Solvent Effects on the Reversible Intercalation of Magnesium‐Ions into V₂O₅ Electrodes

Abstract

The choice for solvents in electrolyte solutions for non‐aqueous magnesium batteries is currently limited to ethers. However, the scientific community regularly uses acetonitrile (ACN) based electrolyte solutions as model systems in order to characterize new cathode materials for rechargeable Magnesium batteries. In this study, we demonstrated the effect of dimethoxyethane (DME), an important solvent for rechargeable magnesium systems, on the reversible intercalation of Mg2+ cations into thin, monolithic V2O5 films. The effect of DME on the intercalation kinetic have been examined via chronopotentiometry, galvanostatic and galvanostatic intermittent titration (GITT) measurements. In addition, we explored basic scientific questions related to the structure of ACN:DME based electrolyte solutions via Raman spectroscopy and surface chemistry of V2O5/Mg(ClO4)2/ACN:DME systems via X‐ray photoelectron spectroscopy. We found that addition of DME to the Mg(ClO4)2/ACN solution results in replacing the ACN‐Mg2+ cation by the more thermodynamically stable 3DME‐Mg2+ solvate structure. We also found that the DME‐Mg interaction forms stable solution structures that kinetically slow down the insertion of the Mg2+ cations into V2O5, compared with the less coordinated situation in solutions based solely on ACN.

Anode-Electrolyte Interfaces in Secondary Magnesium Batteries

“…Moreover, recent research found that DME, which is a very important solvent in non-aqueous Mg electrochemistry, has a negative impact on the intercalation of Mg ions into a V 2 O 5 cathode. 53 Clearly, integration of high-voltage cathode material with a magnesium metal anode in the appropriate electrolyte solution, to form a high-energy magnesium battery, is no trivial undertaking.…”

Rationally Designed Vanadium Pentoxide as High Capacity Insertion Material for Mg‐Ion

“…A stable open circuit voltage (OCV) of 3.42 V versus Li indicates complete oxidation of vanadium. [ 43 ] A typical cyclic voltammogram (CV) of V 2 O 5 spheres at 0.25 mV s −1 is shown in Figure S1 (Supporting Information). The CV curve shows two distinct reduction peaks at 3.34 V, and 3.14 V versus Li along with a shoulder peak at 3.08 V versus Li, indicating the reduction of V +5 into a mixture of V +4 and V +3 along with the formation of ε‐Li x V 2 O 5 and δ‐Li x V 2 O 5 .…”

“…Figure a displays the first galvanostatic charge/discharge profile of V 2 O 5 spheres that exhibit specific discharge capacity of 225 mA h g −1 with distinct and flat charge and discharge plateaus demonstrating significantly improved kinetics than previous reports. [ 26,37,43,46,47 ] Further in order to understand the charge/discharge mechanism, the differential capacity (d Q /d V ) is plotted versus voltage from the galvanostatic data (Figure 3b). During intercalation, two distinct peaks are observed that are positioned at ≈2.04 V (vs Mg/Mg +2 ) and ≈2.01 V (vs Mg/Mg +2 ), while during deintercalation, three peaks appear at 2.17 V (vs Mg/Mg +2 ), 2.18 V (vs Mg/Mg +2 ), and 2.20 V (vs Mg/Mg +2 ).…”

“…Based on the measurement conditions using magnesium perchlorate (MgClO 4 ) 2 in acetonitrile (AN) as electrolyte system and previous studies [ 43 ] to construct the 3‐electrode flooded cell, high surface area (2000 m 2 g −1 ) activated carbon (AC) cloth (507–20 type) procured from Kynol as quasi‐reference electrode (RE) and counter electrode (CE) was considered. Prior to use the AC, it was dried for 48 h at 100 °C under dynamic vacuum.…”

V2O5 as magnesium cathode material with extended cyclic stability

“…In this perspective, multivalent-ion technologies (Mg 2+ , Ca 2+ , Al 3+ ) have been proposed as replacements for Li-ion technology because they can store more charge per ion at the cathode, leading to larger energy density than the univalent ion batteries [3]. Among them, magnesium-ion batteries have attracted attention due to the high abundance of magnesium (1.94 %) [4], high volume specific capacity (3833 mAh cm -3 ) [5] and low reduction voltage (-2.37 V vs. SHE) [6].…”