A Single-Layer Piezoelectric Composite Separator for Durable Operation of Li Metal Anode at High Rates

Piezoelectric ceramic and polymeric separators have been proposed to effectively regulate Li deposition and suppress dendrite growth, but such separators still fail to satisfactorily support durable operation of lithium metal batteries owing to the fragile ceramic layer or low-piezoelectricity polymer as employed. Herein, by combining PVDF-HFP and ferroelectric BaTiO₃, we develop a homogeneous, single-layer composite separator with strong piezoelectric effects to inhibit dendrite growth while maintaining high mechanical strength. As squeezed by local protrusion, the polarized PVDF-HFP/BaTiO₃ composite separator generates a local voltage to suppress the local-intensified electric field and further deconcentrate regional lithium-ion flux to retard lithium deposition on the protrusion, hence enabling a smoother and more compact lithium deposition morphology than the unpoled composite separator and the pure PVDF-HFP separator, especially at high rates. Remarkably, the homogeneous incorporation of BaTiO₃ highly improves the piezoelectric performances of the separator with residual polarization of 0.086 μC cm⁻² after polarization treatment, four times that of the pure PVDF-HFP separator, and simultaneously increases the transference number of lithium-ion from 0.45 to 0.57. Beneficial from the prominent piezoelectric mechanism, the polarized PVDF-HFP/BaTiO₃ composite separator enables stable cyclic performances of Li||LiFePO₄ cells for 400 cycles at 2 C (1 C = 170 mA g⁻¹) with a capacity retention above 99%, and for 600 cycles at 5 C with a capacity retention over 85%.