Tobias Schmitt - Academia.edu (original) (raw)

Papers by Tobias Schmitt

Zinc-air batteries are a promising candidate for stationary energy storage. Zinc metal electrodes... more Zinc-air batteries are a promising candidate for stationary energy storage. Zinc metal electrodes are stable in water relying on non-toxic materials and enabling low manufacturing costs. Current experimental research in this field deals with cycle-life limiting effects, such as anode shape change and electrolyte passivation. We contribute to this topic by performing multi-dimensional simulations. Recently, we developed a theory-based model of aqueous alkaline zinc-air batteries that consistently couples the dynamics of its solid, liquid, and gaseous phases. 1D simulations predicted the effects of inhomogeneous zinc oxide nucleation and growth as well as carbonate formation in the electrolyte. We validated the model predictions of discharge voltage and shelf-life. Here, we present the first multi-dimensional simulations of zinc-air batteries and extend our model by simulating zinc shape change. Our 2D simulations of button cells are enabled by local volumeaveraging theory. We present...

Lithium-ion batteries are the technology of choice for a broad range of applications due to their... more Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithium-ion batteries is heavily impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, referred to as lithium plating. Long-term SEI growth is the biggest contributor to capacity fade in lithium-ion batteries. Lithium plating, which occurs in low temperature or high current charging, can result in capacity fade or even thermal runaway. In our group we develop multiphysical models and perform simulations for various types of batteries. In order to describe the internal processes of Li-ion batteries, we derive thermodynamic consistent transport theories. Based on these, our group has developed models for long-term SEI growth and for lithium plating in 3D electrode microstructures. In...

Lithium-ion batteries are the technology of choice for a broad range of applications due to their... more Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithium-ion batteries is heavily impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, referred to as lithium plating. Long-term SEI growth is the biggest contributor to capacity fade in lithium-ion batteries. Lithium plating, which occurs in low temperature or high current charging, can result in capacity fade or even thermal runaway. In our group we develop multiphysical models and perform simulations for various types of batteries. In order to describe the internal processes of Li-ion batteries, we derive thermodynamic consistent transport theories. Based on these, our group has developed models for long-term SEI growth and for lithium plating in 3D electrode microstructures. In...

2019 European Space Power Conference (ESPC), 2019

Lithium-ion batteries are the technology of choice for a broad range of applications due to their... more Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithiumion batteries is impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, referred to as lithium plating. For both processes we develop physically based models. In this contribution we develop a model to describe the performance and lifetime of the batteries of in-orbit satellite REIMEI developed by the Japan Aerospace Exploration Agency. We extend an existing model for SEI growth and incorporate it into a model for fresh cells. Then we simulate the degradation of batteries under cycling in 1D and 3D. To validate the model, we use experimental and in-flight data of the batteries. We show inhomogeneities in the SEI thickness after cycling.

We distinguish two approaches for the modeling of reactive flows in incompressible, multi-compone... more We distinguish two approaches for the modeling of reactive flows in incompressible, multi-component, multi-phase systems. The standard approach requires a divergence free velocity field. It is used in most of the fields in computational fluid dynamics. However, it is only correct for one-component systems. For dilute solutions, in which the solvent is the dominant species, it is only approximately correct. ∇ ⋅ v = 0 is no longer valid if the concentrations become larger, if the solvent takes part in reactions, or if solvent free electrolytes are modeled. For such cases, the partial molar volumes of all species have to be taken into account. This has a consequence for the convection velocity, which becomes dependent on the change of the fluid composition. It can change or even dominate the overall behavior of the modeled system. Our extended approach for concentrated solutions takes those effects into account. We consider the partial molar volumes of all constituents and the phase ch...

When a lithium ion battery is fully charged, the potential of its negative electrode is outside t... more When a lithium ion battery is fully charged, the potential of its negative electrode is outside the stability window of the electrolyte, typically a mixture of organic solvents (ethylene carbonate, dimethyl carbonate) with a lithium salt. Consequently solvent molecules are reduced at the anode surface and reduction products form a film thus passivating the electrode. This so called solid electrolyte interphase (SEI) slows down the reduction process to acceptable levels and is crucial for stable battery performance. Experiments indicate that the SEI has dual layer morphology [1], i.e. it consists of a dense inner layer (close to the electrode) and a porous outer layer (close to the electrolyte). So far, most theoretical studies describing SEI evolution homogenize the SEI structure, focusing solely on the layer growth [2,3,4]. We present a one dimensional model for porous SEI formation that additionally captures morphology properties of the SEI film. In our simulation the evolution of...

