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Certification and Time-to-Market: The eVTOL Battery Balancing Act umlaut Whitepaper

Content

Urban Air Mobility — an Overview 04

Urban Air Mobility Requirements for Batteries 06

Development 08

Market Trends 14

Design 16

Further Consideration 24 eVTOL Vehicle Companies 26

Future of eVTOL 28

References 30

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Urban Air Mobility — an Overview

Urban Air Mobility is the aerial passenger or cargo Last mile services will typically include delivery Apart from regular transport services, special appli- transport over short- to-medium distances. In of smaller packages currently transported by the cations are also planned. The German ADAC, which addition to numerous companies building smaller delivery companies (FedEx, UPS, etc.) to end cus- is similar to the AAA in the US, has announced plans unmanned air systems, more than one hundred tomers. Both Air Metro as well as Air Taxi services to work with Volocopter, a German eVTOL startup, companies are focused on the development and will transport passengers. Air Metro is doing that to evaluate eVTOLs for their medical transport mis- production of larger eVTOL (electrical vertical take- on a fixed and regular route e.g., from John F. sions currently conducted through a combination of off and landing) vehicles. Kennedy International Airport in New York City to helicopter and ground-based ambulance vehicles.1 lower Manhattan for example -- Air Taxi services There are three main use cases envisioned for the are intended to operate on demand like a taxi or near future: ridesharing operator today, although restricted to • Last mile delivery of goods take-off and landing infrastructure. • Air Metro • Air Taxis

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Urban Air Mobility Requirements for Batteries

The three mentioned use cases have specific de- and aerospace certification. As of today2, no vehicle 3. Different flight phases (vertical take-off, hori- using multiple energy storage systems or battery mands on the energy storage setup, which is a has entered the commercial application phase. zontal flight) require high peak, but comparably cell types each optimized for a specific flight pha- central component for fully electric vehicles, espe- There are three high-level business requirements low average power. Even though peak power is se – which might help to keep weight down but cially with highly weight-sensitive aircrafts. The use driving the development of eVTOL energy storage : not used for most of the flight, this requirement increases system complexity. case in which the specific vehicle will be used has again increases energy storage weight a significant impact on the definition of the energy 1. eVTOL operations benefit from long flight All of these engineering requirements need to be storage system. The biggest differentiators are the times, which in turn necessitates low weight and As typical in engineering, there is no easy answer considered simultaneously along with the critical mission profile, e.g. regarding flight altitude and high energy densities to implement all of these requirements at the same time to market implementations. Due to com- turnaround times, and the ground infrastructure time. Final system design usually is the result of petition, market pressure and the comparatively present at the landing spots. 2. Safety, specifically fire safety, is paramount as careful optimization and is a balancing act. For long certification timelines, an early specification an in-air fire is one of the worst-case scenarios example, the different flight phase requirements freeze needs to be achieved, which hinders the full To win the urban air mobility race, eVTOL companies in commercial aviation; however, additional safety could be fulfilled by increasing the peak power potential of modern battery technology. have to strike a balance between time to market, measures typically increases system weight ability of the primary energy storage system which technological advancements like battery technology increases weight. It might also be implemented by

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Development V-Cycle development Fig. 01 Development Cycle

