What are the internal resistance and measurement method of 18650 lithium battery?

What is the internal resistance of 18650 lithium batteries? For lithium batteries, the internal resistance of the battery is divided into ohmic internal resistance and polarization internal resistance. The ohmic internal resistance is composed of electrode material, electrolyte, diaphragm resistance and the contact resistance of each part. The internal polarization resistance refers to the resistance caused by polarization during an electrochemical reaction, including the resistance caused by electrochemical polarization and concentration polarization. Because the discharge current of the power 18650 lithium battery is generally larger, the internal resistance will be smaller. For example, the Samsung 18650-2200-5C power, the internal resistance is less than 35 milliohms. Ordinary 18650, such as Samsung 18650, the internal resistance is generally less than 80 milliohms, the actual implementation is less than 65 milliohms. The internal resistance of the 18650 lithium battery that performs well at present is about 12 milliohms, and generally about 13-15 milliohms; because the impedance will affect the performance of the battery, generally 50 milliohms is normal, and 50-100 can be. It is used, but the performance begins to decay. It must be used in parallel when it is above 100, and it cannot be used when it is above 200. If the 18650 lithium battery is used for too long, the internal resistance of the lithium battery will increase, and the output voltage will decrease. The internal resistance, static internal resistance and operating internal resistance of lithium batteries are often different. In different environments, the internal resistance also changes under different temperatures. How to measure the internal resistance of the 18650 battery? To measure the capacity and internal resistance of the 18650 lithium battery, a special internal resistance tester and a capacity tester are required. The internal resistance of the 18650 is generally between 20-65 milliohms, and a multimeter can only measure the voltage. ● AC voltage drop internal resistance measurement method because 18650 lithium battery is actually equivalent to an active resistance, so we apply a fixed frequency and fixed current to the lithium battery (currently 1kHz frequency and 50mA small current are generally used), and then voltage After sampling, after a series of processing such as rectification and filtering, the internal resistance of the lithium battery is calculated through the operational amplifier circuit. The measurement time of the lithium battery of the AC voltage drop internal resistance measurement method is extremely 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 Ru003dU/I, the test equipment forces the lithium battery to pass a large constant DC current in a short period of time (usually 2 to 3 seconds) (currently a large current of 40A to 80A is generally used). The voltage at both ends of the lithium battery and the current internal resistance of the lithium battery are calculated according to the formula. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete it. Previous: Do you know what charging method is important for lithium iron phosphate batteries?