Failure modes of valve-regulated lead-acid batteries

The discharge of hydrogen, oxygen, water vapor, and acid mist from the valve-regulated lead-acid battery are all methods of battery loss and the cause of drying up. Dry failure of the battery is unique to valve-regulated lead-acid batteries. The reasons for the loss of water are as follows: ①The efficiency of gas recombination is low. ② Evaporate water from the battery case. ③The grid corrosion consumes water. ④ Loss of water by self-discharge. 1.1 Gas recombination efficiency The gas recombination efficiency has a great relationship with the selection of float voltage. If the voltage is too low, although the oxygen evolution is small and the recombination efficiency is high, individual batteries will fail due to the salting of the negative electrode due to long-term insufficient charging, which will shorten the battery life. The float charge voltage is selected too high, the amount of gas released is increased, and the efficiency of gas recombination is low. Although the negative electrode is warned of failure, the safety valve is frequently opened, water loss is large, and the positive grid is also corroded, which affects battery life. 1.2 Evaporating water from the battery case The permeability of the battery case depends on the type and nature of the case material, its wall thickness and the water vapor pressure difference between the inside and outside of the case. Although some shell materials have higher water vapor permeability, they have good strength, so they are still widely used. 1.3 Grid corrosion Grid corrosion can also cause water consumption. 1.4 Self-discharge The oxygen produced by self-discharge of the positive electrode can be recombined at the negative electrode without losing water, but the hydrogen from the negative electrode cannot be recombined at the positive electrode. It will accumulate in the battery and be discharged from the safety valve to lose water, especially when the battery is higher When stored at high temperature, self-discharge accelerates. 2 Failure mode of premature loss of capacity Early capacity loss of valve-regulated lead-acid batteries is often prone to occur under the following conditions: ① Improper cycle conditions, such as continued high-rate discharge, deep discharge, and low current density at the beginning of charging. ②Lack of special additives such as Sb, Sn, H3PO4. ③High active material utilization rate, excessive electrolyte height, and thin electrode plates during low-rate discharge. ④The apparent density of the active material is too low, the assembly pressure is too low, etc. 3 The failure mode of thermal runaway Most battery systems have heating problems, which are more likely to be in valve-regulated lead-acid batteries. This is because: the oxygen recombination process causes more heat in the battery; the amount of exhaust gas is small, Reduce heat dissipation; if the working environment temperature of the valve-regulated lead-acid battery is too high, or the voltage of the charging device is out of control, the battery charge will increase too fast, the internal temperature of the battery will increase, and the battery will not dissipate well, resulting in overheating , The internal resistance of the battery decreases, the charging current further increases, and the internal resistance further decreases. This repeatedly forms a vicious circle, until thermal runaway causes severe deformation and cracking of the battery casing. In order to prevent the occurrence of thermal runaway, corresponding measures should be adopted: ① The charging equipment should have temperature compensation or current limiting functions. ②Strictly control the quality of the safety valve so that the gas inside the battery can be discharged normally. ③The battery should be installed in a well-ventilated location and the battery temperature should be controlled. 4 Under normal conditions of irreversible sulfation of the negative electrode, the lead sulfate crystals formed during discharge of the battery can be easily reduced to lead during charging. If the battery is used and maintained improperly, such as under-charged or over-discharged, the negative electrode will gradually form a thick and hard lead sulfate, which is almost insoluble, and it is difficult to convert it into active materials by conventional charging methods, thereby reducing The battery capacity even becomes the reason for the end of battery life. This phenomenon is called irreversible sulfation of the plates. In order to guard against irreversible sulfation of the negative electrode, the battery must be charged in time without over-discharge. 5 Grid Corrosion In lead-acid batteries, the positive grid is thicker than the negative grid. One of the reasons is that during charging, especially during overcharge, the positive grid is corroded and gradually oxidized to lead dioxide. If the purpose of the grid is lost, the positive grid must be thickened to compensate for the corrosion. Therefore, in the actual operation process, the appropriate float voltage must be selected according to the ambient temperature. Excessive float voltage will cause accelerated water loss and accelerated corrosion of the positive grid. The design life of the battery is calculated according to the corrosion rate of the positive grid alloy. The more the positive grid is corroded, the less the remaining capacity of the battery; the shorter the battery life. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: High-rate lithium battery performance requirements