Numerical modeling and experimental validation of pouch-type lithium-ion battery

The thermal behavior of pouch-type lithium-ion batteries during discharge and charge cycles is investigated by numerical simulation. A transient thermal model using finite element method software is developed through the modification of an electrochemical-thermal model. The developed model is validated with experimental data. For the experiment, a 304252 pouch cell is fabricated and tested in the laboratory. This model captures the dynamic responses of temperature, and distributions of current density and temperature, during discharge and charge cycles. Our results indicate that the discharge temperature is higher than the charge temperature at cut-off voltage. The temperature distribution upon discharge is similar to that of charge. On the other hand, different temperature distributions are observed at various C rates. The temperature profiles obtained from modeling and experiment are in good agreement.     

Phenomenological model‐based analysis of lithium batteries: Discharge,charge, relaxation times studies,and cycles analysis

The operation of lithium ion batteries in discharge and charge processes is addressed. A simple phenomenological model is developed to predict all variables values. A set of algebraic and differential equations is derived taking into account salt and lithium balances in electrodes, in the separator, and in particles. Balances are developed for finite volumes and appropriate average values of several variables such as concentrations, current densities, and electrochemical reaction rates are introduced. Definitions of current densities as volume fraction functions are critical issues in the computations. Experimental values taken from the literature for discharge processes are predicted very accurately. Constant salt concentration in the separator can be assumed and consequently, the model can be analytically solved. Charge and discharge times, initial cell capacity, lost capacity, and relaxation times are easily estimated from simple equations and cell parameters. The limiting processes taking place during cell discharge can be determined. Energy efficiency and capacity usage are quantified for cycles. © 2014 American Institute of Chemical Engineers AIChE J, 61: 90–102, 2015     

Simulations on simultaneous charging/discharging process of oil sand packed bed thermocline storage tank

A physical mathematical model of oil sand packed bed thermal energy storage (TES) which can be applied in high temperature TES system is established. The charge/discharge outlet temperature and thermocline thickness are investigated when charge and discharge process are operated simultaneously. The results indicate that the small charging power and lower increasing rate of charge outlet temperature are obtained in the end of simultaneous charge and discharge. The smaller the net TES flow rate, the longer it takes to reach a stable charge outlet temperature under the condition of the same TES medium in the TES tank. The conventional TES tank thermocline thickness is thinner than oil sand packed bed when operated at the same net charge flow rate. The stable/unstable simultaneous charge and discharge are investigated based on cycle process of square wave thermal source. The discharge outlet temperature and the thermocline thickness gradually increase after the end of each cycle due to the effect of the superposition of the cycle process. The discharge outlet temperature fluctuates periodically.     

导热油砂石填充床单罐斜温层同时蓄放热特性模拟

针对应用于高温储热场合的导热油砂石填充床储热,建立物理数学模型,采用数值模拟方法,重点探究在稳定热源和非稳定热源同时蓄放热工况下,蓄放热出口温度、斜温层厚度等参数。研究发现：传统蓄热罐同时蓄放热后期,换热功率较小,蓄热出口温度上升较慢;当蓄热罐内部传热工质结构相同时,净蓄放热流量越小,蓄热出口达到稳定的用时越长;同一净蓄热流量下,传统蓄热罐运行过程中斜温层厚度远远小于填充床蓄热罐运行时斜温层厚度;以热源为方波形式的周期性蓄热过程探究非稳定热源同时蓄放热。由于周期叠加性的影响,各工况每周期结束后放热出口温度上升,蓄热罐内斜温层的厚度逐渐增大,放热出口温度呈现周期性波动。     

可溶铅酸液流电池模拟与仿真

可溶铅酸液流电池是一种使用单个容器存储电解液并且不需要微孔隔膜的氧化还原液流电池,这使得电池设计简单并降低了成本。建立二维暂态可溶铅酸液流电池模型,模型基于对质量、电荷以及能量的转移与守恒以及包含铅离子反应的宏观动力学模型为基础,研究了电极间隔、电极形状、电流密度、实验温度、入口电解液流速和电解质初始浓度对电池性能的影响。研究表明：与平板电极相比,弧形电极明显提高了充电时的电池电压。在影响铅酸液流电池性能的诸多条件中,电池温度和电流密度可能是优化电池性能的重要因素。     

