Modified Li₇P₃S₁₁ Glass-Ceramic Electrolyte and Its Characterization

Li7P3S11 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 Li7P3S11 glass ceramics remain mysterious. Herein, modified Li7P3S11 glass ceramics with compositions of 70Li2S–30P2S5 were prepared via two-step mechanical milling and thermal annealing. Li7P3S11 glass ceramics synthesized using the conventional method (mechanical milling and thermal annealing) were again ball-milled to obtain amorphous 70Li2S–30P2S5 with a peculiar glass structure. Further thermal annealing was carried out to crystallize the glass. The obtained crystalline phase was analogous to the original Li7P3S11 phase, but the conductivity was enhanced by a factor of 1.7. Based on 31P solid-state nuclear magnetic resonance (NMR) spectroscopy, the Li7P3S11 phase contained an additional PS43– unit. A rational deconvolution procedure for the 31P solid-state NMR spectra based on crystalline Li7P3S11 was developed and applied to the samples. The analysis can resolve the additional crystalline PS43– unit in the Li7P3S11 structure. Based on two-dimensional double-quantum 31P NMR spectroscopy, the additional PS43– unit is located adjacent to the P2S74– unit, suggesting that P2S74– is divided into two PS43– units in the Li7P3S11 phase. The flip motion of Li+ was also investigated based on the 7Li spin–lattice relaxation time. The independent activation energy of spin–lattice relaxation with respect to temperature in the Li7P3S11 phase was attributed to a conduction path between the two PS43– units. The findings provide a synthetic route that can be used to develop metastable solid-state electrolytes.