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Nickel Metal Hydride (NiMH)
Features
These cells using nickel hydroxide Ni (OH) 2 for the positive electrode (cathode). Hydrogen is used as an active element for absorbing hydrogen negative electrode (anode). This electrode consists of an alloy, usually consisting of lanthanum and metals which serves as a solid source of the reduced hydrogen and can be oxidized to obtain protons. The electrolytes are alkali, usually potassium hydroxide solutions.
Performance
Cell terminal voltage: 1.2 - 1.3 Volts
Charging cycle 500-1000
Used in ambient temperatures of -15 ° C to +40 ° C
Typical energy density: 50 - 60 (70) Wh / kg (theoretically 300 kg Wh /)
Typical power density: 100 - 200 W / kg
Typical self-discharge: within 1 month, about 20 - 50%
Application
Mobile
CD player
Flashlights
Measurement Systems
Games
Exposure
E-Bikes
Power Tools
Cordless Screwdriver
Medicine
Advantages
High Energy Density
Can be discharged
The use of NiMH batteries up to 3000 cycles at a discharge rate of 100% was observed. At a lower discharge, for example, at 4%, can be expected to more than 350,000 cycles
Robust - NiMH batteries tolerate overloads and extreme discharges what battery management systems simplifies
Low internal resistance
Flat discharge characteristics (falls at the end of the cycle but rapidly)
very temperature-resistant
Rapid charging in an hour is possible
Trickle charging (very slow or partial charge) can not normally be used with NiMH batteries. Chargers should therefore have timer to avoid overcharging
A repair is possible
More environmentally friendly than other cell chemistries: No cadmium, mercury or lead, and nickel can be reused
Disadvantages
Very high self-discharge rate, up to ten times higher than lead-acid or lithium batteries
Suffers from the memory effect, although this is not as pronounced as in NiCd batteries is
Battery expires due to long storage. This problem can be solved by repeatedly charging and discharging of the battery before use. This processing may also resolve the problem of the memory effect
The high discharge rate is not as good as NiCds
Less tolerant of overloads as NiCds
As with the cell must NiCds a safety valve in case of a gas formation have
Coulombischen the efficiency of nickel-hydride batteries is typically only 66%, and the decrease is directly related to the load
Even if the battery has a high capacity, this does not necessarily mean that it is also usable, since it emits only 50% of the entire energy, depending on the type of application.
The cell voltage is only 1.2V, which means that many cells are needed to produce a high-voltage battery
Lower capacity and cell voltage as alkaline primary cells.
Charge
Discharging the battery completely each month in order to avoid a memory effect
The battery can not be in the charger
Low loading rate: constant strain rate followed by maintenance charges
Rapid charging methods require dT / dt charge accounts
Timer needed to avoid long maintenance charges
Nickel Metal Hydride (NiMH)
Features
These cells using nickel hydroxide Ni (OH) 2 for the positive electrode (cathode). Hydrogen is used as an active element for absorbing hydrogen negative electrode (anode). This electrode consists of an alloy, usually consisting of lanthanum and metals which serves as a solid source of the reduced hydrogen and can be oxidized to obtain protons. The electrolytes are alkali, usually potassium hydroxide solutions.
Performance
Cell terminal voltage: 1.2 - 1.3 Volts
Charging cycle 500-1000
Used in ambient temperatures of -15 ° C to +40 ° C
Typical energy density: 50 - 60 (70) Wh / kg (theoretically 300 kg Wh /)
Typical power density: 100 - 200 W / kg
Typical self-discharge: within 1 month, about 20 - 50%
Application
Mobile
CD player
Flashlights
Measurement Systems
Games
Exposure
E-Bikes
Power Tools
Cordless Screwdriver
Medicine
Advantages
High Energy Density
Can be discharged
The use of NiMH batteries up to 3000 cycles at a discharge rate of 100% was observed. At a lower discharge, for example, at 4%, can be expected to more than 350,000 cycles
Robust - NiMH batteries tolerate overloads and extreme discharges what battery management systems simplifies
Low internal resistance
Flat discharge characteristics (falls at the end of the cycle but rapidly)
very temperature-resistant
Rapid charging in an hour is possible
Trickle charging (very slow or partial charge) can not normally be used with NiMH batteries. Chargers should therefore have timer to avoid overcharging
A repair is possible
More environmentally friendly than other cell chemistries: No cadmium, mercury or lead, and nickel can be reused
Disadvantages
Very high self-discharge rate, up to ten times higher than lead-acid or lithium batteries
Suffers from the memory effect, although this is not as pronounced as in NiCd batteries is
Battery expires due to long storage. This problem can be solved by repeatedly charging and discharging of the battery before use. This processing may also resolve the problem of the memory effect
The high discharge rate is not as good as NiCds
Less tolerant of overloads as NiCds
As with the cell must NiCds a safety valve in case of a gas formation have
Coulombischen the efficiency of nickel-hydride batteries is typically only 66%, and the decrease is directly related to the load
Even if the battery has a high capacity, this does not necessarily mean that it is also usable, since it emits only 50% of the entire energy, depending on the type of application.
The cell voltage is only 1.2V, which means that many cells are needed to produce a high-voltage battery
Lower capacity and cell voltage as alkaline primary cells.
Charge
Discharging the battery completely each month in order to avoid a memory effect
The battery can not be in the charger
Low loading rate: constant strain rate followed by maintenance charges
Rapid charging methods require dT / dt charge accounts
Timer needed to avoid long maintenance charges