Accelerating Rate Calorimetry Research Articles

Failure and hazard characterisation of high-power lithium-ion cells via coupling accelerating rate calorimetry with in-line mass spectrometry, statistical and post-mortem analyses

Lithium-ion battery safety continues to be an obstacle for electric vehicles and electrified aerospace. Cell failure must be studied in order to engineer improved cells, battery packs and management systems. In this work, the thermal runaway of commercially available, high-power cells is studied, to understand the optimal areas to develop mitigation strategies. Accelerating rate calorimetry is coupled with mass spectrometry to examine self-heating and the corresponding evolution of gases. A statistical analysis of cell failure is then conducted, combined with post-mortem examinations. The methodology forms a robust assessment of cell failure, including the expected worst- and best-cases, and the associated real-world hazards. Cells produce a highly flammable, toxic gas mixture which varies over the course of self-heating. Failure also produces particulate matter which poses a severe health hazard. Critically, the onset of self-heating is detectable more than a day in advance of full thermal runaway. Likewise, voltage drops and leaks are detectable prior to venting, highlighting the potential for highly effective early onset detection. Furthermore, the behaviour of the cap during thermal runaway indicates that ejection of material likely reduces the chance of thermal runaway propagation to neighbouring cells. These findings also emphasise that research must be conducted safely.

Preparation of Spherical HMX/DMF Solvates, Spherical HMX Particles, and HMX@NTO Composites: A Way to Reduce the Sensitivity of HMX.

To reduce the sensitivity of HMX (HMX = high-melting explosive-cyclotetramethylenetetranitramine), spherical HMX/DMF (DMF = dimethylformamide) solvates, spherical HMX particles, and HMX@NTO (NTO = 1,2,4-triazol-5-one) composites are prepared by crystallization. The structure and performance of spherical HMX crystals, HMX particles, and HMX@NTO composites are characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, accelerating rate calorimetry, and mechanical sensitivity test. The results show that the space group of the spherical HMX/DMF solvate is R̅3c with the lattice parameters of a = 15.9159(4) Å, b = 15.9159(4) Å, and c = 30.5136(8) Å. The non-isothermal stability and adiabatic thermal stability of HMX/DMF solvates are similar to those of HMX particles. The non-isothermal stability of HMX@NTO composites is lower than that of NTO and HMX particles, while the adiabatic thermal stability of HMX@NTO composites is higher than that of NTO but lower than that of HMX particles. The mechanical sensitivities of spherical HMX/DMF cocrystals, spherical HMX particles, and HMX@NTO composites are lower than that of raw HMX. This study can provide some guidance for desensitizing HMX and other energetic materials.

Change of safety by main aging mechanism – A multi-sensor accelerating rate calorimetry study with commercial Li-ion pouch cells

The safety of Li-ion batteries is the most critical of many important characteristics and must be carefully considered. However, depending on the aging conditions, safety of batteries can change drastically. We had recently introduced ARC-MS as a new tool for safety investigations, which is an updated accelerating rate calorimeter (ARC) combined with a mass spectrometer (MS). Additionally, our ARC-MS setup is equipped by seven more low cost sensors (temperature, voltage, resistance, audio, strain, and transmitted and reflected ultrasound). In this paper, the dependence of safety on the dominant aging mechanism as a function of aging temperature, and state-of-health (SOH) is investigated on the example of 3.3 Ah commercial pouch cells. The ambient temperature during aging has a strong influence on the dominant aging mechanism (Li plating or SEI growth) of this cell as shown by Arrhenius plots of the aging rate and Post-Mortem analyses (ICP-OES, SEM, EDX, Hg porosimetry, STA) of aged cells. Our in-depth evaluation shows that different sensors can provide indications of safety relevant events (onset of swelling, onset of self-heating, cell venting, stable exothermic reactions, separator melting, and thermal runaway) in the cells independently. Combining these low-cost sensors might be a solution for detection of unsafe cells in applications.

