Rapid, high-temperature microwave soldering toward a high-performance cathode/electrolyte interface

Abstract Solid-state lithium batteries using inorganic electrolytes are expected to revolutionize energy storage systems due to their better safety and high energy density. However, their application is greatly hindered by the poor solid-solid interface between the solid-state electrolyte (SSE) and electrodes, particularly the cathode. Herein, we report a facile strategy to address the high cathode/SSE interfacial resistance through rapid, high-temperature microwave soldering. As a proof-of-concept demonstration, we soldered a garnet-type Li7La3Zr2O12 (LLZO) SSE with a V2O5 cathode, which feature high thermal stability and suitable melting temperatures. Our microwave soldering technique can selectively melt the surface of the granular V2O5 and rapidly form an intact and continuous cathode layer with tightly embedded carbon black nanoparticles, leading to a remarkable 690-time increase of the electronic conductivity of cathode. Additionally, the melted V2O5 cathode is conformally soldered to the garnet electrolyte, resulting in a 28-fold decrease of the cathode/garnet interfacial resistance (from 14.4 kΩ cm2to 0.5 kΩ cm2. As a result, this all-solid-state full cell displays a low overall resistance of 0.3 kΩ cm2 at 100 °C, which enables stable cyclability of the battery without the addition of liquid/polymer electrolyte. The fast microwave soldering strategy constitutes a significant step towards the development of the all-solid-state batteries.