Lithium‐Ion Batteries Containing Surfactants for the Protection of Graphite Anode against the Passivation Layer Byproducts

Surfactant protection: The protective roles of three surfactants added to the electrolyte in the formation of the solid electrolyte interphase (SEI) layer on the graphite anode are compared and analyzed. Through electrochemical testing and surface characterization, it was observed that each surfactant had a distinct impact on the cycling behavior and performance of the cells.

Abstract

The electrolyte is an essential component of all electrochemical devices, including lithium-ion batteries (LIBs). During the initial charging process, a portion of the electrolyte (usually a mixture of organic solvents and lithium salts) decomposes at the anode surface, forming a thin layer of solid electrolyte interface (SEI). This study examines the physicochemical properties of three surfactants: lithium dodecyl sulfate (LiDS), polyoxyethylene ether Forafac 1110D (LiF1110), and lithium perfluoro octanesulfonate Forafac 1185D (LiFOS). Initially, their thermal properties (surface tension and contact angle) are determined. Then, electrochemical tests (cyclic voltammetry, galvanostatic charge-discharge cycling, and electrochemical impedance spectroscopy) followed by ex-situ X-ray photoelectron spectroscopy (XPS) measurements on the graphite anodes in a standard electrolyte ethylene carbonate/propylene carbonate/3 dimethyl carbonate +1 mol L⁻¹ LiPF₆ are conducted to compare the surfactants′ action according to their chemical structure, as well as their effect on the interface properties of the formed SEI. The results indicate that surfactants improve electrode interfaces due to their amphiphilic character, preventing the harmful effects of passivation layer salts (LiF, LiOH, Li2O, etc.) that deposit on the graphite interfaces. The three surfactants affect the cycling behavior and performance of the half-cells differently depending on their ionic or nonionic nature and the polarity or non-polarity of the salt (e. g., lithium fluoride LiF, lithium oxide Li₂O), with LiF1110 demonstrating the best performance.

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