Investigating the Thermal Runaway Behaviour of Fresh and Aged Large Prismatic Lithium-Ion Cells in Overtemperature Experiments

When using lithium-ion batteries (LiBs) with nickel-rich cathodes, safety issues such as thermal runaway (TR) propagation must be considered. To design safe LiBs, effective countermeasures against TR propagation must be developed. For this purpose, knowledge about the TR behaviour, especially the TR onset temperature, of fresh and aged lithium-ion cells is required. Therefore, the aim of this work is to investigate the TR behaviour of several fresh and aged lithium-ion cells with different cathode chemistries in overtemperature tests using an oven test setup to determine changes in the TR behaviour due to cyclisation. For the investigation of the TR behaviour of large format lithium-ion cells, the oven test setup turns out to be an effective alternative to the accelerating rate calorimetry test. Analysing the results shows that the initial TR temperature after cyclisation for one cell chemistry is significantly decreased due to the failure of one cell component. In addition, from a series of tests and the measured TR onset temperatures it can be deduced that an underlying probability distribution should be taken into account when designing safe LiBs.

A Safer High-Energy Lithium-Ion Capacitor Using Fast-Charging and Stable ω-Li3 V2 O5 Anode.

Lithium-ion capacitors (LICs) are flourishing toward high energy density and high safety, which depend significantly on the performance of the intercalation-type anodes used in LICs. However, commercially available graphite and Li4 Ti5 O12 anodes in LICs suffer from inferior electrochemical performance and safety risks due to limited rate capability, energy density, thermal decomposition, and gassing issues. Here a safer high-energy LIC based on a fast-charging ω-Li3 V2 O5 (ω-LVO) anode with a stable bulk/interface structure is reported. The electrochemical performance, thermal safety, and gassing behavior of the ω-LVO-based LIC device are investigated, followed by the exploration of the stability of the ω-LVO anode. The ω-LVO anode exhibits fast lithium-ion transport kinetics at room/elevated temperatures. Paired with an active carbon (AC) cathode, the AC||ω-LVO LIC with high energy density and long-term endurability is achieved. The accelerating rate calorimetry, in situ gas assessment, and ultrasonic scanning imaging technologies further verify the high safety of the as-fabricated LIC device. Theoretical and experimental results unveil that the high safety originates from the high structure/interface stability of the ω-LVO anode. This work provides important insights into electrochemical/thermochemical behaviors of ω-LVO-based anodes within LICs and offers new opportunities to develop safer high-energy LIC devices.

Deep eutectic solvent electrolytes based on trifluoroacetamide and LiPF6 for Li-metal batteries

New generation lithium batteries require better performances, improved safety, and sustainability. Better performances can be obtained with lithium anodes and high-voltage cathodes, which in turn pose more pressure on the electrolyte stability, which is mandatory for safety. Deep Eutectic Solvents (DESs) are promising components for safer and more environmentally sustainable electrolytes. We investigate the physico-chemical properties of DESs made with 2,2,2-trifluoroacetamide (TFA) and LiPF6. The best composition is tested against Li metal and two cathode active materials: LiFePO4 (LFP) and high voltage LiNi1-x-yMnxCoyO2 (NMC). We obtain good electrochemical performance in a Li-metal cell with LFP. Accelerated rate calorimetry shows improved thermal stability of the Li|DES|NMC cell with respect to a commercial liquid electrolyte.

Understanding of thermal runaway mechanism of LiFePO4 battery in-depth by three-level analysis

The complex chemical composition and material interactions of lithium-ion batteries challenge the in-depth understanding of thermal runaway reactions and failure mechanisms. In this study, detailed analysis and implementation have been made from three levels to further explain the thermal failure mechanism, from material interactions to cell-level experiments and applications. The LiFePO4 thermal runaway mechanism is put forward to characterize exothermic peaks from differential analysis of differential scanning calorimetry (DSC) and Accelerating Rate Calorimetry (ARC) data. Furthermore, the development, parameterization, and application of the thermal runaway prediction model are also discussed. Multi-heating rate data is a prerequisite to kinetic analysis and modeling work and provides valuable data set for LiFePO4 thermal failure. And the unraveled mechanism is believed to provide a profound understanding of the thermal failure mechanism, strengthening interactions between material characterization and thermal runaway modeling.

