Blade batteries are extensively used in electric vehicles,but unavoidable thermal runaway is an inherent threat to their safe use.This study experimentally investigated the mechanism underlying thermal runaway propaga...Blade batteries are extensively used in electric vehicles,but unavoidable thermal runaway is an inherent threat to their safe use.This study experimentally investigated the mechanism underlying thermal runaway propagation within a blade battery by using a nail to trigger thermal runaway and thermocouples to track its propagation inside a cell.The results showed that the internal thermal runaway could propagate for up to 272 s,which is comparable to that of a traditional battery module.The velocity of the thermal runaway propagation fluctuated between 1 and 8 mm s^(-1),depending on both the electrolyte content and high-temperature gas diffusion.In the early stages of thermal runaway,the electrolyte participated in the reaction,which intensified the thermal runaway and accelerated its propagation.As the battery temperature increased,the electrolyte evaporated,which attenuated the acceleration effect.Gas diffusion affected thermal runaway propagation through both heat transfer and mass transfer.The experimental results indicated that gas diffusion accelerated the velocity of thermal runaway propagation by 36.84%.We used a 1D mathematical model and confirmed that convective heat transfer induced by gas diffusion increased the velocity of thermal runaway propagation by 5.46%-17.06%.Finally,the temperature rate curve was analyzed,and a three-stage mechanism for internal thermal runaway propagation was proposed.In Stage I,convective heat transfer from electrolyte evaporation locally increased the temperature to 100℃.In Stage II,solid heat transfer locally increases the temperature to trigger thermal runaway.In StageⅢ,thermal runaway sharply increases the local temperature.The proposed mechanism sheds light on the internal thermal runaway propagation of blade batteries and offers valuable insights into safety considerations for future design.展开更多
The safety valve is an important component to ensure the safe operation of lithium-ion batteries(LIBs).However,the effect of safety valve type on the thermal runaway(TR)and gas venting behavior of LIBs,as well as the ...The safety valve is an important component to ensure the safe operation of lithium-ion batteries(LIBs).However,the effect of safety valve type on the thermal runaway(TR)and gas venting behavior of LIBs,as well as the TR hazard severity of LIBs,are not known.In this paper,the TR and gas venting behavior of three 100 A h lithium iron phosphate(LFP)batteries with different safety valves are investigated under overheating.Compared to previous studies,the main contribution of this work is in studying and evaluating the effect of gas venting behavior and TR hazard severity of LFP batteries with three safety valve types.Two significant results are obtained:(Ⅰ)the safety valve type dominates over gas venting pressure of battery during safety venting,the maximum gas venting pressure of LFP batteries with a round safety valve is 3320 Pa,which is one order of magnitude higher than other batteries with oval or cavity safety valve;(Ⅱ)the LFP battery with oval safety valve has the lowest TR hazard as shown by the TR hazard assessment model based on gray-fuzzy analytic hierarchy process.This study reveals the effect of safety valve type on TR and gas venting,providing a clear direction for the safety valve design.展开更多
Developing technologies that can be applied simultaneously in battery thermal management(BTM)and thermal runaway(TR)mitigation is significant to improving the safety of lithium-ion battery systems.Inorganic phase chan...Developing technologies that can be applied simultaneously in battery thermal management(BTM)and thermal runaway(TR)mitigation is significant to improving the safety of lithium-ion battery systems.Inorganic phase change material(PCM)with nonflammability has the potential to achieve this dual function.This study proposed an encapsulated inorganic phase change material(EPCM)with a heat transfer enhancement for battery systems,where Na_(2)HPO_(4)·12H_(2)O was used as the core PCM encapsulated by silica and the additive of carbon nanotube(CNT)was applied to enhance the thermal conductivity.The microstructure and thermal properties of the EPCM/CNT were analyzed by a series of characterization tests.Two different incorporating methods of CNT were compared and the proper CNT adding amount was also studied.After preparation,the battery thermal management performance and TR propagation mitigation effects of EPCM/CNT were further investigated on the battery modules.The experimental results of thermal management tests showed that EPCM/CNT not only slowed down the temperature rising of the module but also improved the temperature uniformity during normal operation.The peak battery temperature decreased from 76℃to 61.2℃at 2 C discharge rate and the temperature difference was controlled below 3℃.Moreover,the results of TR propagation tests demonstrated that nonflammable EPCM/CNT with good heat absorption could work as a TR barrier,which exhibited effective mitigation on TR and TR propagation.The trigger time of three cells was successfully delayed by 129,474 and 551 s,respectively and the propagation intervals were greatly extended as well.展开更多
Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batter...Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety.Moreover,the fluorinated electrolytes are widely used to form stable electrolyte interphase,due to their chemical reactivity with lithiated graphite or lithium.However,the influence of this reactivity on the thermal safety of batteries is seldom discussed.Herein,we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability,while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte.The reduction in fluorinated components(e.g.,LiPF 6 and fluoroethylene carbonate(FEC))by fully lithiated graphite accounts for a significant heat release during battery thermal runaway.The 13%of total heat is sufficient to trigger the chain reactions during battery thermal runaway.This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes,providing guidance on the concept of electrolyte design for safer lithium-ion batteries.展开更多
