Factors affecting the life of rechargeable batteries

The rechargeable battery life generally refers to the cycle life of the rechargeable battery. According to national regulations, when the battery capacity is reduced to 70 % of rated capacity under the conditions of full charge and discharge, the number of cycles that the battery can achieve is the cycle life.

While ignoring other factors(such as memory effects), the number of charges and discharges that can be achieved when the rechargeable battery capacity drops to a rated capacity of 70, varies greatly under different discharge depths. If a rechargeable battery, without regard to other factors, is fully charged after each full discharge, the number of cycles is 500 times. Then when each full charge is performed at 50 discharge(that is, only half of the rated capacity is released), the number of cycles can reach 1,000 times. It can be seen that shallow storage does not reduce the cycle life of rechargeable batteries with very small memory effects. Therefore, some rechargeable batteries with small memory effects, such as lithium batteries and lead-acid batteries, do not have to charge after the power is completely exhausted.

The national standard stipulates the cycle life of lithium batteries as follows: At an ambient temperature of 20 °C ± 5 °C, lithium batteries are first charged with a constant current of 1C5A(during which the charging voltage is gradually increased), When the charging voltage reaches the charging limit voltage of the lithium battery(usually 4.1 V or 4.2 V), replace the lithium battery with a constant pressure(that is, the charging limit voltage)(during which the charging current strength is gradually reduced) until the charging current strength does not exceed 20 mA. The lithium battery is then set aside for 0.5 to 1 hour, and then the lithium battery is discharged in a constant current mode of 1C5A. When the output voltage of the lithium battery is reduced to the discharge termination voltage(that is 2.75 volts), the discharge is stopped, and this is a cycle. Then put the lithium battery on hold for 0.5 to 1 hour and carry out the next charge and discharge cycle. When the two consecutive discharge times are less than 36 minutes, the battery life is considered to end and the test is over. The number of cycles during this period should not be less than 300 times. According to the National standards, lithium batteries used in new mobile phones should be discharged at a constant current rate of 1C5A for no less than 51 minutes.

The meaning of 1C5A: C5 represents the rated capacity of a lithium battery. According to national standards, it means that after charging a lithium battery under specified environmental conditions and in accordance with regulations, 5 hours of continuous discharge and the battery reaches the discharge termination voltage(2.75 volts), the amount of electricity output by the lithium battery; C5A represents the current strength, which means that the battery's rated capacity(in amperes hours or milliamps hours, IE the product of current strength and time) is divided by 1 hour. If the rated capacity(C5) of a certain type of lithium battery is 1200 mA, then C5A is equal to 1200 mA, 1C5A is 1 times that of C5A, it is also 1200 mA, and 0.1 C5A is 120 mA. Obviously, the C5A of lithium batteries with different rated capacities is not equal in value.

The charging battery life has a certain relationship with the number of charges and the charging time. In the case of normal use(full charge and discharge), the charging battery life is directly related to the number of charges, that is, the charging life is reduced once. In the normal use, the biggest impact on the battery life is overcharging, overcharging seriously affects the battery life. The second is over discharge, which affects the battery life second only to over charging.

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