Method for resisting lithium battery and its measurement

　　Author ：Iflowpower – Portable Power Station Supplier

Different types of battery internal resistance. The same type of battery, due to the inconsistency of internal chemical characteristics, the internal resistance is different. The internal resistance of the battery is small, we generally use milliocanels to mean it.

Internal resistance is an important technical indicator for measuring battery performance. Under normal circumstances, the large current discharge capacity of the internal resistance is strong, and the internal battery discharge capacity is weak. On the schematic of the discharge circuit, we can consider the battery and internal blocking, divided into a power string that completely no internal resistance to connect a very small resistance.

At this time, if the external load is light, the voltage assigned on this small resistor is small, and if the external load is heavy, the voltage allocated on this small resistor is relatively large, and some power is consumed in this Introelectric (possibly converted to fever, or some complex reverse electrochemical reactions). A rechargeable battery is factory-in-factory internal resistance, but after long-term use, due to the depletion of the internal electrolyte, the internal chemical activity is reduced, this internal block is gradually added until the internal resistance is large. The battery inside the battery cannot be released normally.

At this time, the battery is ending. Most of the aging batteries are due to the excessive reasons of the internal resistance, there is no use value. Therefore, we should pay more attention to the capacity of the battery is not inheonded.

First, the internal resistance is not a fixed value, when the battery is in different power states, its internal resistance value is different; the battery is in different service life, its internal resistance value is also different. From the perspective of technology, we generally score the electric resistance of the battery to two states: charging state internal resistance and discharge state internal resistance. 1.

The inside of the charging state means the measured battery in the battery is fully charged. 2. Put the internal resistance of the battery to refer to the battery internal resistance measured after the battery is fully discharged (discharging to standard cutoff voltage).

In general, the internal resistance of the discharge is unstable. The results of the measurement are much higher than the normal value, and the charge state is more stable, and the measurement is actually the actual significance. Therefore, in the measurement of the battery, we all made the measurement of the measurement in the charge state.

Second, internal resistance cannot be used to accurately measure the general method may say that the high school physics class has a simple formula + resistance box to calculate the internal resistance of the battery, but the algorithm accuracy of the resistance box of the physical textbook is too low. , Can only be used in theoretical teaching, in the practical application, it is not available. The internal resistance of the battery is small, we generally use micro European or milliocanels to mean it.

In general measurement, we require the internal resistance measurement accuracy error of the battery to be controlled within 5%. Such a small resistance and such accurate requirements must be measured with a dedicated instrument. In the current industry, the accurate measurement of the battery internal resistance is performed by special equipment.

Let me talk about the battery internal resistance measurement method used in the industry. The battery internal resistance measurement method in the current industry is important to have two types: 1. DC discharge internal resistance measurement method according to physical formula R = U / I, the test equipment allows the battery to force the battery in a short time (generally 2 ~ 3 seconds) Through a large constant DC current (currently using a large current of 40A to 80A), the voltage at this time is measured at this time, and the current battery internal resistance is calculated according to 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 battery or battery, a small capacity battery that does not load 40A to 80A in 2 to 3 seconds; (2) When the battery is passed through a large current The electrode inside the battery will cause polarization, and the polarized internal resistance occurs. Therefore, the measurement time must be short, otherwise the measured internal resistance error is large; (3) large current is damaged by the electrode inside the battery through the battery. 2.

AC pressure drop internal resistance method is actually equivalent to an active resistor because the battery is actually equivalent to a fixed frequency and fixed current (currently using 1 kHz frequency, 50mA small current), then sample it. After rectification, the internal resistance value of the battery is calculated by the op amp circuit after a series of processes such as rectification and filtering. The 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) Almost all batteries can be measured using an alternating internal resistance measurement method, including small capacity batteries. The internal resistance measurement of the laptop battery cell 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 for the anti-interference ability in the measuring instrument circuit. (3) Measurement with this method, there will be no too much damage to the battery itself.

(4) The measurement accuracy of the AC pressure drop measurement method is not as good as DC discharge internal resistance measurement. 3. Test instrument component error and test battery connection line problem, no matter which method mentioned, there are some problems that are easily ignored by us, that is, test instruments themselves component error and test line for connecting batteries.

Cable problem. Because the internal resistance of the battery to be measured is small, the electrical resistance of the line will take into account. A short slave from the instrument to the battery itself also has a resistor (approximately Micro-European grade), as well as the contact resistance of the battery and the connection line, these factors must be in the instrument's internal prior error adjustment.

Therefore, the formal battery internal resistance test is generally equipped with a dedicated cable and battery fixing shelf. Fourth, summarizing a lot of aging batteries, the internal power is still a lot, but the internal resistance is too large, it is unfortunately. However, once the internal resistance of the battery has been added, it is difficult to reduce this internal resistance value.

So about the aging battery, even if we want to activate it, such as large current shocks, small current floating, put a refrigerator, but most of them, returning to the heavens. After understanding the above knowledge, we can basically understand that select the battery to choose a battery that is small as possible. In addition, it is important, the battery is not used, and its internal resistance will continue to add.

It is recommended that you still need to use the battery to keep the activity of the internal chemical substance of the battery.