Low-cost, ample and sustainable.
Sulfur might not be probably the most glamorous of parts—some could affiliate it with rotten eggs, smelly nicely water, and even the satan, as invoked in a rustic preacher’s fire-and-brimstone sermon. However as a element of an EV battery cathode, sulfur has so much to supply. The yellow stuff is lighter and cheaper than the cobalt, nickel or iron sometimes present in in the present day’s cathodes, and lithium-sulfur batteries may ship superior efficiency.
Zeta Vitality, which was based in 2019, says it has created “the world’s first and solely profitable lithium-sulfur battery.” Zeta’s sulfur-based cathodes are cheap, and use no cobalt, graphite, nickel or manganese. Sulfur, a by-product of oil refining, is affordable and available worldwide, and it has a modest carbon footprint. The corporate has additionally developed a novel anode which it says boasts increased capability than different present anode applied sciences, and is freed from the pesky dendrites which have inhibited growth of lithium metallic batteries.
Zeta’s battery makes use of metallic lithium as an alternative of intercalating lithium ions, which allows a lot increased vitality density. The corporate has measured particular vitality of 450 Wh/kg—virtually double that of in the present day’s finest lithium-ion batteries—and a cost price of as much as 10C.
Charged spoke with Chief Science Officer Rodrigo Salvatierra.
Charged: What stage are you at with the battery in testing proper now? Have you ever obtained some cells with potential prospects?
Rodrigo Salvatierra: Our primary publicity to the market is thru a current joint growth settlement with Stellantis. The aim of that settlement is to make lithium-sulfur batteries that may outperform in the present day’s lithium-ion batteries. We’re on the stage the place the attributes of the cell are being examined in actual EV setting testing situations.
There are numerous methods to check EV batteries. When you might have—let’s say—a flashlight, you might have a continuing discharge present. When you might have a automobile, you might have fixed pulses of cost and discharge: for instance, once you press the brake or once you speed up. When you find yourself driving, you might have a profile of driving, and the way that profile impacts the cycle life, how lithium-sulfur cells carry out underneath these situations, that was not well-known.
We’ve additionally despatched samples to different OEMs. They’re fascinated with different facets that possibly Stellantis shouldn’t be actually that fascinated with. We’ve got different applications to develop batteries for low-temperature functions, which is one thing that sulfur is notoriously dangerous at. We even have curiosity in quick charging, which lithium-sulfur is thought to be good at. There are different prospects fascinated with shopping for cells from us, to see if they’ll match into their very own inside testing situations.
The testing we’re doing now speaks on to the efficiency of the electrodes. The opposite half, which is extra engineering, entails making cells within the measurement required for use in a module or a battery pack.
Charged: Stellantis is hoping to have lithium-sulfur batteries in a car by 2030. Are you simply testing the cells at this level, or are you already placing the cells collectively in a battery pack and testing it in a prototype state of affairs?
Rodrigo Salvatierra: The testing we’re doing now speaks on to the efficiency of the electrodes. The opposite half, which is extra engineering, entails making cells within the measurement required for use in a module or a battery pack. And a associated query is: Can we execute manufacturing of actually massive quantities of these cells so we will match not just one automobile, however a lot of them? Can we scale up the supplies?
Do not forget that the lithium-sulfur battery entails two streams of supplies which can be utterly totally different from these used within the lithium-ion battery. The lithium-ion battery has supplies for the anode, supplies for the cathode, and you’ve got quite a lot of choices for each. Lithium-sulfur, not a lot.
We nonetheless must outline the place we get the sulfur. If you’re a producer of cathode supplies for lithium-ion batteries, you go to a giant firm that sells metallic oxides, and they’re going to have a battery-grade cobalt and an industrial-grade cobalt. You may’t discover a battery-grade sulfur in the present day—there’s no such factor. After all, we will use sulfur from chemical grades—we will make cells, we will take a look at our cells. However can we extend cells? Are our processes for making the cathodes and the anodes suitable with the identical machines that the lithium-ion battery makes use of in the present day? Or do we want particular machines to make lithium-sulfur batteries? That half, I feel now we have answered. Sure, we will use the identical machines that assemble the lithium-ion battery in the present day. We will use these in our manufacturing.
