A polyethylene microsphere-coated separator with rapid thermal shutdown function for lithium-ion batteries

Thermal runaway is the main factor contributing to the unsafe behaviors of lithium-ion batteries(LIBs)in practical applications.The application of separators for the thermal shutdown has been proven as an effective approach to protecting LIBs from thermal runaway.In this work,we developed a thermal shutdown separator by coating a thin layer of low-density polyethylene microspheres(PM)onto a commercial porous polypropylene(PP)membrane and investigated the thermal response behaviors of the as-prepared PM/PP separator in LIBs.The structural and thermal analysis results revealed that the coated PM layer had a porous structure,which facilitated the occurrence of normal charge-discharge reactions at ambient temperature,although it could melt completely and fuse together within very short time periods:3 s at 110℃and 1 s at 120℃,to block off the pores of the PP substrate,thereby cutting off the ion transportation between the electrodes and interrupting the battery reaction.Consequently,the PM/PP separator exhibits very similar electrochemical performance to that of a conventional separator at ambient temperature.However,it performs a rapid thermal shutdown at an elevated temperature of^110℃,thus controlling the temperature rise and maintaining the cell in a safe status.Due to its synthetic simplicity and low cost,this separator shows promise for possible application in building safe LIBs.

Non-Linear Ion-Acoustic Solitary Waves in Electron-Positron-Ion Plasma with Non-Thermal Electrons

Ion-acoustic solitary (IAS) waves in electron-positron-ion (e-p-i) plasma have been of interest to many researchers probably due to their relevance in understanding the Universe. However, the study of non-linear ion-acoustic waves in e-p-i plasma with non-thermal electrons has not been adequately studied. A theoretical investigation on non-linear IAS waves in e-p-i plasma comprising of warm inertial adiabatic fluid ions and electrons that are kappa distributed, and Boltzman distributed positron is presented here using the Sagdeev potential technique. It was found that existence domains of finite amplitude IAS waves were confined within the limits of minimum and maximum Mach numbers with varying k values. For lower values of k, the amplitude of the solitary electrostatic potential structures increased as the width decreased, while for high values, the potential amplitude decreased as the width of the solitary structure increased.

Thermal annealing induced photocarrier radiometry enhancement for ion implanted silicon wafers

An experimental study on the photocarrier radiometry signals of As^＋ ion implanted silicon wafers before and after rapid thermal annealing is performed. The dependences of photocarrier radiometry amplitude on ion implantation dose （1×10^11-1×10^16/cm^2）, implantation energy （20-140 keV） and subsequent isochronical annealing temperature （500- 1100℃ are investigated. The results show that photocarrier radiometry signals are greatly enhanced for implanted samples annealed at high temperature, especially for those with a high implantation dose. The reduced surface recombination rate resulting from a high built-in electric field generated by annealing-activated impurities in the pn junction is believed to be responsible for the photocarrier radiometry signal enhancement. Photocarrier radiometry is contactless and can therefore be used as an effective in-line tool for the thermal annealing process monitoring of the ion-implanted wafers in semiconductor industries.

Thermal stability of LiPF_6/EC+DMC+EMC electrolyte for lithium ion batteries

The thermal stability of lithium-ion battery electrolyte could substantially affect the safety of lithium-ion battery. In order to disclose the thermal stability of 1.0 mol·L-1 LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC)+ethylmethyl carbonate (EMC) electrolyte, a micro calorimeter C80 micro calorimeter was used in this paper. The electrolyte samples were heated in argon atmosphere, and the heat flow and pressure performances were detected. It is found that LiPF6 influences the thermal behavior remarkably, with more heat generation and lower onset temperature. LiPF6/EC shows an exothermic peak at 212 ℃ with a heat of reaction -355.4 J·g-1. DMC based LiPF6 solution shows two endothermic peak temperatures at 68.5 and 187 ℃ in argon filled vessel at elevated temperature. EMC based LiPF6 solution shows two endothermic peak temperatures at 191 and 258 ℃ in argon filled vessel. 1.0 mol·L-1 LiPF6/EC+DMC+ EMC electrolyte shows an endothermic and exothermic process one after the other at elevated temperature. By comparing with the thermal behavior of single solvent based LiPF6 solution, it can be speculated that LiPF6 may react with EC, DMC and EMC separately in 1.0 mol·L-1 LiPF6/EC+DMC+EMC electrolyte, but the exothermic peak is lower than that of 1.0 mol·L-1 LiPF6/EC solution. Furthermore, The 1.0 mol·L-1 LiPF6/EC+DMC+EMC electrolyte decomposition reaction order was calculated based on the pressure data, its value is n=1.83, and the pressure rate constants kp=6.49×10-2 kPa·-0.83·min-1.

