KyuJung Jun1,Byungju Lee2,Ronald Kam1,Gerbrand Ceder1
University of California, Berkeley1,Korea Institute of Science and Technology2
KyuJung Jun1,Byungju Lee2,Ronald Kam1,Gerbrand Ceder1
University of California, Berkeley1,Korea Institute of Science and Technology2
Since the 1980s, the paddlewheel effect has been proposed as a mechanism to boost lithium-ion conductivity in inorganic materials by using rotating anion groups to assist lithium-ion migrations (<i>1</i>–<i>5</i>). However, to this date, the physical mechanism behind how anion-group dynamics affect lithium-ion diffusion has not been clearly quantified. In this work, we define three types of rotational motions of anion-groups. To detect and differentiate various types of rotational motions, we track rotational motion of anion groups using quaternion-based representations. By applying a quaternion-based algorithms throughout a total of 10’s of ns ab-initio molecular dynamics trajectories of various types of superionic conductors and performing rigorous statistical analysis of various rotational events as well as lithium-ion diffusion events, we reveal how each type of anion rotational motion is related to lithium-ion diffusion. Our work resolves the ongoing debate about the existence of a paddlewheel effect and provides a clear mechanistic understanding of how anion-group rotations are correlated to fast ionic diffusion in inorganic materials.<br/><br/>1. L. Karlsson, R. L. McGreevy, Mechanisms of ionic conduction in Li2SO4 and LiNaSO4: Paddle wheel or percolation? <i>Solid State Ionics</i>. 76, 301–308 (1995).<br/>2. A. Kvist, A. Lundén, Electrical Conductivity of Solid and Molten Lithium Sulfate. <i>Zeitschrift Für Naturforschung</i>. 20, 235–238 (1965).<br/>3. Z. Zhang, L. F. Nazar, Exploiting the paddle-wheel mechanism for the design of fast ion conductors. <i>Nat Rev Mater</i>, 1–17 (2022).<br/>4. J. G. Smith, D. J. Siegel, Low-temperature paddlewheel effect in glassy solid electrolytes. <i>Nat Commun</i>. 11, 1483 (2020).<br/>5. M. Jansen, Volume Effect or Paddle-Wheel Mechanism—Fast Alkali-Metal Ionic Conduction in Solids with Rotationally Disordered Complex Anions. <i>Angewandte Chemie Int Ed Engl</i>. 30, 1547–1558 (1991).