An Agglomerate Model for the Impedance of Secondary Particle in Lithium-Ion Battery Electrode

An agglomerate model for the impedance of a single micro-sized secondary particle, capable of accounting for the internal electrochemical reactions and material transport, is deduced in three steps: (1) A set of basic equations for the porous battery electrode is deduced while adopting a refined structure of the electric double layer and considering the effect of the structure of the electric double layer on the rate of the charge transfer reaction; (2) An impedance model for the primary particles with the reaction only occurring at the surface is developed. The model features a detailed description for the lithium-ion transportation across the SEI film; (3) Using the volume averaging method and coordinate transformation, the impedance model for the primary particle is extended to the secondary particle. The agglomerate impedance model is validated with experimental data of a single secondary particle. A much improved fit, both at the low and high frequency ends, is achieved compared to a previous model in the literature. The previous model, not accounting for the internal reactions, gives a current density on the particle surface one-order greater than that given by the present model. In addition, a parametric study on aging factors is presented.