TiO_2 nanofilm growth by Ti ion implantation and thermal annealing in O_2 atmosphere

TiO2 nanofilms on surface of fused silica were fabricated by Ti ion implantation and subsequent thermal annealing in oxygen ambience. The silica glasses were implanted by 20 k V Ti ions to 1.5 × 1017ions/cm2 on an implanter of metal vapor vacuum arc(MEVVA) ion source. Effects of annealing parameters on formation,growth and phase transformation of the TiO2 nanofilms were studied in detail. Optical absorption spectroscopy,Raman scattering spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy measurements were done to figure out formation mechanism of the TiO2 nanofilms.The formation of TiO2 nanofilms was due to out-diffusion of the implanted Ti ions to the substrate surface,where they were oxidized into TiO2 nanoparticles. Formation, phase, and thickness of the TiO2 nanofilms can be well tailored by controlling annealing parameters.

Influence of Ga^+ ion irradiation on thermal relaxation of exchange bias field in exchange-coupled CoFe/IrMn bilayers

This paper reports that the CoFe/IrMn bilayers are deposited by magnetron sputtering on the surfaces of thermallyoxidized Si substrates. It investigates the thermal relaxations of both non-irradiated and Ca^＋ ion irradiated CoFe/IrMn bilayers by means of holding the bilayers in a negative saturation field. The results show that exchange bias field decreases with the increase of holding time period for both non-irradiated and Ca^＋ ion irradiated CoFe/IrMn bilayers. Exchange bias field is also found to be smaller upon irradiation at higher ion dose. This reduction of exchange bias field is attributed to the change of energy barrier induced by ion-radiation.

Strategies to curb structural changes of lithium/transition metal oxide cathode materials & the changes' effects on thermal & cycling stability

Structural transformation behaviors of several typical oxide cathode materials during a heating process are reviewed in detail to provide in-depth understanding of the key factors governing the thermal stability of these materials. We also discuss applying the information about beat induced structural evolution in the study of electrochemically induced structural changes. All these discussions are expected to provide valuable insights for designing oxide cathode materials with significantly improved structural stability for safe, long-life lithium ion batteries, as the safety of lithium-ion batteries is a critical issue; it is widely accepted that the thermal instability of the cathodes is one of the most critical factors in thermal runaway and related safety problems.

Thermal Equilibration in the Cavity Volume of a Farmer Ion Chamber for Routine Dosimetry

A Farmer ion chamber with an air cavity volume is the most widely used dosimeter for accurate dose determinations in radiotherapy. The quantity of ionization in the cavity volume occurred a given radiation dose has to be corrected to the cavity air temperature according to a dosimetry protocol because the mass of air in the cavity volume is subject to atmospheric variations. In the present study, we aim to measure the thermal equilibration time in the cavity volume of a Farmer ion chamber for the routine dosimetry. The Farmer ion chamber’s electrode was replaced by a thin thermocouple and coated by the PMMA for a waterproofing so that the measurement of the temperature in the cavity performed in water. As a result of the measurement, A Farmer ion chamber in thermal equilibrium with waterproofing equilibrates rapidly, followed by an exponential fall-off. In water, equilibration to less than 10% of the initial temperature difference required only a few minutes. Thermal equilibrium time is hardly affected by the room temperature change.

Optimization of Synthesis Conditions of LiMn_2–xFe_xO₄Cathode Materials Based on Thermal Characterizations

We have synthesized LiMn2–xFexO4 (x = 0, 0.25, and 0.50) cathode materials for applications in Li ion rechargeable batteries via sol-gel method. We studied thermal characteristics of as synthesized materials using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In order to optimize the synthesis conditions, we studied X-ray diffraction (XRD) of synthesized cathode materials at various temperatures, based on the transitions obtained from DSC/TGA. The XRD results can be co-related to the thermal behavior of the synthesized cathode materials and the synthesis conditions optimized.

Surface modification of polyolefin separators for lithium ion batteries to reduce thermal shrinkage without thickness increase

Surface chemical modification of polyolefin separators for lithium ion batteries is attempted to reduce the thermal shrinkage, which is im- portant for the battery energy density. In this study, we grafted organic/inorganic hybrid crosslinked networks on the separators, simply by grafting polymerization and condensation reaction. The considerable silicon-oxygen crosslinked heat-resistance networks are responsible for the reduced thermal shrinkage. The strong chemical bonds between networks and separators promise enough mechanical support even at high temperature. The shrinkage at 150 ℃ for 30 min in the mechanical direction was 38.6% and 4.6% for the pristine and present graft-modified separators, respectively. Meanwhile, the grafting organic-inorganic hybrid crosslink networks mainly occupied part of void in the internal pores of the separators, so the thicknesses of the graft-modified separators were similar with the pristine one. The half cells prepared with the modified separators exhibited almost identical electrochemical properties to those with the commercial separators, thus proving that, in order to enhance the thermal stability of lithium ion battery, this kind of grafting-modified separators may be a better alternative to conventional silica nanoparticle layers-coated polyolefin separators.

