Developing batteries with high energy density, safe operation, low cost, and long life is vital for successful implementation of lithium-ion batteries in the automotive industry. The replacement of the organic liquid electrolytes with nonflammable solid electrolytes in lithium-ion batteries improves safety, offer higher volumetric and gravimetric energy densities, and potentially lower the cost of the battery by increasing the battery life, decreasing the dead space in the battery pack, and simplifying the packaging.

Garnet-type cubic Li₇La₃Zr₂O₁₂ (c-LLZO) has emerged as a promising candidate for solid electrolytes due to its high ionic conductivity (up to ~1 mS/cm at room temperature), good chemical stability against lithium metal, and wide electrochemical stability window. Defect chemistry of this class of materials, yet less studied, is critical to the understandings of the ionic nature of conductivity and the electrode-electrolyte interfacial resistance. In this study we will discuss the defect chemistry of c-LLZO, i.e., the formation of ionic defects and defect pairs as well as their impact on the electrical properties of c-LLZO. The contribution of grain boundaries to the electrical conductivity of polycrystalline samples will also be presented.