Experimental investigation of thermal runaway spread and effects of sprinkler in reused battery storage

초록

Used batteries from electric vehicles (EVs) are increasingly being repurposed for second-life applications such as energy storage systems. These batteries are stored during inspection and preparation before being repurposed. Recently, fire incidents have been reported in used battery storage facilities, owing to thermal runaway (TR) of lithium-ion batteries used in EVs. However, fire safety in used battery storage facilities, particularly rack-type storage facilities, remains inadequate owing to limited research and development. This study experimentally investigated TR behavior and sprinkler suppression performance in a rack-type storage facility. Used EV battery modules were thermally abused, and the temperature, voltage, sprinkler activation, and visual TR were measured under experimental scenarios. Without sprinkler application, thermal runaway propagation (TRP) in the trigger module accelerated as TR progressed, and vertical TR spread occurred. Manual sprinkler discharge delayed the time to voltage collapse in the trigger module by approximately 63% relative to the non-sprinkler experiment. The sprinkler discharge removed visible flames; however, reignition occurred after discharge termination and TR continued within the module, indicating that sustained cooling is required to interrupt TR. Automatic sprinkler application prevented vertical TR spread to the adjacent module in all experiments. The early-response sprinkler produced a stepwise voltage-decrease pattern, indicating delayed TRP within the trigger module. Faster sprinkler activation promoted sequential TRP within the trigger module and prevented simultaneous TR in multiple cells, reducing fire risks. These experimental results can be used to improve fire safety in rack-type battery storage facilities by mitigating fire hazards and improving the effectiveness of sprinkler application.

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