Synthesis and characterization of novel cathode material Li_3V_2(PO_4)_3 by carbon-thermal reduction method

Li3V2(PO4)3 cathode material was prepared by a carbon-thermal reduction (CTR) process. V2O5, LiOH-H2O, NH4H2PO4 and C were used as starting materials to synthesize Li3V2(PO4)3 by sintering the mixture at 800℃for 24 h. The property of the Li3V2(PO4)3 sample was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurement. The results show that the Li3V2(PO4)3 sample has the same monoclinic structure as the Li3V2(PO4)3 sample synthesized by hydrogen reduction method. The particle size is about 1.5μm together with homogenous distribution. The initial discharge capacity of Li3V2(PO4)3 powder is 120 mA·h·g-1 at the rate of 0.1C, and the capacity retains 112 mA·h·g-1 after 30 cycles.

Thickness Dependence of Structural and Optical Properties of Chromium Thin Films as an Infrared Reflector for Solar-thermal Conversion Applications

The thermal emittance of Cr film, as an IR reflector, was investigated for the use in SSAC. The Cr thin films with different thicknesses were deposited on silicon wafers, optical quartz and stainless steel substrates by cathodic arc ion plating technology as a metallic IR reflector layer in SSAC. The thickness of Cr thin films was optimized to achieve the minimum thermal emittance. The effects of structural, microstructural, optical, surface and cross-sectional morphological properties of Cr thin films were investigated on the emittance. An optimal thickness about 450 nm of the Cr thin film for the lowest total thermal emittance of 0.05 was obtained. The experimental results suggested that the Cr metallic thin film with optimal thickness could be used as an effective infrared reflector for the development of SSAC structure.

Thermal analysis of EAST neutral beam injectors for long-pulse beam operation

Two sets of neutral beam injectors(NBI-1 and NBI-2) have been mounted on the EAST tokamak since 2014. NBI-1 and NBI-2 are co-direction and counter-direction, respectively. As with indepth physics and engineering study of EAST, the ability of long pulse beam injection should be required in the NBI system. For NBIs, the most important and difficult thing that should be overcome is heat removal capacity of heat loaded components for long-pulse beam extraction. In this article, the thermal state of the components of EAST NBI is investigated using water flow calorimetry and thermocouple temperatures. Results show that(1) operation parameters have an obvious influence on the heat deposited on the inner components of the beamline,(2) a suitable operation parameter can decrease the heat loading effectively and obtain longer beam pulse length, and(3) under the cooling water pressure of 0.25 MPa, the predicted maximum beam pulse length will be up to 260 s with 50 keV beam energy by a duty factor of 0.5. The results present that, in this regard, the EAST NBI-1 system has the ability of long-pulse beam injection.

航空动力锂离子电池热失控高温与冲击危害的被动防护包容性

锂离子电池热失控造成的热冲击将损坏安装结构,对周围人员和设备安全构成威胁,是限制其在航空领域应用的关键问题。通过自主搭建的锂离子电池热失控高温冲击实验平台研究发现,单节电池热冲击对电池包顶板的冲击压力高达13.23 kPa,致使其外表面温度高达274℃。为了有效包容锂离子电池热失控造成的高温冲击危害,提出了电池包顶板涂敷防火涂层的被动防护方法。通过实验研究发现,环氧树脂基膨胀型防火涂层可通过膨胀有效阻隔锂离子电池热失控冲击压力的影响,通过吸收热量降低并延缓电池包顶板的温度上升。分析锂离子电池热失控包容性验证实验结果可知,1.0 mm厚的E80S20涂层和E85S15B3涂层分别使电池包顶板最高温度下降52.16%和55.80%,结构最高形变分别降低72.2%和44.4%。研究结果表明,防火涂层被动防护技术能够有效提升电池舱体对热失控高温和冲击危害的包容性,可作为航空动力锂离子电池系统安全性设计的有效措施。

低温循环老化航空锂离子电池热失控的爆炸危险性

鉴于全寿命周期内循环老化后航空锂离子电池热失控反应较新电池有显著差异,且低温环境对锂离子电池系统重大失效危险性影响更加贴近低空实际飞行场景,自主搭建了锂离子电池热失控及气体爆炸测试平台,采用锂离子电池的热失控时间、表面峰值温度和热失控超压及热失控气体的爆炸极限、压力及温度为关键参数,探讨低温(-10℃)循环老化对锂离子电池热失控爆炸危险性的影响。实验结果显示,常温循环老化锂离子电池较新电池热失控时间明显提前和电池安全阀开启到完全热失控的时间间隔明显增长,分别为559.86和122.56 s,且热失控气体爆炸下限升高30.95%,气体爆炸压力降低至258.6 kPa;低温环境因素则会使老化锂离子电池热失控的爆炸危险性发生显著变化,导致热失控时间提前至412.38 s,安全阀打开到完全热失控的时间间隔缩短至56.66 s,并使热失控气体爆炸下限降低20.49%,爆炸压力高达319.5 kPa。

