Mitigating the loss of charge capacity is one of the main challenges in developing lithium-ion batteries. Mechanical degradation is one of the causes of charge capacity loss, and insight into these processes is necessary for battery development. This study uses a discrete element method (DEM) framework to model the mechanical properties of a positive electrode active layer. In particular, how the active layer properties are affected by the volumetric change and material degradation of the active material linked to charge cycling. The results show a stiffening of the active layer following charge cycling, stemming from the volumetric expansion of the active particles. These results agree with trends seen in experimental measurements.

Using dilatometer experiments, numerical data can be collected during the sintering process and used to develop a constitutive model for shape changes during sintering. The dilatometer chamber is closed and small compared to a normal industry oven used for sintering. Depending on the final application of the sintered product, different temperatures and heat cycles may be used during the process. It is therefore important for a constitutive model to be robust, giving valid results even when changes are made to the sintering procedure. This is done by optimizing the constitutive parameters with respect to different sintering cycles. Variations of initial density after compaction has also been considered in the constitutive model. The deviatoric part of the model is investigated for experimental results in nonhomogeneous sintered specimens to complete the constitutive model. The model presented is for the full sintering process and relevant physical aspects have been accounted for.

By performing a dilatometer experiment, measured shrinkage can be used to determine the adjustable parameters in a constitutive model for sintering. While the dilatometer machine is excellent at collecting data, its conditions differ from those in an industrial sintering oven. Therefore, the constitutive model must be robust and in the present study, different sintering time cycles have been used to optimize the adjustable parameters in the model. Investigations on initial density has also been performed to better understand the sintering process. Before sintering of particles begins, during the debinding process, densification can be detected, which is dependent on the initial density. The constitutive model for sintering was improved to include this phenomenon by adding particle rearrangement based on the theoretical packing of spheres.

During sintering, a green body of powder particles is heated to high temperatures, fusing the particles together. In cemented carbide production, the sintering process generally results in substantial densification of the material. By using a dilatometer, shrinkage during the sintering process can be measured. For a green body of lower density, early particle rearrangement has been observed. This is investigated here using different initial densities using the same powder, leading to a suggested addition to the constitutive model. The environment in the dilatometer and the sintering furnace differs, especially with respect to heating and temperature during holding. This effect can be minimized by creating robustness in the model, making it independent of the heating cycle. Here, this is done by optimizing the constitutive parameters towards four heating cycles for a specific powder.

Mechanical degradation mechanisms are one of the leading causes of charge capacity loss in lithium-ion batteries. This study further develops a discrete element method (DEM) simulation framework, which investigates how the local contact behaviour affect the global mechanical properties of the active layer. The local microstructure consists of active particles held together by a binder domain, making up a granular medium. This study investigates the impact of the layer's global properties from the type of particle contact model. Experiments were also performed to measure size distribution and the material properties of the active material. The time dependency of the active layer, stemming from the viscoelastic binder domain, was studied in relaxation simulations, which were based on experimental measurements.

One of the characteristic features of sintered steels is the porosity in their microstructure resulting from the compaction and sintering process. This porosity strongly influences the mechanical properties. To enhance the understanding for the structure–property relationship of sintered Astaloy®85Mo with 0.4 wt.%C, a micromechanical modelling approach based on face-centred cubic (fcc) representative volume elements (RVE) is proposed. The fcc-like periodic arrangement of the sintered particles in the RVE enables the consideration of a realistic non-spherical pore morphology. To compare the predictions with experimental results, accompanying uniaxial tensile tests are considered at different pore volume fractions after initial microstructure characterisation. In addition to the effect of pore volume fraction, the influence of sinter necks on the predicted overall strength is also systematically investigated. Despite the fairly simple nature of the underlying fcc structure, the RVE simulations are perfectly capable of reproducing the experimental trend, showing that the elasto-plastic properties decrease with increasing porosity. This is in contrast to analytical predictions, which underestimate the decrease in properties due to spherical pore assumptions. Moreover, the finite element-based simulations reveal a less pronounced influence of the sinter neck shape on the macroscopic behaviour, even though substantial differences in plastic strain localisation are discernible at the microscopic scale.

Porosity and interparticle neck size are microstructural parameters that play an important role for pressed and sintered materials. To understand the effect of sintering parameters such as time and temperature on the microstructure of a pre-alloyed sintered steel (Astaloy® 85 Mo), a mean-field modeling approach tracking the neck size and geometry evolution during sintering is developed in combination with experimental studies. Building upon a mathematical framework describing the geometrical changes in a presently developed two-particle model, due to the diffusion mechanisms active during solid-state sintering, the influence of sintering conditions and of the initial microstructure on various aspects of the geometry is investigated. In addition, the predicted effects of each diffusion mechanism on different geometrical parameters are presented. To calibrate the model, the green-to-sintered dimensional change as well as experimentally observed microstructures of Astaloy® 85 Mo are also studied.

Lithium-ion batteries experience charge capacity loss during their lifecycle caused by mechanical phenomena. In this study, a discrete element method (DEM) simulation model, to link the local mechanical behaviour in the positive electrode active layer to its global mechanical properties, was developed. DEM is a suitable method to use as the electrode active layer has a granular structure and the model includes contact formulations for the active particles and the binder domain. Simulations of the calendering process and the measurement of the active layer's global mechanical properties is possible with the framework. The model developed can capture the pressure sensitivity of the active layer, which has been observed in experiments.

Finite element (FE) simulations are frequently used nowadays in order to analyse powder compaction and sintering, for example, when determining the shape of a cutting blank insert. Such analyses also make it possible to determine in detail the stress state in a powder compact during loading and unloading. This is certainly important as (residual) tensile stresses can lead to cracking, either after unloading or during the subsequent sintering step. The magnitude of plastic deformation is also an issue here. Concerning the stress state in the powder compact, the frictional behaviour (between walls and powder compact) is of great importance. For this reason, in the present study, two frictional models are implemented into a commercial FE software, and numerical results based on the stress state before and during unloading are derived. The two friction models produce quite different results, and it is obvious that the frictional behaviour at powder pressing has to be carefully accounted for in order to achieve results of high accuracy.