Bioinspired Vascular Bundle Structured Nanocellulose/PVDF-HFP Composite Membranes for Efficient Ion Transport and Stable All-Solid-State Lithium Batteries

In-situ polymerization of solid-state polymer electrolytes is a promising approach for achieving mass production of all-solid-state batteries. However, inferior ionic conductivity and separator infiltration limit practical applications. Inspired by the nutrient-transporting vascular bundles in plants, a biomimetic fluorinated nanocellulose/PVDF-HFP porous composite membrane of stacked parallel nanocellulose bundles wrapped by PVDF-HFP sheaths is designed and prepared. The nanocellulose bundles assembled of fluorinated cellulose nanocrystals and cellulose nanofibers through shear-induced alignment create low-curvature ion transport channels, while the PVDF-HFP sheath facilitates lithium salt dissociation and reinforces structural stability. Benefiting from this bundle-sheath structure, the composite membrane exhibits excellent ionic conductivity, stability, and electrolyte wettability. The polymer electrolyte prepared with this composite membrane has a high ionic conductivity of 2.46 × 10^-4 S cm^-1 (30 °C), an electrochemical stability window (5.3 V), and cycle stability. Consequently, Li||LFP cells can retain a superior capacity of 77.48% after 1000 cycles at 1 C, and Li||NCM811 cells can maintain 83.94% capacity after 300 cycles at 0.1 C. Moreover, pouch cells can withstand temperatures up to 130 °C without thermal runaway. This biomimetic strategy provides a promising pathway to advance cellulose separators for high-performance all-solid-state batteries.