Investigation on step overcharge to self-heating behavior and mechanism analysis of lithium ion batteries

To obtain intrinsic overcharge boundary and investigate overcharge mechanism,here we propose an innovative method,the step overcharge test,to reduce the thermal crossover and distinguish the overcharge thermal behavior,including 5%state of charge(SOC)with small current overcharge and resting until the temperature equilibrium under adiabatic conditions.The intrinsic thermal response and the self-excitation behaviour are analysed through temperature and voltage changes during the step overcharge period.Experimental results show that the deintercalated state of the cathode is highly correlated to self-heating parasitic reactions.Before reaching the upper limit of Negative/Positive(N/P)ratio,the temperature changes little,the heat generation is significantly induced by the reversible heat(endothermic)and ohmic heat,which could balance each other.Following that the lithium metal is gradually deposited on the surface of the anode and reacts with electrolyte upon overcharge,inducing selfheating side reaction.However,this spontaneous thermal reaction could be“self-extinguished”.When the lithium in cathode is completely deintercalated,the boundary point of overcharge is about 4.7 V(~148%SOC,>40℃),and from this point,the self-heating behaviour could be continuously triggered until thermal runaway(TR)without additional overcharge.The whole static and spontaneous process lasts for 115 h and the side reaction heat is beyond 320,000 J.The continuous self-excitation behavior inside the battery is attributed to the interaction between the highly oxidized cathode and the solvent,which leads to the dissolution of metal ions.The dissolved metal ions destroy the SEI(solid electrolyte interphase)film on the surface of the deposited Li of anode,which induces the thermal reaction between lithium metal and the solvent.The interaction between cathode,the deposited Li of anode,and solvent promotes the temperature of the battery to rise slowly.When the temperature of the battery reaches more than 60℃,the reaction between lithium metal and solvent is accelerated.After the temperature rises rapidly to the melting point of the separator,it triggers the thermal runaway of the battery due to the short circuit of the battery.

A large-area multi-fingerβ-Ga_(2)O_(3) MOSFET and its self-heating effect

The self-heating effect severely limits device performance and reliability.Although some studies have revealed the heat distribution ofβ-Ga_(2)O_(3) MOSFETs under biases,those devices all have small areas and have difficulty reflecting practical con-ditions.This work demonstrated a multi-fingerβ-Ga_(2)O_(3) MOSFET with a maximum drain current of 0.5 A.Electrical characteris-tics were measured,and the heat dissipation of the device was investigated through infrared images.The relationship between device temperature and time/bias is analyzed.

Analytical workload dependence of self-heating effect for SOI MOSFETs considering two-stage heating process

Dynamic self-heating effect(SHE)of silicon-on-insulator(SOI)MOSFET is comprehensively evaluated by ultrafast pulsed I-V measurement in this work.It is found for the first time that the SHE complete heating response and cooling response of SOI MOSFETs are conjugated,with two-stage curves shown.We establish the effective thermal transient response model with stage superposition corresponding to the heating process.The systematic study of SHE dependence on workload shows that frequency and duty cycle have more significant effect on SHE in first-stage heating process than in the second stage.In the first-stage heating process,the peak lattice temperature and current oscillation amplitude decrease by more than 25 K and 4%with frequency increasing to 10 MHz,and when duty cycle is reduced to 25%,the peak lattice temperature drops to 306 K and current oscillation amplitude decreases to 0.77%.Finally,the investigation of two-stage(heating and cooling)process provides a guideline for the unified optimization of dynamic SHE in terms of workload.As the operating frequency is raised to GHz,the peak temperature depends on duty cycle,and self-heating oscillation is completely suppressed.