二氯二甲基硅烷对锂硫电池性能的影响

采用二氯二甲基硅烷对锂片表面进行预处理,以提高电极的界面稳定性。将预处理的锂片与硫电极组装成锂硫电池,并对其进行充放电测试。结果表明,与以未经预处理锂片作负极的锂硫电池相比,经二氯二甲基硅烷预处理5 min的锂片作负极的锂硫电池的循环性能、倍率性能及库伦效率均得到较大的改善,且预处理时间对电池的性能有一定的影响。     

Impact charging of particulate materials

When a particle impacts on a wall, electrostatic charges may be generated. This is called contact/impact/frictional electrification. One question to be answered is how and what process dominate the amount of the charge. In this respect, the separating process, rather than the contacting one, is important. It is shown that the potential difference between the surfaces can increase so rapidly in the separation process that it can cause gas discharge. Once such a gas discharge takes place, the charge on each surface can relax on the path: the amount of charge after the separation is a kind of residual charge after the charge relaxation. This process has been modeled and the model is called the “charge relaxation model.” It can estimate the amount of the impact charge without any empirical parameters, although the gas discharge itself is only an assumption so far which has not been directly observed or confirmed experimentally. In the experimental aspect, an “impact charging experiment” with single particles was carried out to provide a basis for the fundamental discussions. Polymer as well as metal particles about 3 mm in diameter ones were initially used, and the results showed good agreement with the “charge relaxation model.” The sensitivity of the instrument was enhanced to allow measurements with micrometer particles. These results are also reviewed here.     

Potential application of microporous structured poly(vinylidene fluoride-hexafluoropropylene)/poly(ethylene terephthalate) composite nonwoven separators to high-voltage and high-power lithium-ion batteries

We demonstrate potential application of a new composite non-woven separator, which is comprised of a phase inversion-controlled, microporous polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) gel polymer electrolyte and a polyethylene terephthalate (PET) non-woven support, to high-voltage and high-power lithium-ion batteries. In comparison to a commercialized polyethylene (PE) separator, the composite non-woven separator exhibits distinct improvements in microporous structure and liquid electrolyte wettability. Based on the understanding of the composite non-woven separator, cell performances of the separator at challenging charge/discharge conditions are investigated and discussed in terms of ion transport of the separator and AC impedance of the cell. The aforementioned advantageous features of the composite non-woven separator play a key role in providing facile ion transport and suppressing growth of cell impedance during cycling, which in turn contribute to superior cell performances at harsh charge/discharge conditions such as high voltages and high current densities.     

Model based analysis of lithium batteries considering particle‐size distribution

Performance of lithium ion batteries whose electrodes are composed of particles of different sizes is studied. Simplified model developed in (Henquín and Aguirre, AIChE J. 2015; 61:90–102) is extended and the simulations are compared with experiments from the literature so as to validate this new model. The differences in current density observed in particles of different sizes, which are in contact, depend on particle size and state of charge. Internal particle to particle discharge currents are observed during relaxation times. A parametric study of the applied current and particle sizes of electrodes is performed to evaluate cell performance, with emphasis on cell voltage and final capacity measurement. The evolution of reaction rates on the surface of electrode particles and their corresponding states of charge are depicted. An analysis of relaxation times in terms of cell voltage, current density, equilibrium potentials, and overpotentials is included. © 2017 American Institute of Chemical Engineers AIChE J, 64: 904–915, 2018     

Analysis of capacity–rate data for lithium batteries using simplified models of the discharge process

Simplified models based on porous electrode theory are used to describe the discharge of rechargeable lithium batteries and derive analytic expressions for the specific capacity against discharge rate in terms of the relevant system parameters. The resulting theoretical expressions are useful for design and optimization purposes and can also be used as a tool for the identification of system limitations from experimental data. Three major cases are considered that are expected to hold for different classes of systems being developed in the lithium battery industry. The first example is a cell with solution phase diffusion limitations for the two extreme cases of a uniform and a completely nonuniform reaction rate distribution in the porous electrode. Next, a discharge dominated by solid phase diffusion limitations inside the insertion electrode particles is analysed. Last, we consider an ohmically-limited cell with no concentration gradients and having an insertion reaction whose open-circuit potential depends linearly on state of charge. The results are applied to a cell of the form Li|solid polymer electrolyte|LiyMn2O4 in order to illustrate their utility.     

