EV Battery Safety: Optimal battery pack design considerations

Crafting an optimal battery pack design for electric vehicles (EVs) is a multifaceted endeavour that demands meticulous attention to detail, particularly concerning safety standards like the AIS 156 standard upheld by governments worldwide.  

These standards serve as the bedrock for establishing critical design parameters, performance criteria, and safety protocols necessary for regulatory approval and seamless integration into electric vehicles.

Central to this intricate process is the selection of the appropriate cell chemistry, a decision deeply intertwined with safety considerations. While prevailing wisdom often categorises lithium-ion chemistries, such as NMC, as more thermally volatile, and others, like LFP and LTO, as safer alternatives, the reality is nuanced.

Cell chemistry matters

The choice of cell chemistry must align with anticipated environmental conditions, steering clear of oversimplified categorisations. For instance, in regions characterised by high ambient temperatures and limited thermal management capabilities, opting for LTO or LFP chemistries may appear prudent. However, with advancements in thermal management technology, NMC cells can also be harnessed effectively. Thus, the selection process hinges upon a comprehensive understanding of the operational environment's temperature profiles.

Once the ideal chemistry is identified, rigorous cell characterisation becomes imperative. This entails subjecting cells to extensive testing under varied temperatures and charging conditions to delineate performance boundaries, particularly concerning thermal runaway – a phenomenon that can have catastrophic consequences if left unchecked. Once these critical thresholds are established, attention pivots towards battery architecture design, with safety emerging as the guiding principle. Crucial considerations encompass cell form factors (such as pouch, prismatic, or cylindrical), cell connections, series-parallel configurations, spacing between cells to optimise thermal dissipation, and the integration of fire suppression systems aimed at containing thermal events, should they occur.

Fire risks and thermal management

Material selection within the battery pack emerges as a pivotal aspect in mitigating fire risks. Incorporating non-flammable components and deploying circuit breakers facilitate the swift isolation of malfunctioning cells, effectively preventing overcharging and the potential for thermal runaway. Furthermore, ensuring the seamless connection between the battery and vehicle electronics is paramount to forestalling potential malfunctions that could precipitate thermal events. Effective thermal management systems stand as indispensable safeguards for maintaining safe operating temperatures within the battery pack. The choice of cooling technology is contingent upon several factors, including voltage requirements, vehicle platform, and available space. Passive cooling methods suffice for low-voltage systems, while more intricate solutions, such as liquid cooling or plate cooling, are favoured for higher voltages. Emerging technologies like immersive cooling, where cells are submerged in a dielectric liquid to facilitate efficient heat dissipation, hold promise in bolstering both safety and performance.

The new trend towards replaceable batteries presents a fresh set of challenges. As humans interact with the battery during replacement procedures, there's an elevated risk of accidents, such as inadvertently dropping the battery, potentially compromising its structural integrity.

Moreover, the act of charging replaceable batteries within a domestic setting, especially in instances of low load capacity and improper wiring, can exert undue stress on the electrical infrastructure, heightening the likelihood of household fires. Consequently, there exists an urgent imperative to redouble efforts towards innovating fixed battery solutions that robustly adhere to stringent safety parameters. Continuous monitoring emerges as a linchpin of battery safety. By harnessing cloud-based monitoring systems to aggregate thermal data from batteries, pre-emptive measures can be swiftly implemented to manage and, if necessary, shut down batteries on the cusp of thermal runaway. The deployment of IoT devices, intricately interconnected with batteries, stands as a proactive measure, enabling the dissemination of early warning signals to users, thus forestalling potential accidents before they take place.

Conclusion

The pursuit of optimal battery pack design for electric vehicles demands a holistic approach, underscored by meticulous attention to cell chemistry, rigorous characterisation, robust battery architecture design, effective thermal management systems, and continuous monitoring mechanisms. By steadfastly addressing these critical areas and spearheading innovations in fixed battery solutions, electric vehicle batteries can confidently emerge as a reliable, sustainable, and, above all, safe power source for the burgeoning transportation sector.

Pankaj Sharma is the Co-Founder at Log9 Materials. Views expressed are of the author.