An investigation on thermal runaway behaviour of a cylindrical lithium-ion battery under different states of charge based on thermal tests and a three-dimensional thermal runaway model

A significant risk for lithium-ion batteries (LIBs) is fire and explosions caused by thermal runaway (TR). A TR model for LIBs with various states of charge (SOCs) can help design safer battery modules. In this work, the TR mechanism of a commercial Li[Ni5Co2Mn3]O2/graphite 18650 type cylindrical battery with various SOCs has been investigated through differential scanning calorimetry (DSC) tests on the single and mixed components. Then, a three-dimensional (3D) TR model is developed to predict the battery TR behaviours under different SOCs. This model fits well with the accelerating rate calorimetry (ARC) test results of the batteries with various SOCs. Furthermore, the validated model and ARC experiment results are employed to investigate the TR mechanism of different SOC batteries. The results show that the reaction onset temperature for cathode-anode and anode-electrolyte roughly advances as the SOC increases and the reaction enthalpy of the cathode-anode, anode-electrolyte and cathode increases with the increase of SOC. Cathode-anode, anode-electrolyte are the main heat generation in the process of battery TR, and their proportion of heat generation will decrease with the decrease of SOC.

Impact of safety valves on thermal runaway characteristics of 21 700-size lithium-ion cells.

To demonstrate the impact of safety valves on the thermal runaway characteristics of 21 700-size lithium-ion cells, this work carries out a series of abusive tests including over-heating tests, accelerating rate calorimetry (ARC) tests and overcharge tests; in the meantime, the impact of safety valves on cells with various states of charge (SOC) and states of health (SOH) is unveiled accordingly. Safety valves have a great impact on the thermal runaway behavior of 21 700-size cells, which effectively restrains the thermal runaway risks and hazards of cells under the over-heating conditions. The presence of a safety valve could even prevent a cell from the thermal runaway induced by overcharge. A cell with a larger SOC and/or a lower SOH is prone to the thermal runaway occurring, with an earlier thermal runaway, a lower temperature to thermal runaway and a lower mass loss demonstrated. Besides that, it is found that the advancement ratio of the time to thermal runaway between cells with and without a safety valve was maintained at around 15%; that is, the existence of a safety valve is helpful to delay the encounter of thermal runaway by ∼15%.

X-Ray Computed Tomography for Failure Mechanism Characterisation within Layered Pouch Cells: Part I

The assessment of lithium-ion battery (LIB) safety is a multiscale challenge: from the whole-cell architecture to its composite internal three-dimensional (3D) microstructures. Substantial research is required to standardise failure assessments and optimise cell designs to reduce the risks of LIB failure. In this two-part work, the failure response of a 1 Ah layered pouch cell with a commercially available nickel manganese cobalt (NMC) cathode and graphite anode at 100% state of charge (SOC) (4.2 V) is investigated. The mechanisms of two abuse methods: mechanical (by nail penetration) and thermal (by accelerating rate calorimetry) are compared by using a suite of post-mortem analysis methods.

Thermal and Electrochemical Analysis of Thermal Runaway Propagation of Samsung Cylindrical Cells in Lithium-ion Battery Modules

Thermal runaway propagation analysis at the module and cell level was performed using the Samsung 30Q 18650 cylindrical cells. Measurements such as cell enthalpy, maximum thermal runaway temperature, and thermal runaway onset and initiation temperatures were collected and shown to be consistent by means of accelerated rate calorimetry (ARC). This study showed, using the module billet as a thermal runaway propagation mitigation strategy, the cell energy was successfully absorbed during a failure event and prevented thermal runaway propagation from between cells. However, the module level tests showed average maximum temperatures that were 229 °C higher than the average maximum temperatures in the cell level tests, showing the importance of evaluating both the cell level thermal runaway response and the module level response, as they can be different. This work shows the differences between cell TR and module level TR and an effective mitigation strategy based on effective spacing and thermal mass.

