Characteristics and effects of γ-NiOOH on cell performance and a method to quantify it in nickel electrodes

This study describes the characteristics and effect of gamma (gamma)-NiOOH on cell performance and a method to quantify it in NiCd and NiMH battery systems. gamma-NiOOH is formed in nickel electrodes under conditions of aging, high per cent overcharge, charge rates, and electrolyte concentrations. Formation of this phase results in swelling of the nickel electrode and leads to possible shorting due to fracturing. The fracturing of particles results in increased surface area. It also plays a role in drying the separator. All of these factors lead to cycle-life failure. These failure characteristics were measured in a NiCd cell as a function of charge and discharge cycles. A method to quantify gamma-NiOOH using x-ray diffraction was developed. It was found that the integrated peak intensities obtained from the 003 peak of gamma-NiOOH were approximately three times greater than that of the 001 peak of beta-NiOOH. These peaks were used since they were related to the highest intensities. This information was used in calculating the ratio of gamma/gamma+beta in a charged NiOOH electrode. This technique allows one to quantify the amount of gamma-NiOOH as a function of cycles, rates, and different depths of discharge.