Low-Temperature, Scalable Synthesis of Electrolyte Films: Spray Deposition of Sulfides and Oxides

Given the projected tenfold increase in global battery demand over the coming decade,¹ it is imperative to prioritize the advancement of cost-effective, secure, and high-energy-density energy storage solutions for electric vehicles. Solid-state synthesis methods, those that are traditionally used for inorganic solid-state electrolytes (SSEs), generally require higher process temperatures, are incompatible with roll-to-roll processing, and produce millimeter-thick pellets, barring integration in energy-dense solid-state batteries (SSBs).² New, scalable methods for low-temperature manufacturing of SSEs at thicknesses comparable to polymer separators (~20 μm) are required for widespread adoption of SSBs.^2,3 Here, we describe a spray deposition process to form dense Li₆PS₅Cl (LPSCl) and Li₃BO₃ (LBO) films with room-temperature ionic conductivities greater than or equal to 10^-4 S/cm and 10^-8 S/cm, respectively, as determined by electrochemical impedance spectroscopy (EIS). Through precise control of spray parameters (including total mass, concentration, deposition rate, and substrate temperature), we successfully crafted dense, crack-free amorphous films, reaching thicknesses of 14.2 ± 0.3 μm for LPSCl and 0.188 ± 0.054 μm for LBO, all at remarkably low temperatures, below 200 °C. We augmented our findings with concurrent in situ Raman spectroscopy and EIS during the film annealing process, which revealed the presence of polyamorphism in the deposited films and a crystallization process occurring at temperatures lower than conventional solid-state methods. Our research also delves into the diverse applications of these materials in SSBs and other next-generation electrochemical devices.<br/> <br/>Acknowledgements:<br/>This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships (SULI) program. This project was supported by Laboratory Directed Research and Development (LDRD) funding from Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-06CH11357. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. 2140001. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The authors also acknowledge seedling funding provided by the Applied Materials Division, contributions by Nick O’Reilly, as well as assistance by George Sterbinsky from the APS.<br/> <br/>References:<br/>1. Zhou, Yan, Gohlke, David, Rush, Luke, Kelly, Jarod, & Dai, Qiang. Lithium-Ion Battery Supply Chain for E-Drive Vehicles in the United States: 2010–2020. United States. https://doi.org/10.2172/1778934<br/>2. Balaish, M., Gonzalez-Rosillo, J. C., Kim, K. J., Zhu, Y., Hood, Z. D., & Rupp, J. L. (2021). Processing thin but robust electrolytes for solid-state batteries. Nature Energy, 6(3), 227–239. https://doi.org/10.1038/s41560-020-00759-5<br/>3. Hood, Z. D., Zhu, Y., Miara, L. J., Chang, W. S., Simons, P., & Rupp, J. L. (2022). A sinter-free future for solid-state battery designs. Energy & Environmental Science, 15(7), 2927–2936. https://doi.org/10.1039/d2ee00279e