Negative linear compressibility (NLC) describes a unique property of certain materials that expand in one direction when exposed to external pressure. Solid electrolytes with this counterintuitive effect offer a promising opportunity to enhance the lithium-ion conductivity, as the directional expansion can facilitate the creation of improved ion transport pathways. Here, we reported a high-pressure-induced phase transition in ${\mathrm{Li}}_4{\mathrm{SiW}}_{12}{\mathrm{O}}_{40}$ from the Keggin to the bronze structure. This high-pressure phase remained stable under ambient conditions after decompression, and exhibited the unconventional mechanical behavior of NLC with a compression coefficient $K_{\mathrm{c}}=-9{\mathrm{TPa}}^{-1}$. This transition enhanced lithium-ion conductivity by more than an order of magnitude, from $0.018$ to $0.22\mathrm{mS}{\mathrm{cm}}^{-1}$. The NLC effect synergistically expanded the migration channels and shortened the ${\mathrm{Li}}^{+}\text{−}{\mathrm{Li}}^{+}$ distance from 5.92 to 3.34 Å, collectively lowering the migration barrier. Concurrently, the NLC-induced formation of highly distorted ${\mathrm{Li}}^{+}$ sites within ${\mathrm{SiO}}_5$ polyhedra weakened the binding energy between ${\mathrm{Li}}^{+}$ and the framework. This promoted the formation of new bonds, which shortened interatomic distances and concentrated electron density. The resultant electronic redistribution contracted the transition-state volume, thereby generating a negative activation volume, which indicated higher carrier mobility. These findings provide new approaches for enhancing the conductivity of lithium-ion electrolytes.

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• Electrical conductivity
• Electrical properties
• Structural properties
• Ceramics
• Inorganic compounds
• Electrical transport techniques
• Pressure techniques
• Scanning transmission electron microscopy
• X-ray techniques