Hari Vaidyanathan

Long-term storage of nickel—hydrogen cells

Abstract Representative samples of nickel—hydrogen cells for the INTELSAT VI program were used to evaluate the effects of prolonged storage under passive cond

Effect of KOH concentration and anions on the performance of an NiH2 battery positive plate

Abstract The capacity and voltage behavior of electrochemically impregnated sintered nickel positive plates was examined by galvanostatic charging and discharging in a flooded electrolyte cell. Three different concentrations of potassium hydroxide (KOH) (40%,31% and 26%) and 31% KOH containing dissolved nitrate, sulfate, or silicate were investigated. The end-of-charge voltage at C 10 charge and at 10°C showed the following order: 40% KOH > 31 % KOH alone, and in the presence of the anions > 26% KOH. The mid-discharge voltage at C 2 discharge was higher in 26% KOH, almost the same for 31%Ao KOH with and without the added contaminants, and much lower for 40% KOH. The plate capacity was marginally affected by cycling in all cases except for 40% KOH, where the capacity declined after 1000 cycles at 80% depth-of-discharge (DOD). At the end of cycling all the plates tested experienced a weight loss, except in the case of 31% KOH, as a result of active material extrusion. Cyclic voltammetry of miniature electrodes in 31% KOH showed that the cathodic peak potentials are less polarized at −5 °C (compared to 25 °C) in the presence and absence of silicate. This indicates a slightly higher voltage during discharge in an NiH2 battery. Furthermore, the features of the current-potential profile were practically unchanged in the presence of silicate.

Electrical and thermal characteristics of lithium-ion cells

The 18650-type lithium-ion cells are characterized by a cell resistance of 130 m/spl Omega/ capacity of 1.27 Ah at 25/spl deg/C, and a mid-discharge voltage of 3.6 V. The capacity loss in the 72-hr stand test was 3.39 percent. The heat dissipation properties were determined using a radiative calorimeter. During charge, initial endothermic cooling and subsequent exothermic heating beyond 55-percent state of charge were observed. At C/2 rate of discharge (which is considered medium rate), the heat dissipated was 17 mW/cm/sup 3/. The heat dissipation profile during discharge is also unique in the presence of a minimum that is different from that observed for Ni-Cd, Ni-MH, and Ni-H/sub 2/ cells.

Voltage and capacity stability of the Hubble telescope nickel-hydrogen battery

Abstract The power system of the Hubble Space Telescope includes two orbital replacement units, each containing three nickel-hydrogen (NiH2) batteries of 88 Ah capacity. Since launch in April 1990, the batteries have completed 23 000 charge and discharge cycles and continue to meet the power demands of the satellite. The voltage, capacity, and pressure characteristics of all six batteries were analyzed to determine the state of health of the battery and to identify any signs of performance degradation. The battery pressures have changed to varying degrees. The end-of-charge pressure for battery 4 increased by 96 psi, while that for battery 3 decreased by 37 psi. The voltages of the individual cells show a decay rate of 0.69 mV per 1000 cycles, and the capacity of the batteries has apparently decreased, possibly due to the system being operated at a lower stage of charge. Autonomous battery operation involving charge termination at a preselected voltage continues to restore the energy dissipated during each orbit. The accumulated data on voltages and recharge ratios can be used to design new temperature-compensated voltage levels for similar missions that employ NiH2 batteries.

Effect of storage on performance of SUPER nickel-cadmium cells

A study was undertaken to examine the capacity maintenance features of SUPER nickel-cadmium cells when stored for extended periods to determine whether the features change when the same kind of positive plates as that used in nickel-hydrogen cells are used. The cells maintained their capacity when stored at 0/spl deg/C in the discharged state and at 0/spl deg/C in the charged state by continuously trickle charging. There was a capacity loss when stored in the open-circuit condition at 28/spl deg/C. A cycling test at 17 percent depth of discharge for 2400 cycles using cells stored at various conditions showed that cells maintained good end of discharge voltage regardless of their storage history. However, the EOD voltages of stored cells were lower by 10 mV compared to those of fresh cells. The capacity at the end of the cycling test decreased for the stored cells by 2-7 Ah. The storage related capacity loss is lower for SUPER Ni-Cd cells compared to that of Ni-H/sub 2/ cells containing a hydrogen precharge. The results suggest the pivotal role of hydrogen pressure in the capacity loss phenomenon.

Reactions during reversal of an Ni-H2 cell

Abstract The chemical reactions that occur during reversal of aerospace-design nickel-hydrogen (Ni-H 2 ) cells are examined by determining voltage changes and heat dissipation. Radiative calorimetry is used to measure the rate of heat dissipation during charge, discharge, and reversal. The heat dissipated during reversal at C/10 rate (8.1 A) for a positive precharge cell is four times greater than that for a hydrogen precharge cell. For a cell design with a positive precharge, the reversal reactions consist of completion of nickel electrode discharge and hydrogen evolution on the nickel (positive) electrode, platinum oxide/ hydroxide formation, and subsequent reduction by hydrogen at the hydrogen (negative) electrode.

Comparison of cell encapsulation technologies for single pressure vessel nickel-hydrogen battery

Two single pressure vessel (SPV) batteries containing 22 series-connected nickel-hydrogen (Ni-H/sub 2/) cells of 19-Ah capacity were designed and procured from Eagle-Picher Industries. The two batteries were similar in mechanical design, dimensions, and composition of the active core. However, they differed in cell encapsulation, location and structure of the gas diffusion membrane, and cell activation. Both batteries have been subjected to detailed flight qualification testing at COMSAT Laboratories. The batteries met the requirements in capacity, capacity retention, discharge voltage, impedance, thermal behavior in vacuum, and response to vibration. The batteries are currently being cycle tested in a low earth orbit (LEG) regime using V-T charge control at a depth of discharge of 40 percent and at 20/spl deg/C. The battery design, and its characterization, environmental, and LEO cycle test data are presented herein.

Physico-chemical analysis of rechargeable aerospace cells

Rechargeable aerospace batteries such as nickel-cadmium (Ni-Cd) and nickel-hydrogen (Ni-H/sub 2/) are subjected to a detailed physical and chemical analysis to confirm the suitability of their design, determine whether the manufacturing process is under control, and explain anomalous performance features. The results of a number of cell analyses are presented, including the variation of cadmium precharge, overcharge protection, cadmium migration, swelling, porosity, and active material utilization. The results point to a decrease in positive plate utilization with storage and decrease in negative plate utilization, and overcharge protection, and increase in cadmium migration with cycling for Ni-Cd cells. In the case of Ni-H/sub 2/ cells, the positive plate active material utilization tends to be high when the plaque porosity is 75.6 to 78.8 percent.