Suppressing Dendrites with Garnet–Polyimide Nanofiber Separators for Durable Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries (AFLMBs) are considered promising technologies for future storage applications, capable of achieving superior energy density in a streamlined cell design. Yet, their practical realization remains clouded by persistent challenges, including formation of lithium dendrites and limited cycling durability. Herein, we introduce a composite nanofiber separator composed of polyimide (PI) interwoven with garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZTO) fillers, fabricated via a one-step electrospinning method and subsequently underwent thermal imidization. The fabricated PI/LLZTO membrane forms a robust, three-dimensional fibrous network with well-distributed LLZTO particles. This architecture significantly improves both electrolyte uptake and mechanical strength, while forming a channel for continuous ion conduction that encourages uniform Li+ flux, one of the key factors in suppressing dendrite formation. The separator delivers high ionic conductivity, reaching 3.16 mS cm–1 with a measured Li+ transference number of 0.76. In Li symmetric cells, it enables remarkably stable cycling over 2900 h with an ultralow overpotential (∼0.007 V). When deployed in Cu||NMC622 AFLMB full cells, it delivers smooth and dendrite-suppressed lithium deposition behavior, with a first-cycle discharge capacity of 181 mAh g–1 and retaining 40% capacity after completing 100 charge–discharge cycles. In comparison, the commercial polypropylene separator retains 10% only. This work demonstrates how functional separator design, particularly anchored ceramic–polymer synergy, can unlock pathways toward stable, high-performance AFLMBs.