Sodium-ion cell via PNNL
Power grid energy storage is a big problem. Several tried and true methods exist, but all have their downfalls. Ideally, Lithium-ion rechargeable batteries would like to be used for grid storage, the energy density of the battery is very attractive for the application. But like most other options for grid storage, it is far too expensive to be practical. An alternative to Lithium-ion has been Soldium-sulfur batteries that have similar energy density. However, Sodium -sulfur operates at 300°C which leads to difficulties in function as well as energy loss through heat. (As of 2010, Presidio, Texas built the world's largest Sodium-sulfur battery facility to aid in grid regulation as well as alternative generation source storage.)
Researchers from the Department of Energy's Pacific Northwest National Laboratory (PNNL) with a team from Wuhan University in Wuhan, China has devised a battery that is as cheap as Sodium-sulfur with the operating characteristics of lithium-ion, called a Sodium-ion battery that operates at room temperature.
Like in Lithium-ion cells, the team used the electrode material manganese oxide, but at the nano-scale. Testing two different atomic structures for the electrode material, S-shaped tunnels with peripheral tubes were formed for the sodium ions to travel. After treating the material is several different temperatures, the team found at 750°C the best battery characteristics surfaced.
After dipping the electrode material into an electrolyte, the team went about testing the charge-discharge effects of the new material. After 100 cycles, they cell lost 7% of its capacity. At 1000 cycles it lost 23% of capacity. At peak capacity, 128mAh per gram of electrode material was seen. However, there is one issue with the material. In rapid charging scenarios, the Sodium-ions could not enter the tunnels of the material fast enough which limits the overall capacity of the cell.
The team is currently looking into making the increasing the speed of charging. With renewable energy, the grid needs a way to quickly store sudden bursts of newly made electricity. The storage batteries also need to discharge fast as well, to keep up with demands or dips in the power regulation. They are close, just a little more fine tuning.
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