Tailoring Crystallization Protocols to Boost Ionic Conductivity in Li7P3S11 Solid Electrolytes via Controlled Two-Step Thermal Processing

Fig. 1. (a) XRD patterns of the samples subjected to ball-milling for different time intervals, (b) DSC thermogram of the amorphous powders, (c) XRD analyses of the amorphous powders heat treated at different temperatures for one hour.Fig. 2. (a) DSC peak height after short nucleation at 160–210 ◦C, (b) Effect of holding at 180 ◦C for nucleation on DSC peak height, (c) Thermal profiles for kinetic analysis, (d) DSC peak areas after 250 ◦C growth.Fig. 3. (a) DSC curves at different heating rates, (b) Kissinger and Ozawa plots for Ea, (c) Avrami plots at selected temperatures, (d) Matusita kinetic analysis, (e-f) Local activation energy versus crystallization fraction.Table 1. Comparative crystallization kinetic parameters for amorphous and pre-nucleated Li7P3S11 samples, derived from various thermal analysis models.Fig. 4. Crystallization kinetics of pre-nucleated Li7P3S11 evaluated by (a) DSC at different heating rates, (b-c) modeled via Kissinger and Ozawa, (c) Avrami plots (d) Matusita plot (e-f) local activation energy methods.Fig. 5. (a) XRD patterns of single-step (heated to 250 °C, held 1 h) and two-step (heated to 180 °C, held 30 min; then to 250 °C, held 1 h) crystallized Li7P3S11, (b) UV–Vis derived optical band gaps, FESEM images showing morphological evolution of (c) amorphous, (d) single, and (e) two-step heat-treated samples.Fig. 6. (a) Nyquist plots from EIS measurements of single and two-step crystallized Li7P3S11, (b) Arrhenius plots of temperature-dependent ionic conductivity and corresponding activation energy barriers for lithium diffusion.Table 2. Comparative summary of structural and electrochemical properties for Li7P3S11 processed via single and two-step crystallization strategies.