Researchers at the Dalian Institute of Chemical Physics (DICP) in China have made significant progress in the development of the Organic Flow Battery (OAAB): the new device retains 99.95% of its capacity after 850 charging cycles. This breakthrough was achieved with naphthalene-based organic redox-active molecules (ORAMs), marking a major milestone in battery technology.

What are flow batteries?

Flow batteries, similar to traditional electrochemical cells, generate electricity by utilizing electroactive components dissolved in liquids, which are stored on two sides of a membrane. The structure consists of two electrolyte solutions—one for the positive side (catholyte) and one for the negative side (anolyte)—flowing through electrochemical cells where chemical reactions occur to produce and store electricity. These systems are particularly valued for their scalability and cost-effectiveness, as the energy capacity is determined by the amount of electrolyte solution used, while the power capacity depends on the size of the cell stack.

Advantages and challenges

The advantages of flow batteries include their scalability, long operational life, and the ability to easily replace and replenish the electrolytes. Compared to traditional lithium-ion batteries, flow batteries do not degrade as quickly, making them ideal for large-scale energy storage applications, such as renewable energy integration, grid stabilization, and backup power systems. However, traditional flow batteries often rely on rare metals, such as vanadium, which not only increase the cost but also raise concerns about resource availability and environmental impact.

One of the main challenges in flow battery development is the need to balance high energy density with stable, long-term performance. Organic materials, which are abundant and easier to synthesize compared to metal-based counterparts, have gained attention as a potential solution to these challenges. However, developing organic flow batteries that maintain their capacity and stability over many cycles remains a significant hurdle.

Organic flow batteries: aqueous vs. non-aqueous

Organic flow batteries can be broadly categorized based on the type of solvent used in the electrolyte: aqueous (VOAAB) and non-aqueous (NVOAAB). Each type has distinct characteristics that influence performance, cost, and application potential.

Aqueous organic flow batteries (VOAAB)

Aqueous organic flow batteries (VOAAB) use water-based electrolytes, making them generally safer, cheaper, and easier to scale up. However, these batteries face significant challenges with the stability of organic redox-active molecules (ORAMs). In VOAABs, ORAMs are prone to degradation due to side reactions with water and oxygen, leading to irreversible capacity loss and increased maintenance costs. This degradation typically results from molecular side reactions, where ORAMs undergo decomposition or change structure, reducing their ability to efficiently store and release energy.

Non-aqueous organic flow batteries (NVOAAB)

Non-aqueous organic flow batteries (NVOAAB) use organic solvents, which can provide a broader electrochemical window, allowing for higher voltage operations and improved energy density compared to aqueous systems. However, the use of organic solvents also introduces higher costs and complexity due to the need for careful handling of volatile and potentially toxic chemicals. Despite these challenges, NVOAABs have become a key focus in advancing high-performance flow battery technologies, particularly for applications requiring longer operational lifetimes and greater energy densities.

The breakthrough with naphthalene-based ORAMs

A research team led by Professors Zhang Changkun and Li Xianfeng at DICP has developed naphthalene-based derivatives that significantly improve the atmospheric stability of ORAMs. By combining chemical and in situ electrochemical synthesis methods, the team created naphthalene derivatives that are easier to purify and more stable under operational conditions.

The process involved introducing hydrophobic alkylamine groups into the naphthalene derivatives, which enhanced the molecules’ resistance to degradation. This modification not only stabilized the ORAMs against environmental factors such as moisture and oxygen but also reduced the solubility of active components in the electrolyte, thereby minimizing side reactions.

Testing and results

During testing, the newly developed naphthalene-based flow battery demonstrated remarkable stability and efficiency. With an electrolyte concentration of 1.5 mol/L, the battery maintained 99.95% of its capacity over 850 cycles—a significant improvement over existing organic flow batteries. This performance metric highlights the potential of naphthalene derivatives to revolutionize the field of organic energy storage.

According to Professor Li, “this study may open up new possibilities in the design of atmospheric-stable molecules that can provide sustainable and stable electrochemical energy storage.” The results suggest that naphthalene derivatives could be pivotal in the future design of flow batteries, addressing key issues related to capacity retention and operational longevity.

Implications and future prospects

The development of highly stable naphthalene-based ORAMs presents exciting opportunities for the energy storage industry. As renewable energy sources like wind and solar become more prevalent, the need for efficient, scalable, and durable energy storage solutions is growing. Flow batteries, particularly those based on organic materials, offer a promising pathway to meet this demand.

Potential applications

1. Grid Energy Storage: Flow batteries can provide critical load balancing and energy storage solutions for electrical grids, helping to smooth out the intermittent nature of renewable energy sources.

2. Remote and Off-Grid Power Systems: With their long cycle life and scalability, flow batteries are well-suited for remote and off-grid applications, such as powering islands, mining operations, and remote research stations.

3. Electric Vehicle Charging Infrastructure: The use of flow batteries in EV charging stations could offer rapid, scalable energy storage options that reduce strain on the grid and enable faster charging times.

Despite these promising advances, there are still challenges to be addressed. Scaling up the production of naphthalene-based ORAMs, ensuring cost-effective manufacturing processes, and further enhancing the efficiency of flow batteries will be crucial. Research will also need to focus on improving the compatibility of ORAMs with a broader range of electrolytes to enhance performance across different environmental conditions.

