As the renewable energy market grows worldwide, the need for better energy storage systems grows along with it. At the recent intersolar Europe, the world’s leading exhibition for the solar industry, attracting 50,000 visitors and more than 1,350 exhibitors to the Munich site over three days, for the first time, more than 200 energy storage exhibitors occupied their own dedicated section.
One of the more promising new breakthroughs in energy storage for utility-scale applications comes from a team at the University of Maryland Nanocentre. Researchers there created a sodium-ion battery that uses plentiful, low-cost materials: tin and wood.
While it is the cheapness and abundance of these materials, including sodium, that makes the sodium-ion battery so attractive as a potential solution for large-scale energy storage, there is a built-in problem with the use of sodium, that of sodiation, the process by which sodium causes the anode of a battery to crack after a number of charge-discharge cycles, quickly rendering it useless.
To solve this problem, the Maryland team took their inspiration from the way plants handle sodium. Wood fibers in plants use capillary action to transfer sodium ions from the soil to their leaves, without damage to the plant. The researchers therefore took microfibers of wood from a species of pine tree, coated them with carbon nanotubes, then applied a film of tin over that to create the anode for their battery.
The wood fibers performed well in tests, remaining viable after several hundred charge/discharge cycles.
One of the researchers, Teng Li, said that wood fibers, which once held mineral-rich water when they were part of the living plant, are “ideal for storing liquid electrolytes.” This property makes them both the base and an active part of the battery. And the wood fibers are soft enough to act as a buffer, releasing the mechanical stress associated with the charge/discharge process, during which the anode material can swell by more than 400 per cent. It is this property, said Li, that makes wood the “key” to their long-lasting sodium-ion batteries.
The storage capacity of sodium is lower than that of lithium, which likely means that Na-ion batteries would not be suitable for small, portable applications like cell phones and laptops. Their more likely application is in storing large amounts of energy from solar and wind installations.