磷酸铁锂电池储能系统平抑风电功率波动研究

针对风力发电出力的随机性和间歇性,提出将磷酸铁锂电池储能系统用于平抑风力发电的功率波动。首先,以PNGV等效电路模型为基础,通过HPPC试验实现电池参数的辨识,建立反映磷酸铁锂电池充放电特性的仿真模型;然后,基于磷酸铁锂电池端电压变化小的特点,提出了电池直接耦合在储能系统直流母线上的拓扑结构,给出了储能变流器的功率解耦控制策略和平抑风能波动的控制目标;最后,利用MATLAB/Simulink软件,建立了风电—储能系统仿真模型。仿真结果显示,磷酸铁锂电池储能系统能有效平抑风力发电的功率波动。     

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。     

工作温度对磷酸铁锂电池SOC影响及研究进展

储能电池在新能源并网、新能源汽车等产业领域发挥着重要作用,为了对电池进行有效地控制与管理,需要配备必要的电池管理系统,电池荷电状态（SOC）是其中最为重要的一环。磷酸铁锂（LiFePO4,LFP）电池SOC与多个影响因素密切相关,呈强非线性,本文重点归纳温度对磷酸铁锂电池SOC的影响。首先将工作温度对开路电压、实际容量、充放电效率、自放电率及电池老化等电池特性的影响进行归纳总结,随后通过对工作温度的影响规律进行分析、总结和归纳,基于经典“开路电压 + 安时积分”法将温度参数直接或间接引入到SOC的实时估算模型中,得到考虑温度参数的新模型,进而提高电池SOC的估算精度。     

磷酸铁锂电池优化多因子状态在线评估方法

针对目前锂离子电池在线估计方法不准确的问题,提出了一种基于优化充电电压片段下多个健康因子的磷酸铁锂电池健康状态综合在线评估方法,将充电电压片段内所充电量估计的电池容量与实际电池容量的误差最小作为目标,利用遗传算法寻优充电电压片段。在此基础上,分别对表征电池健康状态的充入电量、充电时间以及内部阻抗三个健康因子进行在线评估,归一化处理得到各健康因子对应的健康状态,再通过最小序列优化法实时获取电池综合健康状态。最后对磷酸铁锂电池进行老化充放电实验,对比仅采用电池内阻单因子评估方法,结果表明该方法能有效减小充电过程中电池健康状态估计误差,且适用性更强。     

N/P比对磷酸铁锂电池性能的影响

为了探究不同N/P对磷酸铁锂电池性能的影响,以磷酸铁锂为正极材料,人造石墨为负极材料,通过叠片工艺制备了4种不同N/P比(1.02、1.06、1.10、1.14)的磷酸铁锂电池,并通过电化学测试表征了不同N/P下电池的首次放电效率、倍率充放电性能、充放电DCR、高低温放电以及45℃循环性能.结果表明:相比于N/P(1....     

储能用大容量磷酸铁锂电池热失控行为及燃爆传播特性

随着电化学储能应用规模的持续扩大,使用锂离子电池的电化学储能电站火灾燃爆事故时有发生,引发社会的广泛关注。锂离子电池的安全性是影响储能电站安全的重要因素,分析储能用锂离子电池的热失控行为及燃爆特性是有效防控储能电站火灾事故的关键。本工作选用储能用280 Ah磷酸铁锂电池为研究对象,基于锂离子电池热失控及产气分析测试平台,采用加热方式触发电池热失控,分析其产热、质量损失以及产气特性。进一步采用傅里叶变换红外光谱仪以及氢气传感器测量热失控过程产气成分,通过卷积分析得到气体组分占比,其中氢气和二氧化碳分别占36.8%和44.2%。通过FLACS软件建立电池储能液冷舱1∶1模型,分析了不同条件下磷酸铁锂电池产气发生燃爆的动压及火焰危害范围。研究发现,在电池储能舱内发生的燃爆行为受到舱室内部泄压开启压力和周边障碍物的影响,而其中当舱门开启压力从10 kPa增长到100 kPa时,爆炸超压峰值增长为2.15倍。该研究可为储能电站锂离子电池火灾事故预警、集装箱结构和防爆设计提供参考。     

