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| Failure Analysis of Panasonic Battery |
| Time：2019-03-04 Source：Panasonic Views：1210 |
Lead-acid batteries have been invented for more than one hundred years, during which they have great development and application. At present, the lead-acid batteries used in the market are: ordinary, sealed, maintenance-free, etc. Because of the advantages of economic and practical lead-acid batteries, they account for more than 70% of the market. However, due to the characteristics, structure, materials, production environment, technology and maintenance of lead-acid batteries, according to relevant statistics, the phenomenon of lead-acid batteries being discarded due to premature failure is more than 75% due to the formation of irreversible lead sulfate on the plate of lead-acid batteries, self-discharge, failure of active substances and falling off. These three major problems have been difficult. Lead-acid battery industry is difficult to overcome the stubborn problems, so far there is no absolute good way to solve these three problems. For example, the design life of ordinary lead-acid batteries is 2-3 years, but it is usually only one year or shorter in actual use. The design life of maintenance-free lead-acid batteries is 7-15 years. Some of them are manufactured because of long storage time and have failed and scrapped without use, which is much shorter than the expected service life, resulting in waste of energy and economic benefits of application.
Basic Structure and Characteristics of Lead-acid Batteries
The main shell, positive and negative plates, separators and electrolytes of lead-acid batteries convert electric energy into chemical electric energy storage under electric field, and chemical electric energy into direct current electric energy, which can be repeatedly charged and discharged several times. The electrochemical reaction formula is as follows:
Discharge of positive plate and negative plate
PbO_2+Pb+2H_2SO_4=PbSO_4+PbSO_4+2H_2O
Lead Dioxide Pure Lead Sulfuric Acid Charging Lead Sulfate Sulfate Lead Sulfate Water
It can be seen from the above formula that lead-acid battery is a complex electrochemical reaction system. The performance and life of lead-acid battery depend on the materials used to manufacture positive and negative plates. The technological environment, the composition of purity of active substances, and the use and maintenance of lead-acid battery have important effects.
Active substances in positive and negative plates of lead-acid batteries have an important relationship with capacity.
Because the capacity of lead-acid batteries is closely related to the amount and area of active substances that can participate in electrochemical reactions in the positive and negative plates, the active substance quality here refers to the real surface area that can participate in reversible electrochemical reactions, rather than the calculated area of geometric size. When lead-acid batteries are added to the electrolyte, the positive and negative plates are immersed in the electrolyte (sulfuric acid). Some sulfuric acid in the electrolyte is absorbed by the positive and negative plates, and the surface of the positive and negative plates is all lead sulfate. Under the action of electric field, compact lead dioxide is formed on the surface of positive plate and negative plate, while compact pure lead is formed on the surface of negative plate. The more compact lead dioxide is formed on the positive plate, the larger the capacity of lead-acid storage ground is. Therefore, in the conventional charging and discharging process, lead dioxide and pure lead are obtained from the positive and negative plates during charging, and lead sulfate is formed from the positive and negative plates after discharging. The active substances of the positive and negative plates should be progressive, and the active substances with interchangeable ionic structure are effective for electrochemical reaction.
The capacity of any lead-acid batteries with rated capacity produced according to specified specifications and standards should be below 95% of the rated capacity under normal charge. This indicates that the lead-acid batteries are not up to standard. The reasons include the aging and failure of the active substances in the manufacturing materials, production process, environment and product storage time.
Plate acidification, self-discharge, active material shedding and lead-acid battery failure
1. Plate vulcanization
The so-called sulfurization refers to the formation of irreversible lead sulfate on the positive and negative plates to form a layer of white coarse-grained crystals of lead sulfate. This kind of crystal is difficult to eliminate during normal charging. The formation degree of sulfuration has a great relationship with the capacity of lead-acid batteries. The more serious the sulfidation is, the less the capacitance is until scrap. There are many factors affecting the sulfidation of plates. The main reason is that the storage time of lead-acid batteries is too long, because sulfuric acid exists on the surface of active substances when the plates are transformed and treated, leading to the aging of lead sulfate on the surface of active substances. Lead-acid batteries are discharged when they are charged and shelved. If the batteries are not charged in time after discharging and the electrolyte density is too high or impure, the surface of active substances in the positive and negative plates will not be vulcanizable. Therefore, vulcanization is the main reason leading to the failure and scrap of the active material of the plate.
2. Self-discharge refers to the self-consumption of electricity in lead-acid batteries. It is generally believed that the capacity of lead-acid batteries decreases by no more than 2% every day and night, which is normal. Because lead-acid batteries have self-discharge shortcomings, if the capacity decreases by more than 2% every day and night, it will be faulty. The main reasons for self-discharge are: impurity of materials (such as excessive antimony or other harmful impurities) in production and electrolyte. Containing harmful impurities (iron, manganese, arsenic, copper, etc.), the pore blockage of the separator after vulcanization of the positive and negative plates leads to the increase of the internal resistance consumption of lead-acid batteries, which leads to the self-discharge of lead-acid batteries. Therefore, it is required that the electrolyte must be dedicated sulfuric acid, and that the water must be distilled water or deionized water.
3. Abscission of Active Material from Polar Plate
Normative use of lead-acid batteries, positive and negative plates in the active material is not easy to fall off. The main reason for the active substance falling off from the positive plate is the large current discharge when the electricity is insufficient or the low temperature is low, while the active substance falling off from the negative plate is mainly the overcharge or the excessive charging current. Overcharge will cause the electrolysis of water to produce a large amount of hydrogen and oxygen. When the hydrogen rushes out into the pore, the active substance will fall off, and the use of lead-acid batteries in the turbulent environment will also accelerate the active substance falling off. Therefore, lead-acid batteries are required to avoid over-charging and over-discharging in use.
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