Abstract:

Due to its high energy density, high safety, wide working temperature range, and long service life, solid-state lithium metal battery has been one of the important development directions of next-generation lithium batteries. As a typical oxide solid electrolyte, Li₇La₃Zr₂O₁₂ (LLZO) presents high lithium-ion conductivity, wide electrochemical window, high mechanical strength, and good thermal stability. Thus, LLZO solid-state lithium metal batteries have attracted significant attention in academic and industrial fields. However, the possible formation of lithium dendrite through the solid electrolyte and the large interface resistance between electrolyte and electrode limit severely its practical deployment. These issues are correlated with the microstructural characteristics of LLZO electrolyte, the chemical and electrochemical compatibility between cathode and LLZO, the solid contact at the cathode/electrolyte interface, and the wettability of lithium anode with LLZO electrolyte. This study reviews the reported advancements and summaries the strategies to solve these problems. For the cathode, the compatibility between the positive electrode and LLZO, and interface resistance can be improved by means of the surface coating of the cathode active particles, the construction of 3D electrolyte interface, the introduction of a flexible polymer or gel electrolyte as interlayer, and composition of positive active particles with flexible or viscous ionic conductive materials. For the anode interface, eliminating the lithium carbonate on the surface of LLZO electrolyte, introducing reactive or flexible intermediate layer, and modulating the lithium anode composition can improve the wettability of lithium to LLZO electrolyte; thus, reducing the interface resistance. Finally, the future research direction and perspective of LLZO-based solid-state battery is proposed.

Key words: Li₇La₃Zr₂O₁₂, garnet-type solid electrolyte, solid-state battery, electrochemical window, interfaces