Structural Evolution of Reversible Mg Insertion into a Bilayer Structure of V₂O₅·nH₂O Xerogel Material

Abstract

Functional multivalent intercalation cathodes represent one of the largest hurdles in the development of Mg batteries. While there are many reports of Mg cathodes, many times the evidence of intercalation chemistry is only circumstantial. In this work, direct evidence of Mg intercalation into a bilayer structure of V2O5·nH2O xerogel is confirmed, and the nature of the Mg intercalated species is reported. The interlayer spacing of V2O5·nH2O contracts upon Mg intercalation and expands for Mg deintercalation due to the strong electrostatic interaction between the divalent cation and the cathode. A combination of NMR, pair distribution function (PDF) analysis, and X-ray absorption near edge spectroscopy (XANES) confirmed reversible Mg insertion into the V2O5·nH2O material, and structural evolution of Mg intercalation leads to the formation of multiple new phases. Structures of V2O5·nH2O with Mg intercalation were further supported by the first principle simulations. A solvent cointercalated Mg in V2O5·nH2O is observed for the first time, and the 25Mg magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to elucidate the structure obtained upon electrochemical cycling. Specifically, existence of a well-defined Mg–O environment is revealed for the Mg intercalated structures. Information reported here reveals the fundamental Mg ion intercalation mechanism in a bilayer structure of V2O5·nH2O material and provides insightful design metrics for future Mg cathodes.

Nanobelts of Beta-Sodium Vanadate as Electrode for Magnesium and Dual Magnesium-Sodium Batteries

“…S2) and agree well with previous reports. 10 For both V 2 O 5 and Na 6 V 6 O 15 the average voltage is ca. 1.1 V vs. Mg/Mg 2+ , but the specific capacity values can be higher for nanobelts Na 6 V 6 O 15 .…”

“…3,8 Intercalation of magnesium into large particles of V 2 O 5 is a slow process, but decreasing the particle size can improve the capacity. 9, 10 Aurbach's group reported V 2 O 5 thin-film electrodes that can be cycled over a potential range of 2.2−3.0 V vs. Mg with a specific capacity of 150 mAh g −1 . 11 Sa et al, using bilayered V 2 O 5 · nH 2 O xerogel obtained a reversible capacity of about 50 mAh g −1 in the voltage region between ca.…”

“…0.1 and 3.0 V vs. Mg, and they found that Mg insertion is accompanied by cointercalation of solvent molecules (diglyme). 10 On the other hand, the hydrothermal synthesis can be a more successful approach to prepare nanomaterials in comparison with the ceramic method. 12 Yu et al reported the synthesis of single-crystals nanobelts of Na 2 V 6 O 16 .3H 2 O (s.g. P2 1 /m) using V 2 O 5 , NaF and hydrothermal conditions.…”

Water‐Lubricated Intercalation in V2O5·nH2O for High‐Capacity and High‐Rate Aqueous Rechargeable Zinc Batteries

“…[ [40][41][42] After heat treatment at 350 °C in vacuum for 2 h (VOG-350, without structural water), the peak corresponding to the interlayer spacing of 12.6 Å disappears. The triclinic phase (space group P1) was further refined by the Rietveld method with TOPAS 5.0.…”

Manganese Dioxide As Rechargeable Magnesium Battery Cathode

“…Chevrel phase and TiS2 showed good cyclability for Mg 2+ -intercalation but with limited energy densities due to the low voltages. Oxide cathodes generally have higher voltages but the reversible intercalation has only been achieved in V2O5, MoO3, and MnO2 at specific conditions (Gregory et al, 1990;Aubach et al, 2000;Gershinsky et al, 2013;Kim et al, 2015a;Nam et al, 2015;Sa et al, 2016;Sun et al, 2016). Among these materials, MnO2 had received perhaps the best attention not only due to the easiness to synthesis but also because the plentiful polymorphism and easily tuned electrochemical properties provide a good platform to gather fundamental knowledge about cathode chemistry.…”