Rational Design of High‐Entropy Garnet Electrolytes via Computational Screening for Stable Lithium Interfaces in All‐Solid‐State Batteries

All-solid-state lithium metal batteries offer enhanced safety and energy density by replacing flammable liquid electrolytes with solid-state electrolytes (SSEs). High-entropy (HE) SSEs, leveraging multi-principal-element compositions, present a vast design space to achieve exceptional ionic conductivity and electrochemical stability. However, the chemical complexity of HE SSEs introduces challenges in interfacial instability with lithium metal anodes due to the unavoidable inclusion of reactive elements. While conventional garnet-type SSEs are considered stable, it is revealed that five HE garnets (HE-LLZOs) undergo corrosion and partial dissolution upon lithium contact. Here, a rational design strategy is introduced to stabilize HE-LLZO by combining thermodynamic assessments of interfacial reactivity with targeted compositional engineering. Through systematic exploration of element-specific degradation mechanisms, selection criteria for lithium-compatible principal elements are established. Guided by computational screening, unstable dopants are excluded (e.g., Nb, Mo, W, Cr, Bi) that drive interfacial degradation and synthesize a novel HE-LLZO (Li_6.6La₃Zr_0.4Sn_0.4Hf_0.4Sc_0.2Ta_0.6O₁₂) that exhibits high ionic conductivity (3.69 × 10^-4 S cm^-1) and stable cycling over 2,500 h. X-ray photoelectron spectroscopy confirms the interfacial stability of Zr, Sn, and Ta while identifying Nb as a destabilizing element. This work provides an integrated computational-experimental framework for understanding element-property relationships in HE oxides, advancing durable SSEs design.