Concept / Design Production

D e fi n i t i o n / D e t a i led D e s i g n Qualification & Integration Aircraft development in general usually follows validation (two critical steps in which umlaut has the classical V-model, due to the structure of the extensive expertise). Specifications will be adjusted Start of „certification lock-in“ time management process and therefore good basis for iteratively if necessary. This approach would result in certification (see Figure 1). the optimal cell for the application and an optimized Vehicle specifications in alignment energy storage system. However, an optimal system with battery system Development, material, overhead, Total Cost of This starts on the vehicle level with defining business might need to be customized and not be able to be Derived from “mission” and power- Vehicle Vehicle train requirements, e.g. redundant Ownership and regulatory requirements. Business require- purchased “from the shelf” and hence might incur systems, swap vs. fast charging ments could be expressed in terms of a mission higher costs. Additionally, due to the constraints in profile including range, speed, load capacities etc. development time, it might be necessary to stop Specifications for each system Interdependencies and Iterations Iterations Development, material, component to fulfil “mission” e.g. Requirements for the powertrain, energy storage, the optimization cycle at a certain point. System System purchasing, quality, Make or weights, volume, cell configuration, and typically battery systems are derived from buy, Strategic Sourcing cooling system, material restrictions these business requirements. In the next level to cell However, it will be extremely valuable for further specifications and potentially even the electrode vehicle generations to document any optimizations Specifications for Cell(s) e.g. voltage, Cost for process time, Cell/ Cell/ level are created from system-level requirements. that could not be included to provide technological internal resistance, homogeneity and Validation depreciation of machines, raw An eVTOL company could definitely take this de- superiority in the next generation. Even if certifi- other components e.g. BMS, Cooling Component Component material, CAPEX and OPEX, tailed approach as this is one of the most critical cation requirements lead to a design freeze with a System quality costs, development components. suboptimal design, subsequent modifications of the Specifications for Electrode, e.g. certified design are much easier to achieve than Cost for raw material, process Thickness of active material, copper Electrode / Part time, depreciation of machines, Following those thoughts, looking at the right side the initial certification. and aluminum Parts of BMS et al., e.g. waste in cutting, recycling of the V-Model, the next steps are testing and reliability of chips/capacitors etc.

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High-level overview of early stages Fig. 03 Development of certification process Aviation Industry Start of „certification lock-in“

Concept / Design Design Organization D e fi n i t i o n / Detailed Design Qualification & Integration Responsibility

Certification Basis Prep. Finalize Certification Basis Compliance Demonstration

Production Development Timeline Organization Responsibility Prep Production

To satisfy aerospace regulators both the Design However, no higher risk commercial applications like This is how the authorities have operated until be compliant. Traditionally, those have been the Organization and the Production Organization have in-city transport may be offered with aircraft flown recently, which is not necessarily what benefits the CS23, 25 and 27 for (small) aircraft and helicopters, to be certified by the authorities, e.g. the FAA in under those rules. rapid developments made in the eVTOL space. respectively. Through the SC more targeted certi- the USA or EASA for Europe, respectively. Nevertheless, both the authorities and the eV- fication specifications will be gradually introduced. This early involvement of the authorities, the certi- TOL companies are working on changing this, e.g. After the design and the certification basis has Only a certified design organization according fication basis preparation in the conceptual design through the release of the SC (special condition) been finalized, the production organization takes to EASA / FAA Part 21.J may design an aircraft. phase, leads to some aspects of the design being VTOL by the EASA accompanying close and active over and produces what has been designed. There, The need is to begin the certification process in determined equally early on. Those aspects cannot communication between the EASA and European of course, further certification aspects come into communication with the certification body early in be easily changed later, which leads to a certifica- eVTOL startups3. play which will not be detailed here. the design phase; the process is finished along- tion lock-in phenomenon that requires the use of side with the finalization of the design. As always, fully understood systems. These might not be fully During the certification basis preparation, the de- there are exceptions like eVTOL flown under FAA optimized for performance. sign organization has to determine and claim with “experimental” class rules which are more flexible. which certification specifications (CS) they plan to

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Automotive Battery Systems Fig. 04 Market Trends Technology Roadmap Automotive Industry

2018 2019 2020 2021 2022 2023 2024 2025+

NMC-622 NMC-622, NMC-811 NMC 811, NCA, LFP tba Cathode Battery cells Liquide electrolyte Solid e. Electrolyte

Graphite Graphite + silicon Li-metal Anode

System 400V 400V, 800 V Battery Voltage systems Cell-to- Cell-to-module-to-pack Cell-to-pack Integration chassis

As the electrification of automotive vehicles is acce- The automotive market shows clear trends in terms At the same time, an interesting trend arises that energy density of the battery. However, looking at lerating, the aviation industry can and should assess of battery cell and the battery system design. Mid- could support usage in aviation but will surely in- the aviation industry this might necessitate huge the automotive roadmap to see where this market term, we will see changes in the cathode design troduce new challenges. Historically, battery cells engineering efforts to ensure safe containment in is going at scale (see Figure 4). Technologies that towards higher energy materials, a change of the have been packed into battery modules which are case of accidents and to verify that the system are currently being developed for ground usage can electrolyte from liquids to solids, and high-capacity integrated into the vehicle. Modern methods like cell- loads are still within acceptable limits. This might be used in aviation later, after their safety has been anodes using silicon or lithium metal. Also a trend to-pack design directly integrate battery cells into prove especially challenging when the battery cells proven, the technology has been optimized further, towards higher battery system voltages can be the battery pack or even the chassis of the vehicle, are an integral part of the structure. and certification specifications have become clearer. observed in some cases. which optimizes the design space utilization and the