Runaway electron current generated during the current quench phase of tokamak disruptions could result in severe damage to future high performance devices.To control and mitigate such runaway electron current,it is im...Runaway electron current generated during the current quench phase of tokamak disruptions could result in severe damage to future high performance devices.To control and mitigate such runaway electron current,it is important to accurately describe the runaway electron current dominated equilibrium,based on which further stability analysis could be carried out.In this paper,we derive a Grad-Shafranov-like equation solving for the axisymmetric drift surfaces of the runaway electrons instead of the magnetic flux surfaces for the simple case that all runaway electrons share the same parallel momentum.This new equilibrium equation is then numerically solved with simple rectangular wall with ITER-like and MAST-like geometry parameters.The deviation between the drift surfaces and the flux surfaces is readily obtained,and runaway electrons are found to be well confined even in regions with open field lines.The change of the runaway electron parallel momentum is found to result in a horizontal current center displacement without any changes in the total current or the external field.The runaway current density profile is found to affect the susceptibility of such displacement,with flatter profiles result in more displacement by the same momentum change.With up-down asymmetry in the external poloidal field,such displacement is accompanied by a vertical displacement of runaway electron current.It is found that this effect is more pronounced in smaller,compact device and weaker poloidal field cases.The above results demonstrate the dynamics of current center displacement caused by the momentum space change in the runaway electrons,and pave a way for more sophisticated runaway current equilibrium theory in the future with more realistic consideration on the runaway electron momentum distribution.This new equilibrium theory also provides foundation for future stability analysis of the runaway electron current.展开更多
Lithium-ion batteries with high-energy density are extensively commercialized in long-range electric vehicles. However, they are poor in thermal stability and pose fire or explosion, which has attracted the global att...Lithium-ion batteries with high-energy density are extensively commercialized in long-range electric vehicles. However, they are poor in thermal stability and pose fire or explosion, which has attracted the global attention. This study describes a new route to mitigate the battery thermal runaway(TR) hazard by poison agents. First, the self-destructive cell is built using the embedded poison layer. Then, the poisoning mechanism and paths are experimentally investigated at the material, electrode, and cell levels. Finally, the proposed route is verified by TR tests. The results show the TR hazard can be significantly reduced in the self-destructive cell based on a new reaction sequence regulation. Specifically, the maximum temperature of the self-destructive cell is more than 300℃ lower than that of the normal cell during TR. The drop in maximum temperature can reduce total heat release and the probability of TR propagation in the battery system, significantly improving battery safety.展开更多
Structurally compact battery packs significantly improve the driving range of electric vehicles.Technologies like Cell-to-Pack increase energy density by 15%-20%.However,the safety implications of multiple tightly-pac...Structurally compact battery packs significantly improve the driving range of electric vehicles.Technologies like Cell-to-Pack increase energy density by 15%-20%.However,the safety implications of multiple tightly-packed battery cells still require in-depth research.This paper studies thermal runaway propagation behavior in a Cell-to-Pack system and assesses propagation speed relative to other systems.The investigation includes temperature response,extent of battery damage,pack structure deformation,chemical analysis of debris,and other considerations.Results suggest three typical patterns for the thermal runaway propagation process:ordered,disordered,and synchronous.The synchronous propagation pattern displayed the most severe damage,indicating energy release is the largest under the synchronous pattern.This study identifies battery deformation patterns,chemical characteristics of debris,and other observed factors that can both be applied to identify the cause of thermal runaway during accident investigations and help promote safer designs of large battery packs used in large-scale electric energy storage systems.展开更多
The effect of tearing modes on the confinement of runaway electrons is studied in Experimental Advanced Superconducting Tokamak(EAST).The general tendency of the radial diffusion coefficient of runaway electrons(REs)D...The effect of tearing modes on the confinement of runaway electrons is studied in Experimental Advanced Superconducting Tokamak(EAST).The general tendency of the radial diffusion coefficient of runaway electrons(REs)Dr is derived based on the time response relation between the tearing modes and runaway electrons.The results indicate that,the magnetic fluctuations of tearing modes will enhance the radial diffusion of runaway electrons when the magnetic island is small.Following the increasing of the magnetic fluctuations of the tearing modes,the formed large magnetic island may weaken the radial diffusion of runaway electrons.The results can be important to understand the confinement of runaway electrons when large magnetic islands exist in the plasma.展开更多
Two different types of MHD instabilities with rapidly chirping frequency were found to arise in the Globus-M2 spherical tokamak in substantially different frequency ranges.The first type arises at frequencies of an or...Two different types of MHD instabilities with rapidly chirping frequency were found to arise in the Globus-M2 spherical tokamak in substantially different frequency ranges.The first type arises at frequencies of an order of 1 MHz in ohmic plasmas at relatively low density(n_(e))<2×10^(19) m^(-3) in a wide range of toroidal magnetic fields and plasma currents.This type of instability was identified as compressional Alfven waves,driven by electrons,accelerated during a sawtooth crush.It was found that the mode frequency is sweeping in time,according to the Berk-Breizman hole-clump nonlinear chirping model.The second type of wave arises in a specific single-swing regime of the central solenoid current with a very narrow plasma column,when the plasma tends to decay at extremely low density(n_(e))<2×10^(18) m^(-3) and,in fact,is an instability of the runaway electron beam.The exited modes cover the whole observed frequency range and are divided into several(two or three)frequency regions:approximately 0-30 MHz,60-120 MHz and sometimes 30-60 MHz.Reconnection of the branches was also observed.Single chirps are more rapid than for 1 MHz Alfven instability and follow an exponential law.This paper,to our knowledge,is the first report of frequency chirping instabilities excited by accelerated electrons at a spherical tokamak.展开更多
In the experiments of actively triggering plasma disruption by massive gas injection, the externally applied resonant magnetic perturbation has been used to mitigate the hazard of runaway electron(RE). Motivated by th...In the experiments of actively triggering plasma disruption by massive gas injection, the externally applied resonant magnetic perturbation has been used to mitigate the hazard of runaway electron(RE). Motivated by the experiment of multimode coupling to suppress REs on J-TEXT, some typical simulation cases with non-ideal MHD with rotation-open discussion(NIMROD) code are carried out to explore the influential mechanism of different relative phases between m/n =2/1 and m/n = 3/1 magnetic islands on the confinement of REs. Results show that the RE confinement is drastically affected by the relative phase between 2/1 and 3/1 magnetic islands. When the O point phase of 2/1 and 3/1 magnetic islands is toroidal 330°, REs can be effectively lost. The fitting curve of the remaining ratio of REs vs. the relative toroidal phase is predicted to approximate a sine-like function dependence. Further studies indicate that the phase difference between coexisting 2/1 and 3/1 islands can affect the radial transport of impurities. The loss of runaway electrons is closely related to the deposition effect of impurity. The impurity is easier to spread into the core region with smaller poloidal phase difference between the radial velocity of impurity and the impurity quantity of Ar.展开更多
