Sodium-ion technology: principle, positioning and electrode materials

As part of sustainable development policies, many technologies are the subject of scientific research in laboratories. Among these technologies, electrochemical accumulators such as alkaline-ion batteries have taken pride of place in our daily lives. This is reflected in the democratization of the lithium-ion battery, widely deployed for mobile applications (cell phones and laptops, electric vehicles). However, other complementary technologies such as sodium-ion batteries need to be optimized in view of the inevitable development of an energy mix. These batteries are particularly interesting electrochemical accumulators for stationary applications, especially for intermittent energy storage (solar, wind). Na-ion batteries have the particular advantage of involving non-critical, eco-responsible elements in the development of electrode materials, which have yet to be optimized.

In this article, the operating principle of a Na-ion battery is explained, and its performance is compared with that of its larger Li-ion sibling. We then present the negative and positive electrode materials used in these batteries, and the solid-state chemistry involved, in the light of current knowledge. Anodes are presented according to the types of chemistry underlying them vis-à-vis sodium (intercalation, alloying, conversion reactions); for materials used as cathodes, a classification according to phase crystallochemistry is provided: Prussian blue analogues, polyanionic systems and transition metal oxides.