Intercalation of Magnesium into a Layered Vanadium Oxide with High Capacity

Abstract

While α-V2O5 has traditionally been considered as a promising oxide to reversibly intercalate high levels of Mg2+ at high potential, recent reports indicate that previously observed electrochemical activity is dominated by intercalation of H+ rather than Mg2+, even in moderately dry nonaqueous electrolytes. Consequently, the inherent functionality of oxides to intercalate Mg2+ remains in question. By conducting electrochemistry in a chemically and anodically stable ionic liquid electrolyte, we report that, at 110 °C, layered α-V2O5 is indeed capable of reversibly intercalating 1 mol Mg2+ per unit formula, to accumulate capacities above 280 mAh g–1. Multimodal characterization confirmed intercalation of Mg2+ by probing the elemental, redox, and morphological changes undergone by the oxide. After cycling at 110 °C, the electrochemical activity at room temperature was significantly enhanced. The results renew prospects for functional Mg rechargeable batteries surpassing the levels of energy density of current Li-ion batteries.

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

“…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 ).…”

Enhanced charge storage of nanometric ζ-V2O5 in Mg electrolytes

“…As a result, Nano ζ-V 2 O 5 possessed a higher energy density than Bulk ζ-V 2 O 5 (250 and 140 W h kg −1 , respectively, on the second cycle), which compares favorably with state-of-the-art sulfide materials such as Chevrel Mo 6 S 8 (77 W h kg −1 ), 10 Spinel Ti 2 S 4 (228 W h kg −1 ), 11 and oxides such as Mo 2.48 VO 9.93 (∼250 W h kg −1 ), 34 and MoO 3 (270 W h kg −1 ), 35 although it is still somewhat short of the highest energy density recorded for an oxide (α-V 2 O 5 , 660 W h kg −1 ). 15 Clearly, nanosizing ζ-V 2 O 5 increased its obtainable energy density by mitigating diffusive limitations on cycling kinetics. Unfortunately, the direct probing of Mg diffusion using standard techniques such as the Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS) are not yet suitable for these prototype systems, given the prevalent side reactions present between the electrodes and the electrolyte.…”

“…The active material loading of 60 wt%, while lower than typical loadings for Li-ion electrode testing, is common for Mg-ion testing given the sluggish reaction kinetics of Mg insertion and removal. 15,32,33 These were pressed (8 tons) and dried at 100°C overnight under vacuum in the glovebox antechamber. Cells that were cycled repeatedly, possessed active material loadings in the range 1.5 to 2.5 mg cm −2 , whereas charged or discharged electrodes used for postmortem analysis were in the range 0.7 to 1.5 mg cm −2 .…”

“…The potential of cathode was calibrated by considering the ACC anode potential, which was originally 2.2 V vs. Mg/Mg 2+ and linearly proportional to the state-of-charge (SoC). 15 The polarization of the ACC electrode was quantified by measuring the voltage change of a symmetric ACC|ACC cell with State of Charge (SoC), using the same electrolyte and cycling temperature used for the ACC|ζ-V 2 O 5 cells within this manuscript. This allowed the unambiguous determination of the cathodic voltage as a function of the SoC.…”

“…[10][11][12][13] In contrast, oxide materials can offer much higher potentials vs. Mg/Mg 2+ , e.g. 2.5 V for V 2 O 5 , 14,15 2.9 V for MgMn 2 O 4 , 16 and 3.5 V for MgCr 2 O 4 , 14,15,[17][18][19] although these materials typically exhibit Mg insertion and removal kinetics that are moderateto-poor (e.g. overpotentials of >0.7 V for V 2 O 5 , corresponding to ∼70% energy efficiency).…”