The generation of runaway electrons(REs)is observed during the low-density helium ohmic plasma discharge in the Experimental Advanced Superconducting Tokamak(EAST).The growth rate of hard x-ray(HXR)is inversely propor...The generation of runaway electrons(REs)is observed during the low-density helium ohmic plasma discharge in the Experimental Advanced Superconducting Tokamak(EAST).The growth rate of hard x-ray(HXR)is inversely proportional to the line-average density.Besides,the RE generation in helium plasma is higher than that in deuterium plasma at the same density,which is obtained by comparing the growth rate of HXR with the same discharge conditions.The potential reason is the higher electron temperature of helium plasma in the same current and electron density plateau.Furthermore,two Alfvén eigenmodes driven by REs have been observed.The frequency evolution of the mode is not fully satisfied with the Alfvén scaling and when extension of the Alfvén frequency is towards 0,the high frequency branch is~50 kHz.The different spatial position of the two modes and the evolution of the helium concentration could be used to understand deviation between theoretical and experimental observation.展开更多
The main works on disruption mitigation including suppression and mitigation of runaway current on the J-TEXT tokamak are summarized in this paper.Two strategies for the mitigation of runaway electron(RE) beams are ap...The main works on disruption mitigation including suppression and mitigation of runaway current on the J-TEXT tokamak are summarized in this paper.Two strategies for the mitigation of runaway electron(RE) beams are applied in experiments.The first strategy enables the REs to be completely suppressed by means of supersonic molecular beam injection and resonant magnetic perturbation which can enhance RE loss,magnetic energy transfer which can reduce the electric field,and secondary massive gas injection(MGI) which can increase the collisional damping.For the second strategy,the runaway current is allowed to form but should be dissipated or soft landed within tolerance.It is observed that the runaway current can be significantly dissipated by MGI,and the dissipation rate increases with the injected impurity particle number and eventually stabilizes at 28 MA s^(-1).The dissipation rate of the runaway current can be up to 3 MA s^(-1)by ohmic field.Shattered pellet injection has been chosen as the main disruption mitigation method,which has the capability of injecting material deeper into the plasma for higher density assimilation when compared to MGI.Moreover,simulation works show that the RE seeds in the plasma are strongly influenced under different phases and sizes of 2/1 mode locked islands during thermal quench.The robust runaway suppression and runaway current dissipation provide an important insight on the disruption mitigation for future large tokamaks.展开更多
In this paper,overcharge behaviors and thermal runaway(TR)features of large format lithium-ion(Liion)cells with different cathode materials(LiFePO4(LFP),Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_(2)(NCM111),Li[Ni_(0.6)Co_(0.2)Mn_...In this paper,overcharge behaviors and thermal runaway(TR)features of large format lithium-ion(Liion)cells with different cathode materials(LiFePO4(LFP),Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_(2)(NCM111),Li[Ni_(0.6)Co_(0.2)Mn_(0.2)]O_(2)(NCM622)and Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O_(2)(NCM811))were investigated.The results showed that,under the same overcharge condition,the TR of LFP Li-ion cell occurred earlier compared with the NCM Li-ion cells,indicating its poor overcharge tolerance and high TR risk.However,when TR occurred,LFP Li-ion cell exhibited lower maximum temperature and mild TR response.All NCM Liion cells caught fire or exploded during TR,while the LFP Li-ion cell only released a large amount of smoke without fire.According to the overcharge behaviors and TR features,a safety assessment score system was proposed to evaluate the safety of the cells.In short,NCM Li-ion cells have better performance in energy density and overcharge tolerance(or low TR risk),while LFP Li-ion cell showed less severe response to overcharging(or less TR hazards).For NCM Li-ion cells,as the ratio of nickel in cathode material increases,the thermal stability of the cathode materials becomes poorer,and the TR hazards increase.Such a comparison study on large format Li-ion cells with different cathode materials can provide deeper insights into the overcharge behaviors and TR features,and provide guidance for engineers to reasonably choose battery materials in automotive applications.展开更多
Alice Munro is one of the famous Canadian writers and is renowned above all for the astonishing subtlety of her short stories.Her theme has often been the dilemmas of the female coming to terms with family, friends in...Alice Munro is one of the famous Canadian writers and is renowned above all for the astonishing subtlety of her short stories.Her theme has often been the dilemmas of the female coming to terms with family, friends in a small town. This paper attempts to make a brief introduction about the stories of Alice Munro's Runaway and explores the protagonist's choices in the dilemma situation, and then exposes the cruelty of reality is that they cannot get rid of the ineluctable reality of life. Escape is only a temporary action which cannot save them from endless triviality of life. What they should do is not to escape from life, but to adapt to the reality of life.展开更多
Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal sta...Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal stability of commercial lithium-ion batteries, and the internal structure of the battery was analyzed with an in-depth focus on the key factors of the thermal runaway. Through the study of the structure and thermal stability of the cathode, anode, and separator, the results showed that the phase transition reaction of the separator was the key factor affecting the thermal runaway of the battery for the condition of a low state of charge.展开更多
