Researchers Find a Way to Create Sodium-ion Batteries

Researchers at University of Maryland have found a way to create Sodium-ion batteries using expanded graphite.

Lithium-ion batteries helped scientists create smaller, faster electronic devices. These batteries are some of the most energy-dense, rechargeable batteries available today. But, Lithium isn't an abundant material and researchers want to use Sodium to create better batteries.

Sodium, which is found in common salt, shares some properties of Lithium and is inexpensive. A major problem with using Na is that its ions are too large to replace Lithium. To create Na-ion battery, researchers had to come up with a solution to fit Na ions in an anode.

Lithium ions are smaller than Sodium ions, so they fit in nicely within graphite layers. University of Maryland researchers have found a way to create additional space between these layers to accommodate Sodium ions.

The first step involved exposing graphite to aggressively corrosive solution that stuffs oxygen atoms between graphite layers. The resulting material, graphite oxide, is already commercially available.

In the second step, researchers removed some of the oxygen atoms to make room for Sodium ions. Yang Wen at Department of Chemical and Biomolecular Engineering (ChBE), found that heating graphite oxide to high temperature in the presence of argon removed some of the oxygen atoms. In the process, oxygen leaves the material as carbon monoxide (CO) or carbon dioxide (CO2) gas, which is taken up by argon.

Wen's technique ensures that only some of the oxygen atoms leave the oxidized graphite. The team tested the material in experimental setting and found that Na-ion battery anodes manufactured using graphite had good energy density. The batteries retained some 73 percent capacity after 2000 charge/discharge cycles, according to a news release.

According to  Chunsheng Wang at the University of Maryland, sodium ion batteries won't be as powerful as Lithium-ion batteries, but they will be much more cheaper than lithium.

"Expanded graphite is already commercially available," explained Wang, an associate professor of ChBE, according to a news release, "but industry uses a different method to make it. If they follow Yang's procedure, they can use it to make expanded graphite suitable for sodium-ion batteries."

The study is published in the journal Nature Communications.

Several researchers have long been trying to find a replacement for Li-ion batteries. Silicon has been widely regarded as the most promising candidate for anodes in the next generation batteries.