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Global Battery Demand in GWh Fig. 05 Market Trends and EVOL market in 2025 and 2030 Global Battery Demand

GWh 2333

2000

1000 808

229 70 0 2015 2020 2025 2030

Looking at the forecasts for eVTOL vehicle de- automotive industry. The electrification of cars will eMobility Energy Storage Consumer electronics mand, which is said to top 100k vehicles in 2030, not stop and their demand for battery cells is rising the demand for eVTOL-specific batteries will rise fast, leading to an expected manufacturing demand Drivers: • Falling price of li-ion batteries • CO2 fleet emission rights • Governmental incentives dramatically. We see that funding in eVTOL com- of 2,300 gigawatt hours in 20304 (see Figure 5). Sources: EU, World Economic Forum 2019, Interact Analysis panies is still bullish, despite the current economic caution due to the effects of COVID-19. Comparing the eVTOL demand to current batte- EVOL Market 2025 2030 ry capacities shows that it might be sufficient to Demand vehicles 10,000 100,000 The forecasted vehicle demand would lead to an justify a Gigafactory, which focuses on producing Battery size (in kWh) 48 96 estimated battery manufacturing capacity demand batteries for the eVTOL sector only. This presents Demand for batteries in GWh 0.48 9.6 of 10 GWh. This number might sound large, but is an opportunity for battery cell manufacturers. Global Demand 971 2620 still insignificant compared to the demand of the Percentage 0.05% 0.37%

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Designing an eVTOL battery system with Fig. 06 Design morphological box Designing the System with Morphological Box Option 1 Option 2 Option 3 Option 4 System 1 System 2 System 3

Charging Not fast charging, Not fast charging, Battery Swap Fast Charging Battery Swap Fast Charging Model No Swap No Swap

Emergency Redundancy Reserve Redundancy Redundancy Reserve Model

Operation 8-92% 15-85% 35-75% 8-92% 15-85% 35-75% Strategy

Passive Air Active Fluid Passive Fluid Passive Air Active Air Active Fluid Cooling Active Air Cooling Cooling Cooling Cooling Cooling Cooling Cooling

When it comes to designing the battery pack, the operating window of 8-92%, but then might Remanu- Screws Weldings Weldings Weldings Screws there are many different options that depend on require at least 3, if not 9 cell strings. In a second facturing the overall strategy of the operation and mission. version with a lower operating window, the reserve Voltage 800V 400V 300V 400V 400V 800V with 3 strings might be sufficient. Also, the strings Cell 2 strings 3 strings 9 strings 2 strings 3 strings 3 strings A classical morphological box might demonstrate might lead to the choice in cell size, depending on Strings that well and can also be used in the design pro- the overall requirement. Two types of chemistries Cell 1 Chemistry 1 Chemistry 2 Chemistries 1 Chemistry 1 Chemistry 2 Chemistries cess. We will share three different design examples mean at least one string being high-power, the Types* 1 Type 2 Types 2 Types 1 Type 2 Types 2 Types Cathode (Figure 6). others a high-energy cell. The third system might LMO NCA NMC Mixes NCA NMC Mixes Material be the long-term optimal, which would require more Anode C SIC LTO C SIC SIC Clearly, some combinations are not really feasible, customized solutions on the cell, but could be the Material and some choices in one feature or strategy almost technically superior choice to fulfill the overall vehicle Cell Round Pouch Prismatic Round Prismatic Pouch requires important choices in another feature or requirements, being optimized for each phase of the Format strategy. For instance, if in the first example which mission, have the least weight, a quick turnaround Cell Size 16Ah 40Ah 60Ah 16Ah 60Ah 40Ah starts with no fast charging and no swap, the at the landing port –all with meeting critical safety *Energy vs Power choice of redundancy instead of reserve allows requirements.

