Lithium-Sulfur Batteries Could Be Cheaper & More Energy Dense

February 11th, 2020 by Jake Richardson

Sales of new electric vehicles have been surging, but there are constraints around battery and vehicle production. New EVs have ranges of about 200-300 miles (322-483 km) or so. Potentially, lithium-sulfur batteries could expand EV ranges considerably and cost less because sulfur is a more abundant material than cobalt. Transportation is a major generator of greenhouse gases, so many more EVs are needed. Lithium-sulfur batteries eventually could help speed up EV production and adoption.

Research at Monash University in Australia led to the development of a very high-performance and energy efficient lithium-sulfur battery. An article on the university’s website mentions the technology is close to commercialization and could have a potential EV range of 1,000 km (621 miles).

Dr. Mahdokht Shaibani, a Research Fellow in Mechanical & Aerospace Engineering at Monash University, who also held a leadership role on the project, answered some questions about the work for CleanTechnica.

For the layperson, how is it potentially possible for lithium-sulfur used in batteries to have six times the energy for a given weight?

In a Li-ion battery, Li+ ions shuttle between the positive electrode intercalation host (theoretical capacity as high as 280 mAh g-1) where they are stored upon discharge; and the graphitic carbon negative electrode, where they are stored on charging to a maximum content of Li0.16C (The 1 to 6 ratio means the capacity is not that great – theoretical capacity is 370 mAh g-1). Cell voltages are in the range of 3.4–3.8 V versus Li/Li+. Theoretical energy densities are around 500 Wh Kg-1on the basis of electrode materials.

The redox reaction-based storage mechanism in Li-S system is fundamentally different from the intercalation process of lithium-ion battery. The theoretical capacity of sulfur (positive electrode) is 1675 mAh g-1, thanks to the formation of Li2S when sulfur combines with lithium (negative electrode). The 2 to 1 ratio clears the holds-a-lot-of-lithium hurdle and promises a wonderful match for the ultra-high capacity lithium anode (3860 mAh g-1). The theoretical energy density of the Li-S system is then determined by the theoretical capacity of sulfur (1675 mAh g-1) and its potential of 2.15 V versus Li/Li+, to be around 2,500 Wh kg–1.

Although lithium-sulfur offers up to a five-fold increase in gravimetric energy density compared to Lithium-ion , from a practical point of view, and considering the breakthrough of our research group and the advancements of other research institutions and companies, you can expect to see around a two-fold increase at the battery pack level when first introduced to the market.

How does your new design prevent lithium-sulfur batteries from breaking down?

Ironically a main challenge to mass adoption of Lithium-Sulfur batteries until now has been that the storage capacity of Sulfur electrode is so large that it cannot manage the resultant stress. Instead it breaks apart, in the same way we might when placed under stress. The progressive breakage leads to destroyed electrical wiring across the electrode and rapid decay of the superior energy performance.

The new design relies on a traditional binding agent, but processed in a different way to form ultra-strong bridging bonds between the carbon matrix and sulfur particles that allow for extra space as the battery expands during charging. In simple words, I gave the sulfur particles some space to breath while they are under the heavy duty of cycling!

If in 2-4 years, you have lithium-sulfur batteries available for commercial use, would that be in the form of very small batteries for electronics, or could it be in the form of batteries for electric vehicles?

On account of projected lower cost, our priority is to test our batteries in large-scale applications, EV and grids. Importantly, we need radical new and clean energy storage technologies to fight climate change in Australia where sustained climate change could have drastic effects on not only the ecosystems but also people’s lives, and we believe Li-S system is a potential promising solution.

Today, new EVs have ranges of 200 – 300 miles, could making lithium-sulfur batteries perhaps add at least another 100 – 200 miles of range per charge?

Currently, the volumetric energy density (Wh L-1) of Li-S system is at best rival to Li-ion battery, however there is great potential given the higher gravimetric energy density of this system and most importantly the projected lower cost of the battery – both of these can affect the mileage range of EV. First, lighter batteries would result in higher EV range; second, a low cost lighter battery means the EV manufactures could explore new concepts where they can allocate more space in the car to the battery pack without having cost and weight concerns! Today’s batteries make up a significant portion of the total EV cost (33% to 57% depending on the car) and EV weight (around 20% to 25%) and using more batteries in the car doesn’t make much sense both cost-wise and weight-wise.

The low-cost and light Li-S battery could unlock this hurdle provided that manufacturers would be interested in exploring new car concepts and the battery researchers could increase the life-span of a Li-S battery to the required level of EV. From my perspective, the second one is highly likely.

If your lithium-sulfur technology becomes commercialized, would you own various patents for it and license the patents to companies who manufacture their own batteries?

This has been the subject of internal discussion and we are yet to decide on our next steps.

Because sulfur is an abundant material, if your technology reaches the commercial markets, could EV batteries be made more cheaply and have greater energy densities?

I hope I already answered this question, short answer is yes.

Would a lithium-sulfur battery have about the same longevity as a current lithium-ion EV battery, or is it too soon to tell?

Not at the moment. Increasing the life-span of a Li-S battery is the biggest challenge of this promising battery technology and similar sort of breakthrough on the stabilization of the Li metal anode is required to achieve the 500 cycle number which is suitable for many applications. This has been the focus of several research and R&D groups such as Fraunhofer IWS in Germany led by Dr. Holger Althues.

It is noteworthy that as opposed to the cathode, the research on the anode is not that mature yet. There is a lot to explore and significant progress is expected in the near future.

Lithium-ion batteries used in EVs, once they are done functioning in electric vehicles, can be re-purposed for other uses, like stationary energy storage. Would that be possible also for lithium-sulfur batteries potentially, or is it too soon to tell?

I believe re-purposing the exhausted Li-S battery for application in grids is highly likely.









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