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What is a Ni-MH battery? What are the advantages and disadvantages of NiMH batteries?

The positive active material of the nickel-hydrogen battery is nickel hydroxide (called nickel oxide electrode), the negative active material is metal oxide, also called hydrogen storage alloy (the electrode is called hydrogen storage electrode), and the electrolyte is 6N potassium hydroxide, which is charged and discharged in the battery The battery reaction in the process is: on the oxidation electrode: NIOOH+H2o+e====Ni(OH)2+OH.



On the hydrogen storage electrode: MH 十oH-e=====M+H2O



The total reaction of the battery: MH+NiOOH====M+Ni(OH),



Among them, M represents hydrogen storage alloy material.



The open circuit voltage of the battery is 1.2V to 1.3V, which varies with hydrogen storage materials and preparation processes.



When overcharged, the reaction on the two poles is:



On the nickel oxide electrode: 4OH-4e一2H2O十O2



On the hydrogen storage electrode: 2H2O+O2+4e一4OH



The total reaction when the battery is overcharged: O



The battery design generally adopts the method of using the negative electrode excessively. When the nickel oxide electrode is fully charged, oxygen will appear, and it will be diffused in the negative electrode to reconstitute water. In this way, the internal pressure of the battery is kept constant and the electrolyte concentration is not reduced. A giant change occurred.



When the battery is over-discharged, the electrode reaction is:



On nickel oxide electrode: 2H2O+2eH2+2OH



On hydrogen storage electrode; H2+2OH-2e2H2O



The total reaction when the battery is over-discharged: O



Although the net result of the total reaction of the battery is zero when over-discharged, the reverse polarity phenomenon will occur. Since the hydrogen that appears on the positive electrode will be newly compounded on the negative electrode, the stability of the system is also maintained. In addition, the negative electrode active material hydrogen can be adsorbed into the dry hydrogen storage alloy at a relatively high density in the hydrogen atom state. On such an electrode, the hydrogen absorption and desorption reaction can proceed smoothly, and the discharge performance is improved compared with the cadmium-nickel battery.



Instructions



1. Under normal circumstances, the new Ni-MH battery only contains a small amount of electricity. You must charge it before using it after purchase. However, if the battery leaves the factory for a short time and has sufficient power, it is recommended to use it first and then recharge it. .The performance of newly-purchased nickel-metal hydride batteries is usually 3-4 times of charging and use before they can reach their best performance. Many friends have small problems with the first charging, for example, the use time after the first charging is unimaginable. so many. The problem was solved after 3-4 times of charging and use.



2. Although the memory effect of the Ni-MH battery is small, it is still recommended that everyone try to charge it after each use, and charge it all at once. Do not charge it for a while and then use it for a while. This is an important point for longevity. When charging the battery, pay attention to the heat dissipation around the Charger. In order to prevent battery loss and other problems, keep the contact points at both ends of the battery and the inside of the battery cover clean. If necessary, use a soft, clean, dry cloth to wipe gently.



3 When not in use for a long time, remember to take the battery out of the battery compartment and place it in a dry environment. It is recommended to put it in the battery box to prevent the battery from short-circuiting. Ni-MH batteries that have not been used for a long time will naturally enter a dormant state after being stored for several months, and the battery life will be greatly reduced. If the Ni-MH battery has been stored for a long time, it is advisable to charge it with a slow charge first. 、Because: According to the test, the best condition for storage of Ni-MH battery is about 80% charged storage. This is because the self-discharge of Ni-MH batteries is relatively large (about 10%-15% a month). If the battery is completely discharged and then stored and not used for a long time, the self-discharge of the battery will cause the battery to over-discharge. It will damage the battery. Do not believe? Then think about whether the newly-purchased Ni-MH rechargeable batteries still have electricity. This is the reason. Suggestion: compare more, correct the wrong point of view, and start maintaining the battery from the right direction, otherwise it will be counterproductive.



4. Discharge the Ni-MH. Experts recommend that you try not to over-discharge the Ni-MH battery. Over-discharging will cause charging failure. This is far more harmful than the memory effect of the Ni-MH battery itself! .The multimeter self-checks whether the battery is full or not. Generally, the voltage of the Ni-MH battery is below 1.2V before charging, and the normal voltage is around 1.4V after being fully charged. With this judgment, it is easy to judge the state of the battery.