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Advantages and disadvantages of the Fig. 07 Design different battery cell designs Advantages and Disadvantages of Cell Design

Cylindrical Pouch Prismatic

Cell Rolled-up electrode sheets in Stacked electrode sheets Rolled-up electrode sheets in Level a rigid metal cylinder. laminated in a coated polymer a rigid plastic/metal container + Low manufacturing costs foil + Efficient space utilization The choice of the battery cell format is almost adapted to electric flight. One solution might be + High robustness + High energy density + Easy module assembly religious in some circles, but the key point is that small battery cell manufacturers looking for a niche. - Low packing density + Flexible design - High number of components optimization cannot happen only at the cell level; The cell might come with a high cost at first, but - More complex manu- - Higher material costs facturing it must happen throughout the entire system. considering the costs of change, due to certifica- - Lack of mechanical stability tion and non-optimized packs later, this might tip System + Mostly high redundancies in + Easy cooling ability + Easy modular design In addition to the technical considerations, there the scale toward these solutions. With the rising Level cells strings due to high + High energy density + High mechanical stability is also a strong business aspect to the choice of demand, as seen before, these companies might number - Requires module design to - Complicated cooling the cell format. Cylindrical cells are commonly also be able to scale up and provide a low-cost, + Easy modular design maintain integrity (swelling) required available and large cell manufacturers might not specialty cell in the mid-term when investing in a - Many connections required - High costs of a flexible - Medium costs - Low module energy density design be very interested in small volume special cells large production facility.

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Design Design Modification

A minor modification has a negligible, or no ap- going up to $5M, this could become rather costly, So, the big uncertainty will be how the changes and in the same scope of a new certification, justifying preciable, effect on the mass, balance, structural let alone time-consuming. updates to the battery management software will be the effort, investment and approach. Once the strength, reliability, operational characteristics, or categorized and this might be interpreted differently volume increases, the question becomes: which other characteristics affecting the airworthiness of A risk in being only a small volume customer when by the FAA in the U.S. as by the EASA in Europe or generation the eVTOL company will satisfy it with. the product. By definition, a major modification purchasing battery cells is that the certified cell the CAAC in China. Looking into the history with “Forget about sunk cost” might become a valid absolutely has a significant impact on the airwort- might be sacrificed by the cell manufacturer in the the Dreamliner, we expect high awareness and high strategy. Looking at current aviation OEMs, this hiness of an aeronautical product. mid-term, due to optimization. The big question standards to be applied5. would mean a major shift in operations, thinking, and will be which changes will lead to which category. culture as lifecycles shorten dramatically, especially There are three subcategories defined as “Major,” If eVTOL companies buy basically “off-the-shelf” However, this approach might still be valid for the in the first generations. “Not Significant,” “Significant” and “Substantial” and solutions, and the big cell OEM companies decide to first generation of eVTOL batteries with a small the re-certification effort depends on the category, change the cell design, whether anode, electrolyte, volume. The interesting part will be how soon the from component testing up to a complete recer- cathode, this could have a significant impact on companies will work on the second and even third tification of the vehicle. With battery prototypes eVTOL companies. generation, in which other improvements might be

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Design Battery test and validation Fig. 08 Testing Mechanical Chemical Safety

Random Vibration Chemical Resistance External short circuitprotection Mechanical Shock Salt Spray TemperatureChange Dust Tests Mechanical Vibrationand Shock Endurancewhile operation

Low Temperature UN Test High Temperature Fire resistance

TemperatureCycles Over-discharge protection Over-temperatureprotection Thermal Transport

When automotive electric mobility with Li-Ion Air Mobility is still in its infancy stage, catalogue for Systems” or the SAE AIR6897 “Battery Management Batteries started about 15 years ago, there were no validation is required. Most likely – and hopefully Systems for Rechargeable Lithium Batteries Used clear guidelines as to what needed to be tested. In – these validation tests will be too harsh at first. in Aerospace Standards” which targets Battery 2021 there is much more clarity in the automotive Nobody wants to see an Air Taxi in flames, even if Management Systems. How those standards will industry. We have mechanical, thermal, chemical it lands safely. be applied, if they are supplemented with lessons tests, tests to validate transport readiness and learned from the automotive world and how the overall combined safety tests. This means that cells Standards for the testing of batteries and systems aviation authorities will adapt remains to be seen. carried over from automotive into aviation could in an aerospace context do exist, like the RTCA DO- skip the component validation step, assuming the 311 “Minimum Operational Performance Standards requirements are comparable. However, given Urban for Rechargeable Lithium Batteries and Battery

