Thermodynamically Consistent Analysis for Lithium-Ion Batteries

Abstract

An approach for the numerical modelling of Lithium Plating on intercalation electrodes with or without phase transition using a thermodynamically consistent (TC) solid-state transport is presented for a positive electrode (Nickel-Cobalt-Aluminum oxide) and a negative electrode (Lithiated graphite). The proposed method considers the positive electrode to be a single-phase regime and the graphite to consist of three phases, each with a Nernstian Equilibrium potential. The phase transition and volume fraction of the species are directly related through modifications to the Avrami’s equation. A thermodynamically consistent approach is used to match experimental results to models at high C-rates (greater than 0.25C). The effect of using thermodynamically consistent approach on discharge/charge is obtained for varying performance characteristics (C-rate, size of particle). The visualization of phase change in graphite is captured through the assumption that each phase of graphite (LiC6, LiC12 and LiC32) are each represented by a sphere whose diffusivity is equal to the diffusivity of the phase. Lithium plating is considered to occur at negative overpotentials that are created locally, through low temperature or high C-rates and is formulated as being a Butler-Volmer type current density which is then directly correlated to the thickness of the Lithium plated metal layer. The effect of temperature and C-rate is observed in this study. C-rate and temperature have equal impact on the performance of the electrode and the formation of lithium plating on the surface of the electrode.