Electrochemical Reduction of Silver Vanadium Phosphorus Oxide, Ag₂VO₂PO₄: The Formation of Electrically Conductive Metallic Silver Nanoparticles

Abstract

As a cathode material, silver vanadium phosphorous oxide (Ag 2 VO 2 PO 4 ) displays several notable electrochemical properties: large capacity, high current capability, and an effective delivery of high current pulses. These cell performance characteristics can be attributed to the presence of silver nanoparticles formed in-situ during the electrochemical reduction of Ag 2 VO 2 PO 4 . Specifically, changes in the composition and structure of Ag 2 VO 2 PO 4 with reduction, especially the formation of silver nanoparticles, are detailed to rationalize a 15,000 fold increase in conductivity with initial discharge, which can be related to the power characteristics associated with Ag 2 VO 2 PO 4 cathodes in primary lithium batteries.

Electrochemical Reduction of Ag0.48VOPO4: A Mechanistic Study Employing X-Ray Absorption Spectroscopy and X-Ray Powder Diffraction

“…characterization.-The structure of Ag 0.48 VOPO 4 •1.9H 2 O can be described as layers (VPO) of corner-sharing VO 5 and PO 4 held together by van der Waals interactions with Ag + and water molecules intercalated between the layers, as shown in Figure 3. Here we report the Rietveld refinement of Ag 0.48 VOPO 4 •1.9H 2 O as shown in Figure 2.…”

“…The silver ions which reside between the layers of corner-sharing VO 5 and PO 4 occupy the center of distorted octahedra. Interestingly, four of the Ag + -O 2− atomic distances are between 2.0 and 2.6 Å, which are consistent with expected bond distances for an Ag + -centered octahedron.…”

“…Specifically, we established through impedance experiments that the metallic particles formed upon reduction of some bimetallic cathode materials can enhance the conductivity by several orders of magnitude. 5 We successfully extended this strategy to four different members of the material family of silver vanadium phosphorous oxides, Ag 2 VO 2 PO 4 , 21 This strategy should lead to a variety of future battery materials, especially for high current applications.To delineate the discharge process in bimetallic materials, the oxidation state changes associated with the two metal cations as a function of discharge should be obtained. Using X-ray absorption spectroscopy (XAS), the oxidation state as well as the local environment can be measured nondestructively.…”

“…Specifically, we established through impedance experiments that the metallic particles formed upon reduction of some bimetallic cathode materials can enhance the conductivity by several orders of magnitude. 5 We successfully extended this strategy to four different members of the material family of silver vanadium phosphorous oxides, Ag 2 VO 2 PO 4 , 21 This strategy should lead to a variety of future battery materials, especially for high current applications.…”

“…The initial Ag 0.48 VOPO 4 •1.9H 2 O material is comprised of layers of corner-sharing VO 5 and PO 4 with Ag + and water molecules intercalated between the layers. Upon electrochemical reduction, a rapid decrease of intensity at the 004 and 006 planes is observed, with concomitant reduction in 002 spacing, both consistent with the displacement of Ag + ions by Li + ions during electrochemical discharge.…”