He left the company that made batteries famous to bet on a cheaper one - made of iron, water, and air.
The batteries Mateo Jaramillo is building right now do something most engineers spent a century trying to prevent: they rust on purpose. Inside a Form Energy cell, iron meets oxygen, turns to rust, and gives up electrons on the way. Reverse the current and the rust turns back into iron. That single, deliberately boring reaction is the bet behind a company that has raised more than $1.3 billion and just signed a deal with Google reported at around a billion dollars.
Jaramillo co-founded Form Energy in 2017 and runs it as CEO from Somerville, Massachusetts. The product is a battery designed to discharge for 100 hours - not the four hours a lithium-ion grid battery typically manages. The number is not marketing. It is the rough length of a polar vortex, a heat wave, a hurricane sitting over a region for days. He picked the duration to match the disasters.
The first commercial cells are now leaving Form Factory 1, a plant built on the carcass of the old Weirton Steel mill in West Virginia. A town that lost its steel jobs is making the metal batteries that may keep the lights on through the next storm. Jaramillo likes that symmetry, and he likes the math behind it even more.
Iron is abundant, cheap, and safe. The trick was making it breathe.
Iron takes in oxygen from the air and rusts, releasing electrons.
The cell pulls oxygen in and pushes it back out as it cycles.
Apply current and the rust converts back to iron. Repeat.
A typical lithium-ion grid battery empties in about four hours. Useful for smoothing an evening peak. Useless when a five-day weather event knocks renewables offline. Jaramillo's analysis kept landing on the same window.
"That 100 hours sounds simple and like a nice, appealing round number," he has said, "but it is actually very much supported by the math." Extreme weather, almost anywhere on Earth, tends to run in roughly 100-hour chunks. Build for that, and a battery can start to do what a gas plant does.
Before he was a battery executive, Jaramillo studied economics at Harvard and earned a master's in theology from Yale Divinity School. It is not the resume you would draft for the person reinventing the electric grid, which is part of why it is worth telling.
He found his way into energy storage early, helping found Gaia Power Technologies. Then in 2009 he joined Tesla, where he started the stationary storage business from scratch and helped put the Powerwall and Powerpack into the world. In 2017 he left to chase the storage problem Tesla's chemistry could not solve cheaply: not hours, but days.
A.B. in Economics, Harvard University.
Master of Theological Studies, Yale Divinity School.
Joins Tesla; leads $600M+ in powertrain contracts, then starts its stationary storage line.
Co-founds Form Energy to build multi-day storage.
Form reveals its 100-hour iron-air battery.
$405M Series F; total funding tops $1.3B.
Google & Xcel deal for a 30 GWh system, reported near $1B.
Form was built by materials scientists, an MIT professor, and the operator who knew how to sell what they made.
Jaramillo brought the commercial playbook from Tesla - product definition, policy, the unglamorous work of turning chemistry into contracts.
Co-founder and chief scientist Yet-Ming Chiang, an MIT professor, anchors the materials side. The team counts decades of battery experience between them.
Co-founders Ted Wiley, Billy Woodford, and Marco Ferrara round out a founding group spanning startups, academia, and earlier storage ventures.
When we founded the company, we didn't anticipate the boom of data center demand that we're currently experiencing.
We're quite confident that we will hit that roughly $20 a kilowatt-hour cost within a very short period of time.
If you could identify a chemistry that's cheap enough, you could have a much longer duration - roughly four or five days.
That 100 hours sounds simple, but it is actually very much supported by the math.
Make multi-day storage cheap enough to retire fossil plants - and call it a reliable, fully renewable grid.