What are the significance and methods of testing the internal resistance of lithium batteries

The internal resistance of a lithium battery mainly includes two parts. The ohmic resistance and the polarization internal resistance are basically stable under the condition of constant temperature, and the polarization resistance will change with the factors that affect the polarization level. The ohmic resistance is mainly composed of the contact resistance of various parts such as electrode material, electrolyte, diaphragm resistance, current collector, and tab connection. It is related to the size, structure, and connection mode of the battery. The terminal voltage of a lithium battery refers to the voltage detected between the positive and negative electrodes of the battery when the lithium battery is connected in the loop. Its value is equal to the voltage of the lithium battery minus the ohmic resistance. . The significance of testing the internal resistance of lithium batteries: 1. One of the items of factory inspection; 2. When assembling the lithium battery pack, select battery cells with similar internal resistance to form a group; 3. Because the capacity of the lithium battery is larger, the internal resistance The smaller the resistance, so the battery capacity can be roughly judged according to the internal resistance; 4. Lithium battery aging and failure after the outstanding performance is the increase in internal resistance, so testing the internal resistance of the battery can quickly determine the degree of aging of the battery; 5. During the maintenance process of the lithium battery pack, the internal resistance of each battery unit should be tested frequently, so that the unit with the increased internal resistance can be picked out and replaced with a better one. Lithium battery internal resistance test method: 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 40A to 80A are generally used). Current), measure the voltage across the lithium battery at this time, and calculate the current internal resistance of the lithium battery according to the formula. 1. Measure the open circuit voltage of the battery: U12. A fixed resistance resistor: R is connected in parallel at both ends of the battery to discharge; 3. Measure the voltage at both ends of the battery during discharge of the lithium battery: U2; 4. Calculate the internal resistance of the battery: ru003d( U1-U2)/(U2/R) For example, if the open circuit voltage of a battery is 12V, and a 10 ohm resistor is connected in parallel, the voltage drop is 10V, then the internal resistance of the battery is: ru003d(U1-U2)/(U2/R )u003d(12-10)/(10/10)u003d2 ohms. Under normal circumstances, the larger the internal resistance r of the lithium battery, the worse the battery load, and the internal resistance r of high-power batteries (such as storage batteries) is usually very small. Low-power batteries (such as 9V laminated batteries) usually have relatively large internal resistance. AC voltage drop internal resistance measurement method: because the 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 the voltage is measured 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%. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Detailed explanation of the difference between lithium iron phosphate power lithium battery and lithium battery