MnO2 cathode in an aqueous Li2SO4 solution for battery applications

A manganese dioxide (MnO₂) cathode with zinc (Zn) as the anode has been investigated using lithium sulphate (Li₂SO₄) as an electrolyte. Previously we demonstrated that cells comprising MnO₂ and lithium hydroxide (LiOH) as an electrolyte can be made rechargeable to over one-electron capacity with a discharge capacity of 150 mAh g⁻¹. Here we have extended our work to assess Li₂SO₄ as an electrolyte and have found that the battery is not rechargeable. Based on the electrochemical (discharge/charge) performance and the products formed following discharge and charge, the mechanism proposed for the sulphate-based media is one of proton insertion into the MnO₂ cathode, rather than the lithium ion insertion observed for the LiOH electrolyte. The addition of bismuth species to the Li₂SO₄-based cell results in a transition to rechargeable behaviour. This is believed to be due to the influence of Bi ions on the formation of soluble Mn³⁺ soluble intermediates. However, the coulombic efficiency of the cell diminishes rapidly with repeated charge/discharge cycles. This confirms that the nature of the Li-containing electrolyte has a marked influence on the electrochemistry of the cell.     

暂态边界电压法在线测试全钒液流电池阻抗

国内首次采用暂态边界电压法在线研究了全钒液流电池（VRB）的特性,建立了由电压源、电阻以及一个电阻与电容并联的3部分串联而成的等效电路模型;研究了电流密度和荷电状态（SOC）对等效电路元件的影响。实验结果表明,极化阻抗随电流密度的增加有轻微下降,在充电初期和放电末期达到最大值。与极化阻抗相比,充、放电过程中的欧姆阻抗最大,是导致电压损失的主要因素,分别为1.905Ω?cm2和 2.139 Ω?cm2,暂态边界电压法是一种简单且有效的表征全钒液流电池性能的新方法。     

Gas Recombination in Sealed Ni–MHx Cells

This paper focuses on investigation of gas recombination in a positive-limited-sealed Ni–MH_x cell. The positive electrodes were prepared by electrochemical impregnation of fibrous nickel plaques. The metal hydride negative electrodes were made by pasting the mixture of rare-earth hydrogen storage alloy powders, conducting and binding agents on foamed nickel substrates. The measurement of the positive capacity at different charge times was used to estimate the partial current for oxygen evolution at the same time. The effects of charge rate, electrolyte saturation level and initial state of charge of the positive electrodes on the recombination were investigated in sealed Ni–MH_x cells. By determining the differential capacity of nickel hydroxide electrodes, an improved mathematical model was used to evaluate the gas recombination parameters during charge, overcharge, rest and discharge of the positive-limited-sealed Ni–MH_x cell. The gas recombination during rest, discharge and overdischarge was also examined. The oxygen recombination on the nickel hydroxide electrodes can be neglected due to the consumption of water when the nickel hydroxide electrodes were discharged. The longer overdischarge produced an increase in cell pressure for the sealed Ni–MH_x cell at an electrolyte unsaturated level and the evolving gas can be recombined by a following recharge operation. © 1997 SCI.     

Reversible and irreversible heat effects in ZEBRA cells

When a sodium-nickel chloride cell is discharged reversibly, heat is liberated. The amount of heat involved has been found from measured values of the open circuit voltage of the cell over a range of temperatures. The thermal capacity of a 40 A h cell has also been measured, at various states of discharge, and is found to be a linear function of the temperature and of the degree of discharge. The information has been combined to find the temperature changes which occur when a fully charged cell undergoes a reversible discharge-charge cycle. Complete discharge of the cell involves a temperature rise of some 30–35 K, depending on the starting temperature; the effect is reversed on charge. The techniques employed in these calculations could be applied to other cells in which all reactants and products of the cell reaction are pure phases, such as the sodium-sulphur cell or ZEBRA cells involving transition metals other than nickel.     

