Hot-pressing at 1050°C lead to near theoretical density (∼98% relative density) tetragonal LLZO. The total conductivity value for dense tetragonal LLZO is ∼2.3×10−5 Scm−1. This is the highest reported value for tetragonal LLZO. This vast improvement in total conductivity is a result of the higher density achieved as a result of hot-pressing compared to conventional solid-state sintering. The value of the Li-ion lattice conductivity for dense tetragonal LLZO is 1.1×10−4 Scm−1. The microstructure of dense tetragonal LLZO consist of twins within the grains. It is suggested that the presence of twin boundaries adds a significant contribution to the total resistance.