Garnet-type solid electrolytes are the most promising materials available, which attract much attention, due to their high ionic conductivity, wide electrochemical window, and stability with lithium. However, some challenges such as surface stability, lithium dendrite penetration, and cost remain critical for its industrialization. This review focuses on the crystal structure and ion conduction mechanisms of garnet-type oxide solid electrolyte (Li₇La₃Zr₂O₁₂, LLZO) to investigate the formation mechanisms and removal strategies for surface passivation layers, including lithium carbonate and lithium hydroxide. For the lithium dendrite penetration of LLZO, potential solutions are explored in view of the black and surface properties electrolyte. For the industrialization, this review analyzes the cost optimization strategies for garnet-type solid electrolytes, aiming to provide valuable insights for industrial advancement.

Garnet-type oxide solid electrolytes hold a significant promise for solid-state batteries due to their high ionic conductivity and wide electrochemical window. However, large-scale production faces several challenges, i.e., 1) poor stability against air leading to the formation of lithium carbonate, 2) preventing the growth of lithium dendrites at the anode interface, and 3) high costs. These issues hinder the application of garnet-type all-solid-state batteries. Future development in garnet oxide solid electrolyte should focus on the following aspects. First, the surface alkalinity and the mechanism of lithium carbonate formation should be characterized accurately. It is crucial to contrude the excessive addition of lithium raw materials. While excess lithium can compensate for lithium losses during the heating and lead to lithium accumulation on the surface. Thus, a dynamic equilibrium must be established between the lithium supplement during sintering and the residual lithium on the surface. Furthermore, the formation of lithium carbonate is a dynamic process. Removing lithium carbonate is thus insufficient. Instead, it is indicated to convert lithium carbonate into a protective barrier that is both conductive to lithium ions and stable in air. Second, previous work proposed to mitigate the growth of lithium dendrites at LLZO/Li interface via incorporating the artificial solid electrolyte interphases (SEI) or buffer layers, which could facilitate a uniform electric field distribution and promote even lithium deposition at the interface. Moreover, the fabrication of highly densified LLZO represents an idea approach to alleviate the lithium dendrite growth. Third, , rare-earth elements are widely used for doping to improve the ionic conductivity, which increases the cost of raw materials. The existing low-cost element doping, such as Si, Fe, Ca and W, are developed. In addition, developing a low-carbon sintering method is also an important way to reduce the cost. All-solid-state lithium batteries show a great potential with the continuous research efforts.