Journal
JOURNAL OF THE ELECTROCHEMICAL SOCIETY
Volume 165, Issue 11, Pages A2741-A2749Publisher
ELECTROCHEMICAL SOC INC
DOI: 10.1149/2.0631811jes
Keywords
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Funding
- OXIS Energy Ltd.
- Engineering and Physical Sciences Research Council (EPSRC)
- Innovate UK
- University of Southampton [EP/P019099/1]
- European Commission through the FET-OPEN project Sulfur-Aluminum Battery with Advanced Polymeric Gel Electrolytes SAL-BAGE project [766581]
- University of Southampton
- EPSRC [EP/M508147/1, EP/M50662X/1, EP/N024303/1]
- EPSRC [EP/P019099/1] Funding Source: UKRI
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Impedance spectroscopy is used to characterize the key transport properties (effective conductivity, MacMullin number, porosity and tortuosity) of electrolyte solutions confined in porous separators and carbon-sulfur composite electrodes useful for application in Li-S batteries. Three relevant electrolyte concentrations, ranging between 1 and 5 molal, are studied. Impedance measurements are performed in symmetrical cells with two identical electrodes, which overcome complications associated with the contributions of the counter-reference electrode. The electrolyte-filled carbon-sulfur composite electrodes can be represented by an open Warburg element, modelling the finite-diffusion of ions through the pores coupled to the double-layer charging of the electrode-electrolyte interface. The carbon-sulfur composite electrodes are at a high enough potential (ca. 3 V vs. Li+/Li) so that charge-transfer reactions of sulfur reduction to polysulfide species are absent during the impedance measurements, and hence capacitive-like behavior is observed at low frequencies. The analysis of the results shows that the rate of transport of ions through porous structures is markedly dependent on the electrode's structure and composition as well as the electrolyte concentration. Synergistic effects, able to enhance the effective conductivity of the electrolyte inside porous composite electrodes, are observed for particular electrode/electrolyte combinations, which are correlated to enhanced performance in Li-S cells. (C) The Author(s) 2018. Published by ECS.
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