Sealing needs to be considered across the components and at a system level. There are so many aspects of the pack where we need to consider sealing:
- cell can/case
- HV contactors
- cooling system
- HV and LV connectors
- pack enclosure
All of these are trying to keep something inside and/or stop dust, gas or liquids entering.
Cooling System
It is really important that any liquid cooling system is sealed as most coolant fluids do not mix well with High Voltage systems.
Enclosure
IP Ratings or Ingress Protection ratings are designed to rate and grade the resistance of enclosures of electric and electronic devices against the intrusion of dust and liquids. Plus how easy it is for individuals to access the potentially hazardous parts within the enclosure.
Surfaces that have steps or even blended changes in height are always difficult to seal. Sealing surfaces that lay in one plane are the easiest to seal.
Here you can see the black lid having to seal against a curved surface.
2013 BMW i3 battery pack enclosure has the lid to base seal all on one plane.
The seal will be cheaper and more reliable.
The wavy top flange on this CATL Naxtra 24V pack shows poor sealing design.
The top flange is too weak compared to the bolting pattern and seal stiffness.
Why IP67 and AIS-156 Are NOT Enough:
The Silent Reliability Crisis Inside Indian EV Battery Packs.
Over time:
- Elastomeric and polymeric gaskets lose their compression set
- Micro-movement develops at sealing interfaces
- Progressive gaps form in the ~10–50 μm range
- These gaps are invisible to visual inspection—and fatal in the long run.
Leaks
Liquids inside a battery system can result in failures from electrical isolation through to thermal runaway. Hence it is really important to detect and/or manage any fluid leaks within the enclosure.
The Tesla Self-Activated Drain Plug operates if coolant leaks inside the battery pack. The coolant causes the component in the plug to swell and operate against the spring loaded plug.
The Kia Niro has a leak detection sensor mounted inside on the bottom of the pack.
The pack uses a rubber seal with washers that limit the compression of the seal.