Synergistic interphase regulation with a KSeCN bifunctional additive for stable and high-performance lithium–sulfur batteries

Lithium sulfur batteries (LSBs) have good potential for next-generation energy storage. However, the practical applications of LSBs are restricted by the shuttle effect of lithium polysulfides (LiPS) and uncontrollable Li deposition. Here, potassium selenocyanate (KSeCN) is proposed as a bifunctional electrolyte additive that can synergistically regulate both the cathode and anode electrode/electrolyte interfaces due to its optimum orbital energy levels. KSeCN promotes the formation of a hybrid organic-inorganic cathode electrolyte interface (CEI) that inhibits the shuttle effect and boosts the conversion kinetics of LiPS by incorporating conductive Se into the cathode. In addition, KSeCN facilitates an inorganic-rich solid electrolyte interface (SEI), promoting homogeneous Li⁺ deposition and suppressing Li dendrite growth. Correspondingly, LSBs with the KSeCN additive achieve a low capacity decay rate of 0.05% per cycle over 1000 cycles with excellent stability, while Li-S pouch cells operate stably for ∼140 cycles. Li‖Li symmetric cells exhibit a reduced hysteresis voltage and extended cycling lifetimes exceeding 1000 h. This work demonstrates a promising additive design strategy for high-performance LSBs through interfacial chemistry engineering.