Nevertheless, the supplies wanted for lithium-sulfur batteries are extraordinarily totally different. We’ve got to make our personal anode and our personal cathode, so we are literally tackling three issues. We’ve got to make actually good, high-performance cells, however we additionally must have quite a lot of cathode supplies and anode supplies. The primary one, the testing, I feel goes nicely. If we didn’t have good efficiency from our cells, we’d not have been in a position to make a take care of Stellantis on creating a cell for an EV collectively. However now, we’re additionally engaged on the engineering aspect, find out how to make extra of these supplies that may go into the cells.
We’re manipulating billions of carbon nanotubes on the identical time, controlling the areas between them exactly, and rising them uniformly on the floor of a metallic foil.
Charged: So, as you’re testing the cells themselves, on the identical time it’s important to determine find out how to get the availability chain rolling.
Rodrigo Salvatierra: That’s right. We’ve got to align ourselves with suppliers of supplies. The advantage of lithium-sulfur is that we don’t must create a brand new provide chain, we simply must primarily adapt an current provider. Sulfur is a byproduct of oil refining. So, now we have to discover a method to qualify that sulfur and acquire it to make our supplies.
Charged: Sulfur is used within the cathode, however you’ve made some improvements with the anodes additionally. Lithiated, vertically-aligned carbon nanotubes—is that this one thing that you just developed?
Rodrigo Salvatierra: No, carbon nanotube (CNT) expertise has existed for possibly 30 years. However making carbon nanotubes the way in which we make them is a really specific course of to Zeta. We will develop this very nice carpet with good management of all of the spacing—we’re manipulating billions of carbon nanotubes on the identical time, controlling the areas between them exactly, and rising them uniformly on the floor of a metallic foil. It is a expertise that we developed. Carbon nanotubes are frequent, however we developed a method to create the carbon nanotubes in a carpet with excellent management to allow them to be related for the functions they’re meant for, which is as a number for metallic lithium anodes.
The CNT itself, it’s not the lively anode materials. The lively materials for the lithium-sulfur battery is metallic lithium. However metallic lithium alone creates quite a lot of issues, that are well-known. These are usually described as dendrites, however this can be a time period which means quite a lot of issues to totally different individuals—let’s simply say it’s a construction that’s undesirable. And one method to take away these undesirable buildings from the metallic lithium is to make use of our technique of internet hosting that metallic lithium—as an alternative of getting a flat foil of metallic lithium, we distribute it over billions of those carbon nanotubes. It’s like when you have this carbon nanotube rising as a vertical pillar, you might be distributing the lithium metallic on the sidewalls. They’re rising conformally round these carbon nanotubes.
How to do this shouldn’t be trivial. It entails quite a lot of information about how the present distribution occurs in these supplies. That’s really our mental property, how to do this. By distributing the metallic lithium inside these carpets, that’s how we forestall the formation of the dendrites.
Metallic lithium alone creates quite a lot of issues involving dendrites. One method to take away these undesirable buildings is to distribute the metallic lithium over billions of carbon nanotubes. That’s our mental property, and that’s how we forestall the formation of dendrites.
Charged: You could have a novel anode and a novel cathode. Are these two issues that essentially work collectively? Might you might have your sulfur cathode with a unique form of anode?
Rodrigo Salvatierra: Good query. The sulfur cathode we developed can also be a particular sort. It’s not primarily based on elemental sulfur—it’s primarily based on one thing we name sulfurized carbon. It’s a really specific element of the cathode that’s accountable for bonding to the lively materials, which is sulfur.
The sulfurized carbon cathode will be paired with totally different anodes. You may mix it with conventional anodes, or you’ll be able to take the metallic lithium anode, with our CNT expertise, and pair it with typical cathodes. It appears easy to do this, but it surely’s more difficult than it sounds.
