Amy C. Marschilok

Silver vanadium oxides and related battery applications

Abstract This review contains references from journals, proceedings volumes, and patents involving the preparation, characterization, reactivity, and battery applications of materials containing silver, vanadium, and oxygen, hereafter referred to as silver vanadium oxide (SVO). SVO has been a subject of regular study for a number of years, with earlier reports involving the synthesis and characterization of the various phases of SVO. However, with the relatively recent discovery of SVO as an important electrode material in batteries, the number of publications and patents involving the preparation, structure, reactivity and related battery applications of SVO has increased markedly. In light of this recent increase in research activity involving SVO and its related battery applications, this review is a timely examination of this exciting and growing area of research.

Batteries used to Power Implantable Biomedical Devices

Battery systems have been developed that provide years of service for implantable medical devices. The primary systems utilize lithium metal anodes with cathode systems including iodine, manganese oxide, carbon monofluoride, silver vanadium oxide and hybrid cathodes. Secondary lithium ion batteries have also been developed for medical applications where the batteries are charged while remaining implanted. While the specific performance requirements of the devices vary, some general requirements are common. These include high safety, reliability and volumetric energy density, long service life, and state of discharge indication. Successful development and implementation of these battery types has helped enable implanted biomedical devices and their treatment of human disease.

Preparation and Electrochemistry of Silver Vanadium Phosphorous Oxide, Ag2VO2PO4

Recently, there has been interest in phosphate cathodes for lithium batteries due to the excellent chemical and thermal stability of LiFePO 4 . Vanadium oxide bronzes have attracted attention due to silver vanadium oxide (Ag 2 V 4 O 11 ) batteries being used as power implantable devices. We report the first investigation of silver vanadium phosphorous oxide (Ag 2 VO 2 PO 4 ) as a cathode material in lithium cells. While the synthesis of Ag 2 VO 2 PO 4 has been previously reported, this is the first exploration of its electrochemistry. The Ag 2 VO 2 PO 4 material yielded 205 mAh/g to 2.0 V and 270 mAh/g to 1.5 V under constant current discharge and supported 50 mA/cm 2 pulses above 1.5 V.

Carbon nanotube substrate electrodes for lightweight, long-life rechargeable batteries

Lighter weight and longer life batteries for electrochemical energy storage are needed for many applications including aerospace, transportation, portable electronics, and biomedical devices. Inclusion of inert materials as part of the battery electrode significantly decreases energy density as they contribute to the weight and volume of the electrode, but not to its energy content. This work demonstrates the viability of using novel metal oxide/carbon nanotube substrate (CNT-S) electrodes in rechargeable cells. To our knowledge this is the first reported use of CNT-S for lithium battery cathodes without the use of a supporting metal current collector. Calculations show that the use of CNT-S can increase the cathode specific capacity by 20–60%, due to the low mass of the CNT-S and elimination of binders and other inert conductive carbons typically added to composite cathodes on foil current collectors. The oxidative stability of CNT-S relative to metal foil current collectors may extend battery lifetimes and enable use of electrolytes that are currently not viable. Two methods of preparing electrodes were demonstrated, the first using material deposited on the CNT substrate after isolation and the second method using direct integration during material synthesis.

Advanced lithium batteries for implantable medical devices: mechanistic study of SVO cathode synthesis

Abstract Silver vanadium oxide (SVO, Ag 2 V 4 O 11 ) was synthesized in solid-state reactions from silver carbonate and silver metal powder starting materials with vanadium oxide (V 2 O 5 ) as the vanadium source. These powders were prepared as primary cathode materials for lithium batteries. Thermal analyses of stoichiometric mixtures of V 2 O 5 and silver sources were used to elucidate the mechanism of Ag 2 V 4 O 11 formation. V 2 O 5 reacts with Ag 2 CO 3 in a two step decomposition/combination (DC) reaction. Weight gain measured by TGA during the reaction of Ag(0)+V 2 O 5 in O 2 indicated the formation of Ag 2 V 4 O 11 . XRD analysis of the synthesis products of the Ag(0)+V 2 O 5 reaction indicated the formation of AgV 2 O 5 under inert atmosphere and Ag 2 V 4 O 11 under oxidizing (air or O 2 ) conditions. The surface area and morphology of the materials were strongly influenced by the synthesis method, linked to the parameters of time, temperature, and reaction atmosphere. The electrochemical performance of the SVO cathode material also depended on the synthesis method, where SVO prepared from the DC reaction mechanism yielded improved long-term performance.

Synthetic Control of Composition and Crystallite Size of Silver Hollandite, AgxMn8O16: Impact on Electrochemistry

Synthetic control of the silver content in silver hollandite, Ag(x)Mn(8)O(16), where the silver content ranges from 1.0 ≤ x ≤ 1.8 is demonstrated. This level of compositional control was enabled by the development of a lower temperature reflux based synthesis compared to the more commonly reported hydrothermal approach. Notably, the synthetic variance of the silver content was accompanied by a concomitant variance in crystallite size as well as surface area and particle size. To verify the retention of the hollandite structure, the first Rietveld analysis of silver hollandite was conducted on samples of varying composition. The impacts of silver content, crystallite size, surface area, and particle size on electrochemical reversibility were examined under cyclic voltammetry and battery testing.

Energy dispersive X-ray diffraction of lithium–silver vanadium phosphorous oxide cells: in situ cathode depth profiling of an electrochemical reduction–displacement reaction

Li/Ag2VO2PO4 cells exhibit high power output and a 15 000 fold decrease in impedance upon initial discharge. Energy dispersive X-ray diffraction (EDXRD) allows dimensional resolution of the reaction progress in situ, revealing that silver metal (Ag0) initially forms at the electrode–electrolyte interface. This report contains the first description of an in situ EDXRD analysis of a cathode located within an intact Li-anode cell.

Synthesis and Electrochemistry of Silver Hollandite

The electrochemical study of silver hollandite is presented, establishing the promise of this material for future secondary battery applications. A low temperature reflux-based strategy for the synthesis of pure silver hollandite is described, where an enhancement in silver loading was achieved relative to other low temperature methods.

Electrodes for Nonaqueous Oxygen Reduction Based upon Conductive Polymer-Silver Composites

Progress toward the development of current collector-conductive polymer-silver (cc-cp-Ag) composite cathodes for nonaqueous metal air batteries is presented here, where the contribution of each component toward the overall oxygen reduction activity of the multifunctional cc-cp-Ag composite is studied. First, the effect of the chemical identity of the current collector (carbon versus gold) on the electrochemical reduction of oxygen is examined, accompanied by a conductive polymer deposition study. These two studies together demonstrate that a conductive polymer deposit can eliminate any competitive electrochemistry due to the current collector. Second, the role of the conductive polymer in improving physical strength of the composite electrode is evaluated using an electrode durability test. Third, a systematic study of the Ag loading effect is undertaken to determine the minimum silver loading required for significant enhancement in oxygen reduction activity.

Metal–Air Electrochemical Cells: Silver–Polymer–Carbon Composite Air Electrodes

Reported herein is the study of the preparation, characterization, and electrochemical activity of a silver-polymer-carbon composite electrode in a nonaqueous cell. An enhanced oxygen reduction activity for the composite electrode in a nonaqueous, aprotic solvent is demonstrated, relative to uncoated glassy carbon or silver disk electrodes. The improvement of oxygen reduction activity increases the current capability and power output of the air electrode, facilitating future development of small, lightweight, long-life power sources.