Sean Rayman

Maximizing the Life of a Lithium-Ion Cell by Optimization of Charging Rates

Using a dynamic optimization method, the optimum charge currents as a function of cycle number during cycling for the lithium-ion cell are obtained. A single particle physics-based model, which includes capacity fade, was applied to simulate the cell performance under low earth-orbit LEO cycling conditions. Useful cell life is defined as the number of cycles before the end of discharge voltage drops below 3.0 V or the cell discharge capacity becomes less than 20% of the original discharge capacity. The simulated useful cell life can be increased by 29.28% by varying the charge current.

Simulation of Reduction of Cr(VI) by Fe(II) Produced Electrochemically in a Parallel-Plate Electrochemical Reactor

A model is presented for the reduction of hexavalent chromium in a parallel-plate electrochemical reactor via a homogenous reaction between Cr(VI) and Fe(II) generated at the iron anode. The effects of the space velocity of the feed solution, the concentration of supporting electrolyte, the distance between the electrodes, and the cell potential on conversion of Cr(VI) to Cr(III), are discussed. This study indicates that for reduction of Cr(VI) using Fe(II), the space velocity must be maintained below 0.02 s -1 or the system becomes limited by the rate of reduction of Cr(VI) by Fe(II). Increasing the current density by increasing the cell potential, increasing the amount of supporting electrolyte, and decreasing the distance between the electrodes increases single pass conversion of Cr(VI) to Cr(III); however, increasing the current density also increases the specific energy required by the system.

Electrochemical Impedance Spectroscopy of Liquid Tin Anode Solid Oxide Fuel Cell

SOFCs present several advantages over other fuel cell technologies, such as their high efficiency of converting the chemical energy into electricity, the ability to use hydrocarbon fuels instead of hydrogen, no noble metals are used in the cell, and they provide a source of high quality heat that can be used for steam generation. Thomas Tao developed a liquid tin anode solid oxide fuel cell (LTA-SOFC) that operates on high sulfur content fuels, such as jet propellant 8 (JP-8). 3 In typical SOFCs the oxidation of the fuel takes place at the interface of the electrolyte and the electron conductor; however, in a LTA-SOFC tin is oxidized at the electrolyte-liquid metal interface, the tin oxide diffuses through the liquid tin to the liquid-tin fuel interface where the fuel is oxidized, and the tin oxide is reduced to liquid tin, as shown in Figure 1. Thus, the LTA-SOFC separates the oxidation of the fuel from the anode of the SOFC eliminating the potential detrimental effects of sulfur. Despite the abundance of literature studying the electrochemical impedance of SOFCs, the literature does not address the anode half of the liquid tin anode solid oxide fuel cell. 4-7 This work develops a first principals model of the electrochemical impedance of a liquid tin anode solid oxide fuel cell anode half cell. Equation1 is used to estimate the Ohmic resistance ( LTA YSZ R R + ),