电站锅炉蛇形管焊接接头加速寿命试验规范的研究

研究制定了旨在研究电站锅炉蛇表管焊接接头可靠性的加速寿命试验的试验规范,在此基础上,对大量的15CrMo和12CrMoV钢摩擦焊管接头进行了高温内压爆破持久试验。通过对试验结果的分析处理,证明了各种加速试验工况下焊接接头的失效机理是一致的。同时也说明了规范是可行的。     

预锂化对锂离子电池贮存寿命的影响

为了研究拓展锂离子电池贮存寿命的方法,本工作研制了两款额定容量为2.0 A·h的软包锂离子电池,分别为采用了预锂化工艺的贮存电池和常规设计的对比电池.对比了预锂化对电池倍率性能、循环性能及贮存寿命等的影响.结果表明,预锂化可以有效降低电池自放电、提升循环容量,但会间接降低电池的倍率性能.在软包电池的设计基础上进行了18...     

基于正交试验的锂离子电池热失控仿真北大核心CSCD

锂离子电池热失控是由多种因素耦合而导致的结果,得到影响锂离子电池热失控影响因素的重要性程度对于提高电池安全性具有极大意义。对此,针对针刺导致的锂离子电池热失控,利用COMSOL软件仿真分析了不同针刺位置、速度、直径、SOC(state of charge)对锂离子电池单体针刺热失控影响,得到对单体电池热失控影响的重要因素。基于单体针刺热失控仿真结果,以4个锂离子电池单体组成的模组为研究对象,利用单因素仿真试验分析不同钢针直径R、电池SOC以及针刺电池个数N对电池模组热扩散影响;基于此,本文分析了针刺电池个数N、钢针直径R及电池SOC耦合作用热失控的正交试验。结果表明:相对于针刺位置、针刺速度对电池单体热失控影响,电池SOC和针刺直径R对电池单体热失控影响较为显著,且针刺直径R越小,单体电池热失控越剧烈;电池SOC越大,热失控时电池温度分布越不均匀;针刺直径R越大,模组热扩散需要时间越长;当SOC在100%~85%范围内时,模组内各电池单体的热失控最高温度变化较为明显;针刺电池个数N越大,模组热失控越剧烈,但位于模组中间位置的电池热失控最高温度有所降低。针刺电池个数N、SOC、针刺直径R对电池模组热失控温度和扩散时间的影响程度主次顺序为:N>R>SOC*R>SOC*N>N*R>SOC,其中,针刺电池个数N对电池模组热扩散影响最显著,且不同因素间的交互作用不容忽视。本工作为提高电池的安全性及电池设计提供了参考依据。     

锂离子电池热效应模型的研究进展

锂离子电池充放电过程中会产生大量的热,若不及时散热会严重影响到电池的整体性能和寿命,严重时还会引发安全问题。文中阐述锂离子电池热效应模型的研究进展,认为在对锂离子单体进行数值模拟时,应从正极板、负极板和隔膜等简化的均匀发热体过渡到分层、细化、精确的模拟;加大对低温及特殊条件下锂离子电池热行为的探究;电池使用环境的精确仿真模拟将会成为人们今后努力的方向。     

锂离子电池加速循环测试研究北大核心CSCD

以圆型21700 4.8 Ah电池为测试样本,采用零和脉冲法进行加速循环测试研究。以所筛选的10%SOC作为最优的荷电态测试区间,对3种不同正负极材料组成的实验电池进行7天的加速循环测试,以基准电池参数为对比,综合多种参数对电池循环性能优劣进行分析评价。通过对电池加速循环前后的容量保持率分析,即可获得与常规循环测试一致的测评结果:负极二元化电池的放电容量保持率最高,为99.75%,其次是基准方案电池,为99.43%,而正极二元化电池的放电容量保持率最低,为96.33%。此外,通过对电池在加速循环过程中的直流内阻和极化电压增长率的分析,正极二元化电池的增长率远高于其他两种电池。进一步通过对电池瞬时及弛豫阻抗的拆解分析,可知导致正极二元化电池循环较差的原因主要是其正极及负极上均发生了大量的副反应,由于界面膜增厚及沉积物增多导致固相扩散阻抗增大,因此弛豫阻抗增长率达40%。通过对循环后电池进行EIS测试及正负极的物性分析发现,正极二元化电池的扩散阻抗显著较高,且其正极二次颗粒碎裂程度较高,此结果可初步解释正极二元化电池在加速循环中因正极碎裂引发副反应导致固相扩散阻抗增长率较高的现象。该加速循环测试方法以实际循环制式为依据,不引入额外的温度及倍率等应力影响因素,通过对各种测试参数的综合分析,达到定性判断实验电池循环性能优劣的目的,不仅可以大大缩短电池循环测评周期,同时可以为电池循环衰减原因分析提供依据。     

