We all know about lithium-ion batteries, from our car batteries to our smartphones; we rely on them for energy. They are used extensively despite the risk of fire and explosions that they carry. A safer alternative is solid-state sodium-ion batteries, but up till now, they have not been able to compete with the lithium-ion batteries in terms of performance.
However, it seems that solid-state sodium-ion batteries are about to gain the advantage over the lithium-ion batteries on account of the research that comes from a group of scientists at the University of Houston. Lead researcher, Yan Yao – associate professor of electrical and computer engineering – has written a paper in the journal Joule outlining the development of an organic cathode that can greatly enhance the stability and the energy density in solid-state sodium-ion batteries.
For those of you who don’t know, the traditional lithium-ion battery features liquid electrolytes that are capable of housing large amounts of energy. The solid-state sodium-ion batteries, on the other hand, feature a solid electrolyte core that cannot produce energy on par with lithium-ion batteries. However, the recent research has presented a solid electrolyte that is as conductive as the liquid electrolytes that are used in lithium-ion batteries.
The last challenge that the team of scientists had to overcome in order to develop a highly efficient solid-state sodium-ion battery was finding solid interfaces. The research has two main findings that address this challenge. The first finding states that ‘the resistive interface between the electrolyte and cathode that commonly forms during cycling can be reversed, extending cycle life.’ Whereas, the second finding states 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.’
The organic cathode is known as PTO for pyrene-4,5,9,10-tetra one. It offers a multitude of benefits as opposed to the inorganic cathodes. Yao said, ‘We found for the first time that the resistive interface that forms between the cathode and the electrolyte can be reversed. That can contribute to stability and improved cycle life.’ Yao is also the principal investigator at the Texas Center for Superconductivity at UH. His research is focused on green and sustainable organic materials for energy generation and storage. The key difference in the new battery is the reversibility of the interface. This enables the solid-state battery to achieve a higher energy density without having to compromise on its cycle life.
The maintaining of good enough contact between the rigid cathode, while it expands and contracts during the battery cycling and the electrolyte, has always posed a problem. However, new research suggests that organic cathode can tackle this issue. The organic cathode remained steady through a minimum of 200 cycles. Fang Hao, a Doctoral student and member of Yao’s team, said, ‘If you have reliable contact between the electrode and electrolyte, you will have a great chance of creating a high-performance solid-state battery.’