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Abstract
Understanding the electrochemical and mechanical behavior of solid electrolytes beyond their electrochemical stability window is crucial for enabling high energy density all-solid-state batteries. Accordingly, this work systematically studies a model working electrode of Li3PS4, ball milled with vapor grown carbon fiber (VGCF). Operando X-ray photoelectron spectroscopy can identify and quantify the potential-dependent redox byproducts, their reversibility, and electrical properties, while operando cell pressure measurements correlate these with volume changes and mechanical instability. The study examines voltages up to 5.0 V and down to -0.05 V vs. Li/Li+, mimicking cathode and anode cycling. It demonstrates that within the 2.4 V – 5.0 V region, Li3PS4 oxidation byproducts are primarily polysulfides composed of bridging sulfurs (P-S-S-P) between PS43- units, free of elemental sulfur (S0), and electrically conductive. The Li3PS4 oxidation process occurs at 2.8 V during 1st charge and ends at 3.4 V, with volume shrinkage at the VGCF interface. During reduction (2.4 to -0.05 V), polysulfides convert reversibly to Li3PS4 between 1.9 – 1.7 V, then to Li2S and LinP (0 ≤ n ≤ 3) between 1.9 – 0.6 V, causing volume expansion and the transition to an electrically insulating interphase. Below 0.6 V, Li2O formation dominates without further evolution of Li2S or LinP.
Supplementary materials
Title
Supporting Information
Description
Cell designs, cross-section and in-plane SEM images (Figure S1); ½ doublet and Al-mesh subtraction (Figure S2); Fitting parameters high voltage (HV) range (Table S1); Fitting parameters low voltage (LV) range (Table S2); Shift corrected BE peak positions (Table S3); Atomic % all components HV and LV range (Table S4); Pressure relaxation of operando pressure cell (Figure S3); LPS specific charge capacity in the HV range (Figure S4); Overpotential operando/standard cell (Figure S5); Electrochemical current response at high voltage (Figure S6); HV: Additional S2p/P2p spectra + Li1s/Al2p (Figure S7); HV: Additional O1s, C1s (Figure S8); XPS core spectra S2p, P2p, O1s and C1s of pristine LPS powder and LPS:VGCF composite WE (Figure S9); LV: Additional S2p/P2p spectra + Li1s/Al2p (Figure S10); Electrochemical current response at low voltage (Figure S11); SEM/EDX operando XPS cell post-mortem (Figure S12); HV: peak shifts (Figure S13); LV: peak shifts (Figure S14); Impedance spectra (Figure S15).
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