68 enhances volumetric efficiency and reduces weight. LFP cells are particularly conducive to C-t-P designs due to their inherent stability and tolerance for larger cell sizes, while high energy-density NMC cells are constrained by safety considerations. Intermediate-sized, cylindrical cells such as those made in the 46XX format are making strides in C-t-P applications. Such designs enhance sustainability by reducing material usage and simplifying recycling processes. For example, integrating batteries directly into the chassis of vehicles, known as ‘cell-tochassis’, represents the next frontier in modularity – reducing the number of components and streamlining the assembly process by focusing on direct electronic and thermal connections between the cells and the vehicle. However, while C-t-P and possibly cellto-chassis architectures can work well in the automotive sector because cars can be designed around the battery pack, this is impractical in other sectors such as ships, boats, agricultural machinery and off-highway vehicles. The latter two, in particular, have been developed over the last century to work as well as possible and there is little or no scope to redesign them around a battery, leading to them being fitted with modular, multi-pack systems (although these packs may use C-t-P architectures). Another consideration is service life. Unlike cars, which may be built for service lives as short as seven to 10 years, marine, agricultural and off-highway vehicles may work for 30-50 years, so the serviceability and repairability that come with modular architecture are even more important. Cell chemistry Cell chemistry affects module design in terms of energy density, safety and thermal management. High energydensity NMC cells require robust systems to control thermal propagation, whereas LFP cells offer design simplicity and higher safety margins. Silicon-based cells, despite their high energy potential, face challenges with volumetric expansion, necessitating structural adjustments within modules to accommodate swelling forces. Cell-form factors are closely tied to chemistry, influencing design choices. For high-power applications, cylindrical cells often outperform prismatic formats due to their mechanical resilience and better cooling efficiency. Modular architectures of standardised design, which incorporate features such as adjustable cooling channels or flexible cellexpansion spaces that can be tweaked before production, can be optimised for specific chemistries and applications. While integrating such flexibility upfront requires more work, in the long term it saves time and money while reducing risk. Safety remains a critical consideration, guiding design decisions at every level. Modules must be engineered to prevent thermal runaway and ensure safe operation, even in the event of cell failure. For example, designs that isolate failing cells and prevent propagation across the module can allow vehicles to remain operational and be transported safely for service. Thermal propagation safety is critical, and advances in materials and layouts enable systems to withstand extreme conditions without resorting to controlled burn scenarios. Smaller cells with enhanced cooling capabilities, such as the 21700 cylindrical format, offer a practical balance between safety and energy density. Advanced BMS integration Battery management systems (BMS) are undergoing a significant evolution, particularly in modular designs. Wireless BMS technologies are emerging as a key innovation, offering remote monitoring capabilities and reducing the complexity of wiring within modules. These systems provide real-time data on cell health, temperature and state of charge, improving overall reliability and enabling predictive maintenance. Modules increasingly include basic cell-monitoring units (CMUs) for internal measurements such as voltage and temperature. This modular, selfmonitoring capability supports secondlife applications and preventative maintenance by retaining operational histories and health metrics. However, higher-level functions, such as state-ofcharge calculation and pack protection, are typically managed at the pack level for reasons of cost and efficiency. Product focus | Modular batteries January/February 2025 | E-Mobility Engineering Ionetic’s configurator software adjusts standardised module design in minutes, removing features that are unnecessary, given the specific vehicle for which it is customised (Image courtesy of Ionetic)
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