LLZO

LLZO, short for lithium lanthanum zirconate, is a garnet-structured solid electrolyte with the formula Li7La3Zr2O12. It has drawn substantial interest for solid-state lithium batteries due to its combination of relatively high lithium-ion conductivity, chemical stability against lithium metal, and a broad electrochemical window.

The material exists in two crystallographic phases: a tetragonal phase at room temperature in many undoped samples and a cubic phase that exhibits much higher ionic conductivity. Aliovalent doping (for example with gallium, aluminum, niobium, or tantalum) and specific processing conditions can stabilize the cubic phase, which yields markedly improved lithium conductivity.

Room-temperature ionic conductivity in doped cubic LLZO is typically in the 10^-4 to 10^-3 S/cm range, with performance strongly influenced by dopant, density, and grain boundary characteristics. LLZO is noted for a wide electrochemical window and stability against lithium metal, making it attractive for solid-state battery configurations. However, interfacial resistance with electrodes and sensitivity to moisture remain practical challenges.

Chemical stability under operating conditions is favorable relative to many other solid electrolytes, but LLZO surfaces react with water and CO2 to form surface layers such as LiOH and Li2CO3, necessitating careful handling, protective coatings, or controlled processing environments.

Synthesis methods include solid-state reactions, sol-gel routes, and other low-adsorption processes, typically requiring high-temperature sintering to achieve dense, crystalline ceramics. Ongoing research focuses on improving grain boundary transport, interfacial engineering, and scalable fabrication for commercial solid-state batteries.