Thermal runaway in lithium-ion battery cells poses significant safety risks due to rapid heat generation and potential thermal propagation within a battery system. This study investigates the total heat released and the fraction of energy contained in gas and particles ejected during thermal runaway using a purpose-built calorimeter setup. The results show that the fraction of ejected heat is significantly influenced by the state of charge (SOC) and cell mass loss. Notably, the non-ejected heat was higher at 75% SOC compared to 100% SOC due to higher fraction of ejected heat at high SOC. This will have implications in thermal propagation scenarios. Additionally, the study compares the results with accelerating rate calorimetry tests, highlighting the limitations of the latter in measuring the total heat released during thermal runaway. The findings show the need for comprehensive testing methods that can improve thermal management and safety in battery systems.

The growing use of high-energy lithium-ion batteries for energy storage raises fire safety concerns, especially under high charge/discharge rates or external heating. This work presents an experimental investigation of different heating rates into the thermal runaway behavior of two large cell formats, a 64 Ah NMC pouch cell and a 100 Ah LFP prismatic cell, focusing on key parameters such as surface temperature evolution, propagation time across cell surfaces, total mass loss, gas composition and volume, and total heat release. The tests were conducted in inert atmosphere in a pressurised vessel. Different heating rates, from 4 °C/min to 24 °C/min, and a test with an initial 24 °C/min increase followed by a plateau, were employed for fully charged cells. Results demonstrated for both cells that heating rates influenced the time to reach thermal runaway, the onset temperature, and the maximum temperatures, but had a minor impact on the total gas volume. The gas composition from LFP prismatic cells was found to correlate with the studied heating rates. The findings provide valuable empirical data that support the development of predictive models for thermal runaway initiation and heat propagation in battery modules, contributing to improved safety strategies and system-level design for energy storage applications.

Accurate measurement of the heat release from a battery fire is vital for risk management, product development and construction of accurate models. Oxygen consumption calorimetry is the most common method for heat release measurements in experimental fire tests. The strength of the method is that it can be applied to unknown compositions of fuel with sufficient accuracy. Despite that this method is used to estimate heat release from battery fires, the method is subject to discussion. In this work, the method is studied in-depth, and potential errors are structured and quantified. Uncertainties associated with self-generated oxygen and internal heat generation, total gas release from the battery and impact on the heat release calculations, as well as the assumed E-factor (i.e., heat release per unit mass of oxygen consumed), are thoroughly discussed. For a Li-ion battery fire, it is concluded that oxygen consumption calorimetry will exclude internal heat generation and underestimate the total heat released from the external flaming fire by up to 10 %. In addition, high rate of combustion reactions can result in that the measured peak heat release rate is underestimated much more, up to 100 %. 

Self-heating during storage of biomass in piles causes material losses, leads to emissions to air, and poses a risk of fire. There are different techniques to assess a biomass material's propensity for self-heating, some of these are briefly reviewed. One of these techniques is isothermal calorimetry, which measures thermal power from materials and produces time-resolved curves. A recently developed and published test standard, ISO 20049-1:2020, describes how the self-heating of pelletized biofuels can be determined by means of isothermal calorimetry and how thermal power and the total heat produced during the test should be measured by isothermal calorimetry. This paper supports interpretation of the result obtained by isothermal calorimetry; the mentioned standard provides examples of peak thermal power and total heat but does not provide any assistance on how the result from isothermal measurements should be interpreted or how the result from measurements on different samples could be compared. This paper addresses the impact of different types of reactions, peak thermal power, total heat released (heat of reaction), activation energy, heat conductivity, and pile size on the temperature development in a generic pile of biomass. This paper addresses important parameters when the result from isothermal calorimetry is evaluated. The most important parameter, with respect to temperature development in large piles, was found to be the total heat released. It was also proposed that safe storage times, that is, the time until a run-away of the temperature in the pile, could be ranked based on the time to the peak thermal power.

Accelerated thermal ageing (ATA) coupled to mechanical testing is widely used to predict the lifetime of polymeric products. ATA implies that the mechanisms of ageing are the same at accelerated and service conditions, which may often not be the case. Hence, ageing closer to service conditions is of high importance, but require very sensitive tools. Therefore, a high sensitivity microcalorimetry (MC) method was applied here to assess if it can be a possible tool for lifetime/ageing prediction closer to service conditions. We chose to focus on a complex, yet commonly used, ethylene-propylene-diene terpolymer (EPDM) rubber. Arrhenius extrapolation of the heat flow data indicated two regimes at low and high temperature, with the former having the lower activation energy. The heat flow values measured by the MC revealed contributions from processes such as the melting of the antioxidant, its consumption at low temperature and the breakdown of residual peroxide. MC tests on the EPDM indicated a very low degree of oxidation appearing above 100 °C, too low to be observed with infra-red spectroscopy (FTIR), but noticeable with MC. The high sensitivity of the MC techniques enabled detection of early signs of polymer degradation/ageing and other thermally activated processes that take place at or close to service temperatures (such as those in nuclear power plants). The MC tests were combined with other techniques, such as scanning electron microscopy/energy dispersive X-ray spectroscopy, gas chromatography techniques, differential scanning calorimetry and FTIR to further understand the degradation mechanisms. © 2023 The Authors