Investigation on safety characteristics of high-nickel lithium-ion cells with anode partially doped by silicon oxide

Considering the prospect of lithium-ion cells with graphite + SiOx anode and the fact that there is rare literature concerning the safety features of graphite + SiOx based cells, this work performed an experimental investigation on the safety characteristics of Li(Ni0.8Mn0.1Co0.1)O2/(graphite+10%SiOx) cells with different states of charge (50% SOC, 75% SOC and 100% SOC). Besides that, the impact of two well-known electrolyte additive components, i.e. 2% vinylene carbonate+1% ethylene sulfate (2VC1DTD) and 2% fluoroethylene carbonate+1% lithium difluorophosphate (2FEC1LFO) on the safety characteristics of cells was also revealed. The safety characteristics of Li(Ni0.8Mn0.1Co0.1)O2/(graphite+10%SiOx) cells seem to be worse than Li(Ni0.8Mn0.1Co0.1)O2/graphite cells with the same capacity, the former illustrates larger the maximum temperature rise rate in accelerating rate calorimetry (ARC) tests (16,651 vs. ∼6000 °C/min). Similar to the other types of lithium-ion cells, the safety features of the cells with graphite + SiOx anode enhance with the decrease of cell SOC in typical safety tests. 2VC1DTD and 2FEC1LFO are unable to effectively improve the safety performance of cells under abusive conditions, which might result from the fact that the electrolytes addicted with 2VC1DTD and 2FEC1LFO are flammable as well, and 2VC1DTD and 2FEC1LFO cannot restrain the reactivity between anode materials and electrolytes.

Study on Thermal Runaway Behavior of Li-Ion Batteries Using Different Abuse Methods

Thermal runaway (TR) and the thermal runaway propagation (TRP) of Li-ion batteries can lead to safety incidents and cause explosion or fire accidents. Therefore, TR is a critical issue for the thermal safety of Li-ion batteries. In this study, the TR and TRP behavior of Li-ion batteries using different abuse methods (nail penetration, side heating, and overcharge) was investigated experimentally. First, the Extended Volume Accelerating Rate Calorimetry (EV-ARC) test was performed using the cell with an internal implantation thermocouple for a comparative study. Three abuse methods were used to induce TR and TRP for the cells and modules. At the cell level, the maximum temperature inside the cell under the EV-ARC test, nail penetration, and side-heating abuse was 994.8 °C, 964.3 °C, and 1020 °C, respectively. The thermocouple inside the cell under the overcharge abuse test was broken, and the experimental phenomenon indicated that the cell was most severely damaged under the overcharging abuse test. At the module level, the TRP behavior using the three abuse methods was different than in the first two TR cells, while the behavior of the other cells was similar. It was evidenced that TRP triggered by the overcharge abuse was the most hazardous, followed by the side-heating abuse, and lastly, the nail-penetration abuse was the least.

Is your ARC data misleading? Heat-transfer limitations and reaction rate underestimation in Accelerating Rate Calorimetry

Accelerating Rate Calorimetry (ARC) is a widely used adiabatic calorimetry technique to evaluate thermo-kinetics of hazardous chemical reactions. Most ARCs rely on measurement of temperature at the external wall of the ARC sphere to evaluate the temperature rise rate, and therefore exothermic reaction rate. We report large temperature gradients between the center and wall for a granulated solid sample tested using an un-stirred ARC that leads to varying spatiotemporal temperature profiles. Such gradients were found to be significantly lowered in organic liquid samples, enabling classifying some granulated solid samples as heat transfer-limited systems. This study reveals that such temperature gradients obviate estimation of representative exothermic reaction rate, manifesting in hazard underestimation through erroneous pressure and apparent conversion profiles. Next, the addition of an inert was demonstrated to reduce the magnitude of such gradients, thereby enabling relatively accurate hazard assessment and offering a potential solution. Lastly, several strategies are outlined to allow researchers to identify and mitigate the influence of gradients during hazard assessment. Researchers must be cognizant of the potential for gradients when analyzing and interpreting ARC data for thermo-kinetic modeling and hazard evaluation. During hazard evaluation, researchers should confirm that no significant gradients exist or find ways to de-sensitize their hazard assessment parameters if gradients exist and cannot be minimized.

