Leak detection is a key test for systems and components within the battery pack from cells, contactors, cooling system and the enclosure.
Cells
Leaks in lithium-ion battery cells can shorten battery life and deplete energy capacity. Leaks also can allow moisture to enter the battery system. Water ingress can lead to a complete failure of the battery or create a potential fire hazard [1].
Agilent [2] give a helium equivalent leak rate for a cell of 10-6 to 10-8 mbar.litre/s.
Electrolyte detection is a possible way of seeing early cell failures where a soft vent results in electrolyte being vented and dispersed into the pack volume. This soft venting of electrolyte happens prior to a cell going into thermal runaway.
Contactors
Nitrogen or hydrogen is used in contactors to quench any arcs that can form when closing or opening under load. For the lifetime performance it is important that the gas remains sealed in the enclosure.
Cooling
A leaking battery coolant system can result in electrical isolation failure, corrosion and potentially a fire hazard. Hence it is important to pressure test the coolant system as a final end of line test. For complex battery packs it is worthwhile testing components such as cooling plates and sub-systems prior to finally assembly.
Tesla Self-Activated Draining System
“A method of managing leakage of liquid inside a battery system comprises: containing leaking liquid in a non-liquid sensitive region of the battery system so as to protect internal electrical components of the battery system from coming in contact with the leaking liquid; and in direct response to the leakage, expunging the leaking liquid from the battery system.” — Patent US9293792B2
Coolant Outside Battery Pack: 2022 Kia EV6
Another option to reduce the risk of coolant leaking and causing an HV short is to place the coolant system outside of the sealed battery pack.
The self-activated drain and coolant outside of the battery pack reduce the risk of an HV short. However, the loss of the coolant will result in a pack that could overheat and hence the loss of coolant or cooling still needs to be detected by the BMS and the pack performance managed accordingly. Along with a system warning.
References
- Standardized Leak Testing for Lithium-Ion Battery Cells, Quality Magazine
- Leak Detection of Lithium-Ion Batteries and Automotive Components, Agilent
See also: Safety Diagnostics