The DC ionic conductivity σDC of all samples between -60 to 180 °C was determined from the frequency independent DC plateaus in the bode plot (cf Supplementary Note 6; Figure ). For LLZO-p, a room temperature bulk ion conductivity of σbulk,RT = 1.1 mS cm -1 could be determined. For LLZO-o the conductivity even slightly increased to σbulk,RT = 1.2 mS cm -1 . The increase in Li-ion conductivity may result from the increasing number of dopants on the Lisites (Ga + Co) associated with e.g., changes in structure, phase, and defects concentration. A further increase in the Co concentration leads, however, to significant drops by > 3 orders of magnitude to an ionic conductivity σbulk,RT = 7.60 × 10 -7 S cm -1 as observed in LLZO-b. This reduction could be related to a lowering in symmetry to the tetragonal garnet phase in certain regions of the crystal, which is like what has been reported for this phase previously. All samples follow Arrhenius-type behavior in accordance with σDC = A exp(-Ea/kBT), with A denoting the pre-exponential factor of the ionic conductivity σDC, Ea being the activation energy, the Boltzmann's constant and absolute temperature are given by kB and T, respectively. LLZO-p and LLZO-o, exhibit comparable activation energies of 0.30 eV and 0.34 eV. For LLZO-b a significant increase in the activation energy Ea = 0.54 eV was observed (see Figure ). In order to differentiate between Li-ion and electron conductivity, we performed DC polarization experiments on LLZO-p, LLZO-o, and LLZO-b (see Figure ). The electron conductivity σeon was calculated from the polarization current I by σe = I/Upol × h/A, where Upol dentotes the polarization potential with Upol = 100 mV and h and A being the thickness and the area of the samples. For LLZO-p, we calculated an electron conductivity of approximately σe = 2 × 10 -10 S cm -1 , which is in accordance with values reported by Philipp et al. No significant changes have been observed for LLZO containing Co, i.e., LLZO-o and LLZO-b (σe » 4 × 10 - 10 S cm -1 ). Interestingly, the ionic conductivity σ, the activation energy Ea and the electron conductivity σe, respectively, exhibited by LLZO-b and values published in literature for tetragonal LLZO are in a good agreement.