Since the early 90s, Lithium Ion batteries have been the golden child in battery technology, powering everything from computers and phones to EVs and even large scale storage. 

But, as demand for batteries increases, so do questions about the supply of raw materials, battery performance levels, and affordability. 

What if there was a battery that could take everything we love about lithium ion batteries and multiply it! Five times the energy density but at a fraction of the price! That’s what the Lithium Sulfur batteries promise. 

For decades, this promising battery technology has remained just out of reach — the very chemistry that makes it so incredible also makes it virtually unusable.  At least… it used to be. But, thanks to a completely accidental discovery, this incredible technology may finally be close at hand!

So — what’s with the hype surrounding Lithium Sulfur batteries?

Compared to Lithium, Sulfur is an electrochemically active material that can accept up to two electrons per atom at approximately 2.1 V compared to Li/Li+. Li-ion cathodes have a reached capacity of around 250 milliamp hours and energy densities around 800 Wh/kg (how much energy a battery contains in proportion to its weight). 

Sulfur cathodes can have significantly higher theoretical capacities, at upwards of 1600 mA h. A milliamp-hour,by the way, is one thousandth of an amp-hour, One Amp-hour is equal to one amp of continuous current flow for one hour.

A lithium-sulfur battery, which uses Sulfur as the cathode — the negatively charged electrode (the minus end of a battery) — and lithium as the anode (the positive end) — can reach theoretical energy densities upwards of 2600 Wh/ kg — that’s over 3 times the energy density of Li-ion batteries! 

So what does that mean in terms of running your electronics? If you were to replace the lithium-ion battery in your computer right now with a Lithium-Sulfur battery of the same weight, you could run that computer for over three times as long, OR you could achieve the same runtime with a battery that weighs three times less!

Now imagine what that could do for an EV? Today’s top performing EVs using Lithium Ion batteries have ranges that top out around 500 miles. Now — imagine replacing that li-ion battery with a lithium sulfur battery, now — a car with a battery that weighs exactly the same could travel up to 1,500 miles on a single charge! And those are just with conservative figures. Some estimates say that Lithium Sulfur batteries could increase energy density by up to 500%! That could mean a range of up to 2,500 miles! You could drive from San Diego to Seattle, WA and BACK on a single charge! 

Using sulfur as the cathode material could also help reduce the cost of batteries while also helping alleviate some of their impact on various materials. Compared to lithium, sulfur is a far more earth-abundant material — almost as abundant as iron. Today, so many devices rely on lithium, and while it’s hardly a rare material, finding other suitable battery materials will only help us down the road as battery technology will become more and more necessary, not only for personal electronics and EVs but for grid storage as well. 

Sulfur would also eliminate the use of other materials like manganese, nickel, and cobalt — elements that carry both global supply concerns as well as humanitarian issues. But the most convincing reason to utilize sulfur is that it is significantly less expensive than just about every other material currently used in batteries today. Cobalt, for instance, is considered a rare metal — typically priced around $75K/ metric ton. But, since the 2020 pandemic wreaked havoc on the global supply chain — prices have skyrocketed by more than 50% in 2021. Lithium has also seen price inflation due to increasing short term production — from $7K/ mt to nearly $40K/ mt.

But then there’s sulfur. And even though it, too, has seen prices climb in the same time period —nearly 47% — the cost is still dirt. Cheap. Coming in around $382/ MT. By comparison — for the price of 1 ton of Cobalt — you could get nearly 200 tons of sulfur! 

But, as we mentioned earlier, while Lithium Sulfur batteries hold so much promise — there’s a reason we have yet to actually see them in production. BUT — thanks to a groundbreaking scientific discovery, made completely by accident, could the Lithium Sulfur battery finally be within reach?

So the reality of Lithium Sulfur batteries may finally be close at hand thanks to a complete accident made by researchers at Drexel University’s College of Engineering. Dr. Vibha Karla and her team were actually testing different methods of overcoming some of the big drawbacks often associated with Lithium Sulfur batteries. 

As we mentioned earlier— the reaction between the positively charged lithium ions in the sulfur cathode comes with all those amazing benefits we listed before. BUT that same reaction has… some unfortunate side effects. 

During the charge-discharge process, sulfur goes through a series of structural changes resulting in the formation of chemical deposits called polysulfides. These deposits form tree-like structures called dendrites that branch up from the lithium anode, degrading both the anode and the electrolyte — the medium that carries the lithium back and forth between the anode and the cathode — effectively killing the battery after a relatively small number of cycles.

While a standard lithium-ion battery remains usable for around 2,000 charge cycles, lithium-sulfur batteries in laboratory conditions max out around half that. Meaning in a practical situation — lithium sulfur batteries would be dead after only a year or two of use. 

One strategy often used to counter this “shuttling” effect has been to use ether electrolytes that can dissolve those polysulfides. But, those types of electrolytes come with their own baggage — namely that they can be expensive, making them less practical for large-scale application. They can also be incredibly volatile and unstable, not to mention the amount needed to actually solve the shuttling problem could hamper the energy density of the batteries which… sort of defeats the purpose. 

Dr. Karla’s solution was to find a way to make the batteries function with a more industrial-friendly carbonate electrolyte — the kind used in most lithium ion batteries. The experiment essentially involved attempting to constrain the sulfur in a carbon nanofiber, effectively trapping the polysulfides so that they wouldn’t react with the electrolyte at all. But… the experiment failed… Or at least it didn’t do what Dr. Karla thought it would. But what her and her team discovered was something completely unexpected.

When mixed with the carbon nanofibre, the sulfide stabilized into an incredibly rare form — called monoclinic gamma sulfur — a form of sulfur that has a rectangular prism form made of eight sulfur atoms packed together. The thing is, this type of sulfur doesn’t typically stay stable at room temperature — in fact it’s usually only created in labs at extremely high temperatures, and only appears in nature in extreme environments like oil wells.

According Rahul Pai, a doctoral student in the Department of Chemical and Biological Engineering and co-author of the research, “In the last century there have only been a handful of studies that produced monoclinic gamma sulfur and it has only been stable for 20-30 minutes at most.” But here, in this laboratory setting, the team was able to create it completely by accident!

So what’s so significant about this discovery? It turns out that this particular, crystalized form of sulfur doesn’t react with the carbonate electrolyte the way other forms of sulfur would — effectively eliminating the polysulfides and the shuttling effect along with them. 

What does this mean for battery performance?

When the team put the carbon nanofibers into a lithium sulfur battery with a carbon electrolyte, they were able to cycle it a total of 4,000 times without losing performance — the equivalent of 10 years of use! 

Not only that, but the battery they tested had three times the capacity of today’s lithium-ion batteries!

So that’s it! Problem solved, right? Let’s get ready to swap out our Lithium-Ion batteries.

Well… not quite. See… as with most accidental discoveries, the team now has to figure out… why the experiment turned out the way it did. How did this phase of sulfur appear? Can they replicate it? And can they ensure that it would stay that way?

So suffice it to say, further research is still needed before we start seeing these batteries for sale. BUT the research doesn’t stop there. The team is using this discovery to further research into other, lithium free battery technology like sodium-sulfur batteries. 

So while this accidental discovery hasn’t fully made lithium sulfur batteries a reality just yet, they have brought us significantly closer than anything before!