水系锂离子电池固态电解质界面SEI膜形成机制研究

Water-in-Salt is a new class of super-high concentrated aqueous electrolytes with very wide electrochemical stable window > 3 V, which strongly supports advanced high voltage aqueous lithium ion batteries. In this system, the electrochemical window of electrolyte is able to be expanded not only by reducing the water activity but also by forming a passivation films named Solid Electrolyte Interphase (SEI), where the former is the thermodynamic improvement and the later provides a kinetic protection. Since Water-in-Salt electrolytes have proposed just only two years, the relative investigations of SEI formation are still at the early stage, where the results we have had is far enough than we want to know and there are a lot of basic scientific problems waiting us to resolve. In this project, our aim is to deeply and fully understand SEI formation and propose the reasonable formation mechanism, including to quantitative the chemical components of SEI, probe the original resources of SEI and understand the influences of the variated electrolytes, dissolving gases and the electrodes-dependence on SEI formation.

Water-in-Salt电解液作为一类超高盐浓度电解液体系具有大于3V的电化学窗口，为实现高电压水系锂离子电池提供了有利保障。该体系一方面由于所有水分子都参与形成溶剂化离子有效抑制了水分解；另一方面由于固态电解质界面SEI膜在负极表面形成起到动力学保护作用，从而从热力学和动力学两方面同时拓宽了电解液电化学窗口。由于该体系提出只有短短两年，SEI膜形成相关机制研究仍处于初级探索和揭示阶段，已有研究结果有限且相对单一，相关解释和结论有待系统性实验去丰富完善，大量基础科学问题有待探究。基于此研究现状，本项目意在从WIS水系电解液物理化学性质入手，通过结合多种电化学测试和先进表征手段以及辅助理论计算模拟，力求深入全面了解水系锂电池中SEI膜形成机制相关科学问题。具体包括精确定量分析SEI成分构成及其具体来源；电解液组分和溶解气体对SEI膜形成的影响以及SEI形成对电极材料的选择性等问题。

本项目聚焦于水系锂离子电池SEI膜成膜机制研究，首次针对水系SEI膜形成和稳定机制研究提出系统性研究方案，通过本项目实施对水系锂离子电池中水系电解液生成和调控SEI膜有一个深刻全面的认识，来填补水系SEI膜形成机理相关研究空白。该项目实施期内发表通讯作者论文：14篇（IF> 10, 9篇），引用次数 > 400次，包括研究类论文11 篇，包括Nature Chemistry、Adv.Mater.（2篇）、Adv. Energ. Mater.（2篇）、Energy Stor. Mater.、ACS Nano和ACS. Materials. Letters.，受邀撰写综述3篇。申请专利：7项（授权1项）。取得研究成果：1）提出低成本富CO2宽电位水系电解液，使宽电位水系电解液不再单纯依赖高盐浓度，提升电池动力学性能又大幅降低电解液成本，为未来实现低成本长寿命高性能水系储能电池提供一条全新思路（Nature Chemistry, 13, 1061, 2021）。2）提出调控电解液界面结构亲疏水性拓宽电化学窗口思路，通过疏水大阳离子实现负极疏水阳离子分子筛概念实现相对低盐浓度宽电位水系电解液（Adv. Mater. 2207040, 2022）。3）提出高盐浓度电解液“界面限域”抑制电极材料溶解机制，解释高盐浓度抑制正极溶解原因（Adv. Energ. Mater. 10,36, 2000665, 2020）。4）提出超高盐浓度电解液类固态超流体骨架锂离子自由气离子传输模型，解释强关联离子传输行为的特异性（J. Phys. Chem. C, 125, 11838, 2021）。5）综述了宽电位水系电解液研究进展和我国水系碱金属电池研究布局和进展（Energy&Fuels, 35, 9228，2021/Current Opinion in Electrochemistry, 29: 100818, 2021）。6）针对高电压水系锂离子电池其他关键材料提出一系列延寿策略（Adv. Energ. Mater., 2202447, 2022/ACS Materials Letter. 9, 1574, 2022/ACS AEM, 4, 4928, 2021）。本项目除对水系SEI膜进行全面研究，还从电解液与电池性能构效关系出发提出新型安全绿色、长寿命高电压水系锂离子电池解决方案。