3.7V 18650 lifepo4 battery

　　What affects the life of 3.7V 18650 lifepo4 battery, and why do batteries swell?

　　Factors such as depth of discharge, degree of overcharge, and temperature will all have an impact on the life of 3.7V 18650 lifepo4 battery. We sometimes find that the battery will swell. The reasons for this include excessive charging time, vulcanization of the plates, and electrolyte viscosity. There are many factors such as being too large, which will be introduced in detail below.

　　1. Factors affecting the life of 3.7V 18650 lifepo4 battery

　　1. Discharge depth

　　The depth of discharge refers to the extent to which discharge stops during use. 100% depth means releasing the full capacity. The life of 3.7V 18650 lifepo4 battery is greatly affected by the depth of discharge. The key design considerations are deep circulation use, shallow circulation use or float charging use. If a shallow cycle battery is used for deep cycle use, the lead-acid battery will fail quickly. Because the positive active material lead dioxide itself is not firmly bonded to each other, lead sulfate is generated during discharge, and returns to lead dioxide during charging. The molar volume of lead sulfate is larger than that of lead oxide, so the volume of the active material expands during discharge. If one mole of lead oxide is converted into one mole of lead sulfate, the volume increases by 95%. Such repeated contraction and expansion gradually relax the mutual bonding between lead dioxide particles and make them easy to fall off. If only 20% of one mole of lead dioxide active material is discharged, the degree of shrinkage and expansion will be greatly reduced, and the bonding force will be destroyed slowly. Therefore, the deeper the discharge depth, the shorter its cycle life.

　　2. Degree of overcharge

　　A large amount of gas precipitates during overcharging. At this time, the active material of the positive plate is impacted by the gas. This impact will promote the shedding of the active material. In addition, the positive plate alloy is also subject to severe anodic oxidation and corrosion, so the battery will be overcharged. The application period is shortened.

　　3. Effect of temperature

　　Lead-acid battery life increases as temperature increases. Between 10℃ and 35℃, for every 1℃ increase, approximately 5 to 6 cycles will be added. Between 35℃ and 45℃, every 1℃ increase can extend the life by more than 25 cycles; above 50℃, the service life will be extended by more than 25 cycles. The negative electrode vulcanization capacity is lost and the service life is reduced. Battery life increases with temperature within a certain temperature range because capacity increases with temperature. If the discharge capacity remains unchanged, the discharge depth will decrease and the solid life will be extended when the temperature increases.

　　4. Effect of sulfuric acid concentration

　　Although the increase in acid density is beneficial to the capacity of the positive plate, the self-discharge of the battery increases and the corrosion of the grid also accelerates, which also promotes the loosening and shedding of lead dioxide. As the acid density increases in the battery, the cycle life decreases.

　　5. Influence of discharge current density

　　As the discharge current density increases, the life of the battery decreases, because under conditions of high current density and high acid concentration, the positive electrode lead dioxide is caused to loosen and fall off.

　　2. Reasons for the swelling of 3.7V 18650 lifepo4 battery

　　1. Charging time is too long: When the charging current of the lead-acid battery is too large or the charging time is too long, a lot of gas will be produced. In addition, excessive current or charging for too long will cause the temperature of the electrolyte to increase rapidly, which will also cause the battery to bulge.

　　2. The plates are vulcanized: If the plates of the lead-acid battery are vulcanized, then during the charging process, the cell voltage and electrolyte temperature will rise rapidly, bubbles will occur earlier, and the reaction will be violent, which will cause serious problems. It is easy to cause the battery to bulge.

　　3. The viscosity of the electrolyte is too high: If the viscosity of the electrolyte is high, it will penetrate into the pores of the plate slowly, which will also increase the internal resistance, so the voltage drop consumed on the internal resistance during discharge will also increase. This will cause the temperature of the electrolyte to rise rapidly and contain a lot of gas, which will then increase the gas pressure inside the battery, causing it to bulge.

　　4. Too little electrolyte: We all know that 3.7V 18650 lifepo4 battery will reduce the electrolyte after being used for a period of time. At this time, electrolyte or distilled water needs to be added. If the electrolyte is reduced and overcharged, the battery will bulge and even cause an explosion.

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