In situ crosslinked gel polymer electrolytes for Li-ion capacitors using sacrificial salt pre-lithiation, enabling high-temperature operation

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In this work the effect of encapsulating a standard liquid electrolyte (1 M LiFSI in EC:DMC) into a polymer matrix for Li-ion capacitors pre-lithiated using Li2C4O4 sacrificial salt is presented. The polymer precursor is added in liquid state, which facilitates the integration in already existing cell manufacturing lines and is polymerized in situ at 60 °C after cell assembly. The application of a gel polymer electrolyte (GPE) is demonstrated to have many benefits such as lowered risk of electrolyte leakage, reduced flammability, improved high-temperature stability and high-temperature performance. The introduction of the polymer component is suggested to improve the stability of the solid electrolyte interface (SEI), enabling capacity retention of >95 % after 1200 h floating at 60 °C first (600 h) and 70 °C after (600 h). The increased performance at higher temperatures over room temperature is explained by an increased capacity of the hard carbon (HC) negative electrode together with an improved ionic conductivity of the GPE. Further increasing the operational temperature window of the LIC to 80 °C enables additional 600 h floating, demonstrating the feasibility of the GPE concept to improve high temperature stability and performance of commercial Li-ion capacitors, importantly, without sacrificing room temperature operation.