Lilium's Battery Strategy: Performance at Scale
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At Lilium, we’re on a mission to create radically better ways of moving. With our unique zero operating emissions eVTOL jet technology, we plan to transform high-speed regional air mobility.
Core to the success of that revolution is the “e” in eVTOL – electric. And the foundation of technical and commercial success for any electric vehicle is inevitably the batteries that hold the energy to power them. While we’ve seen massive progress made in cell performance and industrialization over the last 15 years in everything from electric cars to consumer electronics, designing cells for the unique needs of the aviation industry has probably not been a priority.
Until now.
Lilium has been hard at work developing a high-performance aviation battery system for our jets centered on the two key drivers necessary to achieve our mission: performance and scale, while working towards anticipated certification requirements. Now that Lilium has progressed in filing patents to protect IP and independent 3rd party testing of its target cell technology has been completed, we can share more about our plans in this domain.
Based on this simple approach, we have now:
(i) identified and licensed unique cell technology available exclusively to Lilium in commercial regional eVTOL applications that we believe will meet our specific performance requirements and achieve over 250km of physical range; and
(ii) a manufacturing strategy and partner with the competence to build our cells on a scale that we believe will allow us to achieve our commercial and sustainability goals.
Let's take a closer look.
Performance: power and energy for the mission
Our team scouted more than 100 companies along the entire battery value chain from raw material suppliers through to cell developers, manufacturers, and recycling companies. More than 20 battery cells were shortlisted and analyzed considering the predicted mission profiles before selection of a specific cell technology.
Based on that research, we concluded that Zenlabs’ pouch cells, lithium-ion batteries using high-silicon anode and high-nickel cathode, offered the best solution for achieving our needs through performance, certification, and into scale production. Our engineers have been collaborating with the Zenlabs team for more than 2 years in order to develop and refine an optimal cell technology for the Lilium Jet.
From a battery performance perspective, the central challenge for achieving our mission is to find a battery cell that will:
(i) deliver a high average specific power for a short, 10 second vertical take-off; and
(ii) deliver high specific energy, combined with our low cruise power*, to maximize mission range; and
(iii) deliver a high average specific power again for the landing phase, which is typically shorter than 45 seconds duration**
*Cruise power is projected to be approx. 1/10th of hover power, depending on payload and operational scenario.
**The Lilium Jet is designed to spend minimal time in power-intensive low speed flight and, unlike conventional helicopters, is not intended to spend prolonged time in hover. Consequently, the stated “landing phase” is short in duration and only encountered in the very final phases of flight, when decelerating to a hover and descending to the vertiport.
Typically, lithium-ion cells have been able to achieve either high specific power or high specific energy, but not both. Figure 1 compares a commercially available state-of-the-art high power cell (black), a commercially available state-of-the-art high energy cell (red), and the Zenlabs cell (green).
You can see that the advantage of the Zenlabs cell is its combination of both superior specific energy and specific power capabilities. With this comparison, the Zenlabs cell surpasses both the specific power capability of the high power cell and the specific energy capability of the high energy cell.
Zenlabs recently released test data from Energy Assurance, a third-party testing laboratory, which demonstrates that the Zenlabs cell can maintain high specific power of 2500 W/kg even at a low State of Charge (SOC). The report from Energy Assurance can be found here. Figure 2 below shows the power supported at various SOC at the beginning (blue, Zenlabs data) and at the end (amber, Lilium data, calculated) of a 12C-rate, 30 second pulse, at 30°C.
It is critical to note that, based on the test results from Energy Assurance, the cell is able to support the stated power during the entire discharge at each tested SOC. The cell is able to support high specific power even down to 20% SOC.
Lilium, who became a major investor in Zenlabs in 2021, has the exclusive rights to use Zenlabs’ cells in commercial regional eVTOL applications.
Translating this to the aircraft, we expect these cells deliver the following performance for the Lilium Jet:
(i) The required power for takeoff (hover), cruise and landing;
(ii) A projected Physical Range of over 250km, assuming short duration vertical take-off and landing, at Operational Empty Weight (OEW); and
(iii) A projected Operational Range of ~175km assuming a vertical takeoff at Maximum Take-Off Weight (MTOW) and vertical landing (45 seconds duration†) such that 20% state of charge remains following the landing.
At any point prior to starting the vertical landing sufficient energy reserves, consistent with anticipated aircraft operational regulations, remain for the aircraft to divert to an alternate landing site and perform a short running landing if needed for any reason††. The much lower power demand of this running landing allows more cell energy to be accessed than would otherwise be possible with the higher power vertical landing
†Piloted simulation tests have demonstrated typical vertical landings to be of significantly shorter duration. Furthermore, the aircraft is designed to accommodate longer vertical landing times.
††We intend that the Lilium Jet will be capable of performing a short running landing, as well as a vertical landing.
Figure 3 Projected Physical Range including cell state of charge after each phase of flight. Figure 4 Projected flight profile for a standard operation including cell state of charge after each phase of flight. Power figures correspond to those expected at typical operational speed and altitude.
Importantly, these projected range figures and mission profiles are consistent with anticipated routes, corresponding ground infrastructure, and customer expectations for commercial launch.
The Zenlabs cell technology has other important anticipated advantages for integration and industrialization:
(i) the slim lithium-ion pouch design provides for optimal (space efficient) integration into battery modules in the sides of the aircraft, which is important to meet aviation crash safety requirements and certification;
(ii) the cell can be manufactured with adapted standard lithium pouch cell manufacturing equipment and know-how which we expect will enable us to achieve quality at a competitive price; and
(iii) the silicon-anode technology allows for fast charging, supporting faster flight turnaround time.
