Cooking durable battery materials in the microwave | Research
Simple and sustainable ways to make better anodes for rechargeable batteries are being concocted by chemists at the University of St Andrews, UK.
A team led by a chemist Robert armstrong worked to improve the range of anode materials available for rechargeable sodium-ion batteries. These batteries could compete with lithium-ion batteries and can be made from a much more sustainable and inexpensive source: salt.
Lithium-ion battery anodes are often carbon-based. But while the small lithium ions integrate well in graphite, the larger sodium ions do not. Alternative anode materials under study include molecules containing organic groups with redox activity, including carboxylates, imines and azo. The synthesis generally involves conventional solvent-based reactions.
But in an attempt to find a more sustainable route to these battery materials by avoiding conventional solvents, Armstrong and his team turned to other means of eliciting reactions. One of them was to use microwaves. The team aimed to make the model anode compound sodium naphthalene-2,6-dicarboxylate (Na-NDC) as proof of principle. They mixed 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.1
Na-NDC has been tested for its electrochemical prowess. To do this, the material was mixed with a binder to form an electrode. Different binders have been tested, water-based ones being preferable. When the binder used was carboxymethylcellulose, the resulting anode material had particularly high Coulomb efficiency, which shows promise for commercialization, Armstrong explains. âThey are not good enough to fit into a commercial device at the moment, the downsides are mainly low electronic conductivity,â he says. This means that to make a workable anode, you have to add a lot of conductive carbon, which leads to low energy density, he adds. Armstrong hopes that by developing different composite materials this will improve. “It works at least as well as similar materials prepared by conventional means,” Armstrong says of Na-NDC.
Armstrong’s team also recently published another simple technique for synthesizing anodes, using mechanical stirring to make the reaction proceed, producing sodium carboxylates.2 This mechanochemical method took about an hour and required no solvents.
Sodium battery maker Faradion in Sheffield, UK collaborates to test both microwave and mechanically fabricated materials, once Armstrong and his team have prepared enough anode material to make a device. functional.
The advantage of making the anodes with organic materials is their ability to be easily modified. âThere are so many possibilities for tunability,â says Armstrong. The use of methods such as microwaves and mechanochemical synthesis add to the durability of the resulting battery.
Serena cussen at the University of Sheffield, which uses microwave synthesis to study other battery components, agrees. âOrganic-based electrodes present a potentially more sustainable alternative to some of their inorganic counterparts, which face supply chain or environmental impact issues,â she says. âThere is also the attractive possibility of refining the electrochemical potential thanks to the structural flexibility offered by organic active electrodes. Challenges remain in making microwave synthesis work on a large scale, she says, but adds that “microwave roads are an exciting prospect for more sustainable manufacturing of energy storage materials.”