Universal Anion-Interface-Confinement Strategy to Regulate Robust Solid-Electrolyte Interphase for Lithium Metal Batteries

The inherent high reactivity of lithium metal and the nonuniform deposition/stripping behavior of Li⁺ during the cycle lead to the deterioration of performance and safety risks of lithium metal batteries. Herein, we designed and fabricated a multifunctional ferroelectric (β-PVDF) composite separator with dipole directional arrangement. Detailed characterization indicates that the directional arrangement of negative dipoles caused by spontaneous polarization of ferroelectric coatings induces anion interface confinement and promotes the complete reduction of lithium salts, thereby constructing a robust solid-electrolyte interphase (SEI) rich in inorganic species on the Li metal anode surface. The SEI can ensure the uniform distribution and rapid migration of Li⁺ as well as high interface stability. As a result, the Li||Li symmetrical cell with ferroelectric composite separator achieves an ultralong cycle life of more than 4000 h at 2.5 mA/cm² to 2.5 mAh/cm². The full cell with a high mass loading (12 mg/cm²) of the LiFePO₄ cathode shows a high capacity retention of 96.84% after 960 cycles. This universal strategy may provide a perspective for regulating SEI chemistry by introducing functional coatings with multiphysical fields to regulate and limit anion migration.