Electron-electron correlations and electron-phonon coupling underlie a wide spectrum of quantum phenomena. Electrides are materials in which excess electrons localize in interstitial regions as non-nuclear attractors (NNAs), providing a unique platform to probe their interplay. In this study, using crystal structure prediction and first-principles calculations, we identify two lithium-rich electrides, $I4\text{/}mmm\text{−}\mathrm{L}{\mathrm{i}}_4\mathrm{Ir}$ and $R\overline{3}m\text{−}\mathrm{L}{\mathrm{i}}_8\mathrm{Ir}$. With respect to $\mathrm{L}{\mathrm{i}}_4\mathrm{Ir}$, pressure drives a remarkable evolution of ground states: a Stoner-type ferromagnet at 200 GPa is transformed into a stripe antiferromagnetic (sAFM) type above 252.8 GPa, which is ultimately transformed into a nonmagnetic metal at 450 GPa. The sAFM order results in a spin density wave that stems from the intrinsic instability of flat, NNA-derived bands under strong Coulomb repulsion, rather than Fermi surface nesting. The stability of this phase is improved by long-range electrostatic energy gains from charge redistribution. Notably, the metastable zigzag antiferromagnetic phase exhibits magnetoelastic coupling, inducing a symmetry-lowering structural distortion to the Pmmn space group. In nonmagnetic states, both $\mathrm{L}{\mathrm{i}}_4\mathrm{Ir}$ and $\mathrm{L}{\mathrm{i}}_8\mathrm{Ir}$ are predicted to host phonon-mediated superconductivity. While spin-orbit coupling has a minimal effect on the electronic structure of magnetic phases, it significantly modulates lattice dynamics and electron-phonon coupling by redistributing charge to the NNAs, thereby stabilizing superconductivity and suppressing dynamic instabilities. Our work demonstrates that lithium-rich Ir-based electrides constitute a tunable quantum material platform in which interstitial electrons govern unconventional magnetism, spin-lattice entanglement, and high-temperature superconductivity.

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• Electron-phonon coupling
• Ferrimagnetism
• High-pressure studies
• Quantum phase transitions
• Spin-orbit coupling
• Van Hove singularity
• First-principles calculations