All Things You Need to Know about Internal Resistance of Lithium Battery
As a very important invention in history, the emergence of lithium batteries has indeed solved many problems for its great performance. Since lithium battery still widely used at present, its safety is particularly important.
This article will introduce the basic knowledge of lithium battery internal resistance and explain how to measure the internal resistance of lithium batteries. Before we get a further understanding, we need to know basic information of lithium battery internal resistance.
What is Lithium Battery Internal Resistance?
Internal resistance, as one of the key characteristics of lithium batteries, usually, the internal resistance of lithium batteries is divided into ohm internal resistance and polarized internal resistance. The ohm internal resistance is composed of electrode material, electrolyte, diaphragm resistance and the contact resistance of each part. The internal resistance of polarization refers to the resistance caused by polarization during electric chemical reactions, including the internal resistance of electric chemical polarization and the internal resistance of concentration polarization. The ohm internal resistance of the battery is determined by the total conductivity of the battery, and the polarization internal resistance of the battery is determined by the solid phase diffusion coefficient of lithium ions in the electrode active material.
Above are the simple introduction about internal resistance of lithium battery. Let’s move on.
Is the Internal Resistance of a Lithium Battery as Large or as Small as Possible?
The internal resistance is the most sensitive to battery temperature. And the data of internal resistance can vary greatly at different temperatures. One of the important reasons for the performance degradation of lithium batteries at low temperatures is the excessive internal resistance of the batteries at low temperatures.
As a power supply for lithium batteries, from the outside, the smaller the internal resistance, the better. Especially in power applications, small internal resistance is a necessary condition for lithium battery.
As a power supply for lithium batteries, from the outside, the smaller the internal resistance, the better. The smaller the internal resistance, the less power is wasted for the battery. And it is helpful for producing less heat, charging rate and discharging rate.
In general, in recent years, new energy vehicles have increasingly required high charge rate and discharge rate performance of power batteries. Experience has shown that the larger the volume of a lithium-ion battery, the smaller the internal resistance; and vice versa. The internal resistance of lithium batteries must be tested when needed in order to use the batteries more safely and rationally.
The internal resistance of lithium batteries is different at static and at work, and the internal resistance of batteries will also change in different environments. Of course, the size of the internal resistance of the lithium battery also determines the quality of the lithium battery. Under normal circumstances, we can judge the state of the lithium battery by the size of the internal resistance of the lithium battery. When repairing lithium battery packs, the internal resistance of lithium batteries is also an important basis. In theory, the lower the internal resistance of the battery, the better. When the internal resistance of the lithium battery is zero, how will the performance of the lithium battery change? Under the assumption that the internal resistance of the lithium battery is zero, the discharge performance of the lithium battery in this superconducting state can be infinitely large. But this is a situation that violates the laws of nature, so it is almost impossible to achieve in reality. The internal resistance of the battery will affect the performance of the battery.
Where does the Internal Resistance Come from? What Factors Affect the Internal Resistance of the Lithium Battery?
The hindrance factors in the working process of lithium batteries form the internal resistance of lithium batteries. The internal resistance of the battery includes ohm resistance and polarization resistance. Under the condition of constant temperature, the ohm resistance is basically stable, and the polarization resistance will change with the factors affecting the polarization level.
Ohm resistance is mainly composed of electrode material, electrolyte, diaphragm resistance, collector fluid, pole ear connection and other contact resistance of various parts. Ohm resistance is also related to the size, structure, and connection method of the battery.
Polarization resistance, the resistance generated at the moment of loading current, is the sum of the various trends inside the battery that hinder the arrival of charged ions to their destination. Polarization resistance can be divided into two parts: electric chemical polarization and concentration polarization. Electric chemical polarization is caused by the inability of the speed of the electric chemical reaction in the electrolyte to reach the speed of movement of electrons. Concentration polarization is caused by the embedding of lithium ions out of the positive and negative electrode material and the speed at which they move in the material is less than the speed at which lithium ions assemble at the electrode.
What Factors will Influence Internal Resistance of Lithium Battery?
1.Temperature
Temperature and ambient temperature are important influencing factors for the resistance of lithium batteries. Since temperature affects the activity of electric chemical materials, temperature directly determines the speed of electric chemical reactions and the speed of ion movement.
2.Current
On the one hand, the size of the current is directly related to the internal resistance of polarization. The greater the current, the greater the internal resistance of polarization. On the other hand, the thermal effect of electric current will have an impact on the activity of electric chemical materials.The embedding and de-embedding difficulty degree of lithium ions.
The positive and negative electrode materials, the ease of lithium ion embedding and de-embedding, all determine the size of the internal resistance of the material. These are part of the concentration difference polarization resistance.
4.Electrolyte
The rate of movement of lithium ions in the electrolyte is affected by the conductivity of the electrolyte. This is also the main component of electric chemical polarization resistance.
5.Diaphragm
The resistance of the diaphragm itself directly forms part of the ohm internal resistance. At the same time, its hindrance to the movement rate of lithium ions forms a part of the electric chemical polarization resistance.
6.Collector
The connection resistance of the components is the main component of the ohm internal resistance of the battery.
7.Manufacturing level
The level of battery cell technology roughly includes pole piece production technology, coating, compaction density, etc. The level of craftsmanship in the processing of these cells will also have a direct impact on the internal resistance of polarization.
How to measure the internal resistance of the battery?
There are two methods to measure internal resistance of lithium battery. One is “DC internal resistance measurement method” and another is “AC internal resistance measurement method
DC internal resistance measurement method
According to a easy formula “Ｒ=Ｕ/Ｉ”, we can get our answer.
We use a current source to apply a short pulse to the battery and measure the difference between its terminal voltage and the open circuit voltage. Dividing this difference by the test current is considered to be the DC internal resistance of the battery.
AC internal resistance measurement method
We load the battery with an AC input with a smaller amplitude as an excitation, and monitor the response of its terminal voltage. We use a specific program to analyze the data to obtain the AC internal resistance of the battery. The resistance value obtained through this analysis is only related to the characteristics of the battery itself, and has nothing to do with the size of the excitation signal used.
Above are all things you need to know about internal resistance of lithium battery. If you have any other questions about lithium battery, youcan leave your questions below and we will give you answers.
Q1. What method do you use to detect battery failure at cell/module/pack level?
Q2. Is measuring AC-IR @1KHz sufficient to determine battery failure?
Q3. Is it necessary to measure DC-IR? What does DC-IR measurement result will tell us about the battery?
Q4. Do I need both AC-IR@1KHz and DC-IR measurement results to determine battery failure?
Q5. What other parameters should I look at to detect cell/module/pack failure?
Q6. How do I determine cell/module failure?