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Much of our technology from smartphones to electric cars rely on lithium-ion batteries for energy. While full of advantages these common batteries also pose a risk of fire and explosions. Solid state sodium-ion batteries are far safer but so far have not been able to demonstrate the performance that would offset their safety advantages.
This is all about to change thanks to research from scientists from the University of Houston. Lead researcher Yan Yao, associate professor of electrical and computer engineering has authored a paper in the journal Joule that outlines the development of an organic cathode that dramatically improves both stability and energy density in solid state sodium-ion batteries.
A conventional lithium-ion battery has liquid electrolytes which can store high amounts of energy. Solid state sodium-ion batteries have a solid electrolyte core that is typically unable to produce the same amounts of energy. However recent research has delivered a solid electrolyte that is as conductive as the liquid electrolytes used in lithium-ion batteries.
The last challenge to achieving a highly efficient solid-state sodium-ion battery was to find solid interfaces. The research has two main findings related to this problem. The first is that: "the resistive interface between the electrolyte and cathode that commonly forms during cycling can be reversed, extending cycle life."
The second is that the: "flexibility of the organic cathode allowed it to maintain intimate contact at the interface with the solid electrolyte, even as the cathode expanded and contracted during cycling."
Stable and more powerful
The organic cathode - known as PTO, for pyrene-4,5,9,10-tetraone offers many advantages over previous inorganic cathodes. "We found for the first time that the resistive interface that forms between the cathode and the electrolyte can be reversed," Yao said. "That can contribute to stability and longer cycle life."
Yao also is a principal investigator at the Texas Center for Superconductivity at UH. His research group focuses on green and sustainable organic materials for energy generation and storage. The reversibility of the interface is the key difference in the new battery. This agility allows for the solid-state battery to reach a higher energy density without sacrificing cycle life.
Maintaining intimate contact between the electrolyte and the rigid cathode when the cathode expands and contracts during battery cycling has been a problem in the past. But the new research shows that the organic cathode can overcome this issue.
The organic cathode is much more pliable and can maintain contact at all times with the interface improving cycling life. The researchers said the contact remained steady through at least 200 cycles. “If you have reliable contact between the electrode and electrolyte, you will have a great chance of creating a high-performance solid-state battery," said Fang Hao, a Doctoral student and part of Yao's team.