Redox Activity of Li2s–P2s5 Electrolyte Inducing Chemo-Mechanical Failure in All-Solid-State Batteries Comprising Sulfur Composite Cathode and Li–Si Alloy Anode

Abstract

In this study, all-solid-state batteries consisting of an Li 2 S 5 –P 2 S 5 (LPS) glass electrolyte, a sulfur/LPS glass/carbon composite cathode, and an Li–Si anode are prepared and tested under two different cut-off voltage conditions (0.5–2.7 V and 0.5–3.7 V) to elucidate the effect of LPS redox activity on the chemo-mechanical stability of LPS-based cells. In the voltage range 0.5–2.7 V, which is outside the theoretical stability window for LPS, the cell is stably cycled, indicating that there exists a practical stability window that fulfills each cell condition. On the other hand, the cell cycled in the voltage range 0.5–3.7 V exhibits unstable charging behaviors and voltage noise, with substantial LPS oxidative decomposition. X-ray photoelectron spectroscopy and impedance spectra analyses of a three-electrode system reveal that the cathode resistance is remarkably increased by the oxidative decomposition of LPS when the cell is charged to 3.7 V, which induces dendritic lithium growth at the anode side, resulting in a micro-short circuit through the electrolyte. When the cycles are repeated with voltage noise, the capacity loss becomes significant, which is attributed to cathode degradation (irreversible LPS decomposition) and cracks through the cell, as promoted by the micro-short circuit. This study shows that LPS redox activity outside the practical stability window can lead not only to oxidative degradation of the cathode itself, but also to chemo-mechanical failure in LPS-based cells (especially with high-capacity anode materials such as lithium alloys).

Keywords: All-solid-state Battery, Redox Activity, Sulfur cathode, Sulfide electrolyte, Li-Si anode, Cutoff voltage