Beyond lithium-ion batteries: Recent developments in polymer-based electrolytes for alternative metal-ion-batteries

Li-ion batteries currently dominate the market, but alternative metal-ion batteries will become more important in the future due to the more abundant availability of elements such as sodium (Na), magnesium (Mg), calcium (Ca), potassium (K), aluminium (Al) and zinc (Zn). However, these alternatives face similar and new challenges in their application. Of particular importance are developments related to battery safety, efficient ion transport in the electrolyte and the metal-electrolyte interface. In this context, gel and solid polymer electrolytes are gaining increasing interest as versatile and safe alternatives to overcome various battery design issues. In this review, we provide a comprehensive overview of the latest and most interesting advances in gel and solid polymer electrolytes that can be applied in Na, K, Zn, Ca, Al or Mg ion batteries. In addition, general aspects of each metal are compared and specific challenges related to the corresponding ions are addressed with respect to the design of polymer-based electrolytes. Within each chapter, the key data reported is presented in tabular form, providing convenient access to the most important information.