Cooking up sustainable batteries

Scientists have been working to improve the range of anode materials available for sodium-ion rechargeable batteries. These batteries could rival lithium-ion batteries, and can be made from a much more sustainable and cheaper source – salt.

Anodes for lithium-ion batteries are often carbon-based. But while small lithium-ions fit nicely into graphite, larger sodium ions don’t. Alternative anode materials include various organic molecules including carboxylates. Synthesis usually involves solvent-based reactions.

But in an attempt to find a more sustainable route by avoiding using conventional solvents in these battery materials, the scientists used microwaves. The team aimed to make the model anode compound sodium naphthalene-2,6-dicarboxylate (Na-NDC). To do this, they stirred naphthalene-2,6-dicarboxylic acid and sodium hydroxide with a small amount of ethanol as a solvent in a sealed tube, while microwaving it. After 10 minutes, the reaction was complete and the anode material was cooled and dried.

The Na-NDC was tested for its electrochemical prowess. To do this, the material was mixed with a binder to form an electrode. Different binders were tested, with water-based ones being preferable. When the binder used was carboxymethyl cellulose, the resulting anode material had a particularly high coulombic efficiency, which shows promise for commercialisation.

These new anode materials are not good enough to go into a commercial device at the moment, the drawbacks are mainly low electronic conductivity. This means that to make a workable anode, lots of conductive carbon must be added, and this leads to a low energy density. The scientists hope that by developing different composite materials, this will improve.