Thermal safety boundary of lithium-ion battery at different state of charge

Thermal runaway(TR)is a critical issue hindering the large-scale application of lithium-ion batteries(LIBs).Understanding the thermal safety behavior of LIBs at the cell and module level under different state of charges(SOCs)has significant implications for reinforcing the thermal safety design of the lithium-ion battery module.This study first investigates the thermal safety boundary(TSB)correspondence at the cells and modules level under the guidance of a newly proposed concept,safe electric quantity boundary(SEQB).A reasonable thermal runaway propagation(TRP)judgment indicator,peak heat transfer power(PHTP),is proposed to predict whether TRP occurs.Moreover,a validated 3D model is used to quantitatively clarify the TSB at different SOCs from the perspective of PHTP,TR trigger temperature,SOC,and the full cycle life.Besides,three different TRP transfer modes are discovered.The interconversion relationship of three different TRP modes is investigated from the perspective of PHTP.This paper explores the TSB of LIBs under different SOCs at both cell and module levels for the first time,which has great significance in guiding the thermal safety design of battery systems.

Design study of charge-stripping scheme of heavy ion beams for HIAF-BRing

Charge strippers play an essential role in heavy-ion accelerators by stripping the projectile ions to higher charge states to enhance the acceleration efficiency downstream of the stripper.In the high-energy mode of the booster ring(BRing)of the high-intensity heavy-ion accelerator facility,the pre-accelerated ions from the iLinac will be stripped by a carbon foil to higher charge states and then injected into the BRing.The key parameters of the stripper and stripped ions were calculated,and the influence of stripping on the beam quality was discussed.To get high stripping efficiencies,the foil thicknesses and resultant charge state distributions for the typical ions were determined by the code ETACHA.The equilibrium thickness was obtained for the U beam,while the stripper thicknesses for the Xe and Kr beams were determined based on a compromise between the stripped charge states and the stripping efficiency.The energy loss,energy straggling,and emittance growth due to stripping have a non-negligible impact on the transport of the stripped beams and the injection of the ring.Therefore,these parameters were simulated by GEANT4.In addition,the foil’s temperature evolution,which greatly affects the foil lifetime,was simulated by ANSYS.The maximum temperature of the foil bombarded by the U and Xe beams with the nominal parameters will exceed the safe value in terms of the impact of evaporation on the foil’s lifetime.Given the foil temperature constraint,the highest tolerable beam intensity and the injected ion number into the ring were derived for different beam sizes.The results of this paper will present important reference data for the optimization design and commissioning of the beamline and injection to the BRing for the stripped ions.

Study about thermal runaway behavior of high specific energy density Li-ion batteries in a low state of charge

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.

Effects of surface charges on phonon properties and thermal conductivity in GaN nanofilms

Surface charges can modify the elastic modulus of nanostructure,leading to the change of the phonon and thermal properties in semiconductor nanostructure.In this work,the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated.In the framework of continuum mechanics,the modified elastic modulus can be derived for the nanofilm with surface charges.The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation,phonon group velocity,density of states of phonons in nanofilm with the surface charges.The phonon thermal conductivity of nanofilm can be obtained by considering surface charges.The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm.Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons.The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm.Based on these theoretical results,one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.

Effects ofmodulenumberand firing conditiononchargethermal safetyingunchamber

Thermal safety of modular charge which is fed into and retained in the chamber after gun fires consecutively is first investigated with cook-off method,A two-dimensional cook-off model of modular charge in gun chamber is established and the cook-off process of modular charge in gun chamber is numerically simulated.Then the effects of module number and firing condition on charge thermal safety are evaluated by researching the cook-off response characteristics of modules.The results show that under conditions of different module numbers the cook-off responses all occur on the module closest to the boundary of missile,and the single-base propellants located at the inner surface of cartridge ignite first.When the number of loaded module changes from 1 to 6,the cook-off response temperatures vary little,only in a small range of 478.1 K-482.4 K.The cook-off response times decrease logarithmically in the range of 211.25-166.7 s with the increasing length of residual air gap in gun chamber.The simulation results are well matched with the experimental data.Furthermore,different firing conditions have greatinfluence on the cook-off response time,minor influence on the initial response position and little in-fluence on the response temperature.Under the three conditions of consecutive 32 launches with 5 rounds/min,43 launches with 1 round/min,and 41 launches with different firing frequencies,the cook off response temperatures are 479.2 K,481.1 K and 479.9 K respectively and the response times are 709.25,211.2 s and 214.4 s respectively.The response position is near the middle area of the inner cartridge surface in the former condition and near the right area in the latter two conditions.

