Polydopamine-mediated interface regulation and performance optimization of LLTO/PVDF-HFP composite solid electrolyte

Perovskite-structured Li 0.33 La 0.56 TiO 3 (LLTO) ceramic fillers are widely used for their low cost and environmental friendliness, yet their poor uniform dispersion in polymer matrices and inadequate interfacial compatibility between phases still limit performance. This study fabricated PDA@LLTO/PVDF-HFP composite electrolytes via solution casting, by modifying LLTO with a biodegradable polydopamine (PDA) coating. Dopamine undergoes oxidative self-polymerization on LLTO surfaces to form a PDA layer, whose excellent adhesion ensures firm binding to the LLTO surfaces, reducing filler surface energy and promoting uniform dispersion. Meanwhile, PDA’s phenolic hydroxyl and amino groups interact with PVDF-HFP’s fluorine and carbonyl groups via hydrogen bonding, electrostatic interactions, and physical entanglement, forming a strong interface. PDA reduces interfacial gaps and defects by acting as a “molecular bridge” to improve adhesion between the two phases. Results show the 2.4 wt%-PDA@LLTO/PVDF-HFP composite exhibits well-balanced electrochemical performance: an ionic conductivity of 2.37 × 10 −4 S cm −1 at 25 °C, an interfacial impedance reduced from 367 to 167 Ω, a lithium-ion migration number of 0.81, and an electrochemical stability window expanded to 4.88 V, The critical current density reaches 2.297 mA/cm 2 . The assembled solid-state full batteries deliver an initial discharge capacity of 168.59 mAh/g at 0.5 C, retaining 148.80 mAh/g (88.3% capacity retention) after 180 cycles, with Coulombic efficiency stabilized at 99.6% and significantly improved thermal stability. This work provides new insights for developing high-performance all-solid-state electrolytes, which hold promising applications.