摘要
盐包水(water-in-salt,WIS)电解质凭借其显著拓宽电化学窗口的特性,已成为开发高性能电化学储能器件的关键材料。深入理解盐包水电解质与电极固液界面的微观结构及其浓度变化的响应,对于优化储能器件的性能具有重要意义。本工作采用分子动力学模拟方法,构建了石墨烯电极与LiTFSI水溶液的电极-电解质固液界面模型,系统研究了不同浓度下WIS电解质在电极界面的微观结构特征。结果表明,LiTFSI水溶液在电极表面形成了约0.5 nm厚的吸附层,且界面处的离子和水分子分布在浓度的影响下发生了显著变化,呈现出复杂的结构重构现象。通过分析Li^(+)的溶剂化结构,发现5 mol/kg是界面处Li^(+)溶剂化结构发生突变的临界浓度,超过此浓度时,体系进入“盐包水”状态,表现为脱溶剂化现象。随着电解质浓度的增加,TFSI^(-)离子的分布发生显著变化,从原先垂直于电极表面的取向转向为平行分布。同时,界面处的离子和溶剂分子由均匀分布逐渐转变为更加紧密的聚集态。此外,浓度的增加还显著破坏了水分子间的氢键网络,进一步加剧了界面结构的变化。这些发现为理解盐包水电解质在不同浓度条件下的行为及其与电极界面的相互作用提供了新的理论视角。
Water-in-salt(WIS)electrolytes are promising materials for developing high-performance electrochemical energy storage devices owing to their remarkable capability to broaden the electrochemical stability window,and a comprehensive understanding of their microscopic structures at the electrode-electrolyte interface and their response to concentration variations is critical for optimizing device performance.In this study,molecular dynamics simulations were employed to construct a graphene electrode-lithium bis(trifluoromethanesulfonyl)imide(LiTFS)electrolyte-interface model,which enabled the systematic investigation of the microscopic structural characteristics of the WIS electrolyte at the interface under varying concentration conditions.The results revealed the formation of an adsorbed layer(thickness:0.5 nm)on the electrode surface in the electrolyte(a LiTFSI aqueous solution).The distributions of ions and water molecules within this layer were significantly affected by the concentration,facilitating complex structural reorganization at the interface.Subsequent analysis of the Li^(+)solvation structure identified 5 mol/kg as the critical concentration at which it underwent drastic changes.Beyond this threshold,the system entered the"WIS"state,which was characterized by a desolvation phenomenon.Additionally,the distribution of TFSI^(−) changed significantly with the increasing electrolyte concentration,transitioning from a perpendicular orientation relative to the electrode surface to a parallel alignment.Concurrently,the interfacial ions and solvent molecules transitioned from a uniform distribution to a more tightly packed state.Moreover,the increased electrolyte concentration significantly disrupted the hydrogen bonding network among water molecules,further exacerbating the interfacial structural reorganization.These findings provide new theoretical insights into the concentration-dependent behavior of WIS electrolytes and their interactions with electrode interfaces,offering valuable perspectives for optimizing WIS electrolytes in electrochemical energy storage devices.
作者
杨磊
梁承林
何浩宇
李旭哲
莫唐明
YANG Lei;LIANG Chenglin;HE Haoyu;LI Xuzhe;MO Tangming(School of Mechanical Engineering,Guangxi University,Nanning 530004,Guangxi,China)
出处
《储能科学与技术》
北大核心
2025年第12期4460-4469,共10页
Energy Storage Science and Technology
基金
国家自然科学基金(52406226)
广西壮族自治区自然科学基金(2025GXNSFBA089396)
广西基地与人才专项(AD23026174)
广西青年科技人才托举工程(GXYESS2025036)
广西石化资源加工及过程强化技术重点实验室开放基金(2024K009)。
关键词
锂电池
超级电容器
水系电解质
盐包水
固液界面
分子动力学模拟
lithium-ion batteries
supercapacitors
aqueous electrolytes
solid-liquid interface
molecular dynamic simulation
