氟代溶剂在锂金属电池中的应用

Fluorinated Solvents for Lithium Metal Batteries

近年来,锂金属电池由于具有较高的能量密度而成为储能领域的研究热点。电解液作为锂金属电池的“血液”发挥着至关重要的作用。在传统锂离子电池电解液中,锂金属负极与电解液之间的界面副反应严重并伴随着锂枝晶生长,从而导致安全隐患以及循环寿命缩短等问题。在解决锂金属负极问题上,电解液调控策略具有易操作性和有效性,因而在推动锂金属电池发展方面具有举足轻重的地位。氟代电解液是目前重要的研究方向,氟代电解液在循环过程中能够在电极表面形成富含LiF的固体电解质界面膜(SEI);该界面膜不仅可以有效抑制负极锂枝晶的形成,并且在正极方面能够大幅提高电解液的氧化稳定性,从而提升高电压正极的适配性和锂金属电池的循环稳定性。氟代电解液中氟代溶剂/氟代锂盐的分子结构对电解液的溶剂化结构有重要影响。当氟代溶剂分子中氟原子的位置与数量不同时,氟代溶剂的物理化学性质也会随之发生变化,进而改变了电解液与电极的界面反应性。因此,氟代溶剂能够起到调制SEI膜成分和结构的作用,是决定电池性能的关键因素。本文总结了应用于锂金属电池的主要氟代溶剂,尤其是近几年来发展的新型氟代溶剂;着重介绍了高度氟代的溶剂分子作为局域超浓电解液的稀释剂,以及对溶剂进行精准分子设计得到的部分氟代溶剂等。此外,本文还分析探讨了氟代溶剂分子与电池性能之间的构效关系,展望了构建新型氟代溶剂分子的策略,希望能对电解液溶剂分子的结构设计以及构效关系的评估有一定的启发意义。

Lithium metal batteries,which use lithium metal as the anode,have attracted tremendous research interest in recent years,owing to their high energy density and potential for future energy storage applications.Despite their advantages such as high energy density,the safety concerns and short lifespan significantly impede their practical applications in transportation and electronic devices.Tremendous efforts have been devoted to overcoming these problems,including materials design,interface modification,and electrolyte engineering.Among these strategies,electrolyte regulation plays a key role in improving the efficiency,stability,and safety of lithium metal anodes.As an important class of electrolyte components,fluorinated solvents,which can decompose to form LiF-rich interphase layers on both anode and cathode,have been proven to enhance the stability of lithium metal anodes and improve the oxidative stability of the electrolytes.Meanwhile,the spatial structure of fluorinated solvents,such as the number and sites of fluorine atoms,can influence the physicochemical properties of the electrolytes and the compositions/structure of the solid-electrolyte interphase,which eventually dictates the cycling performance of Li metal batteries.Recently,many fluorinated solvents with different molecular structures have been designed to regulate the solvation structure of electrolytes,and these solvents exhibit novel electrochemical properties in lithium metal batteries.However,there are few comprehensive reviews that summarize the fluorinated solvents used in Li metal batteries and discuss their functions in electrolytes and their physicochemical properties.This review summarizes the novel fluorinated solvents used in lithium metal batteries in recent years,which have been classified into three parts:diluents,traditional solvents,and novel molecules,based on their functions in the electrolytes.In every part,the understanding of the interactions between fluorinated solvents and Li ions,the decomposition mechanism of fluorinated solvents at the interface of the electrode,the functions of fluorinated solvents in the electrolytes,and the structure-activity relationship between the fluorinated solvents and battery performance have been comprehensively summarized and discussed.Moreover,the advantages and disadvantages of fluorinated solvents have been discussed,and the importance of precisely controlling the number of fluorine atoms and the structure of fluorinated solvents has been emphasized.At the end of this review,a perspective for designing new fluorinated solvents has been proposed.We believe that this review can provide insights on designing novel fluorinated solvents for high-performance Li metal batteries.