Advancing Electrification Beyond Roads: Exploring Use Case Requirements and Design Challenges for Battery Packs in Multi-Modal Transport Applications

Decarbonising only the road transport sector is no longer sufficient to meet our climate action goals. Electrification must extend beyond roads to include rail, water transport, airplanes, and non-road mobile machinery, which collectively contribute 2% of the EU27’s total greenhouse gas emissions. Traditionally, Li-ion battery-based power sources faced technological limitations that hindered their adoption in these sectors, resulting in a slow electrification rate. However, the NEXTBAT project, funded under Horizon Europe Grant Agreement No 101103983, aims to address these challenges by advancing battery pack performance and safety characteristics.

The objectives of NEXTBAT include achieving a battery pack-to-cell energy density ratio above 80%, increasing power density by >= 30% at C-rates up to 8C, and enhancing battery lifetime by 20% at a State of Health (SoH) of 80%. These advancements will make Li-ion battery-based energy/power sources more appealing for a broad range of mobile applications. Key innovations include a smart combination of thermal management solution, based on immersion cooling technology, lightweight and environmentally friendly materials, packaging design optimization, and advanced cell-level Battery Management Systems (BMS) with innovative actuation and sensing systems.

Furthermore, these innovations are projected to improve system safety ratings significantly by reducing thermal runaway onset time by 6 hours. The project also aims to contribute to the development of a new framework for standardizing next-generation battery system production chains in the European Union.

The methodology employed by NEXTBAT follows the standard V-cycle as described in ISO-26262 (Road Vehicles – Functional Safety). Figure 1 summarizes the design cycle following a safety-based design methodology. While the left flow develops the system based on operational and safety specifications and principles, the right flow validates each stage of the development at the appropriate level considering thermal and mechanical design, hardware design and software design.

NEXTBAT investigates 10 different use cases from road, non-road mobile machinery, waterborne, airborne, and rail applications in collaboration with industry representatives. These use cases inform the development of application-specific battery system designs, considering factors such as required pack capacity, energy density, charge/discharge rates, cycle/calendar life, operating temperatures, safety requirements, and standards. Please note suitable technology for the battery pack depends highly on the use case characteristics.

Challenges in application-specific battery system design arise from multi-physical domains (mechanical, electrical, and thermal). For instance, energy capacity requirements range from a few kilowatt-hours for light waterborne applications to 600-700 kWh for long-haul trucks and construction machinery. Additionally, the expected calendar life varies from 1-2 years for regional aircraft to up to 15 years for passenger cars, long-haul trucks, forklifts, construction machinery, and passenger trains. Further, cell-to-chassis architecture that offers definite advantages in terms of energy density would be difficult to implement in applications other than passenger cars due to high load sharing requirement even though high energy density is desirable in all applications.

This presentation will discuss some of the conflicting design requirements, necessary tradeoffs, and typical approaches to overcome performance and safety-related issues faced by next-generation, fit-to-purpose battery systems, including BMS for different end-user cases. This work aims to establish use case requirements for next-generation power sources and consolidate technical specifications of anticipated technologies within the short to medium term. Ultimately, it will pave the roadmap to a next generation of battery systems based on safe-by-design architectures applicable to various transport and mobile applications, critical for meeting climate action goals.