How do You Make a Green Battery? Use Zinc.

Battery company Imprint Energy is betting on the widespread metal, and recently announced its latest zinc-ion battery technology: ZinCore. According to the company, ZinCore provides ten times more power for the same volume as its legacy battery technology, ZincPoly. ZinCore is classified as a non-hazardous waste, as it is not ignitable, corrosive, reactive, or toxic.

As a rechargeable battery made from readily available material, ZinCore provides unique environmental and commercial advantages. We wanted to learn more about ZinCore and the advantages of zinc-ion batteries, so we spoke with Christine Ho, cofounder, and CEO of Imprint Energy.

Engineering.com: How did you first become involved in battery technology?

Christine Ho: I went into engineering school [at Berkley] in the materials science field. My sophomore year, I answered an ad to become a undergraduate researcher working for a graduate student who happened to be studying batteries.

I started off doing lithium-ion for electric vehicles, squeezing the energy density out of the materials. It’s meaningful to see some of that kind of technology come to market today. I also started to think a lot about how we can make a safer and more sustainable battery. One that’s made of materials that are much more earth abundant. How can we manufacture things differently?

I was really inspired at the time by the 3D printing industry. I love the idea that you only make what you need, and you don’t have to just make one widget all the time in a low-labor region.

When I was graduating from my bachelor’s degree at Berkeley, I wanted to study more in terms of batteries. I could really perpetuate the battery project forward and take over its leadership as a graduate student. So, I decided to stay. I remained at Berkeley for my degrees, material science, all the way from bachelor’s to PhD.

I was obsessed with this idea of democratizing manufacturing. I liked the idea of printing existing everywhere. There are printers all over the world. The equipment, capital and the skilled labor all exist in almost every city. What if we were to build printed batteries?

It’s almost like our giga-factory already exists. It’s already deployed. Those are the underpinnings of Imprint Energy’s technology. We’re using zinc instead of lithium and a safer, non-toxic technology.

I was trying to make [a] safer battery that was also printable. It was using some very new edge materials that really hadn’t been applied to batteries.

Lithium materials are very hard to handle. They’re very sensitive to the environment, with things like trace moisture in the air at parts per million that can poison the chemistry. You must keep the chemistry away from moisture and keep it clean because [any contamination] can cause a detrimental effect to the chemistry.

To make a lithium battery, you need good sealing. As you shrink those batteries and try to make them more compact, you end up giving up a lot of active volume to packaging to keep its chemistry away from the environment, or the environment away from the chemistry. There’s a crossover point where for batteries that are compact or unusually shaped, it’s no longer beneficial to even use a lithium battery because you won’t get the high practical energy density.

That crossover happens to be with batteries that are usually a millimeter in thickness or lower, or compact, or an unusual shape. Lithium batteries just can’t provide enough energy density or runtime. That’s where there’s this huge opportunity to look at alternative chemistries that are much more environmentally stable, safe, and don’t need that level of packaging.

Packaging zinc is almost like packaging dirt. It’s stable. For the most part, this chemistry is stable in the air. Most of the battery materials are also in vitamins, so they don’t need that packaging. We use a sticker-like material rather than metal to package our batteries because they aren’t that environmentally sensitive.

The upside of everything is that when customers are looking for longer runtime, we’re able to deliver more than lithium-ion in these form factors. Performance is often the table-stakes for customers, and we can deliver there purely because we can fit more in that compact space, without that packaging overhead.

One of the awesome things about the technology is that we’ve been able to step into existing manufacturing environments, literally print shops. Right now, we’re working with one of the biggest label printers in the world. They’re used to printing labels, stickers, and whatnot. We’re using their equipment. We’ll make these batteries without having to add big glove boxes and all this overhead. We can step right into their environment.

We take advantage of technology and existing process lines and make sure our materials are compatible with theirs. That’s not possible with lithium solid-state. It’s a hard material to keep clean, to handle. You need specialty equipment—special lines, build specialty factories, and that’s going to take time.

The base materials of a zinc battery are considered earth abundant and non-toxic. A lot of it is found in vitamins. Disposability is an interesting topic for us, because our batteries are characterized as a non-hazardous or household waste, so they could be disposed of as common household trash.

At Imprint, we have commitments to recycling and reuse. Over the last year, we’ve worked with an outside group to develop a process to recover key materials from the zinc batteries.

