Energy storage units have become important components in residential micro-cogeneration (MCG) systems. As MCG systems are often connected to single residences or buildings in a wide variety of settings, they are frequently unique and highly customized. Lithium-ion batteries have recently gained some profile as energy storage units of choice, because of their good capacity, high efficiency, robustness and ability to meet the demands of typical residential electrical loads. In the present work, modeled scenarios are explored which examine the performance of a MCG system with an internal combustion engine, photovoltaic input and a Li-ion storage battery. An electricity demand profile from new data collected in Ottawa, Canada is used to provide a full year energy use context for the analyses. The demands placed on the battery are examined to assess the suitability of the battery size and performance, as well as control related functionalities which reveal significantly varying battery use, and led to a quantitative expression for equivalent cycles. The energy use simulations are derived from electrochemical fundamentals adapted for a larger battery pack. Simulation output provides the basis for techno-economic commentary on how to assess large-scale Li-ion batteries for effective electrical storage purposes in MCG systems, and the impact of the nature of the control strategy on the battery service life. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.

The performance of a lithium-ion battery is closely related to its manufacturing and can be impacted by variability in the electrodes. Typically, manufacturers must set aside cells which are deemed to be of insufficient quality, thus contributing to the cost of manufacturing high quality cells. The performance of a lithium-ion battery module, that is, a string of cells configured in series, depends on the performance of the weakest cell. In this work, the single particle model was adapted to simulate the coupled behaviour of an arbitrary number of cells configured in series. The impact of slight variations in the manufacturing of electrodes was then investigated with a goal of linking electrode properties such as variations in thickness, electrode density and active material weight fraction with the performance of battery modules made from these cells. Results indicate that the initial capacity, the rate of capacity fade and other important aspects such as the distribution of state-of-charge from one cell to another depends on the extent of variability in the manufacturing of the electrodes. In this work, the variation in the performance of the module has been quantified as a function of manufacturing variation at the electrode level.

This study reports on the physico-electro-chemical characterization of porous composite electrodes made of lanthanum-barium-cobalt oxide (LBC) electrocatalyst and gadolinium-doped-cerium oxide (GDC) oxygen-ion conductor. Four different compositions of LBC-GDC composite electrodes were fabricated and heat-treated at 1150 degrees C. The phase purity of the heat-treated LBC-GDC composite was checked by X-ray diffraction measurements. Thermal expansion coefficient (TEC) was measured from room temperature to 900 degrees C. Porous LBC-GDC composite electrodes were studied in a symmetrical cell configuration by impedance spectroscopy where gadolinium doped ceria (GDC) was used as a solid electrolyte. Impedance spectra obtained at zero dc bias conditions consisted of two semi-circular arcs, which indicate that the overall oxygen reduction comprises at least two distinct processes. The area specific resistance (ASR) for electrode polarization was measured in the 600-800 degrees C temperature ranges. The lowest ASR value of 0.06 Omega cm(-2) at 600 degrees C was exhibited by LBC/GDC composite of composition 60/40. The ASR values at lower temperatures offer the promise of utilizing composite as a cathode for low-temperature SOFCs. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3606475] All rights reserved.

In the present work, microstructural and transport properties of a three-dimensional (3D) microstructure of lanthanum strontium manganite (LSM) are deduced using dual-beam focused ion beam-scanning electron microscopy (FIB-SEM) facility. A series of two-dimensional (2D) cross-sectional images are collected from the LSM sample using FIB-SEM and then reconstructed to 3D structures from the 20 images in a systematic approach. For the first time, the effect of different image processing steps including threshold value, median filter radius, morphological operators, surface triangulation, smoothing filter, etc., on porosity, internal surface area, electronic conductivity and diffusivity are studied. Variation of 33% and 25% on porosity E and internal surface area S. respectively is observed because of improper selection of threshold value, median filter radius, and morphological operator. The number of triangular surfaces used in 3D reconstructions also varied the porosity sand internal surface area S by 14.5% and 4.4%, respectively.Computational domains for calculating effective transport properties are generated using body-fitted cut-cell based finite volume meshes on reconstructed 3D volumes. The normalized effective transport properties are computed on computational domains reconstructed by the FIB-SEM as well as by a numerical model. For the FIB-SEM reconstruction case, the normalized effective properties in z-direction are 25-44% smaller than those properties in x and y directions. This difference is significant and reveals the anisotropy in FIB-SEM reconstructed volume compared to numerically reconstructed volume. The presence of large crater, milling direction and smaller 3D FIB-SEM reconstructed volume could be the main reasons for this local anisotropy. (C) 2010 Elsevier B.V. All rights reserved.

