PRIMARY CURRENT DISTRIBUTION IN A THIN-FILM BATTERY - APPLICATION TO POWER-DENSITY CALCULATIONS FOR LITHIUM BATTERIES

The mathematical formulation required to determine the power density o f a thin-film battery that is governed by ohmic drop in the electrodes and electrolyte is presented along with representative results for a lithium polymer battery. The problem statement is two dimensional, ref lecting the ohmic drop along the length of the electrodes and across t he electrolyte separating the electrodes. Although the analysis corres ponds to steady-state charge transport and current passage, the form o f the governing equations is common to electrostatic-field problems in the absence of separated charge, with the electric potential satisfyi ng Laplace's equation. The power density calculations are a function o f seven dimensionless groups: four geometric ratios, two conductivity ratios, and a group representing the cell's end-plate volume contribut ion.