Singh, R.Khalifa, M.Janakiraman, S.Adyam, V.Anandhan, S.Biswas, K.2026-02-082024Advanced Technologies for Rechargeable Batteries: Alkaline Metal Ion, Redox Flow, and Metal Sulfur Batteries: Volume 1, 2024, Vol., , p. 74-9097810323153489781040106433https://doi.org/10.1007/978-3-032-05855-3_26https://idr.nitk.ac.in/handle/123456789/33556Magnesium (Mg)-ion-based rechargeable batteries are attractive because magnesium is bivalent, abundant, non-toxic, and inexpensive. In the development of Mg-ion batteries (MIBs) with high energy densities, their ionic conductivity and safety have become important features. The most commonly used cathodes are Mo<inf>6</inf>S<inf>8</inf>, MoO<inf>3</inf>, V<inf>2</inf>O<inf>5</inf>, MnO<inf>2</inf>, and TiO<inf>2</inf>, but they are limited due to low voltages (<2.0 V) and low specific capacities. Therefore, electrolytes are needed to improve the voltage stability and ease of synthesis. In this chapter, polymer electrolytes and separators in MIBs with liquid or gel electrolytes are briefly outlined. Polymer electrolytes are classified into two categories, namely solid polymer electrolytes and gel polymer electrolytes (GPEs). Solid polymer electrolytes have several advantages such as high safety, lightweight, and favorable mechanical properties, but their weakness is their relatively lower ionic conductivity. To overcome these issues, GPE, which is a combination of liquid electrolyte and a polymer matrix, is explored. Poly(vinylidene fluoride)-based gel electrolytes showed a high ionic conductivity of the order of 10−3 S cm−1 at room temperature. In GPEs, an electrolyte is used as an ion transport medium between the electrodes, whereas a polymer membrane acts as a separator, thereby eliminating the physical contact between the electrodes. © 2025 selection and editorial matter, Prasanth Raghavan, Akhila Das, and Jabeen Fatima M. J.