Passive cooling means the battery cell or pack is not actively cooled, instead it relies on heat conduction, radiation and convection. This heat transfer will apply in both directions, to and from the environment.
Passive cooling should be the starting assumption for all battery pack designs, the drive cycles and user cases could set requirements for a more aggressive thermal management system. However, it is always good to start with the simplest approach.
Pros
- Cheap
- Lower weight and volume
- No possible coolant leaks
- Simpler to manufacture
- Easier service and repair options
Cons
- Hot and cold ambient limits
- Charge and discharge rate limited by thermal mass and heat loss to surroundings
- Not able to use coolant circulation to minimise cell to cell temperature differences.
Even with no cooling the battery cell(s) must adhere to the temperature limits.
Temperature sensor(s) and algorithm on the BMS must be able to predict the maximum and minimum temperature throughout the pack.
Temperature gradients in cells and between cells will always accelerate ageing.
Opportunities
- Use low discharge rates to heat cells in cold climates.
- Create thermal conduction pathways to case.
- Shrink package to minimum around the cells.
Examples
- Mobile phone
- Laptop
- Cordless power tools
- Nissan Leaf
Battery Cooling Options
There are many different options for battery cooling (and heating). These range in capability and complexity from Passive through to Fully Immersed Dielectric.