Sulfurized Polyacrylonitrile (SPAN) Cathodes in Lithium-Sulfur Batteries: Investigating the Influence of the Cathode Microstructure on the Electrochemical Performance

Abstract

With their unmatched specific energy density, lithium-sulfur batteries are an outstanding example for the potential of next-generation energy storage. However, major challenges such as the well-known polysulfide shuttle effect and the inherent insulating nature of sulfur stand in the way of widespread application. To combat these problems, numerous approaches have been explored, largely focusing on the cathode. [1] One of the most promising approaches is the application of covalently bound sulfur within an organic backbone, which leads to better cyclability by eliminating or suppressing sulfur dissolution. [2]

In this work, a promising organosulfur namely sulfurized polyacrylonitrile (SPAN) serving as the cathode in lithium-sulfur batteries is deeply studied. In particular, the effect of the cathode microstructure including porosity caused from varying degrees of calendering on electrochemical performance is investigated. To elucidate the effect of such microstructure variation electrochemical impedance spectroscopy in a symmetrical two- or three-electrode system is employed. The notable strength of this particular setup lies in the prevention of undesired anode and asymmetry artifacts in the recorded spectra while enabling in-situ measurements at various states of charge. [3] Suitable impedance modelling and fitting are deployed to differentiate between various processes on the cathode side. Impedance investigations are further supported by galvanostatic cycling tests of the cathodes in full cell configuration and scanning electron microscopy. The combination of morphological examination and electrochemical analysis of the heavily calendered SPAN cathodes indicates damage to the electrically conductive network while the active material does not appear to be affected during the calendering process. Moreover, increased overpotentials are detected in the calendered cathodes, leading to incomplete charging and fast capacity decay.

References: [1] M. Nojabaee: 'Ultramicroporous carbon aerogels encapsulating sulfur as the cathode for lithium-sulfur batteries', J. Mater. Chem. A, 2021, 9, 6508-6519 [2] X. Zhao: 'Sulfurized polyacrylonitrile for high-performance lithium sulfur batteries: advances and prospects', J. Mater. Chem. A, 2021, 9, 19282 [3] M. Gerle 'Identification of the Underlying Processes in Impedance Response of Sulfur/Carbon Composite Cathodes at Different SOC', J. Electrochem. Soc, 2022, 169, 030505