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Battery news Home Battery news Nickel metal hydride battery knowledge

Nickel metal hydride battery knowledge

Author:evenbabyPublish:2019-09-23View: 19

Nickel-metal hydride battery is composed of hydrogen ion and metal nickel. Its power reserve is 30% more than that of nickel-cadmium battery. Compared with nickel-cadmium battery, nickel-metal hydride battery is lighter, its service life is longer, and it has no pollution to the environment.The disadvantage of ni-mh battery is that it is much more expensive than ni-cd battery and its performance is worse than lithium battery.

Chemical composition

The “metal” part of the nimh battery is actually intermetallic.Many kinds of intermetallic compounds have been used in the manufacture of nickel metal hydride batteries.The most common category is AB5, where A is A mixture (or combination) of rare earth elements plus titanium (Ti);B is nickel (Ni), cobalt (Co), manganese (Mn), and (or) aluminum (Al).The “multi-component” electrodes of some high-capacity batteries consist mainly of AB2, where A is titanium (Ti) or vanadium (V), and B is zirconium (Zr) or nickel (Ni), plus some chromium (Cr), cobalt (Co), iron (Fe) and (or) manganese (Mn).All these compounds play the same role: reversibly forming metal hydrides.When the battery is charged, the hydrogen ions (H+) in the potassium hydroxide (KOH) electrolyte are released and absorbed by these compounds, avoiding the formation of hydrogen gas (H2) to maintain the pressure and volume inside the battery.When the battery discharges, the hydrogen ions go back in the opposite direction.

The weight of the

In terms of the voltage of each cell, ni-mh and ni-cd are 1.2V, while lithium batteries are 3.6V, which is three times higher than the other two.Moreover, the weight of the same type of battery is almost the same as that of nickel-cadmium battery, while nickel-metal hydride battery is relatively heavy.It can be known that the weight of each battery itself is different, but due to the high voltage of 3.6V, the number of single battery pack combined can be reduced by one-third under the same output voltage, so that the weight and volume of the formed battery can be reduced.

Memory effect

Nickel-metal hydride batteries and nickel-cadmium batteries have the same memory effect.Therefore, periodic discharge management is also necessary.This kind of periodic discharge management is handled in a fuzzy state, and even some discharge is conducted under incorrect knowledge (each discharge or discharge after several times of use varies from company to company). This kind of cumbersome discharge management is inevitable in the use of nimh batteries.Relatively speaking, lithium battery is very convenient and simple to use because it has no memory effect at all.It does not need to care about how much residual voltage, direct charging, charging time can be shortened.

charging

When charging quickly, you can use the microcomputer inside the charger to avoid overcharging the battery.Today’s nickel metal hydride batteries contain a catalyst that removes the danger of overcharging in time.2H2+O2– catalyst — ->2H2O, but this reaction is only effective within C/10 hours from the time the overcharge started (C= the capacity indicated by the battery).When the charging process starts, the temperature of the battery will rise obviously. Some quick chargers (less than 1 hour) contain fans to prevent the battery from overheating.

Some manufacturers believe that the nickel metal hydride battery can be safely charged with or without a timer by using some simple constant current (and current should be small) charger, and the allowable charging current for a long time is C/10h (the nominal charge of the battery divided by 10 hours).In fact, some low-cost wireless phone base stations and the cheapest battery chargers do just that.While this may be safe, it may have an adverse effect on battery life.According to Panasonic’s nickel metal hydride battery charging guide (link at the bottom of the page), long-term use of trickle charging (charging for a long time with a small current) may lead to battery damage;To prevent damage to the battery, the current of trickle charge should be limited to between 0.033×C per hour and 0.05×C per hour, and the maximum charging time is 20 hours.

For the long-term maintenance of ni-mh battery, the low-frequency pulsing and high-current charging method can maintain better battery condition than the trickle charging method.

New, or long-unused, nimh batteries require a period of “activation” to recharge.As a result, some new nimh batteries require several recharge-and-discharge cycles to reach their nominal capacity.

discharge

Care must also be taken in the use of batteries.For several batteries in series (such as the usual arrangement of four AA batteries in a digital camera), it is necessary to prevent the battery from completely running out of energy and causing “Reversecharging”.This can cause irreparable damage to the battery.Usually, however, these devices (like the digital camera mentioned above) can detect the discharge voltage of the battery in series, and when it drops to a certain level, it shuts off automatically to protect the battery.A single battery will not have the above dangers, will only discharge until the voltage is zero.This does not harm the battery. In fact, periodically discharging and then recharging the battery helps maintain the battery’s capacity and quality.

Nickel-metal hydride batteries have a high self-discharge effect of about 30% or more per month.This is higher than the 20% self-discharge rate of nickel-cadmium batteries per month.The fuller the battery, the higher the rate of self-discharge;When the charge drops to a certain level, the rate of self-discharge decreases slightly.The temperature of battery storage has a great influence on self-discharge rate.Because of this, long-unused nimh batteries are best “half-full” at 40%.