火焰检测探头中光电池的加速寿命试验研究

提出一种利用加速寿命试验对火焰检测探头中光电池进行寿命检测的方法。光电池的寿命分布可以用威布尔函数来描述,采用最小二乘法并结合阿伦尼斯加速模型完成对试验数据的统计及分析。该方法能有效地缩短光电池的寿命测试时间,实现了在短时间内对正常应力下火焰检测探头中光电池寿命的科学估计。     

基于VF-DW-DFN的锂离子电池剩余寿命预测北大核心CSCD

锂离子电池作为各类储能系统与设备的重要组成部分,准确预测锂离子电池的剩余使用寿命对于保障电池相关产业和设施的可靠性与安全性起着关键作用。针对锂离子电池剩余寿命预测中存在的非平稳、非线性特性导致单一数据驱动方法的预测精度低、泛化性能差等问题,提出了一种基于变分滤波、数据规整和深度融合网络的数据驱动融合(VF-DW-DFN)方法。首先,利用变分滤波法去除原始电池退化序列中的随机噪声干扰,得到相对平稳的退化特征数据。然后,采用最优嵌入法构造预测滑窗,实现特征数据规整,减少信息损失。其次,设计了一种新型深度融合网络对电池非线性退化数据进行建模,辨识电池数据中的退化模式,实现最终的锂离子电池剩余寿命预测。最后,在钴酸锂锂离子电池数据集上进行了剩余寿命预测实验,实验预测的平均均方根误差为1.41%,平均剩余寿命绝对误差小于2个循环周期。实验结果表明所提出的方法泛化性能好,预测精度高,误差小,能够对锂离子电池的退化过程进行有效建模和准确预测。     

Physicochemical properties of lithium iron phosphate‐carbon as lithium polymer battery cathodes

Lithium iron phosphate‐carbon (LiFePO₄/multiwalled carbon nanotubes (MWCNTs)) composite cathode materials were prepared by a hydrothermal method. In this study, we used MWCNTs as conductive additive. Poly (vinylidene fluoride‐co‐hexafluoropropylene)‐based solid polymer electrolyte (SPE) was applied. The structural and morphological performance of LiFePO₄/MWCNTs cathode materials was investigated by X‐ray diffraction and scanning electron microscopy/mapping. The electrochemical properties of Li/SPE/LiFePO₄‐MWCNTs coin‐type polymer batteries were analyzed by cyclic voltammetry, ac impedance and galvanostatic charge/discharge tests. Li/SPE/LiFePO₄‐MWCNTs polymer battery with 5 wt % MWCNTs demonstrates the highest discharge capacity and stable cyclability at room temperature. It is indicated that LiFePO₄‐MWCNTs can be used as the cathode materials for lithium polymer batteries. Copyright © 2011 John Wiley & Sons, Ltd.     

Lithium iron phosphate with high-rate capability synthesized through hydrothermal reaction in glucose solution

Carbon-coated lithium iron phosphate (LiFePO₄/C) was hydrothermally synthesized from commercial LiOH, FeSO₄ and H₃PO₄ as raw materials and glucose as carbon precursor in aqueous solution at 180 °C for 6 h followed by being fired at 750 °C for 6 h. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and constant current charge–discharge cycling test. The results show that the synthesized powders are in situ coated with carbon precursor produced from glucose. At ambient temperature (25 ± 2 °C), the specific discharge capacities are 154 mAh g⁻¹ at 0.2 C and 136 mAh g⁻¹ at 5 C rate, and the cycling capacity retention rate reaches 98% over 90 cycles. The excellent electrochemical performance can be correlated with the in situ formation of carbon precursor/carbon, thus leading to the even distribution of carbon and the enhancement of conductibility of individual grains.     

