Multivalent Charge Carriers

Abstract

Rechargeable battery technologies based on metal anodes coupled to the use of multivalent charge carrier ions hold promise of breakthroughs in energy density leapfrogging current state‐of‐the‐art Li‐ion battery technology. Cost and sustainability benefits are both a priori expected from the highly abundant metals employed. Yet, the large know‐how from the Li‐ion battery research field is not directly transferable – both the use of metal anodes and the migration of multivalent ions, within both electrolyte and electrodes, are technological bottlenecks to overcome. The concepts exhibit very different degrees of maturity; for magnesium, proof of concept was achieved in the year 2000 using low potential cathodes and a complex corrosive electrolyte with a narrow electrochemical stability window. Further progress since then has been slow, but the development of non‐nucleophilic electrolytes has paved the way for sulfur and organic polymer cathodes. For calcium, reversible plating and stripping of Ca 2+ was achieved only recently and now the development targets suitable cathodes enabling full cell proof of concept. Finally, for aluminum batteries, the main track has been somewhat different concepts based on intercalated anions, often in special carbons, from corrosive and chloride‐based electrolytes, but currently other electrolytes as well as true Al metal anodes are in foci. Overall, many and diverse obstacles remains, but the understanding and progress is indeed catching up rapidly. Given the promises and urgent need for next‐generation batteries, a successful multivalent battery technology would be timely.