Enhanced lithium metal battery performance with a novel poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TrFE)-based separator incorporating a garnet-type filler

The instability of the electrolyte-electrode interphase remains a primary obstacle to realizing high-performance lithium metal batteries. To address this, we report a novel composite separator engineered via temperature-induced phase separation (TIPS), integrating Li 6.26 Al 0.24 La 3 Zr 2 O 12 (LALZO) garnet nanoparticles within a poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TrFE) matrix. The TIPS process enables uniform dispersion of sol-gel-synthesized LALZO particles (150–400 nm) and allows precise control over the separator's morphology, pore architecture, and porosity, without compromising the polymer's chemical or thermal stability. The garnet filler fundamentally enhances ion transport, with an optimal composite containing 4 wt% LALZO achieving a high ionic conductivity of 4.3 mS cm −1 and an elevated lithium-ion transference number of 0.43. When evaluated in Li||LiNi 0.6 Co 0.2 Mn 0.2 O 2 cells, this separator enables exceptional rate capability (discharge capacities of 185.8, 176.5, 165.2, and 129.8 mAh.g −1 at C/5, C/2, 1 C, and 2 C, respectively) and cycling stability, retaining 88.3 % capacity after 80 cycles at 1 C. Post-cycling analysis reveals that the LALZO nanoparticles promote the formation of a robust, inorganic-rich solid-electrolyte interphase (SEI), which stabilizes the lithium anode interface and significantly reduces interfacial resistance. This work demonstrates that microstructure engineering via TIPS is a powerful strategy for developing multifunctional separators that simultaneously enhance bulk transport and interfacial stability in lithium metal batteries. • LALZO/PVDF-TrFE membranes were developed for battery separator applications. • LALZO garnet ceramic with an average diameter of 150–400 nm was synthesized. • LALZO content affects the physical-chemical, and functional properties of membranes. • 4 wt% LALZO membranes showed 88.3 % capacity retention at 2C after 80 cycles. • This work proves the LALZO filler stabilizes the electrode and electrolyte interface.