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nanotimes News in Brief

11-05 :: May/June 2011

Batteries // New Method to Make Sodium Ion-based Battery Cells Could Lead to Better, Cheaper Batteries

visiting researchers from Wuhan University in Wuhan, China used nanomaterials to make elec- trodes that can work with sodium. The researchers have developed a method that improves the electri- cal capacity and recharging lifetime of sodium ion rechargeable batteries, which could be a cheaper alternative for large-scale uses such as storing energy on the electrical grid.

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“The sodium-ion battery works at room temperature and uses sodium ions, an ingredient in cooking salt. So it will be much cheaper and safer,” said PNNL chemist Jun Liu, who co-led the study with Wuhan University chemist Yuliang Cao.

The electrodes in lithium rechargeables that interest researchers are made of manganese oxide. The atoms in this metal oxide form many holes and tun- nels that lithium ions travel through when batteries are being charged or are in use. The free movement of lithium ions allows the battery to hold electricity or release it in a current. But simply replacing the lithium ions with sodium ions is problematic – sodi- um ions are 70% bigger than lithium ions and don‘t fit in the crevices as well. To find a way to make bigger holes in the manganese oxide, PNNL resear-

team of scientists at the Department of Energy‘s Pacific Northwest National Laboratory and

chers went much much smaller. They turned to nanomaterials that have surprising properties due to their smallness. For example, the short distances that sodium ions have to travel in nanowires might make the manganese oxide a better electrode in ways un- related to the size of the tunnels.

To explore, the team mixed two different kinds of manganese oxide atomic building blocks – one whose atoms arrange themselves in pyramids, and another one whose atoms form an octahedron, a diamond-like structure from two pyramids stuck to- gether at their bases. They expected the final materi- al to have large S-shaped tunnels and smaller five- sided tunnels through which the ions could flow.

After mixing, the team treated the materials with temperatures ranging from 450 to 900° Celsius (842° to 1,652° Fahrenheit), then examined the materials and tested which treatment worked best. Using a scanning electron microscope, the team found that different temperatures created material of different quality. Treating the manganese oxide at 750° C (1,382° F) created the best crystals: too low and the crystals appeared flakey, too high and the crystals turned into larger flat plates. Zooming in even more using a transmission electron microscope at EMSL, DOE‘s Environmental Molecular Sciences Laboratory