Cationic surfactant for lithium-sulfur batteries enables efficient use of sulfur and limits lithium dendrite formation

Abstract

Lithium-sulfur batteries (LSBs) are promising energy-storage systems due to their high theoretical energy density. However, LSBs’ practical energy density is limited by a large electrolyte-to-sulfur (E/S) ratio (>5 μL mg−1 S), and their reversible operation encounters challenges from electrode passivation and Li dendrite formation. Herein, we report a strategy for enhancing LSBs’ performance by using a cationic surfactant-based electrolyte additive: tetramethylammonium hexafluorophosphate (TAHP). The stronger electrostatic interaction between the tetramethylammonium cation and the short-chain polysulfide (PS) anion promotes the reduction of long-chain PS to short-chain PS, inducing 3D particulate deposition of Li2S and thus increasing both sulfur utilization and discharge potential, alleviating electrode passivation. Moreover, tetramethylammonium cations can adsorb around Li protrusions to form a lithiophobic protective layer that inhibits the formation of Li dendrites. As a result, the TAHP lithium-sulfur pouch cell maintained an excellent capacity retention ratio with 78.3% after 250 cycles under lean-electrolyte conditions (4.5 μL mg−1 sufur [S]).