Time-Temperature Charge Function of a High Dynamic Thermal Heat Storage with Phase Change Material

A thermal heat storage system with an energy content of 40 kWh and a temperature of 58°C will be presented. This storage system is suitable for supporting the use of renewable energies in buildings and for absorbing solar heat, heat from co-generation and heat pumps or electric heat from excess wind and solar power. The storage system is equipped with a plate heat exchanger that is so powerful that even with small temperature differences between the flow temperature and the storage temperature a high load dynamic is achieved. The storage system has a performance of 2.8 kW at 4 K and 10.6 kW at a temperature difference of 10 K. Thus, large performance variations in solar thermal systems or CHP plants can be buffered very well. Further a storage charge function Q(T, t) will be presented to characterize the performance of the storage.

Comparison Between Thermally Stimulated Discharge Method and Photo-stimulated Discharge Method for Measuring Space Charge Traps Energy

The space charge behavior of a dielectric under HVDC is influenced by the charge trap energy distribution in it. Hence, we in- vestigated the charge trap distributions in several kinds of typical polymer materials using thermally stimulated discharge (TSD) and photo-stimulated discharge (PSD) methods, respectively. The experimental results show that,there is a significant difference between the trap energy distributions obtained by the two methods, but the difference decreases with the increase of the melting point of polymers. This is attributed to the change of the trap center environment during TSD caused by the increasing movements of both main chains and branched chains in polymers. PSD method is more accurate for investigating charge trap distribution in dielectrics, especially for polymers with low melting points.

Charge storage characteristics of hydrogenated nanocrystalline silicon film prepared by rapid thermal annealing

The early stages of hydrogenated nanocrystalline silicon （nc-Si：H） films deposited by plasma-enhanced chemical vapour deposition were characterized by atomic force microscopy. To increase the density of nanocrystals in the nc-Si：H films, the films were annealed by rapid thermal annealing （RTA） at different temperatures and then analysed by Raman spectroscopy. It was found that the recrystallization process of the film was optimal at around 1000℃. The effects of different RTA conditions on charge storage were characterized by capacitance-voltage measurement. Experimental results show that nc-Si：H films obtained by RTA have good charge storage characteristics for nonvolatile memory.

The influence of thermally assisted tunneling on the performance of charge trapping memory

We evaluate the influence of the thermally assisted tunneling （TAT） mechanism on charge trapping memory （CTM） cell performance by numerical simulation, and comprehensively analyse the effects of the temperature, trap depth, distribution of trapped charge, gate voltage and parameters of TAT on erasing/programming speed and retention performance. TAT is an indispensable mechanism in CTM that can increase the detrapping probability of trapped charge. Our results reveal that the TAT effect causes the sensitivity of cell performance to temperature and it could affect the operational speed, especially for the erasing operation. The results show that the retention performance degrades compared with when the TAT mechanism is ignored.

Investigating the Thermal Stress of Millisecond Pulsed Laser Irradiation on Charge-Coupled Devices

In this study, a two-dimensional model describing thermal stress on a charge-coupled device (CCD) induced by ms laser pulses was examined. Considering the nonlinearity of the CCD’s material parameters and the melting phase transition process of aluminum electrode materials was considered by using equivalent specific heat capacity method, the physical process where a laser pulse irradiating a CCD pixel array was simulated using COMSOL Multiphysics software. The temperature field and thermal stress field were calculated and analyzed. In order to clarify the mechanism producing damage on the CCD detector, Raman spectra from silicon were measured with a micro-Raman spectrometer to determine stress change in the CCD chip. The procedure presented herein illustrates a method for evaluating strain in a CCD after laser irradiation.

Supramolecular Thermally Activated Delayed Fluorescence Materials via Through-Space Charge Transfer

Thermally activated delayed fluorescence(TADF)polymeric materials based on through-space charge transfer(TSCT)have emerged as a highly studied topic in recent years.However,the construction of TSCT TADF materials via a supramolecular approach is still a big challenge.In this work,we report the noncovalent synthesis of TSCT TADF materials using a cyclic peptide-based bottle-brushed supramolecular polymer as a scaffold.By bringing the TSCT donor and acceptor in close proximity in space using the supramolecular scaffold,distinctive TADF emission in both solution and solid states could be achieved.Furthermore,the TADF system could be utilized as a sensitizer to coassemble with fluorescence acceptors to build thermally assisted fluorescence systems,resulting in color-tunable delayed fluorescence with high efficiency and color purity.Our findings provide a facile yet effective approach to designing and fabricating TSCT TADF materials,which might hold great potential for applications in the fields of organic light-emitting diode,bioimaging,and sensing.