Self-heating tendency evaluation of sulfide ores based on nonlinear multi-parameters fusion

In order to reveal the nonlinear dynamics characteristics of unsteady self-heating process of sulfide ores, nine different kinds of sulfide ore samples from a pyrite mine in China were taken as experimental materials and their self-heating characteristics were measured in laboratory. Furthermore, the measured temperature was studied by integrating wavelet transform, nonlinear characteristic parameters extraction and fuzzy comprehensive evaluation. The results indicate that only the ore samples 1, 2, 6 and 9 have obvious self-heating phenomenon, and their self-heating initiative temperatures are 220 ℃, 239 ℃, 220 ℃ and 220 ℃, respectively, which means that they are difficult to produce self-heating under normal mining conditions. The correlation dimension of self-heating process is fraction and the maximum Lyapunov exponent is positive, which means that it is feasible to study the self-heating process based on chaotic dynamics theory. The nonlinearities of self-heating process of these four samples （ore samples 1, 2, 6 and 9） are 0.8227, 0.7521, 0.9401 and 0.8827 respectively and the order of the samples according to these results is： sample 6, sample 9, sample 1, sample 2, which is consistent with the measured results of self-heating characteristics. Therefore, the nonlinearity method can be used to evaluate the self-heating tendency of sulfide ores, and it is an effective verification of the reliability of measured results.

Numerical Simulations of Polymer Melt Conveying in Co-Rotating Twin Screw Extruder

The 3 D non isothermal flow of non Newtonian viscous polymer melt in a co rotating twin screw extruder is modeled. The distributions of the velocity, temperature, pressure and the viscous dissipation in the flow domain are presented by using a fluid dynamics analysis package (Polyflow). The numerical results show that the temperatures are high in the intermeshing region and on the screw surface, the maximum pressure and the minimum pressure occur in the intermeshing region, and the flow rate is almost proportional to the screw speed.

Simulation of Polymer Melt Flow Fields in Intermeshing Co-Rotating Three-Screw Extruders

Three-dimension isothermal flows of polymer melt in the kneading blocks of triangularly-arranged and parallelly-arranged intermeshing co-rotating three-screw extruders are simulated using the finite element package POLYFLOW. Based on the velocity fields calculated, the particle trajectories in both machines are visualized using particle tracking technique. The numerical results indicate that the flow patterns in three-screw extruders are similar to those in twin-screw extruders. The triangularly-arranged three-screw extruder has the largest pumping capacity and also the highest extrusion stability in terms of flowrate fluctuation with screw rotation. The instantaneous mixing and cumulative residence time distribution （RTD） characteristics are also analyzed and compared with traditional intermeshing co-rotating twin-screw extruders. It is shown that the start section of the cumulative RTD curve for the triangularly-arranged machine has a small shoulder, which is attributed to the faster flow in the central region of this type of extruder.

Numerical Simulation of the Self-Heating Effect Induced by Electron Beam Plasma in Atmosphere

For exploiting advantages of electron beam air plasma in some unusual applications, a Monte Carlo （MC） model coupled with heat transfer model is established to simulate the characteristics of electron beam air plasma by considering the self-heating effect. Based on the model, the electron beam induced temperature field and the related plasma properties are investigated. The results indicate that a nonuniform temperature field is formed in the electron beam plasma region and the average temperature is of the order of 600 K. Moreover, much larger volume pear-shaped electron beam plasma is produced in hot state rather than in cold state. The beam ranges can, with beam energies of 75 keV and 80 keV, exceed 1.0 m and 1.2 m in air at pressure of 100 torr, respectively. Finally, a well verified formula is obtained for calculating the range of high energy electron beam in atmosphere.

Study on Hardware-in-loop Simulation of Twin-screw Extruder Experiment System

In order to facilitate the teaching of industrial processes and experiments on the twin-screw extruder control debugging,and be closer to the actual testing,to reduce the debugging costs and the risk of debugging process,the paper designs a hardware-in-loop simulation of twin-screw extruder experiment system which is closer to scene,low cost and high safety.The system through the establishment of twin-screw extruder’s mathematical model on computer to simulate the realistic system and there is hardware practicality in the computer simulation loop.The hardware based on C8051F020 can operate in the simulation loop in real time.In computer software design, we desigh man-machine interface that is intuitive and easy to operate,can reflect twin-screw extruder main operation information vividly.Finally,twin-screw extruder’s 3 heater temperature mathematical model and PID incremental control algorithm are presented.

