This paper introduces the current status of standards related to the safety of large-scale batteries, especially international standards, which are expected to become widespread, and describes the actual methods of thermal propagation test, which has been recognized for its importance in recent years. In addition, the problems of safety degradation due to battery operation are pointed out, and it is mentioned to apply laser irradiation method for safety evaluation.

In lithium-ion batteries, there is a hypothesis that electrolyte is reduced at anodes, generating a reductive gas, which then cross-leaks to cathodes. This study presents a comprehensive density functional theory (DFT) analysis of the interactions between reductive gases—acetylene (C₂H₂) and ethylene (C₂H₄)—and lithium nickel oxide (LNO) cathode surfaces across varying states of charge (SOC). Adsorption behavior, charge transfer, and structural effects were systematically evaluated, revealing that gas adsorption intensifies above 60% SOC, particularly at Ni sites, promoting Ni/Li cation exchange and structural destabilization. Surface facet orientation significantly influences adsorption energies, with higher SOCs exacerbating oxygen evolution due to weakened O-(Ni/Li) bonds and strengthened O-C₂H₂ interactions. Oxygen vacancy formation becomes energetically favorable under high-voltage conditions, further accelerating degradation. Incorporation of Mn and Co into the cathode surface mitigates gas-induced damage by lowering adsorption energies. Protective coatings (e.g., metal oxides, phosphates, fluorides) and electrolyte additives (e.g., vinylene carbonate, phosphites, sulfur compounds) are proposed to suppress gas-phase reactions. Managing the SOC by restricting cycling to the 60–80% range is regarded as an effective approach for improving cathode longevity. These findings offer actionable insights for improving lithium-ion battery performance and safety.

Fire safety is a major concern for lithium-ion batteries (LIBs) because of the use of flammable electrolyte solvents, typically carbonate esters. A well-recognized liquid-base fire hazard classification of LIB electrolyte solvents is strongly affected by phase change and may not be appropriate in some situations where vaporized electrolyte solvents are present. This study aims to highlight differences in the liquid- and gas-based fire hazard classifications. Fundamental gas-phase pyrolysis and combustion characteristics of carbonate ester mixtures used in a commercial LIB (ethylene carbonate (EC) with dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) or diethyl carbonate (DEC)) were numerically investigated using a chemical kinetic model, the LIB electrolyte surrogate model. Pyrolysis simulations conducted with a perfectly stirred reactor model showed that carbonate esters are likely to be dominant even after 10³ s at 600 K or lower, but not smaller pyrolysis products like H₂, CO and C₁–C₂ hydrocarbons, in all EC/DMC/N₂, EC/EMC/N₂ and EC/DEC/N₂ mixture cases. Laminar flame speeds of EC/EMC/air and EC/DEC/air mixtures were equally higher than that of EC/DMC/air mixture at 500 K, i.e., the former (EC/EMC and EC/DEC) could be more flammable than the latter (EC/DMC) based on the gas-phase combustion property, whereas the trend is the opposite in the liquid-phase fire hazard classification. As expected from the classical laminar flame theory, thermal diffusivity, a transport parameter, of a mixture exhibits a good correlation against the laminar flame speeds of carbonate ester(s) mixtures. Thus, thermal diffusivity can be a useful index for evaluating the relative magnitudes of laminar flame speeds of electrolyte solvent mixtures of interest. A proper fire hazard classification tailored to the anticipated LIB fire scenario needs to be formulated and applied to evaluate potential fire risks.

The rapid escalation in battery size and energy density has intensified the need for reliable safety technologies capable of preventing catastrophic fires and explosions. Thermal runaway, triggered by a chain of self-accelerating exothermic reactions, remains the most critical safety concern, and its suppression requires a comprehensive understanding of thermal behavior spanning both the material level and the entire battery. Accelerating rate calorimetry (ARC) is widely employed to elucidate the heat-generation characteristics of thermal runaway, as it provides direct and quantitative insight into the associated exothermic processes. However, effective safety screening using ARC is constrained by the substantial material requirements and high fabrication costs of conventional ampere-hour-scale batteries. Here, we introduce cylindrical pouch-type miniature batteries (~21 mAh, ~0.1 g of cathode active material) engineered to exhibit strong thermal responses, enabling battery ARC characterization at the laboratory scale. This platform enables rapid, cost-/material-efficient assessment and provides early design feedback, supporting the development of next-generation high-safety rechargeable batteries.

Efforts are underway in various fields toward achieving a decarbonized society, including the accelerating adoption of renewable energy sources such as solar and wind power. Japan is already experiencing surplus solar power. Furthermore, power fluctuates with weather conditions, creating a need for effective utilization of this generated power and countermeasures to address fluctuations. To address this issue, existing power generation facilities and pumped-storage hydroelectric power generation are being used. However, these facilities have limited capacity, and new construction is difficult. Therefore, the introduction of stationary energy storage systems is expected. While there are various types of stationary energy storage batteries, lithium-ion batteries, which became the basis for the widespread use of electric vehicles, are increasingly being used. Lithium-ion batteries are relatively small and lightweight, have high charge/discharge efficiency, and have recently been extended in lifespan and become more affordable. This paper introduces our stationary lithium-ion batteries, including their features, safety measures, and application examples.

