William Tiedemann

Potential and current distribution in electrochemical cells : interpretation of the half-cell voltage measurements as a function of reference-electrode location

The effects of electrode resistance and electrochemical polarization on potential measurements made with reference electrodes in various locations are demonstrated for electrodes with full‐width tabs and idealized polarization characteristics. Nonuniform current distribution, which changes during discharge, can lead to complex behavior in the measurements, which would be missed in the overall cell potential. To detect individual electrode polarization and limiting‐electrode behavior during discharge, it is recommended that the reference‐electrode probe be placed between the working electrodes reasonably close to the tabs.

Simulation of Recombinant Lead‐Acid Batteries

Modeling of recombinant lead-acid batteries is extended to improve the description of oxygen generation and recombination and to introduce limited rates of transport of Pb 2+ ions on charge as well as hydrogen generation and recombination. A simple, lumped-parameter model is deemed to be adequate to treat system behavior at low rates of charge. The oxygen recombination can be treated as either chemical or electrochemical, and this issue should not be considered to be completely resolved. Model results are compared with experimental results from the literature for cell potential and pressure for several charging rates and extended to the case where the rate is increased or decreased after the battery has been fully charged.

Temperature Rise in a Battery Module with Constant Heat Generation

A three-dimensional battery module in the shape of a block is taken to generate heat uniformly throughout. The temperature rise as a function of time is worked out based on equations for heat conduction in solids. After appropriate nondimensionalization, the maximum temperature rise depends on the thermal aspect ratios (defined herein). By a superposition integral, the method can be extended to a time-dependent heat-generation rate, as appropriate for a driving profile.

A Secondary, Nonaqueous Solvent Battery

A room-temperature battery with nonaqueous organic solvent was developed. The cell contains a lithium negative, a graphite positive, and lithium perchlorate--dimethyl sulfite electrolyte. The cell has an open-circuit voltage of 4.5 V, and delivers 10 mA/cm/sup 2/ at 4 V. (RWR)

Simulation of the Li-CFx system

The Li-CF x system has been successfully used in implantable batteries to power medical devices for humans. Amassed data is analyzed to show that the behavior is dominated by the open-circuit potential and Tafel kinetics. Data from several discharge load resistances can be collapsed onto a single curve on this basis. At the low rates of interest, transport limitations can be neglected. Data for open-circuit relaxation show that the potential is a straight line when plotted against the logarithm of time. This is in harmony with the dominance of Tafel kinetics.

Simulation of pulse discharge of the Li-CFx system

A zero-dimensional model is developed for the CF x system to account for Butler-Volmer kinetics, internal cell resistance, and double-layer (or capacitive) charging. At the low rates involved, other transport processes can be neglected. Furthermore, for this system, Tafel kinetics is appropriate. This model is used to compare with discharge data for periodic pulses superposed on an otherwise low rate of discharge. The internal resistance and high double-layer capacity account for some aspects of the pulses, such as a long time relaxation when the load is changed, but do not account for other time constants of less than 1 s. For a long constant-load discharge without pulses, the model can be simplified further, with the capacitance being negligible and the internal resistance being important only at low load resistances. Development of a modified open-circuit potential function allows all discharge data for cells of different design and load resistance to be collapsed using a generalized design equation.

Microstructural Aspects of Grid Corrosion in the PbO[sub 2] Electrode

A radical change in microstructure was examined for its effect on the mode of corrosive attack and corrosion rate for a 5 weight percent antimonial lead alloy. Metallography on as-cast microstructures indicates a transition from interdendritic to general attack with increasing overpotential. The potential region for general attack corresponds to a breakdown in the passivating abilities of PbO/sub 2/, and is marked by a sharp rise in the corrosion current. A simple heat-treatment, which alters the structure of the eutectic material, reduces interdendritic attack over the entire potential region studied. 8 figures, 2 tables.