ABSTRACT
Side reactions leading to gas evolution are undesirable in batteries and result in reduced coulombic efficiency and shortened lifetime. Quantitative analysis of the gases that evolve is therefore important to improve understanding of the reactions occurring in the battery during cycling and could be used to optimize battery operation. However, the measurements are challenging because batteries are by their nature closed with limited gas space. Nickel metal hydride (NiMH) batteries are widely used due to their good rate capability, reliability, and environmental friendliness. The battery type has been extensively studied in terms of degradation and performance. However, very few studies have been conducted on the gas composition created during a work cycle. In this study, two methods for investigating the internal NiMH battery gas phase composition during different charge/discharge cycles using a mass spectrometer (MS) were developed. In the first method, the battery module was connected by a sampler system. In the second method, the battery was connected directly using a microcapillary, and the gas composition was continuously measured. In addition to the gas composition, the voltage, pressure, and temperature of the battery were recorded. The most abundant component in the measured gas phase was nitrogen, present in the cell from the assembly stage, followed by hydrogen. A clear rising trend of hydrogen pressure as depth of charge (DOC) increased was recorded, while oxygen levels were low except around the end of charge. The methods were found to be a reliable means of investigating NiMH gas composition without negatively affecting the battery and may be adapted to other battery chemistries.
ABSTRACT
Batteries in energy storage systems are exposed to electrical noise, such as alternating current (AC) harmonics. While there have been many studies investigating whether Lithium-ion batteries are affected by AC harmonics, such studies on Nickel Metal Hydride (NiMH) batteries are scarce. In this study a 10 Ah, 12 V NiMH battery was tested with three different harmonic current frequency overlays during a single charge/discharge cycle: 50 Hz, 100 Hz, and 1000 Hz. No effect on battery internal temperature or gas pressure was found, indicating that NiMH battery aging is not affected by the tested harmonic AC frequencies. This can reduce the cost of energy storage systems, as no extra filters are needed to safeguard the batteries. Instead, the capacitive properties of the batteries give the possibility to use the battery bank itself as a high pass filter, further reducing system complexity and cost.
ABSTRACT
The adsorption, electrosorption, and electrodesorption of aqueous, inorganic arsenic on the granular activated carbon (GAC), DARCO((R)) 12x20 GAC was investigated in solutions containing arsenic as the only contaminant, as well as with chromium, nickel and iron. Darco 1220 was selected for these investigations primarily because it is relatively ineffective as a normal (unassisted) arsenic adsorbent in the chosen electrolytes at the low loadings used. It is shown that the application of anodic potentials in the 1.0 - 1.5V range, however, result in enhanced uptake, most probably due to charging of the electrochemical double-layer at the electrode surface. 100% regeneration of electrosorbed arsenic was achieved via electrodesorption at a cathodic potential of 1.50V. The presence of ad-metal ions was observed to have a significant and complex effect on arsenic adsorption, electrosorption, and electrodesorption. In particular, the Cr:As ratio was shown to have complex effects, decreasing adsorption uptake when present as 3:2, but enhancing adsorption when present as 5:1. Nickel was found to have less of an effect than chromium except at the highest anodic potential used of 1.50V, where it exhibited better performance than chromium. The presence of iron significantly enhanced uptake. With a 1.50V anodic potential, the bulk arsenic concentration was reduced to less than detectable limits, well below the USEPA MCL for drinking water. Regeneration efficiency by electrodesorption for the As-Fe system was greater than about 90%.