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Further Technical & Business Considerations

Technical Considerations Business Considerations

Next to the certification, other key challenges are A critical question from a business perspective to how to deal with the needed technical changes in consider: how to ensure to receive high quality a cell, and how the cell development can be alig- cells, especially if cells are bought from a big player. ned with the next generation vehicle or make one Also, it might be of interest to move into long-term generation upgradable, considering the importance strategic partnerships and/or manufacture battery of the certification process. cells in-house. The lifetime of the battery might be There are also some interesting ideas such as using significantly shorter than in automotive applications, the rotor air to cool the battery pack. In addition, the because the daily aircraft usage is higher. This will parallel strings of the battery pack might actually require adapted re-manufacturing and recycling be physically separated for safety reasons, but also concepts, and has to be part of the certification, to implement a quick release swap system or even maintenance and repair requirements and protocols. fast charging with multiple inlets.

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Battery specific comparison of market Fig. 09 eVTOL Vehicle Companies participant categories

Startups Small Aircraft Companies Big OEMs

Certification + Potentially tailored + Tailoring w/ previous + Institutional knowledge approach experience - Often standardized - No previous experience - Limited by existing approach organization

Know-How + Talent appeal, external + Internal knowledge + Internal knowledge Transfer transfer transfer transfer - External knowledge - Low funding for external - Slow to integrate revolu- integration transfer tionary ideas On a very high level, we see three categories of in this new, potentially lucrative market. Hyundai, eVTOL vehicle companies: an automotive company looking to break into this Purchasing + Innovative; automotive + Existing supplier network + Existing supplier network First, there are several start-ups that exclusively work nascent industry through building air taxis, , is funding - Low specific purchasing - Low specific purchasing on the design and production of eVTOL vehicles. somewhere between all of those categories. They - Low purchasing power power power A lot of them are very well-funded and some even claim plans to invest $1.5 billion in the coming years6. have prominent backing, by Google or automotive companies, like Toyota and Daimler. Currently, it is not clear if impossible to say who For example – an OEM might be great at building They might have an easier time with their specific might have the upper hand at conquering this new a turbine or even rotor powered aircraft and lots approach on a greenfield, but might struggle more There are small aircraft companies, like Pipistrel and market. Each company has inherent advantages of that knowledge will be helpful when building an in working with the regulation bodies. Karem, that pivoted or work on an eVTOL vehicle and disadvantages for example when it comes to eVTOL, especially the certification part. However, as an extension of their product line. There are also know-how-transfer. are they able to integrate knowledge from the auto- big OEMs like Embraer, Bell, Airbus, Aurora (a Boeing motive world? Due to their inherent appeal startups company) that are trying to establish themselves might have an advantage when hiring new talent.

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Future of eVTOL

In conclusion, we see that to win this race, a close The demand might be high enough to create a alignment with certification bodies will be key. The Gigawatt Factory that solely produces cells for answer to how modifications in the battery system eVTOLs. Creating strategic partnerships might be will be categorized and need re-certification, will the decisive factor to gain a competitive advan- be critical for the development roadmap. Maybe it tage here. makes even sense to join forces with the competition As with the automotive industry, if the battery is to create standards to suppliers, bundle the voice not treated as the key component and the vehicle towards cell manufacturers and certification bodies is basically designed around it, the solution is likely about change and modifications. not be optimal.

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References Imprint

[1] https://luftrettung.adac.de/volocopter/

[2] February 2021

[3] https://www.easa.europa.eu/document-library/product-certification-consultations/special-conditi- on-vtol

[4] EU, World Economic Forum 2019, Interact Analysis Authors Martin Talke [5] https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems#:~:text=On%20November%20 [email protected] 13%2C%202017%2C%20a,a%20safety%20of%20flight%20issue

[6] https://evtol.com/news/hyundai-envisions-daily-use-air-taxis-by-early-2030s/#:~:text=Last%20 Nicolas Brieger year%2C%20Hyundai%20announced%20plans,years%2C%20forming%20a%20new%20division.&text=Hy- [email protected] undai%2C%20for%20its%20part%2C%20plans,operation%20two%20years%20before%20that

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