Battery nickel metal hydride , abbreviated NiMH or Ni-MH , is a type of rechargeable battery. The chemical reactions in the positive electrode are similar to those in nickel-cadmium (NiCd) cells, both of which use nickel oxide hydroxide (NiOOH). However, the negative electrode uses a hydrogen-absorbing alloy instead of cadmium. NiMH batteries can have two to three times the equivalent size NiCd capacity, and their energy density can approach lithium-ion batteries.
Video Nickel-metal hydride battery
History
Work on NiMH batteries started at the Battelle-Geneva Research Center after the invention of technology in 1967. It was based on Ti sintered 2 Ni TiNi x alloys and NiOOH electrodes. Development sponsored for nearly two decades by Daimler-Benz and by Volkswagen AG in Deutsche Automobilgesellschaft, now a subsidiary of Daimler AG. The battery specific energy reaches 50 W * h/kg (180 kJ/kg), power density up to 1000 W/kg and life with 500 charge cycles (at 100% depth). Patent applications filed in European countries (priority: Switzerland), United States, and Japan. Patents transferred to Daimler-Benz.
Interest grew in the 1970s with the commercialization of nickel-hydrogen batteries for satellite applications. Hydride technology promises an alternative, smaller way to store hydrogen. Research conducted by Philips Laboratories and CNRS France developed a new high-energy hybrid alloy that incorporates rare-earth metal elements for negative electrodes. However, this suffers from instability of alloys in alkaline electrolytes and consequently insufficient cycle life. In 1987, Willems and Buschow demonstrated a successful battery based on this approach (using a mixture of La 0.8 Nd 0.2 Ni 2.5 Co 2.4 Si 0.1 ), which stores 84% ​​of its charge capacity after 4000 charge-charging cycles. A more economical alloy using mischmetal instead of lanthanum was soon developed. Modern NiMH cells are based on this design. The first consumer-level NiMH cells became commercially available in 1989.
In 1998, Ovonic Battery Co. improve the structure and composition of Ti-Ni alloys and patenting its innovations.
In 2008, more than two million hybrid cars worldwide were manufactured with NiMH batteries.
In the EU and due to the Battery Manual, nickel metal hydride batteries replace Ni-Cd batteries for portable consumer use.
About 22% of portable rechargeable batteries sold in Japan in 2010 are NiMH. In Switzerland in 2009, the equivalent statistics were about 60%. This percentage has fallen over time due to the increase in the manufacture of lithium-ion batteries: by 2000, nearly half of all portable rechargeable batteries sold in Japan were NiMH.
By 2015 BASF generates a modified microstructure that helps make NiMH batteries more durable, in turn enabling changes to the design of cells that save considerable weight, allowing gravimetric energy densities to reach 140 watts-per-kilogram.
Maps Nickel-metal hydride battery
Electrochemical
The negative electrode reaction that occurs in NiMH cells is
- H 2 O M e - ? OH - MH
The charge reaction is read left-to-right and the left-to-left right-read reaction.
On the positive electrode, nickel oxyhydroxide, NiO (OH), is formed:
- Ni (OH) 2 OH - ? NiO (OH) H 2 O e -
Metal M in the negative electrode of the NiMH cell is an intermetallic compound. Many different compounds have been developed for this application, but those used today fall into two classes. The most common is AB 5 , where A is a rare-earth mixture of lanthanum, cerium, neodymium, praseodymium, and B is nickel, cobalt, manganese, or aluminum. Some cells use a higher-capacity negative electrode material based on the compound AB 2 , where A is titanium or vanadium, and B is zirconium or nickel, modified by chromium, cobalt, iron, or manganese. These compounds have the same role, reversibly forming a mixture of metal hydride compounds.
When overcharged at low levels, the oxygen generated on the positive electrode passes through the separator and recombinates on a negative surface. The evolution of hydrogen is suppressed, and the filling energy is converted to heat. This process allows the NiMH cells to remain sealed in normal operation and maintenance free.
The NiMH cell has an alkali electrolyte, usually potassium hydroxide. The positive electrode is the nickel hydroxide, and the negative electrode is a hydrogen ion, or proton. Hydrogen ions are stored in metal-hydride structures ie electrodes. Hydrophilic polyolefin nonwovens are used for separation.
Contents
The charging voltage is in the range of 1.4 to 1.6 V per cell. In general, the constant voltage charging method can not be used for automatic charging. When charging fast, it is advisable to charge NiMH cells with smart battery chargers to avoid overcharging, which can damage cells.
Trickle Filling
The simplest of the safe charging methods is with fixed low currents, with or without timers. Most manufacturers claim that overcharging is safe at very low currents, below 0.1Ã, C ( C /10) (where C is a current equivalent to the battery capacity divided by an hour). The Panasonic NiMH manual charging warns that excessive charging for quite a while can damage the battery and suggests limiting the total charging time to 10-20 hours.
