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Lithium transference in a multivalent electrolyte containing bulky, star-shaped anions is compared using three experimental techniques, namely, electrochemical polarization, PFG-NMR and electrophoretic NMR.

We demonstrate that contrary to previous reports, transference number decreases with increasing degree of polymerization in non-aqueous lithium-bearing polyelectrolyte solutions that have been proposed as next-generation battery electrolytes.

Antiperovskite structure compounds (X₃AB, where X is an alkali cation and A and B are anions) have the potential for highly correlated motion between the cation and a cluster anion on the A or B site. This so‐called “paddle‐wheel” mechanism may be the basis for enhanced cation mobility in solid electrolytes. Through combined experiments and modeling, the first instance of a double paddle‐wheel mechanism, leading to fast sodium ion conduction in the antiperovskite Na_3−xO_1−x(NH₂)_x(BH₄), is shown. As the concentration of amide (NH₂⁻) cluster anions is increased, large positive deviations in ionic conductivity above that predicted from a vacancy diffusion model are observed. Using electrochemical impedance spectroscopy, powder X‐ray diffraction, synchrotron X‐ray diffraction, neutron diffraction, ab initio molecular dynamics simulations, and NMR, the cluster anion rotational dynamics are characterized and it is found that cation mobility is influenced by the rotation of both NH₂⁻and BH₄⁻species, resulting in sodium ion conductivity a factor of 10²higher atx = 1 than expected for the vacancy mechanism alone. Generalization of this phenomenon to other compounds could accelerate fast ion conductor exploration and design.