Linking Thermal Runaway and Cycling Degradation of Lithium-Ion Batteries Using Multi-Scale X-Ray Imaging

To meet the increasing energy demands of portable devices and electric vehicles, high-nickel lithium-ion cathode materials with the general formula Li(NixMnyCoz)O2 (NMCXYZ) have been extensively researched. Currently, NMC811 is used commercially due to its high capacity and low cobalt content. However, capacity fade is still a prominent issue, with a variety of degradation mechanisms responsible. Of particular interest is secondary particle cracking, where the stress-strain effect of c-parameter expansion in the NMC crystal lattice leads to fractures. Boundaries between the primary particle grain that make up the secondary particle structure act as nucleation points for particle cracking. The exposed surface then reacts with the liquid electrolyte, leading to oxygen evolution and capacity loss. Single-crystal materials have shown promise as a method of improving cycle life, as the lack of agglomerated primary grains appear to make the monocrystalline particles more resilient to the mechanical strain of expansion during charging1.In parallel with the cycle life concerns, attention over battery safety continues to increase as instances of catastrophic battery failure are publicised across the world. While the specific steps that lead to battery thermal runaway have been extensively researched, the safety and thermal stability of degraded cells remains a scarcely investigated topic2. To that end, the goal of this work is to characterise the safety properties of different NMC morphologies, and study how charge-discharge cycling affects the thermal stability of these materials.In this work, we have combined accelerating rate calorimetry (ARC) with lab-based, post-mortem macro, micro and nano X-ray CT to observe the influence of cell structure on thermal runaway of NMC811 pouch cells with single-crystal and polycrystalline cathode materials in both the pristine and aged state. The results presented show that when pristine, the larger surface area of single-crystal materials provides more reaction sites and leads to a lower self-heating onset and thermal runaway initiation temperature compared to polycrystalline, suggesting a lower thermal stability. However, as polycrystalline particles break up during thermal runaway, the fragments create fresh surface to react with the electrolyte and continue the series of exothermic reactions, leading to a higher peak temperature. Macro-CT has revealed how the wound jellyroll structure of the cell focuses the force of the explosion through the flat sides of the cells, possibly increasing the likelihood of failure propagation. It has also been observed that the polycrystalline materials show a greater material ejection out from the centre of the cell, reinforcing the findings from the ARC investigations that although polycrystalline cells are more thermally stable initially, the peak temperatures produced during catastrophic failure are higher due to particle fracture. Micro and nano-CT are used to probe this idea further, revealing that polycrystalline particles show significant damage and fracturing during failure, whereas single-crystal materials remain largely intact.Both polycrystalline and single-crystal morphologies were cycled to 80% capacity retention, with EIS and diagnostic cycles used to identify prevalent degradation modes for both particle structures. As previously found, the single-crystal cells showed superior cycle life to the polycrystalline materials3. The same combination of ARC and X-ray CT was then applied to aged cells, where it was found that aged cells show lower thermal stability than their pristine counterparts.Overall, this work aims to build understanding of the interplay between material structure, safety and degradation of nickel-rich cathodes, with the goal of informing future material development to produce batteries that are safer throughout their lifetimes. G. Qian et al., Energy Storage Mater., 27, 140–149 (2020) https://doi.org/10.1016/j.ensm.2020.01.027.X. Feng et al., Energy Storage Mater., 10, 246–267 (2018) https://doi.org/10.1016/j.ensm.2017.05.013.D. Ren et al., eTransportation, 2, 100034 (2019) https://doi.org/10.1016/j.etran.2019.100034.

Utility of Deactivation By Saltwater Immersion for End-of-Life Processing of Lithium-Ion Cells

