Surface-Functionalized LLZO-Incorporated Multilayer Composite Solid Electrolytes for Dendrite Suppression and...

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 Li₇La₃Zr₂O₁₂ (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.