Deep Eutectic Interlayer Design for Stability Enhancement in LLZTO Solid‐State Lithium Batteries

Abstract Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is a typical inorganic garnet‐type ceramic solid electrolyte. By combining LLZTO with polyacrylonitrile (PAN), a homogeneous composite electrolyte film can be obtained, which is self‐supporting and can be directly used as a solid‐state electrolyte. However, PAN and its composite electrolyte exhibit low ionic conductivity at room temperature and suffer from poor solid‐solid interface contact with the lithium metal anode. Herein, a method of using succinonitrile (SN) deep eutectic electrolyte is proposed to modify the solid‐state electrolyte interface, thereby preventing corrosion reactions and improving the Li + transference number of the composite solid electrolyte (PALS) to 0.66. The introduction of the interface modification layer enables the formation of a stable and dense solid‐electrolyte interphase (SEI) layer at the interface between the lithium anode and the solid‐state electrolyte, reducing interfacial impedance and improving the ionic conductivity of the solid‐state electrolyte. The Li/PALS/lithium iron phosphate (LFP) full cell exhibits an initial specific capacity of 147 mAh·g −1 at a 0.5 C rate, with 97.3% capacity retention after 190 cycles at room temperature. This work presents a novel approach to improving the interfacial contact between LLZTO and lithium metal anode, offering new insights for the design of fast‐rate, safe, and durable solid‐state electrolytes.