CELL-TO- BODY DESIGNS COULD BENEFIT OVERALL THERMAL MANAGEMENT IN EV BATTERIES
As car manufacturers and battery OEMs are looking to cram more energy into electric vehicles, while cutting materials, weight and costs at the same time, fire safety and thermal management have come to the fore as primary concerns. Will we see more EV fire incidents and bad publicity hurting the transition to electric?
The trend in EV battery design in the last two years has been towards cell-to-pack and cell-to-body; manufacturers eliminate non-functional parts to improve energy density and reduce complexity and cost. Instead of having battery cells packed in modules, they are bonded directly to the cooling plate or even the chassis or car floor.
Price and volume-focused Chinese manufacturers BYD and CATL took the lead, betting on cheaper lithium iron phosphate (LFP) batteries, with cell-to-pack (CTP) designs helping offset the lower energy density of LFP compared to the nickel-rich NCM cells that Tesla used. CATL pioneered CTP in 2019 and claimed 72% volume utilization efficiency for the third generation launched last summer. BYD has used the cell-to-pack concept in its Blade batteries and now applies cell-to-body in their new Seal EV model.
Chinese startup Leapmotor is taking the concept a step further with cell-to-chassis, using the battery cells as an integral part of the structural support of the car. Tesla in recent years has started using CATL LFP batteries for their standard range models and following the cell-to-body concept in their 4680 batteries, but will reportedly now also use BYD’s Blade batteries. Ford announced in February 2023 plans to build a US$3.5 billion LFP battery plant in Marshall, Michigan, licensing some CATL technology, but keeping production in the US.
Are the next-generation EV battery designs increasing the risks of thermal runaways? In 2021 a BYD Han EV reportedly self-immolated after an independent crash test. There were embarrassing recalls of Chevy Bolt and Hyundai Kona/Ioniq Evs in the same year. An increasing number of scooter fires prompted the introduction of new regulation in India.
‘There is obviously a potential risk there,’ says James Edmondson, Principal Technology Analyst at IDTechEx. Removing the extra layer of protection that the module housing provides could make it harder to stop propagation when a single cell goes into thermal runaway. ‘On the other hand, you potentially can improve your overall thermal management, because you now have less interfaces between the actual cells and your cooling structure.’
Currently the most common approach to the cooling system of LFP cell-to-pack designs is to have a large cold plate beneath or above the cells. NCM batteries are often using side-wall cooling as well. Ceramic additives like alumina or boron nitride in compression pads and thermal interface materials (TIM) help with heat transfer and fire protection. IDTechEx predicts a seven-fold increase in TIM demand over the next ten years.
IDTechEx Technology Analyst Yulin Wang will join an Ask the Experts Panel at the Thermal Management Expo 2023 coming up in May in Michigan.