Search

The safety monitoring of lithium-ion batteries (LIBs) is of great significance for realizing all-climate and full-lifespan battery management. In-situ measurement of anode potential with implanted reference electrodes (REs) has proven to be effective to monitor and avoid the occurrence of severe side reactions like Li plating to ensure the safe and fast charging. However, the intrinsic measurement errors caused by local blocking effects, which also can be referred to as potential artefacts, are seldom taken into consideration in existing studies, yet they highly dominate the correctness of conclusions inferred from REs. In this study, aiming at exploring the physical origin of the measurement errors and ensure reliable potential monitoring, electrochemical and post-mortem tests are conducted using commercial pouch cells with implanted REs. Corresponding electrochemical model which describes the blocking effects, is established to validate the abnormal absence of lithium plating that predicted by measured anode potentials under various charging rates. Theoretical derivation is further presented to explain the error sources, which can be attributed to increased local liquid potential of the RE position. Most importantly, with the guidance of error analysis, a novel parameter-independent error correction method for RE measurements is proposed for the first time, which is proven to be adequate to estimate the real anode potentials and deduce the critical C-rate of Li plating with extra safety margin. After error correction, the resulting critical C-rates are all within the range of 0.55 ± 0.03C, which is close to the C-rate of 0.6–0.7C obtained from experiments. In addition, this error correction method can be performed conveniently with only some simple RE measurements of polarization voltages, totally independent of battery electrochemical and geometric parameters. This study provides highly practical error correction method for RE measurements in real LIBs, substantially facilitating the fast diagnosis and safety evaluation of Li plating during charging of LIBs.

Although energy densities of lithium-ion batteries (LIBs) continue to increase, safety problems such as fires and explosions have significantly hindered their large-scale applications. Conventional wisdom tells us the fire of LIBs largely originated from the flammable liquid carbonate solvents, and thus the research on additives with properties of suppressing “liquid-type fire” is the way to fabricate nonflammable batteries. However, the outcome has been proven to be inferior. Here, we carefully examined the evolution of battery fire under thermal abuse condition and found that the “jet fire” caused by flammable gases inside batteries is critical for the fire hazard, and the research effort should be redirected to search proper additives with “gaseous-type fire” suppressing properties. Unfortunately, conventional “gaseous-type fire suppressant” shows poor compatibility with battery electrolytes. Thus, we rationally designed a new kind of supramolecular electrolyte, where the molecules of “gaseous-type fire suppressant” and “SEI&CEI improver” are self-assembled together by intermolecular interactions. Due to this design, the supramolecular electrolyte produces improved cycling stability of Li metal anode and high voltage LiCoO2 cathode (up to 4.4 V). More importantly, it sharply decreases the self-extinguish time of carbonate electrolyte from ∼100 s/g to ∼0 s/g, which is unprecedented and can effectively suppress the “jet fire”, thus preventing the further combustion of commercial pouch cell during thermal runaway. Our work is providing the criteria required to overcome this challenge via supramolecular engineering of the electrolyte, which provides a new way to tune electrolyte functions and may bring numerous new possibilities.

There is an urgent need for high-safety and high-energy lithium-ion batteries to satisfy the rapidly increasing need for energy storage. Nickel-rich layered cathodes have been at the forefront of the revolution for batteries due to their relatively high capacity and low cost. However, with the increase of nickel content, the batteries suffer from severe safety concerns, which caused by thermal runaway. Here we show that the ultraconformal cathode-electrolyte interphase (CEI) protective skin with high inorganic content dramatically enhances the safety of high-energy practical Li-ion pouch cells. We find that the robust CEI skin significantly improves the intrinsic thermal stability, mitigates the evolution of oxygen resulting from phase transition, and effectively suppresses the associated parasitic reactions between the delithiated cathodes and electrolyte. The in-situ CEI engineering strategy is simple and suitable for practical industrial manufacture, and it provides design ideas for aggressive nickel-rich cathodes towards safe and high-energy batteries.

Internal short circuit (ISC) is the major failure problem for the safe application of lithium-ion batteries, especially for the batteries with high energy density. However, how to quantify the hazard aroused by the ISC, and what kinds of ISC will lead to thermal runaway are still unclear. This paper investigates the thermal-electrical coupled behaviors of ISC, using batteries with Li(Ni1/3Co1/3Mn1/3)O2 cathode and composite separator. The electrochemical impedance spectroscopy of customized battery that has no LiPF6 salt is utilized to standardize the resistance of ISC. Furthermore, this paper compares the thermal-electrical coupled behaviors of the above four types of ISC at different states-of-charge. There is an area expansion phenomenon for the aluminum-anode type of ISC. The expansion effect of the failure area directly links to the melting and collapse of separator, and plays an important role in further evolution of thermal runaway. This work provides guidance to the development of the ISC models, detection algorithms, and correlated countermeasures.

