[转帖]Ni-MH battery

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2007-08-31 10:23 | 只看楼主

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2. Recommended Storage Conditions
Storage recommendations for nickel-metal hydride cells parallel those for nickel-cadmium cells:
>Store at the lowest feasible temperatures(0 to 30 celsuis being the generally recommended storage temperatures).
>Store cells/batteries open-circuit to eliminate loaded storage effects(see next page).
>Storage in a clean, dry, protected environment to minimize physical damage to batteries.
>Use good inventory practices(first in, first out)to reduce time cells spend in storage.

08 31 2007 10:22AM

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3. Capacity Recovery After Storage
In normal practice, stored cells will provide full capacity on the first discharge after removal from storage and charging with standard methods. Cells stored for an extended period or at elevated temperatures may require more than one cycle to attain pre-storage capacities. Consultation with the manufacturer is recommended if prolonged storage and rapidrestoration of capacity is planned.

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2007-08-31 10:24 | 只看楼主

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4. Loaded Storage
Cells and batteries intended for storage for extended periods of time(pass the point where they are fully discharged)should be removed from their load. In particular, many portable electronic devices place a very low-level drain requirement on their batteries even when in the "off" position. These micro-current loads may be sustaining volatile memory, powering sense circuits or even maintaining switch positions. Such loads should be eliminated when storing devices for protracted periods.When nickel-metal hydride cells are stored under load, small quantities of electrolyte can ultimately begin to seep around the seals or through the vent. This creepleakagemay result in the formation of crystals of potassium carbonate, which detract cosmetically from the appearance of the cell. In extreme cases, creep leakage can result in corrosion of cells, batteries, or the adjoining componetry. Although such occurrences are rare, positive methods of electrically isolating the cell, such as an insulating tape over the positive terminal or removal from the product, are suggested for applications requiring extended storage of cells.

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2007-08-31 10:25 | 只看楼主

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Safety Characteristics

When the internal pressure of these batteries rises due to overcharge, short-circuiting, reverse charge or other abuse or misuse, the self-resealing safety vent is activated to prevent battery damage. GREENCELL nickel-metal hydride batteries have similar safety characteristics as GREENCELL Ni-Cd batteries

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2007-08-31 10:25 | 只看楼主

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Cycle Life Characteristics
A key determinant of the economic and practical feasibility of using nickel-metal hydride cells and batteries in portable electronic applications is the cell＇s cycle life: the ability of the nickel-metal hydride cell to deliver acceptable capacity on a repetitive basis. Nickel-metal hydride cell cycle life has received intensive development attention with the result that operational life expectations are now competitive with those for nickel-cadmium cells.

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2007-08-31 10:27 | 只看楼主

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1. Limiting Mechanisms
The life of any battery cell is determined by a combination of abrupt failure events and gradual cell deterioration. With the nickel-metal hydride cell, abrupt failures, typically mechanical events resulting in the cell either shorting or going open-circuit, are relatively rare and randomly distributed. Cell deterioration can take two forms:>Oxidation of the negative active material that increases cell internal resistance resulting in reduction of available voltage from the cell(MPV depression). This also affects the balance between electrodes within the cell and may possibly result in reduced gas recombination, increased pressure, and ultimately, cell venting.>Deterioration of the positive active material results in less active material being available for reaction with the consequent loss of capacity.Both phenomena result in a loss of usable capacity, but pose differing design issues. Mid-point voltage depression requires that the application design be able to adapt to variations in supply voltage from cycle to cycle. Capacity reduction simply requires that initial cell selection be sized to provide adequate capacity at end-of-life for the desired number of cells.The actual mechanism that will determine cell life may vary depending on application parameters and the cell characteristics. Development work has reduced oxidation in the negative electrode reducing the depression in MPV as the cell ages.

08 31 2007 10:26AM

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1. Factors Affecting Life
The way the nickel-metal hydride cell is designed into an application can have dramatic effects on the life of the cell. This is especially true of the design of the charging circuitry for the application to ensure adequate return of charge while minimizing overcharge. In fact, effective control of overcharge exposure, time and charge rate is the way of enhancing cell life.

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2007-08-31 10:28 | 只看楼主

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2. Charge Regime
In general, tailoring the charge regime to the application use scenario is even more important with nickel-metal hydride cells than with nickel-cadmium cells because of the increased subtlety of the voltage and temperature indications of full charge and the greater sensitivity of cell life to overcharge history.

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2007-08-31 10:28 | 只看楼主

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Degree of Overcharge
Establishing the appropriate degree of overcharge for a battery-powered application is dependent on the usage scenario. Some overcharge of the battery is vital to ensure that all cells are fully charged and balanced, but maintenance of full charge currents for extended periods once the cell has reached full charge can reduce life. The three-step charge process works to minimize some of the overcharge stress. Details of the charging process and the application context should be carefully reviewed with the cell manufacturer to ensure maximum cell life for the specific application.

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Exposure to High Temperatures
In general, higher temperatures accelerate chemical reactions including those which contribute to the aging process within the battery cell. High temperatures are a particular concern in the charging process as charge acceptance is reduced. Sensing the transition from charge to overcharge is also more difficult at higher temperatures. Although early data indicate that nickel-metal hydride cells may tolerate high-temperature charging better than standard nickel-cadmium cells, close consultation with the cell manufacturer is encouraged to select a charging strategy that meets operational requirements while maximizing cell life.

08 31 2007 10:28AM

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电池论坛电池技术交流镍镉电池/镍氢电池 [转帖]Ni-MH battery