Potassium 3-Thiophenetrifluoroborate Based Preferential Redox toward Highly Efficient Bilateral Protection for Full Li–S Batteries

Electrolyte additives have been promising strategies aimed at lithium metal dendrite growth and active materials loss of sulfur cathode those have troubled the development of Li-S batteries (LSBs), while current interface modulations of electrodes are still challenged by low protection efficiency and high N/P ratio. Herein, potassium 3-thiophenetrifluoroborate (KPTB) is adopted as an additive to construct versatile interface for both lithium metal anode (LMA) and sulfur cathode. The preferentially electrochemical reduction and oxidation of PTB (3-thiophenetrifluoroborate) moiety, as well as electrostatic shielding exerted by K⁺ ion, enable F-rich solid electrolyte interphase for LMA and construct polythiophene based protection layers on the two electrodes, facilitating fast and uniform ion/electron transfer across the interface, suppressing polysulfide outflow and maintaining integrity of electrodes. Electrochemical measurements indicate that optimized dosage of KPTB in electrolyte remarkably enhances reversibility and cyclic stability of the two electrodes, and endows LSBs with excellent performances over wide temperature range (−25–50 °C). Remarkably, the Li-S full cells using a 75 µm of LMA can deliver a capacity of 6.0 mAh cm⁻² and excellent cyclic performances for 350 cycles, at a N/P ratio as low as 1.4. This work can provide new reliable solution for electrolyte additive based interface protections in LSBs.