A tiny protective layer of aluminum oxide makes a sodium metal anode more stable and longer-lasting, engineers at the University of Maryland in College Park say.
As the demand for small-high powered batteries grows, scientists are exploring other elements besides lithium to store and release energy. Sodium, which is a thousand times more common than lithium and easier to harvest, would be cheaper to use for large scale applications and has similar properties. Most recently, researchers are racing to find ways to bring it up to competition with lithium-based batteries.)
Engineers from the departments of materials science, NEES (DOE-EFRC) and University of Maryland's Energy Research Center at the University of Maryland have used a high-tech, low-temperature process called plasma-enabled atomic layer deposition to protect one pole of the battery from the corroding effects of contact with the electrolyte.
“To my knowledge, no other groups have done nanoscale thin film protection on sodium metal, and surprisingly, only a few nanometers of protection layer extend the lifetime three times longer for sodium metal anodes,” said Chuan-Fu Lin, lead author of the study, which was published on Sept 22nd in the journal Advanced Energy Materials.
Batteries like rechargeable lithium-ion batteries, the kind found in your phone and laptop, work by passing the positively-charged ions of the electrolyte back and forth between the negative and positive electrodes. With metal anodes, the positively charged ions will be easily deposited on anodes side and form dendrites that may cause safety hazards (causes fire by shorting positive and negative electrode), Additionally, because of the high reactivity of sodium metal, the electrolyte actually chemically changes the anode surface to form thick undesired layers that also hinders battery performance.
The Maryland scientists’ work put a ultrathin protective layer of aluminum oxide on the sodium metal anode, which allowed the sodium ions to pass back and forth without beginning to grow dendrites. That means it could last three times longer than an unprotected sodium anode. It was still working without defects after 450 hours of charging and discharging, the team said.
Since sodium battery making is still in its infancy, the newly-created battery won’t be in your cell phone in the near future. But, said Lin, “We tested this with a fair amount of batteries, and it’s reproducible; and aluminum oxide is relatively easy to be applied and the processes is now well developed.” The team may also try adding additives to the electrolyte to further improve the battery’s performance.
Ultrathin Surface Coating Enables the Stable Sodium Metal Anode
Adv. Energy Mater. 2016, 1601526
December 15, 2016