Thermal runaway caused by overcharging results in catastrophic disasters. The influences of charging rate, ambient temperature and aging on thermal runaway caused by overcharging are studied qualitatively and quantita...Thermal runaway caused by overcharging results in catastrophic disasters. The influences of charging rate, ambient temperature and aging on thermal runaway caused by overcharging are studied qualitatively and quantitatively in this manuscript. The results of overcharging tests indicate that high charging rate and ambient temperature increase thermal runaway risk. Aging in 40 ℃ decreases thermal runaway risk. The risk increase of battery with high overcharging rate and in high ambient temperature is due to fast lithium plating reaction and accelerated SEI decomposition, respectively. The risk decrease of aged battery is due to the occurrence of SEI before overcharging tests. SEI suppresses the side reactions between lithium plating and electrolyte. The results of orthogonal tests indicate that the rank of effect is: discharging rate > ambient temperature > aging. The heat generation is calculated based on the results of overcharging tests. The calculation results indicate that heat generated by side reactions contributes more to the total heat generation. Although thermal runaway does not occur during overcharging with low current, the heat dissipation of the lithium-ion battery is the most and deserves focus. The results are important to the design of battery management system and thermal management system to prevent thermal runaway induced by overcharging in total lifespan of battery.展开更多
Runaway is a traditional motif in women's writing. But Alice Munro uses this motif differently. In her short story, Runaway, Munro explores the psychological transition of the female protagonist, Carla, and invest...Runaway is a traditional motif in women's writing. But Alice Munro uses this motif differently. In her short story, Runaway, Munro explores the psychological transition of the female protagonist, Carla, and investigates the intricate issue of women's liberation and social reality. This essay discusses how Munro manipulates the focus of narration in order to reveal the mental struggles experienced by showing a complicated runaway experience by a rural Canadian house-wife living an ordinary life.展开更多
The avoidance of runaway electrons(REs) generated during plasma disruption is of great concern for the safe operation of tokamak devices.Experimental study on the suppression of runaway current by electrode biasing(EB...The avoidance of runaway electrons(REs) generated during plasma disruption is of great concern for the safe operation of tokamak devices.Experimental study on the suppression of runaway current by electrode biasing(EB) and limiter biasing(LB) has been performed on the J-TEXT tokamak,which could be an alternative way to suppress the runaway current.The experimental results show that the higher the voltage value,the smaller the runaway current in both EB and LB experiments.The runaway current can be completely suppressed at an electrode biased voltage of +450 V and a limiter biased voltage of +300 V.The comparison of the energy spectra during the runaway plateau phase shows that the maximum energy max(E_(RE)) and radiation temperature T_(HXR)hard x-rays(HXRs)are significantly reduced after the application of +200 V limiter biased voltage.The electric field generated by the biased voltage may be the key factor to suppress the runaway current,and the measured radial electric field increases obviously after the voltage is applied.This may result in an increase in the loss of REs to realize the suppression of runaway current.展开更多
Recently,experimental studies on the soft landing of RE current by ohmic(OH)field have been performed in J-TEXT tokamak,as a possible auxiliary method to dissipate the RE current.With optimized horizontal displacement...Recently,experimental studies on the soft landing of RE current by ohmic(OH)field have been performed in J-TEXT tokamak,as a possible auxiliary method to dissipate the RE current.With optimized horizontal displacement control of the RE beam,the toroidal electric field has been scanned from 1.6 to—0.3 V m^-1 during the RE plateau phase.The growth rate of RE currents and the evolution of hard x-ray(HXR)emissions have been studied.It is found that when the toroidal electric field is less than 7-12 times the theoretical critical electric field,the decay of REs could be achieved.The dissipation rate by the ohmic field can reach a maximum value of 3 MA s^-1.Furthermore,the results of HXR spectra analysis indicate the different behaviors of HXR emissions under the condition of different toroidal electric fields.The analysis of the ionized argon emissions and magnetic fluctuations shows that under the condition of different toroidal electric fields,the physical process of RE generation may be different.展开更多
In EAST,synchrotron radiation is emitted by runaway electrons in the infrared band,which can be observed by infrared cameras.This synchrotron radiation is mainly emitted by passing runaway electrons with tens of MeV e...In EAST,synchrotron radiation is emitted by runaway electrons in the infrared band,which can be observed by infrared cameras.This synchrotron radiation is mainly emitted by passing runaway electrons with tens of MeV energy.A common feature of radiation dominated by passing runaway electrons is that it is strongest on the high field side.However,the deeply trapped runaway electrons cannot reach the high field side in principle.Therefore,in this case,the high field side radiation is expected to be weak.This paper reports for the first time that the synchrotron radiation from trapped runaway electrons dominates that from passing runaway electrons and is identifiable in an image.Although the synchrotron radiation dominated by trapped runaway electrons can be observed in experiment,the proportion of trapped runaway electrons is very low.展开更多
基金supported by the National Key R&D Program-Strategic Scientific and Technological Innovation Cooperation(Grant No.2022YFE0207900)the National Natural Science Foundation of China(Grant Nos.51706117,52076121)。
文摘Blade batteries are extensively used in electric vehicles,but unavoidable thermal runaway is an inherent threat to their safe use.This study experimentally investigated the mechanism underlying thermal runaway propagation within a blade battery by using a nail to trigger thermal runaway and thermocouples to track its propagation inside a cell.The results showed that the internal thermal runaway could propagate for up to 272 s,which is comparable to that of a traditional battery module.The velocity of the thermal runaway propagation fluctuated between 1 and 8 mm s^(-1),depending on both the electrolyte content and high-temperature gas diffusion.In the early stages of thermal runaway,the electrolyte participated in the reaction,which intensified the thermal runaway and accelerated its propagation.As the battery temperature increased,the electrolyte evaporated,which attenuated the acceleration effect.Gas diffusion affected thermal runaway propagation through both heat transfer and mass transfer.The experimental results indicated that gas diffusion accelerated the velocity of thermal runaway propagation by 36.84%.We used a 1D mathematical model and confirmed that convective heat transfer induced by gas diffusion increased the velocity of thermal runaway propagation by 5.46%-17.06%.Finally,the temperature rate curve was analyzed,and a three-stage mechanism for internal thermal runaway propagation was proposed.In Stage I,convective heat transfer from electrolyte evaporation locally increased the temperature to 100℃.In Stage II,solid heat transfer locally increases the temperature to trigger thermal runaway.In StageⅢ,thermal runaway sharply increases the local temperature.The proposed mechanism sheds light on the internal thermal runaway propagation of blade batteries and offers valuable insights into safety considerations for future design.
