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Lithium-ion batteries connected in series are prone to be overdischarged. Overdischarge results in various side effects, such as capacity degradation and internal short circuit (ISCr). However, most of previous research on the overdischarge of a cell was terminated when the cell voltage dropped to 0 V, leaving the further impacts of overdischarge unclear. This paper investigates the entire overdischarge process of large-format lithium-ion batteries by discharging the cell to −100% state of charge (SOC). A significant voltage platform is observed at approximately −12% SOC and ISCr is detected after the cell is overdischarged when passing the platform. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) results indicate that the overdischarge-induced ISCr is caused by Cu deposition on electrodes, suggesting possible Cu collector dissolution at the voltage platform near −12% SOC. A prognostic/mechanistic model considering ISCr is used to evaluate the resistance of ISCr ( R ISCr ), the value of which decreases sharply at the beginning of ISCr formation. Inducing the ISCr by overdischarge is effective and well controlled without any mechanical deformation or the use of a foreign substance.

Concentrated electrolytes usually demonstrate good electrochemical performance and thermal stability, and are also supposed to be promising when it comes to improving the safety of lithium-ion batteries due to their low flammability. Here, we show that LiN(SO 2 F) 2 -based concentrated electrolytes are incapable of solving the safety issues of lithium-ion batteries. To illustrate, a mechanism based on battery material and characterizations reveals that the tremendous heat in lithium-ion batteries is released due to the reaction between the lithiated graphite and LiN(SO 2 F) 2 triggered thermal runaway of batteries, even if the concentrated electrolyte is non-flammable or low-flammable. Generally, the flammability of an electrolyte represents its behaviors when oxidized by oxygen, while it is the electrolyte reduction that triggers the chain of exothermic reactions in a battery. Thus, this study lights the way to a deeper understanding of the thermal runaway mechanism in batteries as well as the design philosophy of electrolytes for safer lithium-ion batteries. Concentrated electrolytes display superior thermal stability due to their non-flammability nature. Here, the authors show that LiN(SO 2 F) 2 -based concentrated electrolytes are incapable of solving the safety issues due to heat release during reaction between the lithiated graphite and electrolyte.

The frequent safety accidents involving lithium-ion batteries (LIBs) have aroused widespread concern around the world. The safety standards of LIBs are of great significance in promoting usage safety, but they need to be constantly upgraded with the advancements in battery technology and the extension of the application scenarios. This study comprehensively reviews the global safety standards and regulations of LIBs, including the status, characteristics, and application scope of each standard. A standardized test for thermal runaway triggering is also introduced. The recent fire accidents in electric vehicles and energy storage power stations are discussed in relation to the upgrading of the rational test standards. Finally, the following four suggestions for improving battery safety are proposed to optimize the safety standards: (1) early warning and cloud alarms for the battery’s thermal runaway; (2) an innovative structural design for a no-fire battery pack; (3) the design of a fire water injection interface for the battery pack; (4) the design of an immersive energy storage power station. This study provides insights for promoting the effectiveness of relevant safety standards for LIBs, thereby reducing the failure hazards.

Ice-templating technology holds great potential to construct industrial porous materials from nanometers to the macroscopic scale for tailoring thermal, electronic, or acoustic transport. Herein, we describe a general ice-templating technology through freezing the material on a rotating cryogenic drum surface, crushing it, and then re-casting the nanofiber slurry. Through decoupling the ice nucleation and growth processes, we achieved the columnar-equiaxed crystal transition in the freezing procedure. The highly random stacking and integrating of equiaxed ice crystals can organize nanofibers into thousands of repeating microscale units with a tortuous channel topology. Owing to the spatially well-defined isotropic structure, the obtained Al 2 O 3 ·SiO 2 nanofiber aerogels exhibit ultralow thermal conductivity, superelasticity, good damage tolerance, and fatigue resistance. These features, together with their natural stability up to 1200 °C, make them highly robust for thermal insulation under extreme thermomechanical environments. Cascading thermal runaway propagation in a high-capacity lithium-ion battery module consisting of LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode, with ultrahigh thermal shock power of 215 kW, can be completely prevented by a thin nanofiber aerogel layer. These findings not only establish a general production route for nanomaterial assemblies that is conventionally challenging, but also demonstrate a high-energy-density battery module configuration with a high safety standard that is critical for practical applications. In this work, the authors present an ice-templating strategy to produce large-scale isotropic nanofiber aerogels using a unique process of freezing the material on a rotating cryogenic drum surface, crushing it, and then re-casting the nanofiber slurry enabling high-throughput and design flexibility.

Lithium dendrites, with their high reactivity, pose a critical challenge to the safety and longevity of lithium-based batteries. Effective regulation strategies are crucial for mitigating battery degradation and enhancing reliability. Conventional approaches, such as relaxation following lithium plating or regulated discharging, often fail to simultaneously address the formation of solid electrolyte interface and isolated lithium. Here, we demonstrate that rational utilization of electric field relaxation following dendrite growth can reduce defective solid electrolyte interface and isolated lithium by balancing solid electrolyte interface growth and dendrite morphology smoothing near the relaxation time constant. Building upon the mechanism, we propose a short-term relaxation method to manipulate lithium plating, which achieves an enhancement of capacity retention from 80% up to 95% at 3 C-rate (20 min) fast-charging on commercial batteries. These findings highlight the importance of relaxation after dendrites formation for safe, long-life and fast-charging batteries, particularly where dendrite growth is the limiting factor. Dendrite growth harms the safety and longevity of Li-ion batteries. Here, authors find that short-term relaxation after lithium plating boosts capacity retention by forming a beneficial solid electrolyte interphase and smoothing morphologies, providing an approach for safe and long-life batteries.

