Tailoring Cathode Interphase with Cyclic Ethers toward Stable Lithium‐Metal Batteries

Lithium‐metal batteries (LMBs) require stable electrode–electrolyte interphases to achieve long‐term cycling stability. Ether electrolytes are attractive for LMBs due to their excellent compatibility with lithium‐metal anodes. However, the influence of cyclic ether molecular structures on cathode interphase chemistry remains poorly understood. Here, we demonstrate that cyclic ether ring structure governs ring‐opening thermodynamics and thereby regulates cathode electrolyte interphase (CEI) formation and electrochemical durability. Two representative cyclic ethers, 1,3‐dioxolane (DOL) and 1,3‐dioxane (DOX), exhibit markedly different performance in Li||LiFePO 4 and Li||NCM811 cells through distinct interfacial reaction pathways. On LiFePO 4 cathodes, DOL forms a thin LiF‐rich inorganic–organic hybrid CEI, enabling 84.6% capacity retention after 1200 cycles. By contrast, DOX delivers superior stability on high‐voltage NCM811 by forming a more stable CEI. These findings establish interfacial reactivity matching as an important design principle for ether‐based electrolytes in LMBs.