基金supported by the National Key R&D Program of China(No.2021YFB2402001)the Postgraduate Innovation and Entrepreneurship Practice Project of Anhui Province(No.2022cxcysj013)+2 种基金the China Postdoctoral Science Foundation(No.2022T150615)the Fundamental Research Funds for the Central Universities(No.WK5290000002)supported by Youth Innovation Promotion Association CAS(No.Y201768)。
文摘The safety valve is an important component to ensure the safe operation of lithium-ion batteries(LIBs).However,the effect of safety valve type on the thermal runaway(TR)and gas venting behavior of LIBs,as well as the TR hazard severity of LIBs,are not known.In this paper,the TR and gas venting behavior of three 100 A h lithium iron phosphate(LFP)batteries with different safety valves are investigated under overheating.Compared to previous studies,the main contribution of this work is in studying and evaluating the effect of gas venting behavior and TR hazard severity of LFP batteries with three safety valve types.Two significant results are obtained:(Ⅰ)the safety valve type dominates over gas venting pressure of battery during safety venting,the maximum gas venting pressure of LFP batteries with a round safety valve is 3320 Pa,which is one order of magnitude higher than other batteries with oval or cavity safety valve;(Ⅱ)the LFP battery with oval safety valve has the lowest TR hazard as shown by the TR hazard assessment model based on gray-fuzzy analytic hierarchy process.This study reveals the effect of safety valve type on TR and gas venting,providing a clear direction for the safety valve design.
基金financially supported by the National Key Research and Development Program(Grant No.2022YFE0207400)the National Natural Science Foundation of China(Grant No.U22A20168 and 52174225)。
文摘Developing technologies that can be applied simultaneously in battery thermal management(BTM)and thermal runaway(TR)mitigation is significant to improving the safety of lithium-ion battery systems.Inorganic phase change material(PCM)with nonflammability has the potential to achieve this dual function.This study proposed an encapsulated inorganic phase change material(EPCM)with a heat transfer enhancement for battery systems,where Na_(2)HPO_(4)·12H_(2)O was used as the core PCM encapsulated by silica and the additive of carbon nanotube(CNT)was applied to enhance the thermal conductivity.The microstructure and thermal properties of the EPCM/CNT were analyzed by a series of characterization tests.Two different incorporating methods of CNT were compared and the proper CNT adding amount was also studied.After preparation,the battery thermal management performance and TR propagation mitigation effects of EPCM/CNT were further investigated on the battery modules.The experimental results of thermal management tests showed that EPCM/CNT not only slowed down the temperature rising of the module but also improved the temperature uniformity during normal operation.The peak battery temperature decreased from 76℃to 61.2℃at 2 C discharge rate and the temperature difference was controlled below 3℃.Moreover,the results of TR propagation tests demonstrated that nonflammable EPCM/CNT with good heat absorption could work as a TR barrier,which exhibited effective mitigation on TR and TR propagation.The trigger time of three cells was successfully delayed by 129,474 and 551 s,respectively and the propagation intervals were greatly extended as well.
基金This work is funded by National Natural Science Foundation of China(Grant No.52006115)Ministry of Science and Technology of China(Grant No.2019YFE0100200)+3 种基金National Natural Science Foundation of China(Grant No.52076121)China National Postdoctoral Program for Innovative Talents(Grant No.BX20190162)China Postdoctoral Science Foundation(Grant No.2019M660631)the Tsinghua University Initiative Scientific Research Program(Grant No.2019Z02UTY06).
文摘Fluorinated electrolytes possess good antioxidant capacity that provides high compatibility to high-voltage cathode and flame retardance;thus,they are considered as a promising solution for advanced lithium-ion batteries carrying both high-energy density and high safety.Moreover,the fluorinated electrolytes are widely used to form stable electrolyte interphase,due to their chemical reactivity with lithiated graphite or lithium.However,the influence of this reactivity on the thermal safety of batteries is seldom discussed.Herein,we demonstrate that the flame-retardant fluorinated electrolytes help to reduce the flammability,while the lithium-ion batteries with flame-retardant fluorinated electrolytes still undergo thermal runaway and disclose their different thermal runaway pathway from that of battery with conventional electrolyte.The reduction in fluorinated components(e.g.,LiPF 6 and fluoroethylene carbonate(FEC))by fully lithiated graphite accounts for a significant heat release during battery thermal runaway.The 13%of total heat is sufficient to trigger the chain reactions during battery thermal runaway.This study deepens the understanding of the thermal runaway mechanism of lithium-ion batteries employing flame-retardant fluorinated electrolytes,providing guidance on the concept of electrolyte design for safer lithium-ion batteries.
