硅酸盐学报

水系电解液在宽温域下的微观结构和动力学性质

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李柱杰 ¹^,² , 刘蕊蕊 ³ , 刘小村 ¹^,²

硅酸盐学报 | 电化学储能材料计算与设计专题—研究论文 2025,53(7): 1893-1901

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硅酸盐学报 |电化学储能材料计算与设计专题—研究论文 2025 , 53 (7) : 1893 -1901

水系电解液在宽温域下的微观结构和动力学性质

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李柱杰¹^,², 刘蕊蕊³, 刘小村¹^,²

作者信息

^1．山东交通学院交通土建工程学院，济南 250357

^2．山东省智能建造装备关键技术与系统重点实验室，济南 250357

^3．山东交通学院轨道交通学院，济南 250357

作者简介:

李柱杰（1989—），男，博士，副教授。

Structure and Dynamic Properties of Aqueous Electrolytes under Wide Temperature Range

Zhujie LI¹^,², Ruirui LIU³, Xiaocun LIU¹^,²

Affiliations

^1.School of Civil Engineering, Shandong Jiaotong University, Jinan 250357, China

^2.Shandong Key Laboratory of Technologies and Systems for Intelligent Construction Equipment, Jinan 250357, China

^3.School of Rail Transportation, Shandong Jiaotong University, Jinan 250357, China

LI Zhujie (1989-), male, Ph.D., Associate Professor. E-mail: zhujieli89@163.com

出版时间: 2025-07-20 doi: 10.14062/j.issn.0454-5648.20250018

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摘要

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水系电解液因其高安全性等优势，在电化学储能领域展现出广阔应用前景。研究表明，水系电解液在宽温域能够保持良好的电化学性能，但其微观作用机制尚未完全阐明。为此，采用分子动力学模拟方法，对双三氟甲磺酰亚胺锂（LiTFSI）基水系电解液的微观结构与动力学行为进行系统研究。通过对比2种不同浓度电解液的温度依赖性发现，高浓度体系在极端温度下仍能维持稳定的微观溶剂化结构，展现出宽温域应用潜力。然而，低温下的盐析出和离子传输受限问题需通过引入共溶剂（盐）或添加剂等策略改善。本工作提出的基于分子动力学的分析方法，为电解液体系的微观机理研究提供了新的技术路径，具有重要参考价值。

关键词

水系电解液 / 双三氟甲磺酰亚胺锂 / 分子动力学

Abstract

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Introduction

Aqueous electrolytes have potential applications in electrochemical energy storage devices due to their intrinsic non-flammable properties. Though its electrochemical stability window is narrow and normally it is hard to form effective solid electrolyte interphase, some researchers conduct in-depth research and propose several related solutions. Water-in-salt (WiS) electrolytes, as one of super-concentrated aqueous electrolytes, become one of the most promising systems. Some studies indicate that they can maintain a good electrochemical performance in a wide temperature range. However, its microscopic mechanism is still unclear. Therefore, in this paper, the microscopic structure and dynamic properties of LiTFSI-based aqueous electrolytes were investigated via molecular dynamics simulations.

Methods

All-atom classical molecular dynamics simulations were performed by using a software package named LAMMPS. The calculated system was composed of Li cation, TFSI anion and water molecules. The 20 mol/kg salt concentration system was selected as a main research object, and the component ratio was LiTFS∶H₂O of 128∶355. In addition, a system with a salt concentration of 3.5 mol/kg (LiTFSI∶H₂O of 32∶507) was also used as a comparison for simultaneous study. The selection principle of the two systems was to be consistent with that of the previous work. The force field parameters also followed the previous selection, where the simulation results were verified via the experimental data. Each system was simulated at different temperatures (i.e., 253, 273, 298, 323 K, and 343 K). For each salt concentration system, a relatively large simulation box was established and randomly put the corresponding number of particles into the box. Afterwards, the equilibrium system at each temperature was obtained through the initial structure optimization, and the heating or cooling procedure under the NPT ensemble. Finally, the production runs of 100-200 ns was carried out under the NVT ensemble, and the results of this step were used for post-analysis. In the whole production runs, the simulation timestep was 1 fs, and the data output interval was 50 fs for stress tensors, 1 ps for unwrapped coordinates, and 10 ps for trajectory-based analysis.

