Interplay among Metallic Interlayers, Discharge Rate, and Pressure in LLZO-Based Lithium–Metal Batteries

Solid-state electrolyte separators play a critical role in improving energy density, charging rate, and safety in next-generation batteries; however, controlling the interface between Li-metal and the separator continues to be challenging. Here, using a garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) ceramic solid electrolyte, we show that sputter-coated thin metallic interlayers (∼300 nm of gold) in combination with controlled discharge rates (0.3 mA/cm 2 ) and practical levels of external pressure (0.7 MPa) play vital roles in mitigating void formation during discharge. These metallic-interlayer, Li-metal full cells achieve a high charging rate capability (up to 2.5 mA/cm 2 ) and stable long-term cycling of 97.4% capacity retention at 500 cycles for ∼12 μm of Li-metal (2.5 mAh/cm 2 ). We report progressive changes in the metallic-interlayer morphology measured with ex situ and in situ methods, revealing that a discontinuous metal interlayer can facilitate hundreds of repeated electrochemical cycles without significant loss in cell energy. Our proposed mechanism suggests that the Li–gold alloy particles act as pinning and/or rewetting points for the Li-metal during discharge.