基金Project supported by the National MCF Energy Research and Development Program of China (Grant No. 2019YFE03010001)the National Natural Science Foundation of China (Grant No. 11905004)
文摘Runaway electron current generated during the current quench phase of tokamak disruptions could result in severe damage to future high performance devices.To control and mitigate such runaway electron current,it is important to accurately describe the runaway electron current dominated equilibrium,based on which further stability analysis could be carried out.In this paper,we derive a Grad-Shafranov-like equation solving for the axisymmetric drift surfaces of the runaway electrons instead of the magnetic flux surfaces for the simple case that all runaway electrons share the same parallel momentum.This new equilibrium equation is then numerically solved with simple rectangular wall with ITER-like and MAST-like geometry parameters.The deviation between the drift surfaces and the flux surfaces is readily obtained,and runaway electrons are found to be well confined even in regions with open field lines.The change of the runaway electron parallel momentum is found to result in a horizontal current center displacement without any changes in the total current or the external field.The runaway current density profile is found to affect the susceptibility of such displacement,with flatter profiles result in more displacement by the same momentum change.With up-down asymmetry in the external poloidal field,such displacement is accompanied by a vertical displacement of runaway electron current.It is found that this effect is more pronounced in smaller,compact device and weaker poloidal field cases.The above results demonstrate the dynamics of current center displacement caused by the momentum space change in the runaway electrons,and pave a way for more sophisticated runaway current equilibrium theory in the future with more realistic consideration on the runaway electron momentum distribution.This new equilibrium theory also provides foundation for future stability analysis of the runaway electron current.
基金supported by the National Natural Science Foundation of China (52076121, 51977131, and 51877138)the Natural Science Foundation of Shanghai (19ZR1435800)+1 种基金the State Key Lab-oratory of Automotive Safety and Energy under Project No. KF2020the Shanghai Science and Technology Development Fund(19QA1406200)。
文摘Lithium-ion batteries with high-energy density are extensively commercialized in long-range electric vehicles. However, they are poor in thermal stability and pose fire or explosion, which has attracted the global attention. This study describes a new route to mitigate the battery thermal runaway(TR) hazard by poison agents. First, the self-destructive cell is built using the embedded poison layer. Then, the poisoning mechanism and paths are experimentally investigated at the material, electrode, and cell levels. Finally, the proposed route is verified by TR tests. The results show the TR hazard can be significantly reduced in the self-destructive cell based on a new reaction sequence regulation. Specifically, the maximum temperature of the self-destructive cell is more than 300℃ lower than that of the normal cell during TR. The drop in maximum temperature can reduce total heat release and the probability of TR propagation in the battery system, significantly improving battery safety.
基金supported by the Natural Science Foundation of Hebei Province (B2021507001)the National Natural Science Foundation of China (52106284, 52076121)+2 种基金the Ministry of Science and Technology (2022YFE0207900)the support of the Science and Technology Project of Langfang (2021011017)the Project to Promote Innovation in Doctoral Research at CPPU (BSKY202302)。
文摘Structurally compact battery packs significantly improve the driving range of electric vehicles.Technologies like Cell-to-Pack increase energy density by 15%-20%.However,the safety implications of multiple tightly-packed battery cells still require in-depth research.This paper studies thermal runaway propagation behavior in a Cell-to-Pack system and assesses propagation speed relative to other systems.The investigation includes temperature response,extent of battery damage,pack structure deformation,chemical analysis of debris,and other considerations.Results suggest three typical patterns for the thermal runaway propagation process:ordered,disordered,and synchronous.The synchronous propagation pattern displayed the most severe damage,indicating energy release is the largest under the synchronous pattern.This study identifies battery deformation patterns,chemical characteristics of debris,and other observed factors that can both be applied to identify the cause of thermal runaway during accident investigations and help promote safer designs of large battery packs used in large-scale electric energy storage systems.
基金Project partly supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2021445)the Science Foundation of Institute of Plasma Physics of Chinese Academy of Sciences(Grant No.DSJJ-2022-05)partly supported by the Comprehensive Research Facility for Fusion Technology Program of China(Grant No.2018-000052-73-01-001228).
文摘The effect of tearing modes on the confinement of runaway electrons is studied in Experimental Advanced Superconducting Tokamak(EAST).The general tendency of the radial diffusion coefficient of runaway electrons(REs)Dr is derived based on the time response relation between the tearing modes and runaway electrons.The results indicate that,the magnetic fluctuations of tearing modes will enhance the radial diffusion of runaway electrons when the magnetic island is small.Following the increasing of the magnetic fluctuations of the tearing modes,the formed large magnetic island may weaken the radial diffusion of runaway electrons.The results can be important to understand the confinement of runaway electrons when large magnetic islands exist in the plasma.
文摘Two different types of MHD instabilities with rapidly chirping frequency were found to arise in the Globus-M2 spherical tokamak in substantially different frequency ranges.The first type arises at frequencies of an order of 1 MHz in ohmic plasmas at relatively low density(n_(e))<2×10^(19) m^(-3) in a wide range of toroidal magnetic fields and plasma currents.This type of instability was identified as compressional Alfven waves,driven by electrons,accelerated during a sawtooth crush.It was found that the mode frequency is sweeping in time,according to the Berk-Breizman hole-clump nonlinear chirping model.The second type of wave arises in a specific single-swing regime of the central solenoid current with a very narrow plasma column,when the plasma tends to decay at extremely low density(n_(e))<2×10^(18) m^(-3) and,in fact,is an instability of the runaway electron beam.The exited modes cover the whole observed frequency range and are divided into several(two or three)frequency regions:approximately 0-30 MHz,60-120 MHz and sometimes 30-60 MHz.Reconnection of the branches was also observed.Single chirps are more rapid than for 1 MHz Alfven instability and follow an exponential law.This paper,to our knowledge,is the first report of frequency chirping instabilities excited by accelerated electrons at a spherical tokamak.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12175078 and 51821005)
文摘In the experiments of actively triggering plasma disruption by massive gas injection, the externally applied resonant magnetic perturbation has been used to mitigate the hazard of runaway electron(RE). Motivated by the experiment of multimode coupling to suppress REs on J-TEXT, some typical simulation cases with non-ideal MHD with rotation-open discussion(NIMROD) code are carried out to explore the influential mechanism of different relative phases between m/n =2/1 and m/n = 3/1 magnetic islands on the confinement of REs. Results show that the RE confinement is drastically affected by the relative phase between 2/1 and 3/1 magnetic islands. When the O point phase of 2/1 and 3/1 magnetic islands is toroidal 330°, REs can be effectively lost. The fitting curve of the remaining ratio of REs vs. the relative toroidal phase is predicted to approximate a sine-like function dependence. Further studies indicate that the phase difference between coexisting 2/1 and 3/1 islands can affect the radial transport of impurities. The loss of runaway electrons is closely related to the deposition effect of impurity. The impurity is easier to spread into the core region with smaller poloidal phase difference between the radial velocity of impurity and the impurity quantity of Ar.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFE0301205 and 2022YFE03050003)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.Y2021116)+1 种基金the National Natural Science Foundation of China(Grant Nos.12005262,12105186,12175277,and 11975271)the Users of Excellence Program of Hefei Science Center CAS(Grant No.2021HSC-UE016).
