Thermal runaway incidents-a serious cause of concern: An analysis of runaway incidents in China

Thermal runaway initiated in an individual cell may transfer heat to adjacent cells, and cause thermal runaway propagation. Thus, mitigation and prevention of thermal runaway propagation using extinguishing agents are significant. In this work, fire and extinguishing tests on 117 Ah LIBs with Li(Ni0.8Co0.1Mn0.1)O2 (NCM)/graphite electrodes are investigated. The suppression effects of different extinguishing agents including HFC-227ea, C6F12O and water spray on thermal runaway propagation in confined space were compared. Results show that thermal runaway propagation can occur in LIBs module even with thermal management measures. When activated immediately after the thermal runaway of the first cell, each agent can extinguish the LIBs module fire. However, the cooling capacity of extinguishing agent is the key factor to suppress thermal runaway propagation. The heat dissipation of HFC-227ea, C6F12O and water spray in fire extinguishing test is 24.8 kJ, 111 kJ and 459.8 kJ, respectively. Thus, HFC-227ea can hardly suppress the thermal runaway propagation. Although C6F12O can not prevent thermal runaway propagation, it can decrease the battery temperature, slow down the heat transfer rate and prolong the propagation time. While water spray has the best cooling effect, which can prevent thermal runaway propagation. 

Experimental Study on Suppressing Thermal Runaway Propagation of Lithium-ion Batteries in Confined Space by Various Fire Extinguishing Agents

Experimental determination of the lower flammability limit and limiting oxygen concentration of propanal/air mixtures under elevated temperatures and pressures

In the view of the thermal runaway scenario phase change material are not capable to withstand thermal propagation phenomenon, hence it is important to provide a novel structure which can delay thermal runaway trigger point and not allows generated heat to propagate at faster rate from one cell to another. In this work, a series of numerical investigations are performed from cell to pack level configuration under heater assisted triggering method by providing a constant heat supply of 500 W until electrochemical kinetics of cell gets trigger. This setup is used to investigate, time delay and thermal propagation phenomenon by integrating submerged layer of phase change material. Conclusive evidence from investigation suggests that by integrating a submerged layer of phase change material, the thermal runaway trigger point can be effectively delayed. However, because phase change material is highly flammable in nature, heat propagates from one cell to another in a very short period, causing the entire pack to go into catastrophic thermal failure within short span of 10s. To delay this thermal propagation phenomenon and compliance GB 38031 and GB 38032 “national safety regulation of battery pack for Electric Bus and Electric Vehicle” that suggest once cell is trigger, neighbouring cell should not run in thermal runaway for at least 300s, we have optimized battery pack structural design by introducing low thermal conductive pyro liner at the wall of PCM. Results showed, this optimize design represents dual functionality of delaying thermal runaway trigger point of cell along with slowing down thermal propagation for at least 800s. 

Battery thermal runaway propagation time delay strategy using phase change material integrated with pyro block lining: Dual functionality battery thermal design

Study on thermal stability and thermal decomposition mechanism of 1-((cyano-1-methylethyl) azo) formamide

The past two decades have seen a rise in university laboratory accidents in China. Although there is a growing awareness due to higher reporting and media coverage, the evaluation and understanding of common hazards and deficiencies in university laboratories remains to be addressed. Aiming to enhance safety in laboratory-related activities, this study analyzed the current status and challenges of university laboratory safety in China and presented future directions to reduce accidents using engineering and administrative controls. A descriptive statistical analysis of 110 publicly reported university laboratory accidents in mainland China since 2000 was performed to investigate the proximate causes of the accidents, and further, to identify potential deficiencies existing in the current safety management of laboratories. It was found that human factors were the most contributing cause and the training element was a vulnerable competency in laboratory safety management. Based on the results, a comparative analysis between the underlying reasons for the poor safety situation and the efforts that have been made has brought the challenges and possible solutions for safety improvements in university laboratories. By suggesting top-down and bottom-up approaches, the present study provides valuable insights and serves as a reference for universities and relevant authorities to enhance safety in university laboratories.

Current status, challenges, and future directions of university laboratory safety in China

Polyethylene is widely used due to its excellent properties. However, the growing demand and higher production of polyethylene have also brought new types of hazards. It is essential to study the pyrolysis of polyethylene for the polyethylene process conditions and the prevention of polyethylene dust explosion. In this paper, the pyrolysis of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) under different heating rates in N2 and different ethylene concentration was studied by the TG-DSC method. The pyrolysis kinetics of polyethylene was analyzed by using Li Chung-Hsiung thermal analysis method, and the pyrolysis characteristic and reaction kinetics parameters of LLDPE and HDPE were found. The research results show that the increase in the heating rate is beneficial to polyethylene pyrolysis in nitrogen. The temperature at the highest rate increases linearly with the heating rate. The rise of ethylene concentration has some inhibitory effect on the pyrolysis reaction of polyethylene, and ethylene has a significant impact on the polyethylene pyrolysis rate. We also found the most suitable mechanism function of polyethylene pyrolysis from the 12 considered mechanism functions. HDPE pyrolysis stability is higher than LLDPE in nitrogen, while LLDPE pyrolysis stability is higher than HDPE in ethylene.

Kinetics of polyethylene pyrolysis in the atmosphere of ethylene

The explosion characteristics of propane–diluent–air mixtures under various temperatures and pressures were investigated using a 20-L apparatus. The explosion limits of propane diluted with nitrogen or carbon dioxide were measured at high temperatures from 25 to 120 °C. The results showed that the upper explosion limit (UEL) increased, and the lower explosion limit (LEL) decreased with the rising temperature. The explosion limits of propane diluted with nitrogen or carbon dioxide were also measured at high pressures from 0.10 to 0.16 MPa. The results showed that the UEL increased, and the LEL almost remainedunchanged along with increased pressure. Under the same initial operating conditions, the concentration of nitrogen required to reach the minimum inerting concentration (MIC) point was higher than the concentration of carbon dioxide. Finally, the study investigated the limiting oxygen concentration (LOC) of propane under various initial temperatures, initial pressures, and inert gases. The LOC of propane decreased approximately linearly with increased temperature or pressure, and the LOC of propane dilution with carbon dioxide was greater than dilution with nitrogen from 25 to 120 °C or from 0.10 to 0.16 MPa, which indicated that the dilution effect of carbon dioxide was better than that of nitrogen.

Mingqi Bai

Papers

Current status, challenges, and future directions of university laboratory safety in China

Thermal runaway incidents-a serious cause of concern: An analysis of runaway incidents in China

Kinetics of polyethylene pyrolysis in the atmosphere of ethylene

Effects of initial temperature and pressure on explosion characteristics of propane–diluent–air mixtures