Duracell further demonstrates that the drip payload at C /300 can be used for batteries that must be stored in a fully charged state. Some chargers do this after the charging cycle, to compensate for natural self-release. A similar approach is suggested by Energizer, which shows that self-catalysis can recombine with the gas formed in the electrode to charge up to C/10. This causes cell heating. Companies recommend C /30 or C /40 for unlimited applications where longevity is important. This is the approach taken in emergency lighting applications, where the design remains essentially the same as in older NiCd units, except for the increase in the value of drip-fill resistors.
The Panasonic Handbook recommends that NiMH batteries in standby state be filled by a lower duty cycle approach, where higher current pulses are used whenever the battery voltage drops below 1.3Ã, V. This can extend battery life and use less energy.
? V fill method
To prevent cell damage, rapid charging should stop their charging cycle before overcharging occurs. One method is to monitor voltage changes with time. When the battery is fully charged, the voltage at the terminal slightly decreases. The charger can detect this and stop charging. This method is often used with nickel-cadmium cells, which show a large voltage drop with a full charge. However, the voltage drop is much less clear for NiMH and can be absent at low charge levels, which may make the approach unreliable.
Another option is to monitor the voltage changes with respect to time and stop when this becomes zero, but this is a risk of premature shutdown. With this method, a much higher fill rate can be used than with droplet loading, up to 1 C . At this cost level, Panasonic recommends to end charging when the voltage drops 5-10 mV per cell from the peak voltage. Because this method measures the voltage across the battery, a constant current charging circuit (not a constant voltage) is used.
? T fill method
The method of temperature change is in principle similar to the V method. Since the charging voltage is almost constant, constant current charging produces energy at an almost constant rate. When the cell is not fully charged, most of this energy is converted into chemical energy. However, when the cell reaches full charge, most of the charging energy is converted to heat. This increases the rate of battery temperature change, which can be detected by sensors such as thermistors. Both Panasonic and Duracell suggest a maximum temperature rise rate of 1 Ã, Â ° C per minute. Using a temperature sensor allows absolute temperature cutoff, which Duracell shows at 60 Ã, Â ° C. With the charging method T and V , the two manufacturers recommend a further droplet filling period to follow early fast charging.
Security
Fuses that can be reset in series with the cell, especially the type of bimetal strip, increase security. This fuse is open if the current or temperature is too high.
Sel NiMH modern mengandung katalis untuk menangani gas yang dihasilkan oleh pengisian berlebih ( ). Namun, ini hanya bekerja dengan arus pengisian yang berlebihan hingga 0,1Ã, C (yaitu kapasitas nominal dibagi dengan sepuluh jam). Reinforce in menyebabkan baterai menjadi panas, mengakhiri process pengisian.
The method for rapid charging called charge control in a cell involves an internal pressure switch within the cell, which breaks the charging current when there is excess pressure.
One inherent risk with NiMH chemistry is that excessive filling causes hydrogen gas to form, potentially breaking down cells. Therefore, the cell is ventilated to release the gas in case of overcharging.
NiMH batteries are made from environmentally friendly materials. The battery contains only a small amount of toxic material and can be recycled.
Loss of capacity
Voltage depression (often mistakenly associated with memory effects) of repeated partial discharges can occur, but can be recovered with multiple full discharge/discharge cycles.
Debit
The fully charged cells supply an average of 1.25 V/cell during discharge, decreasing to about 1.0-1.1 V/cell (further discharges can cause permanent damage in the case of multi-cell packs, due to polarity reversal). Under a light load (0.5 amperes), the initial voltage of the newly loaded NiMH AA cell in good condition is about 1.4 volts.
Excess charging
The complete disposal of multi-cell packets can cause reverse polarity in one or more cells, which can permanently damage it. This situation can occur in the general arrangement of four AA cells in series in a digital camera, where one actually expels before another due to a small difference in capacity between cells. When this happens, good cells start pushing discarded cells into reversed polarity (ie positive anode/negative cathode). Some cameras, GPS receivers and PDAs detect safe end-of-discharge voltage from series cells and perform automatic shutdown, but devices like flashlights and some toys do not.
Irreversible damage from reversal of polarity is a particular danger, even when low-threshold voltage cuts are used, when cells vary in temperature. This is because the capacity decreases significantly when the cell is cooled. This produces a lower voltage under the load of the cooler cells.
Self-discharge
NiMH cells have historically had higher levels of self-discharge (equivalent to internal leakage) than NiCd cells. The release rate itself varies greatly with temperature, where lower storage temperatures lead to slower discharge and longer battery life. Self-emptying is 5-20% on the first day and stable around 0.5-4% per day at room temperature. But at 45 Â ° C it is about three times higher.
