An efficient sodium-sulfur battery based on a sulfurized polyisoprene cathode: In-depth kinetic, diffusion, and electrochemical studies

Both the affordability and high theoretical specific capacity of room temperature sodium‑sulfur (RT Na-S) batteries render them an attractive alternative to conventional batteries. In this study, sulfurized poly(isoprene) (SPI) was utilized for the first time as cathode material in RT Na-S batteries. SPI comprising 50 wt% covalently bound sulfur was synthesized form S 8 and poly( trans -isoprene). The covalently bound sulfur effectively suppresses the formation of long-chain polysulfides i.e. the polysulfide shuttle, and the subsequent loss of active material. The SPI-based cathodes demonstrated excellent performance at high current densities of up to 3C exhibiting a discharge capacity of 325 mAh·g −1 . When the rate was reduced to C/10, the cell exhibited full capacity recovery (100 %). Furthermore, SPI-based cells demonstrated high cycling stability over 250 cycles at C/2 with a capacity retention of 99.36 % and a Coulomb efficiency of 100 %. Applying a 1C rate, the cells were successfully cycled over 1000 cycles with an average decay of 0.048 % per cycle. High Na-diffusion coefficients calculated from galvanostatic intermittent titration technique (GITT) data were found (D Na + , discharge = 1.3 · 10 –10 cm 2 ·s −1 ; D Na + , charge = 2.0 · 10 –10 cm 2 ·s −1 at 1.15 V). A comprehensive post - mortem study was carried out, which indicated that the electrodes exhibit remarkable structural integrity and robustness during cycling, thereby preventing degradation. • SPI cathode with 50 wt% sulfur via one-step synthesis, overcomes the shuttle effect. • Cathode has short-chain polysulfides, improving Na-S battery capacity and stability. • Cells have excellent capacity retention of 99.36 % after 250 cycles at C/2-rate. • Na-S batteries deliver 325 mAh·g −1 at 3C and 1000 cycles at 1C with 100 % efficiency. • Post-mortem analysis confirms stability, structural integrity of SPI after long cycling.