A review on the problems of the solid state ions diffusion in cathodes for rechargeable Mg batteries

Abstract

This work summarizes the results of our studies devoted to Mg ions mobility in Chevrel phases (CPs), M x Mo 6 T 8 (M -metal, T = S, Se) and presents our vision of the problem of multivalent ions' diffusion in intercalation compounds. A simplified analysis of the main factors, which affect the activation energy barriers, as well as experimental data of Mg ions insertion into different hosts, show that low Mg ions mobility in common transition metal oxides or sulfides cannot be explained only by strong ionic interactions, but it is rather caused by a hard redistribution of the bivalent cations charge in inorganic materials. In contrast to these hosts, CPs allow for a high mobility of multivalent cations, because their unusual crystal structure with octahedral Mo 6 -clusters enables a fast and efficient attainment of local electro-neutrality upon insertion of cations of high charge density. Analysis of diffusion pathways based on the detailed structural determinations sheds light on important aspects of the electrochemical behavior of CPs, such as partial Mg ions trapping in the course of reversible Mg insertion and the ways to avoid it.

Manganese Dioxide As Rechargeable Magnesium Battery Cathode

“…It was proposed to introduce species to screen the polarization of Mg 2+ ions (Levi et al, 2009). One of the screening agents was water.…”

“…The challenge to find suitable rMB cathode is widely believed to be a consequence of bivalency of Mg 2+ (Levi et al, 2009(Levi et al, , 2010Yoo et al, 2013;Huie et al, 2015;Ling and Suto, 2017), which not only dramatically reduces the mobility of Mg 2+ but also generates other undesirable effects Zhang and Ling, 2016b;Ling and Suto, 2017). To date, reversible electrochemical Mg 2+ -intercalation was only achieved in a few cathode hosts.…”

Tuning the interlayer of transition metal oxides for electrochemical energy storage

“…MoO 3 hydrates are isostructural with the tungsten oxide hydrates. , which is due to (i) the Coulombic repulsion between the framework transition metals and the diffusing Mg 21 ions, (ii) the need for a transition metal to accept 2e À , which results in an increase in the ionic radius and thus unit cell volume, 70 and (iii) the strong solvation 71 and anion coordination 49 of Mg 21 , which raises the activation energy for charge-transfer at the electrode/electrolyte interface.…”

Electrochemical Properties of Heterosite FePO4 in Aqueous Mg2+ Electrolytes

“…[2][3][4] For example, the Chevrel phase Mo 6 T 8 (T = S and Se) shows fast and reversible Mg 2+ intercalation, because multiple electrons can be accommodated with delocalized orbital of a Mo 6 T 8 cluster to relieve the local structure deformation. 4 and an important host electrode material because of the intercalation capability with various monovalent cations as guest species.…”

“…[2][3][4] For example, the Chevrel phase Mo 6 T 8 (T = S and Se) shows fast and reversible Mg 2+ intercalation, because multiple electrons can be accommodated with delocalized orbital of a Mo 6 T 8 cluster to relieve the local structure deformation. 4 and an important host electrode material because of the intercalation capability with various monovalent cations as guest species. 15,16 Herein, we clarify the electrochemical reaction mechanism of FePO 4 with Mg 2+ in aqueous electrolyte by ex-situ Mössbauer spectroscopy, X-ray diffraction experiments, and ab-initio calculation.…”