A study of self-heating characteristics of a pyrrhotite-rich sulphide ore stockpile

Original surface chemistry of sulphidesis altered upon contact with air, leading to ''oxidation'', which is accompanied by evolution of heat. The current study reports results of an investigation on extent of exothermicity of an experimental nickel-copper sulphide stockpile that was formed at a mining site in Sudbury, Canada. The ore contained pentlandite and chalcopyrite that are accompanied by a large quantity of pyrrhotite. The self-heating characteristics were recorded by temperature sensors placed inside the stockpile. Ambient conditions such as temperature, humidity, and wind velocity were simultaneously recorded. The inner temperature of the stockpile indicated significant fluctuations due to rapid changes, particularly in the outside temperature. The minimum and maximum temperatures recorded in the outside and inside were 5 and 10.5, 44.3 and 32 ℃, respectively. The self-heating capacity of the sulphide ore stockpile observed represents a mild case compared to that experienced by coals. Possible reasons are discussed.

CFD modelling of Iongwall goaf gas flow to improve gas capture and prevent goaf self-heating

CFD models have been developed to investigate the Iongwall goaf gas flow patternsunder different mining and geological control conditions.The Iongwall goaf wastreated as porous regions and gas flow was modelled as a momentum sink added to themomentum equation.Gas desorption from the caved goaf and destressed coal seamswithin the mining disturbed area was modelled as additional mass sources in the continuityequation.These CFD models were developed according to specific Iongwall layoutsand calibrated against field monitoring data.Two case studies were presented demonstratingthe application of CFD modelling of goaf gas flow characteristics for improved goafgas capture and the reduction of oxygen ingress into the goaf areas for self-heating prevention.Results from the case studies indicate that the optimum goaf drainage strategywould be a combination of shallow (near the face) and deep holes to improve the overalldrainage efficiency and gas purity.For gassy Iongwall faces retreating against the seam dip,it is recommended to conduct cross-measure roof hole drainage targeting the fracturedzones overlying the return corner,rather than high capacity surface goaf drainage deep inthe goaf.

Electrothermal simulation of the self-heating effects in 4H-SiC MESFETs

A thermal model of 4H-SiC MESFET is developed based on the temperature dependences of material parameters and three-region I - V model. The static current characteristics of 4H-SiC MESFET have been obtained with the consideration of the self-heating effect on related parameters including electron mobility, saturation velocity and thermal conductivity. High voltage performances are analysed using equivalent thermal conductivity model. Using the physicalbased simulations, we studied the dependence of self-heating temperature on the thickness and doping of substrate. The obtained results can be used for optimization of the thermal design of the SiC-based high-power field effect transistors.

The roles of stress state and pre-straining on Swift effect for an extruded AZ31 Mg alloy

The Swift effect of Mg alloy is sensitive to initial texture.However,dislocation slip is the main deformation mechanism during torsion of Mg alloy.The underlying relation of Swift effect and dislocation slip is still not clarified.The effect of stress state and pre-straining on Swift effect was studied experimentally during free-end torsion for an extruded AZ31 alloy.The free-end torsion was performed with axial tension and compression stress which is lower than yield stress.It is found that the transition of axial deformation from contraction to elongation occurs when the axial stress changes from negative to positive.The pre-dislocations introduced by pre-tension promote axial shortening during torsion.While the pre-twins introduced by pre-compression are inhibition of axial shortening.The change of axial deformation is attributed to competition between twinning and prismatic slip.The axial shortening of extruded Mg alloy is generated by tensile twinning leading to c-axis strain.In contrast,the axial elongation can be generated by the activation of prismatic slip.The magnitude of axial strain generated by twinning is larger than that by prismatic slip.Moreover,the occurrence of detwinning results in axial elongation at low shear strain.

Investigation and active suppression of self-heating induced degradation in amorphous InGaZnO thin film transistors

Self-heating effect in amorphous InGaZnO thin-film transistors remains a critical issue that degrades device performance and stability, hindering their wider applications. In this work, pulsed current–voltage analysis has been applied to explore the physics origin of self-heating induced degradation, where Joule heat is shortly accumulated by drain current and dissipated in repeated time cycles as a function of gate bias. Enhanced positive threshold voltage shift is observed at reduced heat dissipation time, higher drain current, and increased gate width. A physical picture of Joule heating assisted charge trapping process has been proposed and then verified with pulsed negative gate bias stressing scheme, which could evidently counteract the self-heating effect through the electric-field assisted detrapping process. As a result, this pulsed gate bias scheme with negative quiescent voltage could be used as a possible way to actively suppress self-heating related device degradation.

