Li-based materials have garnered significant attention due to their diverse configurations, engaging electronic structures, and promising applications. Based on first-principles predictions, we identified several unusual stoichiometric lithium-gallium metallic phases under pressure, e.g., $\mathrm{LiG}{\mathrm{a}}_3$ and $\mathrm{L}{\mathrm{i}}_6\mathrm{Ga}$. Strikingly, the $\mathrm{LiG}{\mathrm{a}}_3$ with cubic symmetry and ${\mathrm{Ga}}_6$ octahedron is estimated to hold a superconducting critical temperature ($T_c$) of 6.5 K at atmospheric pressure, exceeding the representative superconductor mercury and the boiling point of liquid helium, deriving from the coupled interaction of Ga $4p$ electrons at the Fermi level with the low-frequency Ga atomic vibrations. Remarkably, the $\mathrm{L}{\mathrm{i}}_6\mathrm{Ga}$ exhibits pressure-driven structural transitions accompanied by the evolution of interstitial anionic electrons (IAEs) topologies: the zero-dimensional IAEs in ambient-pressure $R$-3 phase is converted into the one-dimensional (1D) IAEs in the compressed $C2/m$ and $R-3m$ phases, and the 1D IAEs and the valence electrons of Ga constitute a conducting network. Unexpectedly, the coexistence of electride and superconductivity states is uncovered in $\mathrm{L}{\mathrm{i}}_6\mathrm{Ga}$, and $R-3m \mathrm{L}{\mathrm{i}}_6\mathrm{Ga}$ has the highest $T_c$ (15.2 K at 240 GPa) among Li-Ga superconductors, originating from the coupling between the Li $2p$ and Ga $4p$ states and the Li-dominated softened phonon modes at low frequencies. These findings provide design guidance for future exploration of emerging superconductor materials.

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• Electronic structure
• High-pressure studies
• Phase diagrams
• Pressure effects
• Superconductivity
• Crystal structures
• Superconductors
• First-principles calculations