Multilayer Separator-Driven interface stabilization and dendrite suppression for Long-Cycling lithium metal batteries

Lithium metal batteries (LMBs) offer a high theoretical capacity and low electrochemical potential. However, the uncontrolled growth of lithium dendrites and ongoing side reactions during cycling can lead to premature battery failure and increase the risk of thermal runway severely limiting their practical applications. In this work, we designed a multilayer separator composed of methanol-intercalated Li-Al hydrotalcite-like nanosheets with expanded layer spacing, sandwiched between electrochemically stable PVDF-HFP nanofiber membranes. This sandwiched configuration endowed the trilayer separator with exceptional thermal stability, mechanical strength, and electrolyte wettability. Furthermore, the Li-Al hydrotalcite-like nanosheets provided abundant active sites that acted as Lewis acids, interacting with the lithium salt anions to reduce the Li⁺ ions diffusion barrier, while the expanded interlayer spacing facilitated rapid ion transport. This improvement promoted the uniform Li⁺ deposition and effectively suppressed the lithium dendrites growth. As a result, the multilayer separator demonstrated an exceptional Li⁺ transference number (0.89) and high ionic conductivity (1.20 mS cm^-1). Notably, the Li symmetric cell employing the trilayer separator exhibited stable cycling for over 2800 h with significantly low voltage polarization (200 mV) at 10 mA cm^-2. Moreover, the Li||LiFePO₄ cell equipped with the trilayer separator maintained stable cycling for over 1000 cycles at 2C with a capacity retention of 91.6 %. This work provides new insights into designing functional separators with hierarchical porous channels aimed at extending the cycle life of LMBs.