According to a research report published in Advanced Materials journal dated June 3 2011, researchers at the Pacific Northwest National Laboratory (PNNL) of the Department of Energy and Wuhan University in Wuhan, China have utilized nanomaterials to produce electrodes, which can be used with sodium.
Nanotechnology improves electrode performance
In lithium-ion batteries, manganese oxide-based electrodes and lithium ion electrolyte are used. The size of lithium ions is a perfect fit to pass through the holes and tunnels formed by the atoms of manganese oxide. However, sodium ions are 70% larger than lithium ions. In order to create larger holes in the manganese oxide, PNNL scientists used nanomaterials.
In order to develop the desired manganese oxide-based electrodes, the research team blended two varieties of manganese oxide atomic building blocks. One block had atoms arranged in pyramid form, while the other had atoms that formed an octahedron. Scientists predicted that the final material should have small five-sided tunnels and big S-shaped tunnels via which the sodium ions could pass through.
The research team treated the blended materials under temperature range between 450°C and 900°C and then evaluated which treatment produced the desired material by using a scanning electron microscope. As per the results of evaluation, they identified that material treated at 750°C produced the best crystals. At low-level temperatures, the crystals appeared flakey, while at high-level temperatures, they formed flat plates of large size.
Scientists also observed the nanowires treated at 750°C are uniform and crystalline. They then tested the treated manganese oxide electrode by dipping it in the sodium ion electrolyte. They repeatedly discharged and charged the experimental batteries. The peak capacity was measured at 128 mAh/g of electrode material during the discharge of the experimental battery. Increased peak capacity is due to the heat-treated nanomaterial that reduces or eliminates the occurrence of structural changes caused by sodium ions in manganese oxide electrode.
The 750°C-treated electrodes dropped merely 7% of its capacity after 100 cycles of charging-discharging and lost nearly 23% after 1,000 cycles of charging-discharging. Scientists believed that the electrode modified by nanomaterial demonstrated better performance by retaining about 77% of its initial capacity. They also identified that when charged quickly, sodium ions were not able to penetrate the holes quickly, resulting in low battery capacity. In order to overcome the slow sodium ions, scientists recommend smaller nanowires to increase the speed of discharging and charging.