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微晶玻璃（Li7P3S11 glass ceramics）具有可与液态电解质媲美的高电导率，使其成为全固态锂离子电池固态电解质的优质候选材料。然而，Li7P3S11微晶玻璃的亚稳态特性与性能仍未明晰。本文通过两步机械球磨与热退火工艺，制备了成分为70Li2S–30P2S5的改性Li7P3S11微晶玻璃。采用传统方法（机械球磨结合热退火）合成的Li7P3S11微晶玻璃，经再次球磨得到具有特殊玻璃结构的非晶态70Li2S–30P2S5。进一步通过热退火使该玻璃晶化，所得晶相与原始Li7P3S11相结构相近，但电导率提升了1.7倍。基于31P固体核磁共振（solid-state nuclear magnetic resonance, NMR）光谱分析，原始Li7P3S11相中含有额外的PS₄³⁻基团。我们开发了一种基于结晶态Li7P3S11的31P固体核磁共振谱峰去卷积解析方法，并将其应用于样品分析，该方法可有效分辨Li7P3S11结构中额外的晶态PS₄³⁻基团。基于二维双量子31P固体核磁共振光谱，该额外的PS₄³⁻基团紧邻P₂S₇⁴⁻基团，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，本文还探究了Li⁺的翻转运动。Li7P3S11相中自旋-晶格弛豫的活化能随温度呈现独立的依赖特性，这一现象归因于两个PS₄³⁻基团之间的锂离子传导路径。本研究成果为开发亚稳态固态电解质提供了可行的合成路线。