ChemInform Abstract: Silver Vanadium Diphosphate Ag₂VP₂O₈: Electrochemistry and Characterization of Reduced Material Providing Mechanistic Insights.

Abstract

Silver Vanadium Diphosphate Ag 2 VP 2 O 8 : Electrochemistry and Characterization of Reduced Material Providing Mechanistic Insights. -Ag2VP2O8 is prepared by a previously reported method and its structure is confirmed by Rietveld refined powder XRD data (space group P21/c, Z = 4). Taking into account a former study on Ag2VO2PO4 reduction, in-situ formation of Ag metal nanoparticles is observed during galvanostatic reduction and cyclovoltammetric scans of Ag 2 VP 2 O 8 . However, in contrast to Ag2VO2PO4 reduction, Ag2VP2O8 demonstrates a significant decrease in conductivity upon continued electrochemical reduction. The diphosphate anion structure is discussed as the reason for the high thermal stability of the partially reduced Ag2VP2O8 materials which accounts well for enhanced safety of batteries incorporating this material. -(TAKEUCHI*, E. S.; LEE, C.-Y.; CHENG, P.-J.; MENARD, M. C.; MARSCHILOK, A. C.; TAKEUCHI, K. J.; J. Solid State Chem. 200 (2013) 232-240, http://dx.

Impact of Multifunctional Bimetallic Materials on Lithium Battery Electrochemistry

“…A fully discharged cell showed the presence of Ag 0 throughout the cathode. 37 The in situ EDXRD data agrees with previous ex situ XRD data which established that the multimechanism processes during discharge of Ag 2 VO 2 PO 4 (i.e., Ag + → Ag 0 and vanadium reduction) occur in parallel.…”

“…Discharge profiles of the materials are shown in Figure 2 and demonstrate single or multiple plateaus. 37,39,42,43 Ag 2 V 4 O 11 displays two distinct plateaus at 2.7 and 2.5 V, while Ag 2 VO 2 PO 4 demonstrates one long plateau at 2.7 V. The vanadium oxidation state in Ag 0.48 VOPO 4 is mixed valent (V 5+ /V 4+ ), while the vanadium center in Ag 2 VP 2 O 8 is V 4+ . Synthetic approaches 44,45 and the discharge mechanisms of the materials have been studied in detail using spectroscopic, 18,46 magnetic susceptibility, 47 conductivity, 16,47 and diffraction techniques.…”

“…16 Mesoscale Electrode Characterization: Pure Electroactive Material X-ray diffraction (XRD) can be used to detect low quantities of crystalline Ag 0 , formed upon reduction displacement, since Ag 0 is a high Z element which displays intense diffraction peaks. 37 Electrodes comprised of pure Ag 2 VO 2 PO 4 were electrochemically reduced under a constant current C/200 rate, and the process was monitored via ex situ XRD. 16 As discharge progressed, the parent Ag 2 VO 2 PO 4 peak intensity decreased monotonically while the Ag 0 peak intensity increased up to x = 2.4 molar electron equivalents of reduction in Li x Ag 2−x VO 2 PO 4 .…”

“…50 In 2013, the first in situ EDXRD analysis of an intact coin-sized lithium anode cell was performed for a pelletized Ag 2 VO 2 PO 4 cathode. 37 A representative experimental configuration of EDXRD studies is shown in Figure 5a. In a partially discharged cell, Ag 0 was observed on the side of the cathode nearest to the Li-anode while Ag 2 VO 2 PO 4 was dominant on the side of the cathode facing the stainless steel cell, illustrating a clear reaction front within the cathode.…”

Operando Synchrotron XRD Investigation of Silver Metal Formation upon Electrochemical Reduction of Silver Iron Pyrophosphate (Ag7Fe3(P2O7)4)

“…31 The silver vanadium diphosphate, Ag 2 VP 2 O 8 , also demonstrated a significant increase in conductivity via in situ formation of silver metal nanoparticles. 25 Ag 7 Fe 3 (P 2 O 7 ) 4 , a material analogous in structure to Na 7 Fe 3 -(P 2 O 7 ) 4 but with Ag + substituted, was hypothesized to have both excellent electrical and ionic conductivity. We verified that Ag 7 Fe 3 (P 2 O 7 ) 4 functions well as the cathode material in Li based batteries with high rate capability, delivering six electrons at the rate of C/2.5 in the first discharge.…”