What causes the internal resistance of lithium batteries?

In a broad sense, like the ohmic resistance (IR), activation polarization and concentration polarization can be understood as the components of the internal resistance of the battery, or as activation impedance and concentration impedance. The size of activation polarization and concentration polarization requires complex mathematical models to be calculated.
Internal impedance consists of the following components:

ionic resistance

①The electrolyte inside the barrier
Influencing factors
Electrolyte conductivity, barrier area, thickness, porosity, bending coefficient (Gurley)

② Electrolyte inside the positive electrode

Influencing factors
Electrolyte conductivity, cathode thickness, thickness, porosity, bending coefficient

③ Electrolyte inside the negative electrode

Influencing factors

Electrolyte conductivity, cathode thickness, thickness, porosity, bending coefficient

Electronic resistance

①The active material of the two electrodes
Influencing factors
Electrode conductivity, thickness, area

② Current collectors (copper foil and aluminum foil)
Influencing factors
Current collector thickness, width, length, number of tabs, orientation

③ Leads (pole tabs, poles, internal conductive connection elements)
Influencing factors
Dimensions, Conductivity

Touch resistance between active materials and current collectors

Cathode material and aluminum foil

Negative material and copper foil

Electrochemical impedance of the battery

Make an equivalent circuit diagram of the electrode, which is mainly composed of ohmic impedance Rb, electric double layer capacitance Cd, electrochemical reaction impedance Rct and dispersion resistance Rw. Generally speaking, during the intercalation and deintercalation of lithium ions, the Rb value generally does not change much, while the changes of Cd and Rct are more obvious.

The battery impedance is mainly reflected in the electrochemical reaction impedance, and the ohmic impedance is relatively small. It can be seen from the figure below. As the temperature decreases, the battery impedance gradually increases, and after it drops to 0C, the impedance speed increases, and the cathode impedance shows a similar trend. From a numerical point of view, the impedance of the battery mainly comes from the contribution of the cathode impedance.