Analytical Solution to the Impedance of Electrode/Electrolyte Interface in Lithium-Ion Batteries

The structure and quality of electrode/electrolyte interface (EEI) are crucial for the performance, durability and safety of lithium-ion batteries (LIBs). This paper sets up a one dimensional (1D) impedance model for the EEI and develops an analytical solution to it. The model is restricted to 1D to eliminate any interference from the two dimensional distribution of the properties along the interface, so as to focus on the possible coupling effect between the faradaic and double layer charging currents on the EEI. It is found that, firstly, the difference between coupling and decoupling of the faradaic and double layer charging currents decreases with increasing the electrolyte concentration. For LIBs, which has a high electrolyte concentration, the difference is negligible. Hence it is adequate to model the EEI in LIBs using decoupled faradaic and double layer charging currents, that is, i n = C dl (d V /d t ) + i f . Secondly, under the context of Butler-Volmer equation, the charge transfer resistance is much larger when the reactions occur at the outer Helmholtz plane compared with the outer boundary of the diffuse layer. Thirdly, the potential difference across the diffuse layer is a function of the perturbation frequency, which may result in frequency dispersion.