What is the internal resistance of 18650 lithium battery? How to measure the int
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2023/05/23 11:23:09
What is the internal resistance of 18650 lithium battery? How to measure the internal resistance of 18650 battery? The precise calculation of the internal resistance size of the 18650 lithium battery is quite complicated and will change over the course of the battery's use. According to experience, the larger the size of lithium-ion battery, the smaller the internal resistance; And vice versa. The internal resistance of 18650 is generally between 20-65 milliohm, and the voltage can only be measured with a multimeter.
What is the internal resistance of 18650 lithium battery?
For Li-ion batteries, the internal resistance can be divided into ohmic resistance and polarized resistance. Ohm internal resistance is composed of electrode material, electrolyte, diaphragm resistance and contact resistance of each part. The internal resistance of polarization refers to the resistance caused by polarization in electrochemical reaction, including electrochemical polarization and concentration polarization.
Power 18650 lithium battery because the discharge current is generally relatively large, so the internal resistance will be smaller, such as Samsung 18650-2200-5C power, internal resistance is less than 35 milliohm. The internal resistance of an ordinary 18650, such as the Samsung 18650, is generally less than 80 milliohm, and in practice it is less than 65 milliohm.
The current standout 18650 lithium ion battery has an internal resistance of around 12 milliohm, compared to 13-15 milliohm in general. As the impedance will affect the performance of the battery, generally speaking, 50 milliohm is normal, 50-100 can be used, but the performance begins to decay, more than 100 need to be used in parallel, more than 200 can not be used.
18650 lithium battery used for a long time, lithium battery internal resistance increases, the output voltage will be reduced. The internal resistance of lithium batteries, static internal resistance and operating internal resistance is often different, in different environments, different temperature internal resistance also has changes.
How to measure the internal resistance of 18650 battery?
18650 lithium battery to measure the capacity and internal resistance need special internal resistance tester and capacity tester,18650 internal resistance is generally between 20-65 milliohm, with a multimeter can only measure the voltage.
● AC pressure drop internal resistance measurement method
Because 18650 lithium battery is actually equivalent to an active resistance, we apply a fixed frequency and a fixed current to the lithium battery (currently 1kHz frequency and 50mA small current are generally used), and then sample its voltage. After a series of processing such as rectification and filtering, we calculate the internal resistance value of the lithium battery through the operational amplifier circuit. Ac voltage drop internal resistance measurement method of lithium battery measurement time is very short, generally about 100 milliseconds.
The accuracy of this measurement method is also good, the measurement accuracy error is generally between 1% ~ 2%.
According to the physical formula R=U/I, the test equipment forces the lithium battery to pass a large constant DC current (40A ~ 80A current is generally used at present) for a short period of time (generally 2-3 seconds), measures the voltage at both ends of the lithium battery, and calculates the current internal resistance of the lithium battery according to the formula. The accuracy of this measurement method is high, if properly controlled, the measurement accuracy error can be controlled within 0.1%.
The above is the introduction of 18650 lithium battery internal resistance. Resistance is the resistance of the current flowing through the battery when the lithium battery is working. In the design of battery structure, in addition to the riveting and welding of the battery structure itself, the number, size and position of the battery pole lug directly affect the size of the battery internal resistance.
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