Self-discharge low
The low nickel metal hydride self-discharge batteries ( LSD NiMH ) have a much lower self-discharge rate. This innovation was introduced in 2005 by Sanyo, under their Eneloop brand. By using enhanced electrode separators and enhanced positive electrodes, manufacturers claim cells maintain 70-85% of their capacity when stored one year at 20 Ã, Â ° C (68Ã, Â ° F), compared to about half for normal NiMH batteries. They are otherwise similar to other NiMH batteries and can be charged on a typical NiMH charger. These cells are marketed as pre-populated "hybrid", "ready to use" or "refilled". Load retention is largely dependent on battery impedance or internal resistance (the lower the better), and on the physical size and capacity of the load.
The separator keeps the two electrodes separated to slow down the electrical discharges while allowing the transport of ionic charge carriers that close the circuit during the course of the current. High-quality separators are essential for battery performance.
Thick dividers are one way to reduce their own use, but take up space and reduce capacity, while thin separators tend to increase their own release rate. Some batteries may have overcome this tradeoff using thin separators with more precise manufacturing and by using sophisticated sulfonated polyolefin separators.
The low self-discharge cells have a lower capacity than standard NiMH cells because of the greater separation volume. The highest AA low self-discharge cell capacity has a capacity of 2500 mAh, compared to 2,700 mAh for high-capacity NiMH AA cells.
Compared to other battery types
NiMH cells are often used in digital cameras and other high-channel devices, where during their single power usage durations outperform primary batteries (such as base).
The NiMH cell is useful for high current drainage applications, in large part due to its lower internal resistance. A typical AA-size alkaline battery, which offers a capacity of approximately 2600 mAh at low current demand (25 mA), provides only 1300 mAh capacity with 500 mA load. The digital camera with LCD and flashlight can take more than 1000 mA, quickly depleting it. The NiMH cell can provide the current level without losing the same capacity.
Devices designed to operate using primary chemical alkaline cells (or zinc-carbon/chloride cells) may not work with NiMH cells. However, most devices compensate for the decrease in the voltage of the alkaline battery because it throws out to about 1 volt. The low internal resistance allows the NiMH cell to provide almost constant voltage until it is low. Thus the battery level indicator designed to read the alkaline cells exaggerates the remaining charge when used with NiMH cells, since the voltage of the alkaline cells decreases steadily over most discharge cycles.
Lithium-ion batteries have a specific energy higher than nickel metal hydride batteries, but they are significantly more expensive. They also produce higher voltages (nominally 3.2-3.7V), and thus are not a drop-in replacement for alkaline batteries without circuitry to reduce the voltage.
In 2005, nickel metal hydride batteries constituted three percent of the battery market.
Apps
Consumer electronics
NiMH batteries have replaced NiCd for many roles, especially rechargeable small batteries. NiMH batteries are usually available in AA (penlight-size) batteries. It has a nominal charge capacity ( C ) of 1.1-2.8 Ah at 1.2 V, measured at a rate that releases the cell in 5 hours. Useful discharge capacity is a function of decreasing the level of discharge, but to a level of about 1 ° C (full discharge in 1 hour), it does not differ significantly from the nominal capacity. NiMH batteries nominally operate at 1.2 V per cell, somewhat lower than conventional 1.5 V cells, but can operate many devices designed for that voltage.
Electric vehicles
The NiMH electric vehicle battery applications include all plug-in electric vehicles such as General Motors EV1, first generation Toyota RAV4 EV, Honda EV Plus, Ford Ranger EV and Vectrix scooters. Hybrid vehicles such as Toyota Prius, Honda Insight, Ford Escape Hybrid, Chevrolet Malibu Hybrid, and Honda Civic Hybrid also use it.
Stanford R. Ovshinsky invented and patented a popular increase of NiMH batteries and established Ovonic Battery Company in 1982. General Motors purchased Ovonik patents in 1994. By the late 1990s, NiMH batteries had been used successfully in many complete electric vehicles, such as General Motors EV1 and Dodge Caravan EPIC minivans. In October 2000, the patent was sold to Texaco, and a week later Texaco was acquired by Chevron. Chevron's Cobasys subsidiary provides this battery only for large OEM orders. General Motors closed the production of EV1, citing the lack of battery availability as a major obstacle. The NiHas Cobasys battery control creates patent loading for large automotive NiMH batteries.
See also
References
External links
- "Nickel Metal Hydride Bipolar Battery" by Martin G. Klein, Michael Eskra, Robert Plivelich, and Paula Ralston
- Nickel Metal Hydride Energizer User and Application (NiMH) User Manual
- Chevron/Texaco patents on NiMH batteries
- Charging and security of NiMH batteries
Source of the article : Wikipedia
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