航空动力锂离子电池热失控行为与气体燃爆危险性研究进展

动力锂离子电池的安全问题是制约电动航空器运行与适航取证的技术瓶颈问题,影响全球电动航空的发展。由锂离子电池热失控引发的燃烧、爆炸等失效事件会造成机毁人亡的灾难性后果。旨在为相关研究人员介绍锂离子电池热失控爆炸特性的研究现状,从锂离子电池热失控燃爆行为、热失控气体爆炸极限和热失控气体爆炸危险性评估3个方面进行阐述:在锂离子电池热失控燃爆行为方面,介绍了锂离子电池热失控发展过程,分析了热失控冲击特征参数测定方法,总结了热射流演变机制及射流火焰的模拟仿真与实验方法;针对热失控气体的爆炸极限,对比国内外气体爆炸极限测试标准,总结了热失控气体爆炸极限理论计算方法,并介绍了原位检测爆炸极限的创新方法;在热失控气体爆炸危险性评估方面,介绍了老化锂离子电池危险性评估方法,以及爆炸危险性参数指标。提出未来的研究将侧重于先进诊断技术、增强电解质稳定性、多尺度建模、先进抑制技术以及建立标准化测试流程和技术法规等领域。

锂离子电池过充热失控特征和预警策略研究

随着全球对碳中和目标的追求,锂离子电池储能技术的发展前景广阔,而安全问题是制约锂离子电池储能电站发展的重要障碍。分析了不同充电倍率条件下磷酸铁锂电池的热失控动态特性及其影响因素。通过综合电压、温度和气体释放特征的协同分析,揭示了电池过充过程中的风险阶段及其安全阈值。采用云模型计算,建立了基于电压、温度和气体产生的多变量预警系统,通过基本概率分配(BPA)函数和mass函数来融合传感器数据,实现了磷酸铁锂电池过充危险等级的综合判断,为锂离子电池的安全监测和风险管理提供了切实可行的思路和技术支持。

基于高效液冷技术的锂离子电池热管理研究进展

在车用锂离子电池组热管理技术中,液体冷却因其高性能和高能效而被认定为主流技术。它可以进一步分为间接液冷和直接液冷。介绍了依据电池形状采用不同液冷方式如液冷板液冷(包括液冷板流道设计和布置方式)、浸没式液冷和结合相变材料的复合式液冷的电池组温控研究实例,给出了不同液冷方式下的温控数据,并对数据做了比较和分析。通常情况下,方形或袋式电池的液冷板可以灵活地布置在电池模组的底部、电池大面之间或电池两侧小面,液冷板多为蛇形流道、仿生流道和翅片形状等结构;圆柱电池的液冷板流道多采用波浪式、夹套式或螺旋式。

水系铝离子电池针刺试验性能分析

分别以制备的UTAl/Al[TFSI]3/α-MnO_(2)与UTAl/AlO_(2)(SO _(4))_(3)/α-MnOO_(2)两款水系铝离子电池为研究对象,开展了水系铝离子电池针刺试验安全性能研究。在针刺试验中,两款水系铝离子电池均表现出了一定的热失控现象,但其峰值温度分别仅为91℃和88℃;当电池SOC从初始状态的25%增加至100%时,其峰值温度增加接近3倍;在低针速(10 mm/s~40 mm/s)状态下,适当增加针速能够在一定程度上减小电池热失控的风险。

高温浮充鼓胀锂离子电池的安全风险研究

浮充是手机和笔记本电脑等便携式电子产品中锂离子电池常用的充电方法。然而,锂离子电池在高温环境下浮充常常导致容量下降和产气鼓胀,引起消费者对产品安全的担忧。为了明晰高温浮充老化对电池安全性能的影响,选择了同一电芯制造商生产的五款商用软包锂离子电池开展对比研究。对鼓胀电池进行加热测试、外短路测试和挤压实验,分析了产生气体的组分,发现高温浮充老化加速了锂离子电池的容量衰减和气体产生。产气导致电池膨胀,增加了破裂、漏液的风险,产生的混合气体虽然可燃,但由于气体量不多,对风险影响不大。虽然老化膨胀后锂离子电池的电化学性能下降,但在常规电子产品使用条件下,鼓胀电池的安全性能保持良好,热失控的风险较低。