Supercapacitors Based on Propylene Carbonate with Addition of Sulfur Containing Organic Solvents

The widely used mixed electrolytes for supercapacitors are composed of tetraalkyl ammonium salts and mixed solvents such as propylene carbonate (PC), ethylene carbonate (EC) and ethyl methyl carbonate. Cyclic PC and EC have a high dielectric constant, good compatibility with carbon electrodes enabling the dissolution of salts to sufficient concentrations. However, it is highly viscous and gives poor conductivity even at ambient temperatures. When PC or EC is mixed with linear alkyl carbonates, such as diethyl carbonate (DEC), dimethyl carbonate (DMC), or EMC, more rapid ion transport is achieved as a result of lower viscosity and subsequently higher ionic conductivity is observed. The resulting binary or ternary mixed solutions are widely used in commercially available lithium ion batteries. The choice of co-solvent is a critical issue that significantly affects not only the conductivity, but also the electrochemical performance, including the physicochemical properties of solid electrolyte interface (SEI) formation. In recent years, sulfites such as dimethyl sulfite, glycol sulfite, butylene sulfite, and diethyl sulfite have been studied as a film forming and high temperature additives for electrolytes in lithium ion batteries. It should be mentioned that diethyl sulfite (DES) is used as a film forming agent and high temperature additive for electrolytes in lithium ion batteries improving decomposition resistance of the carbonate-based electrolyte. Propylene sulfite (PS) is used as high temperature additive for electrolytes in lithium ion batteries and it improves the decomposition resistance of the electrolyte.

The main aim of this paper is to establish the electrochemical characteristics of the supercapacitors consisting of the two identical mainly microporous titanium carbide derived carbon (TiC-CDC) electrodes in 1 M (C₂H₅)₃CH₃NBF₄ solutions in propylene carbonate (PC) and mixtures of PC with diethyl sulphite (DES), and propylene sulfite (PS) at different volume ratios. Electrochemical analysis has been made for PC:DES or PC:PS mixtures based electrolytes using cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge and constant power methods. The limiting capacitance, characteristic time constants and complex power values calculated depend noticeably on the solvent composition and on temperature applied, i.e., on the viscosity and specific conductivity of electrolyte solution used.

Acknowledgements

The present study was supported by The Estonian Centers of Excellence in Science: High Technology Materials for Sustainable Development, ETF Project 9184, European Regional Development Fund Project SLOKT10209T and Project IUT20-13. Authors of the paper would like to thank Ph.D. Tavo Romann for depositing Al on the electrodes.