Novel Structural Motif To Promote Mg-Ion Mobility: Investigating ABO₄ Zircons as Magnesium Intercalation Cathodes

Abstract

There is an increasing need for sustainable energy storage solutions as fossil fuels are replaced by renewable energy sources. Multivalent batteries, specifically Mg batteries, are one energy storage technology that researchers continue to develop with hopes to surpass the performance of Li-ion batteries. However, the limited energy density and transport properties of Mg cathodes remain critical challenges preventing the realization of high-performance multivalent batteries. In this work, ABO4 zircon materials (A = Y, Eu and B = V, Cr) are computationally and experimentally evaluated as Mg intercalation cathodes. Remarkably good Mg-ion transport properties were predicted and Mg-ion intercalation was experimentally verified in sol–gel synthesized zircon YVO4, EuVO4, and EuCrO4. Among them, EuVO4 exhibited the best electrochemical performance and demonstrated repeated reversible cycling. While we believe that the one-dimensional diffusion channels and redox-active species tetragonal coordination limit the value of many zircons as high-performance cathodes, their unique structural motif of overlapping polyhedra along the diffusion pathway appears instrumental for promoting good Mg-ion mobility. The motif results in a favorable “6-5-4” change in coordination that avoids unfavorable sites with lower coordination along the diffusion pathway and a structural design metric for future Mg cathode development.

First-Principles and Experimental Investigation of ABO4 Zircons as Calcium Intercalation Cathodes

“…On average, the discharged state energy above the hull values of Ca 0.25 AVO 4 and Ca 0.25 ACrO 4 are 82 and 86 meV/atom lower than those of Ca 0.5 AVO 4 and Ca 0.5 AVO 4 , respectively. The poor stability values calculated for Ca 0.5 ABO 4 are consistent with the work previously done for Mg zircon cathodes . Some of the Ca 0.5 ABO 4 zircons have energy above the hull values exceeding 200 meV/atom, which suggests that there is a strong driving force for these compounds to decompose into more stable phases.…”

“…This family of tetragonal materials (space group I 4 1 / amd ) with the ABO 4 zircon-type structure spans a large chemical space and consists of alternating edge-sharing AO 8 dodecahedra alongside BO 4 tetrahedra that form one-dimensional channels . In this work, metastable Ca 2+ intercalation sites and percolating migration pathways were identified in the zircon channels (Figure ) using an insertion algorithm and graph-based migration analysis developed by Shen et al These linear migration pathways for Ca 2+ consisting of 1.6 Å characteristic hops are consistent with the interstitial sites previously reported in magnesiated and unmagnesiated zircons. , In this work, 18 ABO 4 zircon materials are theoretically evaluated as potential Ca cathode candidates (A = [Bi, Dy, Er, Eu, Ho, La, Nd, Pr, Sm, Tb, Y], B = [Cr, V]). Remarkably low Ca 2+ migration barriers in the defect-free structures are confirmed across all compositions, with the lowest barrier being 113 meV in YVO 4 .…”

Zircon Structure as a Prototype Host for Fast Monovalent and Divalent Ionic Conduction

“…These sites are symmetrically equivalent, and the intersite distance is very short, about 1.5 Å, a unique feature of this structural family. Recently multiple compositions in this material family were proposed as cathode materials for Mg-ion batteries, showing reversible cycling in electrochemical tests and extremely favorable intrinsic mobility for Mg …”

“…These sites are symmetrically equivalent, and the intersite distance is very short, about 1.5 Å, a unique feature of this structural family. Recently multiple compositions in this material family were proposed as cathode materials for Mg-ion batteries, showing reversible cycling in electrochemical tests and extremely favorable intrinsic mobility for Mg. 51 In this work, the conduction of multiple mobile species including Na + , Ca 2+ , Mg 2+ , and Zn 2+ in pristine and doped YPO 4 is investigated through first-principles calculations. Nudged elastic band calculations show very low diffusion barriers for Na/Ca/Mg/Zn in pristine YPO 4 , and ab initio molecular dynamics simulations confirm the 1D percolating diffusion channel in the zircon-type framework.…”

Ion Mobility in Crystalline Battery Materials

“…Therefore, we limited ourselves to the materials classes of spinels, olivines, garnets, perovskites, Prussian blue, Chevrel phase, layered oxides, NASICONs, halides, and anion migration systems. We are aware of the plethora of other materials out there, such as postspinels, [94] weberites, [95] zircons, [96] borates, [97] V 2 O 5 , [98] and 𝛼-MoO 3 . [99,100]…”