Cuberg pouch cell. Image credit: Cuberg

Northvolt & Cuberg Unveil Batteries Designed For Electric Aircraft

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In 2015, Cuberb was founded in San Leandro, California, by Richard Wang to commercialize its lithium metal cell technology. The Cuberg battery offers a significantly higher charge density than a conventional lithium-ion battery. According to ArsTechnica, many of the lithium-ion batteries currently available have power densities of approximately 270 Wh/kg. By contrast, a Cuberg pouch cell has been shown in testing to provide 380 Wh/kg, a gain of 40%. When an independent lab placed the battery on a cycle of one hour discharges and two hours of charging, it found the battery took over 670 cycles for its capacity to drop to 80% of its original. By comparison, many lithium-ion batteries target a 500-cycle life span.

In 2021, Cuberg was acquired by Northvolt in order to scale up the technology. At that time, Northvolt CEO Peter Carlsson said, “The Cuberg team has shown exceptional ability to develop world class technology, proven results and an outstanding customer base in a lean and efficient organization. Combining these strengths with the capabilities and technology of Northvolt allows us to make significant improvements in both performance and safety while driving down cost even further for next-generation battery cells. This is critical for accelerating the shift to fully electric vehicles and responding to the needs of the leading automotive companies within a relevant time frame.”

Battery Cost, Energy, & Weight

Today, Cuberg batteries cost more than the lithium-ion batteries used in most electric cars, but price isn’t everything. Two of the primary advantages of lithium metal technology are high energy density and low weight. Regulators in the US and Europe require robust fire suppression systems in order to approve new technologies for use in aircraft. Those systems add weight, which means batteries that have a high energy to weight ratio are critical to advancing the goal of making battery powered aircraft that are certified for commercial service.

“When you add all the safety systems to actually pass the full scope of certification, you end up with a lithium ion battery that’s so heavy that most of the sort of ranges that these companies want to make are not compatible with current generation battery technology,” Wang told Ars Technica. As production of the Cuberb lithium metal batteries ramps up, thanks to the ability to scale provided by Northvolt, the cost of the batteries will inevitably decrease, making them even more attractive to aircraft manufacturers.

In a recent press release, Peter Carlsson said, “Northvolt is establishing itself as a leading global provider of sustainable battery cells for the automotive segment as well as complete battery systems for the heavy industrial and energy storage markets. With our aviation systems program, we will leverage Cuberg’s next generation lithium metal cell technology together with our battery manufacturing experience to bring end to end energy solutions to the skies.”

Since last year, Cuberg has made significant advances toward a fully integrated battery system. First, it has developed a 20 Ah commercial-format lithium metal pouch cell with a specific energy of 405 Wh/kg, which has been shipped to customers worldwide. Second, it has engineered and produced an aviation module, based around its 20 Ah lithium metal cells, with a specific energy of 280 Wh/kg and an energy density of 320 Wh/L. Third, the Cuberg lithium metal module platform has achieved passive propagation resistance during a thermal runaway verification test campaign, a key step in certification of aviation battery systems.

Cleaning Up Commercial Aviation

Richard Wang, Cuberg CEO, commented, “The aviation industry is pursuing cleaner forms of energy and propulsion, but aircraft manufacturers are held back by the weight and immaturity of aviation-certifiable lithium-ion battery systems. With this new program, we will build certifiable battery systems enabling greatly enhanced aircraft performance and deliver a trusted end-to-end solution backed by one of the world’s preeminent battery manufacturers.”

Cuberg technology uses a lithium metal anode and proprietary liquid electrolyte to simultaneously solve the interlocking challenges of battery performance and manufacturability. While incumbent battery technologies, such as lithium-ion, can be too heavy and low performing for use in aircraft, Cuberg’s battery cells are lightweight and high performance. The technology is also compatible with industry standard manufacturing methods, enabling scalability, reliability, and traceability across the value chain.

Cuberg Targets Electric Flight

This week, Cuberg said its module technology can be customized for each customer and provides performance metrics on specific energy and energy density that lead the industry. It made the following relevant battery metrics public for the first time.

• Mass: 16.4 kg
• Size: 95mm x 280mm x 540 mm
• Rated energy: 4.6 kWh
• Energy density: 320 Wh/L
• Specific energy: 280 Wh/kg

The company says aircraft manufacturers will be especially interested in the specific energy of the Cuberg module. At 280 Wh/kg, it is up to 40% higher than comparable modules based on lithium-ion technology. This significant improvement translates into increased flight range, which in turn enables new use cases for electric and hybrid aviation. Some operators could see their practical range more than double, depending on their aircraft and powertrain design. Cuberg says it will deliver modules to select aviation customers throughout 2023.

