Enabling Fluorine‐Free Lithium‐Ion Capacitors and Lithium‐Ion Batteries for High‐Temperature Applications by the Implementation of Lithium Bis(oxalato)Borate and Ethyl Isopropyl Sulfone as Electrolyte

Abstract A novel fluorine‐free electrolyte comprising a solution of lithium bis(oxalato)borate in ethyl isopropyl sulfone is presented. It is characterized by its safety and non‐toxic properties, along with the capability to effectively suppress the anodic dissolution of aluminum. Successful high‐temperature application of this electrolyte in combination with various capacitor‐ and battery‐like electrode materials is shown. Further utilization in a lithium‐ion capacitor and a lithium‐ion battery is demonstrated. To the best of the knowledge, the lithium‐ion capacitor presented in this work represents the first entirely fluorine‐free device suitable for high‐temperature applications. When operating at 60 °C, this device delivers a maximum energy output of 169 Wh kg⁻¹_AM at a power of 200 W kg⁻¹_AM and even 80 Wh kg¹_AM at 10 kW kg^‐1_AM, along with the ability to retain 80% of its initial capacitance after 3500 cycles at 5 A g⁻¹. As such, this novel electrolyte is a promising alternative to conventional fluorine‐containing configurations since its performance is capable to match or even surpass that of most similar laboratory‐scale LICs.