Abstract
In the field of energy storage, all-solid-state batteries (ASSBs) arise as an attractive substitute for traditional liquid electrolyte lithium-ion batteries, offering improved safety along with higher power and energy densities1. Despite considerable advancements in solid-state battery development, the transition from successful lab-scale cells to commercially viable pouch cells remain a significant bottleneck in their commercialization journey. One of the major challenges is manufacturing solid state components for controlled interfaces (cathode/solid electrolyte (SE)) and with a controlled microstructure2,3.
As a result, significant efforts have been directed towards developing large-scale synthesis techniques for Li6PS5Cl solid electrolyte, resulting in the emergence of commercial availability. However, in contrast to small-scale laboratory synthesis, commercial Li6PS5Cl production frequently results in a diverse array of particle sizes and distributions, which leads to significant challenges such as low-quality percolation network. In some cases, these challenges extend to the inclusion of particles larger than the composite cathode thickness when integrated into solid-state batteries, exacerbating difficulties related to achieving proper densification and resulting in suboptimal kinetics.
Hence, in this study we developed a procedure to modify argyrodite Li6PS5Cl with controlled particle size distribution (PSD) while maintaining good Li-ion conductivity. These optimized particles were casted into tapes by using Doctor blade method to study the impact of pressure, temperature, particle size, and particle size distribution on compactability of SE tapes. To systematically study the role of microstructure and porosity on conductivity, we processed argyrodite solid electrolytes Li6PS5Cl (LPSCl) from powders to tapes with varying sizes (1−5 μm) and varying pressures ranging from 0 to 1000 MPa via cold uniaxial pressing. Synchrotron X-ray tomography is implemented with 3-D volumetric quantification approaches to evaluate structural and transport heterogeneity. The study shows that high density (low porosity) solid electrolytes can result in higher ionic conductivity, while low density (high porosity) often results in lower ionic conductivity. A range of characterization tools, including XRD, FIB-SEM, TEM, and temperature and pressure-dependent impedance spectroscopy, are utilized to establish connections between microstructure and Li-ion transport.
References
1. Janek, J. & Zeier, W. G. A solid future for battery development. Nat Energy 1, (2016).
2. Wang, C., Kim, J. T., Wang, C. & Sun, X. Progress and Prospects of Inorganic Solid‐State Electrolyte‐Based All‐Solid‐State Pouch Cells. Advanced Materials 35, (2023).
3. Wang, C. et al. All-solid-state lithium batteries enabled by sulfide electrolytes: From fundamental research to practical engineering design. Energy and Environmental Science vol. 14 2577–2619 Preprint at https://doi.org/10.1039/d1ee00551k (2021).
Acknowledgement
We acknowledge financial support by Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development and the Christian Doppler Research Association (Christian Doppler Laboratory for Solid-State Batteries).