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Ni-MH Rechargeable Batteries

Table 8.0.1

Test

Test Conditions

Test Results

Flat Plate Crush Test

Cell is crushed between

No explosion, sparks, or flames.

two flat surfaces.

Impact Test

A 20 lb. weight is dropped from

No explosion, sparks, or flames.

height of 2 feet on cell.

Short Circuit Test*

Sample is shorted until discharged.

No evidence of venting, leakage, bulging or

Test conducted at 20

C and

other visible changes on individual cells.

C (68

F and 140

F).

Maximum case temperature was
129

C (264

F). In batteries, safety devices

operated, protecting battery from external
short. Maximum battery case temperature
was within 5

C (41

F) of ambient.

Forced-Discharge Test

The cell, after discharge,

No venting, leakage, fire or explosion on test

(Voltage Reversal)

is over-discharged for 1.5

conducted at C/3 discharge rate.

times rated capacity.

Abnormal Charge

Cell is charged for 2.5

No venting, leakage, fire or explosion on

Test

times rated capacity.

test conducted at C/3 charge rate.

Abusive Overcharge

Sample is charged by

Individual cells vented. No explosion or fire.

Test*

power supply up to

Maximum temperature on cell case was

200 watts until sample

200

C (392

F). In batteries, safety devices caused

vents or explodes.

charging circuit to open periodically, protecting
battery as designed. Maximum battery case
temperature was within 25

C (77

F) of ambient.

Heat Test

The cell is heated in an oven to

No damage to cells; no bulging, venting,

150

C (302

F).

fire or explosion.

Fire Exposure Test*

Sample is heated by a burner

Cells and batteries vented without

fueled with methane.

exploding. No significant flaming or spark.
No projectiles.

Table 8.0.1 Results of DURACELL nickel-metal hydride cells and/or batteries tested under UL Standard 2054
test regimes.

*Note: These tests were conducted on both individual cells and batteries. Tests

not marked with an asterisk were conducted on individual cells only,

as deemed adequate by UL to demonstrate safety of both cells and batteries.

Safety Considerations (cont.)

Содержание Ni-MH

Страница 1: ...arge 5 7 Internal Impedance 5 8 Self Discharge and Charge Retention 5 9 Voltage Depression Memory Effect 6 1 General Principles 6 2 Techniques for Charge Control 6 2 1 Timed Charge 6 2 2 Voltage Drop V 6 2 3 Voltage Plateau zero V 6 2 4 Temperature Cutoff 6 2 5 Delta Temperature Cutoff TCO 6 2 6 Rate of Temperature Increase dT dt 6 3 Charging Methods 6 3 1 Duracell s Recommendation Three Step Char...

Страница 2: ...l hydride battery technology is at a very early stage of maturity and manufacturers such as Duracell have identified many opportunities to improve battery performance These improvements will make DURACELL nickel metal hydride batteries an attractive power source for 3C devices for many years to come General Characteristics Many of the operating characteristics of the sealed nickel metal hydride re...

Страница 3: ... the use of AB5 instead of AB2 alloys AB5 alloys offer better corrosion resistance characteris tics resulting in longer cycle life and better recharge ability following storage The composition of the metal alloy is formulated for optimal stability over a large number of charge discharge cycles Other important properties of the alloy include Large hydrogen storage capability for high energy density...

Страница 4: ... become fully charged and pressure does not build up The charge current however must be con trolled at the end of charge and during overcharge to limit the generation of oxygen to below the rate of recombination Thus charge control is required to pre vent the build up of gases and pressure Duracell rec ommends that continuous overcharge not exceed C 300 for optimal performance As shown in Figure 3...

Страница 5: ...to whichthe nickel compounds are pasted Similarly the negative electrode is a perforated nickel plated steel foil onto which the plastic bonded active hydrogen storage alloy is coated The assembly of a cylindrical cell is shown in Figure 4 2 1 The electrodes are separated by the sepa rator which is a synthetic non woven material that serves as an insulator between the two electrodes and as a mediu...

Страница 6: ...and negative electrodes are interspaced by separator sheets The assembly is then placed in a nickel plated steel can and the electrolyte is added The positive electrodes are connected to the metal lid with a tab The cell is then sealed by crimping the top assembly to the can The top assembly incorporates a resealable safety vent a metal lid and a plastic gasket that is similar to the one used in t...

Страница 7: ... Effect of Discharge Rate and Temperature Typical discharge curves for DURACELL nickel metal hydride batteries under constant current loads at various temperatures are shown in Figures 5 2 1 to 5 2 3 Discharge voltage is dependent on discharge current and discharge temperature FIGURE 5 1 1 1 5 1 4 1 3 1 2 1 1 1 0 9 Voltage V Ampere Hour Capacity Comparison of discharge voltage and capacity of same...

Страница 8: ...racteristics of the battery are affected moderately at higher tempera tures At lower discharge temperatures performance decreases more significantly caused primarily by the increase in internal resistance Similarly the effects of temperature on performance are more pronounced at higher discharge rates The capacity of the battery decreases more noticeably as the current increases particularly at lo...

