One of the primary concerns when balancing battery attributes to design high-performance batteries is swelling, the expansion of the battery due to a build-up of gasses inside.
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Batteries can swell for two main reasons. The first, reversible thermal expansion and contraction as batteries warm and cool, is typically minor, predictable in scale and timing, and relatively easily accommodated in product design, for example by designing a volume tolerance in the battery compartment.
The battery promptly exploded (that’s the only word for it) jetting a sheet of flame across the closed-off test cell. Immediately after, we watched one of BYD’s lithium-iron phosphate batteries undergoing the same spike piercing test, and it might has well have been a plank of wood for all the reaction it caused. No smoke, no flames, no nothing.
Irreversible expansion always occurs as a result of a degradation mechanism, such as oxygen evolution, dendrite formation, electrode decomposition or others – see “ Lithium ion battery degradation: what you need to know ” by J. Edge et al. for more background on mechanisms.
In the quest to deliver maximum performance in the most attractive form factor, product engineers must ensure they are not inadvertently increasing the possibility of battery swelling, and as a result, impacting the overall safety of the product or end-user experience.