Modified Li₇P₃S₁₁ Glass-Ceramic Electrolyte and Its Characterization

Li 7 P 3 S 11 glass ceramics have high conductivities competitive with liquid electrolytes, making them good candidates as solid-state electrolytes for all-solid-state lithium-ion batteries. However, the metastable nature and performance of Li 7 P 3 S 11 glass ceramics remain mysterious. Herein, modified Li 7 P 3 S 11 glass ceramics with compositions of 70Li 2 S–30P 2 S 5 were prepared via two-step mechanical milling and thermal annealing. Li 7 P 3 S 11 glass ceramics synthesized using the conventional method (mechanical milling and thermal annealing) were again ball-milled to obtain amorphous 70Li 2 S–30P 2 S 5 with a peculiar glass structure. Further thermal annealing was carried out to crystallize the glass. The obtained crystalline phase was analogous to the original Li 7 P 3 S 11 phase, but the conductivity was enhanced by a factor of 1.7. Based on 31 P solid-state nuclear magnetic resonance (NMR) spectroscopy, the Li 7 P 3 S 11 phase contained an additional PS 4 3– unit. A rational deconvolution procedure for the 31 P solid-state NMR spectra based on crystalline Li 7 P 3 S 11 was developed and applied to the samples. The analysis can resolve the additional crystalline PS 4 3– unit in the Li 7 P 3 S 11 structure. Based on two-dimensional double-quantum 31 P NMR spectroscopy, the additional PS 4 3– unit is located adjacent to the P 2 S 7 4– unit, suggesting that P 2 S 7 4– is divided into two PS 4 3– units in the Li 7 P 3 S 11 phase. The flip motion of Li + was also investigated based on the 7 Li spin–lattice relaxation time. The independent activation energy of spin–lattice relaxation with respect to temperature in the Li 7 P 3 S 11 phase was attributed to a conduction path between the two PS 4 3– units. The findings provide a synthetic route that can be used to develop metastable solid-state electrolytes.