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Sodium not just in salt but in batteries too!

A novel battery using sodium compounds has been developed, which can potentially be used to provide electricity for grid-power storage in remote areas and renewable energy generators like solar cells and wind turbines. Though scientists have been trying to use sodium in batteries for some time, this is the first time they have been able to achieve an operating voltage as high as 3.8 V.

In a paper published in Nature Communications, the investigators report the synthesis of a new material containing sodium, and its application as an electrode in a battery. Prabeer Barpanda of Materials Research Centre at IISc, initiated the research on this new electrode material during his stay in the University of Tokyo.

Batteries are portable sources of electricity which generate electrical energy through chemical reactions. Since their discovery by the Italian scientist Alessandro Volta more than 200 years ago, batteries have powered technological growth in their wake. It is hard to imagine a day run without batteries in a world dominated by a sea of electronic devices. In fact, manufacturing Li-ion batteries, which powers most electronic devices, has grown into a multibillion dollar industry; lithium has become the new “gold” among energy materials, because of its widespread use in batteries and paucity of lithium sources.

All batteries have the same structure, though the materials used for constructing them may differ from one technology to another. They contain two terminals: one is termed the positive, and the other negative. Inside the casing that is visible to us, these terminals are connected to bigger components called electrodes. The electrode connecting to the positive terminal is called the cathode, and the one that is connecting to the negative terminal is called the anode. Electrochemical reactions that produce energy in a battery take place inside these electrodes. In a Li-ion battery, the cathode is made from a chemical compound containing lithium, and the anode from different forms of carbon. Of late, many sodium-based electrodes have also been explored as alternative systems. Prabeer Barpanda and his coauthors have now developed a material containing sodium, which could also be used as a cathode in batteries.

For the past five years, Prabeer has been searching for new electrode materials for both lithium-ion and sodium-ion batteries. While working in France, he discovered a few iron based sulphate materials that could be used as cathodes in lithium-ion batteries. During his stay in Japan, a disastrous earthquake that caused widespread power outages hit the country. As a response to this, the Japanese government initiated projects to develop sodium-ion batteries to store energy in large scales. “This changed our group focus from Li-ion to Na-ion batteries”, said Prabeer in an email interview with the Science Media Centre. “Using my previous experience in France, I pursued new sulphate cathodes for sodium-ion batteries and discovered the current material that delivers the highest operating voltage for sodium batteries”, he explained.

Starting with calculated amounts of sodium sulphate and iron sulphate, the researchers obtained the required compound after many steps, involving processes that are common to us, like milling and drying. However, they were carried out under highly controlled conditions. The researchers also discovered the arrangement of atoms in this material that is new to science. This was achieved by combining synchrotron X-ray diffraction and computational analyses. The entire investigationwas carried out in the University of Tokyo and Kyoto University, Japan.

Raw materials like sodium and iron are abundantly available from the earth’s crust. Sulphate compounds are widely used in fertilizer, pesticide, and other chemical industries. Since the compounds are a by-product of combustion, they can also be obtained from coal plants, very economically.

However, one known limitation of the new battery is that its performance deteriorates when exposed to ambient conditions for a long time. Of course, this can be avoided with careful packaging and storage.  Researchers have also observed that the material begins to lose weight when it is made to operate in temperatures excess of 450°C. Though this can be drawback in special cases, it should not affect its performance in a wide range of applications.

About the author:

PRABEER BARPANDA. Email: prabeer@mrc.iisc.ernet.in; Website: http://mrc.iisc.ernet.in/Faculty/Regular/PRAB/Barpanda_Profile.htm. Please contact over email as the author is currently in Japan.

Link to the paper: http://www.nature.com/ncomms/2014/140717/ncomms5358/full/ncomms5358.html