UP physicist finds a way to boost energy capacity of sodium-ion batteries

Darwin Putungan was a research student at the Institute of Atomic and Molecular Sciences, Academia Sinica in Taiwan (Photo from his LinkedIn page)

Darwin Putungan was a research student at the Institute of Atomic and Molecular Sciences, Academia Sinica in Taiwan (Photo from his LinkedIn page)

Lithium-ion batteries, with their high energy density and long life cycle, are among the most advanced battery technologies available today. But they can be expensive to manufacture due to the limited quantity of lithium on the Earth’s crust. Electrolyte stability can also present problems from long-term use.

This is why other materials that can replace lithium, like sodium, are rapidly being explored. Sodium is a lot more abundant than lithium which will make overall production less costly. It is likewise safer for prolonged application since more stable nonaqueous electrolytes are now accessible.

However, substituting sodium for lithium poses major limitations in application.  Sodium has larger ionic volume and weight that can lower the battery’s energy capacity and in turn restrict the adoption of sodium-ion batteries in the mobile applications segment.

One solution to the problem is finding battery electrode materials that can accommodate sodium in high capacity and with reasonable binding stability.

This is what Darwin Barayang Putungan, associate professor at the Institute of Mathematical Sciences and Physics at the University of the Philippines Los Baños, and his Taiwanese collaborators Shi-Hsin Lin and Jer-Lai Kuo managed to do in their research.

In the paper “Metallic VS2 Monolayer Polytypes as Potential Sodium-Ion Battery Anode via ab Initio Random Structure Searching,” they showed through calculations that VS2 structure remains rigid under sodium adsorption and as such, is sturdy enough as an electrode material. And although their calculated energy capacity is not very high, single layer VS2 polytypes, they said, are still promising as alternative sodium-ion batteries because of their excellent structural and electronic properties.

From the paper of Putungan, et al.: Migration pathway and energetics of sodium ion diffusion on the surface of single-layer VS₂.

The calculations furthermore proved that sodium adsorption on VS2 is not uniform in nature. Instead, it consists of layers that limit the energy capacity of the battery. Other researchers that carried out similar works failed to report this.

All these findings are valuable to the battery industry.

The paper appeared on July 2016 in ACS Applied Materials and Interfaces, a journal focused on newly-discovered materials and interfacial processes that can be developed and used for specific applications. Its impact factor is 7.145.