Conventional EV packs cool cells by pressing cold plates against them, which works but cools unevenly — the surfaces touching the plate run cooler than the rest. Immersion cooling takes a more aggressive approach: submerge the cells in a non-conductive fluid so heat leaves from every surface at once. It is better, more uniform thermal control. It also raises a new question — what happens to all that fluid if a cell fails? A 2024 GM grant answers both halves.
The record: on November 19, 2024, GM Global Technology Operations LLC was granted US12148910B2, “Thermal management systems with passive quenching sacks for liquid immersion cooled battery assemblies.” The CPC classes are battery-cooling and pack-structure classes — H01M 10/6567 and 10/613 (cooling), 10/651 (heat exchange), and 50/249, 50/3425, 50/375 (pack containment and venting). Two ideas: immersion cooling, and a passive quenching sack.
Here is the mechanism. Immersion puts the cells in a dielectric (electrically non-conductive) fluid that conducts heat well. Because the fluid touches the entire cell surface, it pulls heat away uniformly and can also absorb a sudden heat spike better than a plate. The “passive quenching sack” is the safety complement: a device that, without active control, can release or direct fluid to quench a cell that begins to overheat — attacking a potential runaway with the cooling fluid that is already there.
Why pair them? Because immersion cooling's strength — fluid everywhere — is also a resource for safety. If the pack is already full of a heat-absorbing fluid, you can use it to smother a thermal event. A passive quenching mechanism means no sensor or controller has to fire correctly in a crisis; the physics of the device does the work. That passivity is valuable precisely when electronics might fail.
The trade-off, honestly stated: immersion cooling adds fluid mass, sealing complexity, and cost compared with plate cooling. It is the heavier, more capable choice, the same way active beat passive in earlier eras. GM patenting immersion-plus-quenching is a bet that the superior thermal control and the built-in safety resource justify the added complexity — at least for some packs.
The caveat: a granted thermal-management method is a technique, not a guarantee, and immersion cooling is not yet universal in shipping EVs. But it represents the leading edge of the same problem that has run through every era of EV batteries — hold the cells in their thermal window, and have a plan for when one fails. A 2024 GM grant shows that frontier: cool every surface evenly, and keep the firefighting fluid built into the pack.