A mathematical model is presented to study the effect of the particle size distribution (PSD) on the galvanostatic discharge behavior of the lithium/separator/intercalation electrode system. A recently developed packing theory has been incorporated into a first-principles model of an intercalation electrode to provide a rational basis for including the effect of PSD on packing density. The model is used to investigate how binary mixtures of spherical particles affect electrode capacity. The electrode capacity of an insertion electrode is calculated for various parameters including applied current density, thickness of the electrode, and volume fraction, size, and size ratio of the particles. The model shows that an electrode comprised of two different sized particles can have a significantly higher capacity than an electrode consisting of single-sized particles. However, increasing the packing density increases the liquid-phase diffusion resistance. As a result of the trade-off between packing density and liquid-phase diffusion resistance, discharge capacity can be optimized by adjusting the particle size, volume fraction of large and small particles, and the size ratio. Pulse discharge of an intercalation electrode comprised of two different sized particles shows a marked difference in transient behavior from that of an electrode which has single-sized particles. Since there are many parameters which control the performance of the electrode, use of this model should aid greatly in making superior electrodes. InfroductionLithium-ion batteries are now the preferred power source for cellular phones, portable computers, and camcorders, but optimization and development of design criteria is stifi progressing. The distinguishing feature of lithium-ion batteries is the use of intercalation electrodes for both positive and negative electrodes. In a pioneering paper, West et al.1 explained the operation and gave design criteria of intercalation electrodes based on a mathematical model which accounted for coupled transport in the electrode (solid) and electrolyte (liquid) phases. Other workers refined this * Electrochemical Society Student Member. * * Electrochemical Society Active Member.'In this paper the discharge of the cell represents the intercalation of lithium into the electrode with a PSD.

This paper describes approaches to reduce susceptibility of perfluorosulfonic acid membranes such as Nafion® to degradation through chemical attack by oxygen-based radicals and physical degradation as a result of mechanical stress. These approaches include the incorporation of a continuous reinforcing layer and modification of the polymer to stabilize it against attack by peroxide radicals.

A mathematical model is presented for the galvanostatic deposition of Ni(OH)2 films in stagnant Ni(NO,), solutions. The objective is to quantify the anomalous deposition behavior reported previously in which the utilization of the electrochemically generated OW species decreased drastically as the concentration of Ni(N03)2 increased beyond 0.1 M. For example, as the Ni(NO,)2 concentration increased from 0.1 to 2.0 M, the deposition rate decreased by a factor of ten at 2.5 mA/cm2. At this high ratio of concentration to current density, a comparison with Faraday's law indicates that only 10% of the OW species generated at the surface led to deposition. It has been proposed that the inefficient use of electrochemically generated OW species is due to the presence of Ni4(OH)r as an intermediate in the deposition process. As the bulk Ni(N0,), concentration increases, the concentration of Ni4(OH)r at the electrode surface increases. A high concentration of the intermediate results in an increase in the diffusion rate of the species away from the electrode surface and thus a decrease in the deposition rate. Here, this hypothesis is tested by developing a model which includes the generation of OW from the electrochemical reduction of nitrate to ammonia and the diffusion and migration of Ni2t, No;, OW, Ht, and Ni4(OH). The model predictions agree well with previously reported mass deposition data collected using an electrochemical quartz crystal microbalance at different currents and over a range of Ni(N03)2 concentrations. The present work confirms the role that Ni,(OH) plays in the deposition process and provides a fundamental framework for understanding the electrochemical impregnation of nickel electrodes.

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