Accurate prediction of excited states in battery electrolytes is crucial for understanding photostability, oxidative stability, and degradation. We employ hybrid quantum-classical algorithms—the Variational Quantum Eigensolver (VQE) for ground states and the quantum equation of motion (qEOM) for vertical singlet excitations to study LiPF₆, NaPF₆, LiFSI, and NaFSI.

Compact active spaces from frontier orbitals were mapped to qubits and reduced via symmetry tapering and commuting-group measurements to lower sampling cost. Within ~10-qubit models, VQE-qEOM agrees closely with exact diagonalization, while sample-based quantum diagonalization (SQD) in larger spaces recovers near-exact (subspace-FCI) energies.

Spectra show clear anion-cation trends within the VQE-qEOM framework:

• PF₆ salts: Higher first-excitation energies (LiPF₆ ≈ 13.2 eV) and a compact three-state cluster at 12-13 eV.
• FSI salts: Lower onsets (≈ 8-9 eV) with nearly degenerate S₁ and S₂ states and a higher S₃ separated by ~1.3 eV.

Independent TDDFT calculations yield systematically lower absolute excitation energies but reproduce the same anion- and cation-dependent trends, confirming that the relative ordering and physical interpretation of the quantum results are robust.

Replacing Li⁺ with Na⁺ narrows the gap by ~0.4-0.8 eV per anion family. Converting S₁ to wavelengths places onsets in the deep UV:

• LiPF₆: 94 nm
• NaPF₆: 100 nm
• LiFSI: 141 nm
• NaFSI: 148 nm

Results for isolated species or embedded clusters are NISQ-feasible, with solvent shifts incorporable via classical Δ-solvation. Current quantum algorithms capture excitation trends, advancing electrolyte design.