Charge and discharge cycle test is common as an evaluation item of characteristics and reliability of lithium-ion batteries.
By comparing the initial characteristics such as charge and discharge capacity and charge and discharge rate characteristics with the characteristics after the test, reliability can be assessed from the capacity reduction rate and degradation.
The data presented in the specification from the manufacturer is up to about 300 times, and it is common that it is the data with best characteristics during the test.
Input and output characteristics
Input and output characteristics of lithium-ion batteries are related to internal resistance.
The model capable of high current discharge has a characteristic of a low internal resistance, but it becomes a trade-off relationship in which the capacity [Ah] will be low.
On the contrary, for the high capacity [Ah] model, the internal resistance tends to be relatively high.
Example
NCR 18650B standard discharge rate: 1C capacity: 3400mAh
NCR 18650PF standard discharge rate: 3C capacity: 3000mAh
Impedance method is common as a method of measuring internal resistance. This impedance method is a method of measuring from amplitude and phase difference of the response of the lithium-ion batteries at the modulated frequency, and it can measure by excluding the electromotive transfer resistance between the positive electrode and the negative electrode of lithium-ion batteries and the resistance component related to the electrolyte ion.
By measuring lithium-ion batteries before and after the charge and discharge cycle test, it becomes possible to observe the degree of deterioration.