Exploiting the paddle-wheel mechanism for the design of fast ion conductors

As an indispensable component in solid-state devices, superionic conductors can exhibit liquid-like and exceptionally high alkali cation conductivity in their crystalline lattices. A fundamental understanding of the nature of superionic behaviour at the atomic level is crucial for exploiting this behaviour in new technologies such as solid-state batteries, but remains a major challenge. Studies of ion transport in numerous materials over the past three decades have provided insight into cation conduction mechanisms. These efforts have mainly emphasized the impact of the static framework on cation diffusivity, whereas the contribution from cation–anion interplay has been largely overlooked. However, recent reports have revealed intriguing observations of the influence of anion rotational dynamics on cation translational processes through the paddle-wheel mechanism. This Review aims to illuminate this rapidly evolving topic, providing a perspective and direction for future breakthroughs. We summarize the polyanion groups that exhibit anion rotational or reorientational features and describe the advanced techniques available for studying the interaction between cation diffusion and anion rotation. Moreover, we identify strategies to stabilize disordered superionic phases at room temperature, thus enabling the paddle-wheel mechanism to be exploited to achieve super-high conductivity in solid electrolytes.