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Composite phase change materials commonly exhibit drawbacks, such as low thermal conductivity, flammability, and potential leakage. This study focuses on the development of a novel flame-retardant phase change material (RPCM). The material's characteristics and its application in the thermal management of lithium-ion batteries are investigated. Polyethylene glycol (PEG) serves as the medium for phase change; expanded graphite (EG) and multi-walled carbon nanotubes (MWCNT) are incorporated. Moreover, an intumescent flame retardant (IFR) system based on ammonium polyphosphate (APP) is constructed, aided by the inclusion of bio-based flame-retardant chitosan (CS) and barium phytate (PA-Ba), which can improve the flame retardancy of the material. Experimental results demonstrate that the RPCM, containing 15% IFR content, exhibits outstanding flame retardancy, achieving a V-0 flame retardant rating in vertical combustion tests. Moreover, the material exhibits excellent thermomechanical properties and thermal stability. Notably, the material's thermal conductivity is 558% higher than that of pure PEG. After 2C and 3C high-rate discharge cycles, the highest temperature reached by the battery module cooled with RPCM is 18.71 °C lower than that of natural air-cooling; the material significantly reduces the temperature difference within the module by 62.7%, which achieves efficient and safe thermal management. [ABSTRACT FROM AUTHOR]

A large amount of storage may cause large-scale fire or explosion accidents due to the potential fire risk of lithium-ion batteries, which poses a great threat to the safety of personnel and property. In this study, the fire model of an individual cell is established according to the experimental data and the relevant parameters of thermal runaway simulation of large capacity battery are determined. The battery pack model is established according to the real setting of a warehouse. The fire characteristics of the battery pack spreading around in the warehouse environment are studied. The results show that the fire of lithium-ion batteries is preferentially diffused to the upper battery pack in the warehouse environment, and spread to the upper battery pack 19 s after the initial battery thermal runaway. The fire propagation of the horizontal battery pack is greatly affected by the distance. The farther the battery string is from the thermal runaway battery, the later the fire propagation battery string occurs. Furthermore, the role and effect of battery pack spacing, fire warning and automatic sprinkler system in fire are provided, so as to carry out better research on the storage safety of lithium-ion battery warehouses. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) are widely used in electrochemical energy storage and in other fields. However, LIBs are prone to thermal runaway (TR) under abusive conditions, which may lead to fires and even explosion accidents. Given the severity of TR hazards for LIBs, early warning and fire extinguishing technologies for battery TR are comprehensively reviewed in this paper. First, the TR reaction mechanism and hazards of LIBs are discussed. Second, the TR early warning and monitoring methods of LIBs are summarized in five aspects consisting of acoustic, heat, force, electricity, and gas. In addition, to reduce the fire and explosion hazards caused by the TR of LIBs, the highly efficient extinguishing agents for LIBs are summarized. Finally, the early warning technology and fire extinguishing agent are proposed, which provides a reference for the hazard prevention and control of energy storage systems. [ABSTRACT FROM AUTHOR]

Summary: The widespread use of lithium‐ion battery (LIB) urgently needs a thermal management system with excellent performance to manage it. Phase change material (PCM) has been adapted for thermal management of LIB because it can absorb a mass of energy without additional power. In this research, the thermal conductivity of PCM is improved, and its cooling effect is detected. The addition of hybrid thermal conductivity filler is beneficial to its uniform dispersion and improvement of aggregation phenomenon on the surface of materials. The results show that the PCM with hybrid filler has better thermal conductivity, which is increased by 264%. In different proportions of composite materials, the composite phase change material with 1% few‐layer graphene and 2% graphite nanoplatelet can play a better cooling effect in LIB module thermal management, and it respectively decreases the maximal temperature of the battery module by 7.17°C, 10.52°C, and 16.33°C at 1C, 2C, and 3C conditions, and the maximal temperature difference does not exceed the safety range of 5°C. [ABSTRACT FROM AUTHOR]

