There are many different ways of triggering the thermal runaway of a battery cell, primarily grouped as:
- Electrical
- Thermal
- Mechanical
Within these groups, legislation has offered a nail test, external heating pad and the electrical short circuit. All of these methods have pro’s and con’s. Hence the search for a more repeatable and realistic trigger method. The Cell Internal Short Circuit Device as invented by NREL and NASA is interesting, but difficult to implement as it has to be build into the cell.
Laser radiation of the cell has a number of benefits [1] when delivered using a fibre optic to a precise location on the cell:
- No internal modifications required to the test cell
- Helps determine response to localized internal short circuit that resembles defect-induced catastrophic field failures
- Method easily replicated by battery developers for battery safety verification tests
- IR laser method can test battery assemblies with minimal thermal biasing to adjacent cells
The NASA reference describes the use of a 120W IR laser with a fibre optic coupler and describes how this can be used in different scenarios.
Shironita et al [2] look at the energy input in laser pulse and how the cell fails.
In conclusion, the laser irradiation to the battery was effective in generating thermal runaway in a highly controlled manner. Specifically, this technique is considered to be an efficient initiation method in thermal propagation tests that do not increase the temperature of an adjacent battery in a module, and it constitutes as one of the practical uses of laser irradiation. Our findings are expected to be extremely useful for thermal propagation tests of other types and sizes of battery materials.
The table comparing laser irradiation to a ceramic heater and an ARC furnace [2] is a useful comparison. The significant difference is the input energy and the heating time.
This post has been built based on the support and sponsorship from: Thermo Fisher Scientific, Eatron Technologies, About:Energy, Quarto Technical Services and Alvatek.
Liu et al [4] conclude that the trigger time for thermal runaway decreases as the laser power increases. However, the onset temperature of thermal runaway and the associated mass loss remain relatively unaffected by changes in laser power. In contrast, a higher SOC corresponds to a lower thermal-runaway onset temperature or a higher mass loss.
Laser irradiation demonstrates a heating efficiency of 78 ± 7%, which is comparable to coil heating and significantly higher than conventional rod heating methods. Based on experimental data, the critical laser heating powers required to induce thermal runaway are determined.
As the SOC decreases from 100% to 30%, the minimum laser output power for thermal runaway increases from 9.5 W to 15 W, that is, the effective battery heating power increases from 6.7 W to 11.1W. In this study Liu et al used the Samsung INR18650-35E cylindrical cell that is NCA and Graphite.
The latest proposals for UN Regulation 100 [3] is to allow the use of a laser based trigger where recommended by the manufacturer. The selection of lasers that they say can be used is rather wide:
The laser type can be chosen from material process lasers such as used for cutting, welding or hardening, e.g. CO2 laser, YAG laser, semiconductor laser, disk laser, fiber laser, and so on.
The proposal also gives examples of cell targets. Again quite a very high level definition.
It feels like the definition of the Laser Radiation Thermal Runaway Trigger is in the early stages of development and hence definition. However, the benefits of using a laser to trigger thermal runaway in a cell appear to be significant with the energy being targetted spatially and temporally. Heating of the neighborouring cells during prior to thermal runaway being initiated is minimal.
References
- Triggering Li-ion Battery Cells with Laser Radiation, NASA Technology Tranfer Program
- Sayoko Shironita, Hideki Tsuruga, Keizoh Honda, Kenichiroh Koshika, Minoru Umeda, Thermal runaway characteristics of a LiFePO4-based lithium-ion secondary battery using the laser-irradiation method, Journal of Energy Storage, Volume 40, 2021
- Proposal for the 05 Series of Amendments to UN Regulation No. 100 (Electric Power Trained Vehicles), Submitted by the expert from Contracting Parties participating in the SIG Thermal Propagation, ECE/TRANS/WP.29/GRSP/2024/18Rev.1 (76th GRSP, 2 – 6 December 2024 agenda item 12)
- Yanhui Liu, Lei Zhang, Xianjia Huang, Menglong Hao, Xinyan Huang, Laser-induced thermal runaway dynamics of cylindrical lithium-ion battery, Journal of Energy Storage, Volume 86, Part B, 2024