Optimization of the Li₃BO₃ Glass Interlayer for Garnet-Based All-Solid-State Lithium–Metal Batteries

Lithium (Li)-dendrite penetration and poor interfacial wetting between Li-metal anode and the solid electrolyte are two major potential drawbacks concerning the long-term performance of garnet-based solid-state Li-metal batteries (SSLBs). To address these problems, the amorphous Li3BO3 (LBO) glass interlayer in between Li anode and the solid electrolyte was demonstrated as a promising solution. However, this approach requires a thorough optimization to achieve effective performance and safety improve-ments in SSLBs. In this work, systematic design of experiments revealed optimal synthesis parameters stepwise to obtain a thin and uniform LBO interlayer in between Li6.4La3Zr1.6Ta0.6O12 (LLZT) solid electrolyte and Li anode by using a screen-printing technique. The investigated synthesis parameters included LBO slurry compositions, heating rates, heating temperatures, heating times, and cooling rates. As a result, a pinhole-free LBO glass layer with similar to 5 mu m thickness could be coated onto LLZT pellets. The resulting LBO interlayer enhanced Li-metal wetting and increased the interfacial conductivity from 1.32 x 10-4 (from LBO-free) to 1.06 x 10-3 S/cm. Electrochemical characterization of symmetrical cells revealed positive roles of the LBO interlayer such as (i) reducing interfacial impedance and offering uniform current flow across interfaces, (ii) preventing Li-dendrite penetration, and (iii) increasing the critical current density (CCD) and cycle life of SSLBs.