Tennessee startup customizes and innovates both zinc and sodium-ion battery technologies

The sodium and zinc found in our blood and bones can also be used to fuel the next generation of cleaner, greener batteries. This is the fundamental idea driving Coulomb Technology, a startup specializing in both sodium-ion and zinc batteries, co-founded by CEO Tim Vosburgh and CTO Subathra Rajendran.

“That’s the whole motive of Coulomb,” Rajendran said. “Zinc and sodium are there in our bodies. They’re an essential element, more abundant and non-toxic.” 

Coulomb is one of seven companies participating in New Energy New York’s ChargeUp Accelerator, the nation’s premier accelerator program dedicated specifically to mentoring battery technology startups. It offers six months of both online and in-person curriculum, mentorship and workshops that hone startups, regardless of their statuses at the beginning of the program, into investment-ready shape.

With dual technology that can be customized according to user needs, Coulomb has created sustainable, eco-friendly and cheaper batteries capable of powering the smallest tools and phones or storing energy for entire grids.

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Subathra Rajendran, CTO, Coulomb Technologies

“People are doing sodium. People are doing zinc. We, as a company, have both the technologies working in parallel,” Rajendran said. “Even with sodium, we have our own chemistry, especially phosphate-based sodium-ion batteries — which none of the companies in the U.S. had until now.” 

In the realm of sodium-ion batteries, there are a few established chemistries already, each with their own properties and pitfalls. Oxide-based sodium batteries, for example, are at risk of flammability due to the presence of oxygen, according to Rajendran. Meanwhile, batteries using Prussian-based compounds tend to contain cyanide, which can pose problems down the road when it comes to disposal — a similar problem facing lithium-ion batteries.

Coulomb specializes in phosphate-based sodium-ion batteries, utilizing a unique chemistry including NASICON to provide a more durable structure.

“Those have a structure that we think is very stable and long-cycling, and we think it’s safer, very fast-charging, and can handle extreme temperatures well,” Vosburgh said. “Those attributes are very valuable, and the raw material is also very abundant.”

So far, Coulomb has achieved a battery that can provide around 20 years’ worth of life and can operate at a wide range of temperatures, starting at around minus 80 degrees Celsius.

“Their life cycle is so high compared to all other chemistries of sodium,” Rajendran said. 

For its zinc batteries, Coulomb also incorporates a special aqueous electrolyte to tamp down on flammability, combined with an acidic-based chemistry.

“Our zinc battery is super unique, and it’s acidic. Most zinc batteries use an alkaline-based chemistry, which makes it a little easier to control problems with the anode,” Vosburgh said. “We use acidic, which is harder, but we think it gives us better energy density.”

While customers have the flexibility to choose between different battery chemistries, depending on the use-case, Coulomb’s cells are customizable even down to recipe or components. Whether you’re powering telecommunications in remote areas or even replacing the battery in a fire alarm, Coulomb aims to provide the cell that can best accomplish that goal.

“There are multiple factors needed for a battery, but at the moment, we use only one kind of lithium technology to answer all those requirements. That’s what we want to change,” Rajendran said. “Depending on that, we can even modify the recipe. If you need fast charging, we have a cathode for delivering a fast discharge rate. If you need a totally fire-safe battery, we have an anode composition we can use for a fire-safe environment.”

Though Coulomb-produced batteries might ultimately look different from one another, in chemistry and recipe, their biggest commonality is a commitment to innovative sustainability. 

“We cannot measure everything; we can only predict it. But the real impact is something different — so do it right the first time,” Rajendran said. “When you are doing innovation or creating something, think about the next 50 or 100 years, about how it impacts the environment, the people who are using it one, two or three generations across. It has to be sustainable. What we are taking from Mother Earth should be given back in a cleaner and purer form.”

One ideology and dream

Rajendran is an energy specialist, having spent decades working for major oil and gas companies around the world. However, a switch flipped on an assignment to Congo in 2019, where she witnessed the environmental impact and strenuous working practices of cobalt mining. 

“At that time, I wasn’t even aware it was for making batteries. When I dug deeper into that, cobalt was mainly used in lithium-ion batteries,” she said. “I’m a chemical engineer by training, so I can understand the chemistry behind it. That made me think: Is there any alternative?”

She began combing through the literature on batteries, searching for that sustainable option. When she couldn’t find an answer, Rajendran began to think about developing her own. 

Though she spent most of her career at that point working in big corporations, she had harbored an itch for entrepreneurship since childhood. The startup world offered the potential to not only make a difference but also fulfill a lifelong dream.

“At one point, after the Congo experience and I was turning 40, I thought: ‘If not now, when?’ That’s the motivation for me to have my own startup,” Rajendran said. “And energy is my passion, heart and soul — everything.” 

Vosburgh, meanwhile, juggles a background in mechanical engineering and business. Though he isn’t a scientist like Rajendran, he has always been fascinated by the complexity that goes into even a single battery cell. 

“I love technology, and batteries have so many disciplines that you need to know and use to develop them,” he said. “There’s engineering, there’s chemistry, there’s thermodynamics, and it’s cool to be able to use all of that.” 

During his time in the semiconductor industry, Vosburgh began looking at the potential of getting involved in startups. Not every venture went through, but in 2022, as the interest in clean tech solutions began to rocket, Vosburgh decided to return to the battery industry. He founded Coulomb, named after the French physicist and scientist who pioneered the study of electricity. 

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Tim Vosburgh, CEO, Coulomb Technologies

“I always wanted to do something where I was contributing more and making a bigger impact on society,” he said. 

Prior to Coulomb, Rajendran worked on sodium-ion technology in her company Aatral. She and Vosburgh had crossed paths before, having attended the same monthly meetings held by Volta Foundation. But when they got talking as participants in the same Tennessee-based accelerator program, they decided to combine the forces of their respective companies. 

“We both have the same ideology: We want to make batteries sustainably,” Rajendran said. 

A mission to give back

As the company prepares to fundraise, scale and grow in technology readiness, the future looks busy and demanding — but Rajendran and Vosburgh have found their own ways to keep fueling their passions. 

“My biggest inspiration is my kids. I have young kids, and they currently live in Idaho, and I don’t get to see them very often because I’m away,” Vosburgh said. “I tell myself, ‘You have to work hard to be able to come back to them someday.’”

Entrepreneurship is a practice that requires every part and hour a person might have, Rajendran said, but working on something she truly cares about keeps her afloat.

“If you really know the purpose, even though it is hard, if you never give up, you will definitely reach your massive success one day,” Rajendran said. “This is what I am telling myself, and what I want to share with everyone: Today is tough, tomorrow may be much tougher, but the day after tomorrow may be a good day.” 

When the day after tomorrow does come, Vosburgh hopes Coulomb will have played its part in revolutionizing the ubiquity and effectiveness of batteries, all while creating the next generation of well-paying jobs in the U.S. 

“I want to give back as much as I can. I don’t need a ton of money and fame. I just want to provide stuff that is good for the environment and good for people,” he said. “I want our company to reflect those values, where we care about others, we care about safety, and we care about our products being cool and able to be made with good chemistry.”

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