Redoxblox Raises $40.7 Million for ‘Thermochemical’ Energy Storage

Decarbonizing industrial processes such as paper and pulp production, chemical manufacturing, or food processing is a tough sell. As it so often goes, that’s largely due to the efficacy and low cost of natural gas, which can cheaply and efficiently provide the high heat required for these industries. But a number of innovative battery companies are looking to shake up that dynamic, and the latest, Redoxblox, just gained a big vote of confidence.

Today, the San Diego-based startup announced the close of its $40.7 million Series A round, which it raised in two tranches. The first $9.4 million tranche, back in 2022, was led by Khosla Ventures, with participation from Breakthrough Energy Ventures. The latest $31.3 million raise, announced today, was led by the climate tech investor Prelude Ventures, with participation from Imperative Ventures and New System Ventures, alongside BEV and Khosla. While Redoxblox didn’t respond to an inquiry about why it raised these two tranches so far apart, an SEC filing reveals that the company initially aimed to raise $22.4 million in 2022, indicating that it fell far short of its original goal.

Now though, the company looks poised for growth, and has announced the appointment of a new CEO, Pasquale Romano, formerly the CEO of ChargePoint, which operates a network of EV charging stations.

Redoxblox’s technology is known as “thermochemical energy storage,” as the system stores energy both chemically and as heat. “What the founders have discovered is a real scientific breakthrough,” Scott McNally, the company’s vice president of development, told me. He said that Redoxblox is mistakenly lumped in with thermal storage startups such as Rondo or Antora all the time. But the company’s thermochemical solution is a new class of energy storage entirely. “Yes, we store energy as heat, but we also store energy in chemical bonds. That's why fossil fuels are so widely adopted, is because the amount of energy contained in a chemical bond is enormous,” McNally explained. This allows Redoxblox to achieve both very high energy density and very high temperatures.

The system uses grid electricity to charge when prices are low or when there’s excess renewable generation. As electricity passes through the company’s proprietary metal oxide storage pellets, they’re resistively heated (like a toaster!) up to 1,500 degrees Celsius. When they hit a certain temperature, this drives a “redox reaction,” which is a kind of reaction in which electrons are transferred between two substances. In Redoxblox’s case, the pellets release pure oxygen gas and absorb heat, which is stored as chemical energy. To discharge that heat, a pump blows air across the hot pellets; as the air heats up and the pellets absorb oxygen from it, that oxygen-depleted air can then be delivered as heat to power various industrial processes or to gas turbines to generate electricity.

The redox reaction the company relies upon has been understood since the 1800s — what’s exciting is the proprietary metal oxide the company’s founders discovered, which can cycle through this reaction again and again. “The problem with fossil fuels is you can't take a lump of ash from burning coal, run electricity through it, and make coal again. But with this, you actually can,” McNally told me. “We've cycled our material through that more than 1,000 times with no loss of energy density, no degradation.”

Redoxblox’s Series A funding comes in addition to about $17 million in non-dilutive capital that the company has already received from an ARPA-E grant, as well as more recent grants from the Department of Energy and the California Energy Commission, which will go towards building the company's first industrial demonstration projects. The $6.7 million DOE grant supports RedoxBlox’s partnership with Dow Chemicals, in which the startup will retrofit a gas-fired steam boiler with its thermochemical battery at Dow’s manufacturing plant in Charleston, West Virginia. And the CEC grant will support the buildout of a 3 megawatt-hour long-duration energy storage system for UC San Diego’s medical campus, which will provide 24 hours of electricity in the case of a power outage.

Romano told me that Redoxblox also has partnerships with a paper mill and a dairy production operation in Europe, where natural gas is magnitudes more expensive, and thus the startup’s technology is much more economically competitive. Ultimately of course, Redoxblox wants to be cheaper than natural gas in the U.S., which Romano said currently sits at about 3.6 cents per kilowatt-hour.

However, this technology is not yet likely to make much of a dent in the highest temperature industrial heating applications, such as steel and cement manufacturing or certain chemical production processes. While Redoxblox’s tech would theoretically work for these industries, the energy demands would be astronomical.

The company is targeting its first commercialized product in 2026, which will fit inside a shipping container and store up to 20 megawatt-hours of energy at 95% efficiency. Multiple units can be combined to meet the needs of larger facilities, and McNally told me that they’re not necessarily targeting any one specific industry at the moment. As he put it, “We're just targeting anybody that uses natural gas that wants to decarbonize at, in many cases, a lower cost than fossil fuels.”