Recycling of lithium-ion batteries is envisioned to become an important aspect of ensuring future access to the critical materials used in lithium-ion batteries (LIB) (1). This is particularly true for nickel, cobalt, and lithium, which have experienced extreme price fluctuations and projections of supply shortfalls in the near future. Current recycling efforts are focused on recovering the most valuable components like those mentioned above, however emerging efforts have also demonstrated the feasibility of recovering intact active materials and even direct recycling of electrode composites. All recycling efforts have a common logistical challenge – cells and batteries must be aggregated at recycling facilities once they reach the end of their useful life. This aggregation also introduces safety challenges due to the possibility for residual or stranded energy in lithium-ion cells. A 2021 report from the United State Environmental Protection Agency (US EPA) highlighted this issue, reporting that 89% of 245 fires reported from U.S. materials recycling facilities between 2013-2020 were attributed to lithium metal or lithium-ion batteries (2). Energetic failures including thermal runaway has been reported in lithium-ion cells of various chemistries at states-of-charge (SOC) as low as 15% in response to thermal abuse, and cells experienced temperatures above 100 °C in response to external short-circuiting at SOC as low as 30% (3). Saltwater immersion has been reported as an effective method to remove residual energy from lithium-ion cells (4) (5) (6). However, most efforts have focused on the discharge rate of various solution conditions as determined by cell voltage, and offer limited insight into safety impacts and the recoverability of active materials. Qualitative descriptions of corrosion during saltwater immersion, which can be severe, have also been reported in academic literature. This presentation will focus on demonstrating the role of various immersion solution parameters (e.g. solute and other additives, temperature) on the efficacy of removing residual energy from LIB as measured by electrochemical testing of representative systems as well as commercial lithium-ion cells. Impacts of corrosion and cell safety will be discussed through materials analysis (X-ray Photoelectron Spectroscopy, Scanning Electron Microscopy + Energy Dispersive X-ray Spectroscopy) and battery calorimetry (Accelerating Rate Calorimetry). Recycling of Lithium-Ion Batteries—Current State of the Art, Circular Economy, and Next Generation Recycling. Neumann, J, et al. 2102917, 2022, Advanced Energy Materials. United States Envrionmental Protection Agency. An Analysis of Lithium-ion Battery Fires in Waste Management and Recycling. 2021. EPA 530-R-21-002. Safety of Lithium-Ion Cells and Batteries at Different States-of-Charge. Tapesh, Joshi., et al. 140547, 2020, Journal of the Electrochemical Society, Vol. 167. Pretreatment options for the recycling of spent lithium-ion batteries: A comprehensive review. Yu, D, et al. 107218, 2021, Minerals Engineering, Vol. 173. A comprehensive review on the pretreatment process in lithium-ion battery recycling. Kim, S, et al. 126329, 2021, Journal of Cleaner Production, Vol. 294. Aqueous solution discharge of cylindrical lithium-ion cells. Shaw-Stewart, J, et al. e00110, 2019, Sustainable Materials and Technologies, Vol. 22. Figure 1

Role of Heat Release from Inter-Electrode Chemical Crosstalk in Thermal Runaway Propagation Characteristics of Lithium-Ion Battery Modules

While lithium-ion batteries are continually increasing in energy and power density, thermal safety still remains a significant concern. In some thermal abuse scenarios, thermal runaway can be triggered by the exothermic reactions from inter-electrode chemical crosstalk between the cathode and the anode without an internal short circuit. Under these circumstances, the thermal runaway temperature is lower than the separator's thermal shrinkage temperature, implying that the cell's catastrophic thermal runaway occurs without a large-scale short circuit produced by separator failure. These cell failures must be managed such that the neighboring cells in a battery module are not affected, a phenomenon known as thermal runaway propagation. In the present work, we employed a high-resolution cell-level thermal runaway model constructed from the accelerating rate calorimetry data of a commercial Li-ion cell to characterize the cell-to-cell thermal runaway propagation behavior for a basic square arrangement of lithium-ion battery module connected by tabs. We determined safe practices under the effects of different ambient conditions, inter-cell spacing, trigger cell location, and external heating power. Additionally, we have identified the critical pathways for the thermal runaway propagation in the battery module and quantified their statistical distribution in terms of the thermal runaway propagation speed, heat release from exothermic reactions, and heat dissipation to the surroundings. The findings from the study are believed to be of immediate relevance for the safer design of lithium-ion battery packs.

Establishing the Interface Layer on the Pentaerythritol Tetranitrate Surface via In Situ Reaction.