Herein, a series of experiments were performed to illustrate the impact of safety vents on the evolution of thermal runaway behaviors of 18650-size lithium-ion batteries. Meanwhile, the effect of safety vents on the thermal safety of batteries with different states of charge (SOC), i.e. 0%, 50% and 100% and cathode chemistries, i.e. lithium nickel manganese cobalt oxide (NMC), lithium cobalt oxide (LCO) and lithium iron phosphate (LFP) was explored. Compared with the battery with a safety vent, the thermal runaway behaviors of the battery in the absence of a safety vent are greatly worsened with ignition and thermal runaway occurring far earlier. As the battery SOC increases, it is demonstrated that the effect of the safety vent on battery thermal safety is reduced to some extent, with the difference in the times to thermal runaway between the batteries with and without a safety vent decreasing gradually. Besides that, it is found that the effect of the safety vent on the thermal runaway features of LFP-based batteries is relatively minor than in NMC-based batteries and LCO-based batteries. There is a linear-increasing relationship between the thermal runaway time difference and the mass loss difference for batteries with and without a safety vent. [ABSTRACT FROM AUTHOR]

Summary: In the current work, a series of experiments are carried out to investigate the degradation behavior of lithium‐ion batteries during overcharge cycling, as well as the influence of ambient temperature on the degradation. In which, different charge cut‐off voltages (4.5, 4.8, and 5.0 V) and ambient temperatures (0°C, 20°C, 50°C, and 70 °C) are included. During the overcharge process, the batteries demonstrate severe temperature rises, and several key electrochemical parameters such as the charge capacity, energy density, median voltage, and resistances all increase, revealing the deterioration of heat generation and electrode kinetics. Besides that, batteries exhibit serious degradation behavior during the overcharge cycling, which is presented through the evolution of battery temperature curves, charge voltage curves, and internal resistance curves. Moreover, the severity of degradation exacerbates with the increasing overcharge degree. Finally, it is found that deep‐overcharged batteries may be more sensitive to the ambient temperature than slight‐overcharged ones, where an abusive temperature can significantly aggravate the corresponding degradation. [ABSTRACT FROM AUTHOR]

Summary: A set of experiments are performed in the present work to investigate the degradation behavior of lithium‐ion battery during overdischarge cycling, as well as the influence of a high‐temperature environment on the degradation. Among, different discharge cut‐off voltages (1.0, 0.5, and 0.2 V) are included. During the overdischarge process, batteries experience a stage where a violent electro‐thermal behavior is exhibited, involving sharp decreases in the voltage and current, and a fierce increase in the surface temperature; moreover, several parameters such as the discharge capacity, energy density, and internal resistances are all increased after overdischarge. Besides, a poor rate capacity and serious capacity degradation can also be seen during the overdischarge cycling, which is further reflected by the evolution of battery surface temperature, charge/discharge voltage, and internal resistances. What is more, it is found that battery electro‐thermal parameters, eg, temperature rise, degradation rate, and internal resistances, increase exponentially as overdischarge deepens. Finally, a high‐temperature environment is verified to deteriorate the degradation of overdischarged battery. [ABSTRACT FROM AUTHOR]

• Field lithium-ion battery fire experiments at sub-standard atmospheric pressure. • Thermal runaway and fire process of lithium-ion battery are revealed. • The effects of cathode and SOC on combustion is analyzed. • The effect mechanism of pressure on combustion is revealed. The environmental pressure effect on thermal runaway and fire behaviors in the 18650 lithium-ion battery (LIB) with various cathodes and states of charge (SOC) are experimentally investigated in this work. The fire hazards were characterized by the combustion process, total mass loss (TML) and total heat release (THR). The TML and THR increase with the ascending of the SOC at two pressures. The amount of materials ejected by both LiFePO 4 and LiCoO 2 batteries during the combustion is slightly affected by the environmental pressure. Meanwhile, the environmental pressure has a significant influence on the combustion heat that the THR value at high pressure is relatively bigger than that at low pressure. The unit growth rate in combustion heat between the two pressures also increases with the SOC. [ABSTRACT FROM AUTHOR]

Summary: To investigate the impacts of ambient pressure on thermal runaway and fire behaviors of lithium‐ion battery (LIB), experimental measurement and theoretical analysis with serial conditions are conducted at two altitudes. The well‐designed experimental equipment and operating conditions have enabled the accurate evaluation of ambient pressure effects. Results show that the first abrupt temperature change in Hefei (ambient pressure 100.8 kPa) is higher than that in Lhasa (64.3 kPa). The difference in ambient pressure at two altitudes leads to different relief valve crack temperature and time. The average burning rate in Hefei is larger than that in Lhasa, and the estimated pressure effect factor is quite different for detailed pack conditions and varies within the range of 0.083‐1.39. The ambient pressure has a greater effect on the heat release rate and total heat release than the mass loss, and the effective combustion heat under the low pressure is lower than that in normal condition. This work can provide more comprehensive and useful data for the safety management of LIBs at low pressure environments. [ABSTRACT FROM AUTHOR]