Porous carbons with concurrently high specific surface area and electronic conductivity are desirable by virtue of their desirable electron and ion transport ability, but conventional preparing methods suffer from either low yield or inferior quality carbons. Here we developed a lithiothermal approach to bottom–up synthesize highly meso–microporous graphitized carbon (MGC). The preparation can be finished in a few milliseconds by the self-propagating reaction between polytetrafluoroethylene powder and molten lithium (Li) metal, during which instant ultra-high temperature (>3000 K) was produced. This instantaneous carbon vaporization and condensation at ultra-high temperatures and in ultra-short duration enable the MGC to show a highly graphitized and continuously cross-coupled open pore structure. MGC displays superior electrochemical capacitor performance of exceptional power capability and ultralong-term cyclability. The processes used to make this carbon are readily scalable to industrial levels. Porous carbons with high specific surface area and electronic conductivity are of interest for their electron and ion transport ability. Here authors use ultra-high temperature reactions of Li metal and polytetrafluoroethylene to make graphitized porous carbon for electrochemical energy storage.

Preventing thermal runaway propagation is critical to improve the fire safety of electric vehicles. Experiments are conducted on the designed battery modules to study the effects of aerogel, liquid cooling plate, and their combination on the prevention mechanism of thermal runaway propagation. The characteristics of temperature, voltage, mass loss, and venting during the thermal runaway propagation process are compared and analyzed. The results indicate that: (1) adding the insulation material of aerogel can postpone the thermal runaway propagation, but may not completely cut-off the propagation process; (2) there is no obvious delay of thermal runaway propagation by adding the liquid cooling plate only, the propagation speed may be accelerated instead; (3) the thermal runaway propagation can be prevented by using aerogel and liquid cooling plate together. The study reminds us that safety design of battery thermal management system should consider the comprehensive heat transfer pathways in order to effectively prevent thermal runaway propagation.

Oxygen redox at high voltage has emerged as a transformative paradigm for high-energy battery cathodes such as layered transition-metal oxides by offering extra capacity beyond conventional transition-metal redox. However, these cathodes suffer from voltage hysteresis, voltage fade and capacity drop upon cycling. Single-crystalline cathodes have recently shown some improvements, but these challenges remain. Here we reveal the fundamental origin of oxygen redox instability to be from the domain boundaries that are present in single-crystalline cathode particles. By investigating single-crystalline cathodes with different domain boundaries structures, we show that the elimination of domain boundaries enhances the reversible lattice oxygen redox while inhibiting the irreversible oxygen release. This leads to significantly suppressed structural degradation and improved mechanical integrity during battery cycling and abuse heating. The robust oxygen redox enabled through domain boundary control provides practical opportunities towards high-energy, long-cycling, safe batteries. Oxygen redox instability at high voltages hinders the application of high-energy battery cathodes. Here the authors report that elimination of domain boundaries in single-crystal cathodes improves the redox stability and consequently the electrochemical performance in extended high-voltage cycling.

Driven by the goals of carbon neutrality, electrochemical storage technologies play a vital role in supporting the integration of renewable energy and reducing dependency on fossil fuels. The Mn-based rechargeable battery (MnRB) is gaining significant attention in the battery industry due to its high voltage platform and high energy density, making it a potential alternative in the e-bike and energy storage system area. The safety performance of MnRB is crucial for its widespread application. However, there has been a scarcity of studies evaluating the safety of MnRB. In this study, the thermal safety behavior of a commercial Mn-based composite cathode battery from the perspectives of \"heat generation-gas emission- explosion risks\". Its safety performance was compared with that of existing batteries using Li(Ni x Co y Mn z )O 2 and LiFePO 4 (LFP) as cathode materials. The results indicate that MnRB exhibits a higher triggering temperature, 0.8% lower than Li(Ni 0.5 Co 0.2 Mn 0.3 )O 2 (NCM523) and approximately 12.7% lower than LFP. MnRB's normalized gas emission during thermal runway (TR) is 1.3% lower than that of NCM523, with the primary gas components being CO, H 2 , and CO 2 . The lower explosion limit of MnRB is approximately 2.7% lower than NCM523 and 44.0% higher than LFP. MnRB exhibits intermediate thermal stability and combustion-explosion characteristics between NCM523 and LFP. This study provides valuable data on MnRB's TR behavior, offering a comprehensive assessment of MnRB's intrinsic safety performance through quantitative evaluation. The findings present clear directions for designing, optimizing, and implementing safety measures for MnRB against TR.

Lithium-ion batteries (LIBs) are widely used in electric vehicles (EV) and energy storage stations (ESS). However, combustion and explosion accidents during the thermal runaway (TR) process limit its further applications. Therefore, it is necessary to investigate the uncontrolled TR exothermic reaction for safe battery system design. In this study, different LIBs are tested by lateral heating in a closed experimental chamber filled with nitrogen. Moreover, the relevant thermal characteristic parameters, gas composition, and deflagration limit during the battery TR process are calculated and compared. Results indicate that the TR behavior of NCM batteries is more severe than that of LFP batteries, and the TR reactions becomes more severe with the increase of energy density. Under the inert atmosphere of nitrogen, the primarily generated gases are H2, CO, CO2, and hydrocarbons. The TR gas deflagration limits and characteristic parameter calculations of different cathode materials are refined and summarized, guiding safe battery design and battery selection for power systems.