Role of electrolyte in the polysulfide shuttle effect and long-term cycling performance in cathodes for Li-S batteries based on sulfurated polyisoprene

In this study, we present a one-step and scalable synthesis of sulfurated-poly(isoprene) (SPI) containing 48 wt% covalently bound sulfur that avoids the formation of long-chain polysulfides and the polysulfide shuttle effect. Furthermore, a comprehensive comparative electrochemical study was conducted using three electrolytes, i.e. LiPF6 in ethylene carbonate (EC): diethyl carbonate (DEC), LiPF6 in EC: DEC with the addition of 10 wt% of fluoroethylene carbonate (FEC) and LiTFSI in 1,3-dioxolane (DOL): 1,2-dimethoxyethane (DME) with 0.1 M LiNO3. LIPF6/FEC electrolyte-based cells allow for exceptional capacity at high rates up to 5C, with extraordinary stability over 1100 cycles. This may be attributed to the formation of both a stable cathode electrolyte interface (CEI) and solid electrolyte interphase at the anode (SEI). Furthermore, galvanostatic intermittent titration (GIT) and Randles-Sevcik diffusion studies are conducted to investigate the influence of ionic radius and conductivity of PF6- and TFSI- anions on Li+-ion diffusion, as well as the formation of fluorinated interlayers between the electrode and electrolyte, as revealed by post-mortem analysis. The kinetics of the electrochemical mechanisms for the LiPF6/FEC-based electrolyte are also analyzed, demonstrating an exceptionally high diffusive contribution at elevated rates. In view of the elimination of the shuttle effect and its exemplary electrochemical performance in conjunction with the LiPF6/FEC-based electrolyte, SPI is proposed as a potential host material for use as cathodes in Li-S batteries.