Constructing Li-Rich Artificial SEI Layer in Alloy–Polymer Composite Electrolyte to Achieve High Ionic Conductivity for All-Solid-State Lithium Metal Batteries

To achieve high ionic conductivity for solid electrolyte, an artificial Li-rich interface layer of about 60 nm thick has been constructed in polymer-based poly(ethylene oxide)-lithium bis(trifluoromethanesulfonyl)imide composite solid electrolyte (briefly noted as PEO m ) by adding Li-based alloys. As revealed by high-resolution transmission electron microscopy and electron energy loss spectroscopy, an artificial interface layer of amorphous feature is created around the Li-based alloy particles with the gradient distribution of Li across it. Electrochemical analysis and theoretical modeling demonstrate that the interface layer provides fast ion transport path and plays a key role in achieving high and stable ionic conductivity for PEO m -Li 21 Si 5 composite solid electrolyte. The PEO m -5%Li 21 Si 5 composite electrolyte exhibits an ionic conductivity of 3.9 × 10 –5 S cm −1 at 30 ° C and 5.6 × 10 −4 S cm −1 at 45 ° C. The LiFePO 4 | PEO m -5%Li 21 Si 5 | Li all-solid-state batteries could maintain a stable capacity of 129.2 mA h g −1 at 0.2 C and 30 ° C after 100 cycles, and 111.3 mA h g −1 after 200 cycles at 0.5 C and 45 ° C, demonstrating excellent cycling stability and high-rate capability.