Intramolecular spatial charge transfer enhances TADF efficiency

Organic thermally activated delayed fluorescence (TADF)emitters have been advancing fast since 2012, behaving like the next-generation electroluminescent (EL) materials with the advantages of 100%exciton utilization efficiency, full-color emission tunability, and low cost[1].

Charge-transfer interaction of drug quinidine with quinol,picric acid and DDQ: Spectroscopic characterization and biological activity studies towards understanding the drug–receptor mechanism

Investigation of charge-transfer （CT） complexes of drugs has been recognized as an important phenomenon in understanding of the drug-receptor binding mechanism. Structural, thermal, morpholo-gical and biological behavior of CT complexes formed between drug quinidine （Qui） as a donor and quinol （QL）, picric acid （PA） or dichlorodicyanobenzoquinone （DDQ） as acceptors were reported. The newly synthesized CT complexes have been spectroscopically characterized via elemental analysis;infrared （IR）, Raman, 1H NMR and electronic absorption spectroscopy; powder X-ray diffraction （PXRD）;thermogravimetric （TG） analysis and scanning electron microscopy （SEM）. It was found that the obtained complexes are nanoscale, semi-crystalline particles, thermally stable and spontaneous. The molecular composition of the obtained complexes was determined using spectrophotometric titration method and was found to be 1：1 ratios （donor：acceptor）. Finally, the biological activities of the obtained CT complexes were tested for their antibacterial activities. The results obtained herein are satisfactory for estimation of drug Qui in the pharmaceutical form

Multiband nodeless superconductivity near the charge-density-wave quantum critical point in ZrTe(3-x)Sex

It was found that selenium doping can suppress the charge-density-wave（CDW） order and induce bulk superconductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point（QCP） in ZrTe3-xSex near x ≈ 0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe（3-x）Sex single crystals（x = 0.044 and 0.051） down to 80 m K. For both samples, the residual linear term κ0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence of κ0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe（3-x）Sex,which indicates conventional superconductivity despite of the existence of a CDW QCP.

不同荷电状态磷酸铁锂电池热失控温度与产气特性分析

新能源产业的飞速发展使磷酸铁锂电池广泛应用于储能领域。磷酸铁锂电池电解液固有的可燃性使其热稳定性和安全性问题不容忽视。为了更好地防控储能电站的爆炸事故,有必要开展储能电池的热失控过程研究,并对产气过程和产气组分的危害性进行深入分析。开展了不同荷电状态(State of Charge, SOC)60 Ah磷酸铁锂电池热失控试验,根据电池温度演变曲线,将电池热失控过程分成三个阶段;依据电池产气曲线,将电池产气过程分为四个阶段;使用FLACS软件建模对预混气体进行了爆炸仿真,探索了SOC对可燃气体燃爆行为的影响规律,混合可燃气体的爆炸上下限和爆炸超压随着SOC的增大而增大。研究成果对储能电站的安全防护具有理论指导意义。

电动汽车ChaoJi充电连接器温升仿真方法

高功率充电桩在工作过程中,长时间大电流充电使其连接器温升明显。针对此电动汽车大功率充电的发展需求,对ChaoJi充电连接器的温升仿真建模及软件仿真开展研究。首先,简化连接器的结构为圆筒状,结合接触件的结构类型以及接触电阻的影响因素,研究连接器接触点的热效应模型;其次,研究ChaoJi充电连接器的温升仿真方法;最后,对ChaoJi连接器进行软件热仿真,由此验证ChaoJi充电接口温升模型,得出温升值与通电电流约为二次方关系的结论。所研究的ChaoJi充电连接器温升模型及软件热仿真在一定程度上弥补了充电接口温升研究的空白。

