Understanding the Roles of the Electrode/Electrolyte Interface for Enabling Stable Li∥Sulfurized Polyacrylonitrile Batteries

Sulfurized polyacrylonitrile (SPAN) is a promising high-capacity cathode material. In this work, we use spatially resolved X-ray absorption spectroscopy combined with X-ray fluorescence (XRF) microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy to examine the structural transformation of SPAN and the critical role of a robust cathode-electrolyte interface (CEI) on the electrode. LiS_x species forms during the cycling of SPAN. However, in carbonate-based electrolytes and ether-based electrolytes with LiNO₃ additives, these species are well protected by the CEI and do not dissolve into the electrolytes. In contrast, in an ether-based electrolyte without the LiNO₃ additive, LiS_x species dissolve into the electrolyte, resulting in the shuttle effect and capacity loss. Examination of the Li anode by XRF and SEM reveals dense spherical Li morphology in ether-based electrolytes, but sulfur is present in the absence of the LiNO₃ additive. In contrast, porous dendritic Li is found in the carbonate electrolyte. These analyses established that an ether-based electrolyte with LiNO₃ is a superior choice that enables stable cycling of both electrodes. Based on these insights, we successfully demonstrate the stable cycling of high areal loading SPAN cathode (>6.5 mA h cm^-2) with lean electrolyte amounts, showing promising Li∥SPAN cell performance under practical conditions.