Elucidating the Role of Anion Groups in Lithium-Ion Diffusion

Since the 1960s, the paddlewheel effect has been proposed as a way to enhance lithium-ion diffusion in inorganic materials by using rotor-like anion groups to assist lithium-ion movement( 1 – 5 ). However, so far the physical mechanism behind how anion-group dynamics affect lithium-ion diffusion has not been clearly understood. In this talk, we clearly define various types of rotational motions of anion-groups. Based on such definition, we detect and differentiate such distinct anion-group rotational motions throughout a total of 10’s of ns ab-initio molecular dynamics trajectories. By performing rigorous statistical analysis of various rotational events as well as lithium-ion diffusion events, we reveal how each type of anion rotational motions are related to lithium-ion diffusion. Our research has finally resolved the ongoing debate about the existence of the paddlewheel effect and provide a clear physical understanding of how anion-group rotations are related to fast ionic diffusion in inorganic materials. L. Karlsson, R. L. McGreevy, Mechanisms of ionic conduction in Li2SO4 and LiNaSO4: Paddle wheel or percolation? Solid State Ionics . 76, 301–308 (1995). A. Kvist, A. Lundén, Electrical Conductivity of Solid and Molten Lithium Sulfate. Zeitschrift Für Naturforschung . 20, 235–238 (1965). Z. Zhang, L. F. Nazar, Exploiting the paddle-wheel mechanism for the design of fast ion conductors. Nat Rev Mater , 1–17 (2022). J. G. Smith, D. J. Siegel, Low-temperature paddlewheel effect in glassy solid electrolytes. Nat Commun . 11, 1483 (2020). M. Jansen, Volume Effect or Paddle‐Wheel Mechanism—Fast Alkali‐Metal Ionic Conduction in Solids with Rotationally Disordered Complex Anions. Angewandte Chemie Int Ed Engl . 30, 1547–1558 (1991).