Statics and Dynamics of Colloid-Polymer Mixtures Near Their Critical Point of Phase Separation: A Computer Simulation Study of a Continuous AO Model

We propose a new coarse-grained model for the description of liquid-vapor phase separation of colloid-polymer mixtures. The hard-sphere repulsion between colloids and between colloids and polymers, which is used in the well-known Asakura-Oosawa (AO) model, is replaced by Weeks-Chandler-Anderson potentials. Similarly, a soft potential of height comparable to thermal energy is used for the polymer-polymer interaction, rather than treating polymers as ideal gas particles. It is shown by grand-canonical Monte Carlo simulations that this model leads to a coexistence curve that almost coincides with that of the AO model and the Ising critical behavior of static quantities is reproduced. Then the main advantage of the model is exploited - its suitability for Molecular Dynamics simulations - to study the dynamics of mean square displacements of the particles, transport coefficients such as the self-diffusion and interdiffusion coefficients, and dynamic structure factors. While the self-diffusion of polymers increases slightly when the critical point is approached, the self-diffusion of colloids decreases and at criticality the colloid self-diffusion coefficient is about a factor of 10 smaller than that of the polymers. Critical slowing down of interdiffusion is observed, which is qualitatively similar to symmetric binary Lennard-Jones mixtures, for which no dynamic asymmetry of self-diffusion coefficients occurs.Comment: 42 pages, 17 figures, submitted to J. Chem. Phy

Accelerated multiscale & multiphysics modelling tools for battery cell manufacturing improvement

The recent launch of battery factories in Europe, motivates intense efforts to achieve cost-effective, scalable and sustainable battery manufacturing processes. Within DEFACTO project, multiscale multiphysics modelling tools are developed to increase lithium-ion battery (LIB) cell manufacturing process productivity and performance. A novel workflow framework that mimics the main cell manufacturing steps such as the electrode processing and electrolyte filling and later predicts cell performance and ageing is presented to turbocharge the development of next-generation LIBs. In addition, taking advantage of the characterization and manufacturing data to feed and validate the computational tools, the resulting workflow aims at providing deep understanding and therefore guidance to reduce the production process time and cost while increasing the overall efficiency of battery cells

Multiscale modeling of lithium ion batteries : thermal aspects

The thermal behavior of lithium ion batteries has a huge impact on their lifetime and the initiation of degradation processes. The development of hot spots or large local overpotentials leading, e.g., to lithium metal deposition depends on material properties as well as on the nano-und microstructure of the electrodes. In recent years a theoretical structure emerges, which opens the possibility to establish a systematic modeling strategy from atomistic to continuum scale to capture and couple the relevant phenomena on each scale. We outline the building blocks for such a systematic approach and discuss in detail a rigorous approach for the continuum scale based on rational thermodynamics and homogenization theories. Our focus is on the development of a systematic thermodynamically consistent theory for thermal phenomena in batteries at the microstructure scale and at the cell scale. We discuss the importance of carefully defining the continuum fields for being able to compare seemingly different phenomenological theories and for obtaining rules to determine unknown parameters of the theory by experiments or lower-scale theories. The resulting continuum models for the microscopic and the cell scale are numerically solved in full 3D resolution. The complex very localized distributions of heat sources in a microstructure of a battery and the problems of mapping these localized sources on an averaged porous electrode model are discussed by comparing the detailed 3D microstructure-resolved simulations of the heat distribution with the result of the upscaled porous electrode model. It is shown, that not all heat sources that exist on the microstructure scale are represented in the averaged theory due to subtle cancellation effects of interface and bulk heat sources. Nevertheless, we find that in special cases the averaged thermal behavior can be captured very well by porous electrode theory

Thermodynamic derivation of a Butler–Volmer model forintercalation in Li-ion batteries

We present an exclusively thermodynamics based derivation of a Butler–Volmer expression for the inter-calation exchange current in Li ion insertion batteries. In this first paper we restrict our investigationsto the actual intercalation step without taking into account the desolvation of the Li ions in the elec-trolyte. The derivation is based on a generalized form of the law of mass action for non ideal systems(electrolyte and active particles). To obtain the Butler–Volmer expression in terms of overpotentials, it isnecessary to approximate the activity coefficient of an assumed transition state as function of the activitycoefficients of electrolyte and active particles. Specific considerations of surface states are not necessary,since intercalation is considered as a transition between two different chemical environments withoutsurface reactions. Differences to other forms of the Butler–Volmer used in the literature [1,2] are dis-cussed. It is especially shown, that our derivation leads to an amplitude of the exchange current whichis free of singular terms which may lead to quantitative and qualitative problems in the simulation ofoverpotentials. This is demonstrated for the overpotential between electrolyte and active particles for ahalf cell configuration