全氟己酮气体灭火系统在磷酸铁锂电池储能预制舱的应用

“双碳”目标下,需要建设大量与“风”“光”等新能源配套的磷酸铁锂电池储能电站,但磷酸铁锂电池具有较大火灾危险性,其灭火措施研究尚不完善。全氟己酮灭火剂是一种新型哈龙和氢氟烃类灭火剂的优良替代品,对其是否适用于扑灭储能锂电池火灾并抑制其热失控存有争议。基于全氟己酮应用于磷酸铁锂电池火灾的既往研究成果,优化了全氟己酮气体应用于磷酸铁锂电池储能电池舱的灭火方式,采用“局部应用”与“全淹没”灭火方式相结合,通过模型试验验证了灭火效果并得出了相关设计参数,以工程案例详细论述了全氟己酮气体灭火系统在储能电池舱的应用方案。     

预制舱式磷酸铁锂电池储能电站能耗计算研究

目的  基于站内能量损耗来源和设备属性详细分类,提出了预制舱式磷酸铁锂电池储能电站能耗计算方法。 方法  从储能电站的角度论述了预制舱式磷酸铁锂电池储能电站能耗计算中需考虑的主要因素,进而将储能电站的能耗分为2个部分,即储能系统自身的损耗和辅助设备运行的损耗,并分别给出了每部分能耗的计算方法及效率值的选取方法。 结果  通过实际算例,分析了配置规模为2 MW/2 MWh的储能电池预制舱在典型运行方式下的全天运行能耗,并与现场试验结果进行了对比,从储能电池产热和空调传导热能的角度分析了现场试验结果和理论分析的差别,对储能电站的能耗统计提出了建议。 结论  研究提出的能耗计算方法较全面地论述了影响预制舱式磷酸铁锂电池储能电站能耗指标的主要因素,依据设备属性详细分类给出了主要设备的能耗计算方法,具有较好的工程参考价值。     

不同放电功率下的储能用磷酸铁锂电池热失控特性实验研究

以某款52 Ah储能用方形磷酸铁锂电池单体为对象,采用400 W的外部热源、20.8～166.4 W(1～8 h)的恒功率放电以匹配电池工作状态下的热滥用条件,测量电池热失控过程中的表面温度和电压,记录热失控实验现象和关键时间点,对比研究不同放电功率对热滥用诱发热失控进程的影响。结果表明,放电操作会加速热失控的进程,且放电功率越大,热失控越早发生,从不放电到166.4 W恒功率放电,安全阀打开时间缩短了23.4%,热失控触发时间缩短了5.6%;与此同时,四组放电工况由于放出部分能量,最终热失控的严重程度有所降低,放电工况下的热失控最高温度和最大温升速率比不放电工况最高分别下降了9.0%和53.3%;另外,放电操作会造成热失控过程中电压更大的波动,后续电压下降的时间窗口前移至开阀时间附近,这将更有利于利用电压变化对热失控进行预警。总体而言,放电操作在加速热失控进程的同时,降低了热失控最终的严重程度。本工作可对电化学储能电站的日常安全运营和电池管理系统设计提供参考。     

基于直接采样相移法的蓄电池内阻测量

现代通信系统中,蓄电池是直流供电系统的最后一道安全保障屏障。蓄电池的好坏及供电质量,直接影响到整个通信系统的安全可靠运行。蓄电池内阻检测,是评价蓄电池质量的重要参数。本文详细介绍交流法测量蓄电池内阻的基本原理,依据该方法存在的缺陷,提出直接采样相移法测量蓄电池内阻的新方法,并用硬件电路实现该功能。     

Cycling degradation of an automotive LiFePO4 lithium-ion battery

Degradation of a high capacity prismatic LiFePO₄ cell with deep cycling at elevated temperature of 50 °C is studied by electrochemical impedance spectroscopy as well as capacity and power fading characterization at different test temperatures (45, 25, 0 and −10 °C). Capacity fade after 600 cycles is 14.3% at 45 °C and 25.8% at −10 °C. There is little power fade at 45 °C after 600 cycles, whereas the power fade after 600 cycles is 61.6% and 77.2%, respectively, at 0 and −10 °C. The capacity and power fade evidently becomes more severe at lower temperature. In particular, the power fade at low temperatures (e.g., 0 and −10 °C) rather than capacity loss is a major limitation of the LiFePO₄ cell. The primary mechanism for capacity fade is loss of cyclable lithium in the cell resulting from lithium-consuming solid electrolyte interphase (SEI) layer growth and side reactions. The increased interfacial resistance (R_w) due to the catalytic growth of SEI layer on the graphite anode and increased electrolyte resistance are the main sources for power fade.     

