Despite the high energy density of lithium metal batteries (LMBs), their application in rechargeable batteries is still hampered due to insufficient safety. Here, we present a novel flame-retardant solid-state electrolyte based on polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) with nano SiO₂ aerogel as an inert filler but Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) as an auxiliary component to enhance the ion conductivity. The introduction of SiO₂ aerogels imparts the polymer electrolyte with exceptional thermal stability and flame retardancy. Simultaneously, the interaction between hydroxyl groups of SiO₂ particles and PVDF-HFP creates a strong cross-linking structure, enhancing the mechanical strength and stability of the electrolyte. Furthermore, the presence of SiO₂ aerogel and LLZTO facilitates the dissociation of lithium salts through Lewis acid-base interactions, resulting in a high ionic conductivity of 1.01 × 10⁻³ S·cm⁻¹ and a wide electrochemical window of ~ 5.0 V at room temperature for the prepared electrolytes. Remarkably, the assembled Li|Li cell demonstrates the excellent resistance to lithium dendrite and runs stablly for over 1500 h at a current density of 0.25 mA·cm⁻². Thus, we prepare a pouch cell with high safety, which can work normally after short-circuiting under the external folding and cutting.

Metal-covalent organic frameworks (MCOF) as a bridge between covalent organic framework (COF) and metal organic framework (MOF) possess the characteristics of open metal sites, structure stability, crystallinity, tunability as well as porosity, but still in its infancy. In this work, a covalent organic framework DT-COF with a keto-enamine structure synthesized from the condensation of 3,3′-dihydroxybiphenyl diamine (DHBD) and triformylphloroglucinol (TFP) was coordinated with Cu²⁺ by a simple post-modification method to a obtain a copper-coordinated metal-covalent organic framework of Cu-DT COF. The isomerization from a keto-enamine structure of DT-COF to a enol-imine structure of Cu-DT COF is induced due to the coordination interaction of Cu²⁺. The structure change of Cu-DT COF induces the change of the electron distribution in the Cu-DT COF, which greatly promotes the activation and deep Li-storage behavior of the COF skeleton. As anode material for lithium-ion batteries (LIBs), Cu-DT COF exhibits greatly improved electrochemical performance, retaining the specific capacities of 760 mAh g⁻¹ after 200 cycles and 505 mAh g⁻¹ after 500 cycles at a current density of 0.5 A g⁻¹. The preliminary lithium storage mechanism studies indicate that Cu²⁺ is also involved in the lithium storage process. A possible mechanism for Cu-DT COF was proposed on the basis of FT-IR, XPS, EPR characterization and electrochemical analysis. This work enlightens a novel strategy to improve the energy storage performance of COF and promotes the application of COF and MCOF in LIBs.