A few months ago, a team of researchers from the RS2E network presented their first sodium-ion battery prototype. To understand the breakthrough represented by this technology, we need to understand the context of rechargeable batteries used for mobile applications.

The battery market is currently booming, and is dominated by lithium-ion batteries. Lithium, in low abundance on earth (33rd most abundant element, 20mg/kg in the earth’s crust), is an essential component of these storage systems. The largest lithium deposits are limited to a few countries in South America (Chile, Bolivia, Argentina) and Asia (China). It is this small number of producers that gives rise to fears of supply irregularities, making lithium a medium-critical resource. With available reserves estimated at several tens of millions of tonnes, compared with annual extraction of between 33,000 and 38,000 tonnes (36,000t in 2014), a shortage is not envisaged in the long term (several centuries of supply).

In recent years, the development of sodium-ion batteries has become a key objective for research laboratories specializing in rechargeable batteries. Sodium is much more abundant than lithium (the 6th most abundant element, at 23,600mg/kg in the earth’s crust) and much more accessible. The primary reservoir of sodium is seawater, which contains around 10g/kg, making it suitable for use in many countries.

The RS2E team’s production of an 18650 prototype (the standard format used for Li-ion batteries) represents a major step towards the industrialization of these batteries. With an energy density of 90 Wh/kg, equivalent to that of the first Li-ion batteries on the market (half that of the latest generation at 200 Wh/kg), and a lifespan in excess of 2,000 charge/discharge cycles, this prototype offers promising characteristics. Improved energy density could make Na-ion batteries even more competitive.

Although sodium-ion technology cannot compete with Li-ion batteries in the cell phone and tablet markets, it can be fully envisaged as a replacement for Li-ion in electric cars, or as mass storage for intermittent renewable energies (solar, wind, etc.), two fast-growing markets.