Ionic liquids in the scope of lithium-ion batteries: from current separator membranes to next generation sustainable solid polymer electrolytes

A relevant issue associated with the environmental impact of current and future technologies is the balance between performance and sustainability. In this regard, there is an effort to increase the sustainability of energy storage systems and, in particular, of lithium-ion batteries, by replacing the most harmful battery components with environmentally friendlier ones. The application of ionic liquids, both as a replacement for electrolytes or solid polymer electrolytes, is a promising strategy to achieve this goal. In this work, a perspective of the use of ionic liquids for lithium-ion batteries is presented, focusing on the main used types, and their applications in separators and solid polymer electrolytes. The future trends in the use of ionic liquids for battery systems are also presented. Considering their properties and features widely reported in the literature, the use of ionic liquids for energy storage systems has the potential to properly address sustainability issues without jeopardizing their performance. We present a review on the current state-of-the-art of ionic liquids for the development of electrolytes, both conventional and solid-state. This review article provides a thorough summary of the developments achieved in this field.