The global proliferation of battery electric vehicles (BEVs) powered by lithium-ion batteries (LIBs) has increased opportunities for their maritime transport by pure car and truck carriers (PCTCs). However, fire characteristics of BEVs differ significantly from conventional internal combustion engine vehicles (ICEVs), presenting new safety challenges. PCTCs feature Roll-On/Roll-Off systems and multi-deck structures with high-density vehicle stowage (10 cm lateral and 30 cm longitudinal spacing). This configuration facilitates rapid fire spread and makes firefighting extremely difficult. LIB fires involve thermal runaway, generating continuous release of flammable electrolyte vapor and decomposition gases, leading to prolonged smoldering and repeated re-ignition. Fixed high expansion foam fire-extinguishing systems, regulated by IMO's SOLAS Convention and FSS Code, are installed in cargo holds of many PCTCs. On such vessels, the outside air type system with generators installed inside protected spaces generates high expansion foam (expansion ratio: 900 times) using clean external air. A full-scale experiment was conducted using a Nissan Leaf (24 kWh) at the Japan Automobile Research Institute. Thermal runaway was simulated by heating the battery pack with embedded heaters. The foam system successfully covered the burning vehicle and suppressed flames. After initial discharge, flammable gases continued releasing. Upon re-ignition, the second discharge effectively controlled the fire. Complete suppression occurred within 2-3 hours, significantly faster than water spray methods requiring nearly 10 hours. Results suggest high expansion foam suppresses combustion of released gases while allowing safe burnout of battery internals. The foam's mild cooling effect and thermal barrier properties contributed to early suppression and prevented fire spread. Future research should address larger battery capacities and multiple vehicle fire scenarios.

Flame-wall interaction (FWI) is paramount in high-power downsized combustion chambers of gas turbines. Thermal management of walls is therefore mandatory to ensure sufficient durability of combustion liners, which are exposed to harsh environments during long operating periods. The use of cooling technologies is routinely used, including cooling air films. Generated by the coalescence of inclined air jets to create a thermal shield to prevent the reactive flow to interact with the wall, the injection of this additional air is intrusive and can affect the reacting flow. Differing from classical FWI mechanisms, flame cooling air interaction (FCAI) has gained a recent interest in the combustion community due to its multi-physical nature. This article intends to provide the basics on near-wall combustion, and to comprehensively describe the physics retrieved during FCAI. The ambition of this article is to highlight that this research field still requires more efforts in terms of fundamental knowledge, in order to develop robust and predictive modeling tools to fasten the optimization of future low-emission gas turbines.

In this study, we developed a reduced reaction mechanism applicable to computational fluid dynamics (CFD) at the actual scale to evaluate the NOx reduction performance during hydrogen combustion in a duct burner. Specifically, using the duct burner reaction mechanism developed in this study, we reproduced the trend of NOx reduction during hydrogen combustion in duct burner combustion experiments through CFD. We considered the NO reduction reactions during the combustion of hydrogen and hydrocarbons, particularly focusing on the reaction NO + H + H₂ to determine the reaction rates. Through CFD analysis, it became possible to reproduce the NOx reduction mechanisms in the duct burner. However, challenges remain regarding the accuracy of NOx predictions. Variability in the fundamental experimental data affects the results, necessitating careful selection in determining reaction rates. Moving forward, further enhancement of fundamental experimental data is essential for accurately predicting NOx performance in full-scale applications.

Lithium-ion batteries (LIBs) are widely used due to their high capacity, high power, and lightweight characteristics. However, the increasing number of battery fires has become a significant concern as LIB electrolytes contain flammable organic solvents. This study investigated the effect of electrolyte component mixing on the limiting oxygen concentration (LOC) of diffusion flames to understand the combustion characteristics of LIB electrolytes. Propylene carbonate (PC) was mixed with diethyl carbonate (DEC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC) as additives. Laminar diffusion flames were formed using these fuel mixtures, and the LOC was measured using the wick method under multiple ambient air flow velocity conditions (5 and 10 cm/s). The LOC of PC flames was 17-18 % regardless of flow velocity. The LOC of the PC-DEC mixture was 17 %, which was lower than that of pure PC flames. When VC was added to the PC-DEC mixture, the LOC decreased with increasing VC concentration. The LOC of the PC-DEC-5 wt%VC mixture was 16 %. Furthermore, fuel consumption increased and flame height became higher compared to flames without VC addition. When FEC was added to PC, the LOC increased with increasing FEC concentration. The LOC of the PC-3 wt%FEC mixture was 18 %. The addition of FEC to PC decreased fuel consumption, and the flame height was lower than that of pure PC.