Research on structures and processes Research on degradation and safety Evaluation of novel batte... more Research on structures and processes Research on degradation and safety Evaluation of novel battery concepts Lattice-Boltzmann, battery concepts, and interfaces 10.15.2015 DLR.de/tt • Folie 15

In the field of zinc-air batteries, most of the research has an experimental character. We contri... more In the field of zinc-air batteries, most of the research has an experimental character. We contribute to this topic and support experimentalists with electrochemical models and numerical simulations. Experiments have a long preparation time, work only under certain environmental conditions, or take long to complete. The setup or manufacturing process can also be expensive. In those cases it is favorable to carry out simulations and screen a wide range of parameters, cost and time efficiently. Those parameters are modifications of the geometry, the electrode materials, or the electrolyte [1]. Simulations cannot stand without measurements, but a computational study can significantly improve research and production processes. Most models of zinc-air batteries describe the cell dynamics along one dimension [2,3]. They capture the transport of the concentrations, calculate a consistent electric potential, and regard the temporal changes of the different phases. In some cases, the effect ...

Electrochimica Acta, 2019

In this article, we derive a general form of local volume-averaging theory and apply it to a mode... more In this article, we derive a general form of local volume-averaging theory and apply it to a model of zinc-air conversion batteries. Volume-averaging techniques are frequently used for the macroscopic description of micro-porous electrodes. We extend the existing method by including reactions between different phases and time-dependent volume fractions of the solid phases as these are continuously dissolved and reconstructed during operation of conversion batteries. We find that the constraint of incompressibility for multi-component fluids causes numerical instabilities in simulations of zinc-air battery cells. Therefore, we develop a stable sequential semi-implicit algorithm which converges against the fully implicit solution. Our method reduces the coupling of the variables by splitting the system of equations and introducing an additional iteration step.

Journal of Power Sources, 2019

Zinc-air batteries offer large specific energy densities, while relying on abundant and non-toxic... more Zinc-air batteries offer large specific energy densities, while relying on abundant and non-toxic materials. In this paper, we present the first multi-dimensional simulations of zinc-air batteries. We refine our existing theory-based model of secondary zinc-air systems. The model comprises thermodynamically consistent multi-species transport in alkaline electrolytes, formation and dissolution of metallic zinc and passivating zinc oxide, as well as multi-phase coexistence in gas diffusion electrodes. For the first time, we simulate zinc shape-change during battery cycling by modeling convection of zinc solids. We validate our model with in-situ tomography of commercial button cells. Two-dimensional volume-averaged simulations of cell voltage and zinc electrode morphology during discharge agree with these measurements. Thus, we can study how electrolyte carbonation limits shelf-life and how zinc shape-change limits cycle-life. The charging current is found to be the major contributor to cycle-life limitations. Finally, we optimize initial anode structure and charge-discharge protocols for improved performance and cycle-ability.

Zinc-air batteries are a promising candidate for stationary energy storage. Zinc metal electrodes... more Zinc-air batteries are a promising candidate for stationary energy storage. Zinc metal electrodes are stable in water relying on non-toxic materials and enabling low manufacturing costs. Current experimental research in this field deals with cycle-life limiting effects, such as anode shape change and electrolyte passivation. We contribute to this topic by performing multi-dimensional simulations. Recently, we developed a theory-based model of aqueous alkaline zinc-air batteries that consistently couples the dynamics of its solid, liquid, and gaseous phases. 1D simulations predicted the effects of inhomogeneous zinc oxide nucleation and growth as well as carbonate formation in the electrolyte. We validated the model predictions of discharge voltage and shelf-life. Here, we present the first multi-dimensional simulations of zinc-air batteries and extend our model by simulating zinc shape change. Our 2D simulations of button cells are enabled by local volumeaveraging theory. We present...

Lithium-ion batteries are the technology of choice for a broad range of applications due to their... more Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithium-ion batteries is heavily impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, referred to as lithium plating. Long-term SEI growth is the biggest contributor to capacity fade in lithium-ion batteries. Lithium plating, which occurs in low temperature or high current charging, can result in capacity fade or even thermal runaway. In our group we develop multiphysical models and perform simulations for various types of batteries. In order to describe the internal processes of Li-ion batteries, we derive thermodynamic consistent transport theories. Based on these, our group has developed models for long-term SEI growth and for lithium plating in 3D electrode microstructures. In...

Lithium-ion batteries are the technology of choice for a broad range of applications due to their... more Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithium-ion batteries is heavily impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, referred to as lithium plating. Long-term SEI growth is the biggest contributor to capacity fade in lithium-ion batteries. Lithium plating, which occurs in low temperature or high current charging, can result in capacity fade or even thermal runaway. In our group we develop multiphysical models and perform simulations for various types of batteries. In order to describe the internal processes of Li-ion batteries, we derive thermodynamic consistent transport theories. Based on these, our group has developed models for long-term SEI growth and for lithium plating in 3D electrode microstructures. In...

2019 European Space Power Conference (ESPC), 2019

Lithium-ion batteries are the technology of choice for a broad range of applications due to their... more Lithium-ion batteries are the technology of choice for a broad range of applications due to their performance and long-term stability. The performance and durability of lithiumion batteries is impacted by various degradation mechanisms. These include the growth of the solid-electrolyte interphase (SEI) and the deposition of metallic lithium on the surface of the negative electrode, referred to as lithium plating. For both processes we develop physically based models. In this contribution we develop a model to describe the performance and lifetime of the batteries of in-orbit satellite REIMEI developed by the Japan Aerospace Exploration Agency. We extend an existing model for SEI growth and incorporate it into a model for fresh cells. Then we simulate the degradation of batteries under cycling in 1D and 3D. To validate the model, we use experimental and in-flight data of the batteries. We show inhomogeneities in the SEI thickness after cycling.