Numerous accidents including fires and explosions occurring in transportation and storage of batteries enhance the need of studying the fire performances on batteries. In the current work, series bench-scale tests are conducted using a cone calorimeter to explore the fire behavior of lithium-ion battery. The influence of two key factors, namely state of charge (SOC) and incident external heat flux, on the battery fire characteristics is especially investigated. Combustion behavior, time to ignition (TTI), heat release rate (HRR) and fire risk assessment are obtained. The battery with higher SOC under high incident heat flux presents a fierce combustion process and higher surface temperature than the others. It is noteworthy that the time to ignition and time to peak HRR (TTP) decrease with the SOC, whereas the peak HRR (pHRR) and total heat release (THR) increase overall. On the whole, the increment of incident heat flux causes the decrease in TTI and TTP, while the pHRR and THR increase at higher incident heat flux. And the values of TTI agree well with the classical ignition model. Finally, the fire risk of battery with different SOCs under various incident heat fluxes is also highlighted. [ABSTRACT FROM AUTHOR]

As one of the most promising new energy sources, the lithium-ion battery (LIB) and its associated safety concerns have attracted great research interest. Herein, a comprehensive review on the thermal hazards of LIBs and the corresponding countermeasures is provided. In general, the thermal hazards of the LIB can be caused or aggravated by several factors including physical, electrical and thermal factors, manufacturing defect and even battery aging. Due to the activity and combustibility of traditional battery components, they usually possess a relatively high thermal hazard and a series of side reactions between electrodes and electrolytes may occur under abusive conditions, which would further lead to the thermal failure of LIBs. Besides, the thermal hazards generally manifest as the thermal runaway behaviors such as high-temperature, ejection, combustion, explosion and toxic gases for a single battery, and it can even evolve to thermal failure propagation within a battery pack. To decrease these hazards, some countermeasures are reviewed including the application of safety devices, fire-retardant additives, battery management systems, hazard warnings and firefighting should a hazard occur. [ABSTRACT FROM AUTHOR]

In order to have a better understanding of the fire behaviors of lithium-ion battery (LIB) and batteries pack under discharge, a series of fire tests were conducted. The fire behaviors of LIB were characterized by parameters including the flame photographs, surface temperature, mass loss, radiative heat flux and hydrogen fluoride (HF) mass flow. The results indicate that the number of batteries will affect the fire behaviors of LIB. Pack with larger number of LIB possesses a faster temperature rise, a higher peak heat flux and total radiative heat, leading to a quicker thermal runaway. Additionally, the discharging treatment also has a significant impact on LIB. It can accelerate the warming-up process, increase the fire risks of LIB, decrease the combustion efficiency of LIB and reduce the radiative heat. This is the result of the heat generation during discharge and the more reactive materials inside the battery under discharge. Besides, the HF generated during tests is discussed in the paper to note the toxicity of the released gases in LIB fire. [ABSTRACT FROM AUTHOR]

• The homogeneity of LIB including temperature distribution, temperature difference and voltage difference was investigated. • With the increase of cycle rate, the homogeneity of LIB would be worse. • Under abusive temperature environment, the homogeneity of LIB would be exacerbated. • With the aggravation of abusive environment, the severity of non-homogeneity could be deteriorated. A set of experiments were carried out at reduced and elevated temperatures (−10, −5, 0, 20, 50, 60 and 70 °C) to investigate the homogeneity of lithium-ion batteries under abusive temperature environment in combination with different cycle rates (1C, 2C, 3C and 4C). Based on the experimental results, we found that the surface temperature of battery increased gradually along the axial direction from anode to cathode indicating the position closer to cathode possessed larger internal resistance, therefore had larger heat generation. The homogeneity of battery deteriorated under large cycle rate exhibited as severer temperature rise and temperature difference. In addition, it was also found that the homogeneity of battery would be worse under abusive temperature environment by aggravating temperature rise, temperature difference and voltage difference. Compared to high temperature environment, low temperature environment would cause severer homogeneity. Moreover, the severity was exacerbated with the aggravation of abusive environment. [ABSTRACT FROM AUTHOR]

