Nuclear Magnetic Resonance and X-Ray Absorption Spectroscopic Studies of Lithium Insertion in Silver Vanadium Oxide Cathodes

Abstract

Structural studies have been carried out on Ag 2 V 4 O 11 ͑silver vanadium oxide, SVO͒ and Li x Ag 2 V 4 O 11 , lithiated SVO with x = 0.72, 2.13, and 5.59 using nuclear magnetic resonance ͑NMR͒ and X-ray absorption spectroscopy ͑XAS͒. Lithium-7 NMR indicates the formation of a solid electrolyte interphase layer on the x = 0.72 sample and lithium intercalation into both octahedral and tetrahedral sites in the SVO lattice, and that most but not all of the Ag ͑I͒ is reduced prior to initiation of V͑V͒ reduction. Vanadium-51 NMR studies of SVO and lithiated SVO show decreased crystallinity with increased lithiation, as previously reported. Silver XAS studies indicate the formation of metallic silver crystallites in all the lithiated samples. A comparison of X-ray absorption near edge spectroscopy spectra for vanadium in these samples with those of reference compounds shows that some reduction of vanadium ͑V͒ occurs in the lithiated SVO with x = 0.72 and increases with further lithiation leading to the formation of V͑IV͒ and V͑III͒ species. The results of this study indicate that vanadium͑V͒ reduction occurs in parallel with silver ͑I͒ reduction during the initial stages of SVO lithiation, leading ultimately to the formation of vanadium ͑IV͒ and ͑III͒ species with further lithiation.The lithium/silver vanadium oxide ͑SVO͒ primary cell is employed for a number of biomedical applications but its principal use is as a power source in implantable cardiac defibrillators ͑ICDs͒ which are required to produce 25-40 Joule pulses to paralyze the heart during fibrillation events, following which the normal heart beating rhythm resumes. This function requires a cell capable of producing 1-4 A pulses to charge a capacitor in addition to providing the background current of 10-30 A for pacing and sensing functions. Silver vanadium oxide ͓Ag 2 V 4 O 11 ͔, which belongs to the class of vanadium bronzes and possesses semiconducting properties, has been successfully used as the cathode in this system due to the inherent high rate capability of this material.Electrochemical reduction of SVO is a multistep process which occurs between 3.2 and 2.0 V with the following overall reaction: Ag 2 V 4 O 11 + 7Li = Li 7 Ag 2 V 4 O 11 . SVO has a theoretical capacity of 315 mAh/g to a 2.0 V background voltage cutoff. Extensive electrochemical characterization of the Li/SVO system has been carried out by several other groups. 1-3 Mechanistic studies of this multistep reduction have also been conducted and have identified the formation of silver metal in the early stage of the reaction, through the use of X-ray powder diffraction and scanning electron microscopy/ energy-dispersive spectroscopy ͑SEM/EDS͒. 4,5 However, electrochemical and X-ray diffraction measurements yield only average structural changes related to lithium insertion. The primary motivation of this work was to apply spectroscopic methods that reveal atomic level information about the environments of all three metal ions in lithiated SVO; lithium, through 7 Li nuclear magnetic resonan...

Electrochemical reduction of silver vanadium phosphorous oxide, Ag2VO2PO4: Silver metal deposition and associated increase in electrical conductivity

“…(5, 6, 7, 8, 9, 10) Further, the discharge process of SVO in a lithium battery has been investigated by several methods including titration, x-ray powder diffraction and solid state NMR. (10, 11, 12, 13) The discharge process of SVO initiates with the competitive reduction of Ag + to Ag 0 and of V 5+ to V 4+ and then proceeds to some reduction of V 4+ to V 3+ . Notably, the reduction of silver ion was observed to form silver metal nanoparticles and nanowires within the cathode and contribute to a significant increase in cell conductivity on discharge.…”

Mapping the Anode Surface-Electrolyte Interphase: Investigating a Life Limiting Process of Lithium Primary Batteries

“…As has been previously reported for silvervanadium bimetallic materials, some vanadium reduction takes place in parallel with the reduction of silver. 25,[31][32][33]52 Previous studies of discharged Ag 2 V 4 O 11 [25][26] indicate that vanadium 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 12 oxidation states of V, IV, and III can co-exist once the material is discharged past 2 electron equivalents. For Ag 2 VO 2 PO 4 , a recent X-ray absorption spectroscopy study 31 has shown that the vanadium is present as a mixture of oxidation states IV and III when the material is discharged to 3 electron equivalents.…”

“…[22][23] While the reduction process of the cathode in the Ag 2 V 4 O 11 battery has been studied through characterization of the cathode material at various stages of discharge, analysis of the anode surface has not been reported. [24][25][26] There are limited reports of negative electrodes analyses from cells including those containing manganese oxide cathodes. 27 Surface films containing manganese(II) were detected on graphite electrodes using electrolytes contaminated with manganese ions and were associated with a ~15 times increase in the lithium-ion transfer resistance.…”

“…Higher levels of vanadium dissolution are observed for the Li/Ag 2 V 4 O 11 cells discharged to 3 electron equivalents. At this depth of discharge, multiple vanadium oxidation states of V, IV, and III may be present [25][26]. Limited literature exists regarding the influence of vanadium oxidation state on solubility 56.…”

Transport properties and lithium insertion study in the p-type semi-conductors AgCuO2 and AgCu0.5Mn0.5O2

“…However, the crossing composition from where the silver reduction is initiated is complex to be accurately determined from XRD because of the nano-crystallinity of the metal withdrawn. It is noteworthy the low reduction potential of silver ion in comparison with 3.45 V for SVOF [18], 3.35 V for SMOF [24], 3.25 V for SVO [48][49][50] or nearby 3 V for a and b-AgVO 3 [51].…”