Communication—Sol-Gel Synthesized Magnesium Vanadium Oxide, Mg_xV₂O₅· nH₂O: The Role of Structural Mg²⁺on Battery Performance

Abstract

Magnesium intercalated vanadium oxide xerogels, Mg 0.1 V 2 O 5 ·2.35H 2 O and Mg 0.2 V 2 O 5 ·2.46H 2 O were synthesized using an ion removal sol gel strategy. X-ray diffraction indicated lamellar ordering with turbostratic character. X-ray absorption spectroscopy indicated greater distortion of the vanadium-oxygen coordination environment in Mg In this report, Mg x V 2 O 5 ·nH 2 O were prepared by subtracting cations from a crystalline metal vanadate as an alternative strategy in order to adjust the cation amount, Figure 1a, different than the usual V 2 O 5 ·nH 2 O based sol-gel method.3 The as-prepared materials, x = 0.1 (MVO-1) and x = 0.2 (MVO-2), were characterized and electrochemical activity in lithium and magnesium electrolytes was determined. Post mortem analysis was done to determine the magnesium/vanadium ratio after cycling. Implications for use of Mg x V 2 O 5 ·nH 2 O in lithium and magnesium based batteries will be discussed, with particular focus on the structural role of Mg 2+ . ExperimentalSynthesis and characterization.-Mg x V 2 O 5 ·nH 2 O was synthesized via a sol gel process, 19 where aqueous magnesium vanadate (MgV 2 O 6 ) 20 was treated with an ion exchange resin. Characterization included X-ray diffraction (XRD), thermogravimetric analysis (TGA) and inductively-coupled plasma optical emission spectroscopy (ICP-OES).X-ray absorption spectroscopy (XAS) was acquired at the V Kedge (5.465 keV) in transmission mode at the National Synchrotron Light Source at Brookhaven National Laboratory. XAS scans of each sample and a V 2 O 5 reference were aligned to a vanadium foil measured simultaneously and merged in Athena, 21,22 and normalized utilizing AUTOBK. Theoretical FEFF6 23 models were created using orthorhombic V 2 O 5 crystal structure. 24 Distances are not corrected * Electrochemical Society Fellow. * * Electrochemical Society Member.z E-mail: esther.takeuchi@stonybrook.edu; kenneth.takeuchi.1@stonybrook.edu; amy.marschilok@stonybrook.edu for phase shifts, and are represented to be shorter than the actual interatomic distance.Electrochemical testing.-Working electrodes were prepared using Mg x V 2 O 5 ·nH 2 O, carbon and binder. The electrolytes were 1.0 M LiPF 6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) (v/v 30/70) and 0.5 M magnesium bis(trifluoromethylsulfonylimide) (Mg(TFSI) 2 )/0.5 M dipropylene glycol dimethyl ether (dipro-glyme) in acetonitrile. Cyclic voltammetry (CV) was conducted for Li based system at 2.0 to 4.0 V with lithium auxiliary and reference electrodes with a scan rate of 0.1 mV/s. In Mg 2+ containing electrolyte Ag/AgNO 3 reference and carbon auxiliary were used with voltage limits of −1.0 and +0.85 V using a scan rate of 0.1 mV/s. Two electrode lithium cells were used for galvanostatic cycling between 2.0-3.8 V at rates of 0.1 C and 0.5 C, with 1C set as 200 mA/g. In magnesium based electrolyte a 0.1 C rate for both discharge and charge was used,

Fervent Hype behind Magnesium Batteries: An Open Call to Synthetic Chemists—Electrolytes and Cathodes Needed

“…Va nadium oxides continue to receive substantial attention as possible Mg battery intercalation cathodes based on prior encouraging results,p rimarily with V 2 O 5 and particularly when water molecules are incorporated into the V 2 O 5 structure and/or in water-containing electrolytes.Y in et al [96] utilized as ol-gel/ion exchange process to synthesize Mg-intercalated vanadium oxide xerogels (Mg 0.1 V 2 O 5 ·x H 2 O where x = 2.35 and 2.46) and evaluated their performance in 0.5 m Mg(TFSI) 2 /0.5 m dipropylene glycol dimethyl ether/ acetonitrile.T he compound with x = 2.35 exhibited ar eversible capacity for Mg 2+ intercalation of about 140 mAh g À1 at adischarge voltage of about 3Vvs.Mg/Mg 2+ .T he structural Mg was found to remain in the material during cycling and all capacity was attributed to Mg 2+ intercalation/deintercalation. This interesting material should be evaluated using an electrolyte capable of reversible Mg anode electrochemistry, although migration of water molecules out of the cathode would be detrimental to the Mg electrode behavior.…”

“…Va nadium oxides continue to receive substantial attention as possible Mg battery intercalation cathodes based on prior encouraging results,p rimarily with V 2 O 5 and particularly when water molecules are incorporated into the V 2 O 5 structure and/or in water-containing electrolytes.Y in et al [96]…”

Controlling interlayer interactions in vanadium pentoxide-poly(ethylene oxide) nanocomposites for enhanced magnesium-ion charge transport and storage

“…Electrode materials with layered structures show significant potential as Mg-ion cathodes due to their ability to transport Mg-ions within the layers via different ion hopping mechanisms [27][28][29][30]. Among different types of layered metal oxides, vanadium pentoxide (V 2 O 5 ) has attracted a significant attention as a cathode material for Mg batteries [13,26,31,32]. Prior work has demonstrated that V 2 O 5 can reversibly insert and de-insert Mg-ions [13,26,33].…”

“…Crystalline V 2 O 5 evaluated with an electrolyte with low H 2 O levels exhibited very low Mg-ion capacities (~10-60 mAh g -1 ) [26]. V 2 O 5 gels can be synthesized via sol-gel chemistry from both inorganic and metal-organic precursors [31,34], and then dried under ambient conditions to form xerogels or supercritically dried to form aerogels.…”

“…with n typically 1.6-2.0) [34] composed of V 2 O 5 layers and structural interlayer H 2 O have shown to possess among the highest Mg-ion capacities and rate capabilities of V 2 O 5 materials [12,22,31]. Recent characterization of the structural changes that occur during reversible Mg-ion insertion into hydrated V 2 O 5 xerogels showed that Mg-ions and solvent molecules co-intercalate between V 2 O 5 layers which alters the interlayer spacing [22].…”