Liquid‐Catalyst‐Activated Sparingly Solvating Electrolytes for Low‐Temperature Potassium‐Sulfur Batteries

Potassium‐sulfur (K‐S) batteries suffer from sluggish solid‐solid sulfur conversion, severe polysulfide shuttling, unstable interphases, and limited low‐temperature operability. Here, we introduce a sparingly solvating electrolyte (SSE) incorporating dimethyl diselenide (DMDSe) as a liquid catalytic additive to overcome kinetic barriers in quasi‐solid‐state sulfur redox. The use of tetrahydrofuran (THF) induces an aggregate‐dominated solvation structure that suppresses polysulfide dissolution and promotes the formation of a stable, inorganic‐rich solid electrolyte interphase (SEI). Density‐functional theory (DFT), molecular‐dynamics (MD) simulations, and in situ characterizations reveal that the electron‐donating selenium sites accelerate polysulfide binding and charge transfer, enabling rapid solid–solid conversion while minimizing soluble intermediates. Notably, we innovatively discovered accelerated formation of K 2 S 3 , which is detected at 2.35 V during an altered discharge pathway. The optimized electrolyte delivers outstanding low‐temperature performance, achieving 658.9 mAh g − 1 at 0.2 A g − 1 at −20°C with 120 stable cycles and exhibits a reversible capacity of 302.7 mAh g − 1 at 0.2 A g − 1 at −40°C. Under room temperature conditions, it sustains 407.2 mAh g − 1 after 300 cycles at 1C even under minimal electrolyte conditions (60 µL mg − 1 S). This work establishes liquid‐catalyst‐activated SSE as a promising strategy for high‐energy, low‐temperature K‐S batteries, and their deployment in extreme environments.