Kinetics and modeling of sealed secondary batteries

The charge-discharge performance kinetics of sealed secondary nickel-cadmium and lead acid batteries were investigated and modeled.; In the case of nickel-cadmium cells, laboratory fabricated and commercial cells were studied. Nickel and cadmium electrodes were prepared by chemical and electrochemical impregnation using novel fiber substrates as current carriers. The electrochemical impregnation technique was optimized to yield electrodes with high performance.; Recombination characteristics of the electrodes were studied in a positive limited sealed Ni/Cd cell. A model was developed to predict charge and recombination efficiency during constant current overcharge. The model was modified to investigate recombination characteristics during open circuit following overcharge. It was determined that the mechanism of recombination was not purely chemical during overcharge.; The recombination efficiency in small sealed commercial lead acid batteries (capacities ranging from 1.5-140 Ah) was investigated at low overcharge rate (C/20). About two thirds of the electrolyte was found to be absorbed in the glass microfiber separator. The components were determined to have significant voids, which permitted rapid oxygen transport from the positives to the negatives. An experiment which included sealing of the outer negatives did not affect recombination rate, showing that the pathway of oxygen transport was directly from the positives to the negatives through the voids in the separator.; Overcharge at various rates of a series of commercial Ni-Cd and lead acid batteries yielded high recombination efficiency. The charge transfer resistance for some lead acid batteries was determined from the slope of polarization plots at low overvoltage. This was of the same order of magnitude as that obtained from impedance measurements (0.03-0.06 ohms).; A.C. impedance measurements were performed on Ni-Cd cells and lead acid batteries over the frequency range of 2 mHz to 250 Hz. An equivalent circuit was proposed and circuit parameters were extracted from impedance measurements. The state of charge of Ni/Cd cells and lead acid batteries were determined from impedance measurements. A model was developed to simulate battery impedance data at low and medium frequencies using porous electrode theory and equivalent circuit parameter values.; Equivalent circuit analysis was done on the squared impedance data after subtraction of the series ohmic resistance for both Ni-Cd cells and lead acid batteries. As expected, the coefficient n of the constant phase element representing the double layer capacitance was nearly equal to 1 for the squared data (n = 1 corresponds to ideal capacitance).; Mathematical modeling of a lead acid cell with electrolyte reservoir was done using finite difference technique. Solution of the set of simultaneous equations was carried out by IMSL routine NEQNJ. This model predicted the potential profile and electrolyte concentration distribution inside the cell during constant current charge.