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

Abstract 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.