Investigating the Mechanisms of Li Creeping Driven By High Stack Pressure in Sulfide Solid Electrolytes for All-Solid-State Batteries
Authors: Park YongJun , Park Jaehee , Watanabe Toshiki , Yamamoto Kentaro , Matsunaga Toshiyuki , Uchimoto Yoshiharu 
Published: December 2024

As the primary use of Li-ion batteries shifts from small electronic devices to electric vehicles, there is a need to increase the stability and energy density of Li-ion batteries. In order to achieve high energy density, use of lithium metal as an anode has being considered due to its high theoretical capacity (3860 mAh g-1) and low reduction potential (-3.04 V vs. SHE). However, the liquid electrolyte used in Li-ion batteries is not only dangerous due to the risk of fire in case of leakage, but also has the disadvantage of shortening the lifetime of the battery due to the generation of lithium dendrites during cycling when lithium metal is used as anode. To overcome these disadvantages, all-solid-state batteries (ASSBs) using solid electrolytes have emerged, which are expected to improve safety and cycling stability even when using lithium metal anodes. Among the various types of solid electrolytes, sulfide solid electrolytes are widely used due to their high ionic conductivity and ductility, which allows easy formation of good interfaces, resulting in high performance ASSBs.

ASSBs are suffering from the irreversible capacity loss during cycling results from the contact loss between active material and solid electrolyte particles due to the volume change of active materials during cell cycling.1 Applying high pressure has been suggested as a remedy, reported as either recovering irreversible capacity after applying high pressure to cycled cells or mitigating such losses by applying significant high stack pressure.2,3 However, due to the soft nature of lithium, at high pressure, lithium migrates through the electrolyte layer to the opposite electrode, which is known as Li creep, causing the cell to short-circuit. In order to achieve long life of Li metal ASSBs, it is necessary to understand the Li creep phenomenon induced by high stack pressure.

This study endeavors to elucidate the impact of the micro/nano-structure of pore channel in electrolyte layer on the pressure-induced Li creep phenomenon, employing LiI-doped Li3PS4 as the electrolyte due to its stability in contact with Li metal.4 Electrolytes with different particle sizes were prepared and electrolyte pellets were fabricated, and the porosity, pore size and pore channel of the electrolyte pellets were confirmed via micro- and nano-scale X-ray CT. The investigation extends to measuring the time to short-circuit in cells with two different electrolyte pellets under high stack pressure, alongside SEM analysis of the internal structure of the short-circuited cell's electrolyte layer. This analysis aimed to confirm whether lithium migration through the pores is a contributory factor to Li creep, thereby shedding light on the structural factors influencing this phenomenon.

References

[1] Koerver, R., Chem. Mater. 2017, 29, 13, 5574-5582

[2] Shi, T., J. Mater. Chem. A, 2020, 8, 17399

[3] Yamamoto, M., Journal of Power Sources 473 2020 228595

[4] Takahashi, M., Chem. Mater.
2021, 33, 13, 4907–4914