Sonochemically Synthesized Vanadyl Phosphate
change in capacity under high discharge rate of 0.3
C is observed. Sonochemically prepared sample
exhibits also good reversibility for the
Telecommunication Basic Research Lab.,
electrochemical lithium insertion/extraction.
Electronics and Telecommunications Research
Preliminary results on the electrochemical
performance indicate that sonochemically
synthesized VOPO 4 2H2O can be a promising
cathode material for rechargeable lithium battery.
Recently, chemical bonding nature-potential level
correlation has been investigated for Nasicon-type
electrode materials LixM2(XO4)3 (M = transition
metal; X = S, P, As) [1,2], where the higher ionicity of the M-O bond was found to give rise to the higher
potential of the Mn+/M(n+1)+ redox couple. Electrochemical lithium insertion in the
rhombohedral Li3V2(PO4)3  and the β-form of
VOPO4  was investigated. The potentials in
batteries based on these materials showed 3.77 and
3.98 V vs. Li+/Li, respectively. However, less
attention has been paid to vanadyl phosphate
dihydrate VOPO 4 2H2O because of being more interested in its catalytic property. VOPO 4 2H2O has been usually prepared by long-term boiling of a V
suspension in aqueous phosphoric acid according to
Ladwig’s method . We have developed a method for rapid synthesis of VOPO 4 2H2O.
In this paper, we report on sonochemical
Figure 1. First discharge curve for the Experimental References
follows. The aqueous phosphoric solution contained
Goodenough, S. Okada, H. Ohtsuka, H. Arai, and
J. Yamaki, Solid State Ionics, 92, 1 (1996)
2O5 powder was exposed to high-intensity
ultrasound radiation for 15 min by employing a direct
2. C. Masquelier, A.K. Padhi, K.S. Nanjundaswamy,
immersion titanium alloy horn operating at 20 kHz,
and J.B. Goodenough, J. Solid State Chem., 135,
with intensity of ~ 70 W/cm2. The temperature of the
reaction solution rose to 70 oC during sonication. The
resulting yellow solid was filtered, washed several
Masquelier, and L. Nazar, Chem. Mater., 12, 3240
times with acetone and dried at ambient atmosphere.
The synthesized material was characterized
4. J. Gaubicher, T. Le Mercier, Y. Chabre, J.
using X-ray diffraction (XRD), Fourier transformed
Angenault, and M. Quarton, J. Electrochem. Soc.,
infrared (FTIR), transmission electron microscopy
(TEM) and thermogravimetric analysis (TGA).
5. G. Ladwig, Anorg. Allg. Chem., 338, 266 (1965)
Electrochemical studies were carried out using a
Macfile-II galvanostat system. A Swagelok-type cell consisted of the mixture of the synthesized VOPO 4 2H2O, the Super P black (MMM Carbon Co.) and the polytetrafluoroethylene (70:20:10 wt%) as a cathode, Li foil as an anode and 0.95 M solution of LiPF6 in ethylene carbonate/ dimethyl carbonate (50:50 vol%) as an electrolyte, which was discharged and charged under the constant current ranging from 4.16 to 39.4 mA/g. Results and Discussion
XRD confirms the phase purity of tetragonal
VOPO 4 2H2O with a = 6.2 Å and c = 7.4 Å. The particle size of the sonochemically synthesized material is determined to be 1 – 3 µm by TEM, which is smaller than the size (about 10 µm) of the sample prepared by the long-term refluxing method.
Electrochemical reduction of VOPO 4 2H2O under
a constant current of 4.16 mA/g (corresponding to 0.03 C) shows that almost 1 Li can be inserted, which results in the capacity of 135 mAh/g (Fig. 1). The cell potential shows a plateau at 3.6 V. Little
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