A Self‐Healing, Flowable, Yet Solid Electrolyte Suppresses Li‐Metal Morphological Instabilities

Abstract Lithium metal (Li ⁰ ) solid‐state batteries encounter implementation challenges due to dendrite formation, side reactions, and movement of the electrode–electrolyte interface in cycling. Notably, voids and cracks formed during battery fabrication/operation are hot spots for failure. Here, a self‐healing, flowable yet solid electrolyte composed of mobile ceramic crystals embedded in a reconfigurable polymer network is reported. This electrolyte can auto‐repair voids and cracks through a two‐step self‐healing process that occurs at a fast rate of 5.6 µm h ⁻¹ . A dynamical phase diagram is generated, showing the material can switch between liquid and solid forms in response to external strain rates. The flowability of the electrolyte allows it to accommodate the electrode volume change during Li ⁰ stripping. Simultaneously, the electrolyte maintains a solid form with high tensile strength (0.28 MPa), facilitating the regulation of mossy Li ⁰ deposition. The chemistries and kinetics are studied by operando synchrotron X‐ray and in situ transmission electron microscopy (TEM). Solid‐state NMR reveals a dual‐phase ion conduction pathway and rapid Li ⁺ diffusion through the stable polymer‐ceramic interphase. This designed electrolyte exhibits extended cycling life in Li ⁰ –Li ⁰ cells, reaching 12 000 h at 0.2 mA cm ⁻² and 5000 h at 0.5 mA cm ⁻² . Furthermore, owing to its high critical current density of 9 mA cm ⁻² , the Li ⁰ –LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (NMC811) full cell demonstrates stable cycling at 5 mA cm ⁻² for 1100 cycles, retaining 88% of its capacity, even under near‐zero stack pressure conditions.