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Unpacking The Specifics

Regular readers know my brain begins to melt whenever units of measure start flying around. I recall a recent story about CATL claiming it had a developed a new “condensed matter” battery with an energy density of 500 Wh/kg that it thought would be of particular interest to the aircraft industry. I was particularly confused by the difference between specific energy and energy density, so I reached out to Wes Andrews at Cuberg for help. I got back a detailed explanation that is so good, it deserves to be shared in its entirety.

Electric airplanes need a lot of power to take off, less power to coast, and potentially lots of power again to land. Aircraft manufacturers want this power without sacrificing weight. Every gram taken up by a battery is a gram not available for passengers or cargo. That’s why the industry is so focused on specific energy.

Specific energy is expressed in Watt-hours per kilogram (Wh/kg). This is a measure of energy per mass which immediately implies energy by weight. It answers the question: how many grams of battery does it take to make the airplane fly?

Energy density is expressed in Watt-hours per liter (Wh/L). This is a measure of energy by volume. It answers the question: how much physical space does this battery occupy to make the airplane fly?

Cuberg technology packs more energy into a lighter weight and smaller space than mainstream lithium ion technology. Our batteries are “high-performance” due to their excellent specific energy and energy density metrics.

Next, it’s important to understand that when we talk about an EV battery — the thing that you see when you “pop the hood” — what we’re actually talking about is a battery system. That system is made up of many different technologies, all of which will have different performance metrics. Which can be confusing!

Cuberg’s core technology is our battery cell. It has specific energy of 405 Wh/kg. It’s about as big as a magazine folded in thirds. (See featured image above.)

Cells are assembled into modules. A module can have anywhere from 20 to 80 cells inside, depending on many factors (we are not disclosing the number of cells in our module). Our module has specific energy of 280 Wh/kg. You’ll notice that the module number is smaller than the cell number; this is normal. Module packaging and design is also itself very important — it is responsible for ensuring reliable and safe operation, even if a battery cell catches on fire during flight, as the FAA requires companies to demonstrate during certification.

Cuberg Aviation Module

Modules are then assembled into packs; packs are then integrated into a full system; the system interfaces with the technology in the aircraft. This is the inflection point where Cuberg technology begins to blend with technology from the aircraft manufacturer. Our battery system program has a clear path to reaching 350 Wh/kg. You’ll notice this is higher than our current module — it’s a goal that includes successive generational product releases.

In summary, our battery cell and module today post performance at 405 and 280 Wh/kg, respectively. As we successively iterate both the cell and module designs, we migrate cell performance from 405 to 450 Wh/kg, and module performance from 280 to 350 Wh/kg, as we go into certification.

This progression from next generation cell, to module, to pack, to system, is referred to as the “commercialization journey”, which is business-speak for bringing technology out of the lab and into profitable real-world use.

Cuberg is a good distance down the commercialization journey. We are the only known advanced cell company pursuing a full battery system strategy for aviation. Other startups have advanced cells, but not a robust aviation program. Still other companies have an aviation program, but the program is based on lithium ion cells, which we consider fundamentally inadequate for the power-intensive needs of aircraft.

CATL has announced an advanced cell with specific energy *up to* 500 Wh/kg. If you’re making an apples to apples comparison with Cuberg tech, you would put that non-specific figure alongside our customer-validated 405 Wh/kg cell that has already been shipped to customers worldwide.

CATL has not announced an aviation systems program or any steps down the commercialization journey that would compare apples to apples with our module and systems designs. They also did not provide details on technology approach, power capability, or cycle life, which I haven’t dug into in this email but are crucial for aviation.

On a business level, CATL’s interest in the electric aviation market is a strong signal. Electric aviation has the potential to reduce greenhouse gas emissions, revitalize regional aviation, and benefit front line communities who live or work near airports. For more context on electric aviation, I recommend the Target True Zero report by the World Economic Forum, and McKinsey’s Future Air Mobility blog.

That is far and away the best response I have ever gotten from a manufacturer, and I am grateful to Wes for taking the time to share that information. Hopefully, it will allow our CleanTechnica readers to have a deeper understanding of what lies ahead for battery-powered flight and how companies like Cuberg intend to make electric aircraft a reality.

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Steve Hanley

Steve writes about the interface between technology and sustainability from his home in Florida or anywhere else The Force may lead him. He is proud to be "woke" and doesn't really give a damn why the glass broke. He believes passionately in what Socrates said 3000 years ago: "The secret to change is to focus all of your energy not on fighting the old but on building the new." You can follow him on Substack and LinkedIn but not on Fakebook or any social media platforms controlled by narcissistic yahoos.

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