Страница 9: ...onnected in series the greater the possibility of a cell being fully discharged and driven into overdischarge and polarity reversal During reversal hydrogen gas evolves from the positive electrode Hydrogen gas will be reabsorbed by the negative electrode and eventually oxygen gas will evolve from the negative electrode Extended overdischarge will lead to elevated cell pressure and opening of the s...

Страница 10: ...d at 20 C and 45 C 68 F and 113 F particularly after 30 days Generally long term storage of a nickel metal hydride battery in either a charged or discharged condi tion has no permanent effect on capacity Capacity loss due to self discharge is reversible and nickel metal hydride batteries can recover to full capacity by proper recharging For example full capacity of a nickel metal hydride battery t...

Страница 11: ...ften referred to as memory effect However the cell can be quickly restored to full capacity with a few full discharge charge cycles as indicated in Cycles 20 and 21 The voltage drop occurs because only a portion of the active materials in the cell is discharged and recharged during shallow or partial discharging The active materials that have not been cycled change in physical characteristics and ...

Страница 12: ...go into overcharge the volt age profile of the nickel metal hydride battery does not exhibit as prominent a voltage drop as the nickel cadmium battery In Figure 6 1 2 the temperature profiles of the nickel metal hydride and nickel cadmium batteries are compared during charge at a constant current charge rate Throughout the first 80 percent of charge the temperature of the nickel cadmium battery ri...

Страница 13: ...the charge rate Proper charging is critical not only to obtain maximum capacity on subsequent discharges but also to avoid high internal temperatures excessive over charge and other conditions which could adversely affect battery life 6 2 Techniques for Charge Control The characteristics of the nickel metal hydride battery define the need for proper charge control in order to terminate the charge ...

Страница 14: ...e is terminated when the voltage begins to decrease This approach can be used with nickel metal hydride batteries but as noted in Section 6 1 the voltage drop of the nickel metal hydride battery is not as prominent as that of the nickel cadmium battery and may be absent in charge currents below the C 3 rate particularly at elevated temperatures The voltage sensing circuitry must be sensitive enoug...

Страница 15: ...mperature increase of 1 C 1 8 F per minute with a back up temperature cut off of 60 C 140 F is recommended for dT dt A top up charge of C 10 for 1 2 hour is also recommended Usually this method is used in conjunction with other charge control techniques primarily to terminate the charge in the event that the battery reaches exces sive temperatures before the other charge controls activate A charge...

Страница 16: ...tion method is used At the C 3 rate a dT dt termination method should not be used because the rate of temperature increase may not be sufficient to terminate the charge Another method of charging nickel metal hydride batteries in even less time is to charge at the C 2 to 1C constant current rates At these high charge rates it is essential that the charge be terminated early during overcharge Howev...

Страница 17: ...ature and is used to cut off the charge or dis charge when a pre established internal bat tery temperature or current is reached These temperature cutoff TCO devices reset automatically after the overtempera ture or overcurrent condition has decreased below a reset threshold 3 Thermal Fuse This device is wired in series with the cell stack and will open the circuit when a predetermined temperature...

Страница 18: ...dride batteries should be operated at or near room temperature 20 C or 68 F Repeated operation at extreme temperatures during charge and discharge will adversely affect the performance of the cells and thus the battery as shown graphically in Figure 7 1 1 Operation at high temperatures particu larly in the overcharged condition can cause the cell to vent releasing gas and possibly electrolyte thro...

Страница 19: ...ds the oxygen recombination rate oxygen that is generated during overcharge will not react causing a build up in gas pressure and a rise in temperature which will have damaging effects on battery and cycle life Prompt use of an effective charge termination method when deleterious overcharge begins will lessen the effect on cycle life Cycle life is also affected by the depth of dis charge Depending...

Страница 20: ...riters Laboratories in accordance with UL Standard 2054 Outline of Investigation for Household and Commercial Batteries Duracell successfully met all of the test criteria The tests required under this Standard and the results of the tests on DURACELL cells and batteries are summarized in Table 8 0 1 These tests cover operational and abusive conditions to which batteries may be exposed during their...

Страница 21: ...fire or explosion on Test times rated capacity test conducted at C 3 charge rate Abusive Overcharge Sample is charged by Individual cells vented No explosion or fire Test power supply up to Maximum temperature on cell case was 200 watts until sample 200 C 392 F In batteries safety devices caused vents or explodes charging circuit to open periodically protecting battery as designed Maximum battery ...

Страница 22: ...carefully followed 9 1 Care and Handling Disassembly The battery should not be disassembled opened or shredded under any conditions high short circuit currents and fire could result Nickel metal hydride cells contain an alkaline elec trolyte which can cause injury In the event that the electrolyte comes into contact with skin or eyes immediately flush with fresh water and seek medical advice Handl...

Страница 23: ...tteries As a result a number of states and local governments have passed or are considering legislation which may require special procedures for the disposal of these batteries Thus state and local agencies should be contacted for their waste management guidelines Internationally procedures for waste management may vary from country to country In the absence of regulations or guidelines the follow...

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