The dream of sustainable aviation, quiet, emission-free flights connecting cities, hinges on one critical technology: advanced batteries. Lilium, a German pioneer in electric vertical takeoff and landing (eVTOL) aircraft, built its vision around cutting-edge battery systems that powered the Lilium Jet, an innovative aircraft designed for regional air mobility.
By leveraging lithium-ion batteries with silicon-dominant anodes, Lilium aimed to deliver the high energy density, power, and safety needed for practical electric flight. Despite the company’s insolvency in early 2025, its battery innovations left a lasting impact, setting benchmarks for sustainable aviation and influencing ongoing eVTOL developments. This article examines how Lilium’s battery technology has driven the push for greener skies, the engineering behind it, and its enduring legacy in the face of challenges.
The Importance of Batteries in Sustainable Aviation
Batteries are the heartbeat of eVTOL aircraft, providing the energy for vertical takeoffs, transitions, and cruising without the carbon footprint of traditional jet fuel. Unlike electric cars, eVTOLs require batteries that deliver intense bursts of power for lift, often equivalent to hundreds of horsepower, while sustaining efficiency over ranges of 150-250 kilometers. Lilium’s Jet, designed to carry six passengers and a pilot at speeds up to 280 km/h (175 mph), demanded batteries that balanced energy density, weight, and thermal stability.
Sustainability in aviation goes beyond zero tailpipe emissions. It encompasses lower lifecycle emissions through efficient manufacturing, the use of recyclable materials, and reduced noise pollution, facilitating urban integration. Lilium’s battery systems were engineered with these goals in mind, utilizing modular designs for redundancy and safety, and aiming to align with global targets, such as the EU’s Green Deal, which seeks to achieve net-zero aviation by 2050. By replacing kerosene-powered helicopters with electric jets, Lilium promises to significantly reduce CO2 emissions while enabling quieter operations suitable for city vertiports.
Silicon Anode Breakthroughs: Powering the Lilium Jet
Why Silicon?
Traditional lithium-ion batteries with graphite anodes, commonly used in electric vehicles, fall short for aviation due to their limited energy density (250-300 Wh/kg). Lilium turned to silicon-dominant anodes, which can theoretically store ten times more lithium ions, pushing energy densities toward 400-500 Wh/kg. This leap was critical for the Jet’s 155-mile range and high-power VTOL needs.
In 2021, Lilium partnered with Customcells, a German battery specialist, to scale production of these cells, incorporating technology from Ionblox for stability and performance. Silicon anodes excel in delivering rapid discharge rates, which are essential for the Jet’s 30 Ducted Electric Vectored Thrust (DEVT) motors, as they require intense power during hover and transition phases.
Overcoming Silicon’s Challenges
Silicon anodes pose a significant challenge: they expand by up to 300% during charging, which can lead to cell degradation. Lilium and Customcells addressed this through nanostructured silicon designs and advanced electrolyte additives, stabilizing the anode for thousands of charge cycles. These cells were produced at Customcells’ Tübingen facility, with thousands manufactured annually to meet aviation-grade quality standards.
Each Lilium Jet carried ten battery packs, housing roughly 2,000 cells total. These packs, encased in lightweight composite housings, powered the aircraft’s high-voltage harnesses, ensuring efficient energy distribution to the DEVT fans. The result was a system capable of supporting 20-30 minute fast charging at vertiports, which is crucial for high-frequency air taxi operations.
Integration and Energy Management
Modular Design and Redundancy
Lilium’s battery system was designed for reliability. The ten independent packs provided redundancy—if one failed, others compensated, ensuring safe flight. High-voltage harnesses acted as the aircraft’s “arteries,” delivering power with minimal losses. This modularity also simplified maintenance and upgrades, aligning with Lilium’s scalable vision for larger models, like a potential 16-seater.
Smart Energy Systems
Energy management was optimized through the use of intelligent systems. The Jet’s fly-by-wire controls, integrated with AI, dynamically adjusted power draw to prioritize thrust during high-demand phases like VTOL. Regenerative systems captured energy during descent, similar to electric vehicle braking, boosting range by 10-15%. Liquid cooling loops maintained battery temperatures between 20 °C and 40°C, preventing overheating and extending cell life.
Manufacturing for Sustainability
Lilium’s batteries weren’t just about performance; they were designed with sustainability in mind. Custom cells employed dry-coating processes to reduce solvent use, thereby lowering production emissions. Silicon, abundant compared to scarce materials like cobalt, eased ethical supply chain concerns. The packs were also built for recyclability, supporting a circular economy approach.