Cascaded thermal runaway (TR) propagation is the utmost safety issue for large-format lithium-ion battery (LIB) modules because of the high risk of system fires or explosions. However, quenching TR without side effects still remains a challenge. Herein, we delivered an ultrathin smart firewall concept for avoiding the TR propagation in a LIB module. We demonstrate that the firewalls have thermally-triggered switchable thermal physical properties because of the synergistic effect of non-flammable phase change materials (NFPCM) and flexible silica nanofiber mats. Under TR condition, the firewalls give rise to multiple functions simultaneously, including cooling, fire extinguishing and thermal insulation. Consequently, the TR propagation between fully charged 50 Ah LIBs, with a transient thermal shock of up to 53 kW, is successfully suppressed by 1-mm-thick smart firewalls, yielding a maximum cell-to-cell temperature gap of 512 °C. The smart firewall design provides a reliable approach to quench TR propagation in large-format LIBs, which can also be suitable for other dynamically adaptive thermal-protection applications for oil tanks, space exploration, and firefighting equipment.

The development and application of hydrogen energy in power generation, automobiles, and energy storage industries are expected to effectively solve the problems of energy waste and pollution. However, because of the inherent characteristics of hydrogen, it is difficult to maintain high safety during production, transportation, storage, and utilization. Therefore, to ensure the safe and reliable utilization of hydrogen, its characteristics relevant to leakage and diffusion, ignition, and explosion must be analyzed. Through an analysis of literature, in combination with our practical survey analysis, this paper reviews the key issues concerning hydrogen safety, including hydrogen incident investigation, hydrogen leakage and diffusion, hydrogen ignition, and explosion.

Layered Ni-rich LiNixMnyCo1-x-yO2 (NMC) materials are the most promising cathode materials for Li-ion batteries due to their favorable energy densities. However, the low thermal stability typically caused by detrimental oxygen release leads to significant safety concerns. Determining the pathways of oxygen evolution reaction is essential, as the ideal safety countermeasure is to break the reaction chain of thermal runaway. In this study, we demonstrate that two endogenous pathways of oxygen involved in strong exothermic reactions lead the NMC811|graphite pouch cell to an uncontrollable state, and we quantify the individual contribution of the pathways to thermal runaway. Approximately 41% of thermal-induced oxygen reacts aggressively with ethylene carbonate (EC) at the cathode/electrolyte interface with 16% heat generation, accelerating the self-heating rate and thereby further triggering thermal runaway. The residual oxygen that survives the reaction with carbonate spreads to the lithiated anode with major heat generation (65%), bringing the battery to the maximum destructive temperature during thermal runaway. By confirming the significant roles of EC and anode, a deeper understanding on battery fire was achieved. The revealed mechanism can help guide studies on stopping the two reaction pathways, allowing for the safer use of high-energy lithium-ion batteries in the future.

Accompanied by the adoption of aggressive cathodes to continuously improve batteries energy density, enhancing their safety is becoming increasingly urgent for the electric vehicle development. In-situ controllable formation of robust cathode-electrolyte interphase (CEI) with high inorganic content seems to be the most promising strategy to address the thermal runaway concerns. Moreover, the in-situ formation strategy via suitable electrolyte replacement or electrolyte additives is extremely simple yet effective, especially for industrial manufacture of batteries. Here, this paper briefly reviews recent advanced CEIs formed by conventional carbonate-based electrolytes, fluorinated electrolytes, concentrated electrolytes, and solid state electrolytes. The focus on the thermal stability of the cathodes after CEI modification, and at the same time conduct safety tests at the material, cell, and module levels for comprehensive evaluation are encouraged. The review will provide inspiration for future developments in battery safety and push forward the practical applications of newly developed high-energy density batteries.

Water flooding occurs at the output region of the anode side, which is one of the main reasons for performance degradation of automotive fuel cell systems. If liquid water saturation ratio in gas diffusion layers can be observed and regulated within a suitable range, water flooding in anode channels can be avoided. For this purpose, a zero dimensional dynamic model which focuses on the internal states (such as liquid water saturation ratio in gas diffusion layer) for the anode side before water flooding is presented. A nonlinear state observer for the anode side is designed using the unscented Kalman filter algorithm. Influences of the relative humidity sensor and initial values of internal states on the observation results are analyzed. The results show (1) four key internal states (e.g., water vapor pressure, hydrogen and nitrogen pressure, average liquid water saturation ratio) can be observed using this method, and the time constant of the sensor has a smaller influence on the observer than the signal noise. (2) With a suitable sensor (noise power

Safety concerns are the main obstacle to large-scale application of lithium-ion batteries (LIBs), and thus, improving the safety of LIBs is receiving global attention. Within battery systems, the internal short circuit (ISC) is considered to be a severe hazard, as it may result in catastrophic safety failures, such as thermal runaway. Considering this, we provide a comprehensive review on the mechanism and evolutionary process of ISC, including modeling and simulation experiments and the methods of detection and diagnosis. First, ISC types and the inducing mechanism under various inducements are analyzed, and the evolution process of ISC is divided into three stages according to electrical and thermal characteristics. Second, eleven existing ISC substitute experimental methods are listed in detail, and three coupling models of electric-thermal-ISC models are introduced to simulate the characteristics of ISC. Third, existing ISC detection methods are reviewed in detail, divided into six categories. Moreover, we propose methods for ISC detection under four special conditions: ISC detection for the cells before grouping, ISC detection method during electric vehicle dormancy, ISC detection based on equilibrium electric quantity compensation to address negative impact of the equalization function of the battery management system on ISC detection, and effective fault tree diagnosis for the joint identification and early warning of multiple battery faults. Fourth, existing ISC prevention methods are reviewed. Finally, the key technologies of ISC are prospected, revealing that the development of big data and artificial intelligence technology will promote the accuracy and timeliness of ISC detection.

