DEM-based modelling of the structural, mechanical and electrical behaviour of lithium-ion battery electrodes
von Clara Lucía Sangrós GiménezLithium-ion batteries (LIBs) have gained widespread popularity along the past years given the
necessity to substitute conventional combustion engine vehicles. Moreover, they are also
used within an extensive range of devices; including portable electronics, remote control
systems or solar power storage. As a result, the requirements of a LIB are very specific and
these dynamic demands make the manufacturing process extremely challenging. In fact, the
microstructure of the electrodes conforming a LIB cell greatly impacts the ultimate
performance of the battery. In comparison to solely experimental investigations, modelling
and simulating can help to identify and understand the relationships between the structure
and the properties more efficiently, thus ensuring a target-oriented development and
optimization of LIB electrodes.
This doctoral thesis aims to develop a method to give insight into the structural, mechanical
and electrical properties of LIB electrodes by means of discrete element method (DEM)
simulations. In fact, the implementation of a contact model to describe the behaviour of the
active material (AM) particles together with a bond model to represent the additive-binder
matrix enables to analyse the mechanics as well as the electrical pathways of the particulate
structure. Thereby, the following aspects can be comprehensively studied:
• electrode structure: particle size distribution, porosity, thickness, binder distribution
and composition are implemented in the simulation environment and validated
through experimental characterization. Once the electrode is numerically generated
and with the help of post-processing tools, relevant structural characteristics can be
analysed, including the distribution of the porosity, the coordination number of the
AM particles or the contact area between AM particles and the current collector.
• electrode mechanics: the deformation of single AM particles under an external load is
investigated experimentally and integrated in the simulation in terms of the
appropriate contact model. In fact, an elasto-plastic contact model presents itself as
the proper force-displacement relation to describe the studied AM particles.
Moreover, the representation of the additive-binder matrix as a unity is fulfilled with
a bond model that brings additional forces and momentums to the AM particles.
Within the framework of this thesis, the simulations are applied to achieve detailed
information on the evolution of the electrode structure along the calendering process.
Once the numerical approach is calibrated and validated, it can give insight into the
impact of initial structural and mechanical properties on the electrode response.
Thereby, the influence of porosity, particle size distribution and binder´s mechanical
properties is examined. Furthermore, the development of mechanical stresses due to
the application of an external load and during the electrochemical processes is
investigated within the electrode structure. The possibility of AM particle fracture is
also evaluated by comparing the individual stresses of all particles with their
experimental particle strength values.
• specific electrical conductivity of the electrode: the connectivity within the electrode
in terms of direct and bond contacts is considered together with the internal particle
resistances to build a resistor network. Hereby, the specific electrical conductivity of
DEM electrode structures can be assessed. The presented electrical modelling enables
the possibility to account not only for the material properties but also for the
microstructure of the LIB electrode.
In general, the presented DEM simulation strategy is applied with a special focus on
investigating the calendering step. However, the method can be further transferred to other
manufacturing processes such as the drying or the mixing stages, eventually with the
additional coupling of other computational methods. The results introduced along this thesis
are partially based on own publications [1–5], whereas new findings are presented
accordingly.
necessity to substitute conventional combustion engine vehicles. Moreover, they are also
used within an extensive range of devices; including portable electronics, remote control
systems or solar power storage. As a result, the requirements of a LIB are very specific and
these dynamic demands make the manufacturing process extremely challenging. In fact, the
microstructure of the electrodes conforming a LIB cell greatly impacts the ultimate
performance of the battery. In comparison to solely experimental investigations, modelling
and simulating can help to identify and understand the relationships between the structure
and the properties more efficiently, thus ensuring a target-oriented development and
optimization of LIB electrodes.
This doctoral thesis aims to develop a method to give insight into the structural, mechanical
and electrical properties of LIB electrodes by means of discrete element method (DEM)
simulations. In fact, the implementation of a contact model to describe the behaviour of the
active material (AM) particles together with a bond model to represent the additive-binder
matrix enables to analyse the mechanics as well as the electrical pathways of the particulate
structure. Thereby, the following aspects can be comprehensively studied:
• electrode structure: particle size distribution, porosity, thickness, binder distribution
and composition are implemented in the simulation environment and validated
through experimental characterization. Once the electrode is numerically generated
and with the help of post-processing tools, relevant structural characteristics can be
analysed, including the distribution of the porosity, the coordination number of the
AM particles or the contact area between AM particles and the current collector.
• electrode mechanics: the deformation of single AM particles under an external load is
investigated experimentally and integrated in the simulation in terms of the
appropriate contact model. In fact, an elasto-plastic contact model presents itself as
the proper force-displacement relation to describe the studied AM particles.
Moreover, the representation of the additive-binder matrix as a unity is fulfilled with
a bond model that brings additional forces and momentums to the AM particles.
Within the framework of this thesis, the simulations are applied to achieve detailed
information on the evolution of the electrode structure along the calendering process.
Once the numerical approach is calibrated and validated, it can give insight into the
impact of initial structural and mechanical properties on the electrode response.
Thereby, the influence of porosity, particle size distribution and binder´s mechanical
properties is examined. Furthermore, the development of mechanical stresses due to
the application of an external load and during the electrochemical processes is
investigated within the electrode structure. The possibility of AM particle fracture is
also evaluated by comparing the individual stresses of all particles with their
experimental particle strength values.
• specific electrical conductivity of the electrode: the connectivity within the electrode
in terms of direct and bond contacts is considered together with the internal particle
resistances to build a resistor network. Hereby, the specific electrical conductivity of
DEM electrode structures can be assessed. The presented electrical modelling enables
the possibility to account not only for the material properties but also for the
microstructure of the LIB electrode.
In general, the presented DEM simulation strategy is applied with a special focus on
investigating the calendering step. However, the method can be further transferred to other
manufacturing processes such as the drying or the mixing stages, eventually with the
additional coupling of other computational methods. The results introduced along this thesis
are partially based on own publications [1–5], whereas new findings are presented
accordingly.