Challenges, opportunities, and roadmap for ionic liquid-based electrolytes in advancing energy storage devices

The ever-increasing demand for safer, portable, and compact energy storage systems has resulted in the emergence of advanced materials for electrodes and electrolytes. In this context, ionic liquids have emerged as a strong candidate for furthering gel-based and solid-state electrolytes to overcome the fundamental trade-off conceptualized in the Ragone plot. In spite of several distinct advantages, ionic liquids are often perceived as ionic conductors, with a nascent understanding of their interactions with the other components of the electrolyte and the resulting dynamics at the electrode/electrolyte electrified interface. This review aims to comprehensively cover such multi-component interactions of ionic liquids within the gel and solid-state electrolytes that enable further performance and safety in both lithium-ion batteries and supercapacitors. Components ranging from polymers, ceramics, and nanofillers that act as matrices to redox additives that enhance the polarization behavior are elaborated in the course of the review. Furthermore, a section focusing on newer characterization methods for probing and understanding such electrified multi-component interfaces is presented. In addition to summarizing the state-of-the-art developments in this domain, this review also presents a roadmap for the future development of materials and methods to deepen the understanding of interfacial processes.