Influence of self-heating on the millimeter-wave and terahertz performance of MBE grown silicon IMPATT diodes

The influence of self-heating on the millimeter-wave(mm-wave)and terahertz(THz)performance of double-drift region(DDR)impact avalanche transit time(IMPATT)sources based on silicon(Si)has been investigated in this paper.The dependences of static and large-signal parameters on junction temperature are estimated using a non-sinusoidal voltage excited(NSVE)large-signal simulation technique developed by the authors,which is based on the quantum-corrected drift-diffusion(QCDD)model.Linear variations of static parameters and non-linear variations of large-signal parameters with temperature have been observed.Analytical expressions representing the temperature dependences of static and large-signal parameters of the diodes are developed using linear and 2nd degree polynomial curve fitting techniques,which will be highly useful for optimizing the thermal design of the oscillators.Finally,the simulated results are found to be in close agreement with the experimentally measured data.

Machine Learning-Based Predictions on the Self-Heating Characteristics of Nanocomposites with Hybrid Fillers

A machine learning-based prediction of the self-heating characteristics and the negative temperature coefficient(NTC)effect detection of nanocomposites incorporating carbon nanotube(CNT)and carbon fiber(CF)is proposed.The CNT content was fixed at 4.0 wt.%,and CFs having three different lengths(0.1,3 and 6 mm)at dosage of 1.0 wt.%were added to fabricate the specimens.The self-heating properties of the specimens were evaluated via self-heating tests.Based on the experiment results,two types of artificial neural network(ANN)models were constructed to predict the surface temperature and electrical resistance,and to detect a severe NTC effect.The present predictions were compared with experimental values to verify the applicability of the proposed ANN models.The ANN model for data prediction was able to predict the surface temperature and electrical resistance closely,with corresponding R-squared value of 0.91 and 0.97,respectively.The ANN model for data detection could detect the severe NTC effect occurred in the nanocomposites under the self-heating condition,as evidenced by the accuracy and sensitivity values exceeding 0.7 in all criteria.

A new physics-based self-heating effect model for 4H-SiC MESFETs

A new self-heating effect model for 4H-SiC MESFETs is proposed based on a combination of an analytical and a computer aided design （CAD） oriented drain current model. The circuit oriented expressions of 4H-SiC low-field electron mobility and incomplete ionization rate, which are related to temperature, are presented in this model, which are used to estimate the self-heating effect of 4H-SiC MESFETs. The verification of the present model is made, and the good agreement between simulated results and measured data of DC I - V curves with the self-heating effect is obtained.

Single-Screw Laboratory Extruder for Production of Expanded Products:Design,Construction and Performance Testing

In this study,a low-capacity single-screw cooking extruder for the manufacture of expanded snacks was designed based on theoretical models and guided operating data and practices of existing cooking extruders.Construction was carried out using locally available engineering materials in modest machine shops satisfying sanitary design criteria and tested using blends of cassava and defatted soybean flour.The extruder developed has throughput,screw speed,barrel diameter,length-to-diameter ratio and power requirement of 13.0 kg/h,200 rpm,40 mm,12 and 1.908 kW,respectively.The cost of the extruder developed was estimated N650,000 in 2016.Extrudates had expansion ratio and trypsin inhibitor reduction which ranged from 1.82 to 2.98 and 61.07%to 87.93%,respectively,across all treatments.This study demonstrates that a low-capacity and affordable experimental single-screw extruder can be designed and built domestically which can be scaled-up for pilot and industrial applications for the production of expanded snacks.