The takeaway from that exercise was there is a profitable way to do that. That now becomes a part of our technology portfolio. We can deliver to our customers a process that they can step into if they really care about recovering these materials, and there is a way to profitably do that.

Right now, we focus a lot on track and trace applications. One major segment of that is cold chain monitoring. This includes monitoring food that needs to be refrigerated or frozen. It also includes monitoring COVID-19 vaccines that need to be kept frozen while in passage. Low-temperature operation is a critical parameter for a lot of our customers. It’s a big challenge for batteries.

Batteries tend to slow down at lower temperatures and not be as good in terms of performance and runtime. At low temperatures, chemical reactions slow down, and you just can’t force a chemical reaction to move fast. This is an age-old battery problem, especially for thin flexible batteries. It can exacerbate the issue because your battery gets cold very quickly. Big batteries can self-heat and protect themselves from low temperature. Thin, small batteries don’t have that kind of self-heating mechanism. They come to ambient temperature very quickly.

We must counter that with two things. One major thing is chemistry. A water-based system tends to slow down at low temperature or even solidify or freeze. You can play around a lot with the composition of your electrolyte materials. There are certain additives that can push down the freeze temperature. It’s kind of like when you add salt to water, you can change the temperature at which it freezes.

The other piece is the architecture. You can make it easy for your chemistry and your ions to move fast [effectively], even if it’s going slow. The architecture is designed such that ions don’t have to travel a long distance to get to where they need to be. Even with that slowdown brought on by low temperatures, you still can manage to push the chemistry to make it easy for all those ions to move to the right place and react. That comes down to how closely you layer one layer on top of the other, and how intricately you design the different interfaces. Those are usually the biggest knobs that we can control to be able to lower the operating temperature.

We’ve done well here. We have a gen two chemistry called ZinCore. We found this chemistry [operates at] low temperatures, down to about negative 35 to 40 °C, which is well within the zone of frozen seafood, frozen sushi, and some vaccines. Whereas our gen one chemistry [ZincPoly] really slowed down at subzero. It had a hard time getting past -10 degrees.

The one reason ZincPoly is still in production for us and commercially relevant is that it’s a unique technology in terms of manufacturing. We can take advantage of very traditional printing so that we can make unusual shapes, like a donut with a hole or a letter.

The way we manufacture ZincPoly, it truly is printed like t-shirts. ZinCore is not yet there. It’s printed like a separate component that then gets attached to the device. ZincPoly is extremely unique in some of these applications that require that kind of level of integration—compactness or unique shapes. Customers may buy ZincPoly just because of the form factor we can deliver for them.

With this new technology ZinCore, a design tech is designing and manufacturing flexible electronics. And you’re buying a part and then attaching your battery. There’s two pieces to it for the customer.

The device for the use case could be designed by any of our partners. They will specify the battery to support that application or design around what we have.

We’ve also developed our own smart label. It’s a Bluetooth smart label with temperature capability. It’s unique because of how the battery is shaped and how it gets integrated into the label.

We’ve done this so many times with various customers, we realized that we could offer a reference design to the industry. And that’s been very successful. We’ve had end-users come directly to us for a total solution, not just a component and not just the battery, but the smart label.

For example, we’re starting to ramp up to COVID-19 vaccine trials with that smart label. We’re going to do food agriculture trials as well. Imprint has evolved in that not only are we offering best-in-class batteries to the market, but we’re also offering solutions. It’s helped us to know how we validate this market space and understand our customers and the end use cases more so that we can make better technology.

Some of the biggest problems are at the interfaces of putting technologies together. We spend a lot of time making a good, robust, high-quality battery. Some of the biggest vulnerabilities are just the connector that connects the battery to the rest of the device.

That’s one piece. There’s a lot of nuances in manufacturing batteries at scale. When you’re making small volumes of batteries, you can just take a battery out of a box and connect it. But when you’re talking about automation, the batteries need to feed as a roll. They come out to the roll and attach on. There’s a lot of technology that goes into integration and it’s under-appreciated. It is oftentimes left as the last thing that is sometimes the hardest to bring in. There’s a lot of hidden costs, too.

We’re positioning ourselves as a holistic partner, not just a component supplier, and making our smart label has given us the credibility to come in and say, “we’re looking at this from a solution perspective.” We’re not just guaranteeing this battery. We’re guaranteeing the solution because we want it to work in the market and in the field. We’re delivering a lot more value than just the battery itself. We’re really giving a lot of insight and feedback based on our experience.