MOF/Carboxylated Cellulose Nanocrystal Separators Enable Multihub Ion Transport for High-Rate Lithium Battery

The performance of high-rate batteries is primarily constrained by inefficient ion transport across the separator/electrolyte interface. Commercial polyolefin separators depend on passive microporous diffusion and are unable to actively guide Li+ migration pathways, leading to concentration polarization, dendritic growth, and fast capacity decay. Herein, we present a hierarchical cooperative transport strategy that enables active guidance and directed migration of Li+ through the construction of a multihub, cross-scale "ionic highway". In this strategy, metal-organic frameworks (MOFs) and carboxylated cellulose nanocrystals (C-CNC) are integrated to exert a synergistic effect, leading to the design and fabrication of a poly(vinyl alcohol) (PVA)-based electrospun composite separator (PCUS). Nanoscale MOFs serve as the primary pathways for selective PF6- adsorption and facilitate Li+ solvation-shell regulation, thereby accelerating overall ion migration kinetics. Concurrently, abundant carboxyl groups on C-CNC serve as auxiliary hopping sites, lowering ion transport activation energy. Combined with the separator's inherent microporosity, these components establish hierarchical conduction paths from the nano- to microscale, significantly enhancing overall transport efficiency. The separator demonstrates a high ionic conductivity of 2.664 mS cm-1 and a Li+ transference number of 0.81. Assembled into Li|PCUS|LiFePO4 cells, it delivers 120.3 mAh g-1 at 5C, retaining 98.1% capacity over 300 cycles. NCM811|PCUS|Graphite full cell achieves a capacity retention of 95.9% at 1C/150 cycles. In addition, PCUS shows excellent dendrite suppression, enabling stable lithium deposition for over 2000 h at 0.2 mA cm-2. This work offers a rational design paradigm to address ion transport limitations and a sustainable route toward high-safety, long-lifespan energy storage.