What is the internal resistance of 18650 lithium battery? How to measure the int
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2023/09/30 09:55:11
What is the internal resistance of 18650 lithium battery? How to measure the internal resistance of 18650 battery? The exact calculation of the internal resistance size of the 18650 lithium battery is quite complex and will constantly change during the use of the battery. According to experience, the larger the volume of lithium-ion batteries, the smaller the internal resistance; And vice versa. 18650 internal resistance is generally between 20-65 milliohm, with a multimeter can only measure the voltage.
What is the internal resistance of 18650 lithium battery?
For lithium-ion batteries, the internal resistance of the battery is divided into ohmic internal resistance and polarization internal resistance. Ohmic 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 the electrochemical reaction, including the resistance caused by 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, the internal resistance is less than 35 milliohm. Ordinary 18650, such as the Samsung 18650, the internal resistance is generally less than 80 milliohm, and the actual work is less than 65 milliohm.
At present, the internal resistance of the 18650 lithium battery, which is relatively good, is about 12 milliohm, and generally about 13-15 milliohm; Because the impedance will affect the performance of the battery, in general 50 milliohm is normal, 50-100 can be used, but the performance begins to decay, to more than 100 need to be used in parallel, more than 200 can not be used.
18650 lithium battery time is too long, lithium battery internal resistance increases, the output voltage will be reduced. The internal resistance, static internal resistance and operating internal resistance of lithium batteries are often different, and the internal resistance of different temperatures also changes in different environments.
How to measure the internal resistance of 18650 battery?
18650 lithium battery to measure the capacity and internal resistance requires a 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 the 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, and calculate the internal resistance of the lithium battery through a series of processing such as rectification and filtering. The 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, and the measurement accuracy error is generally between 1% and 2%.
According to the physical formula R=U/I, the test equipment forces the lithium battery to pass a large constant DC current (currently a large current of 40A ~ 80A is generally used) in a short period of time (generally 2-3 seconds), measures the voltage at both ends of the lithium battery at this time, 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 the internal resistance of 18650 lithium batteries. Resistance is the resistance of the lithium battery when the current flows through the battery. In the battery structure design, in addition to the riveting and welding of the battery structure itself, the number, size and position of the battery pole ear directly affect the size of the battery internal resistance.
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