Sodium-sulphur (Na-S) batteries have existed for more than half a century. However, they are an inferior alternative, suffering from low energy capacity and short life cycles. Now, a team of researchers is hoping that a new, low-cost battery — which holds four times the energy capacity of Li-ion batteries and is far cheaper to produce — will significantly reduce the cost of transitioning to a decarbonized economy.
The team used a simple pyrolysis process and carbon-based electrodes to improve the reactivity of sulphur and the reversibility of reactions between sulphur and sodium. The result was a battery that exhibits super-high capacity and ultra-long life at room temperature.
The researchers add that the Na-S battery is also a more energy-dense and less-toxic alternative to Li-ion batteries — which are notorious for being expensive to manufacture and recycle, despite their current ubiquity in electronic devices.
The new battery was specifically designed to provide a high-performing solution for large renewable energy-storage systems (e.g., electrical grids) while significantly reducing operational costs.
“Our sodium battery has the potential to dramatically reduce costs while providing four times as much storage capacity. This is a significant breakthrough for renewable energy development which, although it reduces costs in the long term, has had several financial barriers to entry,” said Research Team Leader Dr. Shenlong Zhao, from the University of Sydney’s School of Chemical and Biomolecular Engineering. “When the sun isn’t shining and the breeze isn’t blowing, we need high-quality storage solutions that don’t cost the Earth and are easily accessible on a local or regional level.
“We hope that by providing a technology that reduces costs we can sooner reach a clean energy horizon. It probably goes without saying but the faster we can decarbonize — the better chances we have of capping warming.
“Storage solutions that are manufactured using plentiful resources like sodium — which can be processed from sea water — also have the potential to guarantee greater energy security more broadly and allow more countries to join the shift towards decarbonization.”
The lab-scale batteries (cion batteries) were successfully fabricated and tested in the University of Sydney’s chemical engineering facility.
Here is a Tech Briefs interview with Zhao, edited for clarity and length.
Tech Briefs: What inspired your research?
Zhao: Five years ago, I got my first iPhone X. After three years of use, the capacity reduced by 30-40 percent. After checking the battery information, I knew the used power source was a lithium battery. As we know, lithium is not friendly to the environment. That motivated me to create an idea to develop a high-performing and sustainable battery. The Na-S battery has many advantages in capacity, cost, and environment protection. So, the research project was designed.
Tech Briefs: What were the biggest technical challenges you faced?
Zhao: The most technical challenge of the project was materials component optimization. Many experiments were carried out to alter the chemical components of single-layer MoS2 and single Mo atoms by optimizing the synthesis temperatures.
Tech Briefs: Can you explain in simple terms how the technology works?
Zhao: A sodium-sulfur battery is based on the redox reaction of sulfur. During the discharge process, electrons are stripped off the sodium metal leading to the formation of the sodium ions that dissolve into the electrolyte and move through to the positive electrode. The electrons move through the circuit and then back into the battery at the positive electrode, where and the sulfur electrode is sodiated to long-chain polysulfides, and then short-chain polysulfides. During charge this process is reversed.
Tech Briefs: What’s the next step with regards to your research/testing?
Zhao: Recently, we’re fabricating pouch cells, which is a key step for boosting the technology from the lab to industrial scale. If this stage is successful, we will contact battery-related companies to test and verify the performance of the pouch cells. After that, more experiments will be carried out to overcome the barriers in commercialization and we will market it by collaborating with the company.
Tech Briefs: What’s the timeline for these batteries to potentially hit the market?
Zhao: We have spent two years making the idea come to fruition in our lab. We are planning to finish the pouch cell fabrication and test within 1-1.5 years. After that, we will spend 2-3 years working with company/industry partners to address the problems regarding commercialization and marketing.
Tech Briefs: Do you have any advice for engineers aiming to bring their ideas to market?
Zhao: In my opinion, the gap between company/industry requirements and the ideas of engineers is an important barrier to bringing their ideas to market. I strongly recommend engineers communicate with their peers in the company/industry. In this way, I believe the ideas from the brainstorming of engineers and industry staff are more easily to be converted into the market.