Optimizing Cathode Processing for Enhanced Performance of Li-S All-Solid-State Batteries with Conversion-Type Active Material
Authors: Pavan Matilde , Muench Konrad , Bernges Tim , Benz Sebastian L. , Henss Anja , Zeier Wolfgang , Janek Jürgen 
Published: December 2024

Increasing efforts are needed to meet the growing demand for green energy storage. As lithium-ion batteries reach their theoretical limits, new post-lithium technologies are required.1 Within this frame, Li-S batteries are particularly promising since they are based on conversion reactions that involve more than one lithium ion, leading to high theoretical capacities (e.g., FeS2 lithiation involves 4 Li+, theoretical capacity 894 mAh·g-1).2 In addition, the active materials employed are naturally abundant, inexpensive, and non-toxic, and all-solid-state batteries can provide improved safety. Argyrodites are sulfide solid electrolytes with promising ionic conductivity (e.g., Li5.5PS4.5Cl1.5 6-11 mS·cm−1). They have a narrow electrochemical stability window outside of which sulfur and/or phosphor redox occur. It is known that small particles of conversion-type active material enhance electrochemical performances.3,4 Tuning the cathode composite fabrication can be a cheap and easy mechanical method to tune its structure.5

To investigate the impact of cathode processing, FeS2-based Li-S all-solid-state batteries (FeS2/LPSCl1.5/carbon black | LPSCl1.5 | In/InLi) are fabricated. Different processing methods (i.e., hand grinding, oscillating ball mill, and conventional ball mill) are compared using electrochemical and analytical characterizations (e.g., XRD, SEM-EDX, and XPS). We reveal that the cathode processing has a significant impact on the electrochemical performances of conversion-based cathodes. The achieved specific capacity of the composite mixed via conventional ball mill is more than twice that of the one mixed by oscillating ball mill. Ex-situ SEM images of cathode cross-sections show that the conventional ball mill produces more homogeneous and finely distributed composites compared to the oscillating ball mill (Figure 1). This demonstrates the significant effect of the cathode processing and the importance of composite microstructure and design. Moreover, the experimental capacity achieved using the conventional ball mill is larger than the theoretical one of FeS2. We further investigate the origin of this additional capacity electrochemically.
Figure 1: SEM images of the pristine cathode composites made of FeS2, LPSCl1.5, and carbon black. The composites were mixed via a) hand grinding b) oscillating ball mill c) conventional ball mill.
References

1 Janek, Jürgen; Zeier, Wolfgang G. Nat Energy. 8, 2023. DOI: 10.1038/s41560-023-01208-9.

2 Whang, Grace; Zeier, Wolfgang G. ACS Energy Lett. 8 (12), 2023. DOI: 10.1021/acsenergylett.3c02246.

3 Dewald, Georg F.; Ohno, Saneyuki; Kraft, Marvin A.; Koerver, Raimund; Till, Paul; Vargas-Barbosa, Nella M.; Janek, Jürgen; Zeier, Wolfgang G. Chem. Mater. 31 (20), 2019. DOI: 10.1021/acs.chemmater.9b01550.

4 Wang, Shuo; Tang, Mingxue; Zhang, Qinghua; Li, Baohua; Ohno, Saneyuki; Walther, Felix; Pan, Ruijun; Xu, Xiaofu; Xin, Chengzhou; Zhang, Wenbo; Li, Liangliang; Shen, Yang; Richter, Felix H.; Janek, Jürgen; Nan, Ce-Wen. Adv. Energy Mater. 11 (31), 2021. DOI: 10.1002/aenm.202101370.

5 Ohno, Saneyuki; Koerver, Raimund; Dewald, Georg; Rosenbach, Carolin; Titscher, Paul; Steckermeier, Dominik; Kwade, Arno; Janek, Jürgen; Zeier, Wolfgang G. Chem. Mater. 31 (8), 2019. DOI: 10.1021/acs.chemmater.9b00282.

Figure 1