Modification And Investigation Of Li Metal Anode Through Regulation Of Liquid Electrolyte

With the rapid development of science and technology,and the ever-deteroriating of global climate,it is urgent to develop and renew the current energy system.Secondary batteries,which play an important part in energy system,have significantly facilitated the development of society.However,existing technologies of secondary batteries like Li-ions batteries largely restrict the updatation of the current energy system due to the limited energy density.Therefore,it is urgent to develop the nextgeneration battery technology for new energy system.Compared with Li-ions batteries,Li metal batteries use Li metal with ultrahigh specific capacity and the lowest electrochemical potential to replace the graphite anode with much lower capacity.Therefore,Li metal batteries can provide a very high energy density up to 500 Wh kg1.However,the development and application of Li metal batteries have been severely restricted by the problems of Li metal anode.First,the uncontrollable growth of Li dendrite have always been unavoidable,and unpredictable short-circuit problem and even explosion accident been hidden troubles during the cycling of Li metal batteries.Second,the cycling stability and cycle life of Li metal batteries have been plagued by the constant loss of active Li metal and electrolyte caused by constant and severe parasitic reactions between highly reactive Li and electrolyte.Electrolyte is an essential part of Li metal batteries,which crucially affects the growth behavior of Li metal and the extent of parasitic reactions.Therefore,the cycling performance of Li metal batteries can be effectively improved through an approach of electrolyte regulation,including utilizing novel solvents,solutes and additives.This paper improves the cycling stability of Li metal anode through the method of electrolyte regulation to arrange the physicochemical properties of solid-electrolyte interphase which is formed through the reaction between Li and electrolyte,e.g.,developing novel ester-based and ether-based electrolytes.Meanwhile,we deeply understand the decomposed behavior of electrolyte on the surface of Li and the structure-property relationship between the solid-electrolyte interphase and Li metal anode through the investigation on thermodynamic properties of novel electrolytes and the composition and structure of the solid-electrolyte interphase,which sheds light on the development of novel high-performance electrolyte and practical application of Li metal batteries.This paper is mainly divided into three parts:1.Carbonate ester-based electrolyte possesses good oxidative stability but suffers from poor compatibility with Li metal.This part effectively improves the compatibility between a carbonate ester-based electrolyte and Li metal through the use of novel carbonate ester-based electrolyte with LiNO3 additive enabled by a co-solvent of ybutyrolactone with a high Gutmann donor number.The carbonate ester-based electrolyte with LiNO3 additive can mitigate the vigorous reaction between Li and carbonate ester-based electrolyte and realize chunk-like Li plating morphology,thus enabling good reversibility of Li metal plating/stripping.This provides a new strategy for promoting the cycling stability of Li metal batteries in carbonate ester-based electrolyte.2.Linear ether solvents react mildly with Li metal due to its good reductive stability.This part mainly achieves the stable cycling of Li metal anode through the use of weakly solvating electrolyte of 2 M LiFSI-ethylene glycol dibutyl ether,with weak interaction between Li ions and a novel solvent of ethylene glycol dibutyl ether.The anions in the weakly solvating electrolyte have priority to decompose on the surface of Li metal forming inorganic compounds,followed by the decomposition of solvent with the formation of organic compounds.The inorganic and organic compounds co-act to form a solid-electrolyte interphase with an amorphous framework uniformly distributed by inorganic domains,which realize the chunk-like Li plating morphology and stable cycling of high-voltage Li metal batteries.This provides a direction for the practical application of high-voltage Li metal batteries.3.The solid-electrolyte interphase on the Li metal is faced with the problem of poor mechanical stability in the ether electrolyte with linear ethers as solvents.This part further promotes the performance of Li metal anode through the use of a polymerizable solvent 1,3-dioxolane and LiFSI and LiNO3 solutes to prepare the polymerizable electrolyte for improving the mechanical stability of solid-electrolyte interphase.The polymerizable electrolyte reacts with Li to form a polymer-rich solid-electroltye interphase,which possesses excellent flexibility and stretchability,and can rapidly selfheal on the broken regions.Therefore,column-like Li plating morphology and an ultrahigh coluombic efficiency of 99.73%for Li metal plating/stripping have been achieved,which provides a new approach for promoting the reversibility of Li metal anode.