Briefly describe the internal resistance measurement method of lithium ion battery

　　Author ：Iflowpower – Portable Power Station Supplier

According to the physical formula R = U / I, the test device allows the lithium battery to force the lithium battery to force through a large constant DC current (currently using a large current of 40A to 80A), measurement at this time. The voltage across the lithium battery and calculates the current lithium battery in the formula. The accuracy of this measurement method is high and controlled.

The measurement accuracy error can be controlled within 0.1%. However, this method has a significant shortcomings: (1) can only measure a large-capacity lithium battery or a lithium battery, small-capacity lithium battery cannot be loaded with a large current of 40A to 80A within 2 to 3 seconds; (2) When the battery passes the large current, the electrode inside the lithium battery will cause polarization, resulting in polarized internal resistance.

Therefore, the measurement time must be very short, otherwise the measured internal resistance value is large; (3) large current passing through a lithium battery has a certain damage to the electrodes inside the lithium battery. AC pressure drop internal resistance method is actually equivalent to an active resistance because the lithium battery is actually equivalent to a fixed frequency and fixed current to the lithium battery (currently using 1 kHz frequency, 50mA small current), and then samples its voltage After rectification, filtered, the internal resistance value of the lithium battery is calculated by the op amp circuit after a series of processing, etc. The lithium battery measurement time of the AC pressure dropped internal resistance method is extremely short, generally in 100 milliseconds.

This accuracy of this measurement method is also good, and the measurement accuracy error is generally between 1% to 2%. The advantages and disadvantages of this method: (1) Use an alternating internal resistance measurement method to measure almost all lithium batteries, including small-capacity lithium batteries. Notebook lithium battery cell internal resistance is generally in this way.

(2) The measurement accuracy of the AC pressure drop measurement method is likely to be affected by the ripple current, and there is also possible possible to interfere with harmonic current. This is a test (3) measurement (3) using this method, which does not have too much damage to the lithium battery itself. (4) The measurement accuracy of the AC pressure drop measurement method is not as good as DC discharge internal resistance measurement.

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