Lipo battery overcharge is the enemy of the rechargeable battery

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Description: Though accident caused by lipo battery itself is extremely low,but accident is happen occasionally,What is the cause of the most accidents of lipo battery?Lipo battery overcharge is the enemy of the rechargeable battery.

Accident caused by Lipo battery itself is extremely low. The 26th International Battery Seminar & Exhibit, held in March 2009 in Florida , Sandia National Laboratories announced the probability of accidents caused by the battery itself in less than 1ppm. Engaged in battery safety measures U.S. TIAX LLC said the probability of accidents in between 0.2 ~ 0.5ppm, exceeding the quality administrative limit “Six Sigma”.

Probability of 1ppm is very low and it can be called a rare phenomenon. The probability of dying by lightning in the United States is about 1ppm within a year. In Japan probability of getting lottery jackpot is 0.1ppm. That is to say probability of accidents caused by their own defects of lipo battery probability is slightly higher than a jackpot, the same as death by lightning. This is because multiple safety measures have been taken for the 2200mah lipo battery.

However, the probability of accidents of lipo battery is much higher than the number of ppm level. This is because most accidents are not caused by a defect of the battery itself, but external factors. In the aforementioned Institute, SNL represented the vast majority of the cause of the accident is extrusion, heating, overcharge and so on.

In fact, few people know these situations. Until now, the main reason for many accidents also views as the flaws of cell itself. Japan Battery Industry Association recently proposed test method to test whether the metal sheet into the battery would threat security of battery. The specific method is to insert metal sheet in the element of battery after winding it. We investigated whether heat, smoke, fire and so on would happen through the loading pressure to force the metal sheet and caused internal short circuit. This is because there is an allegation that “in the manufacturing process lipo battery mixed metal sheet will become an internal short circuit fuse, eventually lead to the accident.”

Most accidents from improper use of the lipo battery

Most manufacturers have implemented essentially same test. The representative is Penetrating with nail after charging called penetrating battery with nail .On this basis, if the battery mixed with metal and other impurities, causing weak internal short-circuit, it should be able to be filtered through aging tests. That means the possibility of defective batteries as commodities into the market is very low. It is doubtful that the test proposed by Test Battery Industry is in fact repeating the same test.

Of course, there is no internal short circuit even when manufactured but during the process of using it the battery is also entirely possible getting internal short circuit. We assume that during the time of charging the cell electrode generate dendritic metal, causing an internal short circuit. The main reason for this failure is twofold.

Now, during the process of manufacturing, measures have been taken to completely remove moisture. Such as a drying for a variety of materials. The most important step is to dry the negative carbon which is easily to absorb water. Let the electrolyte through dehydration column to remove trace moisture. And the manufacturing need to be set at a dew point of -60 to -40 in drying chamber. For insurance purposes, after winding elements of battery. It will be dried again in a vacuum dryer.

Taking comprehensive countermeasures means that even the slightest error in the process of manufacturing can cause the battery itself as the major cause of accidents. Therefore, lipo battery manufacturers must bear in mind, it does not allow a trace of slack in the process of battery manufacturing.

However, no matter what battery manufacturers do carefully in the manufacturing process to increase security, users do not use it correctly, accidents will not be prevented. Like SNL and TIAX pointed out, compared with battery itself defect, the possibility of external factors causing the accident is much greater.

What is the correct way to use of batteries? The most important is to avoid overcharging. Trace overcharge may also cause smoke or fire and other accidents. For example, FUJITSU TECHNO RESEARCH has done experiments conducted on batteries under 4.25V and 4.30V voltage. charge the battery and do “squeeze test” and “wearing nail test”. The results, 4.25V charging lipo battery is no problems while the 4.30V charging 3s 11.1v lipo battery appeared smoke and fire. The difference between a mere 50mV, there is likely to lead to a major accident.

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