This article discusses the options and challenges of dynamic models for the diagnosis and operation of Li-ion batteries. It provides a concise yet understandable overview on models and dynamics, and it discusses future developments needed to progress the field. The diagnosis and operation of batteries require an understanding of the main processes and their dynamics, parameters, and time constants. Processes with large time constants, such as thermal transport are equally important for safe high-performance operation as are processes with shorter time constants such as diffusion. Depending on the specific problem or operating condition, taking all of the scales into account is often unavoidable. Three separate, yet closely connected model classes are reviewed in terms of physical insight and their capabilities and limits: mechanistic models, equivalent circuit models, and data-driven models. We provide guidance for the selection of a suitable model for the particular diagnosis and operation problem of interest. The optimization of battery diagnosis and operation require versatile and simple models that span multiple time scales and allow physical insight and ease of parameterization. Fusing the existing modeling approaches may help to fully exploit their potential while integrating first-principles physical insight and measurement data.

A quantitative description of the formation process of the solid electrolyte interface (SEI) on graphite electrodes requires the description of heterogeneous surface film growth mechanisms and continuum models. This article presents such an approach, which uses multi-scale modeling techniques to investigate multi-scale effects of the surface film growth. The model dynamically couples a macroscopic battery model with a kinetic Monte Carlo algorithm. The latter allows the study of atomistic surface reactions and heterogeneous surface film growth. The capability of this model is illustrated on an example using the common ethylene carbonatebased electrolyte in contact with a graphite electrode that features different particle radii. In this model, the atomistic configuration of the surface film structure impacts reactivity of the surface and thus the macroscopic reaction balances. The macroscopic properties impact surface current densities and overpotentials and thus surface film growth. The potential slope and charge consumption in graphite electrodes during the formation process qualitatively agrees with reported experimental results. A long lifetime for lithium-ion batteries is key to reducing battery cost and increasing acceptance for new applications. The most important but still not well understood aging phenomenon is the growth of a solid film at graphite negative electrodes.1-3 Graphite is the common negative electrode and operates at conditions outside the electrochemical stability window of the electrolyte.2,4 Its decomposition takes place at the surface of the electrode particles and leads to the formation of a surface film, i.e. solid electrolyte interface (SEI). The SEI is mainly built during the first cycles prior to use and is considered to be part of the manufacturing process. 5 The aim of the formation process is to create an interface that is a good lithium-ion conductor but insulating for electrons and prohibits direct contact between electrode and electrolyte in order to provide good performance and long lifetime.4 Different compositions of the film have been proposed by different research groups. 6,7 Since the composition and structure and so the film characteristic is determined during the first cycles, 7 a detailed understanding of this growth mechanism is needed to improve cycling performance.The SEI is formed by a complex mechanism. 5 An atomistic reaction mechanism involves lithium salt and solvent as reactants as well as a variety of different organic and inorganic intermediates and solid products. 7,8 The observation of the formation process is challenging, because of the film's thickness of only several nanometers. Additionally, macroscopic properties such as particle size or operating conditions, e.g. C-rate and environmental temperature, have an important impact on the formation process.3,4 Although SEI film formation has been studied for decades using experimental and simulation-based methods, the exact mechanism of chemical and electrochemical reactions and the growth of the solid fi...

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This work reveals the impact of particle size distribution of spherical graphite active material on negative electrodes in lithium-ion batteries. Basically all important performance parameters, i. e. charge/discharge characteristics, capacity, coulombic and energy efficiencies, cycling stability and Crate capability are shown to be affected by distribution shapes. A narrow distribution with smaller particles results in better cell performance than broader and coarser distributions. However, particle size reduction has a limitation as extremely small particles show negative effect in performance. More critically, independent of the particle size distribution, the existence of coarse particles are found to promote lithium plating, which lowers cell performance and threatens the safety of battery operation. Furthermore, impedance analysis and cycling stability show huge differences for different electrodes. Our study shows that a better understanding of the influence of particle size distribution is an important base to engineer electrodes with higher Crate capability, higher performance, and lower safety risk due to lithium plating.