Electrochemical performance of nickel/metal hydride batteries under unconventional conditions and degradation analysis

The charge discharge performance and cycle stability of D size Ni/MH batteries at -20 ℃, 25 ℃ and 55 ℃ were examined. The results show that the decline rate of Ni/MH battery discharge capacity at -20 ℃ and 55 ℃ are 12.1% and 13.6%,and the average discharge voltage decreases by a value of 0.13 V and 0.06 V respectively, cycling stability declines obviously at various temperatures. The capacity degradation of Ni/MH batteries under low temperature is reversible, belonging to transient degradation and that of high and normal temperatures are not reversible, belonging to permanent degradation. Electrochemical impedance spectroscopy, scanning electron microscope and energy dispersive X ray analyzer were introduced to study the main causes of cycling deterioration of Ni/MH batteries.

Degradation Behavior of Electrochemical Performance of Sealed-Type Nickel/Metal Hydride Batteries

The degradation mechanism of electrochemical performance of sealed type nickel/metal hydride batteries was investigated. The results indicate that the degradation behavior of Ni/MH battery is not only owing to the lack of electrolyte, but also the deterioration of the active materials on the positive and negative electrodes of Ni/MH batteries. Scanning electron micrographs (SEM), X ray diffraction (XRD) and laser granularity analyses are presented. The particle pulverization and oxidation during charge/discharge are identified as the main causes for deterioration of the negative and positive electrode in nickel/metal hydride batteries, as well as the cross section cracking of both anode and cathode.

Effects of iron phthalocyanine on performance of MH/Ni battery

Oxygen evolution causes a high inner pressure during charge and overcharge for MH/Ni battery, and an inappropriate eliminating way of the oxygen in the battery results in accumulation of heat. This is the main obstacle to develop and apply high capability and high power battery. How to reduce the ratio of the chemical catalysis rate to the electric catalysis rate in MH/Ni battery is considered as an urgent question. Iron phthalocyanine(FePc) was chosen as an electrochemical catalyst. The batteries were prepared by adding iron phthalocyanine with different dosages. The inner pressure, the capacity attenuation, the discharge voltage and capacity at high current of these three batteries were compared. The battery with 1 mg FePc in the negative electrode exhibits a good performance.

Effect of surface modification of metal hydride electrode on performance of MH/Ni batteries

A novel method was applied to the surface modification of the metal hydride(MH)electrode of MH/Ni batteries.Both sides of the electrode were plated with a thin silver film about 0.1μm thick using vacuum evaporation plating technology,and the effect of the electrode on the performance of MH/Ni batteries was examined.It is found that the surface modification can enhance the electrode conductivity and decrease the battery ohimic resistance.After surface modification,the discharge capacity at 5C(7.5A)is increased by 212 mA.h and the discharge voltage is increased by 0.11 V,the resistance of the batteries is also decreased by 32%.The batteries with modified electrode exhibit satisfactory durability.The remaining capacity of the modified batteries is 89%of the initial capacity even after 500 cycles.The inner pressure of the batteries during overcharging is lowered and the charging efficiency of the batteries is improved.

Effect of Cobalt Phthalocyanine on Floating-Charge Performance of Nickel-Metal Hydride Battery

In Ni-MH battery, oxygen evolution causes a high inner pressure during charge and overdischarge, and an inappropriate eliminating way of the oxygen in the battery results in accumulation of heat. This is the main obstacle to develop and apply high capability and high power battery. In this paper, effect of cobalt phthalocyanine (CoPc) on the floating-charge performance of Ni-MH batteries are examined. Experimental results show that the battery with CoPc additive by appropriate adding way displayed a better capability of floating charge and discharge than the one without CoPc. The battery with CoPc added into electrolyte shows the best charging efficiency and cycleability and the slowest increasing speed of inner pressure after 2000th charge and discharge.

A comparison of iron phthalocyanine and cobalt porphyrin on the electrochemical catalysis in Ni-MH battery

The effects of iron phthalocyanine (FePc) and cobalt porphyrin (CoPp) on inner pressure and cycle behavior of sealed Ni-MH batteries were investigated in this study. The morphology of battery elec- trode was observed by SEM. The electrochemical impedance spectroscopy of floating-charge/dis- charge battery was also measured. Experimental results show that the addition of FePc or CoPp to the alloy electrode is an effective approach to decrease the internal pressure of battery during the process of charge and overcharge. In contrast to CoPp, the battery with FePc exhibits a slower capacity decay and a smaller overpotential at the same charge-discharge rate. As an electrocatalyst, FePc may more effectively speed up the reduction of oxygen, and decrease its reduction potential. As a result, the charge process is accelerated, the gas evolution is reduced and the pulverization of electrode materials is slowed down.

A new regeneration process for spent nickel/metal hydride batteries

Ultrasonic method was used to recycle nickel/metal hydride(MH-Ni) batteries under undestroyed state. The effects of ultrasonic on electrode material performance of MH-Ni batteries were investigated by using SEM, EDAX and XRD. The results indicate that with the ultrasonic time increasing, there are obvious dispersing phenomena in the positive and negative electrodes. This can make the inertia oxidation layer break off from the negative electrode, and the fresh surface comes out. These changes can increase the reaction centers of the active materials, as well as improve the catalysis capability and discharge ability. But if the ultrasonic time is too long, it can make the active materials reunite and accelerate its pulverization, and lead to its degradation. The improvement of electrochemical performance for MH-Ni batteries is obvious by ultrasonic for 6h continuously.

Frequeney-Locking in a Bpatially Extended Predator-Prey Model

The study is concerned with the effect of variable dispersal rates on Turing instability of a spatial Holling-Tanner system. A series of numerical simulations show that the oscillatory Turing pattern can emerge due to period diffusion coefficient. Moreover, we find that when the amplitude is above a threshold, 1： 1 frequency-locking oscillation can be obtained. The results show that period diffusion coefficient plays an important role on the pattern formation in the predator-prey system.