Phase field modeling of intercalation kinetics: a finite interface dissipation approach

What is it about?

This work deals with modeling the interface between electrode and electrolyte using the phase field approach. Pivotal interface phenomena are diffusion and redistribution of particles. This is especially of interest in Lithium ion batteries where the interfacial kinetics determines the battery performance and impact cycling stability. Hence, a simulation tool which investigates these processes is of fundamental interest. A new phase field model was developed in the OpenPhase framework. This model links the atomistic processes to the mesoscale behavior by a parameter called “interface permeability”. The model was validated with experimental data from diffusion couples. Calculations of the concentration profiles of the species at the electrodeelectrolyte interface are reported. Active particle size, morphology and spatial arrangement were put in correlation with diffusion behavior for use in reverse engineering. Furthermore, relationships between the interface permeability and electrochemical bulk properties are shown.

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Why is it important?

One of the major challenges for the success of many clean energy technologies is energy storage. Intercalation electrode materials are promising for electrochemical energy storage. Rational design of novel electrochemical energy storage systems with flexible designs, cheaper prices and more efficiency to meet the power storage needs of everything from handheld gadgets to electric cars heavily relies on the availability of advanced experimental and computational tools. One of the emerging computational tools in the discovery and design of materials is the phase field method. It is widely used for describing phase transformations and kinetics of microstructural evolution in materials sciences. One of its features is the diffuse interface, i.e. a region of space where two (or more) phases are assumed to mix. For electrochemical systems, the interface as the reacting zone plays a very important role. The diffusive nature of the electrical double layer across the electrode-electrolyte interface makes it more suitable for a description with phase field. In this work, the phase field method is employed to study the kinetics of intercalation. The non-equilibrium behavior especially at the beginning of interaction between electrode particles and electrolyte, with slow evolution of equilibrium, was investigated using the Finite Interface Dissipation model. One of its pivotal flux contributions is permeation which is caused by chemical potential difference across the interface. It is scaled by a material parameter called “permeability of the interface”, which was originally estimated by the interdiffusion coefficient for diffusion couples. A new way to estimate this quantity for non-equilibrium electrochemistry is formulated based on the Butler-Volmer kinetics and its estimation from electrochemical measurement systems such as cyclic voltammetery and electrochemical impedance spectroscopy is discussed. An investigation of the influence of geometry and size on the kinetics of intercalation of Li storage particles was performed. It was found that the rate of intercalation relies exponentially on the size of particles. Moreover, particles with high eccentricity and uniform arrangements show faster kinetics of intercalation. Furthermore, potential future applications for this model will be discussed.