A Binder-Free MOF-Based Separator Enabling Highly Selective Ion Sieving in Lithium-Ion Battery

The separator is an indispensable component in batteries. However, the commercial polyolefin separator remains severely hindered by sluggish ion transport and the uncontrollable lithium dendrites. Herein, a novel separator free of binder was successfully fabricated via a facile in situ growth strategy, featuring a dense metal–organic framework (MOF, i.e., HKUST-1) layer integrated onto a flexible porous polyvinylidene fluoride (PVDF) substrate. This design synergistically utilizes the ordered porous channels of HKUST-1 for fast, uniform Li+ migration and its abundant unsaturated metal sites to anchor PF6– anions via Lewis acid–base interactions. Consequently, this dual functionality promotes lithium salt dissociation, yielding superior ionic conductivity (0.29 mS cm–1) and Li+ transference number (tLi+ = 0.71). Moreover, the composite separator exhibits remarkable electrochemical performance. The Li||NCM811 cell maintains an impressive capacity retention of 78.8% after 300 cycles at 1 C (4.5 V cutoff). Additionally, the HKUST-1@PVDF separator enables excellent rate capability and robust cycling stability for Li||LFP cells (98.4% capacity retention after 500 cycles at 2 C). Its ionic sieving capability promises its general permselective applicability to control Li+ plating/stripping behavior. Our approach paves a promising pathway in developing permselective separator technologies with high energy density and long-life cyclability.