Passive Propagation Resistance (PPR) Test

The Passive Propagation Resistance (PPR) test is a specific cell-to-cell thermal runaway containment test: one cell in a pack-representative array is deliberately driven into thermal runaway, and the voltage and temperature of its immediate neighbours are monitored to confirm the event stays contained to that one cell – with no active intervention (no cooling boost, no extra fusing action) allowed to help it along. “Passive” is the operative word: the pack’s own spacing, barriers and venting have to do the job on their own, which is what makes the test a meaningful check on the mechanical and thermal design rather than on the control system.

PPR testing is most closely associated with NASA’s crewed spaceflight battery programme, where a single-cell failure inside a sealed suit or vehicle battery cannot be allowed to become a multi-cell event under any circumstances. NASA’s JSC-20793 safety requirements for crewed spacecraft batteries call for this kind of verification, and NASA-JSC’s own battery group has published test data showing packs that pass and packs that don’t, depending on cell spacing, heat sink design and vent path engineering [1][2]. The same underlying test – and the same PPR terminology – has since been adopted by commercial battery safety vendors such as KULR Technology for CubeSat, drone and other high-consequence applications [3].

How the trigger cell is driven into runaway

The test needs a repeatable way to force exactly one cell into thermal runaway without disturbing its neighbours before the test starts. NASA-JSC’s published work uses an internal short circuit (ISC) device – a small wax-covered conductive pad built into the cell during manufacture, developed originally by NREL, that melts and closes a short between the anode and cathode current collector at a defined temperature when heated from outside [1]. Because the short forms inside the cell, the failure mode matches a real internal fault far more closely than an external abuse test does. KULR’s commercial equivalent, marketed as the LYRA methodology, follows the same principle [3]. Other propagation tests in the wider industry use nail penetration or localised overheating of the trigger cell instead; whichever method is used, the trigger cell is instrumented and the neighbouring cells’ temperature and open-circuit voltage are logged throughout so that any propagation – or any drop in a neighbour’s OCV indicating an induced short – is caught even if it doesn’t visibly ignite.

Pass/fail criteria

A pack passes a PPR test if none of the cells adjacent to the trigger cell reach their own thermal runaway onset temperature, and their open-circuit voltage is unchanged before and after the test. NASA-JSC’s published module-level results illustrate the margins involved: with a 0.5–1.5 mm aluminium interstitial heat sink between cells, interior trigger cells raised neighbouring cell temperatures by roughly 19–30°C above baseline, and edge trigger cells by roughly 42–52°C – in both cases comfortably below the neighbouring cells’ own runaway onset threshold, with post-test OCVs unchanged [1]. The same test series found corner and edge cells consistently more vulnerable to propagation than interior cells, which is now treated as a standard design consideration rather than a surprising result.

PPR testing sits at cell-and-module scale, verifying the physical design choices – cell spacing, interstitial heat sinks, individual cell fusing, vent path geometry – discussed on Propagation Mitigation. It is a narrower, more tightly controlled test than pack- or system-level propagation standards such as GB 38031 or UL 9540A, which are covered on that page.

References

Darcy, E. (NASA-Johnson Space Center), Passively Thermal Runaway Propagation Resistant Battery Module that Achieves >190 Wh/kg, Sustainable Aircraft Symposium, 2016
NASA-Johnson Space Center, JSC-20793 – Crewed Space Vehicle Battery Safety Requirements
KULR Announces Passive Propagation Resistant Lithium-ion Battery Safety Solution for CubeSat and Commercial Battery Applications, KULR Technology Group, 2020

Needs review: the To Do List entry for this item mentioned drilling into the trigger cell’s vent as a typical way to initiate the failure. The published NASA-JSC and KULR sources found for this page describe an internally-implanted short-circuit device (ISC/LYRA) rather than vent drilling as the trigger method, so that detail has deliberately been left out above rather than stated on unverified grounds. If drilling near the vent is a technique you’ve seen used elsewhere, it would be worth adding with a source.