Shanghai scientists achieve breakthrough in calcium battery technology

Shanghai scientists have developed a rechargeable calcium-based battery, which they say can offer a cheaper and more sustainable alternative to the most widely used lithium-ion cells.

Made from calcium, a metal roughly 2,700 times more abundant in the Earth's crust than lithium, the batteries can charge and discharge 700 times at room temperature, exhibiting high safety and stable performance for calcium-based technology for the first time.

A paper about the research by a team of scientists from Fudan University in Shanghai was published on the website of the United Kingdom-based journal Nature on Feb 7.

The abundance of calcium means the battery system has broad prospects in future energy applications, the researchers said.

"Also, cathode materials for our calcium-oxygen batteries come from carbon, which do not contain more expensive metals such as nickel, cobalt and manganese, commonly used in lithium-ion batteries. And therefore, calcium-oxygen batteries will have the advantage of low cost," said Ye Lei, a first author of the paper.

"Such new batteries present prospective applications in portable and wearable electronic devices among others in the foreseeable future."

While a reliable supply of lithium is critical for industries such as new energy vehicles and renewable energy storage, several international organizations and research units, including the International Energy Agency, have predicted a lithium shortage by next year.

Calcium-oxygen batteries have the highest theoretical energy density, or energy storage capacity relative to weight or size, among all the calcium-based batteries as the fuel for the battery comes from oxygen in the air instead of a material stored inside the battery. But previously, no calcium-oxygen battery could stably charge and discharge at room temperature.

Experts said one of the challenges was that calcium anodes have high electrochemical activity. That can easily lead to the reduction and decomposition of the electrolyte, the component in a battery that enables it to charge and discharge, and the formation of a layer on the surface of the anodes that will make it fail.

In their research, the Fudan team created a new liquid electrolyte that met the high requirements for the electrodes of a battery and did not cause calcium reactions that limit battery capacity.

This liquid electrolyte exhibits not only high ionic conductivity at room temperature but also stable electrochemical properties, significantly improving the overall safety of the battery, the researchers said.

"Although a certain gap remains between 700 times — the number of times that the proposed calcium-based batteries are able to charge and discharge — and that regarding the commercial lithium-ion batteries, which can be up to 3,000 times, the performance of our calcium-oxygen batteries showed the potential to be put into practical use," Ye said.

In their research, the calcium-based batteries were also made into flexible battery textiles, providing new insights into the development of flexible batteries.