Thin Yet Strong Composite Polymer Electrolyte Reinforced by Nanofibrous Membrane for Flexible Dendrite-Free Solid-State Lithium Metal Batteries

Abstract

Composite polymer electrolytes (CPEs) are promising for the realization of solid-state lithium metal batteries (SSLMBs) with high energy density and safety. However, CPEs suffer from insufficient ionic conductivity and low mechanical strength at thin films. Herein this study, a porously nanofibrous Li7La3Zr2O12 (LLZO)/polyacrylonitrile (PAN) substrate prepared by electrospinning is filled with polyethylene oxide (PEO)/lithium salt (LiTFSI) to form LLZO/PAN/PEO/LiTFSI (LPPL) CPEs. The robust LLZO/PAN nanofibrous membrane mechanically supports the soft PEO/LiTFSI, while the dispersed LLZO together with the PEO/LiTFSI forms a dual Li+ conductive pathway. Benefiting from the great synergies between the building blocks, the obtained LPPL CPEs possess a high tensile strength (8.2 MPa) with a thickness of only 20 μm, resulting in a good ionic conductivity. In addition, the LPPL CPEs also exhibit a wide electrochemical window (5.5 V), high thermal stability, and excellent stability with lithium metal. As a result, the LiFePO4 (LFP)/LPPL/Li SSLMBs show good rate capability and cycling stability (100.5 mA h g−1@1.0 C after 430 cycles) at 60 °C. In addition, the soft-packaged LFP/LPPL/Li SSLMBs demonstrate high safety under destructive conditions such as bending and cutting. Moreover, the LPPL CPEs are also applicable to the SSLMBs with high-energy LiNi0.8Co0.1Mn0.1O2 (NCM811) or high-capacity sulfur cathodes.