文摘The generation of runaway electrons(REs)is observed during the low-density helium ohmic plasma discharge in the Experimental Advanced Superconducting Tokamak(EAST).The growth rate of hard x-ray(HXR)is inversely proportional to the line-average density.Besides,the RE generation in helium plasma is higher than that in deuterium plasma at the same density,which is obtained by comparing the growth rate of HXR with the same discharge conditions.The potential reason is the higher electron temperature of helium plasma in the same current and electron density plateau.Furthermore,two Alfvén eigenmodes driven by REs have been observed.The frequency evolution of the mode is not fully satisfied with the Alfvén scaling and when extension of the Alfvén frequency is towards 0,the high frequency branch is~50 kHz.The different spatial position of the two modes and the evolution of the helium concentration could be used to understand deviation between theoretical and experimental observation.
基金supported by the National MCF Energy R&D Program of China(Nos.2019YFE03010004,2018YFE0309103,2018YFE0310300,2018YFE0309100,2017YFE0302000,2017YFE0300501)National Natural Science Foundation of China(Nos.11775089,51821005,12205122,11905077 and 11575068)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(No.21KJB140025)
文摘The main works on disruption mitigation including suppression and mitigation of runaway current on the J-TEXT tokamak are summarized in this paper.Two strategies for the mitigation of runaway electron(RE) beams are applied in experiments.The first strategy enables the REs to be completely suppressed by means of supersonic molecular beam injection and resonant magnetic perturbation which can enhance RE loss,magnetic energy transfer which can reduce the electric field,and secondary massive gas injection(MGI) which can increase the collisional damping.For the second strategy,the runaway current is allowed to form but should be dissipated or soft landed within tolerance.It is observed that the runaway current can be significantly dissipated by MGI,and the dissipation rate increases with the injected impurity particle number and eventually stabilizes at 28 MA s^(-1).The dissipation rate of the runaway current can be up to 3 MA s^(-1)by ohmic field.Shattered pellet injection has been chosen as the main disruption mitigation method,which has the capability of injecting material deeper into the plasma for higher density assimilation when compared to MGI.Moreover,simulation works show that the RE seeds in the plasma are strongly influenced under different phases and sizes of 2/1 mode locked islands during thermal quench.The robust runaway suppression and runaway current dissipation provide an important insight on the disruption mitigation for future large tokamaks.
基金supported by the National Natural Science Foundation of China(Nos.U1564206,U1764258)the National Key R&D Program of China(No.2018YFB0105700)+1 种基金the support from China Scholarship Council(No.201806030115)supported by the Department of Energy(DOE),Office of Electricity(OE)at Oak Ridge National Laboratory managed by UL-Battelle LLC under contract DE-AC05-00OR22725。
文摘In this paper,overcharge behaviors and thermal runaway(TR)features of large format lithium-ion(Liion)cells with different cathode materials(LiFePO4(LFP),Li[Ni_(1/3)Co_(1/3)Mn_(1/3)]O_(2)(NCM111),Li[Ni_(0.6)Co_(0.2)Mn_(0.2)]O_(2)(NCM622)and Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O_(2)(NCM811))were investigated.The results showed that,under the same overcharge condition,the TR of LFP Li-ion cell occurred earlier compared with the NCM Li-ion cells,indicating its poor overcharge tolerance and high TR risk.However,when TR occurred,LFP Li-ion cell exhibited lower maximum temperature and mild TR response.All NCM Liion cells caught fire or exploded during TR,while the LFP Li-ion cell only released a large amount of smoke without fire.According to the overcharge behaviors and TR features,a safety assessment score system was proposed to evaluate the safety of the cells.In short,NCM Li-ion cells have better performance in energy density and overcharge tolerance(or low TR risk),while LFP Li-ion cell showed less severe response to overcharging(or less TR hazards).For NCM Li-ion cells,as the ratio of nickel in cathode material increases,the thermal stability of the cathode materials becomes poorer,and the TR hazards increase.Such a comparison study on large format Li-ion cells with different cathode materials can provide deeper insights into the overcharge behaviors and TR features,and provide guidance for engineers to reasonably choose battery materials in automotive applications.
文摘Alice Munro is one of the famous Canadian writers and is renowned above all for the astonishing subtlety of her short stories.Her theme has often been the dilemmas of the female coming to terms with family, friends in a small town. This paper attempts to make a brief introduction about the stories of Alice Munro's Runaway and explores the protagonist's choices in the dilemma situation, and then exposes the cruelty of reality is that they cannot get rid of the ineluctable reality of life. Escape is only a temporary action which cannot save them from endless triviality of life. What they should do is not to escape from life, but to adapt to the reality of life.
