Promoting Cathodic Kinetics and Anodic Stability in Practical Room-Temperature Sodium–Sulfur Batteries with Bifunctional Electrolytes

The development of room-temperature (RT) sodium-sulfur (Na-S) batteries is severely hindered due to the slow kinetics of the S cathode and the instability of the Na-metal anode. To overcome this, we introduced a dual-functional electrolyte cosolvent, trifluoromethanesulfonamide (TFMSA). Short-chain Na₂S_<i>x</i> (1 ≤ <i>x</i> ≤ 2) can be effectively dissolved due to the strong H-S bond interaction between TFMSA and sulfides, which changes the S conversion process, thereby effectively enhancing the conversion kinetics of the cathode. Meanwhile, TFMSA can generate a stable solid electrolyte interphase on the Na-metal surface to protect it from soluble polysulfide attack. Therefore, the RT Na-S batteries using the ether electrolyte show a high initial discharge capacity of 896.6 mAh g^-1 and a capacity retention rate of 73% after 150 cycles at 0.2C, and the pouch cell also demonstrates its practical performance. This work proposes a dual-functional electrolyte cosolvent selection principle to inspire the practical application of high-performance RT Na-S batteries.