Emerging calcium batteries

This review depicts the present landscape in the field of calcium batteries, presenting a critical analysis of the state-of-the-art and estimating performance indicators to foresee the development of this technology. The practical realization of rechargeable Ca batteries still relies on the identification of suitable electrode and electrolytes. Despite reversible calcium plating-stripping being recently demonstrated, efforts are still needed to improve kinetics and efficiency and to allow a wider range of electrolyte formulations. In the very last years the spectrum of searched electrolytes and cathodes expanded to achieve proof-of-concept full Ca-batteries. Widening the electrochemical stability window of the electrolyte is crucial to push the development of positive electrodes operating at high potential. So far, only few interesting examples of inorganic cathode materials have been demonstrated. Sulfur and organic positive electrodes remain interesting pathways to follow. This work reviews electrode (positive and negative, including alloying and conversion compounds) and electrolyte materials, developed or modelled, and goes beyond, by addressing technical issues for potential Ca-cells upscaling. Based on a techno-economic analysis of different cell configurations, the performance figures-of-merit of this technology are discussed and related for the first time to EU targets and priorities established for the successful deployment of post-lithium batteries.