A multifunctional organic additive with diversified elements (F, S, P, and N) for high-performance PEO/LiTFSI electrolytes

Abstract

Polyethylene oxide (PEO)-based all-solid-state electrolytes hold significant promise for application in high-safety and high-energy-density batteries, yet their practical implementation is impeded by low ionic conductivity, a narrow electrochemical stability window, and poor electrolyte/electrode interfacial instability. To address these challenges, we systematically explore (perfluorophenyl)trithiophosphate (FPS) as a multifunctional organic additive featuring diversified elements (F, S, P, and N) for PEO/LiTFSI electrolytes, which simultaneously enhances ionic conductivity, broadens the electrochemical stability window, and improves interfacial properties. Leveraging its semi-rigid structure and strong lipophilicity, FPS reduces PEO crystallinity, promoting the ionic conductivity to 0.15 mS cm⁻¹ at 60 °C. Crucially, thiophosphate and pentafluorobenzene moieties of FPS preferentially react during PEO and lithium salt decomposition, forming a robust Li₂S-rich solid electrolyte interphase (SEI) that facilitates rapid Li-ion diffusion kinetics. Additionally, specific FPS–PEO interactions broaden the electrochemical stability window from 3.9 V (pristine) to 4.8 V. These synergistic effects enable Li//Li symmetric cells to cycle stably over 3000 hours at 0.1 mA cm⁻², while LiFePO₄//PEO-LiTFSI-FPS//Li full batteries deliver an initial capacity of 155.7 mAh g⁻¹ with 67% retention after 1000 cycles at 0.5C.