  Solid-state superionic conductors (SSICs) are promising alternatives to
liquid electrolytes in batteries and other energy storage technologies. The
rational design of SSICs and ultimately their deployment in battery
technologies is hindered by the lack of a thorough understanding of their ion
conduction mechanisms. In SSICs containing molecular ions, rotational dynamics
couple to translational diffusion to create a 'paddle-wheel' effect that
facilitates conduction. The paddle-wheel mechanism explains many important
features of molecular SSICs, but an explanation for ion conduction and
anharmonic lattice dynamics in SSICs composed of monatomic ions is still
needed. We predict that ion conduction in the classic SSIC AgI involves
'electronic paddle-wheels,' rotational motion of lone pairs that couple to and
facilitate ion diffusion. The electronic paddle-wheel mechanism creates a
universal perspective for understanding ion conductivity in both monatomic and
molecular SSICs that will create design principles for engineering solid-state
electrolytes from the electronic level up to the macroscale.