After we develop our system, now we have to think about the principle participant, which is the electrolyte. Our system is designed for use with liquid electrolytes like a lithium-ion battery, however for our battery to function with our anode and our cathode, now we have to have our personal recipe of liquid electrolyte. That liquid electrolyte might not be suitable with a standard cathode like an NMC, and might not be the very best for a standard anode—you would need to develop electrolyte formulations which can be particular to that sort of chemistry.
After all, it’s not going to be like beginning over on the electrolyte growth. One of many analysis tasks now we have ongoing with one other OEM that we can not reveal for the time being is to develop cells utilizing our sulfurized carbon cathode with different anodes.
The advantage of utilizing liquid electrolytes is that we will use a lot of the separator sorts that the lithium-ion battery business makes use of.
Charged: It appears like all of the items of the recipe must work collectively. Cathode, anode, electrolyte…separators?
Rodrigo Salvatierra:
The advantage of utilizing liquid electrolytes is that we will use a lot of the separator sorts that the lithium-ion battery business makes use of. We don’t must have a particular electrolyte separator.
Charged: And you can also make your cells utilizing current battery manufacturing tools?
Rodrigo Salvatierra: We will use virtually all the present lithium-ion battery meeting tools due to the character of our electrodes. What’s totally different about Zeta’s expertise is the way in which we result in these electrodes. Anodes and cathodes for the lithium-ion battery are available in rolls of foil. These foils are launched into machines that calender them, lower them, type them, choose them, and put them into cells. We will produce the identical sort of rolls.
From the uncooked supplies to the electrode degree, we’re totally different, however from cell to pack degree it’s the identical. Proper now, for instance, in our prototype facility, we use the identical strategies that we’d use to make different sorts of chemistries.
We will use virtually all the present lithium-ion battery meeting tools due to the character of our electrodes.
Charged: Do you might have any rivals on this area? Is anyone else getting near sulfur-based cathode?
Rodrigo Salvatierra:
The sector is wealthy in the present day by way of competitors, which I feel is sweet. I feel within the US, the largest one is Lyten. Lyten makes use of their very own graphene expertise to host sulfur, and I feel additionally to host metallic lithium. By way of manufacturing, additionally, they’re producing energy cells with aggressive vitality density.
Charged: What particularly is happening in your labs proper now? Are you able to describe the steps of the testing course of?
Rodrigo Salvatierra: In our lab, now we have processes for making the whole lot. We synthesize the cathode from uncooked supplies. We synthesize the anode’s base construction from uncooked gases. We’ve got some carbon feedstock. We will make the cells as nicely. And we’re very centered on the fabric aspect, as a result of we perceive that to make quite a lot of batteries of business relevance, we want a pilot plant. Proper now we’re qualifying all of the steps by way of supplies, electrodes, coatings, meeting, so we will create a powerful baseline to go to the following step, which is a pilot plant.
We accomplished a Sequence A funding spherical in 2023 and now we’re elevating funds for our pilot facility. The pilot facility can have an automatic meeting line. There will likely be bigger machines to make extra of the cathodes, not a lot variation in the kind of the cathode. We’re going to freeze one recipe of cathodes, one recipe of anodes. And the pilot will likely be extra centered on the engineering aspect to facilitate manufacturing.
It’s infamous that, when you might have pilots originally of your manufacturing, you should have a really massive scrap price since you’re nonetheless adapting your processes. And typically, in different firms that scale up battery applied sciences, they take a while till they considerably scale back the scrap price to allow them to begin producing. We all know that the market is transferring fairly quick, so we can not enable ourselves to have quite a lot of delays. We’ve got quite a lot of discussions with specialists in different firms which have expertise in scaling up manufacturing, so we all know what we must always take note of. We don’t wish to wait till we get greater machines consuming a whole lot of sq. meters per day and now we have to vary one factor or one other. We’ve got to do this now.
Traditionally, they’re not excellent at cold-weather efficiency, however we developed electrolytes and sulfur cathodes which can be wonderful. They really out-perform lithium-ion batteries.
