal batteries enables the effective suppression of lithium dendrite growth at the lithium anode. The issue of the solvation structure at the electrolyte/electrode interface in low- and high-concentration electrolytes must be addressed to understand the electroreduction stability and solid–electrolyte interphase (SEI) formation. The concentration-dependent solvation structure of lithium bis(trifluoromethanesulfonyl)imide (LITFSI)–dimethyl sulfoxide (DMSO) on a gold model electrode has been investigated with various electrolyte concentrations using surface-enhanced Raman spectroscopy. At low concentrations, free DMSO and TFSI^– were found to be chemisorbed on the gold surface to form an adsorption layer. Among these, TFSI^– was chemisorbed via its oxygen atoms based on the observation of the ν(Au–O) bond. Besides, chemisorbed TFSI^– at the gold surface did not coordinate with Li⁺ in the low-concentration electrolyte. As the concentration gradually increased up to 2.31 M, chemisorbed TFSI^– started to coordinate with Li⁺. On further increase in LITFSI concentration above 2.31 M, chemisorbed DMSO was absent in the adsorption layer; instead, chemisorbed TFSI^– became the only species. The chemisorbed TFSI^– is proposed to be coordinated with Li⁺ by two of its oxygens in such high concentration, making its coordination saturated. The DMSO-free adsorption layer in electrolytes with concentration above 2.31 M might help to form a dense and uniform SEI once an electrical field is applied, which contributes to improve the long-term cyclability of batteries.

更新日期：2020-05-13

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