挤压Mg-Y-Ni-Co合金的显微组织、加工性能及塑性变形行为

本工作通过光学显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和万能实验机对挤压Mg-2Y-0.5Ni-0.5Co(%,原子分数)合金的显微组织、加工性能和塑性变形行为进行了研究。挤压合金的显微组织主要由α-Mg、沿挤压方向分布的片层状和细小块状18R-LPSO相、MgY(Co,Ni)_(4)相以及晶粒内细条纹状的14H-LPSO相组成。拉伸测试结果显示,挤压合金具有良好的室温塑性,断裂延伸率均高于15%。随着温度的升高和应变速率的降低,合金的拉伸强度降低,而塑性增强。合金在300℃、1×10^(-3)s^(-1)和1×10^(-4)s^(-1)应变速率下断裂延伸率分别为117.87%和143.9%,具有准超塑性。通过构建的热加工图谱,优化出合金的稳定加工区间为温度275~300℃、应变速率10^(-4)~10^(-3)s^(-1)。挤压合金的变形行为随温度和应变速率的变化而改变,在低温(室温(RT)到200℃)和不同应变速率下,合金的变形机制以位错滑移为主;在高温(300℃)和低应变速率(1×10^(-4)s^(-1)和1×10^(-3)s^(-1))下,合金的变形机制为晶界滑移协调的位错滑移。

复杂条件下高面板堆石坝的特殊结构体安全监测设计体系研究

为了加强高面板堆石坝工程中挤压边墙、高趾墩和高趾墙等特殊结构体的安全监测,基于面板堆石坝安全监测设计资料,总结了特殊结构体在安全监测设计方面存在的不足和缺陷。通过收集整理国内包含高趾墩、高趾墙和挤压边墙等特殊结构体的高面板堆石坝数值分析成果,发掘特殊结构体的变形和应力应变规律,将特殊结构体的变形、应力应变及温度、接缝和渗流明确为安全监测设计重点;结合已有面板堆石坝工程的安全监测设计资料,构建了复杂条件下高面板堆石坝特殊结构体安全监测设计体系。该体系能够为在建和拟建的面板堆石坝特殊结构体安全监测设计提供科学的指导,全面提升面板堆石坝的安全监测水平。

腐植酸凝胶对低淀粉浮性水产膨化颗粒饲料质量的影响

试验旨在研究两种不同腐植酸凝胶对低淀粉浮性水产膨化颗粒饲料质量,如膨化饲料容重、溶失率、软化时间、颗粒饲料耐久性指数(PDI)、硬度、膨化率和黏弹性的影响。共设8个试验组,分别为:NCon组(阴性对照组)为典型低淀粉配方(淀粉含量为8%)的基础混合物料,PCon组(阳性对照组)为在基础混合物料中额外添加高筋面粉,MS0.2、MS0.4和MS0.6组为在基础混合物料中添加0.2%、0.4%、0.6%的木石瑰宝腐植酸凝胶,XD0.2、XD0.4和XD0.6组为在基础混合物料中添加0.2%、0.4%、0.6%的新大能腐植酸凝胶。结果表明:①与NCon组相比,PCon组容重显著降低、膨化率显著升高(P<0.05)。②与NCon组相比,MS0.2、MS0.4组的饲料硬度显著提高、黏弹性显著降低(P<0.05),MS0.2组软化时间显著提高(P<0.05),MS0.2、MS0.4和MS0.6组溶失率和容重显著降低、膨化率显著提高(P<0.05);XD0.2、XD0.4、XD0.6组的饲料膨化率、硬度、软化时间显著提高,黏弹性和溶失率显著降低(P<0.05)。③与PCon组比,MS0.2组膨化率显著提高(P<0.05),MS0.2、MS0.4组黏弹性显著降低、硬度显著提高(P<0.05),MS0.6组容重显著降低(P<0.05),MS0.2、MS0.6组PDI显著提高(P<0.05),MS0.2、MS0.4、MS0.6组溶失率显著降低(P<0.05);XD0.2、XD0.4、XD0.6组的饲料容重、硬度和软化时间显著提高,溶失率和黏弹性显著降低(P<0.05),XD0.4组膨化率显著降低(P<0.05),XD0.6组PDI显著提高(P<0.05)。综合比较,添加腐植酸凝胶优于添加高筋面粉,木石瑰宝添加组的产品质量优于新大能添加组。研究为腐植酸凝胶在低淀粉浮性水产膨化颗粒饲料生产实践中的应用提供数据支持。