Mitigating Chemo-Mechanical Degradation in Sulfide-Based All-Solid-State Batteries Comprising Sulfur Composite Cathode and Li–Si Alloy Anode

Abstract

In this study, all-solid-state batteries consisting of an Li2S5–P2S5 (LPS) glass electrolyte, a sulfur/LPS glass/carbon composite cathode, and an Li–Si anode are prepared and tested under high cut-off voltage conditions (0.5–3.7 V) to elucidate the effect of LPS redox activity on the chemo-mechanical stability of LPS-based cells. 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. Composite anodes of Li3PS4 glass+Li–Si alloy (Type 1) and Li3N+LiF+Li–Si alloy (Type 2) are also prepared for all-solid-state batteries (ASSBs) with LPS glass electrolyte and sulfur/LPS glass/carbon composite cathode. Using a three-electrode system, the anode and cathode potentials are separated, and their polarization resistances are individually traced. Even under high-cutoff-voltage conditions (3.7 V), Type 1 and 2 cells are stably cycled without voltage noise for >200 cycles. Although cathode polarization resistance drastically increases after 3.7 V charge owing to LPS oxidation, LPS redox behavior is fairly reversible upon discharge–charge unlike the non-composite alloy anode cell. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis reveals that the enhanced cyclability is attributed to uniform Li–Si alloying throughout the composite anode, providing more pathways for lithium ions even when these ions are over-supplied via LPS oxidation. These results imply that LPS-based cells can be reversibly cycled with LPS redox even under high-cutoff voltages, as long as non-uniform alloying (lithium dendrite growth) is prevented.