Surface‐Functionalized LLZO‐Incorporated Multilayer Composite Solid Electrolytes for Dendrite Suppression and Efficient Ionic Conduction in Lithium–Metal Batteries

ABSTRACT The development of solid polymer electrolytes is central to safe, high‐energy lithium‐metal batteries (LMBs); however, persistent challenges including dendritic‐lithium‐growth, interfacial instability, and low ionic‐conductivity impede their commercialization. Herein, we report a tri‐layered composite solid electrolyte (CSE) that couples interfacial engineering with mechanical‐reinforcement to address them. The outer layers consist of PEO/LiTFSI, while inner layer comprises a PEO/LiTFSI matrix reinforced with polydopamine‐coated Li 7 La 3 Zr 2 O 12 (PDA@LLZO, 10–40 wt%) and poly(ethylene glycol)‐block‐poly(propylene glycol)‐block‐poly(ethylene glycol) (PPP). The PDA coating promotes strong hydrogen‐bonding with PEO‐matrix, leading to uniform dispersion and reduced interfacial resistance. LLZO enables percolated Li + ‐transport channels and disrupts PEO crystallinity, advancing segmental dynamics. Simultaneously, PPP elastomers offer mechanical compliance, redistribute localized stress, and dissipate dendritic intrusions to suppress crack propagation. The optimized CSE‐30 (30 wt% PDA@LLZO) exhibits an ionic‐conductivity of 5.60×10 −3 S cm − 1 at 60°C and 8.04 × 10 −5 S cm − 1 at 25°C, nearly four‐times higher than PEO, with a Li + ‐transference number of 0.81 and anodic stability up to 5.6 V vs. Li/Li + . In Li/LFP full cells, CSE‐30 delivered a capacity of 133.6 mAh g − 1 at 0.5C with 80% retention after 1000 cycles and Li/Li symmetric cells sustained over 1000 h cycling without short‐circuiting. This multifunctional CSE design advances next‐generation solid‐state LMBs by integrating efficient Li + ‐transport and mechanical resilience.