Sustainability Impacts
Emissions Reduction
Lilium’s electric propulsion eliminated direct CO2 emissions, with a single Jet flight saving 100-200 kg of kerosene equivalent per trip. Scaled to fleets, this could help decarbonize short-haul aviation, a sector that contributes 2-3% of global emissions. By reducing reliance on ground transport for regional routes, the Jet also cut indirect emissions from road congestion.
Noise Mitigation
The battery-powered DEVT system, paired with ducted fans, produced noise levels as low as 60 decibels—far quieter than helicopters. This enabled vertiports near urban centers, minimizing community disruption and supporting the widespread adoption of eVTOLs.
Broader Benefits
Lilium’s push for sustainable batteries created jobs in green technology and bolstered energy independence through domestic production. Their work influenced EU policies, accelerating investment in advanced materials for the aviation industry. The technology’s efficiency—over 90% compared to 30-40% for traditional jets—minimized energy waste, enhancing economic viability with lower operating costs than helicopters.
Engineering Feats and Validation
By 2024, Lilium had begun producing battery packs, with ground tests, such as systems’ power-on, confirming safe integration. Flight tests conducted prior to insolvency demonstrated the Jet’s capabilities, achieving speeds of 155 mph and validating the battery system’s performance under real-world conditions. These milestones demonstrated the potential for electric jets to rival traditional aircraft in terms of reliability and efficiency.
The batteries were designed to meet aviation’s stringent safety standards, pursuing dual certification from the European Union Aviation Safety Agency (EASA) and the U.S. Federal Aviation Administration (FAA). Redundant systems, reinforced pack housings, and ballistic parachutes ensured passenger safety, while low noise and emissions aided regulatory approval.
Challenges: From Promise to Insolvency
Technical Hurdles
Silicon anodes, while promising, required significant R&D to manage expansion and ensure cycle life. Lilium’s heavy investment in partnerships with Customcells and Inobat strained its finances, as did the complexity of aviation-grade certification. Supply chain bottlenecks and the need for consistent cell quality added further pressure.
Financial Struggles
Lilium faced mounting challenges by 2024, with funding shortfalls leading to insolvency filings for its German subsidiaries in October 2024, followed by a complete collapse by February 2025. Customcells, a key supplier, also entered insolvency in May 2025, partly due to unpaid Lilium invoices, underscoring the risks of interdependence in emerging industries. Critics argued that Lilium’s ambitious timelines and short 155-mile range misaligned with market needs, thereby limiting its commercial appeal.
Market Context
The eVTOL sector is capital-intensive, with competitors like Joby Aviation and Archer also racing to market. Lilium’s focus on regional routes, rather than short urban hops, required higher energy demands, straining the limits of battery technology. Despite orders from partners like NetJets and Azul, financial instability halted progress.
Legacy and Future Prospects
Lasting Impact
Lilium’s battery innovations remain influential. The silicon anode technology spurred a surge in related patents in Q2 2025, signaling industry adoption. Companies like Vaeridion acquired Lilium’s Oberpfaffenhofen battery facility, preserving its advancements. Interest from groups like AAMG in Lilium’s intellectual property suggests potential revival.
Future Directions
The path Lilium paved points to next-gen batteries. Solid-state cells, promising 700 Wh/kg, could build on silicon anode foundations. Partnerships like Honda’s with Customcells reflect ongoing momentum. Hybrid systems combining batteries with hydrogen fuel cells may also emerge, potentially extending the ranges of larger eVTOLs.
Industry Influence
Lilium’s work demonstrated that sustainable flight is achievable, pushing competitors to prioritize energy density and lifecycle sustainability. Its focus on quiet, efficient propulsion set a standard for urban air mobility, influencing vertiport designs and regulatory frameworks. As the industry evolves, Lilium’s battery legacy will likely shape the next decade of electric aviation.
Conclusion
Lilium’s battery technology, centered on silicon-dominant anodes and intelligent energy management, was a cornerstone of its mission to revolutionize sustainable flight. By powering the Lilium Jet with high-density, safe, and recyclable batteries, the company showcased a future where electric jets could replace polluting helicopters and shrink regional travel times. Despite its insolvency in 2025, Lilium’s innovations in energy density, thermal management, and sustainable manufacturing left an indelible mark on the development of eVTOLs. As the industry builds on these foundations, Lilium’s vision of greener, quieter skies continues to inspire, proving that batteries can indeed power the future of aviation.
