That depends upon from where does the instrument start from high or low frequency

Dear Fangzheng Liu , the high frequency resistance or series resistance is also referred to as ohmic resistance. It contains the contribution of all components in the battery that behave like simple resistors: connection leads, electrolyte, oxide layers...

Rct or charge transfer resistance is related to the actual Faradaic electrochemical reaction, and to the electronic transfer at the electrode/electrolyte solution.

You might find some additional useful information in the following documents:

How to measure the ohmic resistance in a battery:

https://www.biologic.net/wp-content/uploads/2019/08/eis-high-frequencies-internal-resistance_battery-an62.pdf

What to do with the low frequency impedance:

https://www.biologic.net/wp-content/uploads/2019/08/eis-low-frequencies-diffusion_battery-an61.pdf

A white paper on EIS for batteries:

https://www.biologic.net/wp-content/uploads/2019/08/studying-batteries-with-electrochemical-impedance-spectroscopy-wp1-electrochemistry-battery.pdf

I hope this helps,

Best regards,

Nicolas Murer

In an EIS the leftmost point on the diagram corresponds to the highest frequency; frequency then steadily decreases as we progress from left to right across the diagram. In most electrochemical systems, the real component of impedance will almost always increase (or remain constant) with decreasing frequency.

As Dr. Nicolas Murer explained the reason for Rct appearing as a result of electrochemical reactions. During an electrochemical reaction,

a significant separation of charge occurs across the reaction interface, with electron accumulation in the electrode matched by ion accumulation in the electrolyte. - Double Layer Capacitance- Cdl - This behavior is best observed at mid to low frequencies.

From the Book

- Fuel Cell Fundamentals- by Ryan o Hayre and Suk-Won Cha

The previous answers are all textbook-like replies without responding to the exact question of Liu. I think this is a rather complicated question.

From the result (Rsei is the 1st semiarc), you can think that SEI can reponse quicker to the testing signals than the charge transfer process. However, I don't know how to derived this result solely based on the physical mechanism.

In fact, some researchers make the assignment (1st semiarc → Rsei, 2nd semiarc → Rct) based on the experimental results:

1. Rct is the largest among the total resistance;

2. In many cased the Rsei remains unchaged and Rct changes prominetly.

"The RSEI and CSEI can be linked to the first semiarc. Subsequently, Rct and Cdl can be linked to the second semiarc. This is because Rct is the largest among the total resistance for the lithium-ion battery and as seen in Table I and Table II the resistance linked to the second semi arc is the largest among the others [10.1016/j.jpowsour.2021.229860]."

You can refer to the literature above for more detailed discussions.