A new development by researchers could make solid-state batteries, which are less prone to fires and explosions, a viable alternative to conventional lithium-ion batteries, according to Phys.org. Furthermore, since sodium is cheaper than lithium, the batteries could reduce the cost of energy storage, including for renewable energy like solar and wind.
While solid-state sodium-ion batteries are much safer, they haven’t been able to even come close to the performance of lithium-ion batteries, in terms of their charge capacity and number of recharge cycles.
In a solid-state battery, according to Science, sodium ions move between electrodes through solid materials (instead of flammable liquids as in lithium-ion batteries). Electrons escape from sodium atoms at one electrode (called the anode) and move to the other electrode through a sulfur-based electrolyte. This second electrode is called a cathode and is normally composed of a ceramic oxide compound. The cathode is enlarged by the incoming ions, and then shrinks when the battery is recharged, as sodium ions are pushed back to the anode by electric voltage from charging. This cycle degrades the ceramic material in the cathode, which ultimately breaks away from the solid electrolyte.
In research published last year, the researchers made a cathode from a flexible organic compound using sodium, carbon, and oxygen. This cathode survived through 400 charging cycles without separating from the electrolyte. It also stored almost as much energy as conventional lithium-ion batteries. But the fragile electrolyte was damaged by the operating voltage.
Now, the researchers redesigned the cathode, again using a flexible organic compound. Each molecule of their compound, called PTO (Pyrene-4,5,9,10-tetraone) holds twice as many sodium ions, allowing the battery to hold a charge equivalent to most lithium-ion batteries. The flexible cathode can undergo 500 charge cycles, holding almost 90 percent of its storage capacity. It even operates at a lower voltage, helping to protect the electrolyte from damage.
“That can contribute to stability and longer cycle life,” according to Yan Yao, University of Houston associate professor of electrical and computer engineering and lead author of the paper, which was published in the journal Joule.
With further improvements, such a battery could power low-voltage devices like wearable technology. To support higher voltage technology, like electric cars, the battery will need to boost the difference in electric potential between the anode and the cathode. Yan says the team is already working toward an organic electrode with that potential.