Optimizing the surfactant for the aqueous processing of LiFePO4 composite electrodes

Aqueous processing would reduce the costs associated with the making of the composite electrode. To achieve the incorporation and the dispersion of the carbon black (CB) conductive agent in aqueous slurries, a surfactant is needed. In this paper, three surfactants are compared, an anionic one, the sodium dodecyle sulphate (SDS), a non-ionic one, the isooctylphenylether of polyoxyethylene called commercially Triton X-100 and a cationic one, the hexadecyltrimethylammonium bromide (CTAB), by using rheology and laser granulometry measurements on electrode slurries on one hand, and SEM observations, porosity and adhesion measurements and electrochemical testing on composite electrodes on the other hand. Ionic surfactants were found to be not suitable because a corrosion of the aluminium current collector occurred. The utilization of Triton X-100 favoured a more homogeneous CB distribution, resulted in a better electronic wiring of the active material particles and higher rate behavior of the electrode. Optimal electrochemical performances are obtained for an optimal surfactant concentration which depends on the BET surface area of the CB powder.     

Hydrothermal preparation of LiFePO4 nanocrystals mediated by organic acid

Well-crystallized LiFePO₄ nanoparticles have been directly synthesized in a short time via hydrothermal process in the presence of organic acid, e.g. citric acid or ascorbic acid. These acid-mediated LiFePO₄ products exhibit a phase-pure and nanocrystal nature with size about 50-100 nm. Two critical roles that the organic acid mediator plays in hydrothermal process are recognized and a rational mechanism is explored. After a post carbon-coating treatment at 600 °C for 1 h, these mediated LiFePO₄ materials show a high electrochemical activity in terms of reversible capacity, cycling stability and rate capability. Particularly, LiFePO₄ mediated by ascorbic acid can deliver a capacity of 162 mAh g⁻¹ at 0.1 C, 154 mAh g⁻¹ at 1 C, and 122 mAh g⁻¹ at 5 C. The crystalline structure, particle morphology, and surface microstructure were characterized by high-energy synchrotron X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and Raman spectroscopy, respectively. And the electrochemical properties were thoroughly investigated by galvanostatic test and electrochemical impedance spectroscopy (EIS).     

High temperature electrochemical performance of nanosized LiFePO4

The electrochemical performance of LiFePO₄ was tested at temperatures up to 150 °C for micrometric and nanometric size samples. Among the latter, both highly defective samples obtained by direct precipitation and annealed samples were tested. The comparison of voltage composition profiles for these samples coupled to GITT experiments allowed to conclude that defects seem to be the major factor in inducing the solid solution behaviour at room temperature. Good capacity retention is exhibited upon prolonged cycling at 100 °C in EC LiBOB electrolyte, also for nanosized samples that still maintain 75% of the initial capacity after 170 cycles. These results prove that the enhanced thermal stability of such electrolytes can be extended to temperatures much higher than those usually tested.     

Modeling the capacity degradation of LiFePO4/graphite batteries based on stress coupling analysis

A coupling-analysis-based model to predict the capacity degradation of LiFePO₄ batteries under multi-stress accelerated conditions has been developed. In this model, the joint effect on the battery capacity degradation of any 2 out of 5 stress factors, which include ambient temperature, end of discharge and charge voltage (EODV and EOCV), and discharge and charge rate, is studied through coupling validation tests. Coupling generally exists among these 5 stress factors, and the coupling intensity has a certain relationship with the stress levels. There is a critical stress level at which the coupling can be considered negligible, and when the stress level goes higher, coupling aggravates battery degradation exponentially. Additionally, the study also indicates that battery life shows stronger sensitivity to discharge rate and EOCV than to charge rate and EODV. The developed capacity degradation model based on the input of real operating conditions and coupling intensity calibration achieves error less than 15% when the cycling goes into the stable decay period, and the error converges gradually as the cycling continues.     