Source: nature.com

The Role of Battery Technology in Electric Flight

Background and Significance

Battery technology is a crucial factor in the advancement of electric flight, as it directly affects the performance, range, and feasibility of electric aircraft. Batteries serve as the primary energy storage system, determining the aircraft’s power-to-weight ratio, which is critical for efficient and sustained flight. Historically, the limited energy density of batteries has been a major barrier to the widespread adoption of electric aircraft, constraining their range, payload, and overall usability compared to conventional fossil fuel-powered planes.

Energy Density and Its Impact on Aircraft Performance

Energy density, measured in watt-hours per kilogram (Wh/kg), is the amount of energy stored per unit of battery mass. High energy density is essential for electric flight, as it directly impacts how long an aircraft can stay airborne and the distance it can cover. For electric aviation to be viable, batteries must achieve energy densities significantly higher than those used in electric cars or stationary storage applications.

Current state-of-the-art lithium-ion batteries typically offer energy densities of around 250-300 Wh/kg, which, while suitable for ground vehicles, falls short of the 500-600 Wh/kg needed for most commercial electric aircraft.

Examples of Battery Development Milestones:

• Lithium-sulfur and solid-state batteries have emerged as promising technologies due to their potential for higher energy densities and improved safety profiles compared to traditional lithium-ion cells.
• Companies like QuantumScape and Solid Power are at the forefront of developing these next-generation batteries, aiming to bring prototypes to the aviation market within the next decade.

Battery Weight and Its Implications

The Weight Dilemma

One of the most critical challenges in electric flight is the weight of batteries. Unlike conventional jet fuel, which gradually decreases in mass as it is burned, batteries retain their full weight throughout the flight. This presents a significant issue for aircraft design, as the power-to-weight ratio directly influences takeoff, climb, and cruise performance. The heavy weight of batteries limits payload capacity, reduces range, and can adversely affect the aircraft’s structural design and safety parameters.

Impact on eVTOL and Small Electric Aircraft:

• eVTOL aircraft, such as those being developed by Joby Aviation and Archer Aviation, rely on highly optimized battery systems to achieve vertical takeoff and landing, which demands a precise balance of power, weight, and energy density.
• Small electric planes like the Pipistrel Alpha Electro are designed with lightweight materials and minimalistic features to compensate for the heavy battery packs, which are often the heaviest component of the aircraft.

Charging Infrastructure and Operational Challenges

Charging Speed and Availability

The development of efficient charging infrastructure is another crucial factor that influences the practicality of electric flight. Rapid charging capabilities are necessary to minimize downtime between flights, but high-power charging systems must also be designed to handle the increased electrical demands safely. Airports and urban vertiports will need to be equipped with specialized charging stations to accommodate the unique needs of electric aircraft.

Current Developments:

• Companies like ChargePoint and ABB are working on high-capacity charging systems specifically tailored for electric aviation, designed to reduce charging times and increase operational efficiency.
• The development of wireless or inductive charging systems, while still in early stages, could provide a more seamless and rapid turnaround for electric aircraft, further enhancing their commercial viability.

Grid Impact and Sustainability

The impact of large-scale electric aviation on the electrical grid is a growing concern. Charging multiple aircraft simultaneously requires substantial power, and without proper planning, this could strain local grids, especially in areas where renewable energy integration is still limited. Efficient energy management systems and renewable energy sources must be integrated into charging infrastructure to ensure the sustainability of electric aviation.

Safety Considerations

Thermal Management and Fire Risks

Batteries, especially those used in aviation, pose specific safety challenges, such as thermal runaway, which can lead to fires or explosions if not properly managed. Thermal management systems are essential to maintain optimal battery temperatures and prevent overheating during charging and discharging cycles.

Safety Measures in Development:

• Advanced cooling systems, such as liquid cooling and phase-change materials, are being integrated into battery packs to mitigate overheating risks.
• Research into solid-state batteries, which are inherently less prone to thermal runaway, could provide a safer alternative to traditional lithium-ion technologies in electric flight.

Market Readiness and Future Prospects

Market Adoption and Commercial Viability

The market for electric flight is rapidly expanding, with companies and governments investing heavily in the development of electric aircraft for urban air mobility, regional transport, and cargo applications. However, achieving widespread market adoption depends on continued advancements in battery technology to meet the stringent demands of aviation.

Examples of Market Leaders:

• Lilium, Vertical Aerospace, and Beta Technologies are among the leading companies developing electric aircraft, each leveraging the latest battery technologies to push the boundaries of flight capabilities.
• The FAA and EASA are working on regulatory frameworks to certify electric aircraft, which will be crucial for commercial deployment.

Future Outlook

The future of electric flight hinges on continued innovations in battery technology, specifically achieving higher energy densities, reducing battery weights, and enhancing safety and charging capabilities. With sustained research and investment, electric flight could revolutionize the aviation industry, offering a cleaner, quieter, and more efficient alternative to traditional air travel.

Sources:

Dalian Institute of Chemical Physics | Flow battery | Vanadium | Lithium–sulfur battery | Solid-state battery | QuantumScape | Solid Power | Joby Aviation | Archer Aviation | Pipistrel Alpha Electro | ChargePoint | ABB Group | Lilium GmbH | Vertical Aerospace | Beta Technologies | Federal Aviation Administration | European Union Aviation Safety Agency