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.

Li₇P₃S₁₁玻璃陶瓷具备可与液态电解质媲美的高离子电导率，是全固态锂离子电池固态电解质的优质候选材料。然而，Li₇P₃S₁₁玻璃陶瓷的亚稳特性与相关性能仍未被完全阐明。本研究通过两步机械球磨与热退火工艺，制备了组成为70Li₂S–30P₂S₅的改性Li₇P₃S₁₁玻璃陶瓷：先采用传统方法（机械球磨结合热退火）合成Li₇P₃S₁₁玻璃陶瓷，再对其进行二次球磨，得到具有特殊玻璃结构的无定形态70Li₂S–30P₂S₅，随后通过进一步热退火使其晶化。所得晶相与原始Li₇P₃S₁₁相结构相似，但离子电导率提升了1.7倍。基于31P固态核磁共振（solid-state nuclear magnetic resonance, NMR）光谱分析，Li₇P₃S₁₁相中存在额外的PS₄³⁻基团。本研究建立了以结晶态Li₇P₃S₁₁为基准的31P固态核磁共振谱峰解叠方法，并将其应用于样品分析，该方法可分辨Li₇P₃S₁₁结构中额外存在的结晶态PS₄³⁻基团。通过二维双量子31P核磁共振光谱表征，发现该额外PS₄³⁻基团与P₂S₇⁴⁻基团相邻，表明Li₇P₃S₁₁相中的P₂S₇⁴⁻基团可被拆分为两个PS₄³⁻单元。基于7Li自旋-晶格弛豫时间，本研究还探究了锂离子的翻转运动行为。Li₇P₃S₁₁相中自旋-晶格弛豫的活化能与温度呈现独立相关性，这一现象可归因于两个PS₄³⁻基团之间的锂离子传导通路。本研究成果为亚稳态固态电解质的开发提供了可行的合成路径。