The nickel metal hydride battery with low self-discharge effect was launched on the market in 2005. The manufacturer claimed that 70% to 85% of the power could be stored at 20℃ for one year, and it could be charged with ordinary nickel metal hydride battery charger.Some nickel-metal hydride batteries with low self-discharge effect have better discharge characteristics at low temperature than alkaline batteries and lithium ion batteries.

capacity

Different models (especially the different volume) of the battery, the higher the capacity, provide the longer use. Regardless of the volume and weight of factor, capacity is higher, the better, of course. But the same battery model, with the same nominal capacity (600 mah, for example), actual measurement of the initial capacity is different: for example, a 660 mah, the other one is 605 mah, then 660 mah is better than 605 mah.

The actual situation may be that the high capacity is due to the increase of the initial capacity in the electrode material, and the decrease of the stable use of the electrode. The result is that after dozens of cycles of use, the high-capacity battery quickly fails, while the low-capacity battery remains strong.Many domestic battery manufacturers often obtain high-capacity batteries in this way.And after the user USES half year standby time is bad however.

Civil AA nickel-metal hydride battery (that is, no. 5 battery), is generally 1400mAh, but also has a standard ultra high capacity (1600mAh), the truth is the same.

The cost of increasing capacity is to sacrifice cycle life, manufacturers do not modify the battery material, it is impossible to really improve the battery capacity.The study on specific surface area of battery materials is very important. The test data of specific surface area of battery materials can only be authentic and reliable if the results are detected by BET method. At present, many instruments in China can only test by direct contrast method, which has been eliminated in China.At present, the multi-point BET method is uniformly adopted for specific surface area measurement at home and abroad. The specific surface area measurement standards formulated at home and abroad are all based on the BET test method. Please refer to the national standard of China (GB/ t19587-2004) — the method for determination of specific surface area of solid substances based on the BET principle of gas adsorption.Specific surface area testing is actually the more time-consuming jobs, as the adsorption capacity of sample is different, some sample testing may need to spend a whole day, if not implemented fully automated test process, the testers moment cannot leave, and to be highly concentrated, observation instrument panel, control knob, a bit not careful will lead to the failure of the testing process, it will waste testers a lot of precious time.F – Sorb2400 surface tester is really can achieve BET method detection instruments (both direct comparison method), the more important F – Sorb2400 surface tester is by far the only specific surface area of the fully automated intelligent testing equipment, the test results with the international high consistency, the stability is very good also, at the same time reduce the human error, improve accuracy test results.

Maintenance and use

(1) generally speaking, the new nimh battery only contains a small amount of power. People should charge it first before using it.However, if the battery has a short delivery time and is fully charged, it is recommended to use it first and then charge it again.

(2) the newly purchased nimh battery generally needs 3-4 times of charging and use before its performance can be brought into full play. Many friends have minor problems in the first charge, such as the number of films taken after the first charge is not as large as expected.After 3-4 recharges and use, it all works out.

(3) although the nimh battery has a small memory effect, it is still recommended to charge the battery after each use as much as possible, and it should be filled at one time instead of charging it for a while and then charging it again.This is an important point of “prolonging life”.

(4) when charging the battery, pay attention to the heat dissipation around the charger, it is not necessary to use what fan to blow too deliberately, but pay attention to the charger around not to place too many sundries.Ordinary users in the process of using the battery, the battery often does not have a dedicated storage package;After replacing the battery, the user will habitually put the battery with him or her, regardless of whether the place is clean and damp.As a result, the battery is easy to get dirty and the contact is easy to metal.Such as key contact, easy to get wet, and these are battery enemies.Suggestion: users should set up a battery placement point and keep the battery clean.To avoid power loss and other problems, keep the contact points at both ends of the battery and the inside of the battery cover clean, and wipe gently with a soft, clean dry cloth when necessary.

(5) when not in use for a long time, remember to take the battery out of the battery bin and put it in a dry environment. It is recommended to put it in the brand battery box to avoid short circuit of the battery.

(6) long-term unused nimh batteries will naturally enter a “dormant” state after several months of storage, and the battery life will be greatly reduced.If the nimh battery has been placed for a long time, it is recommended that you use a slow charge to charge it first.Because: according to the test, the best condition for nickel metal hydride battery preservation is about 80% live preservation.This is because the nickel metal hydride battery has a large self-discharge (about 10%-15% in a month). If the battery is saved after full discharge and not used for a long time, the self-discharge of the battery will cause over-discharge of the battery and damage the battery.Don’t believe it?If you think about whether the new nickel metal hydride rechargeable batteries are still electric, this is the truth.Advice: compare more, correct the wrong point of view, from the right direction to maintain the battery, otherwise it will backfire.

(7) discharge nickel hydride.Expert advice.Try not to discharge nickel-metal hydride battery, overdischarge will lead to charging failure, the harm is far greater than the memory effect of nickel-metal hydride battery itself.

