Rutronik News

Strong thanks to sulfur

  Newsletter Article

Here at Rutronik24, we mainly concern ourselves with technological innovations, as you will be only too aware as attentive readers of our newsletter. We are especially interested in the search for alternatives to the conventional lithium-ion battery.

Not just because the materials contained therein, such as nickel and cobalt, are toxic and difficult to dispose of, but also for reasons of pure self-interest: Few things are as annoying as a battery that loses most of its power within less than a year and reduces the life of our smartphones from a day to just a few hours.

Two years ago, we reported on an alternative to lithium-ion batteries: The then 94-year-old US physicist John B. Goodenough had got together with other researchers to develop a solution involving glass as electrolyte, which represented a safer and cheaper alternative with greater capacity. In 2019, Goodenough received the Nobel Prize for chemistry alongside two colleagues – ironically for the development of lithium-ion batteries. The glass battery, meanwhile, has still not made it to the mass production stage and numerous researchers around the world are working on other alternatives.

One promising lithium battery alternative uses sulfur cathodes rather than nickel and cobalt. Australian researchers from Monash University in Clayton have said that initial tests promise a trebling of capacity compared to lithium-ion batteries. This is made possible by a more stable sulfur cathode, which no longer crumbles even with thicker layers of sulfur and achieves energy densities of more than 1,200 milliampere hours per gram, as reported by the researchers in the professional journal Science Advances.

Since sulfur is a waste product – unlike nickel and cobalt – it is considerably cheaper and more easily available, which is hugely important when it comes to industrial battery production. The Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden, which was equally involved in the study, also stressed that the new battery alternative was lighter, cheaper, and more eco-friendly than the conventional lithium-ion solutions. Nonetheless, it seems it will be some time before it is ready for mass production: Even though the technology is promising, it remains in the development stage. The lithium-sulfur cells may well be more effective – being able to store more energy than lithium-ion batteries of the same weight – but they are also bigger.

The fact that lithium-sulfur batteries are yet to make it past the development stage is also down to the as yet insufficient mechanical stability of the sulfur cathode, which expands and contracts as the lithium is absorbed and released during operation. Microcracks and fractures appeared, causing the cell to wear quickly. The researchers have apparently found a solution to this problem and have even patented it.

The team of researchers borrowed an idea used in the production of detergent for the architecture of the specially designed layer of carbon and binding agent, which can counterbalance the higher mechanical loads, thereby reducing the loss of power and capacity. The binding agent is based on a water-soluble polymer and binds the sulfur and carbon particles from the cathode using polymer bridging when the electrode expands while charging and contracts when discharging.

However, for the moment at least, sulfur batteries are still not a viable alternative for new forms of transport such as electric cars. Despite the new process, the lithium-sulfur batteries can only withstand just over 200 charging cycles before they begin to lose their power – and that is far too little. The aim is to achieve between 2,000 and 3,000 stable charging and discharging cycles. As soon as this aim has been achieved, the battery can also be used in practical applications. The focus here will be on areas where low weight is of considerable importance, such as the aerospace industry. The batteries do not (yet) represent a serious alternative for electric mobility, because even though they are very light, they require much more space, as already mentioned.

So, whether we like it or not, we will have to make do with our ever diminishing smartphone batteries for a while yet. That said, since there has been a trend toward ever larger models and phablets and the batteries will probably be as large as an A4 sheet of paper in two or three years anyway, the time of the lithium-sulfur battery will surely come one day.