Testing Carbon‐Coated VO_x Prepared via Reaction under Autogenic Pressure at Elevated Temperature as Li‐Insertion Materials

Abstract

V 2 O 3 powder is frequently used in conductive polymer composites and in catalysts. [1][2][3] In addition, a variety of VO x and MVO x (e.g., V 2 O 5 , V 6 O 13 , CaV 3 O 7 ) compounds have been suggested and tested as cathode materials for rechargeable Li batteries. [4][5][6][7][8][9][10] These vanadium oxide-based compounds are still among the most intensively studied cathode materials for rechargeable Li batteries. It should be noted that studies related to Li-battery materials are of high interest in materials science. [11][12][13][14] The synthesis of spherical V 2 O 3 nanoparticles by the reductive pyrolysis of ammonium oxovanadium(IV) carbonato hydroxide has been reported. [15] Nanocrystalline V 2 O 3 was synthesized by the thermal decomposition of divanadium pentoxide by Su and Schlogl. [16] In this report, we present results of the RAPET dissociation (RAPET: reaction under autogenic pressure at elevated temperatures) of VO(OC 2 H 5 ) 3 , which produces carbon-coated vanadium oxide (CCVO). This novel method, using only a metallic alkoxide precursor in the absence of a catalyst or a solvent, is a one-step process yielding a core/shell morphology. Further oxidation of the CCVO produces carbon-coated V 2 O 5 (CCV 2 O 5 ) nanoparticles. In the present study, we explore to what extent the carbon shell enables electrical contact among the CCVO particles, while not interfering with a smooth Li intercalation with the V 2 O 3 particles. It is interesting to discover whether these active materials can be used in composite electrodes for Li batteries, as they would possibly reduce the need for significant addition of carbonaceous materials, in order to maintain electrical contact among the particles and between the active mass and the current collector. Usually, composite cathodes based on Li-intercalating transition-metal oxides or sulfides have to include additional carbon particles (5-15 wt %) [17,18] in order to achieve electrical contact between the active mass and the current collector (and among the particles themselves). As the particles are smaller (which may be very important for achieving high rates), critical problems may arise regarding the electrical properties of the composite electrodes, because the carbon particles may not be in direct contact with all of the very small particles of the active mass. Hence, the use of an active mass where each particle is coated by a thin (conductive) carbon layer that is permeable to Li ions may be very advantageous for Li-battery application. This paper is the first report on the use of CCVO as the active mass in composite cathodes for rechargeable Li batteries. The carbon and hydrogen content in the CCVO samples was determined by elemental analysis measurements. The calculated elemental percentage of carbon in the precursor, VO(OC 2 H 5 ) 3 , was 44.3 %, while the elemental percentage of hydrogen was 9.6 %. The measured percentage of carbon in the carbon-coated V 2 O 3 (CCV 2 O 3 ) product is usually 30 %, while the percentage of hydrogen is only 0.3 %. Hence, it...

Synthesis and Electrode Performance of Nanostructured V2O5 by Using a Carbon Tube‐in‐Tube as a Nanoreactor and an Efficient Mixed‐Conducting Network

“…This rate capability is higher than those of carbon-coated V 2 O 5 and other V 2 O 5 -based electrodes. [13,15,17] The experi- mental results obtained show that the mixed-conducting nanostructure favorably reduces the diffusion length for lithium ions and enables the high rate performance of lithium-based batteries. In summary, an optimized nanostructured electrode design has been proposed.…”

“…[26] The third plateau at 2.3 V can be ascribed to a further lithium insertion into LiV 2 O 5 , which is also highly reversible [Eq. (3)], [5,13] LiV…”

Designed synthesis of tunable amorphous carbon nanotubes (a-CNTs) by a novel route and their oxidation resistance properties

“…Figure 3(c) represents a typical Raman spectrum of a-CNTs, which is characteristic for amorphous carbon because of the presence of the D-(1348 cm -1 ) and G-bands (1595 cm -1 ) (Ilie et al 2002; Odani et al 2006). It was reported that the D-band (1348 cm -1 ) is usually associated with the vibrations of carbon atoms with dangling bonds for the in-plane terminations of disordered graphite, and the G-band (corresponding to the E 2g mode) is closely related to the vibration in all sp 2 -bonded carbon atoms in a two-dimensional hexagonal lattice, such as in a graphitic layer, corresponding to the E 2g mode (Dresselhaus et al 1999;llie et al 2002;Odani et al 2006;Sun et al 2006;Zhang et al 2012d,e). These two peaks are broad in figure 3(c), indicating that the carbon in the as-prepared a-CNTs is of poor crystallinity, corresponding to the previous report (Sun and Li 2004;Zhang et al 2011bZhang et al , 2012b.…”

Facile Synthesis and Electrochemical Performance of Carbon-Coated V2O5 Cathode Materials Using Carboxylic Acids as Carbon Source

“…The high theoretical capacities of V 2 O 5 are especially attractive, for example, 294 mA h g −1 for two lithium insertion/extractions at 4.0 − 2.0 V. Despite these advantages, V 2 O 5 has a low intrinsic electrical conductivity (10 −2 to 10 −3 S cm −1 ) and sluggish lithium-ion diffusion (∼10 −12 cm 2 s −1 ), leading to poor capacity retention and rate capabilities [11][12][13][14]. In addition, phase transformations of Li x V 2 O 5 during repeated charge/discharge processes (e.g., ␣ phase for x < 0.1, phase for 0.35 < x < 0.7, ␦ phase for x = 1, ␥ phase for 1 < x < 3, and phase for x = 3) often cause structural instabilities, and they degrade the cycling performances [15][16][17]. These drawbacks have hampered the practical applications of this cathode material in commercial LIBs.…”