基于磷酸铁锂电池变电站直流系统BMS的研究与应用

磷酸铁锂电池管理单元（BMS）是文中研究的重点,如何把握电池内部状态的变化规律以及外部因素对电池容量的影响、建立合理有效的电池模型和SOC算法、实现SOC在线估计并减少估算误差,是电池安全管理最基本、最重要的方面。电池管理单元（BMS）与变电站直流系统监控器通过CAN通信,能有效的保证磷酸铁锂电池组及整个直流系统安全可靠的工作。     

A review on lithium iron phosphate cathode materials

目前全球高动力锂离子电池系统的发展主要集中在锂锰电池,锂钴镍锰电池以及锂铁电池,其中磷酸亚铁锂材料具有高电容量,高放电功率,极佳的长循环寿命以及良好的热稳定性与高温性能等优点,已成为动力锂离子电池首选的高安全性正极材料.然而,磷酸亚铁锂材料在工业化量产时,必须解决电池芯加工性差及材料一致性不佳等问题,作者曾结合多项新颖观念与技术于磷酸亚铁锂材料制做过程,在粉体表面涂布碳层,在晶体内部掺杂金属,分别改善材料电导率与锂离子扩散速度以及有效地控制碳含量,粉体比表面积,碳层均匀性,粒径大小与分布,制备出高质量磷酸亚铁锂产品.该文将回顾并探讨上述研发工作的一些重要结果.     

Improving electrochemical properties of lithium iron phosphate by addition of vanadium

The poor conductivity, resulting from the low lithium-ion diffusion rate and low electronic conductivity in the LiFePO₄ phase, has posed a bottleneck for commercial applications. Well-crystallized LiFePO₄-based powders with vanadium addition were synthesized with solution method. The synthesized powders are coated with carbon. The powder containing the well-mixed LiFePO₄ and Li₃V₂(PO₄)₃ phases (LFVP) with narrow distributed particle size ranging between 0.5 and 2.5 μm exhibits improved electrochemical performance. The small particle size and the presence of the electronically conductive mixed phases can be the reasons why the cells containing LFVP exhibit the high discharge capacity of about 100 mAh g⁻¹ at 10 C, whereas the samples with single phase, such as LiFePO₄ and Li₃V₂(PO₄)₃, have the discharge capacity less than 80 Ah g⁻¹ at the same rate.     

Cresyl diphenyl phosphate effect on the thermal stabilities and electrochemical performances of electrodes in lithium ion battery

To improve the safety of lithium ion battery, cresyl diphenyl phosphate (CDP) is used as a flame-retardant additive in a LiPF₆ based electrolyte. The electrochemical performances of LiCoO₂/CDP-electrolyte/Li and Li/CDP-electrolyte/C half cells are evaluated. The thermal behaviors of Li_0.5CoO₂ and Li_0.5CoO₂-CDP-electrolyte, and Li_xC₆ and Li_xC₆-CDP-electrolyte are examined using a C80 micro-calorimeter. For the LiCoO₂/CDP-electrolyte/Li cells, the onset temperature of single Li_0.5CoO₂ is put off and the heat generation is decreased greatly except the one corresponding to 5% CDP-containing electrolyte. When Li_0.5CoO₂ coexists with CDP-electrolyte, the thermal stability is enhanced. CDP improves the thermal stability of lithiated graphite anode effectively and the addition of 5% CDP inhibits the decomposition of solid electrolyte interphase (SEI) films significantly. The electrochemical tests on LiCoO₂/CDP-electrolyte/Li and Li/CDP-electrolyte/C cells show that when less than 15% CDP is added to the electrolyte, the electrochemical performances are not worsen too much. Therefore, the addition of 5-15% CDP to the electrolyte almost does not worsen the electrochemical performance of LiCoO₂ cathode and graphite anode, and improves theirs thermal stability significantly; thus, it is a possible choice for electrolyte additive.     

A novel sol-gel method based on FePO4·2H2O to synthesize submicrometer structured LiFePO4/C cathode material

Carbon coated LiFePO₄/C cathode material is synthesized with a novel sol-gel method, using cheap FePO₄·2H₂O as both iron and phosphorus sources and oxalic acid (H₂C₂O₄·2H₂O) as both complexant and reductant. In H₂C₂O₄ solution, FePO₄·2H₂O is very simple to form transparent sols without controlling the pH value. Pure submicrometer structured LiFePO₄ crystal is obtained with a particle size ranging from 100 to 500 nm, which is also uniformly coated with a carbon layer, about 2.6 nm in thickness. The as-synthesized LiFePO₄/C sample exhibits high initial discharge capacity 160.5 mAh g⁻¹ at 0.1 C rate, with a capacity retention of 98.7% after 50th cycle. The material also shows good high-rate discharge performances, about 106 mAh g⁻¹ at 10 C rate. The improved electrochemical properties of as-synthesized LiFePO₄/C are ascribed to its submicrometer scale particles and low electrochemical impedance. The sol-gel method may be of great interest in the practical application of LiFePO₄/C cathode material.     

