Fe–Ti MOF functionalized electrospun PVDF-HFP separators with improved transport and dimensional stability for LiFePO4‖Li cells

Separator design can improve electrolyte wetting, ion transport and dimensional stability in lithium metal cells with LiFePO 4 cathodes. Here, an Fe–Ti metal–organic framework (MOF) was prepared by a solvothermal route and incorporated into poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membranes by electrospinning. The effects of filler loading were evaluated against pristine PVDF-HFP and a commercial Celgard separator. Among the investigated compositions, PVDF-HFP/MOF-10 exhibited an electrolyte contact angle of 18°, an ionic conductivity of 1.7 × 10⁻ 3 S cm⁻ 1 at 30 °C, and an apparent Li⁺ transference number of 0.56 under the Bruce–Vincent measurement protocol. The composite also showed improved thermal dimensional stability. Li‖Li cells operated for over 500 h at 1 mA cm⁻ 2 and 1 mAh cm⁻ 2 , while LiFePO 4 ‖Li cells retained 92.3% of their initial discharge capacity after 500 cycles at 1 C. These observations support the use of the composite separator for improving performance under the tested conditions. Adsorption calculations provide a possible molecular explanation for electrolyte affinity, but do not establish ion desolvation, selective anion immobilization or a unique bimetallic synergy in the operating electrolyte. The contribution is the integration and loading optimization of an Fe–Ti MOF within a porous PVDF-HFP separator, with the microscopic transport mechanism remaining to be resolved.