In Operando Synchrotron Diffraction and in Operando X-ray Absorption Spectroscopy Investigations of Orthorhombic V₂O₅ Nanowires as Cathode Materials for Mg-Ion Batteries

Abstract

Orthorhombic V2O5 nanowires were successfully synthesized via a hydrothermal method. A cellconfiguration system was built utilizing V2O5 as the cathode and 1 M Mg(ClO4)2 electrolyte within acetonitrile, together with MgxMo6S8 (x ≈ 2) as the anode to investigate the structural evolution and oxidation state and local structural changes of V2O5. The V2O5 nanowires deliver an initial discharge/charge capacity of 103 mAh g-1 /110 mAh g-1 and the highest discharge capacity of 130 mAh g-1 in the 6 th cycle at C/20 rate in the cell-configuration system. In operando synchrotron diffraction and in operando X-ray absorption spectroscopy together with ex situ Raman and X-ray photoelectron spectroscopy reveal the reversibility of magnesium insertion/extraction and provide the information on the crystal structure evolution and changes of the oxidation states during cycling.

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

“…The shear motion of the ladder and rotation of the ladder is characterized by the B 1 g and B 2 g modes. [ 40 ] The peak positions are well consistent to previous studies on orthorhombic V 2 O 5 , [ 16,26 ] validating the XRD results. The claim and surface analysis is further preciously mapped through the elemental and compositional information via X‐ray photoelectron spectroscopy (XPS).…”

“…The pattern discards the possibility of any lattice water content as it differs significantly from hydrated V 2 O 5 . [ 26 ]…”

“…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 ).…”

“…The irreversible γ phase belongs to the same crystal structure with [VO 5 ] square pyramid but even higher puckered interlayers, whereas the ω phase belongs to tetragonal structure with completely different atomic arrangement than that of orthorhombic V 2 O 5 . [ 26 ] It is evident from some recent studies that orthorhombic V 2 O 5 is a potential host for reversible Mg intercalation with a limit of x Mg ≈ 0.5 [ 11,16,26–29 ] which is significantly lower than the Li system. However, the extent of intercalation and hence the specific capacity of V 2 O 5 can be bumped up using a bilayered xerogel phase (V 2 O 5 * 1.8 H 2 O), [ 29,30 ] which incorporate the water molecules within the interlayers of V 2 O 5 polymorph.…”

“…[ 16,30,35–37 ] The studies clearly evident the choice of nanostructured materials and thin films of V 2 O 5 as promising strategy to overcome the sluggish mobility of Mg ions into the cathode. Recently Fu et al [ 26 ] demonstrated reversible Mg intercalation in V 2 O 5 nanowires with discharge capacity of 130 mA h g −1 at C/20 after few activation cycles using Mg(ClO 4 ) 2 and AN electrolyte with capacity retention of <30% after 100 cycles. Banerjee et al [ 37 ] synthesized a metastable phase of V 2 O 5 (ζ‐phase) nanowires and demonstrated 1st discharge capacity of 140 mA h g −1 , and retained 90 mA h g −1 after 100 cycles using magnesium bis (trifluoromethylsulfonyl)imide (Mg‐(TFSI) 2 ) in PC as electrolyte.…”