Electro-Chemo-Mechanical Model for Polymer Electrolytes

Polymer electrolytes (PEs) are promising candidates for use in next-generation high-voltage batteries, as they possess advantageous elastic and electrochemical properties. However, PEs still suffer from low ionic conductivity and need to be operated at higher temperatures. Furthermore, the wide variety of different types of PEs and the complexity of the internal interactions constitute challenging tasks for progressing towards a systematic understanding of PEs. Here, we present a continuum transport theory which enables a straight-forward and thermodynamically consistent method to couple different aspects of PEs relevant for battery performance. Our approach combines mechanics and electrochemistry in non-equilibrium thermodynamics, and is based on modeling the free energy, which comprises all relevant bulk properties. In our model, the dynamics of the polymer-based electrolyte are formulated relative to the highly elastic structure of the polymer. For validation, we discuss a benchmark polymer electrolyte. Based on our theoretical description, we perform numerical simulations and compare the results with data from the literature. In addition, we apply our theoretical framework to a novel type of single-ion conducting PE and derive a detailed understanding of the internal dynamics.Comment: 16 pages, 8 figure

Electro-Chemo-Mechanical Model for Polymer Electrolytes

Polymer electrolytes (PEs) are promising candidates for use in next-generation high-voltage batteries, as they possess advantageous elastic and electrochemical properties. However, PEs still suffer from low ionic conductivity and need to be operated at higher temperatures. Furthermore, the wide variety of different types of PEs and the complexity of the internal interactions constitute challenging tasks for progressing toward a systematic understanding of PEs. Here, we present a continuum transport theory which enables a straight-forward and thermodynamically consistent method to couple different aspects of PEs relevant for battery performance. Our approach combines mechanics and electrochemistry in non-equilibrium thermodynamics, and is based on modeling the free energy, which comprises all relevant bulk properties. In our model, the dynamics of the polymer-based electrolyte are formulated relative to the highly elastic structure of the polymer. For validation, we discuss a benchmark polymer electrolyte. Based on our theoretical description, we perform numerical simulations and compare the results with data from the literature. In addition, we apply our theoretical framework to a novel type of single-ion conducting PE and derive a detailed understanding of the internal dynamics

Effect of the 3D Structure and Grain Boundaries on Lithium Transport in Garnet Solid Electrolytes

Lithium metal anodes are vital enablers for high-energy all-solid-state batteries (ASSBs). To promote ASSBs in practical applications, performance limitations such as the high lithium interface resistance and the grain boundary resistance in the solid electrolyte (SE) need to be understood and reduced by optimization of the cell design. In this work, we use our 3D microstructure-resolved simulation approach combined with a modified grain boundary transport model for the SE to shed some light on the aforementioned limitations in garnet ASSBs. Using high-resolution volume images of the SE electrode sample, we are able to reconstruct the SE microstructure. Using a grain segmentation algorithm, we further distinguish individual grains and account for the influence of the SE grain size and grain boundaries. We focus our simulation work on the trilayer cell architecture, consisting of two porous SE electrodes separated by a dense layer. Even though the highly porous SE electrodes reduce the lithium interface resistance by providing a higher active surface area, the increased electrode tortuosity also reduces the effective ionic conductivity in the SE. We confirm via impedance simulation studies and validation against experimental results that with increasing SE electrode porosity, the lithium transport becomes limited by grain boundaries. We also correlate the area-specific resistance to different lithium infiltration stages in the trilayer cell by spatially resolving the current density distribution. This analysis allows us to suggest a plausible deposition mechanism, and moreover, we identify current density hot spots in the proximity of the dense layer. These hot spots might lead to dendrite formation and long-term cell failure. The joint theoretical and experimental study gives guidelines for cell design and optimization which allow further improvement of the trilayer architecture