Recent EV battery fires: Maintain Cell Spacing to Ensure Battery Safety

 In Blog, Safety

Past few weeks, there is a lot of discussion in different forums about EV battery safety. While EV fires are not new, they are neither limited to Indian two wheelers. Recalls due to battery safety concerns by well-known global OEMs in the recent past also have been in the news.

We need to look at EV batter safety at multiple levels. Firstly, it is important that the designers take all the precaution possible and ‘design’ and package the battery for maximum safety. Carrying out enough tests is equally important.  When the vehicle is launched, safety related information should be always handy and accessible to the first respondents. (Sometimes, this leads to funny instructions such as GM asking Bolt customers to park their vehicles 50 feet away from other vehicles!)

Maintaining safe distance is the key!

One of the safety issues, I feel, arises out of the race to make two-wheeler battery packs as energy dense as possible. The competition forces new designs to keep reducing the distance between the cells, to the extent that there is zero gap between the cells in some packs.

While I am sure designers do take all possible care within the constraints that they have, I thought it would be a good idea to share some tips. Here are the tips that I have combined from three very reputed sources:

1. From NASA’s “lessons learned in passive Thermal Runaway propagation resistant design”

 5  Battery Design Guidelines for Reducing Hazard Severity from a Single Cell TR :

      • Reduce risk of cell can side wall breaches
      • Provide adequate cell spacing and heat rejection
      • Individually fuse parallel cells
      • Protect the adjacent cells from the hot TR cell ejecta (solids, liquids, and gases)
      • Prevent flames and sparks from exiting the battery enclosure

2. From UL’s “Safe Lithium-Ion Battery Designs for Use, Transportation & Second Use”

Approaches for Safe Designs for Use and Transportation

      • Prevent Cell to cell thermal runaway propagation
      • Cell to cell spacing; barriers between cells, etc. to prevent cell to cell thermal runaway in the unlikely event of single cell thermal runaway.
      • Use of extinguishers and other fire suppression methods installed internal to battery container

3. From the Journal of the Electrochemical Society’ article “Experimental analysis of thermal runaway and propagation in lithium-ion battery modules” by Lopez CF, Jeevarajan JA, Mukherjee PP

Lopez et al. investigated different spacing between the cells in the thermal runaway situation and reported that the spacing between the cells in the battery pack greatly affects thermal runaway propagation.

      • In general, a spacing of at least 2 mm is recommended. 

Keep safe distance. That is important.

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