By Elan Head

An award-winning journalist, Elan is also a commercial helicopter pilot and an FAA Gold Seal flight instructor with helicopter and instrument ratings. Follow her on Twitter @elanhead


Independent testing confirms Cuberg’s progress toward next-gen eVTOL batteries

The next-generation battery startup Cuberg has received independent validation of its lithium-metal battery technology, confirming an increase in specific energy of up to 80% relative to lithium-ion cells of comparably high power output.

Idaho National Laboratory tested Cuberg’s five-amp-hour battery cells on behalf of the U.S. Department of Energy (DOE). It determined the cells to have a specific energy of 369 watt-hours per kilogram at a discharge rate of C/20 (down to 303 Wh/kg at 1C), a specific power of 2,000 W/kg, and around 370 cycles with C/2 charging before the cells reached end of life at an 80% capacity cut-off. (Excerpts of the test results can be viewed here.)

Cuberg lithium-metal battery cells
INL tested around 20 of Cuberg’s battery cells, covering multiple cell variants across a spectrum of performance tests. “While the testing all looked good, our announcement addresses the specific metrics that are of most impact to our industry,” Cuberg CEO Richard Wang told Cuberg Photo

According to Cuberg co-founder and CEO Richard Wang, the independent validation is significant for two reasons. First, it provides a measure of credibility in an industry that has often been plagued by hype and inflated claims.

“We think for the industry as a whole to move forward effectively, more and more independent testing will be a very positive development and allow our customers to efficiently compare technologies and screen them and assess them for viability,” he told

Further, the test results themselves suggest that Cuberg is on the right track to developing a battery that hits the “sweet spot” for electric aviation and eVTOL aircraft in particular, he said.

“There are three key parameters that most people care about,” Wang explained. “[There] is the energy of the cell, [which is] basically how much energy per weight and that determines how far you can fly. There is the power of the cell, which is how quickly can you get that energy out, and that’s especially needed for those intensive vertical take-offs. And then the third thing is the cycle life. You also need respectable cycle life because cycle life often determines the operating cost of your [aircraft].

“What we found in talking to our customers is there [are] very few battery technologies in development that really meet all three of those requirements for electric aviation,” he continued. “In our view, our technology is coming closest to presenting a next-generation solution because it does deliver that much higher performance envelope that people are looking for.”

While Cuberg believes its cells are now “very, very competitive compared to other technologies,” the company continues to work on improving its product, with a focus on cycle life in particular. “In the next few years, we anticipate getting to 2C charging and 1,000 cycles, along with 400 Wh/kg, which is the holy grail for eVTOL,” Wang said. He added that the company is also in the process of developing a 20-Ah cell for aviation applications — a size that will balance the installation efficiency of larger cells with thermal safety and certifiability considerations.

Founded in 2015, Cuberg grew out of Wang’s graduate research work in the materials science department at Stanford University. To date, the Emeryville, California-based company has secured $10 million in funding from Boeing HorizonX Ventures and various government grants, including a Small Business Innovation Research grant from the DOE.

Cuberg CEO Richard Wang
Cuberg CEO Richard Wang

It was that relationship with the DOE that provided the opportunity for independent validation with the Idaho National Laboratory as part of its battery cell benchmarking program.

The DOE also maintains the Battery500 program, a research consortium that aims to develop next-generation electric vehicle batteries with specific energies of up to 500 Wh/kg based on lithium metal anodes and advanced liquid electrolytes.

“This is probably the [United States’] premier research effort on next-generation battery technology,” Wang explained. “They’re doing a lot of exciting work in the government and with academia on developing next-gen solutions.”

Cuberg’s pouch cells are designed to be compatible with existing lithium-ion battery manufacturing techniques, which Wang said is critical for scalability. The company has partnered with a lithium-ion battery maker that uses its current manufacturing processes and materials to build a nearly complete cell that, according to Wang, “leverages all the efficiencies and quality improvements from the lithium-ion world. The only thing that’s missing is the electrolyte — that’s our secret sauce.”

After Cuberg receives the cells, it injects the electrolyte in-house, completes manufacturing and quality checks, then ships the cells directly to customers. “For the next couple years, we see this as the most efficient model, because it allows us to scale up very easily and maintain good quality control, and also competitive pricing,” Wang said.

Cuberg’s “secret sauce” has the additional advantage of being non-flammable, something that could prove to be a particular selling point in the high-stakes, safety-critical world of aviation.

“All historic electrolytes with lithium-ion batteries are made of organic solvents that are highly combustible,” Wang said. “[Our] more stable electrolyte allows it to be much more tolerant to abuse in different kinds of conditions.”

Wang said that over the past few months Cuberg has been ramping up commercialization “very aggressively,” and shipping samples to top electric aircraft developers around the world. Initial results have been encouraging.

“Right now we’re at a stage where many customers are testing our cells and starting to progress to the next stages in terms of co-development,” he said. “Our hope is that we’ll be able to work with some key customers to integrate our technology into their systems . . . and get to the point of maturity and performance where we can start actually doing full-scale system and even flight testing.”

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1 Comment

  1. Hello,
    A great work by research team towards carbon free mission..In India we are developing 2seater and 6seater Airtaxi along with Indian premier institute “The Indian Institute Of Technology, Kanpur “ and tested prototype. Appreciate if we can get this cells for testing so that we can incorporate in our VTOL Aircraft..

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