Tuning the moisture stability of multiphase β-Li3PS4 solid electrolyte materials

Efficiently improving the moisture stability of β-Li₃PS₄ materials could significantly reduce production costs and eventually enable the mass application. Nanoporous multiphase β-Li₃PS₄ materials prepared via solvent-assistant routes usually contain solvent or solvent decomposition segments associated with the amorphous Li₃PS₄ phase in their structures. Herein, the solvent ethyl propionate (EP) remains in the β-Li₃PS₄ even after 220 h of annealing at 220°C. The possibility of tuning the moisture stability of β-Li₃PS₄ by adjusting the content of the solvent is investigated by environmental scanning electron microscopy (ESEM) combined with other structural analysis techniques. The results demonstrated that the hydrogen-containing amorphous Li₃PS₄ not only stabilizes the β-phase at room temperature but also improves the moisture stability of the material. Although the rapid hydrolysis occurs on the surface of solvent-containing β-Li₃PS₄ materials under ambient conditions within 10 s, with 4 wt% EP content, the material can be exposed to 1.6% relative humidity (R.H.) for at least 8 h without any structural or microstructural change. Even with the lower amount of EP (1.2 wt%) in the Li₃PS₄ structure, the material can withstand 1% R.H. for more than 8 h, which allows the material to be manufactured in a dry room. Our observation proposes a simple method to slightly modify the moisture stability of β-Li₃PS₄ to match the different manufacturing conditions.