Sujeet Kumar

Twenty years, one material

Most battery breakthroughs get announced before they get built. Sujeet Kumar has spent the better part of his career on the second, harder half of that sentence.

The pattern in Sujeet Kumar's career is easy to miss until you line up the companies. Nanogram. Greatbatch. Nanoexa. Envia Systems. Zenlabs. And now Ionblox, the Fremont, California company he co-founded and runs as CEO. Different names, different funding rounds, different decades. Underneath all of them sits the same technical bet: that silicon can replace graphite in the anode of a lithium-ion cell, holding far more energy in the same space, if you can only tame the way it swells and cracks.

Kumar came to that problem through materials science. He earned a bachelor's degree from IIT (BHU) in Varanasi, India, then a Ph.D. in Materials Science from the University of Rochester. Early in his career he worked as a principal scientist at Nanogram Devices Corporation and a senior scientist at Greatbatch, developing cathode materials, before moving into technology leadership at Nanoexa. In 2009 he won an R&D 100 award for work on high-energy lithium-ion batteries, one of the field's long-running honors for applied invention.

His most public chapter before Ionblox came at Envia Systems, where he served as chief technology officer. There, as the company's own account puts it, he "led his team to develop the world's first 400 Wh/kg LIB with a silicon anode." That figure matters: energy density, measured in watt-hours per kilogram, is the number that decides how far an electric car goes or whether an aircraft can carry enough battery to fly. Pushing past 400 Wh/kg with silicon was a lab milestone that most of the industry was still circling.

From lab cell to something you can build

A milestone cell in a lab and a cell you can manufacture at low cost are two very different things, and the gap between them has buried more than one battery startup. That gap is where Ionblox lives. Founded in 2017 as Zenlabs Energy and later renamed, the company is built around a pre-lithiated silicon-oxide anode - silicon that has been dosed with extra lithium up front to offset the losses that normally plague silicon cells over their first charges.

The pitch Kumar makes is deliberately about not choosing. Batteries usually force a tradeoff: you can have high energy or high power, long cycle life or fast charging, good performance or low cost. Ionblox claims to hold several of those at once.

Why the aircraft people came knocking

Weight is the tyrant of electric flight. Every kilogram of battery is a kilogram that has to be lifted, so the cells that work in a car are often too heavy, or too weak on power, for an aircraft that needs to take off vertically. That is the exact seam Kumar has aimed Ionblox at, and it is why the company's most notable partner was not a carmaker but the German eVTOL developer Lilium, which licensed Ionblox's cell technology and invested in the company.

In an interview, Kumar framed the collaboration in plain terms: "Our proprietary pre-lithiated silicon oxide anode provides higher energy density and power output, allowing for longer-range electric vehicles and improved performance in eVTOL applications. Additionally, our technology enables up to 1,000 fast charge cycles."

The story is not without hard turns. Lilium, the eVTOL maker that had bet on Ionblox's cells, filed for insolvency, with its German assets slated for acquisition by a consortium in a deal signed in late December 2024. For a battery supplier, a marquee customer's collapse is the kind of event that tests both the technology and the founder. It also underscores how young and unforgiving the electric-aviation market still is, and how much of Ionblox's future depends on finding the next set of customers who need cells that are light, powerful and fast to charge all at once.

The through-line

What holds the arc together is temperament as much as chemistry. Kumar is, by the record, a persistent technologist - someone who returns to the same material across company after company because he is convinced it wins, and who talks less about moonshots than about manufacturability and cost. In a field crowded with promises about solid-state cells that are always a few years out, his argument is quieter and more near-term: silicon is here, it is scalable, and the work is to get it into cars and aircraft, not to wait for the perfect chemistry.

With more than 60 patents to his name, an R&D 100 award behind him and a core team of Rochester-trained materials scientists around him, Sujeet Kumar has assembled the credentials of a lifer in a field that rewards patience. Whether Ionblox becomes the company that finally makes silicon anodes ordinary is still an open question. But the bet itself is not new for him. It is the one he has been making his whole career.