For instance, once you purchase the large machines, there’s all the time a studying curve, and that may take months or years. We’re partnering with the those who have these machines, and we’re already studying what works and what doesn’t work earlier than we transfer to the following step, as a result of we all know that there’s a rush to supply quicker, to get our cells to market quicker.
Charged: You stated earlier that there are particular functions for which sulfur batteries aren’t very appropriate.
Rodrigo Salvatierra: Traditionally, they’re not excellent at cold-weather efficiency, however we developed electrolytes and sulfur cathodes which can be wonderful. They really out-perform lithium-ion batteries. That’s due to the precise sort of fabric we use for the cathodes.
One of many issues that possibly sulfur shouldn’t be good at is voltage. The voltage of the lithium-sulfur battery is half that of the lithium-ion battery. It’s lighter, however the voltage can also be decrease. So, for instance, for functions reminiscent of cellphones, you may want two batteries in collection to succeed in the required voltage.
Each sort of cell has good attributes and dangerous attributes. There’s not a single chemistry that checks all of the packing containers, together with lithium-ion. Lithium-sulfur has its sturdy attributes, but additionally has others that aren’t so good. From my private standpoint, I just like the sustainability facet—sustainable within the sense that there’s a lot sulfur out there.
Charged: Inform us extra concerning the sources of sulfur provide.
Rodrigo Salvatierra: I’m not going to say any political orientation, however one fascinating facet about sulfur expertise is its connection to grease. Oil is a non-sustainable vitality supply, and batteries are thought-about to be the sustainable selection. Sulfur batteries provide the solely alternative for making oil a part of the sustainable round financial system.
How? The principle supply of sulfur—above 90%—comes from refining oil. Each 10 occasions you refill your automobile with gasoline, you in all probability devour the quantity of crude oil that you would need to refine to generate sufficient sulfur to make one battery pack for a automobile.
That sulfur battery has no metals, so it requires a lot much less transportation of supplies. Metals for batteries like cobalt, nickel, manganese, usually are not geographically well-distributed. They’re produced in a single place, they must journey to a different place after which be distributed. That creates quite a lot of price. Sulfur, then again, is native. Each nation that may extract or refine oil will produce sulfur.
So, you can also make batteries regionally—that’s the primary level. The second is bringing oil into the round financial system—nobody has ever really proposed that. Within the Eighties, there was this factor known as acid rain, and this occurred since you didn’t take away the sulfur out of your oil. The US has possibly probably the most superior expertise to desulfurize oil. However the place do you assume that sulfur goes? That sulfur goes again to the nicely that you just obtained the oil from.
The principle supply of sulfur comes from refining oil. Each nation that may extract or refine oil will produce sulfur. Sulfur batteries provide the solely alternative for making oil a part of the sustainable round financial system.
Charged: Is there any important marketplace for that byproduct?
Rodrigo Salvatierra: There’s a large marketplace for sulfur, however there’s such a lot of sulfur that you just don’t ever have issues with worth oscillation. Simply to present an instance: Batteries traditionally use cobalt, however there’s quite a lot of stress to scale back the quantity of cobalt as a result of cobalt comes from the Republic of Congo, [which has environmental and child-labor issues]. So, we go for nickel-rich cathodes. Nickel is extra out there, however nickel is in demand by the metal business and different industries. One of many main producers of nickel on the earth is Russia. When Russia entered the warfare with Ukraine, there was an enormous spike within the spot worth of nickel.
The costs of nickel, cobalt and all these metals are above $20 per kilogram. The value of sulfur stays underneath 60 cents per kilogram. It’s two orders of magnitude cheaper.
In the present day, nobody cares about sulfur. Sulfur goes to the fertilizer business, goes to sulfuric acid for the chemical business. However these industries don’t care when you introduce one other large stream of demand, as a result of there’s a lot sulfur on the planet. There’s a pyramid of sulfur in Alberta that’s wider than the Giza pyramids in Egypt. A few of my colleagues made a calculation: In the event you substitute all of the batteries on the planet with sulfur, you’ll use possibly half of this pyramid.
This text first appeared in Concern 72: April-June 2025 – Subscribe now.
