Multivalent Ion Conduction in Inorganic Solids

Abstract

Multivalent ion-based batteries are the subject of substantial research interest as next generation battery technologies due to the potential for superior performance at a lower cost. A key fundamental process to their operation is the conduction of the multivalent ion in the solid state. Solid state conduction impacts the charge storage processes at the electrode materials, conductivity and stability of metal–electrolyte interfaces, and conductivity of potential solid state electrolytes. However, multivalent ionic conduction in inorganic solids has struggled to keep pace with the monovalent analogues because of the challenges posed by the high charge density. In this perspective, we discuss why it is difficult to conduct multivalent ions by considering electronic and structural properties of materials. Using literature reports, we highlight the specific challenges that arise from the high charge density of multivalent ions and consider strategies to address them. We discuss charge screening by electrons and water, the geometry of conduction pathways, the polarizability of the anions, the coordination environment, and the structural flexibility. We also highlight the difficulty in characterizing the conductivity of these unconventional working ions and emphasize the need for new characterization techniques to advance the field. Ultimately, we provide suggestions for structural factors that are likely to facilitate MV ion diffusion.

Ionic Dynamics of the Charge Carrier in Layered Solid Materials for Mg Rechargeable Batteries

“…Iton and See, reviewed the latest findings in inorganic solid-state conductors of Mg 2+ , Zn 2+ , and Ca 2+ and summarized generally high values of diffusion barriers (≥0.8 eV) from experimental and computational measurements. The authors also highlighted leveraging complex migration mechanisms as one of the strategies to overcome the challenge facing multivalent ion battery . Our simulation results demonstrate the promising role of cation–anion concerted motion in reducing the diffusion barrier of multivalent ions in solid materials for practical battery applications.…”

“…The authors also highlighted leveraging complex migration mechanisms as one of the strategies to overcome the challenge facing multivalent ion battery. 25 Our simulation results demonstrate the promising role of cation−anion concerted motion in reducing the diffusion barrier of multivalent ions in solid materials for practical battery applications.…”

“…AIMD does not require prior knowledge of the diffusion mechanism, but it comes with a high computational cost due to longer-scale dynamic simulations based on a first-principles approach. The challenges of using AIMD to study solid-state conduction of multivalent ions arise from their high charge density and strong Coulombic interactions with the anion sublattice, which results in sluggish diffusion through solid materials. − Owing to the high computational cost of AIMD simulation and the rare occurrence of multivalent ion hopping, we adopted learning on-the-fly molecular dynamics (LOTF-MD) driven by machine-learned interatomic potentials with automated density functional theory (DFT) retraining to capture the rare transition events of multivalent ions . A layered material, BiOCl, which has been characterized and computed as an effective Mg anode protection layer in our recent study, was selected as a representative host material for this investigation.…”

Pushing Forward Simulation Techniques of Ion Transport in Ion Conductors for Energy Materials

“…The physical quantity characterizing ionic movement in materials (i.e., in solids) is the “jump” diffusivity (or diffusion coefficient), D J of eq . ln ( D J ) = ln ( D * ) − ( E m k B T ) D * is a prefactor, E m is the energy of ionic migration, T is the temperature, and k B is the Boltzmann constant. The physical origins of D J and D * and related physical quantities have been extensively reviewed elsewhere. − Figure shows graphically the main elements enclosed by eq .…”

Impact of Structural Deformations on the Performance of Li-Ion Insertion Hosts

“…The classical picture of diffusion through the solid state depicts the migration of ions between empty interstices or vacancies in the lattice. , This hopping is strongly influenced by the nature of the bonding in the host framework because of electrostatic interactions that occur between the positively charged alkali ions and the negatively charged anions. − In layered oxides, the distortions that occur as lithium ions move in and out of a structure trigger substantial changes to the lattice due to the looser packing of the anions. Similarly, the framework of spinel LiMn 2 O 4 is known to undergo a Jahn–Teller distortion as Mn 4+ is reduced to Mn 3+ , which causes an elongation along the c -axis of the cubic cell and lowers the symmetry to the tetragonal polymorph of λ-MnO 2 …”