We distinguish two approaches for the modeling of reactive flows in incompressible, multi-compone... more We distinguish two approaches for the modeling of reactive flows in incompressible, multi-component, multi-phase systems. The standard approach requires a divergence free velocity field. It is used in most of the fields in computational fluid dynamics. However, it is only correct for one-component systems. For dilute solutions, in which the solvent is the dominant species, it is only approximately correct. ∇ ⋅ v = 0 is no longer valid if the concentrations become larger, if the solvent takes part in reactions, or if solvent free electrolytes are modeled. For such cases, the partial molar volumes of all species have to be taken into account. This has a consequence for the convection velocity, which becomes dependent on the change of the fluid composition. It can change or even dominate the overall behavior of the modeled system. Our extended approach for concentrated solutions takes those effects into account. We consider the partial molar volumes of all constituents and the phase ch...

When a lithium ion battery is fully charged, the potential of its negative electrode is outside t... more When a lithium ion battery is fully charged, the potential of its negative electrode is outside the stability window of the electrolyte, typically a mixture of organic solvents (ethylene carbonate, dimethyl carbonate) with a lithium salt. Consequently solvent molecules are reduced at the anode surface and reduction products form a film thus passivating the electrode. This so called solid electrolyte interphase (SEI) slows down the reduction process to acceptable levels and is crucial for stable battery performance. Experiments indicate that the SEI has dual layer morphology [1], i.e. it consists of a dense inner layer (close to the electrode) and a porous outer layer (close to the electrolyte). So far, most theoretical studies describing SEI evolution homogenize the SEI structure, focusing solely on the layer growth [2,3,4]. We present a one dimensional model for porous SEI formation that additionally captures morphology properties of the SEI film. In our simulation the evolution of...

Research on structures and processes Research on degradation and safety Evaluation of novel batte... more Research on structures and processes Research on degradation and safety Evaluation of novel battery concepts Lattice-Boltzmann, battery concepts, and interfaces 10.15.2015 DLR.de/tt • Folie 15

In the field of zinc-air batteries, most of the research has an experimental character. We contri... more In the field of zinc-air batteries, most of the research has an experimental character. We contribute to this topic and support experimentalists with electrochemical models and numerical simulations. Experiments have a long preparation time, work only under certain environmental conditions, or take long to complete. The setup or manufacturing process can also be expensive. In those cases it is favorable to carry out simulations and screen a wide range of parameters, cost and time efficiently. Those parameters are modifications of the geometry, the electrode materials, or the electrolyte [1]. Simulations cannot stand without measurements, but a computational study can significantly improve research and production processes. Most models of zinc-air batteries describe the cell dynamics along one dimension [2,3]. They capture the transport of the concentrations, calculate a consistent electric potential, and regard the temporal changes of the different phases. In some cases, the effect ...

Electrochimica Acta, 2019

In this article, we derive a general form of local volume-averaging theory and apply it to a mode... more In this article, we derive a general form of local volume-averaging theory and apply it to a model of zinc-air conversion batteries. Volume-averaging techniques are frequently used for the macroscopic description of micro-porous electrodes. We extend the existing method by including reactions between different phases and time-dependent volume fractions of the solid phases as these are continuously dissolved and reconstructed during operation of conversion batteries. We find that the constraint of incompressibility for multi-component fluids causes numerical instabilities in simulations of zinc-air battery cells. Therefore, we develop a stable sequential semi-implicit algorithm which converges against the fully implicit solution. Our method reduces the coupling of the variables by splitting the system of equations and introducing an additional iteration step.

Journal of Power Sources, 2019

Zinc-air batteries offer large specific energy densities, while relying on abundant and non-toxic... more Zinc-air batteries offer large specific energy densities, while relying on abundant and non-toxic materials. In this paper, we present the first multi-dimensional simulations of zinc-air batteries. We refine our existing theory-based model of secondary zinc-air systems. The model comprises thermodynamically consistent multi-species transport in alkaline electrolytes, formation and dissolution of metallic zinc and passivating zinc oxide, as well as multi-phase coexistence in gas diffusion electrodes. For the first time, we simulate zinc shape-change during battery cycling by modeling convection of zinc solids. We validate our model with in-situ tomography of commercial button cells. Two-dimensional volume-averaged simulations of cell voltage and zinc electrode morphology during discharge agree with these measurements. Thus, we can study how electrolyte carbonation limits shelf-life and how zinc shape-change limits cycle-life. The charging current is found to be the major contributor to cycle-life limitations. Finally, we optimize initial anode structure and charge-discharge protocols for improved performance and cycle-ability.