What is the relationship between the capacity and discharge rate of Panasonic battery
Panasonic battery capacity decreases with the increase of discharge current. This is because the current distribution on the plate is not uniform, and the electrochemical reaction current preferentially distributes on the surface nearest to the main solution, which results in the formation of lead sulfate on the surface of the electrode and blockage of the hole. It is difficult for the electrolyte to diffuse and can not adequately supply the needs of the porous electrode. Therefore, when discharging at high current, the active material has limited action depth along the thickness direction. The greater the current, the shallower the depth of its action, the lower the utilization of active substances, and the smaller the capacity of Panasonic battery. Because of the existence of polarization and internal resistance, the increase of voltage drop loss at high current density makes the terminal voltage of Panasonic battery drop rapidly, which is also the cause of capacity reduction.
When the battery is discharged regularly, its terminal voltage decreases gradually from 2.10 volts of open circuit voltage. But by the end of the discharge, the voltage will drop sharply, which indicates that the capacity of the battery is about to be exhausted. When the discharge reaches a specified level (the terminal voltage has dropped to a specified value or its nominal capacity has been released), the discharge shall be stopped immediately. Otherwise, it will cause overdischarge, which will damage the "gas" of the battery, even the reverse pole. Because when the new battery is not charged after injection of electrolyte, its terminal voltage is 1.80 volts, and when it is still for a few hours, the voltage can reach 2.0 volts. The value of the voltage that has not been recharged is the "energy" of the battery. This is the reason why the terminal voltage of battery discharging should be set at 1.80 volts.
The nominal capacity of the battery is for a certain discharge rate and a certain time. That is to say, if we want to release its nominal capacity, we must discharge according to its discharge rate. The characteristics of batteries are: the larger the discharge rate, the more the remaining capacity and the smaller the discharge capacity. This is because when discharged with a larger current, the effective substance on the plate will quickly produce lead sulfate to cover its surface, thus increasing the internal resistance of the battery and limiting its capacity. The results of discharge experiments with the same batteries show that when the discharge rate is doubled, the capacity with high discharge rate is 32% less than that with low discharge rate.
It can be seen that the voltage of the battery also varies with the discharge rate (current). In this case, the relationship between discharge rate and terminal voltage and battery capacity is inversely proportional.
The maximum allowable discharge current and discharge time are specified for different types and capacities of batteries. For example, the allowable time of maximum discharge current for fixed lead-acid batteries is 5-10 seconds, the allowable time of first discharge for mobile lead-acid batteries is 3 minutes at room temperature and 2.5 minutes at low temperature (18 C). The maximum allowable discharge current can not be used as the basis for testing the characteristics of storage battery. But because of the need of operating equipment, the instantaneous impulse current is allowed. This phenomenon is taken into account when designing and choosing the capacity of storage battery. Normally, when discharging in order to check the existing capacity of battery pack, the discharge rate of nominal capacity should be used instead of high current value. In this way, not only does not damage the battery plate or reduce its service life, but also accurately achieves the purpose of checking capacity.