Triboelectrification of particulate flows on surfaces: Part II — Mechanisms and models

Triboelectric charge accumulation both poses problems and offers opportunities for dry particulate processing. It generates hazards in many industrial systems, but is exploited in several important applications, including electrophotographic toner charging and triboelectric separation. However, the charging of continuous particulate flows on solid surfaces is poorly understood, and design of devices to optimise triboelectric behaviour is often qualitative or based on trial and error. This study attempts to identify the main charging mechanisms for a continuous particulate flow on a flat surface. The proposed charging models incorporate contact time, velocity and mode of contact. A model incorporating contact area effects arising from sliding and rolling contact is consistent with experimental data, as long as a charge limit is imposed on bouncing particles. A mechanism for this charge limit, involving separation discharge, is proposed. The effect of delocalised image charge on the system is estimated and found to be negligible. Some general design principles are proposed for triboelectric optimisation of particle processing devices.     

The prediction of the state-of-charge of some commercial primary cells

Research carried out at Loughborough during the last five years on the impedance of Leclanché, alkaline Zn-MnO₂, alkaline Zn-HgO, Li-CuO, Li-SO₂, Li-SOCl₂ primary cells is briefly reviewed. The use of alternating current methods for the estimation of the state of charge of the cells is discussed. A search was made for properties of the impedance of each cell system which change in a marked and reliable manner when a prescribed amount of charge is withdrawn from the cell. It is concluded that simple tests based upon an assessment of these properties are adequate for the estimation of the state of charge of some of the systems studied. However, other systems are not so ‘well-behaved’. The impedance of each cell changed significantly during discharge and, although making measurements of these changes would enable the state of charge to be estimated, the test techniques required would not necessarily be simple. Using the results obtained on the impedance of the cells, test sets have been constructed which provide a digital presentation of the open-circuit voltage and the state of charge of Leclanché cells (Ever Ready type SP11), mercury cells (Mallory, type RM502R) and lithium cells (Mallory, type L032S and SAFT, type LC01). The electronic techniques employed in these test sets are described in outline with reference in block-schematic diagrams. A proposal is made for the construction of a general-purpose tester for primary cells which would incorporate microprocessors and provide an indication of state of charge based upon data relating to impedance, temperature and discharge history. The tester might also be made self-calibrating for field use.     

An electrochemical impedance spectroscopy and scanning electron microscopy study of the influence of positive plate compression on the electrochemical behaviour of lead-acid batteries

This study has developed an electrochemical impedance spectroscopy (EIS) method for the in situ investigation of the influence of positive plate compression on the electrochemical behaviour of lead-acid batteries during charge/discharge cycling. The EIS data for a fully charged and fully discharged battery are internally consistent with the expected kinetics of a battery in the opposite states of charge, and demonstrate that EIS measurements may be recorded with a high level of reproducibility. Furthermore, this study has necessitated the development of a special cell incorporating horizontally orientated battery plates that can be subjected to elevated pressure through the stacking of lead bricks on top of the cell, as well as a physically robust reference electrode system that can withstand the application of pressure. For this purpose, a platinum-wire pseudo-reference electrode has been developed, and has been shown to exhibit sufficient electrode stability over the period of an EIS recording, enabling the measurement of reproducible and meaningful EIS data. Additionally, the influence of positive plate compression on the behaviour of the lead-acid battery has been investigated by using scanning electron microscopy (SEM). Clearly, the experimental data show that plate compression enhances significantly the kinetics and concomitant performance of the lead-acid battery, and this is related to the enhanced reactivity of the active material, as rationalized by using the agglomeration-of-spheres (AOS) model.     

三元材料扣式电池测评条件的研究

以正极浆料配方、极片尺寸及充放电倍率等关键因素为研究对象,探求扣式电池在三元材料测评中的技术条件。极片进行SEM观察,并制成扣式电池,进行相关电化学测试。结果表明,PVDF用量6%,极片直径12 mm,压片压力20 MPa,充放电倍率0.2 C时,材料比容量及首次库伦效率测评结果较稳定,离散较小。     

On the use of pyrrole black in zinc-halogen batteries

The storage of Br₂/Br^– and I₂/I^– couples in a conducting polymer matrix, polypyrrole coated on a reticulated vitreous carbon disc, is described and the application of these positive electrodes in zinc-halogen model batteries is discussed. The cell based on the polypyrrole bromine adduct shows the higher open circuit voltage which, however, depends on the state of charge. Such cells self discharge thus limiting their usefulness. In the case of the iodine cell the self discharge is due to loss of iodine from the polymer to the bulk solution, but with the bromine cell the cause is oxidative bromination and depolymerization of the polypyrrole.