Elsevier

Fire Safety Journal

Volume 125, October 2021, 103417
Fire Safety Journal

Experimental study on thermal runaway behaviors of 18650 li-ion battery under enclosed and ventilated conditions

https://doi.org/10.1016/j.firesaf.2021.103417Get rights and content

Highlights

  • A comparison study of thermal runaway behaviors was done under enclosed and ventilated conditions.

  • Gas explosion was determined by ejecting substance temperature.

  • 50% was the critical SOC (state of charge) for LIB to trigger gas explosion.

  • The two thermal runway behaviors was dominated by ambient pressure.

Abstract

A novel study was done using a designed 6.7L chamber for experiments under both enclosed and ventilated conditions. Under enclosed condition, for LIB (li-ion battery) above 0% SOC (state of charge), the cases ruptured. Above 50% SOC, an explosion was even triggered. Though the analysis of collected gas from the enclosed condition, the flammable gas (e.g., CH4, CO) concentration increased as SOC increased, even a gas explosion occurred. Under ventilation, the tendency of case rupture decreased and the gas explosion risk was reduced. Whether the case rupture occurred was depended on the rate of generated gas venting. Fick's Law was adopted to describe this phenomenon. It was found that the external pressure was the key factor impacting the case rupture. This work studied the LIB thermal runaway behaviors from a novel perspective, and provided a reference for the safety protection of the LIBs.

Introduction

Recent years, LIBs are widely used in various fields (i.e., portable electronic devices, electric vehicles, etc.) due to their higher energy density, longer calendar or cycle life, and increased reliability [1]. Nevertheless, LIBs contain reactive and flammable materials, therefore safety issues are always a concern and a number of incidents involving LIBs have been reported over the years [2,3]. When LIBs are subjected to abuse conditions (i.e., thermal abuse [4,5], electrical abuse [6,7] and mechanical abuse [8]), they may fail through a rapid self-heating and thermal runaway [9]. The thermal runaway of the LIBs will produce a significant amount of gas (flammable and toxic gas), smoke and eventually develop into a fire or explosion [10,11].

The thermal runaway behaviors have attracted researches’ much attention, including the propagation characteristics [12,13], the fire characteristics [[14], [15], [16]], the components of releasing gas [17,18]. However, most experiments for thermal runaway tests were done in a limited space to ensure the accuracy of measurement parameters. Can-Yong Jhu et al. evaluated the thermal runaway hazards of various 18650 Li-ion batteries in an adiabatic calorimeter with vent sizing package 2 (VSP2) [19,20]. Tsai-Ying Hsieh et al. measured characteristics on thermal hazards of lithium-ion batteries in a confinement apparatus of 500 ml, charactering onset temperature, maximum temperature, maximum self-heat rate, maximum pressures, battery mass loss, etc. [21]. Yajun Zhang et al. revealed the gaseous and solid emission characteristics of a 50 Ah commercial prismatic cell in a sealed chamber with nitrogen atmosphere [22].

In some full-scale fire experiments of lithium batteries, they were often carried out in open or semi-open spaces [13,23,24]. Yang Peng investigated the thermal and toxic hazards resulting from the thermally-induced failure of a 68 Ah pouch LIB by 1/2 ISO full scale test room [25]. The gas was discharged by a pump at a stable rate to monitor the gas composition and concentration changes. Mingyi Chen conducted an experimental study to assess the fire hazards of lithium-ion batteries at different atmospheric pressures by means of the in-situ calorimeters built in a sea-level city Hefei (100.8 kPa, 24 m) and a high-altitude city Lhasa (64.3 kPa, 3650 m), respectively [26]. Binbin Mao studied the more refined combustions on 18650-type batteries in an open space [27]. The jet flame in open space and the combustion characters in semi-open space was detailly researched. Zhi Wang and Jian Wang studied the degradation and combustion behaviors associated with lithium ion batteries after different aging treatments in an open space [28]. Chengshan Xu et al. studied the thermal runaway propagation of LIB modules with different parallel-series hybrid connections [29].

As stated above, though many studies have either conducted thermal runaway experiments in open spaces or in limited spaces, rarely considering the comparative study of the two conditions. Factually, the compared studies were needed in order to understand the thermal runaway behaviors of LIBs at different using scenarios. More importantly, the emergency inhibition measures might be different and it will provide guidances. Therefore, in this paper, the experimental study focused on thermal runaway behaviors of 18650-type batteries under enclosed and ventilated conditions. The LIB with LiNi0.5Co0.2Mn0.3O2 cathode was tested in a designed 6.7L chamber. Under enclosed condition, the thermal runaway behaviors, explosion process and gas components were investigated. In addition, the explosion of the LIBs at 100% SOC under four different ventilation conditions (i.e., 0 L/h, 1000 L/h, 1500 L/h and 3000L/h) were performed. This study novelty found two different thermal runaway behaviors and revealed the mechanism of this transformation.

Section snippets

Experimental apparatus

To carry out unrestricted thermal-runaway experiments, a custom-designed test stand was built (Shown in Fig. 1). The test stand includes a test device, heating module, data acquisition module and ventilation module. The test device is a cylindrical chamber which is made of 316 L stainless steel with a volume of 6.7 L (Inner diameter: 145 mm; Height: 400 mm). A quartz glass with a diameter of 99 mm and a thickness of 25 mm is installed on the viewing window. The device can withstand pressures

Pressure and temperature analysis

The LIBs at five different SOCs (i.e., 0%, 25%, 50%, 75% and 100%) were tested in an enclosed chamber. The pressure change in the chamber during thermal runaway of LIB was divided into four stages, which was shown in Fig. 3.

  • (1)

    Stage I: Heating

According to Ideal Gas Law, the relation between pressure and temperature could be described as Eq. (1) and Eq. (2). Under the heating of the heater, the temperature in the chamber rose. Since the experiments were conducted in an enclosed chamber, the n and V

Conclusion

In this paper, a novel study was done to investigate the thermal runaway behaviors under both enclosed and ventilated conditions. The pressure and temperature data were acquired. In addition, to understand the explosion process more clearly, the flammable gas under enclosed condition was analyzed. The important conclusion could be concluded as follows:

  • (a)

    Under enclosed condition, LIBs were prone to rupture cases. The case rupture caused a pressure increase of 55–69 kPa. 50% was the critical SOC

CRediT authorship contribution statement

Junchao Zhao: Conceptualization, Formal analysis, Investigation, Data curation, Writing – original draft. Song Lu: Resources, Formal analysis. Yangyang Fu: Resources, Conceptualization, Investigation, Data curation, Writing – review & editing, Supervision. Weitong Ma: Investigation, Data curation. Yuan Cheng: Formal analysis, Data curation. Heping Zhang: Resources, Writing – review & editing, Supervision, Project administration.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 51804288). Also, it was supported by the National Key R&D Program of China (No. 2018YFC0807605), the National Natural Science Foundation of China (No.51974284), the Fundamental Research Funds for the Central Universities under Grant No. WK2320000046.

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