5. The Charger is mainly divided into fast charging and slow charging. The slow charging current is small, usually around 200mA. For example, our common charging current is around 160mA. Her charging time is long, about 16 hours to charge a 1800mAh Ni-MH battery. Although the time is a bit slower, the charging will be sufficient and will not damage the battery. The fast charging current is usually above 400mA, and the charging time is significantly reduced. It can be done in 3-4 hours, and it has won everyone's love. There are many types of fast charging, with different prices. So everyone often wonders why the price of the same fast charge is so different? Good chargers, especially good fast charging, are equipped with anti-overcharging protection function. For example, our common Panasonic Premium Charger BQ390 performs particularly well in this regard. The excellent chip software design ability is also effective when charging the battery. Minimize the damage of fast charging to the battery.



6. Contradictions: slow charging does not damage 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 in the world can only reduce the damage very well. Degree, but cannot be completely prevented. The way to solve the contradiction is to buy a fast charge and a slow charge. Use fast charging for a period of time, for example, after 5 or 10 times, switch to slow charging once or twice. In this way, the performance of the battery is restored to the best condition. Batteries are generally battery packs, that is, 4 or 6 cells are connected in series. At this time, it is very important to maintain the balance of each battery, otherwise the operation of the entire battery pack will be affected by the problem of one of the batteries. First of all, it is necessary to ensure that the battery capacity is the same. It is best to choose batteries of the same brand and model purchased at the same time. Then, it is necessary to keep the internal power of the battery consistent. Simply put, the power of the battery pack is either full or empty. If there are more batteries to form several battery packs, you can try to select them. Specifically, the battery cells with similar parameters such as capacity and voltage are connected in series to form a set of battery packs. Due to insufficient conditions, in general, it is sufficient to measure the voltage after the discharge point and the charged voltage.



7. The high-end NI-MH charger uses -DELTAV to detect the battery voltage to determine whether the battery is full. The voltage curve of the battery during charging is similar to that during discharging. At the beginning, it rises relatively quickly and then rises slowly. When the battery is fully charged, the voltage begins to fall rapidly, but the drop is not very large. The nickel-cadmium batteries commonly used before are similar, but the speed and amplitude of the decline are greater than that of NI-MH. The most common chargers on the market (the cheaper ones) often use constant voltage charging. For example, the old GP power bank is 1.4V constant voltage, that is, when the battery is charged to 1.4V, because there is no voltage difference, the charging is over. . The result of this is often that the battery cannot be fully charged, especially for some older batteries, due to the increased internal resistance, the voltage actually applied to the battery is lower. Moreover, the current of such a charger is often small, and charging often takes more than 10 hours. And the charger with -DELTAV automatically cut off, because it can accurately control the charging time, it can use high current charging more reliably. High-current charging does not have the benefits that everyone thinks about the damage of Ni-MH batteries. On the contrary, the use of DC requires high-current charging. The first is the question of time, so I don't need to talk about it. Then, the Ni-MH battery has a characteristic, that is, the greater the current you charge, the greater the current it can discharge. DC is an electric tiger, and the current is not small, so relatively speaking, use a relatively large current. Charging is a wise choice to keep the battery cleaner. Generally, the charging current of No. 5 can not exceed 1.5C, and C is the battery capacity, which is a 1000mAh battery, and should not exceed 1.5A. Generally use 0.5C for charging (some chargers can adjust the current). In terms of discharge, under normal circumstances, the DC can be charged after a black screen, and the memory effect of NI-MH is very small. However, after a period of use, and when the battery is to be balanced and activated, the termination voltage of battery discharge must be controlled. The final voltage of NI-MH battery is 0.9V. Be careful not to over-discharge when discharging. Discharge can be stopped when each battery is 0.9V. NI-MH batteries are not as powerful as nickel-cadmium batteries, and are more sensitive to overcharge, overdischarge, and high temperature. Charge and discharge temperature. Generally speaking, do not let the temperature of the battery exceed 45 degrees. When the battery is fully charged, the battery will heat up, and the temperature should be around 42 degrees when it is fully charged with high current, and should not exceed 45 degrees, otherwise the life will be quickly reduced and the internal resistance of the battery will increase. In addition, the temperature of the battery is relatively high after charging, and it can be charged after cooling down, and the battery must be cooled before charging. To re-use after a long period of non-use, it is best to charge and discharge several times to reactivate the battery. In normal use, pay attention to keeping the packaging intact and not damaged to avoid short circuit. Don't hit the battery, don't burn it, etc.

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