ABSTRACT Garnet‐type Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolytes exhibit high bulk ionic conductivity but suffer from poor interfacial compatibility with polymer matrices and lithium metal, due to surface Li 2 CO 3 formation and high interfacial resistance. Here, we construct a dual‐functional interfacial structure via sequential in situ phosphating and silane grafting. The phosphating forms a Li 3 PO 4 layer, which chemically bonded to LLZO with P─O─La covalent bonds, serving as an ionic bridge to lower Li + transport barriers. Silane grafting creates a flexible, cross‐linked network, transforming the filler surface from rigid to viscoelastic. The dual‐coated LLZO enables uniform dispersion in PEO/PAN blends, establishing continuous ionconducting pathways with a stress‐dissipative framework. This enables the composite electrolyte to achieve a high ionic conductivity of 2.82 × 10 −4 S cm −1 while exhibiting exceptional mechanical integrity. Li symmetric cells cycle stably for over 2000 h at 0.4 mA cm −2 , and cells coupled with LiFePO 4 or LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode deliver high‐capacity retention over extended cycling. This work elucidates a synergistic interface‑engineering mechanism where the inner Li 3 PO 4 layer optimizes ion transfer kinetics and the outer silane network ensures lithium dendrite suppression, collectively overcoming the long‑standing trade‑off between ionic conductivity and interfacial stability in garnet‑based composite solid‑state electrolytes.
Zhao et al. (Sun,) studied this question.