We investigated the fundamental Li diffusion mechanism in LNCl using AIMD simulations. We found that Li diffuses through the edge of edge-sharing tetrahedral Li sites. The affinity for jumps between two Li sites depends on the N/Cl-composition of the tetrahedra enclosing the Li sites and of the bottleneck-edge composition. We found that jumps into Cl4 Li sites and jumps through Cl-Cl edges have the largest Ea, jump values indicating that they are unfavorable compared to other jump events. Our EIS experiments confirmed the previously reported Li conductivity of 1•10 -3 mS cm -1 and an Ea of 0.47 eV. Much faster Li motion was detected with Li NMR (>0.1mS cm -1 ) with a lower Ea ~0.25 eV. We propose that the fast Li motion may arise from readily occurring jumps with low Ea, jump values and that the long-range conductivity probed by EIS is limited by jumps with large Ea,jump values. Introducing a 4h mechanochemical milling step after solid state synthesis improves the RT conductivity of LNCl by an order of magnitude to 0.01 mS cm -1 and lowers the activation energy to 0.42 eV. It was shown that LNCl can be synthesized mechanochemically without any annealing step and these samples reached conductivities of 0.015 mS cm -1 . Re-annealing of milled LNCl samples at 600 °C eliminates the beneficial effects of milling as the conductivity is reduced and the activation energy increased to values obtained for non-milled samples.