About Propel Aero
Propel Aero develops battery systems for electric mobility. Its main technology is a sodium-air fuel cell, which it calls a REDOX engine. The cell consumes sodium metal and runs on humidified air. The company aims it at electric aircraft, and its test work covers maritime use.
The company is based in Sunnyvale, California. Its website has a Flight Estimator page. MIT professor Yet-Ming Chiang presented its REDOX engine work at the PROPEL-1K program annual meeting on July 15, 2025. The presentation names MIT and the University of Michigan alongside Propel Aero. It reports a demonstrated stack specific energy of 1,700 Wh/kg.
Funding Rounds (SEC Form D)
| First sale | Filed with SEC | Amount sold | Investors | Avg. check | Terms | Filing |
|---|---|---|---|---|---|---|
| Mar 24, 2026 | Oct 21, 2026 | $10,485,078fully sold | 16 | $655K | EquityRule 506(b) | Form D ↗ |
| Oct 5, 2026 | Oct 21, 2026 | $4,930,166of $11.9M target | 4 | $1.2M | EquityRule 506(b) | Form D ↗ |
| Total, two offerings | $15,415,244 | |||||
First sale is the date the first investor in the offering committed to invest. Companies must file Form D within 15 days of that date, so filing dates run later.
Why Investors Backed Propel Aero
Propel Aero builds sodium-air fuel cells meant to power electric aircraft. MIT professor Yet-Ming Chiang and colleagues developed the cell. In June 2025, MIT's materials department described Propel Aero as prototyping it for a large drone. The company's stated goal is over 1,000 watt-hours per kilogram at a cost on par with jet fuel.
The problem it targets
Propel Aero's project aim is an engine that offers more than 1,000 Wh/kg at cost parity with jet fuel. According to The Boston Globe, as cited by MIT, the cell packs three to four times more energy per pound than common lithium-ion batteries. Chiang told the Globe that passenger flights of up to 300 miles could eventually be possible. He said FAA certification will take time and is the hardest part.
What the product does
The cell is a sodium-air fuel cell that consumes sodium metal. In test cells, adding humidified air lowers overpotential and raises accessible capacity, because the discharge product is removed continuously. The team measures stack performance. System-level performance is modeled from those stack results.
Progress so far
A July 15, 2025 program presentation reports continuous operation consuming up to 2.5 cm of sodium metal. It reports that maritime continuous and pulse power targets were exceeded. Stack specific energy reached 1,700 Wh/kg. Under a maritime duty cycle in air, cells reached about 1,550 Wh/kg at stack level and a modeled 1,050 Wh/kg at system level. Next steps are air electrode and solid electrolyte work for higher power, then module and system design, build and test.
We wrote this summary from public statements by Propel Aero and its investors. It is not investment advice.
Propel Aero in the News
Leadership Team
Executive officers and directors listed on Propel Aero's Form D filed Oct 21, 2026.