Electrochemical data collected for the porous La1-xSrxMnO3+delta (LSM) cathode-yttria-stabilized zirconia electrolyte system were analyzed using a mathematical model capable of simulating both the steady-state and impedance responses. The model considered the distributed nature of the porous electrode and a parallel pathway for oxygen transport including gas transport and surface diffusion. Data were collected in low oxygen partial pressures ranging between 10(-4) and 10(-3) atm, where LSM was considered to be stoichiometric with respect to oxygen. Thermodynamically consistent kinetic and transport parameters were regressed from the steady-state polarization data. Three different parameter sets fit the general trend of the experimental data. The surface diffusion and adsorption/desorption parameters were cross-correlated, which underlines the difficulty in finding a unique set of fitting parameters. The parameter set with four adjustable parameters resulted in a high surface diffusion coefficient but slower adsorption/desorption kinetics compared to the other two parameter sets for which a lower surface diffusion coefficient was fixed. The predicted overall impedance at zero-dc bias conditions for three parameter sets had varying degrees of agreement with the data. Low and high frequency arcs attributed to adsorption and an oxygen transport process were observed in the faradaic impedance response. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3432410] All rights reserved.

A numerical framework to compute the effective transport coefficients for porous electrode microstructures is presented. The anode and cathode electrodes of solid oxide fuel cells are discretized as porous microstructures that are formed by randomly distributed and overlapping spheres with particle size distributions that match those of actual ceramic powders. The technique involves the construction of the composite electrode microstructure based on measureable starting parameters and the subsequent numerical evaluation of the effective transport coefficients. We use both the finite volume method and the Monte-Carlo simulation to enumerate effective transport coefficients. The results of the calculations are compared with experimental data for electron conductivities for a range of solid-matrix compositions. Comparisons are also made with theoretical correlations for effective coefficients. The effect of Knudsen diffusion on effective gas diffusivity is also addressed in this paper. Numerical results are compared with a harmonic average approximation based on Bosanquet's formula.

A numerical technique for generating the solid oxide fuel cell composite electrode structure based on measurable starting parameters has been developed. This method can be used to calculate all relevant electrode microstructural parameters. The structures are formed of randomly distributed overlapping spheres with particle size distributions that match the particle sizes of actual ceramic powders. In this work, the triple phase boundary length, internal surface area, pore size and the percolation of all relevant phases within the porous composite electrode were computed. It was found that the triple phase boundary length computed for particles with real particle size distributions was as much as 40% lower compared to mono-sized particles with the same mean particle sizes. Percolation thresholds were in the range of 30–40vol% for solid phases and over 99% of pores were found to belong to a percolating network at porosities as low as 25%. In addition, the average pore size was found to be 0.19μm for typical electrode compositions, smaller than what is commonly assumed and in certain circumstances, the distribution of pore sizes may place gas transport in the free molecular flow regime.

The electrochemical performance of a SOFC cathode depends not only on the activity of the cathode, but also on the relative facility by which the reaction participants are transported to the reaction site. The microstructure and the geometry of the cathode influence the relevant transport and reaction characteristics, and thereby the distribution of current density, in a complex manner. In this study, the influence of electrode porosity and thickness as well as current collector layer thickness and interconnect coverage was examined using a 2-dimensional across-the-channel model of a planar SOFC LSM-YSZ composite cathode. The results indicate that for a fixed functional layer thickness for the electrode, increasing the porosity of the electrode actually reduces the electrochemical performance but improves the oxygen distribution. Addition of a porous current collector layer improved both oxygen distribution and overall electrochemical performance. The results of varying interconnect coverage were very interesting in that an improved performance was observed upon reduction of coverage from 50% to 25% but no further change was observed upon further reduction to 12.5%. A closer examination of current density distribution for the cases of 25 and 12.5% coverages showed that a reduction of the coverage from 25% to 12.5% results in improving mass transport limitations under the interconnect but reduces electron transport under the channel. However, the electron transport limitation is offset by enhancement in oxygen distribution. The study highlights the need for simultaneous optimization of electrode microstructure and geometry.

Abstract not Available.