It is important to note that development on this Zenlabs cell technology is ongoing – and that we will likely use a further evolution of this cell technology in our production aircraft in order further improve operational performance while meeting anticipated certification requirements.
Scalability: On Quality, On Cost; Right first time, Right every time
We’ll never be able to achieve our mission and effectively contribute to the decarbonization of air mobility if our batteries cannot be built in very large quantities, with aerospace levels of quality, and at a sustainable price.
That’s why we’ve engaged with CUSTOMCELLS as one of our key partners to manufacture our battery cells using Zenlabs’ technology under license.
CUSTOMCELLS is one of the world's leading companies in the production of highly specialized lithium-ion battery cells for tightly regulated industries. They have already shown their ability to build highly reliable batteries at scale with all sorts of unique capability sets for several battery-powered applications from sports cars to the maritime industry and even medical devices.
Manufacturing in CUSTOMCELLS factory, Germany.
For the past 18 months, the Lilium team has been working hand in hand with CUSTOMCELLS and our other industrial partners, establishing and testing processes, aligning Quality Management Systems to aerospace standards, monitoring implementation of series-production equipment, and preparing the industrial ramp-up. Initial production of our cells was started in February 2022, and we have prepared and are now working with CUSTOMCELLS to finalize the industrialization of the production processes following our detailed qualification and audit roadmap for the cell that will power our series production aircraft. We hope to share more news to come on this topic in the future.
From a certification and safety perspective, our cells and the battery modules into which they will be integrated, are being manufactured to meet both EASA and FAA anticipated safety regulations – to ensure both system redundancy as well as thermal runaway containment. On this last point, we have received detailed guidance from both regulators, which is the basis for our specific test campaigns.
Getting to scale requires more than manufacturing capability, it also is going to require scarce raw materials, such as lithium, nickel, manganese, and cobalt. Due to increasing demand for electric applications, especially in the mobility sector, these raw materials are becoming increasingly sought after. Ensuring our supply of key raw materials is therefore one of the key challenges facing the eVTOL industry.
As of today, we have contractual arrangements with our battery cell suppliers to provide sufficient quantities for us to deliver the first conforming aircraft and our initial production ramp up. We are currently looking to secure supplies further down the value chain. Over the past year, we have been engaged in very constructive discussions with major suppliers at various levels in the supply chain.
Most recently, Lilium and Livent – a pioneer in lithium technology innovation and production – have agreed to collaborate on the advancement of lithium metal technology for use in high-performance battery cells. This is an important step towards securing Lilium’s future access to the high-performance battery cell technology that will power Lilium’s jets.
But we also won’t cut corners on our own values. Our goal is to avoid all use of raw materials from sources linked to armed conflict, human rights abuses, or child labor. As part of our sourcing strategy, Lilium requires that suppliers adopt a responsible minerals sourcing policy and that they respond to corporate social responsibility surveys to assess compliance down the supply chain.
In terms of recycling strategy, we are seeking through our partners second-life applications for used batteries as well as raw material recycling from our batteries (I.e. extraction back into original compounds) in order to be able to repurpose the majority of the materials we use in our batteries.
Looking further into the future, Lilium is also researching the potential for batteries that can be built without certain rare materials.
Delivering on our strategy
As we said from the start, our priority has always been delivering a capable eVTOL jet that can open up truly sustainable regional air mobility. We have focused on the development of a novel, world-class battery system with the performance and scalability required for aviation – we believe this battery will allow us to move confidently towards certification and commercialization.
Based on the capabilities of Zenlabs’ high-silicon anode and high-nickel cathode Lithium-Ion pouch cells produced by CUSTOMCELLS performing as expected, our Lilium Jet would have an estimated ~250km of physical range.
Importantly, our energy system and the supply chain behind it (including CUSTOMCELLS) have been designed to meet the rigorous safety and certification standards that we expect regulators to adopt.
But this is only the start.
While we believe we have identified our initial solution, we will not be resting on our laurels. We will continue to push the performance envelope with Zenlabs and likewise to engage both with technology and production suppliers on the next generation of battery cells that will provide the targeted performance levels and scalability needed for our program.
We are also excited by the potential strategic synergies between sustainability and supply assurance.
The battery is hugely important to our mission. The long-term success of the air mobility revolution depends on it. So we are always actively monitoring technological developments and can incorporate new battery technologies into the aircraft system in the future subject to a rigorous safety and certification process. We hope to be able to share more exciting news of our progress in the months to come.
Update March 28, 2023:
As announced in our FY-2022 Shareholder Letter, third-party independent laboratory testing confirmed 88% energy retention – well above our already impressive 80% target – in the full-size prototype cells after 800 charging cycles with 100% depth of discharge (1C/1C cycles). The 1C/1C is a strenuous industry standard test involving full discharge of the cell. Full discharge causes faster aging than to be expected in regular use. Lilium expects the number of charging cycles in regular use to be significantly higher than that achieved in the industry standard 1C/1C test.
About Lilium
Lilium (NASDAQ: LILM) is creating a sustainable and accessible mode of high-speed, regional transportation for people and goods. Using the Lilium Jet, an all-electric vertical take-off and landing jet, offering leading capacity, low noise, and high performance with zero operating emissions, Lilium is accelerating the decarbonization of air travel. Working with aerospace, technology, and infrastructure leaders, and with planned launch networks announced in Germany, the United States, Brazil, and the UK, Lilium’s 800+ strong team includes approximately 450 aerospace engineers and a leadership team responsible for delivering some of the most successful aircraft in aviation history. Founded in 2015, Lilium’s headquarters and manufacturing facilities are in Munich, Germany, with teams based across Europe and the U.S. To learn more, visit www.lilium.com.
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