Pentaerythritol tetranitrate (PETN) was coated by tannic acid (TA), polydopamine (PDA), and melamine-formaldehyde (MF) resins via in situ reaction to prepare PETN@TA, PETN@PDA, and PETN@MF microcapsules for reducing sensitivity and enhancing thermal stability of PETN. The coating effects of TA, PDA, and MF shells on PETN surfaces are characterized by scanning electron microscopy and atomic force microscopy. The structures of PETN@TA, PETN@PDA, and PETN@MF microcapsules are characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and Fourier-transform infrared spectra. The performances of PETN@TA, PETN@PDA, and PETN@MF microcapsules are characterized by differential scanning calorimetry, accelerating rate calorimetry, explosion point, vacuum deflation volume, and mechanical sensitivity. The study results show that TA, PDA, and MF shells can coat the PETN surface well. Compared with pure PETN, the explosion point has an increase while the vacuum deflation volume and mechanical sensitivity have a decrease for PETN@TA, PETN@PDA, and PETN@MF microcapsules, illustrating that the safeties of PETN@TA, PETN@PDA, and PETN@MF microcapsules are enhanced. In addition, the initial decomposition temperature (T0) and peak decomposition temperature (Tp) of PETN@TA, PETN@PDA, and PETN@MF microcapsules have a slight increase, demonstrating that the thermal stabilities of PETN@TA, PETN@PDA, and PETN@MF microcapsules are better than that of pure PETN. The obtained method can provide some guidance for the desensitizing of other energetic materials with high sensitivities.

Experimental study on non-isothermal oxidative characteristics and kinetics of methane in accelerating rate calorimetry tests

The non-isothermal oxidative characteristics and kinetics of natural gas have important effects on performance of gas reservoir combustion, which directly determines temperature distribution, playing a significant role in hydrogen generation boundary. In this paper, the non-isothermal oxidation of methane, as main component of natural gas, is in depth analysis, which is rarely studied. At first, the non-isothermal oxidative characteristics at different pressure, oxygen/methane ratio, and debris were investigated by accelerating rate calorimetry (ARC). Afterwards, the non-isothermal oxidation kinetic parameters were analyzed and calculated. The difference of onset self-exothermic, ignition temperature, and kinetics parameters under different conditions were extraordinarily emphasized, aiming achieving successful and stable gas reservoir combustion for high efficiency hydrogen production. The results indicated that there is no even self-exothermic phenomenon at depleted reservoir condition (7.1–9.8 MPa and 100–150 °C), and the minimum starting self-exothermic temperature ignition temperature of methane oxidation are 220.6 °C and 312.7 °C. The pressure did not have effect on oxidation temperature in methane oxidation while did in catalytic oxidation. It was observed that rock debris has catalytic effect on methane oxidation suggested by obviously lower onset self-exothermic temperature detected and significantly smaller activation energy calculated in oxidation process of methane with debris. Moreover, the oxidation reaction rate of methane with debris is lower than that of methane, assisting more methane undergoes a more thorough HTO reaction conducive to combustion and decreasing the possibility of explosion in the injection air ignition process. According to the results obtained by ARC tests, we suggested that the near-wellhole places of gas reservoirs should be better heated over 313 °C for successfully achieving stable combustion. Some new knowledge got from this study is conducive to achieve rapid and stable combustion, thus achieving high-efficiency hydrogen generation.

Thermal inertias and confidence intervals in the determination of activation energy by isoconversional methods applied for accelerating rate calorimetry

Isoconversional method has been preliminarily applied in accelerating rate calorimetry (ARC) and achieved good results. However, it is a new subject and needs to be explored in depth. In this study, the Friedman and the Vyazovkin methods were applied to investigate the influences of thermal inertia on the activation energy estimation of the single-step reaction and autocatalytic reaction. The accuracy and adaptability of the two kinetic methods are compared, and the confidence intervals for activation energy estimated by the Friedman and the Vyazovkin methods are evaluated based on the corrected Student's distribution and F distribution. Finally, the validity of the simulation result is verified by the experiments. The results show that the sets of thermal inertia have different effects on the estimation of activation energy in single-step reaction and multi-step reaction, and the activation energies in multi-step reaction change obviously under different sets of thermal inertia. The thermal inertia increment of 0.03-0.5 and the Vyazovkin method are recommended. This study is helpful to promote the development of isoconversional methods applied for ARC data.