基金financial supports from National Key R&D Program of China (2018YFC1902200)the key technologies R&D program of Tianjin (18YFZCGX00240)key R&D Program of China Automotive Technology and Research Center Co., Ltd. (18200116)。
文摘Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal stability of commercial lithium-ion batteries, and the internal structure of the battery was analyzed with an in-depth focus on the key factors of the thermal runaway. Through the study of the structure and thermal stability of the cathode, anode, and separator, the results showed that the phase transition reaction of the separator was the key factor affecting the thermal runaway of the battery for the condition of a low state of charge.
基金the support given by National Natural Science Foundation of China(51874184)the Key Natural Science Foundation in Jiangsu Province(18KJA620003)Jiangsu Project Plan for Outstanding Talents Team in Six Research Fields(TD-XNYQC-002)。
文摘Thermal runaway caused by overcharging results in catastrophic disasters. The influences of charging rate, ambient temperature and aging on thermal runaway caused by overcharging are studied qualitatively and quantitatively in this manuscript. The results of overcharging tests indicate that high charging rate and ambient temperature increase thermal runaway risk. Aging in 40 ℃ decreases thermal runaway risk. The risk increase of battery with high overcharging rate and in high ambient temperature is due to fast lithium plating reaction and accelerated SEI decomposition, respectively. The risk decrease of aged battery is due to the occurrence of SEI before overcharging tests. SEI suppresses the side reactions between lithium plating and electrolyte. The results of orthogonal tests indicate that the rank of effect is: discharging rate > ambient temperature > aging. The heat generation is calculated based on the results of overcharging tests. The calculation results indicate that heat generated by side reactions contributes more to the total heat generation. Although thermal runaway does not occur during overcharging with low current, the heat dissipation of the lithium-ion battery is the most and deserves focus. The results are important to the design of battery management system and thermal management system to prevent thermal runaway induced by overcharging in total lifespan of battery.
文摘Runaway is a traditional motif in women's writing. But Alice Munro uses this motif differently. In her short story, Runaway, Munro explores the psychological transition of the female protagonist, Carla, and investigates the intricate issue of women's liberation and social reality. This essay discusses how Munro manipulates the focus of narration in order to reveal the mental struggles experienced by showing a complicated runaway experience by a rural Canadian house-wife living an ordinary life.
基金supported by National MCF Energy R&D Program of China(No.2019YFE03010004)National Key R&D Program of China(No.2018YFE0309100)+1 种基金National Natural Science Foundation of China(Nos.11775089 and 51821005)National Magnetic Confinement Fusion Science Program of China(Nos.2015GB111002 and 2015GB104000)
文摘The avoidance of runaway electrons(REs) generated during plasma disruption is of great concern for the safe operation of tokamak devices.Experimental study on the suppression of runaway current by electrode biasing(EB) and limiter biasing(LB) has been performed on the J-TEXT tokamak,which could be an alternative way to suppress the runaway current.The experimental results show that the higher the voltage value,the smaller the runaway current in both EB and LB experiments.The runaway current can be completely suppressed at an electrode biased voltage of +450 V and a limiter biased voltage of +300 V.The comparison of the energy spectra during the runaway plateau phase shows that the maximum energy max(E_(RE)) and radiation temperature T_(HXR)hard x-rays(HXRs)are significantly reduced after the application of +200 V limiter biased voltage.The electric field generated by the biased voltage may be the key factor to suppress the runaway current,and the measured radial electric field increases obviously after the voltage is applied.This may result in an increase in the loss of REs to realize the suppression of runaway current.
基金supported by the National Key R&D Program of China(No.2017YFE0302000)the National Magnetic Confinement Fusion Science Program of China(Nos.2015GB111002,2015GB104000)+1 种基金National Natural Science Foundation of China(Nos.11775089,51821005,71762031,11575068,11905077)the China Postdoctoral Science Foundation(2019M652615)。
文摘Recently,experimental studies on the soft landing of RE current by ohmic(OH)field have been performed in J-TEXT tokamak,as a possible auxiliary method to dissipate the RE current.With optimized horizontal displacement control of the RE beam,the toroidal electric field has been scanned from 1.6 to—0.3 V m^-1 during the RE plateau phase.The growth rate of RE currents and the evolution of hard x-ray(HXR)emissions have been studied.It is found that when the toroidal electric field is less than 7-12 times the theoretical critical electric field,the decay of REs could be achieved.The dissipation rate by the ohmic field can reach a maximum value of 3 MA s^-1.Furthermore,the results of HXR spectra analysis indicate the different behaviors of HXR emissions under the condition of different toroidal electric fields.The analysis of the ionized argon emissions and magnetic fluctuations shows that under the condition of different toroidal electric fields,the physical process of RE generation may be different.
基金the National Natural Science Foundation of China(Grant No.11775263)the National Magnetic Confinement Fusion Energy Research Project of China(Grant No.2015GB111003).
文摘In EAST,synchrotron radiation is emitted by runaway electrons in the infrared band,which can be observed by infrared cameras.This synchrotron radiation is mainly emitted by passing runaway electrons with tens of MeV energy.A common feature of radiation dominated by passing runaway electrons is that it is strongest on the high field side.However,the deeply trapped runaway electrons cannot reach the high field side in principle.Therefore,in this case,the high field side radiation is expected to be weak.This paper reports for the first time that the synchrotron radiation from trapped runaway electrons dominates that from passing runaway electrons and is identifiable in an image.Although the synchrotron radiation dominated by trapped runaway electrons can be observed in experiment,the proportion of trapped runaway electrons is very low.
