Published on June 11th, 2014 | by Christopher DeMorro3
Researchers Testing Expanded Graphite Anode For Sodium-Ion Batteries
June 11th, 2014 by Christopher DeMorro
Most of us are familiar with graphite as the stuff pencils are filled with, but it has another use as anodes in lithium-ion batteries. Alas, lithium-ion batteries are expensive, and cheaper alternatives like sodium-ion batteries can’t use regular graphite anodes.
Researchers at the University of Maryland have developed an expanded graphite anode that could make cheaper sodium-ion batteries commercially viable. It all centers on the larger sodium-ions, which can’t penetrate the graphite anode as well as the smaller lithium-ions. The result is a low charge capacity, making sodium-ion batteries with standard graphite anodes impractical to use.
But by expanding the graphite via newly developed methods, the sodium-ions can better fit. It’s all very technical, so I’ll let Green Car Congress take it from here.
“The team starts with graphite oxide, a common industrial material formed by exposing graphite to an aggressively corrosive solution that stuffs oxygen between its layers. The oxygen atoms bond with each carbon layer, pushing and holding them apart. However, the resulting material is inevitably “overstuffed,” leaving no room for sodium ions to get in. To make the material suitable for use in Na-ion batteries, some of the oxygen must be removed.
The solution to this second problem was developed by the paper’s first author, Department of Chemical and Biomolecular Engineering (ChBE) graduate student Yang Wen. Wen heats the expanded, oxidized graphite to high temperatures and floods it with argon gas, causing it to decompose. In this process, oxygen bonded to carbon breaks away in the form of either carbon monoxide (CO) or carbon dioxide (CO2) gas, which is caught up and removed by the argon gas flow.
Wen’s key discovery was the precise combination of temperature and duration for the reaction. Her technique ensures that enough oxygen atoms have been removed to let the sodium ions in, but enough are left behind to prevent the expanded graphite from collapsing. The process may be likened to jacking up every floor of a multi-storey building to accommodate taller tenants, and then removing excess scaffolding until only the required support beams remain.”
This means that much-cheaper sodium-ion batteries could be used as grid-level storage for renewable energy. Unfortunately, they’re too heavy to fit into cars right now, but as a battery for say, solar or wind power, it sodium-ion batteries are one step closer to being an affordable storage solution.