Abstract
Sulfone-based electrolytes, known for their higher oxidative stability compared to the typically used organic carbonate-based electrolytes, are considered promising electrolytes for high voltage cathode materials towards the objective of obtaining increased energy density in lithium ion batteries. Nevertheless, sulfones suffer from high viscosity as well as incompatibility with highly graphitic anode materials, which limit their application. In this paper, the effect of fluoroethylene carbonate (FEC) as an electrolyte additive for the application of ethyl methyl sulfone (EMS) electrolytes containing LiPF6 as conducting salt, is studied in graphite-based cells by means of selected electrochemical and spectroscopic methods. In addition, influence of ethylene acetate (EA) as co-solvent on the electrolyte viscosity and conductivity of the EMS-based electrolytes is discussed, revealing improved overall nickel cobalt manganese oxide (NMC)/graphite cell performance. X-ray photoelectron spectroscopy (XPS) measurements provide information about the surface chemistry of the graphite electrodes after galvanostatic cycling. The concept of EA as co-solvent is found to be applicable for other sulfones such as isopropyl methyl sulfone (MeiPrSO2) and ethyl isopropyl sulfone (EtiPrSO2).
Highlights
Nowadays, lithium-ion batteries (LIBs) find application in a very broad field of industrial applications [1,2,3] as they are, for instance, used in small portable devices, such as mobile phones or laptop computers, as well as traction batteries in the automotive industry [4]
The decomposition of fluoroethylene carbonate (FEC) on the graphite composition of sulfur in the solid electrolyte interphase (SEI) decreases from 6% to 2%, indicating formation of a passivation surface, results in formation of hydrofluoric acid (HF) and vinylene carbonate (VC)
HF reacts on the graphite surface to lithium fluoride (LiF) whereas VC polymerizes on the relative composition of theWe organic obtained for the electrolyte formulation containing expectThe an increase of results the relative composition of the inorganic part and a decrease the relative of thedeviation organic part
Summary
Lithium-ion batteries (LIBs) find application in a very broad field of industrial applications [1,2,3] as they are, for instance, used in small portable devices, such as mobile phones or laptop computers, as well as traction batteries in the automotive industry [4]. One of the possibilities is to replace graphite with lithium titanate (LTO), this anode material delivers lower energy density [23] To overcome this challenge, SEI-forming electrolyte additives can be added to the sulfone-based electrolyte, leading to the formation of an effective SEI on the graphite surface [13]. Fluoroethylene carbonate (FEC) shows promising results on both graphite anode and high voltage cathode materials [29]. Another challenge arising with the use of sulfone-based electrolytes is related to their low wettability of separator and electrodes as well as their poor electrolyte conductivity when used as electrolyte solvents [22]. To analyze the main decomposition products and to show the beneficial behavior of FEC in the electrolyte, X-ray photoelectron spectroscopy (XPS) and XPS sputter depth profiling measurements were performed
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