Liquid Binary and Ternary Electrolytes Mixtures for Low-Temperature Sulfurized Carbon Batteries

Abstract

Active sulfurized carbon (SC) has been proposed as promising alternative to enable sulfur as the next generation cathode material due its ability to confine sulfur and suppresses polysulfide shuttling. Pragmatic cell performance of SC electrodes needs to extend over a wide range of temperatures from -20 °C to 60 °C. Low-temperature performance of SC cells is mainly limited by electrolyte wettability, ionic mobility between the electrodes, and the nature of the formed solid electrolyte interphase. In this work we have utilized electrolyte binary and ternary mixtures based on carbonates, ethers, and fluorinated solvents to enhance the SC cell discharge performance up to -20 °C. To understand the effects of electrolyte mixtures in the cell performance we have utilized electrochemical impedance spectroscopy (EIS) as a function of temperature and voltage. The lower cell resistance translates into a higher rate capability, cyclability, and low-temperature performance. Based on the EIS response and its spectra deconvolution we proposed an apparent electrical equivalent circuit that permits the elucidation of resistance elements and their magnitude such as the ohmic, electron charge transfer, surface film, and mass transport resistance to provide a phenomenological understanding on how the mixtures can enhance the electrochemical performance. Furthermore, differential capacity analysis and Hybrid Pulse Power Characterization (HPPC), are utilized to support the characterization. Finally, best performance electrolyte mixtures were utilized to build >0.5 Ah pouch cells for testing at low temperatures, discharge rates, and pressure conditions.