Thermal failure propagation is one of the most severe challenges for battery modules and it usually aggravates the thermal hazards, further resulting in serious accidents. This work conducted two groups of experiments to investigate the influence of discharging treatment and module shape on the thermal failure propagation of battery modules, where the triangle module, rectangle module, parallelogram module, line module, hexagon module, and square module were researched. Based on the results, it can be found that an evident domino effect existed on the thermal failure propagation of battery modules. Namely, the failure propagation process consisted of several phases and the number of phases depended on the shape of the module. Besides, it is indicated that discharging treatment on a battery module when it was in a high-temperature environment would aggravate its thermal failure propagation by bringing an earlier thermal failure, a quicker failure propagation, and a larger mass loss. Combining the results of safety and space utilization, it is revealed that the triangular module may be the best choice of battery module due to its smaller failure propagation speed and higher space utilization. [ABSTRACT FROM AUTHOR]

To have a better understanding of the thermal behaviors of lithium-ion batteries (LIBs) under discharge and overcharge conditions, some tests were conducted by a cone calorimeter. Several parameters were measured such as the battery surface temperature, voltage, the time to thermal runaway, the time to maximum temperature, heat release rate and total heat released. The results indicate that the lithium-ion battery will have obvious warming up during discharge owing to the reversible heat and irreversible heat. It was observed that the current treatment (discharge) has a significant influence on the thermal behaviors of LIBs. It can accelerate the warming up, result in earlier thermal runaway, and reduce the heat released. In addition, overcharge will make LIBs more unstable and easier to attain the thermal runaway. [ABSTRACT FROM AUTHOR]

Aging and thermal runaway are two significant reasons why lithium-ion batteries are struggling to become more widely available. Aging at different temperatures causes differences in the aging mechanism and thermal runaway behaviour of lithium-ion batteries. In this paper, four sets of commercial lithium-ion batteries are aged at 25 °C, 40 °C, 60 °C and 80 °C respectively for 100 cycles. Then the morphology and composition of the electrodes and separators are analysed in order to reveal the mechanism of changes in electrical performance and thermal stability due to aging at different temperatures. The differences in the decomposition products of the solid electrolyte intermediate (SEI) layer are an important factor in inducing changes in thermal runaway behaviour. At 60 °C, the accumulation of SEI decomposition products results in thicker SEI layers and shorter thermal runaway times. At 80 °C, the SEI decomposition products are heavily transformed into particles with a loose structure, generating a large amount of gas in the process, which further leads to the rupture of the aluminium-plastic film and the evaporation of the electrolyte, with a longer duration of thermal runaway and a lower maximum temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

Extensive utilization of lithium-ion batteries due to their high energy density and portable features necessitates urgent solutions to potential safety issues associated with thermal runaway (TR). In this work, a 3D mathematical model based on COMSOL Multiphysics coupling side reactions and complex heat transfer in a 3 × 3 battery pack was developed to investigate TR propagation process and the effect of a new anode material, annealed Ti 3 C 2 T z MXene. Reliability of the model was first verified by simulating experimental temperature evaluation of a traditional graphite-anode-based battery. Then a series of simulation scenarios using annealed-Ti 3 C 2 T z -MXene-based anodes were studied to reveal the impact of modified anode on TR propagation. Up to 22 TR propagation scenarios with varying spacings (0–2 mm) among batteries, heating powers (100–400 W), and SOCs (state of charge, 25%−100%) were examined. The results showed that TR of modified cell was delayed, implying better performance in preventing TR. The modified battery not only reduced the maximum temperature and temperature rising rate of TR, but also significantly inhibited TR propagation in pack. This study provides a theoretical basis for annealed Ti 3 C 2 T z MXene as a new anode material and suggests an alternative way for designing safer and higher energy density LIBs. [ABSTRACT FROM AUTHOR]

• Lengthwise thermal propagation indicating multi-layer propagation was studied. • Detailed propagation mechanism inside battery was studied with infrared imager. • The effects of heating modes on thermal failure propagation were investigated. Because of the multi-layer structure and the diversified connection modes of most battery modules, systematically investigating the thermal failure propagation principles and mechanisms of lithium-ion batteries is critical to provide early warnings and protection for thermal runaway. In this work, a series of experimental studies and mathematical deductions were conducted to investigate the propagation behavior of thermal failures within two types of cells under various heating modes, and their heat transfer mechanisms were analyzed. In general, the thermal runaway phenomenon in Li (Ni 1/3 Co 1/3 Mn 1/3) O 2 cells is more severe than that in LiCoO 2 cells. For different heating modes, lengthwise thermal failure propagation is more unlikely to occur in comparison with transversal thermal failure propagation; however, the former involves a more violent combustion. For different heating positions, heating near the positive pole results in the most violent phenomena. Additionally, a higher T max of 185.6 °C was obtained via middle heating in comparison with that obtained via heating on the poles. The temperature rising rate also varied, taking 1619, 1578, and 1699 s for the temperature to rise from 20 °C to 168.9 °C, 185.6 °C, and 173.4 °C through bottom, middle, and top heating, respectively. These phenomena were consequently ascribed to the different heat transfer rates along different directions inside the cells, including transversal/lengthwise propagation, and positive-pole-directional/negative-pole-directional propagation. These encouraging results may raise concerns about developing more precise and suitable surveillance and control measures to further enhance the thermal safety performance of cells/modules from both external and internal perspectives. [ABSTRACT FROM AUTHOR]

