Engineering Lithiophilic Silver Sponge Integrated with Ion- Conductive PVDF/LiF Protective Layer for Dendrite-Free and High- Performance Lithium Metal Batteries

Although lithium metal anode has attracted much attention as the "Holy Grail" because of its high specific capacity and the lowest reduction potential, its practical applications are largely hindered by the short circuit resulted from the unfavorable growth of lithium dendrites and the unstable interface caused by the parasitic reactions between the highly active lithium metal and the nonaqueous liquid electrolyte. Herein, a multifunctional bilayer structure integrating the spongelike lithiophilic Ag layer and the ion conductive polyvinylidene difluoride (PVDF)/LiF layer is fabricated for highperformance lithium metal anode. The porous lithiophilic Ag sponge layer provides abundant lithium nucleation sites and deposition space for the uniform growth of lithium, thereby endowing the compact deposition of lithium without the overgrowth of lithium dendrites. The ion-conductive and electronically insulating PVDF/LiF layer improves the lithium-ion transfer and guarantees the interface stability by suppressing the parasitic reactions between the lithium metal and the nonaqueous electrolyte. Moreover, the artificial PVDF/LiF layer can avoid the probability of unfavorable contact between dendrites and the cathode, even though the spongelike Ag layer is "swollen" by the Li metal. Therefore, the PVDF/LiF-Ag@Cu||Li half cell exhibits a more stable average Coulombic efficiency of similar to 98.2% and a longer cycle life than Cu||Li and Ag@Cu||Li half cells. Additionally, the symmetric cell of PVDF/LiF-Ag@Li||PVDF/LiF-Ag@Li exhibits a longer cycling time without short circuit and still retains a lower polarization of similar to 35 mV for at least 700 h than compared samples. The PVDF/LiF-Ag@Li||LiFePO4 full cell exhibits the longest cycle life, the best rate performance, and the highest capacity retention, especially with a high LiFePO4 mass loading of similar to 10 mg cm-2.