Effects of Fe2P and Li3PO4 additives on the cycling performance of LiFePO4/C composite cathode materials

In this study, a solution method was employed to synthesize LiFePO₄-based powders with Li₃PO₄ and Fe₂P additives. The composition, crystalline structure, and morphology of the synthesized powders were investigated by using ICP-OES, XRD, TEM, and SEM, respectively. The electrochemical properties of the powders were investigated with cyclic voltammetric and capacity retention studies. The capacity retention studies were carried out with LiFePO₄/Li cells and LiFePO₄/MCMB cells comprised LiFePO₄-based materials prepared at various temperatures from a stoichiometric precursor. Among all of the synthesized powders, the samples synthesized at 750 and 775 °C demonstrate the most promising cycling performance with C/10, C/5, C/2, and 1C rates. The sample synthesized at 775 °C shows initial discharge capacity of 155 mAh g⁻¹ at 30 °C with C/10 rate. From the results of the cycling performance of LiFePO₄/MCMB cells, it is found that 800 °C sample exhibited higher polarization growth rate than 700 °C sample, though it shows lower capacity fading rate than 700 °C sample. For Fe₂P containing samples, the diffusion coefficient of Li⁺ ion increases with increasing amount of Fe₂P, however, the sample synthesized at 900 °C shows much lower Li⁺ ion diffusion coefficient due to the hindrance of Fe₂P layer on the surface of LiFePO₄ particles.     

Improved thermal stability of lithium ion battery by using cresyl diphenyl phosphate as an electrolyte additive

To enhance the safety of lithium ion battery, cresyl diphenyl phosphate (CDP) is explored as an additive in 1.0 M LiPF₆/ethylene carbonate (EC) + diethyl carbonate (DEC) (1:1 wt.). The electrochemical performances of LiCoO₂/CDP-electrolyte/C cells are tested. At the thermal aspect, the thermal stability of the electrolyte with CDP is detected firstly by using a C80 micro-calorimeter, and then the charged LiCoO₂/CDP-electrolyte/C cells are disassembled and wrapped to detect the thermal behaviors. The results indicate that CDP-containing electrolyte enhances the thermal stabilities of electrolyte and lithium ion battery, and the electrochemical performances of LiCoO₂/CDP-electrolyte/C cell become slightly worse by using CDP in the electrolyte. Furthermore, the cell with 10% (wt.) CDP-containing electrolyte shows better cycle efficiency than that of other CDP-containing electrolyte, such as containing 5% (wt.) CDP and 15% (wt.) CDP. This maybe because that the mass ratio between CDP and electrolyte is close to the reaction stoichiometric ratio in the 10% (wt.) CDP-containing electrolyte, where stable solid electrolyte interphase (SEI) is formed. Therefore, 10% CDP-containing electrolyte improves the safety of lithium ion battery and keeps its electrochemical performance.     

磷酸铁锂电池及其新能源汽车启动电源性能研究

鉴于汽车启动电源铅酸电池存在严重环境污染隐患,本文采用环保型32650圆柱磷酸铁锂电池组装成25.6 V/65 A•h电池组代替铅酸电池应用于汽车启动电源,并分别对磷酸铁锂电池组的常温和低温启动能力、倍率性能和低温放电性能等进行测试。实验结果表明,电池组0.33 C放电容量为67.028 A•h,3 C放电容量为0.33 C放电容量的98.24%,电池组具有较好的倍率性能;电池组在 −30℃放电容量为额定容量的84.7%,具有良好的低温性能;电池组在25℃和 −20℃下以600 A电流放电,单串电池电压均高于放电保护电压;电池组在25℃搁置28 d之后,容量恢复率为99.37%;磷酸铁锂电池组性能均满足汽车启动电源性能要求,可以代替铅酸电池作为汽车启动电源。