Thermal runaway, a critical problem that hinders the application of lithium-ion battery, is always a thermal-electrical coupled process where exothermic chemical reactions and internal short circuit coincide and interact with each other. Clarifying the contributions of chemical reactions and internal short circuit to thermal runaway is crucial for developing safer lithium-ion battery. In this paper, the relationship between internal short circuit and thermal runaway of lithium-ion battery under thermal abuse condition is investigated through experimental and modeling approaches. Internal short circuit is observed to happen before thermal runaway but leads to little heat generation during thermal abuse test of a lithium-ion battery with Li(NiCoMn)1/3O2 cathode. Liquid-nitrogen-ceased thermal runaway test and postmortem analysis are designed to characterize the cause of internal short circuit. Thermal shrinkage of the separator is found responsible for the occurrence of internal short circuit. However, the joule heat from internal short circuit is limited by the sharp-increased battery resistance and thus contributes little to battery thermal runaway. Moreover, exothermic reactions between the anode and electrolyte are determined as the trigger of thermal runaway of the Li(NiCoMn)1/3O2–based battery, in contrast to the conventional views that the highly reactive oxygen released from cathode or internal short circuit is the critical factor for thermal runaway of lithium-ion battery. Finally, a model-based discussion on the effect of internal short circuit on the thermal runaway of batteries with different designs is presented. The results provide new insights into battery thermal runaway mechanism and can benefit the safety design of lithium-ion battery.

Summary This paper summarizes the mitigation strategies for the thermal runaway of lithium-ion batteries. The mitigation strategies function at the material level, cell level, and system level. A time-sequence map with states and flows that describe the evolution of the physical and/or chemical processes has been proposed to interpret the mechanisms, both at the cell level and at the system level. At the cell level, the time-sequence map helps clarify the relationship between thermal runaway and fire. At the system level, the time-sequence map depicts the relationship between the expected thermal runaway propagation and the undesired fire pathway. Mitigation strategies are fulfilled by cutting off a specific transformation flow between the states in the time sequence map. The abuse conditions that may trigger thermal runaway are also summarized for the complete protection of lithium-ion batteries. This perspective provides directions for guaranteeing the safety of lithium-ion batteries for electrical energy storage applications in the future.

Self-humidification with anode/cathode recirculation was found to be an alternative in the place of external humidifier according to the previous studies in the last decade, however, there is still a lack of quantitative experimental and theoretical comparison between them. In this study, the dynamic PEM fuel cell system model with anodic and cathodic exhaust gas recirculation is proposed and related model calibration and verification are carried out by measured output voltage, gaseous pressure and mole concentration during the dynamic process. The model simulation shows quite good agreement with the experimental result and source of error is discussed. Based on developed model, it is simulated that the humidification effect is much better for cathode recirculation compared with anode recirculation, resulting in performance improvement, especially under the condition of low inlet RH. However, this improved humidification effect is weakened, considering the structure limit of recirculation pump and gas channel in this case. Besides, the power consumption of cathode recirculation pump is found to be much higher than that of anode recirculation. As a result, the anode recirculation is found to be a better solution considering the energy efficiency and mechanical structure limit. In contrast, cathode recirculation conducts better humidification effect, which is more suitable for the short-time low-inlet-humidity working conditions.

Battery thermal management systems are critical for high performance electric vehicles, where the ability to remove heat and homogenise temperature distributions in single cells and packs are key considerations. Immersion cooling, which submerges the battery in a dielectric fluid, has the potential of increasing the rate of heat transfer by 10,000 times relative to passive air cooling. In 2-phase systems, this performance increase is achieved through the latent heat of evaporation of the liquid-to-gas phase transition and the resulting turbulent 2-phase fluid flow. However, 2-phase systems require additional system complexity, and single-phase direct contact immersion cooling can still offer up to 1,000 times improvements in heat transfer over air cooled systems. Fluids which have been considered include: hydrofluoroethers, mineral oils, esters and water-glycol mixtures. This review therefore presents the current state-of-the-art in immersion cooling of lithium-ion batteries, discussing the performance implications of immersion cooling but also identifying gaps in the literature which include a lack of studies considering the lifetime, fluid stability, material compatibility, understanding around sustainability and use of immersion for battery safety. Insights from this review will therefore help researchers and developers, from academia and industry, towards creating higher power, safer and more durable electric vehicles.