Japan launches new high-energy sodium battery

Introduction: Scientists in Japan have demonstrated a hard carbon electrode that can greatly improve the capacity of sodium-ion batteries. With further research on long-term performance, this discovery could allow sodium-ion batteries to better compete with lithium-ion batteries in energy density .

Sodium-ion batteries are a promising energy storage technology that has seen limited commercialization in the stationary energy storage sector. Sodium-ion has also attracted a lot of attention from researchers because it offers an alternative to lithium-ion batteries, which rely on cheaper and more abundant materials.

Sodium-ion technology lags behind lithium-ion in terms of energy density . This means it is widely considered impractical for applications such as electric vehicles or consumer electronics, where battery size and weight are primary concerns. However, a new discovery by scientists at Tokyo University of Science (TOS) may overturn this assumption.

A team at the university has set its sights on carbon electrode materials to improve the capacity of sodium-ion batteries and has developed a technique for making porous hard carbon anodes. The technique is described in the paper New hard-carbon anode material for sodium-ion batteries will solve the lithium conundrum, published in the international edition of Angewandte Chemie.

The key to the process is the use of magnesium oxide (MgO) as a "template" for pore size and structure. MgO particles form a carbon matrix and are pretreated at 600 degrees Celsius, followed by acid leaching and carbonization at 1500 degrees Celsius to complete the process. After a series of experiments to optimize the MgO template and calculate the ideal manufacturing conditions, the research team was able to produce hard carbon with a capacity of 478 mAh/g and a Coulomb efficiency (charge transfer efficiency) of 88% in the first cycle.

TOS professor Shinichi Komaba noted that the highest value previously reported for this material was 438 mAh/g, which was achieved by processing at higher temperatures. TOS presented calculations showing that a sodium-ion battery using this anode would operate at a slightly lower voltage drop than today's standard lithium-ion batteries, but would still achieve a roughly 19% increase in energy density (1,600 Wh/kg versus 1,430 Wh).

"Our study proves that it is possible to realize high-energy sodium-ion batteries, overturning the common belief that lithium-ion batteries have higher energy density," Komaba said. "The hard carbon we developed with extremely high capacity opens the door to designing new sodium storage materials."

Other battery concepts being investigated promise energy densities far exceeding what TOS has achieved here, and it's unclear how much more performance this new concept can squeeze out. However, this work may force researchers to think again about the possibilities of sodium-ion batteries. The next steps will be to assess the practicality of this approach and whether the materials can remain stable over many cycles and achieve a lifespan at least comparable to today's lithium-ion technology.