• Poorer cooling leads to a higher likelihood of thermal runaway. • Voltage platforms vary in different environments. • Overcharge increases R s , R SEI , R ct , and reduces lithium-ion diffusion coefficient. • Transition metals Ni, Co, Mn appear at the anode. Lithium-ion batteries (LIBs) are widely used, but there are few studies on their behaviour under different heat dissipation conditions. This paper comparatively investigates the electro-thermal behaviour of LIBs in air, quasi-adiabatic, and adiabatic environments during thermal runaway caused by overcharging. Our study reveals the internal mechanism of overcharging that leads to battery degradation. We find that the battery is more prone to thermal runaway under deteriorating heat dissipation conditions or with an increase in charging rate, but the state of charge (SOC) at the time of thermal runaway is not necessarily correlated with it. Regardless of the conditions, the battery develops a voltage plateau, and the temperature rises during this phase due to the decomposition reaction of the solid electrolyte interface (SEI) film or the electrolyte's reaction with the intercalated lithium. Inconsistent airflow and temperature can affect the battery's temperature and voltage during overcharging. Increased impedance, cathode destruction-including an increase in particle distance, dissolution and deposition of transition metals on the anode, and lithium precipitation on the anode's surface are significant reasons for the battery's degradation due to overcharge. These observations play a crucial role in the storage, transportation and use of LIBs in different environments. [Display omitted] [ABSTRACT FROM AUTHOR]

• New PCM filling methods with gradient thickness or conductivity were proposed. • PCM thickness optimization was studied via experiments and theoretical calculation. • A parameter of δ ct has been proposed for the PCM application in cylindrical batteries. • How the laying-aside time influenced cooling performance of PCM was studied. Phase change material (PCM) cooling, as an excellent option for ensuring safety via balancing heat distribution, has been widely used in the thermal management of lithium-ion battery. In this work, a simple PCM cooling structure has been designed. Then we systematically investigate its cooling behavior and the influence of several detailed factors on the performance, including the thickness and phase change temperature (PCT) of the PCM, as well as the laying-aside time during dynamic cycling. The experimental results show that a PCM module with a thickness of ∼10 mm presents the optimal cooling performance, consistent with the theoretical calculation, but the lower heat dissipation capability at the bottom of the battery should be taken into account when designing the PCM module. In addition, increasing the laying-aside time is also beneficial to enhancing the cooling efficiency, whereas the selection of the PCT is variable based on different specific applications and comprehensive requirements, particularly those targeting guaranteeing a higher capacity of the batteries. [ABSTRACT FROM AUTHOR]

The thermal runaway (TR) propagation of lithium-ion batteries (LIBs) is characterized by fast spread and violent reaction, which can cause a massive fire and even explosion. Blocking TR propagation of LIBs and cooling batteries are crucial to avoid the exacerbation of hazards. In this study, three porous materials (nickel foam, glass wool and nanoporous aerogel) were selected as barriers for LIBs and the corresponding blocking mechanism on TR propagation of LIBs were investigated. Based on this, water mist is released at the moment of thermal runaway of the lithium-ion battery and used to cool the battery. In this work, further research on the inhibition of thermal runaway and its propagation in lithium-ion batteries by porous materials and water mist is carried out. The results show that a good suppression effect can be obtained by a synergistic mechanism of pre-insulation and subsequent heat dissipation with the synergistic action of porous materials and water mist. This study also used the failure mode effects analysis (FMEA) method to evaluate the reliability of the inhibition methods and reveal the application effect of FMEA in the field of LIBs. • Glass wool is more suitable for inhibiting thermal runaway propagation. • Fine water mist and porous material have an excellent synergistic inhibition effect. • Porous materials are more suitable for blocking the vertically-arranged batteries. • FMEA can be used to assess the reliability and safety of battery management systems. [ABSTRACT FROM AUTHOR]