Driven in part by pandemic-related slowdowns, renewable energy reached a new milestone in 2020, surpassing coal-generated energy for the first time. For all the gains that renewable energy generation has made, it’s easy to forget that any power produced needs to be stored. Despite leaps in lithium-ion battery technology, we are reaching the theoretical and practical energy limits of battery technology; lithium is also too expensive and too scarce to meet our energy storage needs, more so if scaled up to meet demand.
Lithium’s abundant and inexpensive chemical cousin, sodium, is its prime successor. When built into room-temperature sodium-sulfur batteries (NaSBs), it theoretically holds triple the energy density of lithium-ion batteries. But NaSBs have their flaws, said Zhi Wei Seh, a Senior Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE). “Issues that plague lithium–sulfur batteries continue to affect NaSBs,” he said. For one, NaSBs burn out fast: the sodium anode gets smothered by sulfur intermediates from the cathode, while the cathode disintegrates from repeated expanding and contracting during use.
To tackle both issues, Seh and his IMRE colleague, Alex Yong Sheng Eng, focused on the battery binder, the material used to hold the battery together. Though it forms only a small part of the overall battery, the binder plays a crucial role, giving structure to the battery and affecting the stability and performance of the electrodes.
Since the discharge products of NaSBs are ionic and polar, the researchers hypothesized that a polar binder would help the battery maintain its structure and perform better. In collaboration with Man-Fai Ng from A*STAR’s Institute of High Performance Computing (IHPC), the team used simulations to show that polar binders would indeed stabilize a sulfurized cathode and prevent sulfur intermediates from reaching the anode at the same time.
To test their predictions, the researchers constructed NaSBs using common and naturally derived carboxyl-rich polymer binders such as polyacrylic acid, carboxymethyl cellulose or sodium alginate. The result was a more robust battery that outperformed traditional cathode binders in longevity and stability tests at 1,000 cycles, which is among the best performance for such batteries to date. The team is now working on developing other battery configurations and improving the safety and charging rate of their batteries, with an eye to commercialization within the next five years.
“Our findings can not only be applied to portable batteries, but also to stationary grid storage, to store excess renewable energy and release it on demand during times of shortfall,” Seh said. “This will enable us to decarbonize our energy landscape and power a sustainable energy future based on renewable energy.”
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE) and the Institute of High Performance Computing (IHPC).