Abstract
An elemental sulfur electrode was imaged with X-ray micro and nano computed tomography and segmented into its constituent phases. Morphological parameters including phase fractions and pore and particle size distributions were calculated directly from labelled image data, and flux based simulations were performed to determine the effective molecular diffusivity of the pore phase and electrical conductivity of the conductive carbon and binder phase, Deff and σeff, that can be used as an input for Li-S battery modelling. In addition to its crucial role in providing electrical conductivity within the sulfur electrode, the intrinsic porosity of the carbon binder domain was found to significantly influence Li-ion transport within the electrode. Neglecting this intrinsic porosity results in an overestimation of the electrical conductivity within the sulfur electrode, and an underestimation of the tortuosity of the Li-ion conducting phase by ca. 56%. The derivation of effective transport parameters directly from image data may aid in the development of more realistic models of Li-S battery systems by reducing the reliance on empirical correlations, and the uncertainties arising from assumptions made in these correlations.
Highlights
Lithium–sulfur (Li–S) batteries are rapidly emerging as a viable successor to Li-ion technology, and have garnered significant interest in automotive and aerospace applications, due to their higher gravimetric energy density compared to transition metal oxide based cathodes.[1]
Nano-porosity was calculated from the weighed mass of the electrode, known mass fraction of the CBD and the volume fraction of the carbon binder domain obtained from the micro-computed tomography (CT) data
When compared to the use of empirical correlations to determine effective electrical conductivity in Li–S battery models, the image-based approach we have presented to measure effective electrical conductivity based on the actual microstructure of the sulfur electrode can be used to generate more realistic models for the design and optimization of sulfur electrodes when combined with experimental measurements of bulk conductivity.[40]
Summary
Lithium–sulfur (Li–S) batteries are rapidly emerging as a viable successor to Li-ion technology, and have garnered significant interest in automotive and aerospace applications, due to their higher gravimetric energy density (ca. 2567 W h kgÀ1) compared to transition metal oxide based cathodes (ca. 387 W h kgÀ1).[1]. 387 W h kgÀ1).[1] the practical implementation and commercialisation of Li–S batteries has been plagued by a multitude of factors that have been discussed in detail by various authors2–4 – namely, poor electrical conductivity of elemental S8 and the discharge product Li2S; complex multi-step reaction mechanisms involving solid–liquid–solid phase transitions; the polysulfide shuttle effect stemming from soluble polysulfides in the electrolyte phase; and lithium metal anode degradation. The need to develop a better mechanistic understanding of the electrochemical reactions occurring within the Li–S battery has driven increased interest in the application of continuum modelling techniques commonly used in Li-ion battery research. Paper than the molecular dimensions.[9] Li–S battery modelling is complicated by the inherent heterogeneity in cathode architecture and the fundamentally different reaction mechanisms occurring with the active material between conversion- and intercalation-type cathodes respectively
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