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Abstract One approach to creating physics-based reduced-order models (ROMs) of battery-cell dynamics requires first generating linearized Laplace-domain transfer functions of all cell internal electrochemical variables of interest. Then, the resulting infinite-dimensional transfer functions can be reduced by various means in order to find an approximate low-dimensional model. These methods include Pade approximation or the Discrete-Time Realization algorithm. In a previous article, Lee and colleagues developed a transfer function of the electrolyte concentration for a porous-electrode pseudo-two-dimensional lithium-ion cell model. Their approach used separation of variables and Sturm–Liouville theory to compute an infinite-series solution to the transfer function, which they then truncated to a finite number of terms for reasons of practicality. Here, we instead use a variation-of-parameters approach to arrive at a different representation of the identical solution that does not require a series expansion. The primary benefits of the new approach are speed of computation of the transfer function and the removal of the requirement to approximate the transfer function by truncating the number of terms evaluated. Results show that the speedup of the new method can be more than 3800.

The influence of microporous layer (MPL) design parameters for gas diffusion layers (GDLs) on the performance of polymer electrolyte fuel cells (PEFCs) was clarified. Appropriate MPL design parameters vary depending on the humidification of the supplied gas. Under low humidification, decreasing both the MPL pore diameter and the content of polytetrafluoroethylene (PTFE) in the MPL is effective to prevent drying-up of the membrane electrode assembly (MEA) and enhance PEFC performance. Increasing the MPL thickness is also effective for maintaining the humidity of the MEA. However, when the MPL thickness becomes too large, oxygen transport to the electrode through the MPL is reduced, which lowers PEFC performance. Under high humidification, decreasing the MPL mean flow pore diameter to 3 μm is effective for the prevention of flooding and enhancement of PEFC performance. However, when the pore diameter becomes too small, the PEFC performance tends to decrease. Both reduction of the MPL thickness penetrated into the substrate and increase in the PTFE content to 20 mass% enhance the ability of the MPL to prevent flooding.

Abstract Differential scanning calorimetry (DSC) has been used to measure the thermal interactions between several binder materials and representative anode carbons both in the presence of cell electrolyte (EC:DEC/1M LiPF 6 +2 wt .% vinylene carbonate) and after washing/drying. Binders consisting of homo- or copolymers of vinylidene fluoride (VDF) were examined as well as other fluorinated and non-fluorinated binder materials. The heat evolved by the reactions of these materials was compared to that arising from other exothermic phenomena occurring in charged anodes at elevated temperatures. A matrix of anode material combinations was designed to investigate the role of carbon structure, carbon surface area, state of charge, binder level and presence of electrolyte. The temperature and magnitude of the exothermic reactions were measured up to 375 °C and average enthalpy values were obtained over several duplicate samples to allow good quantitative comparison of the material reactions. The exothermic anode reactions were sensitive to the state of charge and presence of electrolyte. The magnitude of the reactions increased with increasing surface area of the carbon particles. However, similar reaction enthalpies were seen for all binder materials and binder levels.

Abstract During the operation of vanadium redox flow battery, the vanadium ions diffuse across the membrane as a result of concentration gradients between the two half-cells in the stack, leading to self-discharge reactions in both half-cells that will release heat to the electrolyte and subsequently increase the electrolyte temperature. In order to avoid possible thermal precipitation in the electrolyte solution and prevent possible overheating of the cell components, the electrolyte temperature needs to be known. In this study, the effect of the self-discharge reactions was incorporated into a thermal model based on energy and mass balances, developed for the purpose of electrolyte temperature control. Simulations results have shown that the proposed model can be used to investigate the thermal effect of the self-discharge reactions on both continuous charge–discharge cycling and during standby periods, and can help optimize battery designs and fabrication for different applications.

Abstract A high temperature polymer electrolyte membrane water electrolyser (PEMWE) was investigated at temperatures between 80 and 130 °C and pressures between 0.5 and 4 bar. Nanometer size Ru 0.7 Ir 0.3 O 2 and Pt/C were employed as anode and cathode catalysts respectively. The catalyst coated on membrane (CCM) method was used to fabricate the membrane electrode assemblies. The membrane, oxygen evolution catalysts and MEAs were characterized with SEM, XRD and TEM. The influence of high temperature and pressure was investigated using in situ electrochemical measurements. Increasing temperature and pressure produced higher current densities for oxygen evolution, and smaller terminal voltages. The high temperature PEMWE achieved a voltage of 1.51 V at a current density of 1 A cm −2 , at 130 °C and 4 bar pressure.

Abstract Conventional polymer electrolyte fuel cells (PEFCs) require a means of placing the series of laminar components that make up cells under mechanical compression so as to ensure effective electrical conduction, mass transport and gas-tight operation. This review describes the effect of mechanical compression and dimensional change on the components of PEFCs and reviews the range of methods used to achieve desired stack compression. The case is made for improved understanding of the mechanisms of fuel cell component compression and greater attention to the development of technological approaches for stack compression.

Abstract Extensive models have been developed to study the performance of aqueous redox flow batteries, especially for all-vanadium flow battery. Nevertheless, there are few established models to study the non-aqueous deep eutectic solvent (DES)-based flow batteries, which have wider electrochemical window and higher energy density than do the aqueous redox flow batteries. In this study, a stationary two-dimensional model is set up to study the performance of iron-vanadium redox flow battery using DES as electrolyte, in which the property parameters of the DES are experimentally determined. The effects of temperature on the over-potentials, pump power loss, distribution of ions concentration and local current density are studied. The simulation results show that with the increase of temperature, the over-potentials decrease mildly; the electrochemical reactions inside the DES-electrolyte redox flow battery mainly happen in the area close to the membrane, which is different from the aqueous one, and the rise of temperature also leads to an improvement of electrode utilization. For the DES electrolyte with higher viscosity, the pump power loss could not be neglected. It is found that the pumping loss of the entire porous electrode largely decreases from 0.138 W at 25 °C to 0.022 W at 55 °C (with 84.05% reduction). These results are in good agreement with the experimental outcomes. Therefore, this model can be applied to predict the performance of DES based battery and further to develop new kinds of non-aqueous flow batteries.

Fluorinated carbon used as a cathode substance in lithium cells with a high and stable discharge potential is of great practical and theoretical importance. Its electrochemical activity has been reported earlier [l-3] to be determined in many respects by the nature of fluorinated substance, degree of fluorination, particle size and crystal lattice parameters. The latter two factors are of paramount importance and can be controlled in technological conditions of fluorination. We have studied 25 types of fluorocarbon substances which differ both in nature, initial substances and the conditions of fluorination.

Abstract Aromatic isocyanate, 4-fluorophenyl isocyanate and phenyl isocyanate, were first used to reduce the initial irreversible capacities during the formation of the solid electrolyte interface (SEI) on a graphite surface. Results showed that the addition of 1–5 wt.% isocyanate to propylene carbonate-containing electrolytes could effectively reduce the initial irreversible capacities in the SEI formation and increase the cycleability of Li-ion batteries. The improvement is attributed to the high reactivity of isocyanate with chemisorbed oxygen groups, such as carboxyl and phenol, which are inevitably present in the prismatic (edge) sites of graphite and are known among the sources to cause the initial irreversible capacities of a graphite anode. It is proposed that the isocyanate reacts with carboxyl and phenol groups to form more stable products, and that the resulting products have a better affinity to the subsequently formed SEI. In addition, the presence of isocyanate assists in scavenging water and acidic HF impurities from the electrolyte.