What is the reason for the battery life of electric vehicles?

The process of charging and discharging lead-acid batteries is an electrochemical reaction process. When charging, lead sulfate forms lead oxide, and when discharging, lead oxide is reduced to lead sulfate.

How it works

The process of charging and discharging lead-acid batteries is an electrochemical reaction process. When charging, lead sulfate forms lead oxide, and when discharging, lead oxide is reduced to lead sulfate. Lead sulfate is a very easy to crystallize substance. When the concentration of lead sulfate in the electrolytic solution in the battery is too high or the static idle time is too long, it will "hold" into a group and form small crystals, and these small crystals attract the surrounding The lead sulfate forms large inert crystals like a snowball. When the crystallized lead sulfate is charged, not only can it not be reduced to lead oxide, but also precipitate and adhere to the electrode plate, resulting in a decrease in the working area of ​​the electrode plate. This phenomenon is called Vulcanization, also known as aging. At this time, the battery capacity will gradually decrease until it can no longer be used.

work environment factors

As long as it is a lead-acid battery, it will be vulcanized during use, but lead-acid batteries in other fields have a longer life than the lead-acid batteries used in electric bicycles. This is because the lead-acid batteries of electric bicycles have an easier vulcanization. work environment.

1. Deep discharge

The lead-acid battery used in the car is only unidirectionally discharged during ignition. After ignition, the generator will automatically charge the battery without causing deep discharge of the battery. Electric bicycles cannot be charged when riding, and often exceed 60% of the deep discharge. During deep discharge, the concentration of lead sulfate increases, and the vulcanization will be quite serious.

2. High current discharge

The cruising current of an electric vehicle for 20 kilometers is generally 4A, which is already higher than the working current of batteries in other fields, and the working current of an electric vehicle that is overspeed and overloaded is even greater. Battery manufacturers have conducted cycle life tests of 70% charge at 1C and 60% discharge at 2C. After such a life test, there are many batteries that can reach a lifespan of 350 charge-discharge cycles, but the actual effect is far from the same. This is because high current operation increases the depth of discharge by 50%, and the battery will accelerate vulcanization. Therefore, the battery life of the electric three-wheeled motorcycle is shorter, because the body of the three-wheeled motorcycle is too heavy, and the working current is more than 6A.

3. High frequency of charge and discharge

Batteries used in the field of backup power supply will only be discharged when there is a power failure. If the battery is stopped 8 times a year, to achieve a life of 10 years, it only needs to achieve 80 cycles of charging life, while electric vehicles charge and discharge cycles 300 times a year. Times and above are common.

4. Short charge

Since the electric bicycle is a means of transportation, there is not much time for charging. It needs to complete the 36V or 48V 20A charging within 8 hours, which requires increasing the charging voltage (usually 2.7~2.9V for a single section). When charging When the voltage exceeds the oxygen evolution voltage (2.35 volts) or the hydrogen evolution voltage (2.42 volts) of a single cell, the battery will open the valve and exhaust due to excessive oxygen evolution, resulting in water loss, increasing the electrolyte concentration, and increasing the vulcanization of the battery. .

5. Can not be charged in time after discharge

As a means of transportation, the charging and discharging of electric bicycles are separated, and it is difficult to charge in time after discharge. If a large amount of lead sulfate formed after discharge is not charged and reduced to lead oxide for more than half an hour, it will vulcanize and form crystals.

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