(8) multimeter self-test whether the battery is full or not.Before charging, the voltage of nimh battery is below 1.2v, and the normal voltage is about 1.4v after charging.If you look at it that way, it’s easy to figure out what the battery is doing.

(9) charger is mainly divided into fast charge and slow charge.Slow charge current is small, usually around 200mA, for example, our common charge current is around 160mA.Charging time is long, charging 1800mAh nimh battery takes about 16 hours.Although the time is slow, but the charge will be charged enough, and do not hurt the battery.Fast charge flow often in 400mA above, charging time significantly reduced a lot, 3-4 hours can be done, also won everyone’s love.There are many kinds of quick charge and different prices.So we often have a question, the same is fast charge, why the price is very different?A good charger, especially a good fast charge have anti-overcharge protection function, such as our common panasonic best charger BQ390 in this aspect is particularly excellent, excellent chip software design ability in the battery charging, also put the fast charge to the battery damage to the minimum.

(10) conflicts appear. Slow charging does not harm the battery, but the charging time is too long;Fast charging can save time, but it is harmful to the battery. Even the best panasonic charger BQ390 can only reduce the damage degree very well, but it can’t be avoided completely.The solution is to buy a fast charger and a slow charger.After using fast charging for a period of time, say 5 to 10 times, switch to slow charging once or twice.This returns the battery to its best performance.

(11) when the battery is used, it is generally a battery pack, that is, four or six batteries are connected in series. At this time, it is very important to maintain the balance of each battery, otherwise the work of the whole battery pack will be affected due to the problem of one of the batteries.Want to assure battery capacity is consistent above all, had better choose the battery that same brand is same model buys at the same time.Then, to keep the battery in line, simply put, the battery pack is either full or empty.If you have more than one battery pack, try chosing it.That is to say, will capacity, voltage and other parameters similar battery monomer series into a group of battery, due to insufficient conditions, under normal circumstances to measure a lower power point after the voltage and the voltage of good electricity.

Finally, about charging and discharging.High-end ni-mh charging devices use the -deltav to detect the battery voltage to determine whether the battery is full.When the battery is charged, the voltage curve is similar to that of discharge. At the beginning, the voltage rises rapidly, then slowly rises. When the battery is charged, the voltage starts to drop rapidly, but the drop is not very big.Nickel-cadmium batteries used previously were similar, except that they fell faster and more steeply than ni-mh.However, the most popular charger on the market (the cheaper one) often USES constant voltage charging. For example, the old GP charger is 1.4v constant voltage, which means the charging ends when the battery reaches 1.4v due to no voltage difference.As a result, the battery is often not full, especially some older batteries, due to increased internal resistance, the actual voltage on the battery is lower.The charger also tends to have a small current and takes more than 10 hours to charge.The charger automatically cut off by -deltav can control the charging time accurately, so it can be charged with high current reliably.The damage of large current charging to ni-mh battery is not as severe as everyone imagined. On the contrary, the current use of DC requires large current charging.First is the question of time.However, nickel-metal hydride batteries have a characteristic that the more current you charge, the more current they can release. Nowadays, DC is a kind of battery, and the current is not small. Therefore, it is a wise choice to charge with a relatively large current, which can make the battery cleaner.Generally, the charging current of no.5 should not exceed 1.5c. C is the battery capacity, which is A 1000MAH battery.I usually charge it with 0.5c (my charger can adjust the current).Discharge, in general, DC after the black screen to charge it is ok, ni-mh memory effect is very small.However, after a period of use, and to balance the battery, when activating the battery, to control the battery discharge termination voltage.The termination voltage of ni-mh battery is 0.9v. When discharging, please pay attention to not discharging. The discharge can be stopped when each battery is 0.9v.Ni-mh battery is not as strong as ni-mh battery, and is more sensitive to over charge and over discharge as well as high temperature.Charge and discharge temperature.In general, don’t let the battery temperature go above 45 degrees.When the battery is full, the battery will generate heat. When the large current is full, the temperature should be about 42 ° c, not more than 45 ° c. Otherwise, the service life will decrease quickly and the internal resistance of the battery will increase.Also, the battery temperature is higher after charging, and it can only be charged after cooling, and also wait for the battery to cool before charging.Use again after long time need not, had better charge put a few times reactivate battery.At ordinary times, we should pay attention to maintain the integrity of the packaging skin, no damage, so as to avoid short circuit.Do not hit the battery, do not fire and so on.

Electrochemical principle

Mainly used as electrolyte for KOH (electrolyte 7moL/LKOH+15g/LLiOH)

When charging

The positive: Ni (OH) 2 + OH – – > NiOOH + H2O + e –

Negative: M + H2O + e – – MH + OH –

Total reaction: M+Ni(OH)2→MH+NiOOH

When the discharge

The positive: NiOOH + H2O + e – – > Ni (OH) 2 + OH –

Negative: MH + OH – – M + H2O + e –

Total reaction: MH+NiOOH→M+Ni(OH)2