Hello everybody
I'm going to simulate a Lithium ion battery whose no load voltage depends on its DoD (DoD=1-SoC).
I used the book of Soylu in which he obtained a 10th order polynomials for no-load voltage of the battery.
https://www.intechopen.com/books/electric-vehicles-modelling-and-simulations
I plotted the voltage versus its DoD. However, the obtained figure is not reasonable.
I am so thankful if you let me know what is the problem?
I put my mfile and the obtained figure.

 

It is worth mentioning that the datasheet of the battery gives the voltage according to the C-rate. Indeed, there is no information about the open-circuit voltage of the battery.
Thank you

 

Why do you need such precise data on the open circuit battery? You really can't do anything with it until you connect a load.
Regards,
Keith

 

Why do you need such precise data on the open circuit battery? You really can't do anything with it until you connect a load.
Regards,
Keith

Yes, you're right, the battery is connected to the load. But, I should create a lookup table for no-load voltage irrespective of the load. This open-circuit voltage equation is needed for Electric vehicle simulation.
Besides, I figured out how to calculate this open-circuit voltage. I'm going to use the datasheet for two C-rates and then according to the two look-up table, I want to achieve the open-circuit voltage.
I hope this work.

 

Calculating the internal resistance of a cell is much more useful for most applictions.
Regards,
Keith

 

Calculating the internal resistance of a cell is much more useful for most applications.
Regards,
Keith

Thank you for your reply. I calculate the discharge resistance, and now, I am going to calculate the charge resistance.
I put the picture of discharge resistance and the open-circuit voltage in this post. The horizontal axis is the DoD of the battery (DoD=1-SoC)

 

In addition, I plotted the terminal voltage of the battery according to open circuit and discharge resistance.
According to the datasheet I obtained a lookup table and then, I calcullated the polynomials that fits to the very lookup table. I inserted terminal voltage versus DoD. There is a little difference between them.
I hope my method is correct.

 

It looks as though you are getting some very usable results.

 

It looks as though you are getting some very usable results.

Thank you. Yes, it makes sounds reasonable. However, I 'm not sure my method is correct.
The discharge resistance achieved by my code does not look like other discharge resistance I saw in a website.
I inserted picture of the discharge resistance I got from the website.
https://www.powerstream.com/1922/battery_1922_WITTE/batteryfiles/chapter08.htm

The below figure is obtained by my methods.

 

What units are you using on the X axis? From practical experience, you discharge curve is much more realistic but the final 10% puzzles me. What is the discharge cut-off criteria?

 

The X-axis is DoD, which is 1-SoC. when the battery is full the DoD is 0 and when the battery is empty its DoD is 1.
Sorry, I don't understand your latter question.

 

If you discharge a lithium ion battery until it is empty, it is no longer a battery because it can no longer be re-charged. The discharge point of no return is about 2.7V per cell. Usually the discharge is terminated at 3V to be safe.

 

Thank you for your point. The cut-off voltage is 2.5V.

 

Thank you for your point. The cut-off voltage is 2.5V.

OK. Now it all makes sense.