Fluorinated-oligomeric ionic liquids for high-performance wide-temperature solid zinc batteries

Abstract

Zn-based solid polymer electrolytes (SPEs) hold immense potential for developing high-performance and safe zinc ion batteries (ZIBs) that can operate effectively even at high temperatures. However, typical plasticizers like ionic liquids (ILs) exhibit limitations regarding Zn²⁺ ion transport and compatibility with the polymer matrix, causing a low Zn²⁺ transference number (t<inf>Zn²⁺</inf>) and serious phase separation in SPEs. In this study, we develop a novel fluorinated IL (F-IL) plasticizer containing an imidazole cation with a fluoro alkyl substituent as an extended side chain for zinc-based SPEs. This innovative imidazole cation effectively modifies the Zn²⁺ solvation structure. It significantly enhances the compatibility between ILs and the polymer matrix, enabling fast Zn²⁺ ion transport (with a notable t<inf>Zn²⁺</inf> of 0.46 and high ionic conductivity of 2.8 × 10⁻³ S cm⁻¹) when incorporated in SPEs. Using the F-ILs-based SPE, we achieve dendrite-free Zn plating/stripping cycling over 2000 h, even at high temperatures. A Zn‖Cl4Q battery assembled with the designed SPE outperforms other solid ZIBs, demonstrating a wide working temperature range (−15 °C to 120 °C) and a long cycling life (capacity retention 70.9% after 2000 cycles at 90 °C). In addition, the pouch cell exhibits a remarkable shelf life (90 days) and a low self-discharge rate (capacity loss of 0.09% per day) at 60 °C, thanks to the high thermal and chemical stability of the SPE during operation. The F-IL-based SPE, with its advanced ion transport structure, provides solid ZIBs with significant performance improvement, high safety, and enduring durability.