This magnified image shows aluminum deposited on carbon fibers in a battery electrode. Image: Cornell University.
This magnified image shows aluminum deposited on carbon fibers in a battery electrode. Image: Cornell University.

The cost of harvesting solar energy has dropped so much in recent years that it's giving traditional energy sources a run for their money. However, the challenges involved in storing an intermittent and seasonally variable supply of solar energy have kept the technology from becoming economically competitive.

Researchers at Cornell University, led by Lynden Archer, professor of engineering, have been exploring the use of low-cost materials to create rechargeable batteries that will make energy storage more affordable. Now, they have shown that a new technique based on aluminum results in rechargeable batteries that offer up to 10,000 error-free cycles.

This new kind of battery could provide a safer and more environmentally friendly alternative to lithium-ion batteries, which currently dominate the market but are slow to charge and have a knack for catching fire. The researchers report their work in a paper in Nature Energy.

As well as being abundant in the Earth's crust, aluminum is also trivalent and light, giving it a higher capacity for storing energy than many other metals. However, aluminum can be tricky to integrate into a battery's electrodes: it reacts chemically with the glass fiber separator that physically separates the anode and the cathode, causing the battery to short circuit and fail.

The researchers' solution was to design a substrate of interwoven carbon fibers that forms an even stronger chemical bond with aluminum. When the battery is charged, the aluminum is deposited into the carbon structure via covalent bonding, i.e. the sharing of electron pairs between aluminum and carbon atoms.

"A very interesting feature of this battery is that only two elements are used for the anode and the cathode – aluminum and carbon – both of which are inexpensive and environmentally friendly," Zheng said.

While electrodes in conventional rechargeable batteries are only two dimensional, this technique uses a three-dimensional – or nonplanar – architecture and creates a deeper, more consistent layering of aluminum that can be finely controlled.

"Basically, we use a chemical driving force to promote a uniform deposition of aluminum into the pores of the architecture," Zheng explained. "The electrode is much thicker and it has much faster kinetics."

These aluminum-anode batteries can be reversibly charged and discharged many more times – by one or more orders of magnitude – than other aluminum rechargeable batteries under practical conditions. "When we calculate the cost of energy storage, we need to amortize it over the overall energy throughput, meaning that the battery is rechargeable, so we can use it many, many times," said Zheng. "So if we have a longer service life, then this cost will be further reduced."

This story is adapted from material from Cornell University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.