Abstract
Due to its success in the domain of power electronics, the lithium ion battery technology is currently being considered for electric vehicle propulsion and even electric grid storage.1,2 However, the implementation of a lithium based technology on a large scale faces controversial debates on lithium availability and cost. Alternative lower cost and sustainable chemistries would be specially suited for large scale applications even if they involve a penalty in energy density. The most appealing alternative is to use sodium, instead of lithium. Indeed, it exhibits a rich intercalation chemistry3,4 and its resources are in principle unlimited (high concentrations in seawater) being very easy to recuperate. Sodium technology has already been successfully implemented in today's commercialized high-temperature Na/S cells for MW storage and for Na/NiCl2 ZEBRA-type systems for electric vehicles, both of which take advantage of the highly conducting solid beta-alumina ceramics at temperatures of ca. 300 C. Mindful of these considerations, and within the current knowledge gained in Li-ion technology, a room temperature analogous Na-ion cell is a realistic target. If achieved, it would bring about a radical decrease in cost with respect to lithium ion technology while ensuring sustainability.