The increasing use of lithium-ion batteries requires further efforts in safety testing and evaluation. It is of utmost importance that the effects of different test conditions are understood, particularly for validation of computer models. While plenty of data from thermal runaway tests are available in literature, few are from large test series. The missing systematic approach to evaluate the impact of different test conditions implies uncertainty when comparing test results. In addition, the fast pace in cell development, including an increasing utilization of larger cells, necessitate the validation of previously published results. This work presents thermal runaway data from 37 tests on one type of large format prismatic lithium-ion cell (157 Ah). The tests are conducted in a closed pressure vessel with inert atmosphere as well as in an open setup below an exhaust collector hood. Further, six different thermal runaway trigger methods are employed as well as four different states of charge. Emphasis is put on the gases produced, a key aspect for safety evaluation. The results are compared with literature data and a new modified method is proposed for calculating the characteristic venting rate in a closed pressure vessel. It is concluded that the trigger method affects the gas production rate, mass loss, and maximum temperature of the cell as much as its state of charge. The large cell format potentially impacts the specific total gas production and enhances the effects of different trigger methods, but has a small impact on other evaluation parameters. No significant differences were observed in the test results due to the different test setups, apart from differences due to potential combustion of the released gases in ambient atmosphere. 

Microencapsulated phase-change-materials (PCMs) incorporated in cementitious grout can be used as a source of energy in an underground thermal energy storage system. Differential scanning calorimetry (DSC) is a widely used technique to measure the latent heat or specific heat of PCM-embedded cementitious materials. However, using milligram sample sizes (as required by DSC) of a cementitious material fails to represent the actual scale of cementitious components. This is the reason why, in the present paper, non-isothermal heat conduction microcalorimetry (MC) was evaluated as a tool for determining the thermal properties of PCM-embedded grout as well as pure PCM (three PCMs were used). An MC experimental protocol (using both single and 5–6 temperature cycles) was developed and used to measure latent heat and melting and crystallization temperatures, which were in good agreement with those reported for pure PCMs by the producers. In addition, the specific heats of the PCM-containing grout also agreed with measurements using the hot disk technique. Overall, the results show that the MC technique can be used as a potential standard method in determining thermal processes in complex systems, such as in PCM-embedded cementitious systems, where a large sample size is needed to represent the material.

Self-ignited fires at municipal solid waste (MSW) storage sites are relatively common. The minimization of the phenomenon of self-heating in the waste can reduce the risks for smouldering combustion. The purpose of this work was to develop a method that can be used to measure and characterize the heat production in MSW. The method is based on isothermal heat conduction microcalorimetry (IMC). The heat production in MSW was determined based on sampling from two sites in two different geographical locations in Sweden. Both the original waste and milled/homogenised waste were tested. The heat production was measured at different temperatures together with gas analysis using micro-gas chromatography. The activity in the waste, in terms of its heat flow, increased when the temperature increased up to 60 °C and decreased at higher temperatures, e.g., 70 and 80 °C. The consumption of oxygen and the production of carbon dioxide, together with the heat production, indicated that aerobic metabolism was responsible for the heat production. This is further strengthened by the marginal heat production observed for ultraviolet treated waste. The results showed that IMC is a valuable tool for characterising the self-heating in municipal and industrial waste. © 2021, The Author(s).

Online measurements of the raw gas composition, including tars and water, during biomass gasification provide valuable information in fundamental investigations and for process control. Mainly consisting of hydrocarbons, tars can, in principle, be measured using Fourier transform infrared (FT-IR) spectroscopy. However, an instrument subjected to raw gas runs the risk of condensation of tars on optical components and subsequent malfunction. Therefore, an external cell, heated to at least 400 ℃, has been designed to ensure that tars remain in the gas phase during FT-IR measurements. The cell was used for on-line FT-IR measurements of permanent gases (CO, CO2, CH4), water, and tars during the operation of a lab-scale downdraft gasifier using wood pellets, bark pellets, and char chips. Based on calibration, the measurement error of permanent gases was estimated to be 0.2%. Concentrations evaluated from spectral signatures of hydrocarbons in tar are in good agreement with results from solid-phase adsorption measurements and correlated well with operational changes in the gasifier. 

Gasification of biomass results in release of tar and alkali metal compounds that constitute a significant challenge to the optimization of the gasification process. Here we describe on-line measurements of alkali, condensable tar, and particle concentrations in product gas from a 2-4 MWth dual fluidized bed gasifier, with the aims to characterize typical concentrations and contribute to the understanding of alkali-tar interactions. The influence of bed material, additives, and operational parameters on the concentrations is investigated. Alkali concentrations are measured with a surface ionization detector, and particle and tar concentrations are determined using aerosol measurement techniques. The gasification of wood chips using quartz or olivine as bed material results in an alkali concentration of 30-250 mg m-3, and the observed alkali levels are consistent with a significant release of the fuel alkali content. Addition of ilmenite to a quartz bed and additions of K2SO4 and K2CO3 to an olivine bed influence both alkali and heavy tar concentrations. The additions result in changes in alkali concentration that relaxes to a new steady state in tens of minutes. The concentration of condensable tar is lower for the olivine bed than for the quartz bed, and tends to decrease when potassium or sulfur is added. The concentration of condensable tar compounds is anticorrelated with the alkali concentration when a quartz bed is used, while no clear trend is observed with an olivine bed. An increase in steam flow rate results in a substantial decrease in heavy tar concentration from a quartz sand bed, while the alkali concentration increases slightly with increasing flow rate. This is in contrast to the alkali concentrations observed when using an activated olivine bed, where concentrations are higher and tend to decrease with increasing steam flow rate. The study confirms that several primary methods are available to optimize the alkali and tar behavior in the gasifier, and suggests that on-line monitoring is needed to systematically change the operational conditions and to study the underlying processes.