多脉冲飞秒激光切割加工炸药装药过程的热响应

为分析多脉冲飞秒激光切割加工炸药过程的安全性,建立多脉冲飞秒激光切割加工炸药装药的二维数值计算模型,对飞秒激光切割加工HMX、TATB、RDX和TNT 4种炸药装药的情况进行数值计算,获得不同加工状况下炸药装药的热响应规律。实验结果表明:飞秒激光切割加工炸药装药过程中,当激光光斑的移动速度为80~300 mm/min时,4种炸药均未发生点火,反应光斑移动速度越慢,热累积效应越明显,且HMX相比其他3种炸药,动态分析区内HMX的热累积效应最明显;当激光重复频率和能量分别为0.1~200 kHz和50~200μJ/pulse时,提高飞秒激光的重复频率和能量对切割速率提升效果呈先上升后降低趋势;飞秒激光对炸药装药的切割加工速率和安全性,会受到炸药的性能参数的影响,切割速率与炸药的激光吸收系数呈正相关,切割安全性与炸药的热感度呈负相关。

不同充电条件下三元锂电池过充热失控研究

为了研究充电倍率以及充电倍率的调整方式对过充条件下三元锂电池热失控的影响,分别以0.5C、1.0C、1.5C充电倍率将锂电池过充至热失控。此外,以0.5C充至电池表面温度不再上升时,分别以0.5C和0.07C的幅度逐步调高充电倍率,直至发生热失控。结果表明:以0.5C过充时,在短时间内不会发生热失控;以1.0C和1.5C过充时,均会发生热失控,且1.5C下热失控所需时间更短,热失控的危害更大。相比于采用0.5C幅度提高充电倍率的调节方式,采用0.07C幅度的调节方式会显著提高临界充电倍率,从而降低热失控的风险;以0.07C逐步提高充电倍率的过程中存在一个拐点倍率,当充电倍率小于此拐点倍率时,充电倍率与其对应的峰值温度呈线性关系,而当充电倍率大于拐点倍率后,继续提高充电倍率会导致热失控;先以0.5C过充,而后提高充电倍率导致热失控,其热失控危害远低于1.0C和1.5C过充的危害。因此,应当在符合实际需求的前提下采取较低的充电倍率。如需增加充电倍率,采取缓慢增加的方式有助于降低电池发生热失控的风险。

电动车跨临界CO_(2)热系统充注定量需求规律及非适充系统失稳特性

跨临界CO_(2)热系统是解决电动车“低温续航衰减”和“热系统工质温室效应强”主要问题的最佳技术之一,而电动车多变场景耦合跨临界循环复杂性,系统性能及运行稳定性强依赖于充注量。通过仿真研究了跨临界CO_(2)热系统在不同工况下的CO_(2)充注量定量需求变化规律。重点研究了环境温度、室内风量和室外风速这3个关键因素对不同模式下的系统制冷剂需求量的影响机理和定量表征;并探讨了在非适充场景下的系统动态特性。结果表明:热泵模式下,制冷剂需求下限随环境温度的升高、室内风量的降低和室外风速的增加而增大,其定量影响幅度为18.6%、6.16%和18.9%。制冷模式下,制冷剂需求下限则随环境温度的降低、室内风量的降低和室外风速的增加而增大,其定量影响幅度为7.03%、7.85%和2.27%。在非适充工况下,因非适充下的系统控制量与目标量作用关系发生潜在变化,导致系统出现失控,需要通过制冷剂分布调控缓解特殊工况的系统不稳定性。研究结果对于优化电动汽车空调系统储液器设计、提高其能效和舒适性具有重要参考价值。

B/KNO_(3)点火药装药的烤燃特性研究

为研究B/KNO_(3)点火药的热安全性,建立多点测温烤燃实验装置,对不同升温速率、不同装药密度条件下的B/KNO_(3)点火药装药进行多点测温烤燃实验,以获得点火药装药发生点火的准确时间与烤燃过程中不同监测点的温度历程。建立B/KNO_(3)点火药装药烤燃实验的数值计算模型并进行了数值模拟,计算中考虑了点火药的自热分解反应与相变吸热。通过与实验结果的对比,标定B/KNO_(3)点火药装药的热物性参数和反应动力学参数。研究结果表明:B/KNO_(3)点火药的指前因子为7.763×10^(13)s^(-1),活化能为2.0787×10^(5)J/mol;在点火药装药的烤燃过程中,随着升温速率的减小,点火延期时间逐渐增加,点火区域逐渐向中心移动,点火环境温度逐渐降低;在装药密度变化不太大的情况下,点火药的点火特征差别不大。