Study of the Li-insertion/extraction process in LiFePO4/FePO4

The structural properties of LiFePO₄ prepared by the hydrothermal route and chemically delithiated have been studied using analytical electron microscopy and Raman spectroscopy. High-resolution transmission electron microscopy and selected area electron diffraction measurements indicate that the partially delithiated particles include LiFePO₄ regions with cross-sections of finite size along the ac-plane, as a result of tilt grain boundary in the bc-plane, and dislocations in other directions. Only the boundary along the bc-plane is accompanied by a disorder over about 2 nm on each side of the boundary. The Raman spectrum shows the existence of both LiFePO₄ and FePO₄ phases in the shell of the particles at a delithiation degree of 50%, which invalidates the core–shell model. This result also invalidates the recent model according to which each particle would be single-domain, i.e. either a LiFePO₄ particle or a FePO₄ particle. On the other hand, our results, like prior ones, can be understood within the framework of a model similar to the spinodal decomposition of a two-phase system, which is discussed within the framework of morphogenesis of patterns in systems at equilibrium. Both end-members, however, are well crystallized, suggesting a recovery similar to that observed in superplastic alloys, with dynamics that are due to the motion of nucleation fronts and dislocations, and not due to a diffusion phenomenon associated with a concentration gradient.     

LiFePO4 with enhanced performance synthesized by a novel synthetic route

Pure LiFePO₄ was synthesized by heating an amorphous LiFePO₄. The amorphous LiFePO₄ obtained through lithiation of FePO₄·xH₂O by using oxalic acid as a novel reducing agent at room temperature. FePO₄·xH₂O was prepared through co-precipitation by employing FeSO₄·7H₂O and H₃PO₄ as raw materials. X-ray diffraction (XRD), scanning electron microscopy (SEM) observations showed that LiFePO₄ composites with fine particle sizes between 100 nm and 200 nm, and with homogenous sizes distribution. The electrochemical performance of LiFePO₄ powder synthesized at 500 °C were evaluated using coin cells by galvanostatic charge/discharge. The synthesized LiFePO₄ composites showed a high electrochemical capacity of 166 mAh g⁻¹ at the 0.1C rate, and possessed a favorable capacity cycling maintenance at the 0.1C, 0.2C, 0.5C and 1C rate.     

Thermal characteristics of a FeF3 cathode via conversion reaction in comparison with LiFePO4

The thermal stability of a FeF₃ cathode via a conversion reaction was quantitatively studied using differential scanning calorimetry (DSC). Mixtures of charged and discharged FeF₃ electrodes and electrolyte were measured by changing the ratio of electrode to electrolyte. A mild exothermic peak was observed at temperatures ranging from 210 to 380 °C for the mixtures of charged electrode and electrolyte even if the electrode/electrolyte ratio was changed. Moreover, the cycling depth had no effect on the thermal stability of the charged electrode in the electrolyte. For the mixtures of discharged electrode and electrolyte, exothermic reactions occurred in the range of 250-350 °C, which varied with the electrode/electrolyte ratio. Although the exothermic reactions of the mixtures varied with the electrode/electrolyte ratio, the thermal risk for both charged and discharged electrodes coexisted with the electrolyte appeared to be mainly due to electrolyte decomposition. By comparing the heat values of mixtures of the charged and discharged electrodes and electrolyte, the FeF₃ electrodes in the electrolyte demonstrated better thermal stability than LiFePO₄ electrodes at elevated temperatures.     

A comparative study of polyacrylic acid and poly(vinylidene difluoride) binders for spherical natural graphite/LiFePO4 electrodes and cells

Anodes containing spherical natural graphite (SNG12) and cathodes containing LiFePO₄, both from HydroQuebec, were prepared with aqueous-based polyacrylic acid (PAAH), its neutralized derivatives polyacrylic acid (PAAX) (X = Li, Na, and K), and with conventional poly(vinylidene difluoride) (PVDF) binders. A comparison of electrode performance was made between these three binder systems. The electrodes were optimized by adding elastic styrene butadiene rubber (SBR) and conductive vapor grown carbon fiber (VGCF) in the place of some of the PAAX. Initially, SNG12 and LiFePO₄ electrodes were characterized in half cells with Li as the counter electrode. The electrochemistry results show that the use of PAAX binders can significantly improve the initial coulombic efficiency, reversible capacity, and cyclability of SNG12 anodes and LiFePO₄ cathodes as compared to that of electrodes based on a PVDF binder. By using an optimized composition for the anode and cathode, SNG12/LiFePO₄ full cells with PAALi binder cycled 847 times with 70% capacity retention, which was a significant improvement over the electrodes with PVDF (223 cycles). This study demonstrates the possibility of manufacturing Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like NMP, thereby improving performance, reducing cost, and protecting the environment.