Results and discussions

The RDF calculations indicate that in the super-concentrated system (20 mol/kg), it is hardly affected by temperature, and at a lower concentration (3.5 mol/kg), the peak value is slightly affected by temperature. This indicates that the microscopic solvation structure between Li and water molecules in the high concentration system is more thermodynamically stable. To further explain this phenomenon, we calculate the potential of mean force (PMF). The results show that the solvation binding energy and activation energy of Li-Ow in the high concentration system both are almost temperature-independent, while the low concentration system shows a certain temperature dependence for the activation energy differences of 1-2 k_BT in the temperature range.

Furthermore, the connection matrix analysis (where the red region represents a closer contact distance between the two atoms and a higher binding strength) show that this part is mainly from Li-Ow, Li-O, Hw-O, Hw-O four pairs. The first two pairs represent O atom from the first solvation shell of Li, and the latter two groups represent the hydrogen bonds. In addition, the yellow region represents that although the contact distance between atoms is relatively far (i.e., still within 3 Å), the binding strength is still high, such as Li-Hw, Li-S, Hw-S, Ow-O, Ow-Ow, O-O pairs. The connection matrix also gives important information that the Li-Li pair is formed at a distance of about 3 Å, which is an interesting phenomenon.

The properties of Li-Li dimers in high concentration systems are investigated. Through the RDF, the first peak appears at 3 Å, and the peak gradually increases as the temperature decreases, implying a more intense binding or a longer binding time. From the auto-correlation function (ACF) and the lifetime of the dimer existence, the ACF decreases rapidly with the increase of temperature, and the lifetime decreases significantly from 8500 ps to 160 ps, which is consistent with the Brownian motion and can also be confirmed via the analysis of dynamic properties.

Also, the relationship among the viscosity, diffusion coefficient, ionic conductivity and their temperature dependence of the two studied systems is analyzed. In general, the dynamic properties are obviously affected by temperature, both in high concentration system and low concentration system. In the analysis of the ionic conductivity, the Haven ratio is calculated to characterize the effect of collective diffusion in the system. The results show that the collective diffusion behavior in the high concentration system significantly affects the ionic conductivity, and is independent of temperature. At a low concentration, the effect of collective diffusion on ionic conductivity changes with temperature, and the effect gradually disappears at high temperatures.

Conclusions

In this work, molecular dynamics simulations were used to investigate the microscopic structure and dynamic properties of a typical aqueous electrolyte at two concentrations and their performance in a wide temperature range. The thermal stability of the micro-solvation structure of the high concentration system was analyzed via the RDF and PMF, providing a microscopic explanation for the excellent performance of super-concentrated aqueous electrolyte at extreme temperatures. The analysis of the connection matrix could further clarify the microscopic picture of the studied system. The analysis of the properties of Li-Li dimers could be related to the structure and dynamic behavior. The study of dynamic properties such as viscosity, diffusivity and conductivity showed the intrinsic coupling between them and their relationship with structural properties. In particular, the coupling relationship between collective dynamics and conductivity in two different concentration electrolyte systems was proposed and compared.

Key words

aqueous electrolyte / lithium bis trifluoromethanesulfonyl imide / molecular dynamics

引用本文

李柱杰, 刘蕊蕊, 刘小村. 水系电解液在宽温域下的微观结构和动力学性质. 硅酸盐学报, 2025 , 53 (7) : 1893 -1901 . DOI: 10.14062/j.issn.0454-5648.20250018

Zhujie LI, Ruirui LIU, Xiaocun LIU. Structure and Dynamic Properties of Aqueous Electrolytes under Wide Temperature Range[J]. Journal of the Chinese Ceramic Society, 2025 , 53 (7) : 1893 -1901 . DOI: 10.14062/j.issn.0454-5648.20250018

基金

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国家自然科学基金(22202011)
山东省自然科学基金(ZR2022 QB056)
山东省高等学校青创科技支持计划(2024KJN002)

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2025年第53卷第7期

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文章信息

doi: 10.14062/j.issn.0454-5648.20250018

接收时间：2025-01-09
首发时间：2026-10-21
出版时间：2025-07-20

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收稿日期：2025-01-09
修回日期：2025-02-27

基金

国家自然科学基金(22202011)

山东省自然科学基金(ZR2022 QB056)

山东省高等学校青创科技支持计划(2024KJN002)

作者信息

^1．山东交通学院交通土建工程学院，济南 250357

^2．山东省智能建造装备关键技术与系统重点实验室，济南 250357

^3．山东交通学院轨道交通学院，济南 250357

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https://castjournals.cast.org.cn/joweb/gsyxb/CN/10.14062/j.issn.0454-5648.20250018

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2种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

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